JP2014209083A - Absolute humidity sensor and absolute humidity sensor chip used for the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absolute humidity sensor as a heat conduction type sensor, allowing influence of ambient temperature to be corrected and dew point information and the like to be obtained, having high sensitivity, high accuracy, and high-speed response, and down-sized.SOLUTION: A heater and a thin film thermocouple as a temperature sensor are mounted on a thin film thermally separated from a base plate, the temperature of the thin film is made to reach different predetermined preset temperatures Tl, Th, comparison of power consumption of heating by the heater and comparison in time integration values of temperature sensor output in a cooling process after the stop of the heating by the heater are performed. The comparison of the power consumption for Tl, Th and the time integration output after the stop of the heating are performed by using a single thin film or two thin films having the same shape. There is provided an absolute humidity sensor which utilizes the deducted power consumption and the deducted integration value, corrects the ambient temperature including information of the absolute temperature of the base plate, and utilizes prepared calibration data. Moreover, information of dew point and the like is acquired from the response by minute power heating of the thin film. Also, a sensor chip suitable therefor is provided.

Description

  The present invention relates to an absolute humidity sensor as a heat conduction sensor for measuring the amount of water vapor in a gas.

The applicant first formed a platinum (Pt) thin film temperature sensitive resistor into a thin film thermally separated from the substrate, used it as a heater and temperature sensor, operated as a heat conduction type sensor, and formed a Wheatstone bridge. Use each of the power consumption (applying to the heater) required to raise the temperature from room temperature to two different temperatures Th and Tl in a short time while the ambient temperature does not change We proposed a method for measuring the absolute humidity of wet air by subtracting the squares of the voltages Vh and Vl to cancel the effect of room temperature (see Patent Document 1).

There, the thermal conductivity of water vapor, which is humidity, is smaller than the thermal conductivity of air at a temperature lower than about 120-150 ° C., and rapidly increases at a temperature higher than about 120-150 ° C. That is, in the vicinity of 120 to 150 ° C., the thermal conductivity of water vapor is equal to the thermal conductivity of air and is not related to the amount of water vapor. Therefore, the temperature in the vicinity of 120 to 150 ° C. is set as one predetermined lower temperature. Then, it becomes easier to calibrate the absolute humidity, and when the other predetermined temperature is set to a high temperature of about 400 ° C. and the power supplied to each is measured at the same time and the difference between them is obtained, It was shown that absolute humidity excluding the influence is required.

However, since the thermal conductivity of water vapor increases as the temperature rises, it is desirable to heat the heater to a high temperature of 400 ° C. or higher. Since a resistance temperature detector such as a Pt thin film having a large resistance temperature coefficient is used as a heater and an absolute temperature sensor, it is problematic that operation at a high temperature is difficult. This is because the resistance value of the sensing unit is required to be sufficiently larger than the wiring resistance value in the function as a resistance temperature detector, and a thin and long Pt thin film pattern is required. However, on the other hand, when this is made to function as a heater, among the thin and long Pt thin film patterns, the resistance of the narrow pattern part is particularly large, so the heat generation at this part increases. The problem of being connected to the disconnection of the pattern occurred, and a solution for this was necessary.

Further, the electric power required to raise the thin film from room temperature to temperature Th and temperature Tl is Vh ² / R and Vl ² / R, where R is the internal resistance of the heater. In order to cancel the effect of room temperature, the power must be subtracted. From the viewpoint of power, the applied voltages to the heater, Vh and Vl, are 1/2 power of each power. The difference between Vh and Vl is not so large, that is, there is a problem that the sensitivity is low for absolute humidity measurement.

The applicant of the present invention divides a thin film suspended in the air into two parts and further has a thermal resistance. One thin film 10A is formed with a heater and a temperature sensor 20A as an absolute temperature sensor, and the other is formed. A temperature sensor 20B, which is an absolute temperature sensor, is formed on the thin film 10B. As an absolute humidity sensor, a low temperature Tl of two predetermined different temperatures Th and Tl by applying two heating pulse heater voltages is changed from 150 ° C. It shows that even if it is raised to 270 ° C, it does not cause a large error, and the temperature is measured by measuring the absolute humidity, airflow, vacuum, etc. A sensing system was proposed (see Patent Document 2). In this case, the heater and the temperature sensor for measuring the temperature are independent from each other, and the absolute temperature sensor capable of directly measuring the absolute temperature is used as the temperature sensor. Settled. However, since an absolute temperature sensor is used here, two absolute temperature sensors are always required to measure the temperature rise of the thin film floating in the air due to heater heating. Since there is always an error to come, it is not suitable for measuring high-accuracy temperature rise.

Further, the applicant of the present invention often has a very small Seebeck current based on the thermoelectromotive force of the thermocouple, and in order to amplify this with a high S / N and output it, the Seebeck current may be integrated over time. This was proposed (see Patent Document 3). By integrating the Seebeck current with time, instantaneous Seebeck current measurement includes noise and poor reproducibility, but noise has the property that the integration value becomes zero when integrated for a long time, which can be used. Therefore, it is considered that a high S / N can be obtained, and further, by integrating over time, a small change in the Seebeck current can be increased by integration, so that the change in the Seebeck current can be expanded (amplified). Yes.

When the thin film thermocouple which is a temperature difference sensor is used for temperature measurement, the applicant of the present invention outputs a temperature change based on the temperature of the substrate (room temperature), that is, only outputs the temperature difference, when heated with a predetermined power, The temperature rises on the basis of room temperature regardless of the ambient temperature (room temperature), and when heating is stopped, the temperature rise will eventually return to zero, that is, return to room temperature, and the output will be zero. I noticed that. In addition, the heat conductivity of the thin film heated by the heater is equivalently changed by physical use such as atmospheric pressure, flow, and gas concentration of the surrounding gas, so that the heat is removed from the thin film during the heating of the heater and during the cooling process. A temperature difference sensor that can apply the zero method to the heat conduction sensor based on the principle that the physical quantity of the ambient medium gas is measured by measuring the output change of the temperature sensor formed in the thin film by changing the cracking method. It has been found that a thin film thermocouple is most convenient. Furthermore, it was examined whether this thin film thermocouple could be used as a heater.

From the above, the applicant of the present invention not only uses a thin film thermocouple as a temperature difference sensor, but also has an internal resistance and good ohmic characteristics, so that it can be used as a heater for heating, and one thin film thermocouple. It was proposed that the operation as a heater and the operation as a temperature difference sensor can be performed by time-sharing the pair (see Patent Document 4).

Then, if a thin film thermocouple, which is a single temperature difference sensor, is also used as a heater, the structure becomes extremely simple, the manufacturing process can be simplified, and a sensor chip with good yield can be easily formed. Since the thin film thermocouple is a temperature difference sensor, the thin film heated from room temperature as described above is a heater in addition to the advantage that an inexpensive sensor chip can be manufactured because it is easy to downsize and mass production is possible. By returning to room temperature after stopping, there is a great advantage that if the temperature difference from room temperature is measured, the zero position method, which is a highly accurate measurement technique, can be applied. However, as described above, as a heat conduction sensor, we would like to measure the temperature when a thin film is heated by a heater. It was also proposed that the temperature after a predetermined time after stopping heating can be measured and replaced with the temperature during heating of the heater.

The absolute humidity sensor is the measurement of the amount of water vapor contained in the gas to be measured, that is, the impurity gas, and the principle of the thermal conductivity sensor that measures the change in thermal conductivity in the gas into which the impurity gas is introduced. It is what was used. In general, a thermal conductivity sensor is heated by a change in the thermal conductivity of the surrounding medium (or an equivalent change in thermal conductivity) based on a change in the measured physical quantity such as impurity gas in the surrounding medium or the flow of the surrounding medium. The basic principle is to measure the temperature change of a thin film. However, the thermal conductivity of the surrounding medium itself depends on the absolute temperature of the surrounding medium. In general, when the surrounding medium is a gas, the higher the absolute temperature, the larger the thermal conductivity. When the same thin film is heated with a constant power at room temperature, a substantially constant temperature increase ΔT from room temperature is achieved. For example, if the temperature rise ΔT is approximately 100 ° C., whether the temperature of the thin film becomes 100 ° C. or 150 ° C. depending on whether the room temperature at that time is 0 ° C. or 50 ° C., for example. It turns out that. Due to the temperature dependence of the thermal conductivity, the cooling method when the maximum temperature of the thin film 10 reaches 100 ° C. and the cooling method when the maximum temperature of the thin film 10 reaches 150 ° C. are different. What is the temperature is greatly related to the measurement of physical quantities such as absolute humidity. Thus, canceling the effect of ambient temperature (room temperature) is important for measuring absolute humidity, which is a highly accurate physical quantity.

JP-A-8-184576 JP 2004-286492 A JP 2011-38951 A JP 2009-79965 A

  The present invention has been improved in order to eliminate the above-described problems of the conventional inventor's absolute humidity sensor, and measures the amount of water vapor in a gas such as air as a measurement target gas, that is, the absolute humidity. Therefore, using a heater and thin film thermocouple formed in a thin film thermally separated from the substrate and an absolute temperature sensor formed on the substrate, temperature measurement is performed to know the absolute temperature of the thin film during heating or after the heater stops heating. The purpose is to provide a high-sensitivity, high-accuracy, high-speed response, absolute humidity sensor as a miniaturized heat-conducting sensor that can perform and correct the influence of ambient temperature and obtain dew point information. Yes.

  In order to achieve the above object, an absolute humidity sensor according to claim 1 of the present invention includes an absolute humidity sensor chip having a heater 25 and a temperature sensor 20 on a thin film 10 thermally separated from a substrate 1. In the absolute humidity sensor in which the temperature sensor 20 measures the temperature change of the thin film 10 due to the heating of the heater 25 due to the change of the thermal conductivity based on the amount of water vapor in the gas to be measured, the temperature sensor 20 It is a difference sensor, a voltage is applied to the heater 25, the first heater is heated to heat the thin film 10 from room temperature to a predetermined absolute temperature Tl, and then the first heater is continuously heated. Or the second heater is heated by the heater 25 in a short time such that the temperature variation of the gas to be measured is negligible, and the thin film 10 is moved from room temperature to the predetermined position. It is heated until it reaches a predetermined absolute temperature Th different from the absolute temperature Tl, and is corrected so as to remove the influence of the ambient temperature using information on the power consumption in the heater 25 necessary for each heater heating, The absolute humidity is obtained using calibration data prepared in advance, the output of the absolute temperature sensor 21 provided on the substrate 1 and the output of the temperature sensor 20 are combined, or the thin film 10 is also subjected to the absolute temperature. In the case where the sensor 22 is provided, an absolute temperature measuring means that knows the absolute temperature of the thin film 10 from the output is provided, and the thin film 10 is heated to the absolute temperatures Tl and Th by using the absolute temperature measuring means. It can be set so that it can be set.

The temperature difference sensor as the temperature sensor 20 includes a thermocouple and a thermopile. Since the temperature sensor 20 is formed on the thin film 10, it is easier to form the temperature sensor 20 using the MEMS technique or the like because the heat capacity is smaller and the response is faster. When the measurement point (hot contact) of the temperature difference sensor is formed on the thin film 10 together with the thin film heater 25 using the temperature of the substrate 1 as a reference point (for example, a cold junction), the temperature rise due to the heater heating changes the room temperature. However, if other conditions are equal, the temperature rises in proportion to the supplied power, and when the heater heating is stopped and cooled, the temperature returns to room temperature again. As described above, in general, in the heat conduction type sensor which is the basic principle of the absolute humidity sensor of the present application, the heat radiation from the heating unit to the room temperature which is the temperature of the surrounding gas (measured gas) is used as described above. A thin-film temperature difference sensor is suitable as the temperature sensor 20 having a large surface area and a small heat capacity.

In general, the thermal conductivity of a gas containing water vapor increases almost linearly as the temperature rises, and the slope of the straight line with respect to the temperature of the thermal conductivity of water vapor is greater than the gradient of air with respect to the temperature. Intersect around 120 ° C to 150 ° C. That is, the same thermal conductivity is obtained in this temperature range. Since the room temperature is generally lower than 120 ° C. to 150 ° C., when heating from room temperature to a predetermined low set temperature Tl, the temperature Tl is changed to a temperature in the range of 120 ° C. to 150 ° C. It is preferable to set so that there is no problem even if there is a slight temperature increase, and the measurement error of absolute humidity can be reduced. Since this temperature range is a temperature range where the thermal conductivity does not depend on humidity (water vapor concentration dependency), the thin film 10 is heated by the heater 25 from room temperature, which is the ambient temperature of the gas to be measured, to a predetermined low set temperature Tl. The output of the temperature sensor 20 at the time when the temperature is raised, and the output of the temperature sensor 20 when the temperature of the thin film 10 is raised by the heater 25 from the subsequent room temperature to a predetermined high set temperature Th, for example, 500 ° C. The difference output will subtract the effect of room temperature. This is the output information based on the difference from the low set temperature Tl to the high temperature Th, and the low set temperature Tl is an output almost irrelevant to the amount of water vapor, so the output information based on this difference It is known that the amount of water vapor is strongly related to the amount of water vapor, so the absolute humidity, which is the amount of water vapor in the gas under measurement, should be determined with high accuracy using calibration data prepared in advance. (See Patent Document 1).

In the present invention, when a temperature difference sensor, for example, a thin film thermocouple is used as the temperature sensor 20, the output is a function of only the temperature rise from the substrate temperature of the thin film 10. Therefore, for example, the absolute temperature sensor 21 measures the temperature of the thin film 10 and further measures the temperature difference of the thin film 10 from the substrate 1 with the temperature sensor 20, which is a temperature difference sensor. The temperature when the thin film 10 is heated by the heater 25 by the measuring means can be measured while heating the heater. In this way, it is possible to provide a control circuit that measures while heating a high temperature Th or a low temperature Tl, which is a predetermined set temperature, and stops heating the heater when the predetermined temperature is reached. Of course, when the heater heating is stopped, the thin film 10 is cooled to the original room temperature by Newton's law of cooling. When the amount of water vapor, which is the absolute humidity in the humid gas, is large, the heat conductivity of the humid gas increases when the predetermined high temperature Th exceeds 150 ° C. Therefore, the heating power of the same heater 25 increases the temperature. Therefore, it is expected that a small electric power does not reach a predetermined high temperature Th, for example, 500 ° C. In order to raise this to a predetermined high temperature Th, it is driven by a large heater power that can be raised to a high temperature Th, and the amount of power that is the product of the time and power consumption required to reach the high temperature Th at that time Must be increased. As described above, the absolute humidity can be measured by comparing the power consumption required for raising the temperature from the predetermined low temperature Tl to the predetermined high temperature Th. Assuming that the respective power consumptions Ph and Pl when the thin film 10 is heated to the set temperatures Th and Tl, the resistance value does not substantially change when the heater 25 is formed of a nichrome thin film having a very low resistance temperature coefficient. Therefore, it can be approximated as being proportional to the square of each heater voltage Vh and Vl. Accordingly, by measuring the heater voltages Vh and Vl, the respective power consumption can be obtained. Since the power consumption is a value obtained by dividing the square of the voltage applied to the heater by the heater resistance, the power consumption is raised from room temperature to a predetermined low temperature Tl (for example, 150 ° C.) and a predetermined high temperature Th (for example, 500 ° C.). When the heater voltages required for each of these are equal, Vh and Vl (Va = Vh = Vl), the power consumption will be equal, so the comparison of power consumption will eventually reach Tl and Th. It may be considered that each time required for this is a comparison between tl and th. Therefore, by obtaining the value of Δt = th−tl, correction can be made so as to eliminate the influence of the ambient temperature (room temperature).

Here, as described above, the theoretical basis that the value of Δt = th−tl can be corrected so as to eliminate the influence of the ambient temperature (room temperature) will be described. In the present invention, since the difference between the arrival times th and tl, which are measured quantities, is obtained by comparing the electric energy, the heater voltages Vh and Vl which are measured quantities are used in the conventional measurement principle described above. Thus, it can also be seen that the sensitivity measurement is higher than when the difference between Vh ² / R and Vl ² / R, which is a comparison of power, is obtained. Here, a heat conduction type sensor chip having a single thin film 10 having a simple structure thermally separated from the substrate 1 as shown in FIG. 1 in Example 1 described below is used, and the present invention shown in FIG. The operation of the absolute humidity sensor will be described with reference to a time chart of one embodiment. FIG. 3 shows that the heater 25 formed on the thin film 10 is heated at an applied voltage Va, and the thin film 10 is heated to room temperature Tr, for example, 20 ° C. to a predetermined low absolute temperature Tl, for example, 150 ° C. When the first heater is heated until the absolute temperature Tl is reached, the heater is stopped and cooled to return to room temperature Tr. Then, the room temperature continues to change. In the meantime, the heater 25 is heated at the same applied voltage Va, and the second heater is heated from the same room temperature Tr to the predetermined high absolute temperature Th, for example, 500 ° C. in the same wet air. Then, when the absolute temperature Th is reached, the state of temperature rise and temperature drop of the thin film 10 is shown when heating / cooling is repeated such that heating by the heater is stopped and cooled to return to room temperature. The broken line shown in FIG. 3 is an expected temperature rise curve of the thin film 10 when the heating of the heater 25 is continued for a long time. When the heater 25 is heated with the same applied voltage Va, the time required to reach the absolute temperature Tl is tl, and the time required to reach the absolute temperature Th is th. , Assuming that the resistance of the heater 25 is R, Jl = Va ² · tl / R = P · tl and Jh = Va ² · th / R = P · th. Here, when the heater 25 is made of a nichrome thin film, its resistance temperature coefficient is extremely small, and therefore the value of the resistance R of the heater 25 has no temperature dependency. Here, P is a common power of Va ² / R.

When the thin film 10 is in humid air and heated with electric power P, the equation of heat can be considered that C is a constant value when C is the heat capacity of the thin film and G is the thermal conductance. Is a function of absolute humidity (water vapor amount) H, and even with the same absolute humidity H, the thermal conductivity of wet air changes with increasing temperature, so it must be viewed as a function of time and temperature. The thermal equation is expressed as:

ここで、ΔTは、室温Trからの温度上昇分である。

Here, ΔT is a temperature rise from room temperature Tr.

This is the difference between the electric energy Jh time-integrated with the required time th until the thin film 10 reaches the predetermined temperature Th and the electric energy Jl time-integrated with the required time tl until the thin film 10 reaches the predetermined temperature Tl. The subtraction electric energy ΔJ is expressed as follows. As shown in FIG. 3, the heater 10 is heated with the same electric power P, and the thin film 10 reaches the predetermined temperature Th in a short time when the absolute humidity H of the humid air does not fluctuate with time. Since they overlap on the same temperature rise curve up to the predetermined temperature Tl, the subtraction power amount ΔJ expressed by the following simple expression is obtained.

In Equation 2, G (t) ΔT (t) is expressed as an average value from time tl to th, and G (t) is a function of absolute humidity H, and is expressed as G _av (H). , ΔT (t) is expressed as ΔTav. ΔTav is a constant of an average value from Tl to Th, and G _av (H) is a function of the absolute humidity H, and between the temperature Tl and Th under a certain absolute humidity H. Average value. This G _av (H) is extracted and 1 / ΔTav is expressed as α as follows.

In Equation 3, the power consumption P and the set temperatures Th and Tl in the heater 25 are set from here and are known amounts. The times th and tl are observable quantities, and the heat capacity C and the constant α of the thin film 10 are inherently constants and are found based on calibration data prepared in advance under these conditions. G _av (H), which is a function of absolute humidity H, is the difference between the respective times th and tl (Th−Tl) until reaching a predetermined (set) temperature Th and Tl that can be measured. It turns out that it becomes only a monotonous function. From this, it was found that G _av (H) is uniquely determined by measuring (th−tl) with respect to the absolute humidity H under a predetermined heater heating setting power P 2.

In this case, as shown in FIG. 3, it is necessary to measure (th−tl), which is a comparison between tl and th appearing in different time zones, in order to compare the power consumption. For example, when measuring a time of each of tl and th, if a constant current is continuously supplied to the capacitor C during these times, the voltage across the capacitor C increases linearly with time. At least one of the voltage Vlp corresponding to tl and the voltage Vhp corresponding to th with the voltage at both ends of the capacitor is held by a peak hold circuit or the like, and these can be directly subtracted. Of course, tl and th can be measured and stored in the memory, and the subtraction operation can be performed in software. It is also possible to measure time from a high-speed count of clock pulses.

In the first aspect of the present invention, since the heater 25 and the temperature sensor 20 are provided on the single thin film 10 having a cantilever shape or a crosslinked structure, a predetermined absolute temperature that is higher than room temperature (for example, 20 ° C.). When the temperature of the thin film 10 is raised to a temperature (set temperature) Th and a predetermined absolute temperature (set temperature) Tl, the heater heating needs to be shifted in time, and the heater must be continuously heated with two applied heater heating voltages. There is. Moreover, even when the room temperature, which is the temperature of the measured wet gas, slowly changes, for example, from 20 ° C. to 25 ° C., in order to correct so as to cancel the effect of the room temperature, these temperature fluctuations of the room temperature are ignored. The two heaters must be heated as fast as possible. For that purpose, first, the thin film 10 needs to be a thin film having a very small heat capacity and high-speed response. For this purpose, the thin film 10 needs to be a small thin film thermally separated from the substrate 1. As can be seen from Equation 3, the predetermined lower temperature (set temperature) Tl is not necessarily a temperature region where the thermal conductivity of gas and the thermal conductivity of water vapor are equal (when the gas is air, It can be seen that this temperature range does not need to be set to 120 to 150 ° C. as described above. However, if Tl is set in this temperature region, this temperature region is a temperature region insensitive to absolute humidity, and therefore there is an advantage that the measurement error of absolute humidity is reduced even if the set temperature slightly deviates.

In order to measure the absolute temperature of the thin film 10, when an absolute temperature sensor 21 formed on the substrate 1 and a thin film thermocouple as a temperature difference sensor as the temperature sensor 20 are used, The temperature of the substrate 1 is measured from the output of the absolute temperature sensor 21, and further, the temperature rise from the reference point of the substrate 1 (temperature difference) using a thin film thermocouple having a measurement point (hot junction) on the thin film 10. , And the absolute temperature of the thin film 10 is obtained by calculating the sum of these values. As the absolute temperature sensor 21, a temperature sensor having good linearity with respect to temperature is prepared, and the output and the thin film 10 have a measurement point (hot contact), corresponding to a temperature rise with the substrate 1 as a reference point. The output of the thin film thermocouple (as the temperature sensor 20) is adjusted by, for example, an amplifier circuit so as to have the same temperature coefficient, and these outputs are summed on the circuit, or summed on the software 2. a method for obtaining the absolute temperature of the thin film 10 by, for example, It is a temperature difference sensor necessary for knowing the absolute temperature of the substrate 1 from the output of the absolute temperature sensor 21 and using the absolute temperature of the substrate 1 to raise the temperature from the temperature to the predetermined set temperatures Th and Tl. There is a method of obtaining respective output voltages of the thin film thermocouple and determining that the predetermined set temperatures Th and Tl have been reached when these outputs are obtained. The absolute temperature measuring means for raising the temperature of the thin film 10 to the set temperatures Th and Tl that are predetermined absolute temperatures uses these methods, or when the absolute temperature sensor 22 is formed on the thin film 10. By using this, when it is determined that the predetermined set temperatures Th and Tl have been reached, the signal at that time can be taken out to the outside. The absolute temperature sensor 21 of the substrate 1 uses a pn junction between the emitter base of a pn junction diode or a transistor as an absolute temperature sensor having a good linearity with respect to temperature, and a forward voltage under a constant forward current. It can also be used as a thermo-diode that measures changes due to temperature, or a resistance temperature detector using a platinum resistor or the like. When the thin film 10 is provided with the absolute temperature sensor 22, the signal of the absolute temperature sensor 21 of the substrate 1 is not necessary, and the predetermined set temperatures Th and Tl are simply reached from the output signal of the absolute temperature sensor 22. You just have to judge. Then, when it is determined that the thin film 10 has reached the set temperatures Th and Tl by a signal from an absolute temperature measuring means equipped with a comparator or the like, for example, a control circuit that stops heater heating may be assembled. Then, the respective times th and tl from when the heater heating is started to when it is determined that the thin film 10 has reached the set temperatures Th and Tl may be measured by the method described above.

The absolute humidity sensor according to claim 2 of the present invention includes a heater 25a and a temperature sensor 20a in one thin film 10a out of at least two thin films 10a and 10b having the same shape thermally separated from the substrate 1. The other thin film 10b is also provided with an absolute humidity sensor chip having a heater 25b and a temperature sensor 20b, and the heaters 25a, 25b are changed by a change in thermal conductivity based on the amount of water vapor in the gas to be measured. In the absolute humidity sensor in which the temperature changes of the thin films 10a and 10b due to heating of the thin film 10a and 10b are measured by the temperature sensors 20a and 20b, the temperature sensors 20a and 20b are temperature difference sensors, and a voltage is applied to the heater 25a. Then, the heater is heated so that the thin film 10a changes from room temperature to a predetermined temperature Tl, and at the same time, a voltage is applied to the heater 25b to apply the heater. The thin film 10b is heated from room temperature to a predetermined temperature Th different from the predetermined temperature Tl, and each of the heaters 25a and 25b necessary for heating to the temperature Th and the temperature Tl is used. Using the information regarding the power consumption amount, the correction was made so as to eliminate the influence of the ambient temperature, the absolute humidity was obtained using the calibration data prepared in advance, the absolute temperature sensor 21 provided on the substrate 1 When the absolute temperature sensor 22 is also provided in the thin film 10a, 10b from the output obtained by combining the output and the output of each of the temperature sensors 20a, 20b, the absolute temperature of each of the thin films 10a, 10b is determined from the output. An absolute temperature measuring means is provided which can be set so that the thin film 10a and the thin film 10b are heated to the absolute temperatures Tl and Th, respectively, using the absolute temperature measuring means. It is characterized by that.

Here, a sensor chip including at least two thin films 10a and 10b having the same shape thermally separated from the substrate 1 is used. In Claim 1, since it is the single thin film 10, it heats to predetermined temperature Tl and predetermined temperature Th different from it, and in order to obtain | require the difference (subtraction electric energy) regarding those heater heating electric energy Therefore, it is necessary to shift the heater heating in time, and it is necessary to perform a subtraction operation by using a peak hold circuit or a memory. Here, since the two thin films 10a and 10b are provided, they are simultaneously heated by the same heater power, the time tl for the thin film 10a to reach the predetermined temperature Tl, and the thin film 10b at the predetermined temperature Th. The arrival time th can be measured simultaneously. Accordingly, the absolute humidity can be measured at high speed, but it is necessary to consider the arrangement in consideration of the influence of the convection effect by mutual heating by the two thin films 10a and 10b. Since the time th is longer than the time tl, for example, as described above, the time tl is reached in order to obtain the difference between the time when the thin film 10a reaches the time tl and the time when the thin film 10b reaches the time th. The time difference can also be measured from the magnitude of the voltage across the capacitor C and the count of the number of clock pulses flowing from the above-mentioned constant current starting from the time.

The absolute humidity measurement method is the same as the measurement method described in claim 1, and therefore the description thereof is omitted here.

The absolute humidity sensor according to claim 3 of the present invention is provided with an absolute humidity sensor chip having a heater 25 and a temperature sensor 20 on the thin film 10 thermally separated from the substrate 1, and is based on the amount of water vapor in the gas to be measured. In the absolute humidity sensor in which the temperature sensor 20 measures the temperature change of the thin film 10 due to the heating of the heater 25 due to the change in thermal conductivity, the temperature sensor 20 is a temperature difference sensor, and the heater 25 A voltage is applied to the heater, the heater is heated, and the thin film 10 is heated from room temperature to the predetermined absolute temperature Th. In the cooling process after the heating is stopped, the output voltage of the temperature sensor 20 is set for a predetermined period. Using time integration, information on the output of the time integration value and the output voltage of the temperature sensor 20 at a predetermined absolute temperature Tl different from the absolute temperature Th are used to determine the ambient temperature. The correction is made so as to eliminate the resonance and the absolute humidity is obtained using the calibration data prepared in advance, from the combined output of the output of the absolute temperature sensor 21 and the output of the temperature sensor 20 provided on the substrate 1, or When the absolute temperature sensor 22 is also provided in the thin film 10, an absolute temperature measuring means that knows the absolute temperature of the thin film 10 from the output is provided. Using the absolute temperature measuring means, the thin film 10 has the absolute temperature. It can be set to be heated by Th.

The major difference between the present invention and the above-described first aspect of the present invention is that, in the first aspect, the information on the power consumption in each heater 25 necessary for heating to the temperature Th and the temperature Tl is used. The absolute humidity was corrected using the calibration data prepared in advance to eliminate the influence of the ambient temperature. Each of the 20 output voltages is integrated over time for a predetermined period, and the output information of each time integrated value is used for correction so as to eliminate the influence of the ambient temperature, and the calibration data prepared in advance is used. The absolute humidity was calculated. As a method for time integration of the output voltage for a predetermined period, a signal current generated by the output voltage is passed through the capacitor in combination with the OP amplifier to store charges, and the voltage at both ends thereof is used as the time integration value. It is possible to make additions on software using a memory. Of course, at the end of time integration, resetting can be achieved by a known technique so that the output becomes zero.

That is, in claim 1, the information on the power consumption in the heater 25 is used to determine the absolute humidity, whereas here the output voltage of the temperature difference sensor (thermocouple) as the temperature sensor 20 is used. The time integration value is used, and the time integration of power consumption and thermocouple output is also common. In the cooling process after stopping heating here, each output voltage of the thin film thermocouple is integrated over time for a predetermined period, and the output information of each integrated time is used, so there is no noise during heater heating , Signal-to-noise and S / N can be expected to increase. Therefore, a highly accurate absolute humidity sensor can be provided. Further, when the thin film 10 reaches a predetermined temperature Tl or a predetermined temperature Th using an absolute temperature measuring means for measuring the absolute temperature of the thin film 10, the heating of the heater 25 is stopped and the cooling process immediately after them is stopped. Integrate the thermocouple output for a predetermined time at, and subtract those outputs to correct the effect of room temperature so that it corresponds to the absolute humidity based on the calibration data prepared in advance. It is.

In the first aspect of the invention, the voltage applied to the heater 25, Vl and Vh, can be compared only by the time until the thin film 10 reaches the absolute temperature Tl and Th, only tl and th. Although there is a restriction that it is simple, in the invention according to claim 3, the heater heating of the thin film 10 may be performed once, and the thin film 10 only needs to reach the higher (set) temperature Th by the heater heating. There is also a difference. However, the second heater heating may be performed, but here, the case where the heater of the thin film 10 is heated only once will be described. Since the output voltage of the thin film thermocouple which is the temperature sensor 20 at the lower set temperature Tl of the thin film 10 has the absolute temperature sensor 21 on the substrate 1, the absolute temperature measuring means is used based on the information from there. Use it to know. Therefore, in the cooling process after the heater heating is stopped, the integration operation can be stopped when the temperature of the thin film 10 is cooled from the initial higher (set) absolute temperature Th and reaches the set temperature Tl. That is, the predetermined time integration time (integration time) is, for example, after the heater heating of the thin film 10 is stopped, the temperature of the thin film 10 is cooled from the higher (set) absolute temperature Th to the predetermined temperature Tl. It is the time to reach. The time integration operation of the thermocouple output is stopped when the output voltage Vsl of the temperature sensor 20 corresponding to the predetermined absolute temperature Tl of the thin film 10 is reached. The time integration operation of the thermocouple output is performed by constantly changing the value of the output voltage Vsl from the output voltage of the temperature sensor 20 in the process in which the temperature of the thin film 10 is cooled from the initial higher (set) absolute temperature Th. The subtracted output voltage may be integrated, or the output voltage Vsl is integrated for the same integration time from the integration value Sh after always integrating the output voltage of the temperature sensor 20 for the above integration period. The absolute humidity may be obtained by using the subtracted integral value ΔS (integrated value Sh−Sl) obtained by subtracting the value Sl.

Rather than measuring the temperature when the thin film 10 is heated by the heater 25, the temperature can be measured with a higher S / N ratio by measuring the temperature of the thin film 10 during the cooling period. Since the temperature decreases rapidly as the heat capacity of the thin film 10 decreases, the temperature measurement at a specific time in the cooling period has a large error. However, this error can be reduced by integrating the output voltage of the temperature sensor 20 mounted on the thin film 10 for a predetermined period of the cooling period, and further, thermal fluctuation, noise of the measurement electronic circuit, etc. Positive and negative fluctuations (fluctuations) are canceled out by integration over a long period of time, and a difference in small temperature changes is greatly extracted by continuous time integration rather than measurement of the output value of the temperature sensor 20 at a specific time. That is, there is an amplification effect. In this way, if the time integration of the output of the temperature sensor 20 during the cooling period is performed, it is not always necessary to measure the temperature of the thin film 10 during heating of the heater with much noise.

In general, when the surrounding medium is a gas, the thermal conductivity of the gas increases as the temperature rises. When the temperature rise from room temperature is increased to about several hundred degrees Celsius, it is the basis for operation as an absolute humidity sensor. It is necessary to perform a measurement operation that fully considers the temperature dependence of the thermal conductivity of the surrounding gas. In this way, after heating the thin film 10 to a high temperature, the heating is stopped, and when the cooling process is started, the high temperature is quickly cooled due to the high thermal conductivity, and as the temperature approaches room temperature, the thermal conductivity becomes small. It will be cooled more slowly than at high temperatures. Also, for example, when the heater is heated to a high temperature with a predetermined power, water vapor (absolute humidity) having a high thermal conductivity is included, and if the thermal conductivity is further increased, the temperature is higher than that in the case where water vapor is not included. Since the increase is small and cools quickly, the time integral value of the output of the temperature difference sensor is even smaller than when there is no water vapor. In this way, the magnitude of the thermal conductivity of the ambient gas from the time integral value of the output of the temperature difference sensor during the cooling process after stopping the heater heating, that is, using the calibration data acquired in advance, for example, Thus, the absolute humidity can be measured by corresponding to the absolute humidity.

The absolute humidity sensor according to claim 4 of the present invention is provided with an absolute humidity sensor chip having a heater 25 and a temperature sensor 20 on the thin film 10 thermally separated from the substrate 1, and heat based on the amount of water vapor in the gas to be measured. In the absolute humidity sensor in which the temperature change of the thin film 10 due to the heating of the heater 25 is measured by the temperature sensor 20 due to the change in conductivity, the temperature sensor 20 is a temperature difference sensor. A voltage is applied and the first heater is heated to heat the thin film 10 from room temperature to a predetermined absolute temperature Tl. Thereafter, the first heater is continuously heated, or the temperature of the gas to be measured The second heater is heated by the heater 25 in such a short time that the fluctuation of the temperature is negligible, and the thin film 10 is moved from room temperature to a predetermined absolute temperature different from the predetermined absolute temperature Tl. In the cooling process after stopping heating, until the temperature vs. temperature Th is reached, each output voltage of the temperature sensor 20 is integrated over time for a predetermined period, and the output information of each time integrated value is used. The correction is made so as to eliminate the influence of the ambient temperature, the absolute humidity is obtained using the calibration data prepared in advance, and the combined output of the output of the absolute temperature sensor 21 and the output of the temperature sensor 20 provided on the substrate 1 Or, if the thin film 10 is also provided with the absolute temperature sensor 22, the thin film 10 is provided with an absolute temperature measuring means that knows the absolute temperature of the thin film 10 from its output. Can be set to be heated to absolute temperatures Tl and Th.

The major difference between the present invention and the above-described invention of claim 3 is that, in claim 3, the heater of the thin film 10 is heated only once until the predetermined absolute temperature Th is reached. In the present invention, the heater heating of the thin film 10 is performed twice until the predetermined absolute temperature Tl is reached following the first heater heating until the predetermined absolute temperature Th is reached. Reach the predetermined absolute temperatures Th and Tl, maintain the absolute temperatures Th and Tl as necessary, and check the output voltage of the temperature sensor 20 which is a temperature difference sensor. Is set to Vsl. However, since there is a time difference between the first heater heating and the second heater heating, in the comparison of the time integral values of the output voltages of these temperature sensors 20, at least one time integral value is held, It is necessary to compare. The integration operation is the same as that described in claim 3, and a detailed description thereof is omitted. In this way, in the cooling process after the heating is stopped, the output voltage of the temperature sensor 20 is integrated over time for a predetermined period (integration time), and the information on the output of each time integrated value is used to calculate the ambient temperature. The correction is made so as to eliminate the influence, and the absolute humidity is obtained using calibration data prepared in advance.

In the same manner as described above for claim 3, in the cooling process after stopping heating, each output voltage of the thin film thermocouple is integrated over time for a predetermined period, and the output information of each time integrated value is used. There is no noise when heating the heater, and signal-to-noise and S / N can be expected to increase. Therefore, a highly accurate absolute humidity sensor can be provided. Further, by using an absolute temperature measuring means for measuring the absolute temperature of the thin film 10, when the thin film 10 reaches a predetermined temperature Tl and a predetermined temperature Th by each heater heating, the heating of the heater 25 is stopped and a predetermined temperature is measured. The output voltage Vsl of the temperature sensor 20 when the temperature Tl is reached is held by, for example, a peak hold circuit or the like, and this is held by the thin film thermocouple (temperature sensor 20) in the cooling process from the set temperature Th on the high temperature side. By subtracting from the value of the output voltage Vs, the voltage of this subtraction is integrated over time until the thin film 10 reaches Tl, and is corrected so as to cancel the influence of room temperature. You may make it respond | correspond with humidity.

In the absolute humidity sensor according to claim 5 of the present invention, the start of a predetermined period of time integration of the output of the temperature sensor 20 is immediately after the heating of the heater 25 is stopped.

In general, the heating / cooling cycle of the heater 25 is often performed in synchronization with a clock pulse. Therefore, it is possible to integrate the output of the temperature sensor in the middle of the cooling cycle (cooling process), but using the clock pulse heater heating stop timing is achieved with an inexpensive circuit configuration, Since the time integration of the output of the temperature sensor 20 is started immediately after the heater heating is stopped, the error in calculating the absolute humidity is reduced even in the subtraction calculation of the output for canceling the effect of the room temperature. Further, since the output of the temperature sensor 20 is greater immediately after the heating is stopped, the integrated output signal is increased, and a highly sensitive and highly accurate absolute humidity sensor can be provided.

In the absolute humidity sensor according to claim 6 of the present invention, at the end of a predetermined period of time integration of the output of the temperature sensor 20 in claims 3 to 5, the thin film 10 is in the cooling process after stopping the heater heating. This is a case where the temperature is cooled from the predetermined higher temperature Th and becomes equal to the predetermined lower temperature Tl.

The main purpose is to cancel the effect of the ambient temperature (room temperature) by utilizing the difference in time integration of the output voltage of the temperature sensor 20, for example, even if the room temperature is 0 ° C., the environment is 30 ° C. However, the measured absolute humidity H is not related to the temperature at room temperature. For this purpose, during the time integration of the output voltage of the temperature sensor 20 at a portion where the temperature is higher than the predetermined lower (set) temperature Tl, an output voltage component obtained by subtracting the output voltage Vsl of the temperature sensor 20 at the temperature Tl. The time integration of Therefore, at the end of the predetermined period of time integration of the output (voltage) of the temperature sensor 20, the thin film 10 is initially heated to the predetermined higher absolute temperature Th, so that the cooling process after the heater heating is stopped. Then, when it is determined that the temperature has dropped from the higher absolute temperature Th in the humid gas and has become equal to the predetermined lower temperature Tl, the period (integration time) may be integrated over time. . Then, when the temperature of the thin film 10 is heated by the heater and reaches a predetermined lower (set) temperature Tl, the output voltage of the temperature sensor 20 mounted on them is measured by a peak hold circuit or the like. Hold this value during time integration, for example, while cooling from the higher absolute temperature Th to the predetermined lower (set) absolute temperature Tl, at that time the higher temperature side The difference may be integrated while subtracting from the output voltage of the temperature sensor 20.

In the absolute humidity sensor according to claim 7 of the present invention, the thin film 10 or the thin films 10a, 10b is in a wet gas that does not reach the dew point, is in a wet gas that has reached the dew point, or is submerged in water. Alternatively, a minute electric power that can determine at least one of the items of whether solid matter including ice is attached is supplied to the heater 25 or the heaters 25a and 25b, and the thin film 10 or the thin film based thereon When the time change of the temperature rise of 10a, 10b is measured by the temperature sensor 20 or the temperature sensors 20a, 20b, and the item is determined using the output of the absolute temperature sensor 21 as necessary. It is.

The sensor chip of the absolute humidity sensor is composed of a thin film 10 having a minute size created by MEMS technology, for example, a cantilever shape having a length of 1 mm, a width of 0.2 mm, and a thickness of about 0.01 mm, a bridge structure, or a diaphragm shape. Has been. For example, the heater 25 and the temperature sensor 20 are formed on the cantilever-like thin film 10. If wet air, which is the gas to be measured, has reached the dew point, there is a possibility that water droplets are attached to the thin film 10. Further, when the ambient temperature (room temperature) is below freezing point, there is a possibility that ice particles are attached on the thin film 10. Further, the sensor chip temperature is submerged, and the thin film 10 is also It is also assumed that the environment is submerged together. Under such circumstances, for example, if a voltage is applied to the heater 25 or the like and the heater is heated so that the predetermined set temperature Th becomes 500 ° C., the cantilever-like thin film 10 may be destroyed. is there. What is required as an absolute humidity sensor is the amount of water vapor in the humid air. If the absolute temperature sensor 21 formed on the substrate 1 is 0 ° C. or less, there is a possibility that ice is attached. Further, as a result of measuring the ambient temperature (room temperature) with the absolute temperature sensor 21, there may be water droplets on the thin film 10 because the dew point has been reached even at a temperature of 0 ° C. or higher. In absolute humidity measurement under such an environment, if necessary, the ambient temperature (room temperature) is measured by the absolute temperature sensor 21, and first, the possibility that ice is attached is determined. Better.

In addition, the heater 10 is not suddenly heated so that the two predetermined temperatures Tl and Th described above are reached from room temperature. First, the thin film 10 or the thin films 10a and 10b is not supplied with a small predetermined power (after all). A small voltage is applied to the heater 25 or the heaters 25a and 25b, and the temporal state of the temperature increase of the thin film 10 or the thin films 10a and 10b at that time is examined. When these thin films are in water, the dew point is reached. If there is an ice-containing substance on the surface, its heat capacity will increase, so if it rises slowly compared to the rate of temperature rise in humid air or is in water, By not raising the temperature, it is in a wet gas that does not reach the dew point, is in a wet gas that has reached the dew point, is submerged in water, or has a solid substance that contains ice attached. This absolute humidity sensor for the item can be given a judgment function. When the dew point has been reached or when ice particles have adhered to the surface, the thin film such as the thin film 10 has melted until the water drops when the dew point is reached, The temperature rises slowly, but suddenly rises when there are no water drops. In this state, the relative humidity is 100%, and the absolute humidity at that time is also measured from the saturated water vapor amount at that temperature (room temperature) by measuring the ambient temperature using the absolute temperature sensor 21 of the substrate 1. Desired. Of course, the absolute humidity sensor can be calibrated by creating a saturated water vapor state that reaches such a dew point.

The absolute humidity sensor according to claim 8 of the present invention is the case where the lower one of the different temperatures Th and Tl is set to a temperature in the range of 100 ° C. to 270 ° C.

When the lower temperature Tl is in the range of 120 ° C. to 150 ° C., the thermal conductivity of air and the thermal conductivity of water vapor (H ₂ O) are almost equal, so the amount of water vapor, that is, the absolute humidity is An irrelevant region of thermal conductivity. Therefore, if this temperature region is used as a lower set temperature Tl as a reference for room temperature correction such as power consumption by heating from room temperature, there is an advantage that measurement error of absolute humidity is reduced as described above. is there. However, as shown in the result from Equation 3, the lower temperature Tl is essentially higher than room temperature, and room temperature can be corrected if it is lower than the predetermined higher set temperature Th. is there. Here, the lower absolute temperature Tl is set to about 100 ° C. to about 270 ° C., and the measurement error is also reduced in obtaining calibration data prepared in advance for calculating the absolute humidity. . At this time, the larger the difference between the lower set absolute temperature Tl and the higher set temperature Th, the greater the difference when time integration is performed, and the absolute humidity can be measured with high accuracy. It is better to make the temperature as high as ℃.

The absolute humidity sensor according to claim 9 of the present invention is a case where a semiconductor is used as at least one thermoconductor of the temperature difference sensor.

When using a thermocouple or a thermopile as a temperature difference sensor, in order to generate a large thermoelectromotive force, using a thermoconductor having a large Seebeck coefficient provides a highly sensitive and accurate temperature difference sensor. It has been found that the Seebeck coefficient of a semiconductor is about an order of magnitude higher than that of metal, and that the same semiconductor has a higher Seebeck coefficient when the resistivity is higher. Therefore, by using a semiconductor, particularly a silicon single crystal thin film as the thin film 10 and the like, a sensor device using the MEMS technology is inexpensive and easy to make. Of course, when a thin film thermocouple is formed by combining p-type and n-type semiconductors having positive and negative polarities of the Seebeck coefficient, the output will increase further, but from the viewpoint of the simplicity of the manufacturing process, at least one of the thermoconductors will be used. It is better to use a semiconductor.

The absolute humidity sensor according to claim 10 of the present invention is a case where the thin film 10 or the thin films 10a and 10b are made of a silicon semiconductor.

More than 90% of current integrated circuits are made of silicon semiconductors on silicon semiconductor substrates. Also, MEMS technology using silicon semiconductors is in a mature area. Thus, by using the silicon semiconductor substrate 1 for the sensor chip of the absolute humidity sensor, the absolute temperature sensor 21 such as a diode formed on the substrate 1, the thin film thermocouple formed on the thin film 10 and the like can be easily manufactured. An integrated circuit such as an arithmetic circuit, a control circuit, a display circuit, and a drive circuit can be mounted, and a small and inexpensive absolute humidity sensor can be provided.

The absolute humidity sensor according to claim 11 of the present invention is a case where the absolute temperature sensor 21 and the absolute temperature sensor 22 are semiconductor diodes.

In semiconductor diodes such as pn junction diodes and Schottky diodes, it is known that the temperature dependence of the forward voltage (forward voltage) under a constant forward current is linearly related to the absolute temperature T. It is used as a temperature sensor. It has also been found that the logarithm of the diode current under a constant forward voltage is linearly related to the reciprocal of the absolute temperature T, and is used as a diode thermistor. As these semiconductor diodes, a pn junction diode between the emitter E and the base B of the bipolar transistor may be used. In this case, the collector C and the base B are short-circuited externally to connect the emitter E to one terminal. The base B and the collector C are preferably used as a two-terminal semiconductor diode having the other terminal as the short-circuited portion. As an absolute temperature sensor 21 that is formed on the substrate 1 and measures the ambient temperature (room temperature), if the room temperature is 150 ° C. or lower, a forward voltage is applied to the semiconductor diode described above, and It is suitable for measuring room temperature, which is an absolute temperature, from the temperature dependence of current and forward voltage.

In a pn junction diode as a semiconductor diode, it is possible to make a pn junction small, and it is suitable for measuring a local absolute temperature. Further, in particular, a constant reverse voltage (reverse voltage) is applied to the pn junction. ) And using the temperature dependence of the reverse current, absolute temperature measurement at a relatively high temperature (150 ° C. or higher) is possible. When the thin film 10 is an SOI layer, the pn junction diode as the absolute temperature sensor 22 is exposed to a high temperature of, for example, 400 ° C. or higher, and the absolute temperature needs to be measured. It is preferable to apply a small reverse voltage, measure the reverse current at that time, and convert it to an absolute temperature. However, when the thin film 10 of the SOI layer common to the substrate 1 is used, it is necessary to consider the points of common grounding with the heater heating, the absolute temperature sensor 21, the temperature sensor 20, and the like in view of the circuit configuration.

The absolute humidity sensor according to claim 12 of the present invention is a case where the temperature sensor 20 is also used as the heater 25.

In general, the temperature sensor is an absolute temperature sensor using the resistance temperature coefficient of a resistance temperature detector such as a metal such as a platinum resistor, and the temperature dependence of the current when a diode such as a pn junction diode is applied in the forward or reverse direction. There is an absolute temperature sensor that uses the temperature dependence of the forward voltage at a constant current or a predetermined current, and a temperature difference sensor that uses a thin film thermocouple or the like. Here, a temperature difference sensor such as a thin film thermocouple is used as the temperature sensor 20, and this temperature sensor 20 is also used as the heater 25.

When a temperature difference sensor such as a thin film thermocouple is used, it is difficult to operate the heater operation and the temperature sensor at the same time, and it is necessary to alternate these operations in a time division manner. A thin film thermocouple as a temperature difference sensor has one thermoelectric conductor formed of a semiconductor thin film constituting the thin film 10 or the like, and the other thermoelectric such as a metal thin film via an insulating film such as a silicon oxide film (SiO ₂ film). The conductor can be easily formed, the ohmic contact only needs to be formed as a measurement point (hot contact), can withstand high temperature operation of 500 ° C. or more, and the manufacturing process is extremely simple. In addition, at the end of the cooling process, the temperature returns to room temperature, which is the temperature of the surrounding medium, and the output of the temperature sensor 20 also returns to zero, so that there is little error even with respect to time integration and some fluctuations in integration time. High-precision measurement is possible.

In this way, when the temperature sensor 20 is also used as the heater 25, the absolute temperature sensor 22 such as the semiconductor diode as described above is mounted on the thin film 10 or the like separately from the temperature difference sensor as the temperature sensor 20. In addition, it is possible to measure the absolute temperature of the thin film 10 etc. when the heater is heated. When measuring the predetermined temperature Tl and Th during the heater heating, the heater action and temperature difference detection are performed in a time-sharing manner. Since it is not necessary to alternate the operation of the action, the circuit becomes simple.

The absolute humidity sensor according to the thirteenth aspect of the present invention includes at least a power supply circuit, an amplifier circuit, an arithmetic circuit, and a control circuit.

The power circuit is a circuit related to driving the heater 25 and the like and supplying power to other circuits, and the amplifier circuit is a circuit that amplifies the output of the temperature sensor 20 and the like. Although it is expressed as the output of the temperature sensor 20 in the above description, generally, the raw output of the temperature sensor 20 is small, so it indicates the output after the first stage amplification. Of course, the raw output signal of the temperature sensor 20 is Sometimes it points. The arithmetic circuit uses the output from the temperature sensor 20 or the temperature sensors 20a and 20b, the subtraction or integration based on these, and the output signals thereof, and further calculates the absolute humidity by combining with the memory circuit. This circuit is mainly used. The control circuit is a circuit that performs temperature control of the heater 25, etc., setting of energization time, cooling period, integration time, pulse integration of the heater 25, etc., control of time integration operation and subtraction operation, feedback control, and the like. .

The absolute humidity sensor according to claim 14 of the present invention obtains the relative humidity based on the output of the absolute temperature sensor 21 and the information on the absolute humidity from the absolute humidity sensor according to any one of claims 1 to 12. It is a case where it is possible to do.

Absolute humidity is, for example, expressed in grams (g), the unit of weight of the amount of water vapor dissolved in 1 cubic meter of wet air. The amount of water vapor can dissolve without saturating, but the upper limit is only temperature dependent and is essentially independent of the temperature of the humid air unless the dew point is reached. On the other hand, there is a limit to the amount of water vapor that can be dissolved depending on the temperature of the humid air, and the limit value when no further water can be dissolved is the saturated water vapor amount at that temperature. At this time, the relative humidity is 100%. Therefore, if the temperature of the humid air is known, the saturated water vapor amount of a gas such as air is determined. Therefore, the absolute humidity, which is actually the water vapor amount of the wet air, is a ratio of the relative humidity to the saturated water vapor amount at that temperature. Therefore, if the temperature of the humid air is measured by the absolute temperature sensor 21 provided on the substrate 1 and the absolute humidity is measured by the absolute humidity sensor of the present invention, the known data relating to the saturated water vapor amount at each temperature is used. Thus, the relative humidity can be calculated by calculation. Here, an absolute humidity sensor having a function of calculating relative humidity is provided in this way.

The absolute humidity sensor chip according to the fifteenth aspect of the present invention is a heater 25 or heaters 25a and 25b and a temperature difference sensor corresponding to each of the cantilever-like thin film 10 or thin films 10a and 10b thermally separated from the substrate 1. A temperature sensor 20 or temperature sensors 20a, 20b, and the temperature difference sensor is provided with a measuring point (hot contact) near the tip of the cantilever-shaped thin film 10 or thin film 10a, 10b, heater 25 or heater 25a. , 25b are arranged so as to surround the measurement point (hot junction) of the temperature difference sensor so that the cantilever-like thin film 10 or the vicinity of the tip of the thin film 10a, 10b is uniformly heated. Is.

In the absolute humidity sensor, the thermal conductivity of wet air exceeds the temperature range of 120 ° C to 150 ° C, which is a temperature range of Tl that does not depend on the magnitude of absolute humidity, and the higher the temperature, the more linear In particular, it has been found that the thermal conductivity of wet air increases. Therefore, the temperature of the thin film 10 or the like by the heater heating (the thin film 10 or the like includes the thin film 10 and the thin film 10a and the thin film 10b are expressed in this way) is, for example, 500 ° C. I want to make it very hot. For this purpose, the cantilever-like thin film 10 or the like is preferable because heat is less likely to escape to the substrate than the thin film 10 or the like having a cross-linked structure. Further, heat dissipation from the heated thin film 10 or the like should be promoted, and if the volume of the same thin film 10 or the like is the same, the thin film shape has the largest surface area, so the thin cantilever shape is preferable. It is desirable that the temperature of the temperature difference sensor (temperature contact point) for temperature detection be so set as to surround the temperature difference sensor so that the temperature of the tip is uniform because the temperature of the tip is the highest. Further, it is better to increase the area of contact with wet air by increasing the area of the tip where the measurement point (hot contact) of the temperature difference sensor such as the cantilever thin film 10 is formed. For this purpose, it is necessary to arrange the heater wiring so as to surround the measurement point (hot junction) and to uniformly generate heat in the large area cantilever thin film 10 and the like. Further, as the heater material, a material having a high resistivity, a high melting point, and not rusting is desirable. Therefore, nichrome (NiCr) is preferable. Nichrome has a very low temperature coefficient of resistance, but is not a problem because it is used as a heater material.

The absolute humidity sensor chip according to claim 16 of the present invention corresponds to each of the thin film 10 or the thin films 10a, 10b thermally separated from the substrate 1, and the temperature sensor 20 which is a temperature difference sensor with the heater 25 or the heaters 25a, 25b. Alternatively, the temperature sensor 20a, 20b is provided, and the absolute temperature sensor 22 or the absolute temperature sensor 22a, 22b is also provided corresponding to each of the temperature sensors 20a, 20b.

Since a temperature difference sensor such as a thin film thermocouple is used as the temperature sensor 20 or the like, the absolute temperature of the thin film 10 or the like is known in some form for heating to a predetermined (designated) absolute temperature Tl or absolute temperature Th. There is a need. In order to know the temperature of the thin film 10 during the heating of the heater, the temperature rises from the substrate 1 by operating as a temperature difference sensor during an instantaneous period when the heating of the heater is stopped, for example, by intermittently heating the heater. The minute temperature is checked, combined with the absolute temperature sensor formed on the substrate 1, the temperature of the thin film 10 at that time is measured, and this is repeated, and the temperature rising state of the thin film 10 is grasped. Although there is a method of measuring the temperature at the time and stopping the heater heating when the temperature reaches a predetermined specified temperature, the heat capacity of the thin film 10 is small, so that the temperature difference between heating and cooling is large, and such measurement is performed. Is also difficult in terms of circuit. Therefore, here, an absolute temperature sensor is formed on the thin film 10 or the like so that the temperature of the thin film 10 or the like can be directly measured in real time. It is suitable for heating and heating the thin film 10 and the like to a specified absolute temperature Tl or Th.

An absolute temperature sensor 22 or the like formed on the thin film 10 or the like is formed near the measurement point (hot contact) so that the temperature near the measurement point (hot contact) of the temperature difference sensor such as the temperature sensor 20 can be measured. Better to do. If the thin film 10 or the like is in the shape of a cantilever, the tip portion thereof is the end portion of the thin film 10, and therefore, if the absolute temperature sensor 22 or the like is formed there, the influence of the heater current during heater heating can be reduced. In addition, by forming the absolute temperature sensor 22 and the like near the measurement point (hot junction) of the temperature difference sensor (thin film thermocouple), the absolute temperature near the measurement point (hot junction) can be measured. When the thin film thermocouple is also used as the heater 25 or the like, the measurement point (hot junction) is the region where the temperature is highest when provided near the tip of the cantilever, and further, the measurement point of the thin film thermocouple such as the temperature sensor 20 Since the (hot junction) is a location where the temperature is measured with respect to the reference point (cold junction) (formed on the substrate 1), the absolute temperature sensor 22 and the like are also formed in the vicinity so that the temperature is the highest. The absolute temperature near the measurement point (hot junction) in the high area is measured. As an absolute temperature sensor that is a heat conduction sensor, the higher the temperature, the greater the sensitivity. Therefore, it is important to measure the temperature in the highest temperature region of the thin film 10 or the like.

The absolute humidity sensor chip according to claim 17 of the present invention is a case where the heater 25 or the heaters 25a and 25b are also used as the temperature sensor 20 or the temperature sensors 20a and 20b which are temperature difference sensors.

When an absolute temperature sensor such as a platinum resistor is also used as a heater, it is easy to operate the temperature sensor 20 or the like while heating the heater 25 or the like. However, in high temperature operation, there is a problem of aging of the platinum resistor made into a thin wire. Furthermore, since it is an absolute temperature sensor, the output from the absolute temperature sensor does not generally become zero even if it returns to room temperature in the cooling process, or the accuracy including the reproducibility of the time integral value does not improve because it does not approach zero. There are difficulties. A semiconductor junction absolute temperature sensor such as a pn junction diode can be easily formed on the semiconductor thin film 10 or the like, or a minute pn junction can be easily used as the heater 25 and the temperature sensor 20. It is difficult to perform these operations, and it is necessary to alternate these operations in time division. Further, even when a temperature difference sensor such as a thin film thermocouple is used, it is difficult to operate the heater operation and the temperature sensor at the same time, and it is necessary to alternately perform these operations in a time division manner. However, by mounting the absolute temperature sensor 22 or the like on the thin film 10 or the like separately from the temperature difference sensor 20 or the like mounted on the thin film 10 or the like, the absolute temperature Tl or Th of the thin film 10 or the like can be measured. Therefore, operating the temperature sensor 20 or the like as a heater and operating the temperature sensor 20 or the like as a temperature difference sensor in the cooling process that gradually approaches the room temperature after the heater heating is stopped is very important from the viewpoint of temperature compensation. Has an advantage.

When the heater 25 or the like is also used as the temperature sensor 20 or the like that is a temperature difference sensor, it is necessary to flow a large current when acting as a heater. In the operation as a temperature difference sensor such as a thermocouple, generally, since the release voltage is measured without passing current, the wiring as the thermoconductor of the temperature difference sensor may have a large resistance or a thin wiring. . However, since a large amount of current flows to serve as a heater, a large resistance requires a large applied voltage, so the resistance is small and the wiring is wide and thick enough to withstand a large current. There is a need to.

In an absolute humidity sensor chip according to claim 18 of the present invention, the absolute temperature sensor 22 or the absolute temperature sensors 22a and 22b are semiconductor diodes, and at least a part of the supply voltage to the heater 25 or the heaters 25a and 25b is the semiconductor diode. In this case, wiring is performed so that it can be used as a drive power source.

A semiconductor diode is used as a known absolute temperature sensor by using a pn junction of one of two pn junctions of a pn junction diode or a bipolar transistor, for example, a pn junction between an emitter E and a base B. Can do. When measuring room temperature, which is a temperature of 150 ° C. or lower, apply a forward voltage and measure the rising voltage under a constant forward current or measure the magnitude of the forward current under a constant forward voltage. The temperature is measured from their temperature dependence. This is suitable when a semiconductor diode is used as the absolute temperature sensor 21 formed on the substrate 1. Here, particularly in the case of the absolute temperature sensor 22 or the like formed on the thin film 10 or the like, a temperature of 150 ° C. or higher is measured. In this case, a predetermined fixed reverse voltage of about 0.5 V to 1 V is applied, and the temperature is measured from the magnitude of the reverse current at that time.

When the thin film 10 or the like is formed in a cantilever shape, the voltage is supplied to the heater 25 or the like through a metal thin film wiring that extends to the vicinity of the tip. In particular, in the operation as a temperature difference sensor / heater, the metal thin film wiring is used as a thermoelectric thin film that can withstand high temperatures and hardly rust, and often has a resistance value of several Ω or more. Moreover, it can also design and manufacture so that it may become the predetermined resistance value. In order to obtain a temperature increase of about 200 ° C., for example, the supply voltage to the heater 25 is about 5V, and the voltage drop in the metal thin film wiring is about 0.5V. This voltage may be used as it is as a reverse voltage of a semiconductor diode used as the absolute temperature sensor 22 or the like. When this voltage is large, a terminal is taken out from the middle of the metal thin film wiring to reverse the semiconductor diode. If wiring is performed so that it can be used as a directional voltage, the semiconductor diode can be operated as the absolute temperature sensor 22 or the like by using this voltage when the heater is heated. Further, when the driving power supply voltage necessary for operating the semiconductor diode as the absolute temperature sensor 22 or the like for applying a reverse voltage is not reached, for example, a necessary voltage is newly introduced from the outside to The wiring may be formed so that the drive power supply voltage can be obtained.

The semiconductor diode may further include a voltage terminal for measuring a voltage applied to the semiconductor diode when a current flows, and a current terminal for measuring the current flowing through the semiconductor diode. good. When heating the heater, a voltage of 5 V or more is applied to the heater resistance of about 50Ω as necessary. Therefore, the voltage generated at both ends of the wiring resistance to the heater 25 of several Ω cannot be ignored. In the present invention, a semiconductor diode as the absolute temperature sensor 22 or the like is often formed on a single crystal silicon thin film made of an SOI layer. In this case, the thin film thermocouple as the temperature sensor 20 or the like is used in combination with the heater 25 or the like, and is formed in the same SOI layer as the semiconductor diode as the absolute temperature sensor 22 or the like. When driven, a large heater current flows through the common SOI layer, and the semiconductor diode is in the reverse direction due to problems such as voltage drop, common ground on the circuit configuration, and relatively low heater resistance. Even when the voltage is high, the reverse current becomes very large at a high temperature of 400 ° C. to 500 ° C., and the internal resistance becomes equivalently small. become. Therefore, here, it is necessary to measure the voltage applied only to the semiconductor diode independently of the voltage drop due to the heater current. For this reason, only the current terminal for measuring the current flowing through the semiconductor diode and only the semiconductor diode are measured. It is more accurate to form a voltage terminal for measuring a voltage applied to the semiconductor device so that an accurate voltage applied to the semiconductor diode can be measured as a four-terminal method. Of course, in the four-terminal method, when the voltage drop due to the resistance of the wiring on one current terminal side can be ignored, the terminal side can be used as three terminals with the voltage terminal and current terminal in common.

In the absolute temperature sensor of the present invention, a temperature difference sensor such as a heater 25 formed on a single thin film 10 thermally separated from the substrate 1 and a thin film thermocouple as the temperature sensor 20 is used, and if necessary, an absolute temperature sensor. 22 is formed on the thin film 10, and the first heater is heated from room temperature from about 100 ° C. to about 200 ° C. as a predetermined absolute temperature Tl that is higher than room temperature and has almost no humidity dependence. Heating is continued until a predetermined absolute temperature Th of a high temperature, for example, 500 ° C., or the second heater is heated from the room temperature at different times, and the ambient temperature (room temperature) is determined by the amount of subtraction power required for these heatings. There is an advantage that the absolute humidity excluding the influence of) can be obtained.

In the absolute temperature sensor of the present invention, the electric energy up to the temperature Tl by the first heater heating and the subtraction electric energy of the electric energy up to the subsequent temperature Th or the electric energy up to the temperature Th by the second heater heating are the same. As a result, it was found that the heater material with extremely small resistance temperature coefficient such as Nichrome thin film is proportional to the difference in time required to reach the predetermined temperature, and the measurement of absolute humidity is simplified. In addition, there is an advantage that a highly sensitive absolute humidity sensor can be provided as compared with the case where a difference in power by conventional heater voltage measurement is used.

In the absolute temperature sensor of the present invention, the single thin film 10 thermally separated from the substrate 1 may be continuously heated from a predetermined absolute temperature Tl to a higher temperature Th. However, at least two thin films 10a having the same shape may be used. Since the heater 25a and the thin film 10b, and the temperature difference sensor as the temperature sensor 20a and the like can be heated simultaneously, the electric energy can be subtracted in real time and the influence of the ambient temperature (room temperature) can be obtained. There is an advantage that the time required for obtaining the absolute humidity excluding the time is shortened.

In the absolute temperature sensor of the present invention, a temperature difference sensor such as a heater 25 formed on a single thin film 10 thermally separated from the substrate 1 and a thin film thermocouple as the temperature sensor 20 is used, and if necessary, an absolute temperature sensor. 22 is formed on the thin film 10, and the first heater is heated from room temperature from about 100 ° C. to about 200 ° C. as a predetermined absolute temperature Tl that is higher than room temperature and has almost no humidity dependence. The first heating is continued until a predetermined absolute temperature Th of a high temperature, for example, 500 ° C., or the second heater is heated from room temperature at a different time, and the temperature is reduced in the cooling process after the heating is stopped. Each output voltage of the sensor 20 is integrated over a predetermined period of time, and the absolute humidity excluding the influence of the ambient temperature (room temperature) can be obtained by using the subtracted integrated value information of each time integrated value. There is an advantage that.

In the absolute temperature sensor of the present invention, the single thin film 10 thermally separated from the substrate 1 may be continuously heated from a predetermined absolute temperature Tl to a higher temperature Th. However, at least two thin films 10a having the same shape may be used. And the thin film 10b, and the heater 25a and the temperature difference sensor as the temperature sensor 20a and the like can be heated simultaneously, so that the output voltage of each of the temperature sensors 20a and 20b is set to a predetermined value in the cooling process after the heating is stopped. In this period, time integration is performed to obtain each subtracted integral value information in real time, and there is an advantage that time is reduced to obtain the absolute humidity excluding the influence of the ambient temperature (room temperature).

In the absolute temperature sensor of the present invention, the output of the temperature sensor 20 is integrated over time for a predetermined period in the cooling process after the heater heating is stopped, and the absolute humidity in the ambient gas is utilized using the output of the time integration value. Therefore, the output of the temperature sensor 20 after the heater is stopped is taken out rather than measuring the temperature in a heating cycle with a lot of noise, and the time integration of the output is performed in the cooling process. Since the time integration value is taken out as an output, noise that fluctuates positively and negatively is removed by time averaging, and even a small temperature sensor output is taken out as a large change because of the product of time and temperature sensor output by time integration. be able to. Therefore, there is an advantage that a high S / N sensor output can be obtained, and an absolute temperature sensor with high accuracy and high sensitivity can be provided.

In the absolute temperature sensor of the present invention, the heating / cooling cycle of the heater can be performed in synchronization with the clock pulse. At this time, since the start of a predetermined time integration period of the output of the temperature sensor 20 or the like can be determined in synchronization with the clock pulse during the cooling cycle, a simple circuit can be used and an inexpensive absolute temperature sensor can be provided. is there.

In the absolute temperature sensor of the present invention, the temperature sensor 20 can be a temperature difference sensor, and the temperature sensor 20 can also be used as the heater 25, so that an extremely simple structure and circuit configuration can be achieved, and an extremely compact absolute temperature sensor. There is an advantage that a sensor chip and an inexpensive and handy absolute temperature sensor using the sensor chip can be provided.

In the absolute temperature sensor chip of the present invention, the measurement point (temperature contact) of the temperature difference sensor such as the temperature sensor 20 is provided in the vicinity of the tip of the cantilever-like thin film 10 and the heater 25 and the like are measured by the temperature difference sensor. Since it is arranged so as to surround the point (warm contact) and the vicinity of the tip of the cantilever-like thin film 10 etc. is uniformly heated, in order to increase the contact area with wet air, the vicinity of this tip Even if designed to have a large area, there is an advantage that heat can be generated uniformly.

The absolute temperature sensor chip of the present invention includes a semiconductor diode as an absolute temperature sensor in addition to the temperature difference sensor as the temperature sensor 20, and a semiconductor for measuring the absolute temperature of the thin film 10 when the heater 25 is heated. Since the diode driving power source can utilize a part of the voltage drop at the heater 25 when the heater 25 is heated, there is an advantage that the absolute temperature of the thin film 10 can be easily measured.

The plane schematic of one Example of the absolute humidity sensor chip | tip used for the absolute humidity sensor of this invention is shown. (Example 1, Example 4, Example 7) FIG. 2 is a schematic sectional view taken along line XX in FIG. 1. (Example 1, Example 4, Example 7) It is a time chart of one Example which shows operation | movement of the absolute humidity sensor of this invention. (Example 1, Example 2) 1 is a schematic plan view of an embodiment of an absolute humidity sensor chip of the present invention. FIG. (Example 2, Example 5, Example 9) Schematic plan view showing one embodiment of another absolute humidity sensor chip used in the absolute humidity sensor of the present invention (Example 3, Example 6) It is a time chart of other one Example which shows operation | movement of the absolute humidity sensor of this invention. (Example 1, Example 3) FIG. 6A is a time chart of heater heating temperature for helping understanding of the operation of the absolute humidity sensor of the present invention. FIG. It is an example of the output signal waveform of the sensor 20. Example 4 It is a time chart which shows operation | movement of other Example of the absolute humidity sensor of this invention. (Example 4, Example 5, Example 6) FIG. 3A is a time chart showing the operation of another embodiment of the absolute humidity sensor of the present invention, FIG. 1A shows a first time integral value Sh, and FIG. 2B shows a second time. Indicates the integral value Sl. (Example 4, Example 5, Example 6, Example 8) It is a time chart which shows operation | movement of other Example of the absolute humidity sensor of this invention. (Example 4, Example 5, Example 6) It is a time chart which shows operation | movement of other Example of the absolute humidity sensor of this invention. (Example 6) The schematic of the output of a thin film thermocouple is shown in one Example at the time of giving the determination function to operation | movement of the absolute humidity sensor of this invention. (Example 7) It is the plane schematic of another Example of the absolute humidity sensor chip | tip of this invention. (Example 8) The time chart of other one Example regarding the temperature rise of the thin film by the heater heating of the absolute temperature sensor of this invention is shown. (Example 8) The block schematic diagram of one Example of the structure for operating the absolute humidity sensor of this invention is shown. Example 9

  Hereinafter, the absolute humidity sensor and the absolute humidity sensor chip of the present invention can be formed of a silicon (Si) substrate using mature semiconductor integration technology and MEMS technology. The silicon (Si) substrate, particularly an SOI substrate, will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic plan view of an embodiment of an absolute humidity sensor chip having a single thin film 10 thermally separated from a substrate 1 used in the absolute humidity sensor of the present invention. FIG. 2 is a schematic sectional view taken along the line XX. This can be formed by known MEMS fabrication techniques. Here, a thin film 10 in the form of a cantilever 12 is formed using the SOI layer 11 of the SOI substrate, and a thin film thermocouple, which is a temperature difference sensor, is formed here as the temperature sensor 20. In this embodiment, the heater This is an example in which a thin film of a resistor of a nichrome thin film is formed on an insulating film 50 of a silicon oxide film formed on the SOI layer 11 as 25. The tip of the cantilevered thin film 10 has a large area, and the nichrome thin film resistors are arranged in a zigzag shape so as to surround the measurement point (hot junction) 26 of the thin film thermocouple so as to generate heat uniformly. It is. The thin film thermocouple is a silicon oxide film formed by using an SOI layer 11 (for example, an n-type silicon single crystal film having a thickness of about 10 μm) as a first thermoconductor 120a and thermally oxidizing the SOI layer 11 thereon. A second thermoelectric conductor 120b (for example, a nickel thin film or a nichrome thin film) formed through the insulating film 50 is formed, and an ohmic contact 60 as a measurement point (hot contact) 26 is formed. . A thin film thermocouple reference point (cold junction) 27 is formed on the substrate 1. The length of the cantilever 12 may be about 700 μm. Here, in order to measure the temperature of the substrate 1, a pn junction diode (semiconductor diode) is formed on the substrate 1 and used as an absolute temperature sensor 21 for measuring the absolute temperature of the substrate 1. . Note that the method of using the semiconductor diode as the absolute temperature sensor 21 is based on the temperature dependence of the diode current at that time when a constant forward voltage is applied to the semiconductor diode in measurement at room temperature, which is a relatively low temperature of 150 ° C. or less. There is a method for obtaining the current from the temperature dependence of the diode forward voltage at a constant current. In high temperature measurement at 150 ° C or higher, the reverse of the diode with a fixed reverse applied voltage of about 0.5V to 1V. It can be determined from the temperature dependence of the directional current. As shown in FIGS. 1 and 2, heating a single thin film 10 with less dependence on the direction of the absolute humidity sensor chip in the direction of gravity reduces thermal correction for thermal convection and the like. There is an advantage that less.

FIG. 3 is a time chart of an embodiment showing the operation of the absolute humidity sensor of the present invention, and the heat conduction provided with a single thin film 10 having a simple structure thermally separated from the substrate 1 as shown in FIGS. The heater 25 formed on the thin film 10 is heated with an applied voltage Va using a type sensor chip, and the thin film 10 is heated to a predetermined low absolute temperature Tl from room temperature, for example, 20 ° C. When the first heater is heated to 150 ° C and the absolute temperature Tl is reached, the heater is stopped and cooled to return to room temperature. Next, the room temperature changes. In the meantime, the heater 25 is heated at the same applied voltage Va, and the first heater is heated from the same room temperature to the predetermined high absolute temperature Th, for example, 500 ° C. in the same wet air. When the absolute temperature Th is reached In, stopped heater heating, allowed to cool illustrates how the temperature rise and temperature drop of the thin film 10 when repeated heating and cooling, as the temperature returned to room temperature. The broken line shown in FIG. 3 is an expected temperature rise curve of the thin film 10 when the heating of the heater 25 is continued for a long time. When the heater 25 is heated at the same applied voltage Va, the time required to reach the absolute temperature Tl is tl, and the time required to reach the absolute temperature Th is th. Assuming that the resistance of the heater 25 is R, Va ² · tl / R and Va ² · th / R are obtained. Here, when the heater 25 is made of a nichrome thin film, its resistance temperature coefficient is extremely small, and therefore the value of the resistance R of the heater 25 has no temperature dependency. Here, since the power consumption of the heater 25 is Va ² / R and is common, these subtraction electric energy is (th−tl) Va ² / R and may be proportional to (th−tl). I understand. In the humid air having the same absolute humidity, when the thin film 10 reaches the predetermined high absolute temperature Th from room temperature, the thin film 10 always passes the predetermined low absolute temperature Tl from the room temperature. Therefore, (th−tl) Va ² / When R is obtained, the influence of room temperature is removed as shown in Equation 3 above. The absolute temperature Tl is set so that the thin film 10 has a temperature of 120 ° C. to 150 ° C. that is not affected by the absolute humidity, particularly in order to reduce the measurement error of the absolute humidity. The temperature is increased from the Tl to an absolute temperature Th, for example, 500 ° C., which is a temperature region having a strong influence of absolute humidity.

FIG. 6 is a time chart of another embodiment showing the operation of the absolute humidity sensor of the present invention. In FIG. 3, the heating from the room temperature to a predetermined low absolute temperature Tl by the first heater heating, This is a case where heating from room temperature to a predetermined high absolute temperature Th is performed by shifting the time with heater heating, but here, heating is performed at a predetermined constant applied voltage Va that can be heated to at least a predetermined high absolute temperature Th. Shows the case. Then, when the time tl to reach the predetermined low absolute temperature Tl and the time th to reach the predetermined high absolute temperature Th are measured, these subtraction electric energy is (th−tl) Va ² / R. Since being proportional to (th−tl) is the same as described above, detailed description thereof is omitted.

Since (th-tl) Va ² / R, which is the amount of subtraction power, is a measurable amount, this value is obtained and is absolute from calibration data relating to absolute humidity that is obtained and prepared in advance under the same conditions. Humidity can be determined. When the absolute humidity is high, the thermal conductivity of the wet air increases at a temperature higher than the absolute temperature Tl of 120 ° C. to 150 ° C. Therefore, even if the same applied voltage Va is applied to the heater 25, the thin film 10 is predetermined. It is also expected that the high absolute temperature Th will not be reached. Therefore, the magnitude of the applied voltage Va to the heater 25 needs to be a value that can sufficiently reach a predetermined high absolute temperature Th under the expected absolute humidity condition.

The thin film 10 of the absolute humidity sensor chip shown in FIGS. 1 and 2 is an example when no absolute temperature sensor is mounted. Since the structure is simple, the manufacturing process is simple and the absolute humidity sensor chip is inexpensive. In such a case, it is necessary to devise to measure whether the thin film 10 has reached the absolute temperature Tl or the absolute temperature Th described above. In order to raise the temperature of the thin film 10 to the set temperatures Tl and Th, which are predetermined absolute temperatures, absolute temperature measuring means is used. Although this has been described above, by using a thin film thermocouple which is a temperature difference sensor as the absolute temperature sensor 21 and the temperature sensor 20 formed on the substrate 1. The temperature of the substrate 1 is measured from the output of the absolute temperature sensor 21, and the temperature rise (temperature difference) with respect to the substrate 1 is measured with a thin film thermocouple having a measurement point (hot junction) on the thin film 10. 1. A method for obtaining the absolute temperature of the thin film 10 by obtaining the sum of these, The absolute temperature sensor 21 is provided with a temperature sensor having good linearity with respect to the temperature, the output thereof, the thin film 10 has a measuring point (hot contact), and the thin film thermoelectric device corresponding to the temperature rise relative to the substrate 1 The output of the pair is adjusted by, for example, an amplifier circuit so as to have the same temperature coefficient, and these outputs are summed on the circuit or summed on the software to obtain the absolute temperature of the thin film 10. 2. Method A thin film thermocouple which is a temperature difference sensor required to measure the absolute temperature of the substrate 1 from the output of the absolute temperature sensor 21 and raise the temperature to predetermined set temperatures Th and Tl in consideration of the substrate temperature. There is a method of obtaining the respective output voltages of each of them and determining that the predetermined set temperatures Th and Tl have been reached when these respective outputs are obtained. Measures that the set temperatures Th and Tl have been reached, so that the signal at that time can be extracted. In either method, a voltage signal related to the temperature of the thin film 10 when the predetermined set temperatures Th and Tl are reached is compared with a reference voltage of the predetermined set temperatures Th and Tl prepared in advance and a comparator, etc. The fact that the temperatures Th and Tl have been reached is output as a signal, and this output can be used to control the heater 25 to stop heating.

The example shown in FIG. 3 in the above embodiment is a case where the heater 25 is heated by a periodic clock pulse. However, it is not always necessary to repeat heating and cooling at a constant cycle, and a predetermined setting is used. After about 2 to 3 times the thermal time constant of each cooling process after reaching the temperatures Tl and Th, it can be approximated that the thin film 10 has returned to room temperature. You can start a heating cycle. By doing in this way, the measurement time of absolute humidity can be shortened.

FIG. 4 is a schematic plan view of an embodiment of an absolute humidity sensor chip of the present invention having a simple structure having a single thin film 10 as in FIGS. 1 and 2 in the first embodiment. The major difference from FIG. 1 and FIG. 2 is that in FIG. 4, the thin film 10 has a temperature sensor 20 that is a thin film thermocouple of a temperature difference sensor also used as a heater 25, and the temperature sensor 20 that is a thin film thermocouple. In addition, an absolute temperature sensor 22 is provided. In this embodiment, a semiconductor diode is used as the absolute temperature sensor 22. The wiring 110 is formed from the measurement point 26 of the thin film thermocouple as the temperature sensor 20 and is connected to one electrode 80a of the semiconductor diode. The other electrode 80b is connected to the current terminal 115 and the voltage by the wiring 110. The terminal 116 is connected to the electrode pad 71b. In this way, when an applied voltage for heating, for example, 10 V, is applied to the heater 25 between the electrode pad 70 serving as the electrode terminal and the SOI layer common electrode pad 75, a part of the heater 25 is applied. Also, the circuit configuration is such that the voltage drop in one of the thermoconductors 120b used is at least part of the driving power source of the semiconductor diode. One thermoconductor 120b is formed of a metal such as a nickel thin film or a nichrome thin film, and thus has a small resistance value, for example, about 5Ω. On the other hand, the temperature of the SOI layer 11 of the other thermoconductor 120a is low. Since the resistance value is about 50Ω, the voltage drop in the thermoconductor 120b is about 1V. The circuit is configured outside the absolute humidity sensor chip shown in FIG. 4 so that about 1V of this voltage is applied as a reverse voltage of the semiconductor diode when a heater heating voltage of 10V is applied. In this external circuit configuration, since it is a known technique, details are omitted here, but a reverse voltage, for example, a reverse current that flows when a constant voltage of 1 V is applied to the semiconductor diode, is measured, and from that value An absolute temperature of about 150 ° C. or more near the tip of the cantilever-like thin film 10 can be measured. Since the position of the pn junction that is the temperature sensing part of the semiconductor diode is formed near the measurement point (warm junction) 26 of the thin film thermocouple as the temperature sensor 20, the absolute temperature of the measurement point 26 is almost the same. You may think that you are measuring. In the external circuit configuration, if necessary, a circuit mechanism for adjusting the voltage drop at the thermoconductor 120b to be a predetermined drive voltage from the outside when the voltage drop of about 1V is not sufficient as the drive voltage of the semiconductor diode. It can also be prepared.

In the above description, in driving the semiconductor diode as the absolute temperature sensor 22 formed near the tip of the thin film 10 in the cantilever 12 shape, the absolute temperature is determined from the temperature dependence of the flowing reverse current so that a predetermined constant reverse voltage can be applied. In contrast to this, the absolute humidity sensor chip is configured so that a predetermined constant current flows through the semiconductor diode in consideration of the 1 V drive power supply that is a voltage drop in the thermoconductor 120b. An external circuit can also be configured. At this time, since it is necessary to measure the voltage applied to the semiconductor diode, the voltage terminal 116 from the one electrode 80a through the wiring 110 from the measurement point 26 side of the thin film thermocouple of the semiconductor diode through the wiring 110 is used. An electrode pad 71a is formed. Further, an electrode pad 71b that becomes the current terminal 115 and the voltage terminal 116 is formed from the other electrode 80b of the semiconductor diode via the wiring 110, and a precise application voltage of the semiconductor diode is applied by a pseudo four-terminal method. The current terminal 115 and the voltage terminal 116 are separately formed so that measurement is possible. However, here, the voltage drop in the thermoconductor 120b, which is a part of the heater 25, becomes a large value for flowing a large current for driving the heater, but the semiconductor diode has a small value for measuring the absolute temperature. Since only the drive current is present and the internal resistance in the reverse direction of the semiconductor diode is substantially large, the voltage drop in the metal wiring 110 from the other electrode 80b is negligible. Therefore, the current terminal 115 and the voltage terminal 116 connected thereto can be shared to be one. The semiconductor diode here is the same example as the bipolar transistor as the absolute temperature sensor 21 formed on the substrate 1, but a miniaturized one is used. There, a pn junction diode between the emitter E and the base B is used. The collector C and the base B are short-circuited, and a bipolar transistor is used as a diode.

In the absolute humidity sensor of the present embodiment, as shown in FIG. 4 described above, a semiconductor diode as the absolute temperature sensor 22 is formed near the tip of the single cantilever 12-shaped thin film 10 and the heater 25 is heated. However, the absolute temperature near the tip of the cantilever 12-shaped thin film 10 can be measured. The operation of measuring the absolute humidity of the absolute humidity sensor in the present embodiment may be considered to be the same as that in FIG. The difference from the first embodiment is that, in the first embodiment, the heater 25 is a metal material such as a nichrome thin film, whereas in this embodiment, the thin film thermocouple as the temperature sensor 20 is also used as a heater. doing. Since one thermoconductor 120a of the thin film thermocouple is the SOI layer 11, the tip of the cantilever-like thin film 10 can be obtained by appropriately selecting the resistivity so that the SOI layer 11 of the thermoconductor 120a serves as a heating element. The heater is heated almost uniformly. In the present embodiment, as in the case of the first embodiment, the temperature of the thin film 10 is increased to the set temperatures Tl and Th, which are predetermined absolute temperatures, and an absolute temperature measuring means is used to measure those temperatures. Although the absolute temperature sensor 22, which is a semiconductor diode, is mounted on the thin film 10, the absolute temperature sensor 22 measures the set temperatures Tl and Th and indicates that the set temperatures Tl and Th have been reached, such as a comparator. This is a case where the absolute temperature measuring means is provided with a control circuit that detects the above and stops the heating of the heater 25.

Therefore, in this embodiment, the time chart showing the operation of the absolute humidity sensor of the present invention shown in FIG. 3 is used. The subtraction electric energy in Embodiment 1 is also the resistance temperature when a semiconductor with a high impurity concentration is used for the SOI layer. Since the coefficient is small, it can be considered that the heater resistance R is substantially the same, and can be approximated as (th−tl) Va ² / R. Of course, the temperature dependence of the small heater resistance R can also be corrected by linear approximation. Thus, as in Example 1, the subtraction power amount (th−tl) Va ² / R is a measurable amount. Therefore, this value is obtained and calibration data relating to absolute humidity prepared in advance is obtained. The absolute humidity can be obtained from the comparison.

FIG. 5 is a schematic plan view showing an embodiment of an absolute humidity sensor chip including two thin films 10a and 10b having the same shape thermally separated from the substrate 1 used in the absolute humidity sensor of the present invention. 1 shows a case where only two thin films equivalent to the thin film 10 of the embodiment of the absolute humidity sensor chip shown in FIG. In FIG. 1 of the first embodiment, the thin film 10 is a single thin film 10 and the heater 25 and the thin film thermocouple as the temperature sensor 20 are provided here. When heating the heater with a large predetermined heater drive applied voltage Va, it was possible to measure the respective times tl and th until reaching the set temperature Tl and Th in the heating process, but this example Then, it is a case where it applies to the absolute humidity sensor chip provided with the thin film 10a and the thin film 10b of the same shape using the same FIG. 6 in Example 1. FIG. One thin film 10a is heated to the set temperature Tl and the other thin film 10b is simultaneously heated to the set temperature Th. 6 is a thin film in which the heater 25a and the heater 25b are driven by the same heater driving applied voltage Va, and the heater 25a and the heater 25b are formed, respectively, as shown in FIG. 3 of the first embodiment. It is a time chart of one Example which shows operation | movement of the absolute humidity sensor of this invention when 10a and the thin film 10b are heated simultaneously until it becomes set temperature Tl and set temperature Th, respectively. Here, it is a case where it is assumed that the thin film 10a and the thin film 10b have completely the same shape. However, since there is actually a slight shift in heat capacity or the like, the temperatures of the thin film 10a and the thin film 10b are the same. It is necessary to assume that the ascending curves do not overlap and shift slightly. At this time, it is sufficient to correct the deviation.

Since the absolute temperature measuring means for raising the thin film 10a and the thin film 10b to the set temperature Tl and the set temperature Th, which are predetermined absolute temperatures, is the same as in the first embodiment, the detailed description thereof will be given here. Is omitted. Thus, as in the first embodiment, since the subtraction power amount (th−tl) Va ² / R is a measurable amount, this value is obtained and calibration data relating to absolute humidity prepared in advance is obtained. Absolute humidity can be obtained from Since the temperature raising operation by heating the heater to the set temperature Tl and the set temperature Th can be performed at the same time, the measurement time can be shortened, which is effective for measuring the absolute humidity when the room temperature fluctuates. However, since there are two heaters, thermal interference occurs between them, so it is necessary to install them in consideration of the influence of convection of wet air such as the inclination of the absolute humidity sensor chip. Thus, since it is the same as that of Example 1, detailed description is abbreviate | omitted.

Here, using the absolute humidity sensor chip of FIG. 1 and FIG. 2 used in Example 1, each output voltage of the temperature sensor 20 which is a thin film thermocouple is set to a predetermined value in the cooling process after the heating of the heater 25 is stopped. One implementation that integrates the period and time, uses the output information of each time integral value, corrects it to remove the influence of the ambient temperature, and obtains the absolute humidity using calibration data prepared in advance An example will be described.

FIG. 7 is a time chart of the heater heating temperature for helping understanding of the operation of the absolute humidity sensor of the present invention, FIG. 7A is a clock pulse signal waveform used for heater heating, and FIG. It is an example which shows the output signal waveform proportional to the temperature when the thin film 10 from the temperature sensor 20 which is a thin film thermocouple is heated. A heater 25 formed on the thin film 10 is supplied with a predetermined constant power P using an absolute humidity sensor chip having a thin film 10 thermally separated from a single substrate 1 having a simple configuration as shown in FIGS. It is a case where it heats and cools by. An example of the output signal waveform is shown in the heating cycle (here, the term “cycle is used because heating / cooling is repeatedly performed, not heating and cooling only once) and cooling cycle”. FIG. 7B shows an expected waveform when the thermal conductivity of the ambient moist air (measured gas) is large and an expected waveform when the thermal conductivity is small.

When a thin film thermocouple (temperature difference sensor) is used as the temperature sensor 20 in this way, the heated thin film 10 finally returns to room temperature, which is the temperature of the surrounding gas (measurement gas), in the cooling process. The sensor output asymptotically approaches zero. Since the temperature sensor output is the output of the temperature difference sensor, which is a thin film thermocouple, it can be considered to be approximately the temperature rise of the thin film 10. That is, zero temperature sensor output corresponds to zero temperature increase. As shown in FIG. 7 (B), when the thermal conductivity of the surrounding gas is large, since the heat to the surrounding gas is intense at the same heater supply power P, the temperature of the thin film 10 hardly rises and the temperature rises low. Furthermore, in the cooling process (cooling cycle), since heat radiation is intense, the cooling rate is large and the thermal time constant is small. On the other hand, when the thermal conductivity of the surrounding gas is small, heat radiation is small at the same heater supply power P, and it is heated to a high temperature and reaches saturation. Also, in the cooling process, since the heat radiation is small, it is cooled slowly and its thermal time constant increases. For this reason, the time integration of the output of the temperature sensor 20 from immediately after stopping the heater heating in the cooling cycle to the beginning of the next heating cycle (area of the hatched portion in the cooling cycle in FIG. 7B) is It can be seen that the smaller the thermal conductivity of the gas, the greater the thermal conductivity than when the thermal conductivity is large. That is, the ratio of the time integral value (area of the hatched line) in the cooling cycle is set to the ratio of the value at the end of the temperature sensor output waveform in the heater heating cycle when the thermal conductivity of the surrounding gas is small and large. It can also be seen that it is amplified by the effect of time integration and can be many times larger. In this way, even if the output of the temperature sensor is not measured during heating of the heater, it is possible to obtain a stable and amplified output by time integration in the cooling cycle with less noise after heating is stopped. I understand. Therefore, since the equivalent thermal conductivity of the ambient gas changes due to a change in the absolute humidity (water vapor amount) of the ambient gas (measured gas), the absolute humidity sensor of the present invention is used to achieve high sensitivity and high It can be seen that it can be measured accurately.

FIG. 8 shows the operation of the absolute humidity sensor of the present invention by using the absolute humidity sensor chip shown in FIGS. 1 and 2 to eliminate the influence of ambient temperature (room temperature) due to subtraction of time integral values (subtraction integral value). 2 is an example of a time chart showing the state of the temperature of the thin film 10 periodically heated by the heater. Here, in order to easily maintain the thin film 10 at a predetermined high temperature Th, a voltage Va is applied to the heater 25 in accordance with a clock pulse as shown in FIG. This is an embodiment set to be heated to a predetermined absolute temperature Th. Of course, without using a periodic clock pulse, for example, Va, which is an applied voltage, is applied to the heater 25, and the time integration is stopped at about twice or more of the thermal time constant in the cooling process to the next heating cycle. You can enter.

FIG. 8 shows the temperature change of the single thin film 10 obtained from the output (voltage) of the thin film thermocouple, which is the temperature sensor 20 in the heating cycle and the cooling cycle, as described above, and the heater with a single driving power. After heating, the temperature of the thin film 10 is reached from room temperature to a predetermined high temperature Th, these temperatures are maintained, and then the heater heating is stopped and the cooling process is started. Here, since the thin film thermocouple which is a temperature difference sensor is used as the temperature sensor 20, the origin of the temperature of the thin film 10 in FIG. 8 is the temperature of the substrate 1 having the reference point (cold junction) and the room temperature. Then, a predetermined high set temperature Th (a function of the equivalent thermal conductivity of the surrounding gas, in the measurement of the wet gas to be measured, for example, electric power that increases the temperature from about 400 ° C. to about 500 ° C. is supplied to the heater 25. When the temperature dependence of the resistance of the heater 25 can be ignored, the thin film 10 is driven at a predetermined voltage or at a predetermined current, and eventually driven at a predetermined power. The heater is heated. The output (voltage) Vs of the thin film thermocouple which is the temperature sensor 20 in the cooling cycle immediately after the stop of the heating is integrated over time. At this time, in order to correct so as to eliminate the influence of the ambient temperature, a predetermined low value is used. The value of the output voltage Vsl of the thin film thermocouple, which is the temperature sensor 20 corresponding to the absolute temperature Tl, is the absolute temperature measurement using the information of the absolute temperature sensor 21 formed on the substrate 1 and the information of the temperature sensor 20. Since the output voltage Vsl can be subtracted from the output voltage Vs of the thin film thermocouple during the cooling cycle, that is, (Vs−Vsl) is integrated over time to obtain a subtraction integral value ΔS (FIG. 8). The integration time at this time is the time until the output voltage Vs of the thin film thermocouple becomes the output voltage Vsl, that is, until (Vs−Vsl) = 0. In FIG. 8, the temperature of the thin film 10 and the output (voltage) of the thin film thermocouple are plotted on the vertical axis. This is because the thin film thermocouple, which is a temperature difference sensor, is used as the temperature sensor 20. This is because the axis can be considered that the temperature based on the room temperature of the thin film 10 and the output voltage of the temperature sensor 20 are the same. In this way, the subtraction integral value ΔS is a time integral value obtained by subtracting the time integral value below the predetermined temperature Tl from the common room temperature, and therefore becomes an irrelevant value even if the room temperature fluctuates, and the absolute humidity of the humid air It is a function of H. The subtracted integration value ΔS is a function that becomes a small value when the absolute humidity H is large and increases monotonously when the absolute humidity H becomes small. From this value, based on the absolute humidity calibration data acquired in advance under the same conditions, the absolute humidity H can be uniquely determined without depending on the size of the room temperature.

FIG. 9 shows another embodiment of a time chart showing the temperature of the thin film 10 periodically heated by the heater using the absolute humidity sensor chip shown in FIG. 1 and FIG. It is. In the above measurement, the thin film thermocouple output (voltage) Vsl corresponding to the lower set temperature Tl is subtracted from the thin film thermocouple output (voltage) during the cooling process from the set temperature Th. In this example, the subtracted output voltage is integrated for the integration time period to obtain the output value, and the correction is made so as to eliminate the influence of the room temperature, but as shown in FIG. In the course of cooling from the temperature Th, the output voltage of the thin film thermocouple (temperature sensor 20) is time integrated until the output voltage Vsl corresponding to a predetermined Tl is reached, and from the first time integrated value Sh at that time. As shown in FIG. 9B, the output voltage Vsl is also obtained by obtaining a second time integral value Sl obtained by integrating the same integration time period, and subtracting these values to obtain a subtraction integral value ΔS. . The setting of the predetermined temperature Th and the magnitude of the output voltage of the temperature sensor 20 corresponding to the predetermined temperature Tl can also be measured using the absolute temperature measuring means described in the first embodiment. Under the condition that the room temperature fluctuates sufficiently slowly compared to these integration times, the time integration value Sh (shaded portion) of the high set temperature Th in FIG. 9A is a time equal to or lower than a predetermined low set temperature Tl. The integral value (rectangular portion) is the same as the time integral value Sl (rectangular portion) of the predetermined low set temperature Tl in FIG. 9B, and the second time integral value from these first time integral value Sh. The subtraction integral value ΔS obtained by subtracting Sl is the subtraction integral value of the time integration values of these output waveforms, and thus almost eliminates the influence of the ambient temperature in measuring the absolute humidity.

FIG. 10 shows another embodiment of a time chart showing the state of the temperature of the thin film 10 periodically heated by the heater using the absolute humidity sensor chip shown in FIG. 1 or 2. In FIG. 8 and FIG. 9 described above, since the value of the output voltage Vsl is known before heating the heater to obtain the subtraction integral value ΔS using the single thin film 10, the subtraction operation is performed simultaneously in time. In this case, as shown in FIG. 10, the clock pulse is used to heat the first integral heater to a predetermined temperature Th, as shown in FIG. This temperature is maintained and the next clock pulse is repeated so as to become a cooling cycle. In the subsequent heating cycle after the first heater is heated, the second heater is heated to the predetermined low temperature Tl. After that, this temperature is maintained. And in these heating and cooling cycles, in the course of cooling from Th, the output voltage Vs of the thin film thermocouple is integrated over time, and in the same manner as described with reference to FIG. 8 and FIG. The integration time is defined as the time until the output voltage Vs of the thin film thermocouple becomes equal to the output voltage Vsl to obtain the first time integration value Sh, and the second heater heating is performed only for the time equal to the integration time. After the heating is stopped, the output voltage Vsl of this actual thin film thermocouple is time-integrated to obtain a second time integration value Sl. Then, the subtraction integrated value ΔS = (Sh−Sl) can be obtained from these by calculation. Since various noises are generated in the measurement circuit, these components are obtained by time integration of the output voltage of the actual thin film thermocouple by the first heater heating and the second heater heating. By subtraction, there is an advantage that noise components common to these can be canceled.

More specifically, as shown in FIGS. 1 and 2, since the substrate 1 has the absolute temperature sensor 21, the temperature of the surrounding medium (room temperature) is known. The temperature rise is determined substantially in proportion to the power supplied to the thin film 10 (if the change due to the temperature of the heater resistance is negligible, it is determined by the applied voltage and supply current). And when the surrounding gas is air and it is known that it is one kind of gas (in the case of pure air, it is a mixed gas with a clear mixing ratio of nitrogen gas and oxygen. In general, the thermal conductivity increases linearly with increasing temperature, and the gradient of the thermal conductivity with respect to the temperature and the magnitude of the thermal conductivity differ depending on the type of gas. . Therefore, in the air heated to a predetermined set temperature Th of 150 ° C. or higher in the air, when the absolute humidity is high, the thermal conductivity increases and corresponds to the set temperature Th compared to the case where the absolute humidity is low. The first time integral value becomes small. Since the second time integrated value corresponding to a predetermined set temperature having no humidity dependency, for example, Tl of 150 ° C. is constant in heating and cooling from the same room temperature, the first time integrated value The subtracted integrated value ΔS obtained by subtracting the second time integrated value decreases as the absolute humidity increases. In this way, based on the subtraction integral value ΔS obtained by subtracting the second time integration value Sl from the first time integration value Sh, the calibration data relating to the absolute humidity prepared in advance is used. The absolute humidity in the air is obtained by removing the influence of the room temperature from the room temperature.

Here, using the absolute humidity sensor chip of FIG. 4 used in Example 2, the output voltage of the temperature sensor 20 which is a thin film thermocouple is set for a predetermined period and time in the cooling process after the heating of the heater 25 is stopped. Another embodiment that integrates and corrects to remove the influence of the ambient temperature using the output information of each time integral value, and obtains the absolute humidity using calibration data prepared in advance Will be described.

Here, the major difference from the fourth embodiment is just the difference between the second embodiment and the first embodiment, that is, in the first embodiment, the thin film 10 shown in FIGS. 1 and 2 is not provided with an absolute temperature sensor. In addition, the absolute humidity sensor chip provided independently for the heater 25 and the temperature sensor 20 was used. However, in Example 2, the absolute temperature sensor 22 is provided as shown in FIG. Although there is a difference that an absolute humidity sensor chip that also serves as the temperature sensor 20 is used, a single thin film 10 is used, and a heater 25 and a temperature sensor 20 that is a thin film thermocouple are included therein. In the cooling process after the heating of the heater 25 is stopped, each output voltage of the temperature sensor 20 which is a thin film thermocouple is integrated over time for a predetermined period, and information on the output of each time integrated value is used. The influence of ambient temperature The absolute humidity is obtained by using calibration data prepared in advance, and the method of measuring the absolute humidity in Example 5 of the present invention is as shown in FIGS. The operation is the same as that using FIG. However, since the absolute humidity sensor chip of FIG. 4 is used in the fifth embodiment, a semiconductor diode as the absolute temperature sensor 22 is formed on the thin film 10. Therefore, since the absolute temperature of the thin film 10 can be directly measured, it becomes simple to measure and control the predetermined set temperatures Tl and Th, and the configuration of the absolute temperature measuring means is simplified correspondingly. . In addition, since the heater 25 and the temperature sensor 20 can be used together by switching, the corresponding structure is simplified, and the cantilever-like thin film 10 is also the heater 25 because the SOI layer 11 as the thermoconductor 120a becomes the heater 25. Various heat generation becomes possible.

In the case shown in FIG. 10, the measurement time is different between the data acquisition of the first time integration value Sh and the data acquisition of the second time integration value Sl. It is possible to obtain a difference from the second time integration value Sl by using a circuit that holds the time integration value in terms of time, for example, a software holding using a peak hold circuit or a digital memory circuit. it can.

Of course, a semiconductor diode is used as the absolute temperature sensor 22 here, but a resistance temperature detector such as a Pt thin film may be used. The method of measuring the absolute humidity is the same as in the case of FIGS. 8, 9 and 10 in the fourth embodiment, and is omitted here.

Here, using the absolute humidity sensor chip of FIG. 5 used in Example 3, each of the temperature sensor 20a and the temperature sensor 20b, which are thin film thermocouples, is cooled in the cooling process after the heating of the heater 25a and the heater 25b is stopped. The output voltage is time-integrated for a predetermined period, and the output information of each time-integrated value is used to correct so as to eliminate the influence of the ambient temperature, and the absolute humidity is obtained using calibration data prepared in advance. Another embodiment will be described.

When the thin film 10b is heated by applying a rectangular wave pulse of 10V, for example, to the heater 25b of the thin film 10b of the absolute humidity sensor chip shown in FIG. Control is performed using absolute temperature measuring means so as to maintain the temperature. In the cooling cycle after heating stop designated by a clock pulse or the like, this time, the heater 25b is operated as a temperature sensor 20b which is a temperature difference sensor, and the output is charged in a capacitor, etc. Time integration). At this time, the thin film 10a is heated to a predetermined set temperature Tl, for example, 150 ° C., for example, with the applied voltage Vl of the heater 25a being 3.0 V in synchronization with the heater heating of the thin film 10b. Control is performed using absolute temperature measuring means so as to maintain this temperature. Then, in the cooling cycle after the heating is stopped, this time, the heater 25a is operated as the temperature sensor 20a which is a temperature difference sensor, and the output is charged in a capacitor, for example, and time integration (second time integration) is performed. . FIG. 11 shows the situation at this time. FIG. 11 is a time chart showing the operation of another embodiment of the absolute humidity sensor of the present invention. The heating cycle when the thin film 10b is heated to the higher set temperature Th (for example, heated at 10V) A cooling cycle and a heating cycle and a cooling cycle when the thin film 10a is heated to a lower set temperature Tl (for example, heating at 3.0 V) are shown. Further, the temperature sensors 20a and 20b in each cooling cycle are shown. The first time integration and the second time integration are also shown as time integration (shaded portions) of the respective output voltages. The vertical axis indicates that the temperatures of the thin film 10a and the thin film 10b and the output voltages of the temperature sensors 20a and 20b have the same waveform.

In this case, as described above, the difference between the respective integration result values (time integration values) of the first time integration and the second time integration is obtained, and the output voltage difference (subtraction integration value) is output. However, the difference between the temperature sensor 20b and the temperature sensor 20a may be charged to a capacitor or the like and integrated. Of course, these may be input and recorded in an IC memory without using a capacitor and digitally added. In this embodiment, since the temperature sensor 20b and the temperature sensor 20a are both temperature difference sensors that are thin film thermocouples, in FIG. 9, the temperatures of the thin film 10a and the thin film 10b are plotted on the vertical axis. However, when this is expressed by the temperature sensor output voltage corresponding to the temperature, the origin Vo on the vertical axis is essentially zero. For this reason, since the zero method, which is a high-precision measurement, can be applied, high-precision absolute humidity measurement can be performed.

In this embodiment, the method of obtaining absolute humidity is the same as in the case of FIGS. 8, 9 and 10 used in Embodiment 4 and Embodiment 5, and the difference is simply that in FIG. In contrast to the time integration of the first time integration and the second time integration, in FIG. 11, since the time integration is obtained at the same time, it does not have an output holding function such as a peak hold circuit in real time. There is only a difference that a subtraction integral value ΔS (a dense hatched portion in FIG. 11) which is a difference between the first time integration and the second time integration can be obtained. Of course, the measurement time can be shortened for this purpose, but since the method for obtaining the absolute humidity is the same, the detailed description is omitted here.

FIG. 12 shows an embodiment in which the operation of the absolute humidity sensor of the present invention has a determination function. The thin film 10 or the thin films 10a and 10b are in a wet gas that does not reach the dew point, or the dew point is reached. With a heater 25 or the like provided on the thin film 10 or the like when it has a function of determining whether it is in a wet gas, submerged in water, or a solid substance including ice is attached. The schematic diagram of the output of the thin film thermocouple which uses electric power heating and the time passage of the temperature rise at that time as temperature sensor 20 grade is shown. Here, the case where the absolute humidity sensor chip shown in FIGS. 1 and 2 is used will be described. The micro power heating by the heater 25 etc. provided on the thin film 10 etc. means, for example, a heater power P such that the thin film 10 etc. only rises in temperature from room temperature to about 10 ° C., for example, about 10 mW in normal humid air. In this case, since the heat capacity of the thin film 10 or the like is extremely small, there is a rapid temperature rise with the heater heating time as shown in the characteristic curve A in FIG. The temperature rises to a saturation value determined by G and heater power P. In FIG. 12, the thin film thermocouple output is displayed on the vertical axis, but since the thin film thermocouple output and the temperature rise of the thin film 10 and the like from the room temperature are in a proportional relationship, the characteristic curve of the thin film thermocouple output over time. May be considered as a characteristic curve for the temperature rise of the thin film 10 or the like. When this characteristic curve is recorded in advance and such a minute electric power heating is performed and a characteristic curve almost similar to the characteristic curve A in FIG. 12 is obtained, the predetermined set temperature as described above is used as it is. The normal absolute humidity described above may be measured by supplying electric power to a large heater 25 or the like that reaches Tl and Th.

However, as a result of the above-mentioned micro power heating, as shown in the characteristic curve B, the temperature does not increase during the initial stage of micro power heating (the thin film thermocouple output is almost zero), and then the temperature starts to increase. In such a case, there is a possibility that the moist air reaches the dew point and the surface of the thin film 10 or the like has minute water droplets or minute ice. At this time, from the output of the absolute temperature sensor 21 provided on the substrate 1, if the substrate 1 is 0 ° C. or less, fine particles of ice are attached, and if the temperature is higher than that, the dew point is reached. It is determined that the water droplets are attached. In the case of the characteristic curve C, from the output of the absolute temperature sensor 21, if it is 0 ° C. or less, the substrate 1 itself is almost in ice, and if it is 0 ° C. or more, the dew point is reached and submerged. Or a large amount of water droplets may be attached. If the dew point has been reached, the relative humidity is 100%, the ambient temperature is measured from the output of the absolute temperature sensor 21 at that time, and the saturated water vapor amount at that time is known. I want. If the dew point is reached in the characteristic curve B or the characteristic curve C, the absolute humidity is obtained from the saturated water vapor amount. In the case of the characteristic curve B due to ice adhesion, after evaporating the ice particles on the surface of the thin film 10 etc., the absolute humidity is measured by heating to the predetermined set temperatures Tl and Th as described above. can do.

When the absolute humidity sensing probe equipped with the absolute humidity sensor chip of the present invention clearly shows that the dew point has not been reached or the ice has not adhered in the measurement environment of absolute humidity, the above-mentioned minute heating is performed. There is no need to do. However, in order to cope with any environment, it is preferable to configure the system so that a minute power heating operation is performed at the initial stage of absolute humidity measurement.

Here, using the absolute humidity sensor chip shown in FIG. 13, in the cooling process after the heating of the heater 25 is stopped, each output voltage of the temperature sensor 20, which is a thin film thermocouple, is integrated over time for a predetermined period, A description will be given of an embodiment in which the information on the output of the time integral value is corrected to eliminate the influence of the ambient temperature and the absolute humidity is obtained using calibration data prepared in advance. FIG. 13 is a schematic plan view of another embodiment of the absolute humidity sensor chip according to the present invention, which is the same as FIG. 1 used in Embodiment 1, except that the heater 25 and the temperature sensor are different in FIG. The thin film thermocouple 20 is formed independently, but in FIG. 13 of the present embodiment, the heater 25 and the temperature sensor 20 are combined with the so-called heater 25 temperature sensor. That is 20. Therefore, the thin film thermocouple which is the temperature sensor 20 has the inconvenience that the operation as the heater 25 and the operation as the temperature difference sensor as the temperature sensor 20 cannot be performed simultaneously. In addition, even when the absolute temperature of the thin film 10 is known, the thin film 10 is not provided with an absolute temperature sensor, so the thin film 10 is formed on the substrate 1 using the absolute temperature measuring means provided in the above-described absolute humidity sensor of the present invention. The substrate temperature (ambient temperature) is known by the absolute temperature sensor 21, and the temperature rise from the substrate 1 is measured by the thin film thermocouple as the temperature sensor 20 having the measurement point 26 on the thin film 10 with the substrate 1 as the reference point 27. Although there is a circuit complexity such as knowing the absolute temperature of the thin film 10, there is an advantage that the structure of the absolute humidity sensor chip itself is very simple.

As described above, the absolute humidity sensor chip shown in FIG. 13 does not have the independent heater 25 that does not serve as the absolute temperature sensor 22 or the temperature sensor 20, so that the thin film 10 has a predetermined set temperature Tl, Even if the heater is heated to Th, it is necessary to raise the temperature in a cycle in which the operation as the heater 25 and the operation as the temperature sensor 20 are alternately repeated at high speed. FIG. 14 shows a time chart of another embodiment relating to the temperature rise of the thin film by the heater heating of the absolute temperature sensor of the present invention, and shows a case where heating and cooling of the thin film 10 by the heater 25 are repeated. Here, the heating period of the heater 25 is referred to as a heating cycle, and the cooling period is referred to as a cooling cycle. The time lapse of the thin film temperature T of the temperature increase in the heating cycle when the thin film 10 is heated by the heater 25 and the time lapse of the temperature decrease of the thin film 10 in the cooling cycle after the heater heating is stopped are shown. For example, when the thermal time constant of the thin film 10 is about 30 milliseconds (msec), the heater is heated only for a time Δt of about 10 microseconds (μsec), which is 1/100 or less of the thermal time constant. Even if it is stopped, the temperature of the thin film 10 hardly decreases because of a large thermal time constant, and it can be considered that the temperature at which the heater heating is not stopped is maintained even during the short time Δt. it can. Even when the heater heating is stopped during the heating cycle of such a short time Δt, or when the heater heating cycle ends and the next cooling cycle is entered, during the short time Δt immediately after the heater heating stop of the heater heating cycle, Again, it can be considered that the temperature at the end of the heater heating cycle is maintained.

FIG. 14 shows the thermal time constant of the thin film 10 periodically during the heating cycle when the thin film 10 is heated by the heater 25 with sufficient heating power to reach a desired set (absolute) temperature Th. In this example, the heater heating is stopped for a sufficiently short time Δt, and the absolute temperature in the middle of the thin film 10 is measured by operating as a thin film thermocouple. Then, within this short time Δt, the temperature sensor 20 measures the output voltage Vsh corresponding to a predetermined set temperature Th, for example, the absolute temperature of the measurement point 26 by the above-described absolute temperature measuring means, and performs a desired setting ( Absolute) temperature, for example, when the value of the output voltage Vsh corresponding to Th = 500 ° C. is reached, the heating cycle of the heater 25 is stopped and the next cooling cycle is started. But there is.

FIG. 14 shows a case where the heating cycle is stopped at the time tn from the beginning of heating in the heater heating cycle, and the process proceeds to the next cooling cycle. For this purpose, although not shown here, a voltage for comparison equal to the value of the corresponding output voltage Vsh when the set (absolute) temperature Th = 500 ° C. is generated, and this voltage corresponds to 500 ° C. The output voltage Vsh is compared with a comparator or the like to output a signal, and the heating cycle of the heater 25 is preferably stopped. In addition, the next cooling cycle is determined by setting a desired time with a timer IC or the like, and once the operation is completed, the heating cycle can be changed to a heating cycle. It is. In this way, the temperature of the measuring point 26 which is a predetermined absolute temperature of 500 ° C. is periodically achieved. This is used as the set temperature Th on the high temperature side where the thermal conductivity of wet air in the absolute humidity sensor is increased, and in the same way, the predetermined set absolute temperature Tl can be made independent of the absolute humidity as described above, for example. In the temperature region, for example, Tl = 150 ° C. can be set, and when the thin film 10 reaches this temperature, the heater heating is stopped and the cooling cycle can be started. Of course, as described above, it is not necessary to set Tl to a temperature in a temperature range that can be independent of the absolute humidity. However, if the temperature is set in this temperature range, a measurement error as the absolute humidity is reduced. Then, during the cooling cycle, as described in the above-described fourth embodiment, for example, in the cooling process after the heating of the heater 25 in FIG. 9 is stopped, the respective output voltages of the temperature sensor 20 which is a thin film thermocouple. Is integrated for a predetermined period of time to obtain a subtraction integral value ΔS between the first time integration value corresponding to Th and the second time integration value corresponding to Tl, and information on the output of the subtraction integration value ΔS Is used to correct the ambient temperature to be removed, and the absolute humidity can be obtained using calibration data prepared in advance. Here, for example, since it is similar to the case of FIG. 9, the detailed description thereof is omitted.

FIG. 15 shows a block schematic diagram of an embodiment of a configuration for operating the absolute humidity sensor of the present invention. At least the power supply circuit for supplying power to the above-described absolute humidity sensor chip of the present invention and other circuits, an amplifier circuit for amplifying the output from the absolute humidity sensor, and the absolute humidity using the output from the absolute humidity sensor It has a calculation circuit for obtaining and converting to relative humidity, and a control circuit for the operation of the absolute humidity sensor. Here, a case where a display unit for displaying absolute humidity and relative humidity is further provided is shown. ing. Since these constituent circuits are achieved by a known technique, the description thereof is omitted here.

In the above-described embodiment, the thin film 10 as shown in FIG. 4 is provided with the absolute temperature sensor 22 and only the single thin film 10 has been described. Of course, the same shape having the absolute temperature sensor 22 is provided. Although two thin films 10 are formed on one substrate 1 and the absolute humidity can be measured in the same manner as in the sixth embodiment, the description thereof is omitted here.

In the above-described eighth embodiment, a method for obtaining the absolute humidity using the time integral value of the output of the temperature sensor 20 in the cooling process after stopping the heater heating when the single thin film 10 shown in FIG. 13 is used. Although the embodiment has been described, the absolute humidity can also be obtained by comparing the power consumption during heating as in the first embodiment. In this case as well, the method for obtaining the absolute humidity is the same as in the case of the first embodiment, and the description is omitted here. In addition, two thin films 10 shown in FIG. 13 in Example 8 are provided on the same substrate 1 as in Example 3, and the absolute humidity can be obtained by comparing the power consumption. As in Example 6, two thin films 10a and 10b provided on the same substrate 1 are used, and the absolute humidity is obtained using the time integral value of the output of the temperature sensor 20 in the cooling process after stopping the heater heating. You can also In these cases as well, the method for obtaining the absolute humidity is the same as in the case of Example 3 or Example 6, and thus the description thereof is omitted here.

The absolute humidity sensor and the absolute humidity sensor chip of the present invention are not limited to the present embodiment, and various modifications can be naturally made while the gist, operation and effect of the present invention are the same.

  The absolute humidity sensor of the present invention includes a heater and a temperature sensor mounted on a thin film thermally separated from a substrate, and depends on the amount of water vapor in the gas to be measured to the ambient gas of the heater heated thin film, that is, the difference in absolute humidity This is a so-called heat conduction type sensor that measures a temperature change based on a difference in heat dissipation state with a temperature sensor. The absolute humidity of the surrounding gas (the gas to be measured) is measured through a change in thermal conductivity. In the absolute humidity sensor of the present invention, the temperature sensor is a thin film thermocouple, and the heater is heated to change the thin film to a predetermined difference. The absolute humidity is calculated based on the power consumption required to reach the two temperatures Th and Tl, and the thin film is made to reach two different temperatures Th and Tl and cooling after the heater heating is stopped. The process is divided into the case of obtaining the absolute humidity based on the time integration of each output of the temperature sensor.

When measuring absolute humidity during heater heating, each power consumption required to reach a predetermined high set temperature Th of 150 ° C or higher and a predetermined set temperature Tl of about 150 ° C lower than the high set temperature Th Measure based on quantity. Further, in the case of the same heater heating voltage, it was found that the subtraction electric energy is proportional to the difference between the required time tl and th required to reach the set temperature Tl or Th from room temperature. Thus, the absolute humidity can be measured with a simple calculation in combination with calibration data prepared in advance.

Further, in the measurement in the cooling process after the heater heating is stopped, unlike the case in which the heater is heated, the output from the temperature sensor is time-integrated and output in a period in which the noise in the cooling process is small. Is obtained. Furthermore, since amplification of a minute signal is achieved by time integration, a highly sensitive absolute humidity sensor can be provided. When a thin film thermocouple, which is a temperature difference sensor, is used as a temperature sensor, it can also be used as a heater, so that it becomes a heat conduction type sensor chip with a very simple structure, and the operation as a temperature sensor / heater is just The heater operation in the heating cycle and the temperature sensor operation in the cooling cycle can be operated alternately, which is preferable.

Since it can be formed with a very small thin film suspended in the air using MEMS technology, the thermal response time is very high, about several tens of milliseconds, and furthermore, absorption of water vapor into a porous film is used. Since it is not based on the principle of a humidity sensor, it can be said that there is essentially no problem of deterioration. However, it is necessary to take measures against dew point and icing, and the absolute humidity sensor of the present invention makes it possible to judge the state of dew point and icing and measures to evaporate these and measure absolute humidity. Has been. In this manner, mass production by MEMS technology is possible, power consumption is small, and high-speed operation makes it possible to provide a handy absolute humidity sensor. Since this absolute humidity sensor is a thermal sensor based on MEMS technology, it is better to cover the absolute humidity sensor chip with a porous cap so as not to be affected by airflow. In addition, it is an absolute humidity sensor that can be used even in a high temperature environment of 200 ° C or higher. It can measure humidity in dryers, humidity in the vicinity of automobile engines, and humidity in general air. It is expected to be used in various fields such as humidity in soil and humidity control of air conditioners.

DESCRIPTION OF SYMBOLS 1 Substrate 10, 10a, 10b Thin film 11 SOI layer 12 Cantilever 15 Base substrate 20, 20a, 20b Temperature sensor 21 Absolute temperature sensor 22, 22a, 22b Absolute temperature sensor 25, 25a, 25b Heater 26 Measurement point (hot contact)
27 Reference point (cold junction)
40 Cavity 50 Insulating film 60 Ohmic contact 70, 70a, 70b Electrode pads 71a, 71b, 71c Electrode pads 72a, 72b Electrode pad 75 SOI layer common electrode pads 80a, 80b Electrode 110 Wiring 115 Current terminal 116 Voltage terminals 120a, 120b Thermoconductor

Claims (18)

The thin film (10) thermally separated from the substrate (1) is provided with an absolute humidity sensor chip having a heater (25) and a temperature sensor (20), and the change in thermal conductivity based on the amount of water vapor in the gas to be measured. Thus, in the absolute humidity sensor in which the temperature change of the thin film (10) due to the heating of the heater (25) is measured by the temperature sensor (20), the temperature sensor (20) is a temperature difference sensor, Whether a voltage is applied to the heater (25) and the first heater is heated to heat the thin film (10) from room temperature to a predetermined absolute temperature Tl, and then the first heater is continuously heated. Alternatively, the second heater is heated by the heater (25) in a short time such that the temperature variation of the gas to be measured is negligible, and the thin film (10) is moved from room temperature to the predetermined absolute temperature Tl. Different Heat up to the specified absolute temperature Th, and use the information on the power consumption in the heater (25) necessary for each heater to correct it so as to eliminate the influence of the ambient temperature. The absolute humidity is obtained using data, the output of the absolute temperature sensor (21) provided on the substrate (1) and the output of the temperature sensor (20) are combined, or the thin film (10) is used. In the case where the absolute temperature sensor (22) is provided, the absolute temperature sensor is provided with an absolute temperature measuring means for knowing the absolute temperature of the thin film (10) from the output, and the thin film (10) is formed using the absolute temperature measuring means. An absolute humidity sensor characterized in that it can be set to be heated to absolute temperatures Tl and Th. Of at least two thin films (10a) and (10b) having the same shape thermally separated from the substrate (1), one thin film (10a) has a heater (25a) and a temperature sensor (20a). The other thin film (10b) is also provided with an absolute humidity sensor chip having a heater (25b) and a temperature sensor (20b), and due to a change in thermal conductivity based on the amount of water vapor in the gas to be measured, In the absolute humidity sensor in which the temperature sensors (20a) and (20b) measure the temperature change of the thin films (10a) and (10b) due to the heating of the heaters (25a) and (25b), the temperature sensor ( 20a) and (20b) are temperature difference sensors, a voltage is applied to the heater (25a), and the heater is heated to bring the thin film (10a) from room temperature to a predetermined absolute temperature Tl, At the same time A voltage is also applied to the heater (25b) to heat the heater, and the thin film (10b) is heated from room temperature to a predetermined absolute temperature Th different from the predetermined absolute temperature Tl. The calibration data prepared in advance is corrected using information on the power consumption in each heater (25a) and (25b) necessary for heating to the absolute temperature Tl and excluding the influence of the ambient temperature. From the combined output of the output of the absolute temperature sensor (21) provided on the substrate (1) and the output of each of the temperature sensors (20a) and (20b), or When the thin film (10a) and (10b) are also provided with the absolute temperature sensor (22), an absolute temperature measuring means is provided so that the absolute temperature of each of the thin films (10a) and (10b) is known from the output. , Absolute humidity sensor using absolute temperature measurement means, a thin film (10a) and a thin film (10b) has to be set to be heated to an absolute temperature Tl and Th, respectively, characterized by. The thin film (10) thermally separated from the substrate (1) is provided with an absolute humidity sensor chip having a heater (25) and a temperature sensor (20), and the change in thermal conductivity based on the amount of water vapor in the gas to be measured. Thus, in the absolute humidity sensor in which the temperature change of the thin film (10) due to the heating of the heater (25) is measured by the temperature sensor (20), the temperature sensor (20) is a temperature difference sensor, A voltage is applied to the heater (25), the heater is heated, and the thin film (10) is heated from room temperature to the predetermined absolute temperature Th. In the cooling process after the heating is stopped, the temperature sensor (20 ) Is integrated over time for a predetermined period, and the output information of the time integrated value and the output voltage of the temperature sensor (20) at a predetermined absolute temperature Tl different from the absolute temperature Th are used. , Ambient The correction was made so as to eliminate the influence of the temperature, and the absolute humidity was obtained using the calibration data prepared in advance, the output of the absolute temperature sensor (21) provided on the substrate (1) and the temperature sensor (20). From the combined output with the output, or when the absolute temperature sensor (22) is also provided in the thin film (10), the absolute temperature measuring means that knows the absolute temperature of the thin film (10) from the output is provided, An absolute humidity sensor characterized in that the absolute temperature measuring means can be used to set the thin film (10) to be heated to the absolute temperature Th. The thin film (10) thermally separated from the substrate (1) is provided with an absolute humidity sensor chip having a heater (25) and a temperature sensor (20), and the change in thermal conductivity based on the amount of water vapor in the gas to be measured. Thus, in the absolute humidity sensor in which the temperature change of the thin film (10) due to the heating of the heater (25) is measured by the temperature sensor (20), the temperature sensor (20) is a temperature difference sensor, Whether a voltage is applied to the heater (25) and the first heater is heated to heat the thin film (10) from room temperature to a predetermined absolute temperature Tl, and then the first heater is continuously heated. Alternatively, the second heater is heated by the heater (25) in a short time such that the temperature variation of the gas to be measured is negligible, and the thin film (10) is moved from room temperature to the predetermined absolute temperature Tl. Different In the cooling process after heating is stopped until the predetermined absolute temperature Th is reached, each output voltage of the temperature sensor (20) is integrated over time for a predetermined period, and the output information of each time integrated value is obtained. It was corrected to eliminate the influence of the ambient temperature, and the absolute humidity was obtained using calibration data prepared in advance. The output and temperature of the absolute temperature sensor (21) provided on the substrate (1) The absolute temperature from which the absolute temperature of the thin film (10) is known from the combined output with the output of the sensor (20) or from the output when the thin film (10) is also provided with the absolute temperature sensor (22). An absolute humidity sensor characterized by comprising a measuring means and using the absolute temperature measuring means so that the thin film (10) can be set to be heated to the absolute temperatures Tl and Th. The absolute humidity sensor according to any one of claims 3 to 4, wherein the start of a predetermined period of time integration of the output of the temperature sensor (20) is immediately after the heating of the heater (25) is stopped. At the end of the predetermined period of the time integration of the output of the temperature sensor (20), the thin film (10) is cooled from a predetermined higher temperature Th in the cooling process after stopping the heater heating, and the predetermined lower one 6. The absolute humidity sensor according to claim 3, wherein the absolute humidity sensor is set to be equal to the temperature Tl. The thin film (10) or thin film (10a), (10b) is in a wet gas that does not reach the dew point, is in a wet gas that has reached the dew point, is submerged in water, or is a solid that also contains ice A minute electric power that can determine at least one of the items of whether the substance is attached is supplied to the heater (25) or the heaters (25a) and (25b), and the thin film (10) or the The temperature change of the thin films (10a) and (10b) is measured by the temperature sensor (20) or the temperature sensors (20a) and (20b), and the output of the absolute temperature sensor (21) is also measured if necessary. The absolute humidity sensor according to claim 1, wherein the item is determined using the absolute humidity sensor. The absolute humidity sensor according to any one of claims 1 to 7, wherein a lower temperature Tl of different temperatures Th and Tl is set to a temperature in a range of 100 ° C to 270 ° C. The absolute humidity sensor according to any one of claims 1 to 8, wherein a semiconductor is used as at least one thermoelectric conductor of the temperature difference sensor. The absolute humidity sensor according to any one of claims 1 to 9, wherein the thin film (10) or the thin films (10a), (10b) is a silicon semiconductor. The absolute humidity sensor according to any one of claims 1 to 10, wherein the absolute temperature sensor (21) and the absolute temperature sensor (22) are semiconductor diodes. The absolute humidity sensor according to any one of claims 1 to 11, wherein the temperature sensor (20) is also used as a heater (25). The absolute humidity sensor according to claim 1, comprising at least a power supply circuit, an amplifier circuit, an arithmetic circuit, and a control circuit. The absolute humidity according to claim 13, wherein the relative humidity can be obtained based on the output of the absolute temperature sensor (21) and information on the absolute humidity from the absolute humidity sensor according to any one of claims 1 to 12. Humidity sensor. Corresponding to each of the cantilever-like thin film (10) or thin films (10a), (10b) thermally separated from the substrate (1), there is a temperature difference sensor with a heater (25) or heaters (25a), (25b). A temperature sensor (20) or temperature sensors (20a) and (20b), and a temperature contact of the temperature difference sensor is provided near the tip of the cantilever-shaped thin film (10) or thin films (10a) and (10b) The heater (25) or the heaters (25a), (25b) are arranged so as to surround the hot junction of the temperature difference sensor, and the tip of the cantilever-like thin film (10) or thin film (10a), (10b) An absolute humidity sensor chip characterized in that heat is generated uniformly in the vicinity of the part. In correspondence with each of the thin film (10) or the thin films (10a) and (10b) thermally separated from the substrate (1), the heater (25) or the temperature sensor (25a) and (25b) is a temperature difference sensor. 20) or temperature sensors (20a) and (20b), and further, corresponding to each, an absolute temperature sensor (22) or absolute temperature sensors (22a) and (22b) are also provided. Absolute humidity sensor chip. The absolute humidity sensor chip according to claim 16, wherein the heater (25) or the heater (25a), (25b) is also used as a temperature sensor (20) or a temperature sensor (20a), (20b) which is a temperature difference sensor. The absolute temperature sensor (22) or the absolute temperature sensors (22a) and (22b) are semiconductor diodes, and at least part of the supply voltage to the heater (25) or the heaters (25a) and (25b) is driven by the semiconductor diode. The absolute humidity sensor chip according to claim 16, wherein the absolute humidity sensor chip is wired so as to be used as a power source.

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