JP2014122870A - Absolute temperature output sensor formed by combination of temperature difference sensor and absolute temperature sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an absolute temperature output sensor that can configure an output of a measurement point of a temperature difference sensor for measuring physical quantities such as gas flow, gas concentration, pressure and radiation with only a hardware circuit configuration.SOLUTION: The absolute temperature output sensor utilizes a fact that a temperature difference sensor 20 such as a thermopile, and an absolute temperature sensor 30 such as a diode and a resistance temperature sensor each have substantially constant temperature coefficients in a specific temperature range within a predetermined service temperature range. The absolute temperature output sensor is formed by combination of the temperature difference sensor 20 and the absolute temperature sensor 30, and comprises: adjustment means 200 amplifying output voltages of the sensors on request, and performing adjustment so that the temperature coefficients of the sensors are identical to one another in a desired temperature range; and adding means 300 adding the outputs. The output thus obtained is an output proportional to an absolute temperature at a measurement point of the temperature difference sensor 20.

Description

  The present invention relates to a temperature sensor, which combines a temperature difference sensor such as a thermocouple or a thermopile with an absolute temperature sensor such as a diode or a resistance temperature detector, and the absolute temperature sensor outputs the absolute temperature at the reference point of the temperature difference sensor. This is related to an absolute temperature output sensor in which the temperature (reference temperature) is corrected and the measurement point of the temperature difference sensor can be displayed as an absolute temperature.

Conventionally, thermocouples, which are temperature difference sensors, and thermopiles that are connected in series to increase sensitivity, and temperature sensors such as platinum (Pt) and absolute temperature sensors such as diodes are used to measure the room temperature. The absolute temperature of the reference point is measured to correct the room temperature. This is because two absolute temperature sensors are used when a thermal sensor that measures physical quantities such as gas flow, gas concentration, absolute humidity, and radiation temperature is composed of only the absolute temperature sensors, with the ambient temperature being room temperature. Because, for example, a resistance temperature detector is required, one must measure the room temperature, and the other must measure the absolute temperature changed by the physical quantity to be detected, and find the difference between them. is there. Since these two absolute temperature sensors do not have the same temperature coefficient and resistance value, the temperature coefficient and the resistance value can be equalized with high accuracy at the same time for large fluctuations in room temperature. There wasn't. For this purpose, first of all, it is better to measure the absolute temperature of the room temperature with an absolute temperature sensor and measure each temperature using a temperature difference sensor that outputs only the temperature changed by the detected physical quantity from there. This is because there is little error and the detected physical quantity can be measured with high accuracy. Then, in the measurement of the absolute temperature at the measurement point of the temperature difference sensor exposed to the physical quantity to be detected, the output is converted to the temperature or the output converted to the temperature and then added.

  Conventionally, an absolute temperature sensor such as a platinum resistance thermometer, a pn junction diode, a transistor, or a thermistor is formed or installed at the same temperature as the reference temperature at the reference point of the temperature difference sensor. The digital signal output is converted, the temperature difference output between the standard temperature of the temperature difference sensor and the measurement point is also digitally converted, and the zero point correction of the reference point and linearization processing are performed based on data prepared in advance. Thus, the absolute temperature at the measurement point of the temperature difference sensor is obtained by using memory data of each temperature characteristic on software via an arithmetic processing unit MPU (microprocessor Unit) (Patent Document 1). Also, the absolute value of the measurement point can be determined using the digital conversion after amplification of each thermocouple output and absolute temperature sensor output and the temperature-thermo-electromotive force reference characteristics of the thermocouple based on 0 ° C built in the memory. The temperature was calculated via the MPU (Patent Document 2). For this purpose, it is necessary to provide an MPU with a built-in memory function, a linearization correction processing circuit, and the like, and it has been necessary to be an expensive absolute temperature sensor.

The present applicant forms a heater and a thermocouple on a thin film thermally separated from a semiconductor substrate through a cavity, heats the thin film with a heater, and allows the thermocouple to measure the temperature of the thin film. A type sensor was invented (Patent Document 3). If a thermocouple, which is a temperature difference sensor, is used for temperature measurement, only the temperature difference from the substrate with the reference point is output, and when heated at a predetermined power, the temperature from the room temperature at the reference point does not depend on the ambient temperature (room temperature). This is because if the temperature rises and the heating is stopped, the temperature rise will eventually return to zero, that is, return to room temperature and the output will become zero, and the zero-position method, which is high-precision measurement, is easy to apply. In addition, since the thermal conductivity of the medium is equivalently changed by physical quantities such as atmospheric pressure, flow, and gas concentration of the surrounding medium, a sensor using the fact that the amount of heat released from the heater-heated thin film is changed by these physical quantities It is a heat conduction type sensor. A temperature difference sensor to which the zero-point method can be applied is suitable for such a heat conduction type sensor utilizing the fact that the heat deprivation changes from the thin film during heating of the heater or during the cooling process. There, an absolute temperature sensor such as a diode is also formed on the substrate on which the reference point of the thermocouple is formed, and the absolute temperature (reference temperature) of this reference point is measured with a diode. The temperature difference was measured with a thermocouple. In general, it is not always necessary to know the absolute temperature of the measurement point, but in the case of physical quantity measurement related to the thermal conductivity of gas, it is necessary to know the absolute temperature because the thermal conductivity of gas depends on the absolute temperature. There is. The absolute temperature of the reference point, which is the temperature of the substrate, and the temperature difference between the measurement points based on this can be summed on the software as described above, but the output of the absolute temperature of the reference point and the reference point The electrical output based on the temperature difference from the measurement point is directly converted to the same temperature coefficient and added as it is. Absolute temperature output that can be obtained simply and inexpensively, and can easily determine the absolute temperature of the measurement point using a hardware circuit as much as possible as a small and inexpensive sensor. A sensor was sought.

The present applicant further invented the use of a thermocouple as a temperature difference sensor / heater (Patent Document 4). When one thin film thermocouple is used as both a temperature difference sensor and a heater, the structure becomes extremely simple, the manufacturing process can be simplified, and it is easy to form a sensor chip with a good yield. The thin film thermocouple is a temperature difference sensor in addition to the advantage that an inexpensive sensor chip can be manufactured because it can be mass-produced. Therefore, as described above, a thin film heated from room temperature must be at room temperature after the heater is stopped. Since it returns, measuring the temperature difference from room temperature has the great advantage that the zero position method, which is a highly accurate measurement technique, can be applied. However, when the thermocouple is operated as a heater, it is necessary to stop the operation as the temperature sensor and to operate as the temperature sensor (temperature difference sensor) from the time when the heating as the heater is stopped. That is, it is extremely difficult to operate the heater function and the temperature sensor function simultaneously. Therefore, in order to measure the temperature of the thin film being heated, it is necessary to devise a time-division operation.

Japanese Patent No. 1610529 Japanese Patent No. 4212952 Patent No. 4996617 Japanese Patent No. 5076235

  The present invention has been made to solve the above-described problems. The temperature difference sensor of a thermocouple or a thermopile outputs only a voltage based on the temperature difference between the reference point and the measurement point. And extract the voltage output related to the absolute temperature of the reference point (the reference point may be a hot junction, but in this specification the cold junction is used as a reference point) so that the same temperature coefficient is obtained. The aim is to provide an absolute temperature output sensor that can easily determine the absolute temperature of the measuring point of the temperature difference sensor in such a way that, after adjustment, these voltage outputs can be summed at least on the circuit. . This is because, for example, the forward voltage of the diode when a constant current is passed and the voltage drop of the resistance temperature detector change almost linearly to the absolute temperature, and the output of the temperature difference sensor is also Utilizing the fact that voltage output is obtained almost linearly in proportion to the temperature difference over a wide temperature range from 0 ° C to several hundreds of ° C. Therefore, these combinations are almost linearized (linearization processing). ) To provide an absolute temperature output sensor. Of course, this includes, for example, compensating for some linearity by inserting a non-linear resistance element into the feedback resistor of the amplifier circuit. In particular, a semiconductor temperature difference sensor such as a semiconductor thermocouple or a thermopile with a large temperature coefficient such as a cantilever formed by thermal separation through a cavity on a semiconductor SOI substrate, a diode such as a pn junction diode or a measurement that can be easily formed on the substrate. By using a temperature resistor as an absolute temperature sensor and combining them, the absolute temperature at the measurement point of the temperature difference sensor is obtained.In other words, the absolute temperature sensor is used to correct the temperature difference of the temperature difference sensor in a circuit. Although the measurement temperature accuracy is lacking automatically, the absolute temperature at the measurement point of the rough temperature difference sensor is automatically known. Then, the output of the absolute temperature at the measurement point is used to make it possible to use it for an operation such as stopping the application of the heater voltage when the set desired thin film temperature is reached.

  In order to achieve the above object, an absolute temperature output sensor according to claim 1 of the present invention comprises a temperature difference sensor 20 and an absolute temperature sensor 30 installed so as to have the same temperature as the temperature of its reference point. In the absolute temperature output sensor for converting the temperature at the measurement point of the temperature difference sensor 20 into an absolute temperature, the magnitude of the temperature coefficient between the output Vot from the temperature difference sensor 20 and the output Voa from the absolute temperature sensor 30 is used. Includes an adjusting unit 200 that adjusts the measurement points to be the same in a desired temperature range, and an adding unit 300 that adds the output Vot and the output Voa, and outputs the measurement point from the output of the adding unit 300. The absolute temperature is obtained.

The absolute temperature sensor 30 configured to have the same temperature as the reference temperature of the reference point of the temperature difference sensor 20 is a high thermal conductivity of metal or the like on the substrate when the temperature difference sensor 20 is formed on the substrate. An absolute temperature sensor 30 such as a commercially available pn junction diode may be provided through a material having a sufficient thermal contact in the vicinity of the reference point of the temperature difference sensor 20 formed on the substrate. The sensor 30 may be formed near the reference point. When the absolute temperature sensor 30 is a semiconductor device such as a diode or a transistor, the substrate may be a semiconductor substrate or a non-semiconductor substrate, and a semiconductor layer is formed on the substrate, and a diode or the like is formed therein. You can leave it. Of course, in the case of a resistance temperature detector such as a platinum (Pt) resistor, a platinum film may be formed directly on a non-semiconductor substrate such as an alumina substrate by sputtering or the like and patterned by photolithography or the like.

In order to use a diode as the absolute temperature sensor 30, when a constant forward current, for example, 1 milliampere (mA) is passed through the diode, the magnitude of the forward voltage at that time is relative to the junction temperature (absolute temperature) of the diode. It is known to change linearly. In this case, the forward voltage decreases linearly as the junction temperature increases, and the temperature coefficient varies depending on the diode and its forward current value, but in the case of a silicon pn junction diode, it is about -2.0 to -2.5 mV / K. It is known to be large. On the other hand, the temperature coefficient of the thermoelectromotive force, which is the Seebeck coefficient of silicon, is n-type and the resistivity is 0.01 Ωcm. When the temperature of the measurement point is increased, the measurement point has a positive heat with respect to the reference point. Although an electromotive force appears and there is temperature dependence, it is known to be approximately 0.7 mV / K, which is smaller than the temperature coefficient of the forward voltage of the diode. In this n-type silicon and metal thermocouple, the metal Seebeck coefficient is negligibly small compared to n-type silicon, so the temperature coefficient of this thermocouple may be considered to be almost the n-type silicon Seebeck coefficient. . When the diode is used as the absolute temperature sensor 30 in this way, the raw output voltage from the absolute temperature sensor 30 (referred to as a direct output voltage) is amplified using the adjustment means 200a as the adjustment means 200. To obtain an output Voa. Further, the output voltage Vot is obtained by amplifying the direct output voltage from the temperature difference sensor 20 using the adjusting means 200t as the adjusting means 200. In these desired temperature ranges, for example, 200 ° C. to 250 ° C., these temperature coefficients (for example, the unit is (V / K)) are made to substantially coincide. In this way, since the output Voa and the output Vot have the same temperature coefficient, the output proportional to the absolute temperature can be obtained by simply adding them using the adding means 300. For amplification in the adjusting means 200, an operational amplifier (OP amplifier) is suitable. Note that the meaning of amplification described above includes not only an amplification factor of 1 or more but also attenuation of 1 or less. Of course, when the amplification factor is 1, the operational amplifier itself may not be provided, for example, it may be connected by direct wiring, or the impedance conversion may be simply performed using the operational amplifier. .

In the above description, both the adjusting means 200a for the absolute temperature sensor 30 and the adjusting means 200t for the temperature difference sensor 20 are used as the adjusting means 200. However, as the adjusting means 200, the absolute temperature sensor 30 and the temperature are adjusted. The difference sensor 20 may use the direct output voltage of the larger temperature sensor as the output Voa or the output Vot without using the adjusting means 200a or the adjusting means 200t for the larger temperature coefficient. For example, of the direct output voltage from the absolute temperature sensor 30 and the direct output voltage from the temperature difference sensor 20, when the direct output voltage from the absolute temperature sensor 30 is large, the smaller temperature difference sensor The direct output voltage may be amplified using the adjusting means 200t (in this case, the amplification factor is 1 or more) so as to match the temperature coefficient of the direct output voltage Voa of the larger absolute temperature sensor 30. In this case, the adjustment means 200a for the larger absolute temperature sensor 30 is not necessarily required, and only the adjustment means 200t for the smaller temperature difference sensor may be used.

When a resistance temperature detector such as platinum (Pt) is used as the absolute temperature sensor 30, its resistance temperature coefficient is about 3.9 × 10 ⁻³ / K, but is amplified using the adjusting means 200a and output Voa When the temperature coefficient is obtained, the temperature coefficient (V / K) varies depending on the current flowing through the resistance temperature detector. Accordingly, an appropriate driving current is supplied to the resistance temperature detector 30 serving as the absolute temperature sensor 30, the voltage at both ends thereof is amplified as necessary, and the temperature coefficient of the output Vot from the temperature difference sensor 20 matches the desired temperature range. It is good to adjust so that. When a thermocouple is used as the temperature difference sensor 20, the thermoelectromotive force (Seebeck voltage) based on the temperature difference between the reference point and the measurement point is small, and therefore, the Seebeck coefficient itself of the thermoelectromotive force is small. Since it is a difference sensor, its own temperature coefficient is small. However, by amplifying this, a voltage output Vot that increases the effective temperature coefficient can be obtained, and the temperature coefficient of the output voltage reflecting the thermoelectromotive force can be adjusted. The Seebeck coefficient of the thermocouple is somewhat dependent on the temperature coefficient, and an average Seebeck coefficient (corresponding to the temperature coefficient) in a desired temperature range (for example, 200 ° C. to 250 ° C.) is selected. It is good to decide the amplification factor by the thermocouple amplifier.

As the adjusting means 200t and 200a, there is an amplifier that increases the output with an amplification factor of 1 or more as described above, but conversely, an amplifier with an amplification factor of 1 or less is also included, and the output voltage of the absolute temperature sensor 30 is further increased. When the temperature coefficient of Voa is large, the direct output voltage based on the Seebeck coefficient of the thermocouple 20 is amplified to obtain an output Vot that is equal to the temperature coefficient of the output Voa. For example, the output voltage can be effectively reduced so as to obtain an output Voa having a small temperature coefficient by resistance division or the like, and can be made equal to the temperature coefficient of the output Vot of the thermocouple 20.

Further, a thermopile in which a plurality of thermocouples as the temperature difference sensor 20 are connected in series has a larger thermoelectromotive force, and the raw temperature coefficient before amplification of the absolute temperature sensor 30 which is a diode or a resistance temperature detector. That is, the direct temperature coefficient is often exceeded. In this case, the direct output from the absolute temperature sensor 30 which is a diode or a resistance temperature detector that is carrying a predetermined current is amplified via the adjusting means 200a to obtain the output voltage Voa, and its effective The temperature coefficient can be made equal to the temperature coefficient of the thermopile of the thermopile.

The absolute temperature output sensor according to claim 2 of the present invention is a case where the absolute temperature sensor 30 is a diode.

Examples of the diode include a semiconductor pn junction diode and a Schottky junction diode. Further, a diode between the emitter and base of the transistor may be used. At this time, it is effective to use the collector and base short-circuited. When a predetermined constant current is passed through the diode, the voltage drop at the diode, which is the forward voltage of the diode at that time, is linear with changes in the absolute temperature of the diode temperature (precisely, the junction temperature such as the pn junction). It is known to change to the principle of the thermo diode.

The absolute temperature output sensor according to claim 3 of the present invention is a case where the absolute temperature sensor 30 is a resistance temperature detector.

Examples of the resistance temperature detector include a thermistor and a platinum (Pt) resistor. A platinum (Pt) resistor is suitable because it can be easily formed by sputtering and photolithography, and the resistance change linearity with temperature is good and stable.

The absolute temperature output sensor according to the fourth aspect of the present invention is configured to output the output Voa from the voltage across the absolute temperature sensor 30 when a predetermined constant current is passed through the absolute temperature sensor 30. .

When a predetermined constant current is passed through the diode or the resistance temperature detector as the absolute temperature sensor 30, the voltage at both ends thereof is proportional to the internal resistance of the absolute temperature sensor 30, but the direct output voltage which is the voltage at both ends. Is amplified through the adjusting means 200a as necessary to obtain an output Voa. Since the internal resistance of the absolute temperature sensor 30 has temperature dependence, the temperature coefficient of the output Voa from the absolute temperature sensor 30 is equal to the temperature coefficient of the output Vot from the temperature difference sensor 20 and a desired temperature range. Adjustments are made so that they are the same, and the absolute temperature at the measurement point of the temperature difference sensor 20 is obtained via the adding means 300.

The absolute temperature output sensor according to claim 5 of the present invention is a case where the temperature difference sensor 20 and the absolute temperature sensor 30 are formed on the same substrate 1.

Since the reference point of the temperature difference sensor 20 and the absolute temperature sensor 30 such as a diode need to have the same environmental temperature, at least the reference point of the temperature difference sensor 20 and the absolute temperature sensor 30 have good thermal conductivity. It is desirable to form them on the same substrate 1, for example, a semiconductor substrate such as silicon, and it is desirable to install them close to each other.

The absolute temperature output sensor according to claim 6 of the present invention is a case where the substrate 1 is made of single crystal silicon.

The absolute temperature output sensor of the present invention is practically applied to a gas concentration sensor (including absolute humidity and hydrogen gas), a vacuum sensor (atmospheric pressure sensor), a radiation thermometer, etc., which are thermal sensors, and a thermocouple and a diode. However, it is preferable to fabricate the semiconductor on a single crystal substrate of silicon, in which an integrated circuit can be easily formed. Therefore, in view of this, for example, it is desirable to form a temperature difference sensor, a heater, and a diode, which are sensing parts of an absolute temperature output sensor, on the same single crystal silicon substrate. If the substrate is a single crystal silicon substrate, an integrated circuit (IC) for performing these signal processings can also be mounted on the substrate.

The absolute temperature output sensor according to claim 7 of the present invention is a case where one thermoelectric material of the temperature difference sensor 20 is the material of the substrate 1.

Since the temperature difference sensor 20 and the heater 25 often require a large temperature change at low speed with small power consumption, they are a part of the material of the substrate 1 through the cavity, but the thin film is thermally separated from the substrate 1. It is desirable for production to be formed in a cantilever or the like. For this purpose, for example, an SOI substrate is used as the substrate 1, and a part of the SOI layer is formed into a cantilever-like thin film 10 through a cavity, and a temperature difference sensor or a heater is formed there. Of course, the temperature difference sensor 20 can also be used as a heater. Also, the absolute temperature sensor 30 such as a diode is formed in the vicinity of the reference point of the temperature difference sensor 20 in the substrate 1. Even if the cantilever-like thin film 10 is heated, the temperature near the reference point of the substrate 1 increases. Even if it is, the temperature in the vicinity of the substrate 1 may be regarded as a reference temperature, and the room temperature may be corrected so that an output linearly related to the absolute temperature of this temperature is output.

The absolute temperature output sensor according to claim 8 of the present invention is a case where the temperature difference sensor 20 is formed on the thin film 10 thermally separated from the substrate 1 through the cavity.

As described above, in the application to the thermal sensor, the temperature difference sensor 20 and the heater 25 are preferably a thin film that is thermally separated from the substrate 1 through the cavity because it is desired to change the temperature at high speed with small power consumption and at high speed. It is preferable to form a cantilever or a cross-linked structure of 10 or a diaphragm.

The absolute temperature output sensor according to claim 9 of the present invention is a case where an operational amplifier is used as the adding means 300.

As the adding means 300 for adding the output Vot and the output Voa, they may be respectively input to a memory and added in software. However, in this case, an operational amplifier that is particularly useful as a hardware adding means is used. This is the case.

The absolute temperature output sensor according to claim 10 of the present invention is a case where the heater 25 is also formed on the thin film 10.

When measuring the absolute temperature of the light receiving part of a thermal infrared sensor or thermal radiation thermometer, the heat source is radiant heat from the target, but as a heat conduction sensor such as a flow sensor, gas concentration sensor or absolute humidity sensor When used, it is more compact and easier to heat the thin film 10 with the heater 25 formed therein. Of course, the temperature rise is measured by a temperature difference sensor 20 such as a thermocouple or a thermopile formed on the thin film 10 in the same manner.

The absolute temperature output sensor according to the eleventh aspect of the present invention is a case where a periodic heating voltage is applied to the heater 25 so that the thin film 10 is repeatedly heated and cooled in a predetermined cycle.

Since the thermal time constant of the cantilever-like thin film 10 provided on the silicon substrate can be shortened by, for example, about 10 milliseconds (msec), a periodic heating voltage to the heater 25, for example, a rectangular wave voltage By inputting, heating and cooling of the thin film 10 on which the heater 25 is formed can be repeated many times per second. Of course, in this way, the gas or liquid around the thin film 10 can also be heated periodically. For example, it is possible to obtain an output with a large S / N by repeating heating and cooling 10 times or more per second, acquiring data on the temperature each time, and averaging the data with a capacitor or the like.

The absolute temperature output sensor according to the twelfth aspect of the present invention is a case where the temperature difference sensor 20 can also be used as the heater 25.

Since the temperature difference sensor 20 such as a thermocouple is also a resistor, it can also be used as the heater 25 by passing an electric current, and since it is not necessary to prepare the heater 25 separately, it becomes a compact absolute temperature output sensor. However, as described above, when the heater action is performed, the action as the temperature difference sensor must be stopped except in special cases. Since the thin film 10 on which the temperature difference sensor is mounted has a heat capacity and has a thermal time constant, an extremely short heater heating stop time is provided, and the temperature of the thin film 10 is measured during this period. It can also be done.

The absolute temperature output sensor according to the thirteenth aspect of the present invention stops the heating of the heater 25 during the heating cycle for a short heating stop time Δt that is not more than one-tenth of the thermal time constant of the thin film 10, and this heating stop time Δt. The output Vot is obtained by measuring the temperature of the thin film 10 with the temperature difference sensor 20 or measuring the temperature of the thin film 10 with the temperature difference sensor 20 within the heating stop time Δt immediately after the end of the heating cycle. In this way, the absolute temperature at the measurement point during heating of the thin film 10 is estimated.

In the case where the temperature difference sensor 20 and the heater 25 are provided separately, it is not always necessary to stop the heating of the heater 25 and measure the temperature with the temperature difference sensor 20 at that time. Since there is a lot of noise, the heating of the heater 25 may be stopped to measure the temperature in order to improve the S / N. However, in order to use the temperature difference sensor 20 also as the heater 25, it is desirable to stop the heating of the heater 25 and measure the temperature with the temperature difference sensor 20 within the stop time. When the heat capacity of the thin film on which the temperature difference sensor 20 is mounted is 20 milliseconds, for example, the heater heating is stopped for 10 microseconds (μsec) as the heating stop time Δt. The temperature of the thin film 10 is measured by the temperature difference sensor 20, and the temperature is repeatedly measured every 1 millisecond continuously during a heater heating cycle period, for example, a 100 millisecond (msec) heater heating cycle period. For example, the rising state of the temperature of the thin film 10 and the temperature rising state where the temperature rising stops and becomes saturated can be measured with little error. In addition, when it is simply desired to know the final value at which the temperature rise of the thin film 10 is saturated, a short time immediately after the end of the heater heating cycle period is used by using the heater input applied voltage signal at the end of the heater heating cycle period. By measuring the temperature of the thin film with the temperature difference sensor 20 during Δt = 10 microseconds, it is possible to measure the temperature of the thin film 10 almost at the end of heating in a state where the cooling effect does not effectively appear. It is convenient to perform temperature measurement in such a short heater heating stop period in combination with a sampling hold circuit.

The absolute temperature output sensor according to the fourteenth aspect of the present invention joule-heats the heater 25 with a rectangular wave-shaped predetermined constant power, and differentiates the output voltage from the temperature difference sensor 20 based on the temperature rise during the joule heating. This is a case where a differentiation means for obtaining the slope and an integration means for integrating the output after the differentiation means are provided, and the absolute temperature of the measurement point is estimated using the output of the integration means.

The predetermined constant power is equivalent to constant current drive or constant voltage drive if the temperature coefficient of resistance of the heater 25 is almost zero and can be ignored. In general, to raise the temperature of the thin film 10 to 200 ° C., an applied voltage of about 3 V is required for the heater 25, but the output voltage of a thermocouple (comprised of a low-resistance semiconductor and a metal) that is the temperature difference sensor 20 Is about 28 mV at most according to experiments. That is, it is about 1/100 of the applied voltage. When the resistance temperature coefficient of the heater 25 is negligible, driving the heater 25 with a predetermined constant power corresponds to driving the heater 25 with a predetermined constant voltage, and the heater is heated with a driving voltage of the heater 25 having a rectangular waveform. As described above, the constant voltage is a direct current component, and if it is differentiated, it should be an output of zero. On the other hand, the output of the temperature difference sensor 30 based on the temperature rise of the thin film due to the heater heating is The output voltage changes with time substantially in proportion to the temperature rise. Therefore, an output voltage proportional to the temperature rise of the temperature difference sensor 30 is superimposed on the voltage during heating of the heater, and this component can be taken out by the differentiation circuit. Then, by further integrating this, the temperature rise of the thin film 10 can be taken out. This value is essentially equal to the temperature difference from the substrate 1 to the measurement point of the temperature difference sensor 30. Here, as described above, the output voltage component of the temperature difference sensor 30 that is a time-varying output voltage proportional to the temperature rise superimposed on the applied voltage of the DC component of the rectangular wave-shaped constant voltage is extracted. In this way, the temperature rise at the measurement point of the temperature difference sensor 30 from the substrate 1 is taken out.

When the thin film 10 is heated by the heater 25 at a predetermined constant power, the temperature of the thin film 10 rises with a certain thermal time constant and eventually saturates in balance with heat dissipation. Even if the heater 25 drive voltage has a rectangular waveform, the heater 25 drive voltage is rectangular at the initial stage of heater heating drive of the heater 25 or immediately after the heater heating drive is stopped due to stray inductance or capacitance when a current flows through the heater 25. Instead of the shape, it becomes an excessive state and causes time fluctuation. Since the time change at the initial stage of the heater heating drive or immediately after the heater heating drive is stopped is very large, the time domain (temporarily DC in terms of time) of the rectangular waveform heater 25 drive voltage is excluded from these time areas. It is necessary to take out the differential output of the output voltage only in the component region). It is important to add the temperature rise of the thin film 10 based on the heating time other than the differential time region so as to obtain the temperature rise from the substrate 1 at the measurement point. This measure is also taken. There is a need.

The differentiating means and integrating means may be a circuit using a combination of an operational amplifier and a capacitor, or a hardware integrating means that is simply a circuit combining a resistor and a capacitor. Alternatively, differentiation or integration may be performed on software (software) using a digital circuit using a memory circuit.

In the absolute temperature output sensor of the present invention, the temperature difference sensor 20 has an almost constant temperature coefficient of thermoelectromotive force from around 0 ° C. to several hundred ° C. That is, the temperature difference sensor has a reference point and measurement. The thermoelectromotive force is generated almost proportionally to the temperature difference between the points (almost linearly), and the forward voltage of the diode and the resistance temperature detector with a constant forward current flow are almost linearly related to the ambient temperature. Therefore, it is not necessary to have a special software linearization mechanism using a memory or MPU, and a simple hardware circuit can be used to achieve temperature accuracy. Although it is difficult, there is an advantage that an absolute temperature output sensor capable of displaying the temperature at the measurement point of an inexpensive and compact temperature difference sensor as an absolute temperature can be provided.

In the absolute temperature output sensor of the present invention, the temperature coefficient of the thermoelectromotive force of the temperature difference sensor 20 is amplified by the amplification circuit so that temperature accuracy is easily obtained near the absolute temperature of the measurement point of the desired temperature difference sensor 20. Since it can be adjusted by the magnitude of the rate, the temperature accuracy can also be increased. Further, a non-linear resistance element such as a diode or a thermistor is inserted as a part of the feedback resistance element for adjusting the gain of the amplifier circuit by inserting the temperature coefficient of the thermoelectromotive force of the temperature difference sensor 20 or as a hardware alternative to this. By inserting a simple circuit, there is an advantage that temperature accuracy of absolute temperature can be easily achieved over a wide temperature range.

In the absolute temperature output sensor of the present invention, when the semiconductor substrate 1 having high thermal conductivity is used, the measurement points of the heater 25 and the temperature difference sensor 20 are formed on the thin film 10 such as a cantilever thermally separated from the semiconductor substrate. In addition, when the absolute temperature sensor 30 such as a diode or a resistance temperature detector and the reference point of the temperature difference sensor 20 are formed in a portion excluding the cavity of the semiconductor substrate, the temperature of the thermoelectromotive force output of the temperature difference sensor 20 is set. By amplifying and adjusting the coefficient so that it coincides with the temperature coefficient of the output from the resistance temperature detector, the temperature at the measurement point of the thin film 10 such as a cantilever can be easily displayed as an absolute temperature only with a simple hardware circuit. There are advantages. Further, there is an advantage that an integrated circuit including an operational amplifier can be formed on a semiconductor substrate as required, and can be provided as an absolute temperature output sensor including this simple hardware integrated circuit.

In the absolute temperature output sensor of the present invention, since the temperature difference sensor 20 and the heater 25 can be used together, there is an advantage that a compact absolute temperature output sensor can be provided.

In the absolute temperature output sensor of the present invention, even when the temperature difference sensor 20 and the heater 25 are combined, the generation of the thermoelectromotive force of the temperature difference sensor 20 is extremely fast. The absolute temperature of the measurement point during heating of the heater is also measured within this time after the heater heating is stopped for a very short time compared to the thermal time constant of the thin film 10, for example, a time Δt that is about 1/100 of the thermal time constant. it can. Of course, after the heating is finished, the absolute temperature of the thin film 10 can be measured at any time using the thermoelectromotive force output based on the original temperature difference of the temperature difference sensor 20. And if the short measurement time immediately after a heater heating stop is utilized, there exists an advantage that it can recognize as the temperature just before the heating stop of the temperature during heating.

In the absolute temperature output sensor of the present invention, the heater 10 is heated at a constant driving voltage (rectangular wave voltage) or the like even while the heater is driven, and the thin film 10 is combined by combining the differentiating means and the integrating means. There is an advantage that the absolute temperature can be measured by restoring the temperature rise from the substrate 1 at the measurement point of the formed temperature difference sensor 20.

It is one Example which shows the outline of the electronic circuit structure of the absolute temperature output sensor of this invention. (Examples 1, 3, 4, 5, 6) It is another Example which shows the outline of the electronic circuit structure of the absolute temperature output sensor of this invention. (Examples 2, 3, 5, 6) 1 is a schematic plan view showing an embodiment of a sensor chip for implementing an absolute temperature output sensor of the present invention. (Examples 3 and 6) It is the cross-sectional schematic along the XX line of the sensor chip shown in FIG. 3 of the absolute temperature output sensor of this invention. (Examples 3 and 6) It is another Example of the sensor chip for implementing the absolute temperature output sensor of this invention. (Examples 3, 4, and 6) It is a time chart of other one Example of the temperature of the thin film by the heater heating of the absolute temperature output sensor of this invention. Example 4 It is a time chart of other one Example of the temperature of the thin film by the heater heating of the absolute temperature output sensor of this invention. (Examples 4 and 6) It is one Example of the absolute temperature estimation circuit of the thin film by the rectangular wave voltage heater heating of the absolute temperature output sensor of this invention. (Examples 5 and 6) It is a time chart of the output of a thermocouple, temperature waveform, etc. of one Example of the absolute temperature estimation of the thin film by the rectangular wave voltage heater heating of the absolute temperature output sensor of this invention. (Example 5)

  Hereinafter, the absolute temperature output sensor chip of the present invention can be formed on a silicon (Si) substrate using mature semiconductor integration technology and MEMS technology. With reference to the drawings in the case of manufacturing using the silicon (Si) substrate 1, a detailed description will be given based on examples.

  FIG. 1 is an example showing an outline of an electronic circuit configuration when a diode is used as the absolute temperature sensor 30 in the absolute temperature output sensor of the present invention. The degree of amplification by the adjusting means 200 is either the magnitude (absolute value) of the temperature coefficient of the thermoelectromotive force of the temperature difference sensor 20 or the magnitude (absolute value) of the temperature coefficient of the forward voltage of the diode under a constant current. By the adjustment, the magnitude of the temperature coefficient between the output Vot from the temperature difference sensor 20 and the output Voa from the absolute temperature sensor 30 is the same in a desired temperature range of the measurement point of the temperature difference sensor 20, and The addition means 300 can cope with the absolute temperature display. It is known that the temperature difference sensor 20 generates a thermoelectromotive force proportional to the temperature difference between the measurement point 22 and the reference point 21 with a substantially linear dependency. The configuration and operation of the absolute temperature output sensor of the present invention will be described with reference to the drawing of FIG. An absolute temperature sensor 30 such as a pn junction diode is installed at the same temperature as the reference point 21 of the temperature difference sensor 20. For example, the absolute temperature sensor 30 is formed as close as possible to the reference point 21 on the semiconductor substrate 1 on which the temperature difference sensor 20 is formed, or, for example, a commercially available diode is used to improve the thermal contact and You may install in the vicinity of the point 21. The diode is preferably a pn junction diode, a pn junction of a transistor, or a diode such as a Schottky diode. The forward voltage of the diode (forward voltage) shows a linear absolute temperature dependence when the forward current (forward current) flowing therethrough is constant, and the diode temperature (precisely, junction temperature) It is known that the forward voltage decreases linearly with increasing. In the circuit of FIG. 1, in order to allow a constant current to flow through the diode, the value of the input resistance R1 of the adjusting means 200a needs to be sufficiently larger than the resistance of the forward voltage of the diode at that time. In silicon (Si) pn junctions, the direct (raw) temperature coefficient is known to be -2.0 mV / K to -2.5 mV / K, although it depends on the magnitude of the forward current and the shape of the junction. ing. However, if the diode is specified and the forward current flowing therethrough is specified, for example, it can be fixed at -2.3 mV / K. Since the diode is a semiconductor such as Si, the temperature range of this semiconductor is rather on the low temperature side and can be used within a range of about 77K to 400K. The temperature coefficient value is larger than the temperature coefficient of the thermoelectromotive force of a general metal or semiconductor thermocouple. For example, the thermoelectric coefficient is a Seebeck coefficient of an n-type semiconductor having a resistivity of 0.01 Ω · cm. This is an absolute value larger than the performance (temperature coefficient of thermoelectromotive force) −0.5 mV / K.

The amplification factor of the thermoelectromotive force of the thermocouple which is the temperature difference sensor 20 can be adjusted by the adjusting means 200t having the amplifier A1. By adjusting the amplification factor, for example, the temperature coefficient of the output voltage V0t of the adjusting unit 200t can be adjusted to 10 mV / K by the variable resistor VR1 in the adjusting unit 200. Next, the forward voltage (the magnitude of the temperature coefficient is, for example, -2.3 mV / K) when a predetermined constant current (about 50 microamperes to about 1 milliampere) is passed from the constant current source to the diode. Using the temperature dependency, the magnitude of the temperature coefficient (expressed in absolute value) of the output voltage V0a of the diode adjustment means 200a by the adjustment means 200a having the amplifier Aa is similarly 10mV in the desired absolute temperature range. Adjust with variable resistor VRa2 to be equal to / K. Next, the output voltage V0t from the temperature difference sensor 20 adjusted to have the same temperature coefficient and the output voltage V0a from the diode are added to the inverting input terminal of the operational amplifier A2 as the next adding means 300. Then, the currents of the respective output voltages having the same temperature coefficient are added and passed through the variable feedback resistor VR2 of the operational amplifier A2, and the output voltage V0 proportional to the absolute temperature is obtained in the absolute temperature range of the desired thin film 10. To be obtained. Adjustment of the magnitude of the variable feedback resistor VR2 of the operational amplifier A2 is, for example, so that the output voltage V0 is 3 when the temperature of the measurement point 22 is 300K so that the value is suitable for the absolute temperature display of the measurement point 22 in a desired temperature range. At 0.0V and 500K, the output voltage V0 is preferably 5.0V. Furthermore, a circuit that changes the sign of the output voltage V0 (for example, an inverting circuit using an operational amplifier) may be added as necessary.

When an operational amplifier is used as the amplifier A1 to amplify the thermoelectromotive force of the temperature difference sensor 20 with a desired amplification factor, the sum of the feedback resistance, the internal resistance of the temperature difference sensor 20, and the series resistance thereto is obtained. It is preferable because the amplification factor can be easily determined by the ratio to the resistance. In this case, it is also possible to insert a large series resistance that can ignore the influence of the internal resistance of the temperature difference sensor 20, but the internal resistance of the temperature difference sensor 20 has temperature dependence, so this temperature change is used. Thus, the amplification characteristics can be nonlinear with respect to temperature. In general, the temperature coefficient of the thermoelectromotive force of a thermocouple tends to increase as the temperature increases. For example, in a degenerate semiconductor or a general metal, the internal resistance generally increases as the temperature rises, so that the amplification factor of the operational amplifier of the amplifier A1 decreases as the temperature rises. Therefore, in this case, the magnitude of the temperature coefficient of the amplified temperature difference sensor decreases in a direction to cancel the temperature difference as the temperature increases, which is convenient. In addition, for example, when the thermoelectromotive force of the thermocouple increases (corresponding to a high temperature), the current to the feedback resistor increases, so that the resistance element Rn such that the resistance value decreases, and such an action. Is inserted in series with the feedback resistor VR1, or such a circuit is provided in the middle so that the amplification factor of the amplifier A1 becomes a non-linear amplification with a slight saturation tendency. By adjusting the nonlinear component of the temperature coefficient of power, it is possible to adjust so that the absolute temperature display can be performed with high accuracy in the temperature region of a desired measurement point. For example, a non-linear resistance element such as a diode or a thermistor may be used as the resistance element Rn.

FIG. 2 is an example showing an outline of an electronic circuit configuration when a resistance temperature detector is used as the absolute temperature sensor 30 in the absolute temperature output sensor of the present invention. In the first embodiment in which the absolute temperature sensor 30 is a diode and the second embodiment in the case of being a resistance temperature detector as the absolute temperature sensor 30, a constant current is passed through the absolute temperature sensor 30. Since it utilizes the fact that the potential difference (denaturation) drop at both ends thereof changes substantially linearly with respect to the temperature of the absolute temperature sensor 30, it is essentially the same. When the ambient temperature becomes higher, the voltage drop of the diode is smaller, whereas the resistance temperature detector such as platinum (Pt) has a difference that the voltage drop becomes larger. 2 except that the input terminal of the adjusting means 200t of the temperature difference sensor 20 is connected to the inverting input terminal in FIG. Similarly to the circuit of FIG. 1, in the circuit of FIG. 2, in order to allow a constant current to flow through the resistance temperature detector, the value of the input resistance R1 of the adjusting means 200a with respect to the resistance of the resistance temperature detector at that time Must be large enough. The adjustment and the like in the operation of the absolute temperature output sensor of the present invention are almost the same as those in the first embodiment, and thus detailed description thereof is omitted here.

FIG. 3 is a schematic plan view showing an embodiment of a sensor chip for implementing the absolute temperature output sensor of the present invention. FIG. 4 is a schematic cross-sectional view of the sensor chip taken along line XX of FIG. This is an example in which the temperature difference sensor 20 and the heater 25 are separately formed on the thin film 10 in a sensor chip of an absolute temperature output sensor, and is an example in which a silicon (Si) substrate 1, particularly an SOI substrate is used. The thin film 10 is formed in the shape of a cantilever 12 composed of an n-type SOI layer 11 from the substrate 1 through the cavity 40 and is thermally separated from the substrate 1. The reference point 21 of the temperature difference sensor 20 is formed in a frame having a large heat capacity excluding the cavity 40 of the substrate 1, and a (pn junction) diode as the absolute temperature sensor 30 is formed in the vicinity thereof. Since single crystal silicon has a thermal conductivity similar to that of metal, when the absolute temperature sensor 30 is formed on the substrate 1 in the vicinity of the reference point 21 of the temperature difference sensor 20, the temperature and the absolute temperature of the reference point 21 are almost the same. It can be considered that the temperature of the sensor 30 is equal. In addition, the n-type SOI layer 11 is electrically connected to the n-type region of the diode as the absolute temperature sensor 30 and the thermoconductor 120 a composed of the n-type SOI layer 11 of the temperature difference sensor 20. Accordingly, since the electrode pad 70b at the reference point 21 of the temperature difference sensor 20 and the electrode pad 72a on the SOI layer 11 side of the diode are electrically connected through the SOI layer 11, they are equipotential. In view of the circuit configuration of the absolute temperature output sensor, the electrode pad 70b and the electrode pad 72a at the reference point 21, which are the common potential, can be handled as a common ground potential. Here, as the other thermoconductor 120b of the temperature difference sensor 20, a high melting point formed on the insulating film 50 which is a silicon oxide film so that it can be formed simultaneously with the heater 25 formed on the thin film 10. In this case, a thin film is formed by sputtering deposition of nichrome. Even in a thermocouple made of a semiconductor having a low resistivity of about 0.01 Ω · cm and nichrome metal, the thermoelectromotive force on the metal side is almost negligibly small compared to the thermoelectromotive force of the semiconductor, so the heat of the temperature difference sensor 20 It is no exaggeration to say that the electromotive force is almost determined by the Seebeck coefficient of the semiconductor. As described above, the thermoelectromotive force of the temperature difference sensor 20 between the semiconductor of the n-type SOI layer 11 and the metal is almost determined by the semiconductor, and the measurement point 22 where the temperature is higher is more positive than the reference point 21. It has been found that it becomes a potential (+ potential).

When the thin film 10 is heated by applying a predetermined voltage to the electrode pads 71 a and 71 b to the heater 25, the thermoelectromotive force of the temperature difference sensor 20 becomes the reference point 21 of the temperature difference sensor 20 formed on the substrate 1. The measurement point 22 and the reference point are set so that the electrode pad 70b on the n-type SOI layer 11 side has a negative potential (−potential) and the electrode pad 70a at the same temperature has a positive potential substantially equal to the potential of the measurement point 22. It is generated almost in proportion to the temperature difference from 21.

When a diode is used as the absolute temperature sensor 30, the output of the forward voltage of the diode that flows a predetermined constant forward current, for example, 1 milliampere (mA), and the temperature between the measurement point 22 and the reference point 21 from the temperature difference sensor 20. By applying the output of the thermoelectromotive force generated approximately in proportion to the difference to the circuit shown in FIG. 1 described in the first embodiment, the temperature of the measurement point 22 of the thermocouple of the thin film 10 heated by the heater 25 is determined. The absolute temperature can be displayed. For example, in the circuit of FIG. 1, the output of the thermoelectromotive force of the temperature difference sensor 20 is the temperature of the output from the diode of the forward voltage when the effective temperature coefficient of the thermoelectromotive force from the temperature difference sensor 20 using the amplifier A1 A method for equalizing the coefficient, a method for adding these outputs, and a method for making the temperature at the measurement point 22 of the temperature difference sensor 20 proportional to the absolute temperature are described in the first embodiment. Therefore, detailed description thereof is omitted here. The thermoconductor 120a made of the SOI layer 11 and the thermoconductor 120b made of a nichrome thin film at the measurement point 22 are electrically connected by an ohmic contact 60, and similarly, the thermoconductor 120a made of the SOI layer 11 and its reference. The electrode pad 70 b at the point 21 is also conducted by the ohmic contact 60. The same applies to the case where a resistance temperature detector is used as the absolute temperature sensor 30 in FIG.

The absolute temperature output sensor of the present invention is suitable for an absolute humidity sensor as a heat conduction type sensor, for example. Humidity in the air, can be represented by the absolute humidity of the moisture content contained in one cubic meter (m ^3), is generally expressed in grams (g) / cubic meter (m ^3). If the temperature of the air is known, the absolute humidity can be converted into relative humidity because the amount of saturated water vapor at that temperature is known. The amount of moisture contained in the air increases rapidly with temperature, but the thermal conductivity of air containing moisture (humid air) is approximately equal to the thermal conductivity of air at a temperature of about 120 ° C to 150 ° C. At a temperature lower than this, as the amount of water vapor increases, the thermal conductivity of pure air decreases. At higher temperatures, the thermal conductivity of wet air rapidly increases. Therefore, in the principle of measuring the absolute humidity using the thermal conductivity of wet air as an absolute humidity sensor, it is possible to measure using the sensor chip shown in FIGS. 3, 4 and 5 shown in the first embodiment. it can. Therefore, it is necessary to measure the temperature of the thin film 10 on which the heater 25 serving as a sensing unit and the measurement point 22 of the temperature difference sensor 20 are mounted at a high temperature of 200 ° C. or more, and to know the absolute temperature. Rather, it is required to increase the temperature to a predetermined absolute temperature having a high thermal conductivity, for example, 400 ° C., and to measure the heat radiation state in the thermal equilibrium state of the air in the atmosphere of the thin film 10 at that time.

For that purpose, the absolute temperature of the measurement point 22 of the temperature difference sensor 20 such as a thin film thermocouple formed on the thin film 10 is measured, and the temperature of the thin film 10 is set to 400 ° C. which is a predetermined absolute temperature by heating the heater. When it becomes, it is necessary to stop the heating of the heater 25. Even if the room temperature changes, it is necessary to set the absolute temperature of the measurement point 22 to a predetermined temperature, for example, 400 ° C. For this purpose, it is preferable to use the absolute temperature output sensor of the present invention. That is, when the absolute temperature of the measurement point 22 representing the temperature of the thin film 10 reaches 400 ° C., which is the desired absolute temperature, by heater heating, the output V0 of the electronic circuit shown in FIGS. Using the corresponding value, the heating of the heater 25 is stopped using a comparator or the like. Then, the absolute humidity in the air can be obtained from the output change during the cooling period. At this time, it is also known that the effect of the temperature at room temperature can be counteracted by measuring with reference to a temperature in the vicinity of 120 ° C. to 150 ° C., which is a temperature at which the thermal conductivity becomes irrelevant to the amount of water vapor contained. ing. The temperature rise of the thin film 10 in such an absolute humidity sensor as a heat-conducting sensor does not matter the accuracy of the predetermined temperature. Even if it is repeatedly measured, for example, it is repeated at a temperature around 400 ° C. If it is reproducible, it is enough. In this way, the temperature dependence of the temperature coefficient of the thermoelectromotive force of the temperature difference sensor 20, that is, the linearity between the thermoelectromotive force and the temperature difference need not be a problem.

  FIG. 5 shows another embodiment of a sensor chip for implementing the absolute temperature output sensor of the present invention. In this example, the temperature difference sensor 20 is also used as the heater 25. Of course, it is possible to form a resistance temperature detector on the thin film 10 and measure the absolute temperature of the thin film 10. However, a resistance temperature sensor made of metal such as platinum has a small resistance value and a fine fine line pattern. It is necessary to create a uniform pattern, and it is difficult to produce a uniform pattern. Further, when a semiconductor such as a diode is used, it can only be used at a temperature of 150 ° C. or lower. When the absolute temperature of the thin film 10 is about 400 ° C., the temperature difference sensor 20 such as a thermocouple and the substrate are used. The absolute temperature output sensor of the present invention using a combination with the absolute temperature sensor 30 such as a diode formed in 1 is suitable.

FIG. 6 is a time chart of an example of the temperature of the thin film 10 by the heater heating of the absolute temperature output sensor of the present invention, in which 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 passage of time of the thin film temperature T (represented by the temperature at the measurement point 22) in the heating cycle when the thin film 10 is heated by the heater 25 and the thin film 10 in the cooling cycle after the heater heating is stopped. It shows the status of the temperature decrease over time. 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 its thermal time constant, and it can be considered that the temperature at which the heater heating is not stopped is maintained even during this short time Δt. 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. 7 is a time chart of another embodiment of the temperature of the thin film due to the heater heating of the absolute temperature output sensor of the present invention. During the heating cycle when the thin film 10 is heated by the heater 25, the above-mentioned temperature is periodically described above. An example is shown in which the heater heating is stopped for a time Δt that is sufficiently shorter than the thermal time constant as in FIG. Then, within this short time Δt, the temperature difference sensor 20 measures the output voltage V0 corresponding to the absolute temperature of the measurement point 22 with the circuit shown in FIG. 1, and when the desired temperature, for example, 400 ° C. is reached. In this example, the heating cycle of the heater 25 is stopped when the value of the corresponding output voltage V0 reaches, and the next cooling cycle is started. FIG. 7 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 comparison voltage equal to the value of the output voltage V0 corresponding to 400 ° C. is generated, this voltage, the output voltage V0 corresponding to 400 ° C., a comparator, etc. In comparison, the heating cycle of the heater 25 is preferably stopped.

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 set again. This can be easily achieved by a known technique with a pure hardware circuit configuration. Is. In this way, the temperature of the measuring point 22 of 400 ° C. of the desired absolute temperature is achieved periodically. This is used as a high temperature setting temperature with high thermal conductivity of wet air in the absolute humidity sensor. For example, the temperature drop characteristic of the measurement point 22 of the thin film 10 during the cooling cycle or the heater 25 for reaching a predetermined high temperature is used. From the magnitude of power consumption, the absolute humidity in the humid air can be obtained by converting to absolute humidity by comparing with calibration data prepared in advance. At a high temperature of 150 ° C. or higher, if the amount of water vapor in the moist air is large, the thermal conductivity of the moist air increases, so the temperature drop at the measurement point 22 occurs quickly. In this state, for example, by integrating the output voltage V0 of the circuit shown in FIG. 1 in the cooling cycle with time, the speed of temperature drop can be evaluated by the magnitude of the integrated value. If the time integral value is small, the temperature drops quickly, and the absolute humidity is correspondingly high. Similarly, if the absolute humidity is high, a large heater power consumption is required to reach a predetermined temperature, for example, 400 ° C. On the contrary, if the power consumption is large, the absolute humidity is correspondingly large. In this way, absolute humidity can be determined.

When the temperature difference sensor 20 is operated as the heater 25, the temperature difference sensor 20 cannot be easily operated as an original temperature sensor. That is, there is an order of magnitude voltage difference between the heating voltage required to heat the heater 25 to several hundred degrees C. and the thermoelectromotive force based on the temperature difference of the thermocouple which is the temperature difference sensor 20. This is because the voltage is only negligible. However, if the driving voltage of the heater 25 is a constant value, the time differential value is essentially zero, whereas the temperature rise of the thin film 10 due to the heater heating changes with time. Therefore, this component can extract an output related to a non-zero temperature rise by performing time differentiation. Furthermore, the temperature rise of the original thin film 10 can be reproduced by time integration of the time-differentiated output characteristics. FIG. 8 shows the absolute temperature of the thin film 10 by heating the heater with a rectangular wave voltage that can make the time differentiation zero in the absolute temperature output sensor of the present invention in order to reproduce the temperature rise of the original thin film 10 in this way. 1 is an example of a circuit including a block diagram for estimating.

The embodiment shown in FIG. 8 shows a case where a diode is used as the absolute temperature sensor 30 as in FIG. Of course, a resistance temperature detector may be used as the absolute temperature sensor 30 as shown in FIG. The outline of the operation will be described as follows. FIG. 9 shows a time chart of the output from the thermocouple, the temperature waveform, etc. of one embodiment of the absolute temperature estimation of the thin film 10 by heating the rectangular wave voltage heater of the absolute temperature output sensor of the present invention. Since the temperature difference sensor 20 is also used as the heater 25, a repetitive rectangular wave power supply voltage Vh ′ for heating the heater is applied to the heater 25 as shown in FIG. At this time, the voltage actually applied to the heater 25 generally has an excessive state immediately after the heater voltage application or immediately after the heater voltage application is stopped as shown in FIG. Although it becomes a voltage waveform, excluding these time regions in an excessive state (referred to as an excessive region), it becomes a DC component-like heater applied voltage Vh in a differential time region that is substantially flat in time. Originally, when a rectangular wave power supply voltage Vh ′ is applied to the heater 25, the heater applied voltage Vh should be a DC component time zone that is completely flat in time except for an excessive region. Since the sensor 20 is also used as a thermocouple, based on the temperature rise (saturation value temperature Th) of the heater 25 as shown in FIG. . For this reason, the substantially flat time region (differential time region) in FIG. 5B is small and cannot be drawn here, but a voltage waveform that slightly rises to the right with time and eventually saturates is superimposed. Yes. The differential time region, which is a substantially flat time region in FIG. 6B, is extracted as a time region excluding the excessive region of heater heating using the time setting means shown in FIG.

When the differential time region, which is a substantially flat time region in FIG. 5B, is differentiated in terms of time by the differentiating means, a waveform obtained by differentiating the temperature waveform in FIG. 5C as shown in FIG. Is obtained. Here, the temperature difference sensor 20 is a thermocouple, and it is assumed that the thermoelectromotive force is proportional to the temperature rise from the substrate 1 at the temperature of the thin film 10 (represented by the temperature at the measurement point 22). Such a differential waveform as shown in FIG. 6D is integrated by an integrating means, and the gain is adjusted by an amplifier circuit so that the waveform is similar to the waveform within the differential time of FIG. An output voltage waveform (final value: Vth-Vts) as shown in e) can be obtained. Then, for example, the thermal time constant is obtained from the output waveform of (e) in the figure, and the temperature of the thin film 10 reaches the temperature td from the start of heating of the heater 25 (time 0) to the time td when the differentiation avoiding the excessive region is started. Fig. 3 (c) shows how the voltage Vts is calculated based on the thermoelectromotive force corresponding to the temperature rise within that time, and is added electronically or on the software. The reproduction voltage waveform (saturation value: Vth) as shown in FIG. 6 (f) corresponding to the ultimate temperature Th of the thin film 10 shown in FIG. Of course, from the reproduced voltage waveform (saturation value: Vth) in this figure (f), the ultimate temperature Th of the thin film 10 in this figure (c) is obtained using calibration data prepared in advance.

Differentiating means and integrating means may be an electronic circuit using a combination of a known capacitor and resistor, or may be combined with an operational amplifier to obtain an amplified output voltage. Of course, a differentiating means or integrating means for differentiating and integrating the output voltage with respect to time using a digital circuit and software may be used.

The absolute temperature output sensor of the present invention is applied to a flow sensor, a hydrogen gas sensor, etc. by heating the thin film 10 to a predetermined absolute temperature using the sensor chip shown in FIGS. can do. As shown in FIG. 7 applied to the absolute humidity sensor in the fourth embodiment and FIG. 8 of the fifth embodiment, the method of heating the thin film 10 to a predetermined absolute temperature is performed by heating the heater when the predetermined absolute temperature is reached. This can be achieved by stopping it. In the gas flow sensor, the thermal conductivity of the gas varies depending on the ambient temperature of the gas, so it is necessary to know the absolute temperature of the heated thin film 10. Further, even in the hydrogen gas sensor, in the heat conduction type hydrogen gas sensor, the thermal conductivity of air varies depending on the environmental temperature, and it is necessary to know and correct the temperature of the heated air around the thin film 10 heated by the heater. Thus, the correction of the thermal conductivity based on the absolute temperature of the heated thin film 10 used as the heat conduction type sensor is achieved by the absolute temperature output sensor of the present invention with the simple circuit shown in FIGS. Therefore, it is preferable.

The absolute temperature output sensor of the present invention is not limited to the present embodiment. Naturally, various modifications can be made while the gist, operation, and effect of the present invention are the same.

Finding the absolute temperature of the measurement point of a temperature difference sensor that has been subjected to room temperature correction that is exposed to the physical quantity to be measured using only an analog circuit is a simple circuit and does not require an expensive MPU. An absolute temperature output sensor can be provided. Since the output of a temperature difference sensor such as a thermocouple and the forward voltage output of a diode that passed a constant current and the voltage output due to a voltage drop at a resistance temperature detector both use good linearity with respect to temperature changes, In particular, in a temperature range where the temperature change is not so large near room temperature, it can be provided as an extremely accurate absolute temperature output sensor. In particular, when a semiconductor substrate is used, a semiconductor thermocouple, a pn junction diode, and a platinum (Pt) resistance temperature detector can be formed on the same semiconductor substrate, so that it can be provided as an extremely compact absolute temperature output sensor. Moreover, even if the measured physical quantity is measured at a high temperature of 400 ° C. or higher or at a temperature of 100 ° C. or lower, it is sufficient that the predetermined high temperature by the heater heating is achieved with good reproducibility, and a high-precision absolute temperature value is not desired. If the absolute temperature output sensor of the present invention is applied to an absolute humidity sensor, a gas flow sensor, a hydrogen gas sensor, an atmospheric pressure sensor, etc. as a heat conduction type sensor, it is possible to achieve a simple circuit configuration, a high-speed response and a small size. An inexpensive heat conduction sensor device can be provided. In addition, ear-type thermometers and radiation thermometers that can measure the temperature of the target in a non-contact manner, and physical quantity measurement that uses heaters outside and uses the magnitude and change of the thermal conductivity of the fluid via a fluid such as gas or liquid It is also possible to provide a physical quantity measuring apparatus that does not have a heater in the chip of the absolute temperature output sensor of the present invention, such as the above sensor.

DESCRIPTION OF SYMBOLS 1 Substrate 10 Thin film 11 SOI layer 12 Cantilever 15 Base substrate 20 Temperature difference sensor 21 Reference point 22 Measurement point 25 Heater 30 Absolute temperature sensor 40 Cavity 50 Insulating film 60 Ohmic contact 70a, 70b Electrode pads 71a, 71b Electrode pads 72a, 72b Electrode pads 120a, 120b Thermoelectric conductors 200, 200a, 200t Adjusting means 300 Adding means

Claims (14)

Using the temperature difference sensor (20) and the absolute temperature sensor (30) installed so as to have the same temperature as the reference point, the temperature at the measurement point of the temperature difference sensor (20) is converted into an absolute temperature. In the absolute temperature output sensor, the magnitude of the temperature coefficient between the output Vot from the temperature difference sensor (20) and the output Voa from the absolute temperature sensor (30) is the same at least in a desired temperature range of the measurement point. An adjusting means (200) for adjusting the output Vot and an output Voa, and an adding means (300) for adding the output Vot and the output Voa. The absolute temperature of the measurement point is obtained from the output of the adding means (300). An absolute temperature output sensor characterized by The absolute temperature output sensor according to claim 1, wherein the absolute temperature sensor (30) is a diode. The absolute temperature output sensor according to claim 1, wherein the absolute temperature sensor (30) is a resistance temperature detector. The absolute temperature according to any one of claims 1 to 3, wherein the output Voa is output from a voltage across the absolute temperature sensor (30) when a predetermined constant current is passed through the absolute temperature sensor (30). Output sensor. The absolute temperature output sensor according to any one of claims 1 to 4, wherein the temperature difference sensor (20) and the absolute temperature sensor (30) are formed on the same substrate (1). The absolute temperature output sensor according to any one of claims 1 to 5, wherein the substrate (1) is single crystal silicon. The absolute temperature output sensor according to any one of claims 1 to 6, wherein one thermoelectric material of the temperature difference sensor (20) is a material of the substrate (1). The absolute temperature output sensor according to any one of claims 1 to 7, wherein the temperature difference sensor (20) is formed in a thin film (10) thermally separated from the substrate (1) through a cavity. The absolute temperature output sensor according to any one of 1 to 8, wherein an operational amplifier is used as the adding means (300). The absolute temperature output sensor according to any one of claims 1 to 9, wherein a heater (25) is also formed on the thin film (10). The absolute temperature output sensor according to any one of claims 1 to 10, wherein a periodic heating voltage is applied to the heater (25) so as to repeat heating and cooling of the thin film (10) in a predetermined cycle. The absolute temperature output sensor according to claim 10 or 11, wherein the temperature difference sensor (20) can also be used as a heater (25). Heating of the heater (25) during the heating cycle is stopped for a short heating stop time Δt that is not more than one-tenth of the thermal time constant of the thin film (10), and the temperature of the thin film (10) is changed to the temperature during the heating stop time Δt The output Vot is obtained by measuring with the difference sensor (20) or by measuring the temperature of the thin film (10) with the temperature difference sensor (20) within the heating stop time Δt immediately after the end of the heating cycle. The absolute temperature output sensor according to claim 12, wherein the absolute temperature of the measurement point during heating of the thin film (10) is estimated. Differential means for Joule heating the heater (25) with a predetermined rectangular wave-shaped constant power, differentiating the output voltage from the temperature difference sensor (20) based on the temperature rise during the Joule heating, and obtaining the slope thereof; 13. An absolute temperature output sensor according to claim 12, further comprising an integrating means for integrating the output after the means, and estimating the absolute temperature of the measurement point using the output of the integrating means.

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