JP5076235B2 - Thermocouple heater and temperature measurement device using the same - Google Patents

Description

  The present invention relates to the use of a thermocouple, which is a temperature difference sensor, as a heater, and a thermocouple heater used for a heat conduction type sensor capable of measuring physical quantities such as atmospheric pressure, degree of vacuum, flow rate, concentration, and enthalpy change of a substance, The present invention relates to a temperature measuring device for measuring a physical quantity to be measured using a temperature change based on the physical quantity of a medium around the sensor, comprising a heat conduction type sensor in combination with the thermocouple heater. It is.

  Conventionally, the present inventor has invented an “electric heater” (Japanese Patent Application No. 54-027559; Japanese Patent No. 1398241) which forms a heater by forming a resistor such as a platinum thin film on a thin film that has been suspended in the air. Currently, it is applied as a micro heater for flow sensors and vacuum sensors. Further, the applicant of the present invention uses a semiconductor diode as a heater “a heating diode temperature measuring device, an infrared temperature measuring device using the same, a flow rate measuring device, and a method for manufacturing a flow rate sensing unit” (Japanese Patent Application No. 2005-68266; 250736) was invented. Since the semiconductor diode can also be used as a temperature sensor, it has been proposed to use it as a heater / temperature sensor. Thereafter, the present applicant has made the following: “Temperature difference detection method, temperature sensor and infrared sensor using the same” (Japanese Patent Application No. 2004-026247; JP 2005-221238), “Current detection type thermocouple calibration method, current detection, etc. Type thermocouple, infrared sensor, and infrared detector "(Japanese Patent Application No. 2005-332341; Japanese Patent Application No. 2006-582260; Japanese Patent Application No. 2006-262343; Japanese Patent Application No. 2006-300301), and a conventional thermocouple using a pair of thermocouples. Rather than measuring the temperature difference by measuring the open-circuit voltage, it is theoretically shown that measuring the short-circuit current based on the thermoelectromotive force of the thermocouple is more sensitive than the thermopile. Named as a pair. This high-sensitivity current detection type thermocouple can receive and absorb infrared rays from the outside like a thermal type infrared sensor, and can be used to measure the temperature rise. When used for the above, it was necessary to provide a separate heater.

In general, in a thin film thermally separated from a substrate, when the heated thin film is stopped, the temperature of the substrate (ambient temperature before heating) Tc and the temperature T of the heated thin film are determined by Newton's law of cooling. Heat is dissipated and cooled in proportion to the temperature difference (T-Tc), and finally becomes equal to the substrate temperature. Thus, the temperature change of the temperature sensor when the temperature of the heated object conducts heat to the surrounding medium and the temperature rises or falls in relation to the current thermal conductivity of the surrounding medium. The thermal conductivity sensor used to measure and measure the physical quantity to be measured of the surrounding medium, for example, flow velocity, degree of vacuum, impurity concentration, enthalpy change, etc., the substrate temperature Tc and the heated thin film rather than the absolute temperature sensor The temperature difference from the temperature T is important.

A thermistor with high temperature sensitivity, which is an absolute temperature sensor formed on a thin film floating in the air, needs to use two thermistors to measure the temperature difference between the substrate and the heated thin film. However, due to variations in the characteristics of the two thermistors, it is extremely difficult to measure with high accuracy when the ambient temperature Tc including the substrate temperature varies.

The thermopile, which has high sensitivity as a temperature difference sensor, has a structure in which a large number of thermocouples are connected in series, so that the production yield is poor and it is difficult to make it small.

Further, in order to reduce the size and the simple structure of the heat conduction type sensor, a highly sensitive temperature difference sensor and a device that can also be used as a heater have been demanded.
Japanese Patent No. 1398241 JP 2006-250736 A JP 2005-221238 A

  The present invention has been made to solve the above-described problems. A thermocouple such as a current detection type thermocouple is used as a temperature sensor, but a current is supplied to the thermocouple itself without using a separate heater. It is also operated as a heater by self-heating by Joule heat, gas and liquid that are environmental media surrounding this thermocouple, and if necessary, solid flow rate, flow rate, vacuum, concentration, radiation and infrared amount, liquid It is a thermal sensor that can be used as a heater for heating to measure physical quantities such as enthalpy changes in solids and solids, and has a simple structure, high sensitivity, high accuracy, and a wider measurement range. An object of the present invention is to provide a heating heater for a heat conduction type sensor and a temperature measuring device using the same.

In order to achieve the above object, in the thermocouple heater according to claim 1 of the present invention, a thermocouple is formed on the thin film 10 thermally separated from the substrate 1 or the main body of the thin film 10 is a thermocouple. By switching the switch, the thermocouple can be used as a thermocouple heater section so that the thin film 10 can be Joule-heated with a predetermined power, a predetermined voltage or a predetermined current, or until a predetermined temperature is reached. The thin film 10 can be Joule-heated by passing an electric current, and the heat conduction to the thermocouple is stopped by switching the switch so that the thermocouple can be used as a temperature difference sensor. When the temperature decreases with the passage of time after stopping the heating, measure the time until it reaches the predetermined temperature, measure the thermal time constant, or measure the temperature after the predetermined time and its change Accordingly, it has to be able to measure the measured physical quantity related to the heat conduction of the surrounding medium, it is an characterized.

Thus, the thermocouple originally measures the temperature difference ΔT between the hot junction and the cold junction, measures the thermoelectromotive force V generated by the temperature difference ΔT, and calibrates the temperature difference ΔT and the thermoelectromotive force V. In the present invention, by switching the switch, the thermocouple is used as a thermocouple heater unit, and the thin film 10 is Joule-heated with a predetermined power, a predetermined voltage, or a predetermined current. The current is passed through the thermocouple so that the thin film 10 can be joule-heated until the temperature reaches a predetermined temperature, and self-heating by Joule heat is performed by the internal resistance of the thermocouple, and the surroundings of the thermocouple This medium (gas, liquid, solid) is used as a heater that heats and raises the temperature.

Further, in the present invention, the switch is switched to stop the heating energization to the thermocouple , and the thermocouple is used as an original temperature difference sensor, and the temperature of the thin film 10 is the time after the heating is stopped. When it decreases over time, it is related to the heat transfer of the surrounding medium by measuring the time until it reaches the predetermined temperature, measuring the thermal time constant, or measuring the temperature and its change after the predetermined time. The physical quantity to be measured can be measured .

Since the electric power required for heating the thermocouple heater is generally large, the applied voltage and current become much larger than the thermoelectromotive force. In the present invention, for example, an analog switch or the like is used to stop heating energization of the thermocouple and switch the switch so that the temperature can be measured as a thermocouple as a temperature difference sensor.

The thermocouple heater according to claim 2 of the present invention is a case where a plurality of thermocouples are formed on the thin film 10 and at least one of the thermocouples operates as a thermocouple heater section.

Since a plurality of thermocouples are formed on the thin film 10, a pair of them can be Joule-heated as a thermocouple heater part, and the remaining thermocouple is used in the thin film 10 while being Joule-heated by the thermocouple heater part. The temperature difference at the location of the thermocouple heater may be obtained, or the pair of thermocouple heaters may be operated as an original thermocouple. You may make it operate | move as an original temperature difference sensor.

The thermocouple heater according to claim 3 of the present invention is an original temperature difference sensor in which a plurality of thermocouples are connected so as to be able to perform differential operation thereof, and between the locations in the thin film 10 or the thin film 10. This is a case where the temperature difference from the outside location can be measured. A thermocouple essentially does not generate a thermoelectromotive force unless there is a temperature difference. For example, a minute temperature difference between thermocouples connected so that differential operation between two thermocouples can be detected.

For example, when the thin film 10 is divided into two thin films A and B, and thermocouples are formed on each of them, these thermocouples are once operated as a thermocouple heater unit. Then, the thin film A and the thin film B are heated, and then the heater operation is stopped. Next, these thermocouples are used as thermocouples, which are the original temperature difference sensors, and the temperature difference between the thin film A and the thin film B. Connect and operate so that differential operation can be measured. By doing so, reflecting the heat conduction to the surrounding medium such as gas, the temperature of each of the thin film A and the thin film B decreases with the passage of time after the heating is stopped, so that these predetermined temperatures are reached. Measurement of physical quantities related to the heat conduction of the surrounding medium, such as the degree of vacuum, concentration, mass change, etc. And can measure the flow velocity.

The thermocouple heater according to claim 4 of the present invention is a case where the thermocouple is operated as a current detection type thermocouple.

The current detection type thermocouple is invented and named by the applicant of the present invention as described above, and measures a temperature difference by measuring a short-circuit current based on the thermoelectromotive force of the thermocouple. A smaller short-circuit current flows when the value of the internal resistance r of the thermocouple is smaller for the same temperature difference. Therefore, in general, a material having a large Seebeck coefficient, a low electrical resistivity, and a low thermal conductivity is desirable. This eventually corresponds to the desirability of a material with a high figure of merit Z for the thermoelectric material. Actually, when combined with a semiconductor integrated circuit as one conductor of the thermocouple, the thermal conductivity is large, but a silicon (Si) single crystal substrate is often used, and Si is advantageous. In this case, n-type Si in which the resistivity is reduced by adding impurities as much as possible is advantageous because the resistivity can be made smaller than that of the p-type. As the other heat conductor, a metal thin film is desirable because the resistance value becomes small. Of course, it is also possible to use a compound semimetal such as BiTe or BiSe, which is a material having a large figure of merit Z of the thermoelectric material as the thermocouple.

In order to measure the short-circuit current based on the thermoelectromotive force of the thermocouple, it is preferable to use a virtual short circuit of the input terminal of the OP amplifier.

A temperature measuring device according to claim 5 of the present invention uses the thermocouple heater according to any one of claims 1 to 5 described above, a thermocouple of a thermocouple heater portion of the thermocouple heater, or another thermocouple. It is characterized by comprising at least an amplification circuit, an arithmetic circuit and a control circuit necessary for measuring a temperature change based on the heat conduction environment around the pair.

The amplification circuit of the temperature measuring device of the present invention is mainly a circuit that amplifies a signal of temperature difference information of a thermocouple as a temperature difference sensor, and the arithmetic circuit is combined with a memory circuit therein to This circuit mainly calculates the measured physical quantity of the surrounding medium from the temperature difference information. The control circuit is a circuit that controls switching between the thermocouple temperature difference sensor operation and the thermocouple heater operation, temperature control during heater operation, energization time and interval during pulse driving of the heater, and the like.

The thermocouple heater of the present invention is advantageous in that a thin film thermocouple that can be made extremely small can be formed on the thin film, and that this small thermocouple can also operate as a heater, so that an extremely small heat conduction type sensor can be provided.

In the thermocouple heater of the present invention, a plurality of thin film thermocouples are formed on one ultra-small cantilever-like thin film, and some of these thin film thermocouples are used, and a pair of thermocouples performs Joule heating operation. In addition, while performing the heating operation, it is possible to measure the temperature distribution in the micro cantilever by connecting the differential operation using the remaining thin film thermocouples. There are advantages.

In the thermocouple heater of the present invention, a pair of thin film thermocouples are respectively formed on a plurality of ultra-small cantilever-like thin films, and one pair of thin-film thermocouples formed on the ultra-small cantilever-like thin film is a thermocouple. Between the ultra-small cantilevers that are configured to operate as a pair of heaters and surround the ultra-small cantilever where the thermocouple heater is formed by using the thin film thermocouples formed on other ultra-small cantilevers by their differential operation By measuring this temperature difference, there is an advantage that a minute change in the measured physical quantity of the medium can be measured.

In the temperature measuring device of the present invention, the thermocouple is used as an original temperature difference sensor and can also operate as a heater. Therefore, the structure is simple, and an ultra-compact heat conduction type sensor can be obtained. This has the advantage that a small and inexpensive temperature measuring device can be provided.

  Hereinafter, the thermocouple heater 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 this silicon (Si) substrate, a detailed description will be given based on examples. Moreover, the temperature measuring apparatus using the thermocouple heater of this invention is demonstrated using the block diagram.

  FIG. 1 shows an embodiment of a thermocouple heater according to the present invention, in which a heat conduction type sensor chip 100 portion (plan view schematic) and its thermocouple 24 are operated as a thermocouple heater section 25, and an original thermocouple. An example of a circuit diagram for operating the temperature difference sensor 20 is also shown. FIG. 2 is a schematic cross-sectional view of the heat conduction type sensor chip 100 taken along the line XX of FIG. As a circuit diagram, the switches S1 and S2 are linked to each other, and both show the state of the switch when the thermocouple is operated as a heater. Here, this is a case where an SOI substrate is used as the substrate 1, and the thin film 10 having a structure floating in the air for thermal separation from the substrate 1 is formed as a cantilever 15 in the substrate 1 by the cavity 40. It has become. In this case, the thermocouple 24 is the main material of the cantilever 15 formed in the SOI layer 11 made of p-type silicon (Si) single crystal. As the thermocouple conductor of the thermocouple 24, one thermocouple conductor 120 a is formed as an n-type diffusion region 21 formed by diffusing impurities so as to degenerate into the SOI layer 11, and the other thermocouple conductor 120 b is used as the SOI layer 11. For example, a case where a double layer in which cobalt (Co) and nickel (Ni) are overlapped with each other through the thermally oxidized silicon oxide film 50 is shown.

FIG. 1 also shows a state in which a pn junction diode 23 is mounted on the heat conduction sensor chip 100 as a temperature sensor 200 for detecting the absolute temperature of the substrate 1. Can be operated as a diode thermistor or a thermo diode as an absolute temperature sensor. The temperature sensor 200 can be considered as the temperature Tc of the surrounding medium before the thermocouple 24 is heated as the thermocouple heater unit 25. Further, in the state of the switches S1 and S2 shown in FIG. 1, the thermocouple 24 is joule heated to a predetermined temperature using the power source E, for example, and then the heating is stopped, and then the thermocouple 24 is operated as a temperature difference sensor. In this case, the cold junction of the thermocouple 24 is formed on the substrate 1 on which the pn junction diode 23 is formed, and the thermocouple 24 at the tip of the cantilever 15 is based on the temperature of the substrate 1 (cold junction). Therefore, the temperature difference ΔT is measured by the thermocouple 24 of the cantilever 15. The operation of the current detection type thermocouple as a temperature difference sensor is as follows. The switches S1 and S2 are both turned to the opposite side of the state shown in FIG. 1, and the thermocouple 24 is an operational amplifier (OP amplifier; shown as OP in FIG. 1). The thermal electromotive force is converted into a short-circuit current using a virtual short circuit of the input terminal. This short-circuit current is detected as a temperature difference by converting it to an output voltage V ₀ due to a voltage drop across the feedback resistor Rf of the OP amplifier. Here, the switch S1 is connected to the non-inverting input terminal of the OP amplifier. Since no current flows therethrough, the connection method is such that the magnitude of the contact resistance of the switch S1 does not become a problem. In FIG. 1, the thermocouple 24 is formed as a thin film thermocouple, and the electrode pads 70a and 70b of the thermocouple 24 for the operation as a temperature difference sensor and the operation as a thermocouple heater are the thermocouple 24. Are drawn from two thermocouple conductors 120a and 120b. The wiring 110 is used to control the thermocouple 24 as a temperature difference sensor or as a thermocouple heater, a control circuit for operating as a thermocouple heater, a signal amplification circuit, and an OP amplifier or switch S1 that is a power supply circuit for heating. , S2 and the heat conduction type sensor chip 100 are connected.

Next, referring to FIG. 1 and FIG. 2 using the thermocouple heater of the present invention, the operation as the thermocouple heater unit 25 using the thermocouple 24 as a heater and the original temperature difference sensor 20 of the thermocouple 24. One embodiment when applied to a thin film Pirani vacuum sensor will be briefly described. In order to operate the thermocouple 24 as the thermocouple heater section 25, the switches S1 and S2 in the circuit diagram of FIG. 1 are turned down as shown in FIG. The current I of the heater unit 25 is supplied. Output voltage V ₀ which OP amp circuit diagram of FIG. 1, since the feedback resistor Rf are short-circuited by the switch S2, indicating the value equal to the voltage V of the output voltage V ₀ is applied to the thermocouple heater unit 25. Therefore, it is preferable to adjust to the predetermined voltage V while looking at the reading of the output voltage V ₀ . According to the experiment, when the length of the cantilever 15 is about 1 mm, the thermal time constant τ is about 50 ms (milliseconds), and the resistance of the thermocouple heater 25 that is the thermocouple 24 is about 20Ω. In order to raise the temperature of the thermocouple heater 25 by 10 ° C. from the temperature of the substrate 1, it is known that about 10 mW (milliwatts) of power should be supplied under 1 atmosphere of air. Therefore, the applied voltage V to the thermocouple heater section 25 is 0.45 V, and the tip of the cantilever 15 where the thermocouple heater section 25 is formed is raised by about 10 ° C. at 1 atm. Next, the interlocking switch S1 and switch S2 are tilted to the opposite side as shown in FIG. 1 to stop the power supply to the thermocouple heater 25 and operate the thermocouple 24 as the temperature difference sensor 20. . Then, for example, the temperature difference ΔT of the temperature difference sensor 20 which is the thermocouple 24 after the elapse of t ₀ = 50 ms is measured from the power supply stop switch operation. Next, a predetermined constant power (for example, a constant power of 10 mW for supplying about 10 ° C. at 1 atm) is supplied to the thermocouple heater unit 25 in a vacuum state of ambient gas as various physical quantities to be measured. Each time, the temperature difference ΔT of the temperature difference sensor 20 which is the thermocouple 24 after t ₀ = 50 ms elapses is measured, and the degree of vacuum at that time is measured using a calibration curve prepared in advance. measure. The calibration curve may be stored in a semiconductor memory and calculated by an arithmetic circuit using this.

A predetermined constant power supply to the thermocouple heater 25, for example, P = 10 mW constant, under high vacuum and low vacuum at that time, after being sufficiently heated and saturated, heating was stopped An outline of the temperature difference ΔT ₀ between the substrate 1 and the tip of the cantilever 15 immediately after that (temperature difference ΔT _{h0 at} a high vacuum level, temperature difference ΔT ₁₀ at a low vacuum level) and the respective cooled states are shown. The cooling curve is shown in FIG. In the thermocouple heater unit 25 heated by a predetermined constant power supply to the thermocouple heater unit 25, the same atmospheric gas and the same vacuum level result in a predetermined temperature increase ΔT, and the lower the high vacuum level. Then, since the escape of heat from the thermocouple heater 25 to the surrounding gas is reduced, the temperature rise ΔT _h0 is increased correspondingly, and the thermal time constant τ _{h of} cooling is also increased. The temperature difference ΔT _h from the substrate 1 after t ₀ has also been high. However, when the degree of vacuum decreases (under a low degree of vacuum), heat dissipation increases, so that the temperature rise ΔT ₁₀ of the thermocouple heater 25 decreases and the thermal time constant τ ₁ also decreases to a predetermined constant value. The temperature difference ΔT ₁₀ after the time t ₀ has also become very small. Thus, under a predetermined constant power supply, the temperature difference ΔT from the substrate 1 of the thermocouple heater section 25 after the elapse of the predetermined constant time t ₀ and the temperature rise ΔT of the thermocouple heater section 25 are in the degree of vacuum. This is a function, and further, the downward tendency of the temperature difference ΔT is spurred and the difference is widened, which is convenient for measuring the degree of vacuum.

In the above description, an example in which the thermocouple heater of the present invention is applied to a thin film Pirani vacuum sensor has been described. However, this can also be used, for example, for checking the degree of vacuum of a thermal infrared sensor in a sealed package. . As shown in FIG. 1 and FIG. 2, the light receiving part of the thermal infrared sensor is a cantilever 15, and an infrared absorption film is formed thereon to raise the temperature by infrared rays from the target (when the temperature of the target is higher than the light receiving part). The temperature change of the light receiving part based on the temperature drop (when the temperature of the target is lower than the light receiving part) is detected by the thermocouple 24 formed in the light receiving part. If the thermocouple 24 is a current detection type thermocouple, the sensitivity becomes higher. Of course, a thermopile may be used. This is the operation as a thermal infrared sensor. When the degree of vacuum inside the package is high, the heat escape from the light receiving part is only the heat escape to the substrate 1 through the cantilever 15, so that a highly sensitive thermal infrared sensor is achieved. However, when the degree of vacuum is lowered, heat dissipation to the surrounding gas becomes intense, and the temperature rise due to infrared absorption is reduced, so that the infrared light receiving sensitivity is lowered. In order to operate as a stable infrared sensor, it is necessary to check the degree of vacuum. For this purpose, it is preferable to operate as the above-mentioned thin film Pirani vacuum sensor. That is, a predetermined current is passed through the thermocouple 24 and Joule heating is performed, and a temperature difference ΔT is measured from the substrate 1 after a predetermined time at that time, and whether or not the magnitude has decreased from the initial state, The degree of vacuum can be checked. If the degree of vacuum is lowered, the temperature difference ΔT is reduced accordingly. As the thermocouple 24, a current detection type thermocouple is suitable as shown in FIG.

In the manufacturing process of the heat conduction type sensor chip 100 in the thermocouple heater of the present invention shown in FIGS. 1 and 2, when the SOI layer 11 (p type) of the substrate 1 is used, a pn junction diode as the temperature sensor 200 or The thermocouple 24, the thermocouple heater 25, the cantilever, and the like as the temperature difference sensor 20 can be easily formed by the known semiconductor microfabrication technology for MAEMS, and detailed description thereof is omitted.

FIG. 4 is a schematic plan view showing another embodiment of the thermocouple heater according to the present invention, including another example of the heat conduction type sensor chip 100 having the thermocouple heater portion 25 and the wiring of the thermocouple. Here, as in the first embodiment, a p-type SOI substrate is used as the substrate 1, and the thin film 10 having a structure floating in the air for thermal separation from the substrate 1 is 3 The thin film 10 at the center is a case where the thermocouple 24 is operated as the thermocouple heater unit 25. Since the thermocouple heater unit 25 is Joule-heated while being a thermocouple, for example, a current of 50 mA flows, so the two thin films 10 on both sides of the central thermocouple heater unit 25 are the thermoelectromotive force of the thermocouple 24. And the accompanying short circuit current (temperature difference detection current when used as a current detection type thermocouple), the SOI layer 11 has a BOX layer 51 (not shown in FIG. 4). A groove 41 is formed to reach a structure having an equivalent cantilever 15 (shown in FIG. 2 which is a cross-sectional view of the structure), and the thermocouple heater portion 25 of the central thin film 10 and the two thin films on both sides thereof. 10 is electrically separated from the thermocouple 24 formed in FIG. The structure and operation of the thermocouple 24 formed on each of the three thin films 10 are substantially the same as those of the first embodiment shown in FIG. 1 and FIG. Is omitted.

The thermocouple heater having the three thin films 10 shown in FIG. 4 of the embodiment of the thermocouple heater of the present invention can be used as a gas or liquid flow sensor, for example. For example, the thermocouple heater portion 25 of the thin film 10 at the center of the three thin films 10 is Joule-heated so that the temperature is increased by 10 ° C. above the ambient temperature Tc in the absence of fluid flow. The supply control. Since two equivalent thin films 10 are formed at symmetrical positions with respect to the thermocouple heater section 25 of the central thin film 10, when there is no such flow, the thermoelectric of the thin film 10 on both sides of the thermocouple heater section 25 is formed. The pair 24 has the same temperature rise, but is away from the thermocouple heater 25, and therefore has a temperature rise of less than 10 ° C. When a flow is generated (in the direction of the arrow in FIG. 4), the fluid at the ambient temperature Tc flows through the thermocouple 24 of the thin film 10 upstream of the thermocouple heater 25 of the thin film 10 at the center. Although the temperature is lowered, the thermocouple heater unit 25 receives a little heat, so that the temperature is higher than the ambient environment temperature Tc. However, since the thermocouple 24 of the thin film 10 on the downstream side receives heat from the thermocouple heater section 25, the temperature tends to rise as compared to when there is no flow. Therefore, in order to obtain an output of a temperature difference between the upstream thermocouple 24 and the downstream thermocouple 24, the electrode pads 70b are short-circuited using the external wiring 110 to form the terminal C, Further, the external wiring 110 is used to form the terminal B and the terminal A from the electrode pad 70a and the electrode pad 70a, respectively. The output of the temperature difference between the upstream thermocouple 24 and the downstream thermocouple 24 can be measured between the terminal B and the terminal A, and the output of the upstream thermocouple 24 is downstream between the terminal B and the terminal C. The output of the side thermocouple 24 can be measured between the terminal C and the terminal A. These outputs are a function of the fluid flow velocity or the mass flow rate, and are converted into the fluid flow velocity or mass flow rate using the calibration curve.

In the above description, the thermocouple 24 that is the temperature difference sensor 20 on each of the upstream side and the downstream side is used with respect to the thermocouple heater unit 25 when measuring the velocity of the fluid flow (flow) or the mass flow rate. Although the temperature differences associated with the flow are used, Joule heating of the thermocouple heater unit 25 may be periodically performed to use the time difference to reach the temperature difference sensors 20 on the upstream side and the downstream side. Further, in order to detect a finer flow rate, the phase difference between the temperature rise and fall reaching the temperature difference sensor 20 on the upstream side and the downstream side may be detected.

In the above description, an example of Joule heating by constant power supply is shown. However, the thermocouple heater unit 25 is controlled so as to have a constant temperature difference with respect to the ambient environment temperature Tc, or by application of a constant current or voltage. A Joule heating method may be used.

In FIG. 4, the temperature sensor 200 for measuring the temperature of the substrate 1 is not shown, but the pn junction diode 23, the Schottky diode, which is the temperature sensor 200, A transistor or the like is formed, and this can be used for measuring the ambient temperature Tc.

FIG. 5 is a schematic plan view showing another embodiment of the heat conduction type sensor chip 100 having the thermocouple heater portion 25 in the thermocouple heater of the present invention. Here, the thin film 10 having a structure that protrudes from the substrate 10 into the cavity 40 as a cantilever 15 is divided into a thin film 10A and a thin film 10B. The thin film 10B is formed into a cantilever 15 shape from the thin film 10A through the thermal resistance portion 45. Further, the thin film 10 </ b> A also has a structure in which the thin film 10 </ b> A protrudes from the substrate 1 through the thermal resistance portion 45 in a cantilever shape. The thermal resistance portion 45 has a narrow structure due to the slits 42 formed in the thin film 10, and the thermal conduction to the substrate 1 is reduced to increase the temperature change. A thin film thermocouple 24 is formed on the thin film 10 </ b> A so that it can operate as a thermocouple heater 25. Further, the thermocouple 24 formed on the thin film 10B is provided with an ohmic contact 29 closer to the thin film 10A among the current detection type thermocouples, and from there toward the substrate 1, the thermocouple conductor 120b of the thermocouple 24 and Since the same metal material 110 is led to the electrode pad 71a, the thermocouple 24 formed on the thin film 10B is substantially based on the temperature of the thermocouple heater section 25 formed on the thin film 10A (since it is near the heater, The temperature difference is measured from there to the ohmic contact 29 which is the cold junction of the thermocouple 24 formed on the thin film 10B at the tip of the cantilever 15. When the thermocouple 24 formed on the thin film 10B is operated as a current detection type thermocouple using the electrode pad 71a and the electrode pad 71b, a temperature difference can be detected with high sensitivity.

In the structure shown in FIG. 5 of the thermocouple heater of Example 3 of the present invention, the operation when applied to a Pirani type thin film vacuum sensor will be described as follows. When the thin film 10A is Joule-heated by the thermocouple heater 25 formed on the thin film 10A floating in the air, the temperature becomes, for example, about 100 ° C. higher than the ambient environment temperature Tc at a high degree of vacuum, for example, 10 ⁻⁵ Pa. Thus, heating control is performed so that constant power is supplied. At this time, the thin film 10B has a structure protruding from the thin film 10A in a cantilever shape. Further, since the thermal radiation due to radiation is extremely small at about 100 ° C., the temperature of the thin film 10B and the thin film 10A is high under a high degree of vacuum. Is approximately the same temperature. That is, at a high degree of vacuum, the temperature difference between the thin film 10B and the thin film 10A is almost zero, and the thermoelectromotive force of the thermocouple 24 of the thin film 10B is zero. Therefore, if this is used as a current detection type thermocouple, Short circuit current is also zero. As described above, when a current detection type thermocouple that measures only a temperature difference with respect to the thin film 10A is used as the thermocouple 24 of the thin film 10B, the zero reference method can be applied. Can be measured. The temperature of the thin film 10A is determined by stopping the heating of the thermocouple heater 25 and operating the thermocouple heater 25 as the original thermocouple by operating the temperature immediately after that or the temperature after the elapse of time. be able to.

In the above description, the case where the thin film 10A is implemented as a Pirani type thin film vacuum sensor by maintaining the temperature of the thin film 10A at a constant temperature of approximately 100 ° C. by supplying constant power to the thermocouple heater 25 has been described. Since it is small, its thermal time constant is, for example, about 20 milliseconds. Since such a thin film 10 is used, even a current flowing through the thermocouple heater section 25 can sufficiently respond even with a rectangular wave pulse of about 50 milliseconds. Therefore, since the change in ambient temperature is generally slow, the temperature of the thin film 10A can be periodically raised to, for example, about 100 ° C. with such a short pulse current. Further, although the temperature sensor for measuring the absolute temperature of the substrate 1 is omitted, for example, a pn junction diode may be formed on the substrate 1 and used.

Further, in FIG. 5 of the above-described third embodiment, the thermocouple 24 of the thin film 10B has a structure based on the temperature of the thin film 10A. However, the substrate 1 can be used as a reference. . In such a case, the n-type diffusion region 21 of the thermocouple 24 of the thin film 10B in FIG. 5 is extended to the substrate 1, and an ohmic contact 29 and an electrode are also formed there, and the substrate 1 is used as a reference. Sometimes, the temperature difference between the temperature of the substrate 1 and the temperature of the tip of the thin film 10B may be measured using the electrode formed on the substrate 1 and the electrode pad 71b. In the high vacuum state, as described above, the temperature of the thin film 10B is the same as that of the thin film 10A. Therefore, the temperature of the thin film 10B from the substrate 1 is measured, and the temperature of the thin film 10A is adjusted while Joule heating the thin film 10A. As described above, the temperature can be controlled to be kept constant at 100 ° C.

In each of the above-described embodiments, the thermocouple 24 is added with one of the thermocouple conductors 120a to the p-type SOI layer 11 by thermal diffusion or the like so that n-type impurities (for example, phosphorus P) are degenerated. A thin film layer such as nickel (Ni) or cobalt (Co), which is durable to hydrazine used during anisotropic etching of silicon, may be used as the thin film layer and the other thermocouple conductor 120b. Further, the thin film 10A and the thin film 10B in FIG. 5 in Example 3 are formed by the p-type SOI layer 11, and one thermocouple conductor 120a is the n-type formed there, so that a pn junction is formed. The thermocouples formed on the thin film 10A and the thin film 10B are electrically separated from each other. Ni is more preferable because it is a Seebeck coefficient having an opposite sign to that of the n-type semiconductor. However, since the Seebeck coefficient of the n-type semiconductor is an order of magnitude larger than that of Ni, even if aluminum (Al) having the same sign as the Seebeck coefficient of the n-type semiconductor is used, it does not change so much. In forming the thin film 10 by DRIE without using an anisotropic etchant such as hydrazine, aluminum (Al) may be used. Since Al is widely used as a wiring material in IC technology, the wiring 110 and the thermocouple conductor 120b may be aluminum (Al) for the purpose of integration.

In the above-described embodiment, the cantilever 15 is used as the thin film 10 having a structure floating in the air for heat separation from the substrate 1. However, the cantilever 15 is not necessarily required, and the cavity 40 is bridged. It may be a bridge shape that is supported at both ends, or may be a diaphragm structure formed on the cavity 40.

FIG. 6 is a block schematic diagram showing an embodiment of a temperature measuring device using the thermocouple heater of the present invention. Here, a thermocouple heater of the temperature measuring device, a basic section including at least an amplifier circuit, a control circuit and an arithmetic circuit necessary for measuring a temperature change based on the heat conduction environment around the thermocouple are surrounded by a broken line. The block schematic diagram of the whole temperature measurement apparatus shown in the section and including the power supply unit and the display unit of the physical quantity to be measured is shown. Since the amplification circuit, control circuit, arithmetic circuit, power supply unit and display unit are achieved by conventional techniques, details thereof are omitted here.

The thermocouple heater of the present invention and the temperature measuring device using the same 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 thermocouple heater of the present invention measures physical quantities such as gas and liquid flow rates, flow rates, specific substance concentrations, vacuum levels, and enthalpy changes of materials by thermal analysis with high sensitivity and high accuracy as temperature changes. It is used for heat conduction type sensors. For example, when the thermocouple heater of the present invention is applied to a Pirani-type thin film vacuum sensor, it is an ultra-compact current detection type thermoelectric sensor that detects only a temperature difference with high sensitivity and high accuracy on a thin film suspended in a cantilever shape. Since a pair can be used, only one thermocouple heater and one temperature difference sensor, or one thermocouple that is used as both a thermocouple heater and a temperature difference sensor, It can be used as a vacuum sensor with a wide band, especially with a measurement area extended to the high vacuum side. Furthermore, since an extremely minute temperature difference can be detected by the zero reference measurement method, it is suitable for measuring the concentration of a minute amount of a specific gas or the like and a minute flow rate. In addition, the temperature measuring device equipped with the thermocouple heater of the present invention includes a control system, and is suitable for, for example, a vacuum gauge, a velocimeter, a thermal analyzer, and the like.

It is the plane schematic which shows one Example of the thermocouple heater of this invention. Example 1 It is the schematic of the cross-sectional view of the heat conductive type sensor chip along the XX line in FIG. 1 of the thermocouple heater of this invention. Example 1 It is the schematic of the cooling curve after the predetermined constant electric power supply to the thermocouple heater part in the thermocouple heater of this invention. Example 1 It is a schematic plan view showing another embodiment of the thermocouple heater of the present invention. (Example 2) It is a schematic plan view showing another embodiment of the thermocouple heater of the present invention. (Example 3) The block schematic diagram of the temperature measuring device of the present invention is shown. Example 4

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate 10, 10A, 10B Thin film 11 SOI layer 12 Base substrate 15 Cantilever 20 Temperature difference sensor 21 N-type diffusion region 23 Pn junction diode 24 Thermocouple 25 Thermocouple heater part 29 Ohmic contact 40 Cavity 41 Groove 42 Slit 45 Thermal resistance Part 50 Silicon oxide film 51 BOX layer 70a, 70b Electrode pad 71a, 71b Electrode pad 100 Thermal conduction type sensor chip 110 Wiring 120a, 120b Thermocouple conductor 200 Temperature sensor

Claims (5)

A thermocouple is formed on the thin film (10) thermally separated from the substrate (1), or the main body of the thin film (10) is a thermocouple. As a unit, the thin film (10) can be Joule-heated with a predetermined power, a predetermined voltage or a predetermined current, or a current is allowed to flow until a predetermined temperature is reached so that the thin film (10) can be Joule-heated. In other words, by switching the switch, the heating power supply to the thermocouple is stopped, and the thermocouple can be used as a temperature difference sensor. The temperature of the thin film 10 decreases with the passage of time after the heating is stopped. The physical quantity to be measured related to the heat conduction of the surrounding medium by measuring the time to reach the predetermined temperature, measuring the thermal time constant, or measuring the temperature and its change after the predetermined time. It has to be able to measure, thermocouple heater according to claim. Thin film (10) Yes forming a plurality of thermocouples, at least one thermocouple heater according to claim 1, wherein the thermocouple is configured to operate as a thermocouple heater of them. A plurality of thermocouples are connected so that the differential operation of the temperature difference sensor can be performed, and the temperature difference between the locations in the thin film (10) or the locations outside the thin film (10) can be measured. The thermocouple heater according to claim 2 . The thermocouple heater according to any one of claims 1 to 3 , wherein the thermocouple is operated as a current detection type thermocouple. Use of the thermocouple heater according to any one of claims 1 to 4 , for measuring a temperature change based on a heat conduction environment around a thermocouple of a thermocouple heater portion of the thermocouple heater or other thermocouple A temperature measuring device comprising at least a necessary amplification circuit, arithmetic circuit and control circuit.

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