JP7509054B2 - Thermal Sensor - Google Patents

Description

The present invention relates to a thermal sensor.

Conventionally, a flow sensor has been proposed that can perform high-precision temperature compensation over a long period of time and that allows for simplified circuitry. The flow sensor includes a heater (3) that generates heat when current is passed through it, a temperature sensor (4a, 4b) disposed near the heater, a resistance temperature detector (5) that measures the ambient temperature, and a control circuit that controls the current passed through the heating resistor. The temperature sensor detects the state of temperature distribution caused by heat from the heater, which changes according to the flow rate or flow speed of the fluid. The control circuit includes a bridge circuit that connects in parallel a first branch in which the resistance temperature detector and a first fixed resistor (8a) are connected in series, and a second branch in which the heating resistor and a second fixed resistor (8b) are connected in series, and the bridge circuit is formed on the same semiconductor substrate (1) (see, for example, Patent Document 1).

A flow sensor (1) has also been proposed that can suppress deterioration of responsiveness and sensitivity to fluid flow even when chip resistors arranged on the surface of an insulating substrate (5) are used as the heating resistor (2) and the temperature compensating resistor (3). The flow sensor has a signal processing unit that processes signals from the heating resistor and the temperature compensating resistor, the heating resistor being a chip resistor arranged on the front surface (5a) of a resin insulating substrate, and the temperature compensating resistor being a chip resistor arranged on the back surface (5b) of the insulating substrate. A temperature compensating resistor is arranged on the path of heat dissipation from the heating resistor through the insulating substrate, and the insulating substrate reduces the chance of contact between the temperature compensating resistor and the fluid compared to the chance of contact between the heating resistor and the fluid (see, for example, Patent Document 2).

In the two inventions mentioned above, the resistance value of the resistor that generates heat when electricity is passed through it increases over time, which can cause the amount of heat generated by passing electricity through the resistor to change gradually. As a result, the accuracy of the measuring device can decrease.

JP 2002-310762 A JP 2017-067724 A JP 2011-174814 A

The present invention was made in consideration of the above problems, and has as its ultimate objective the provision of a thermal sensor that can suppress changes in the amount of heat generated by a resistor (hereinafter also referred to as a "heater resistor") that generates heat when current is passed through it, even when the resistance value of the heater resistor increases due to repeated heating, thereby suppressing a decrease in the measurement accuracy of the measuring device.

To solve the above problems, the present invention provides:
A plurality of resistors that generate heat when supplied with power from a power source;
A substrate having an opening in a cavity area on a surface thereof;
a thin film portion formed so as to cover an opening of the cavity area;
a temperature detector for detecting a temperature of at least one of the plurality of resistors or a temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors include
a first resistor disposed on the thin film portion, the first resistor indicating a change over time in a heat generation amount caused by power supply from a power source based on a change over time in a resistance value;
a second resistor having a different manner of increase in resistance over time or a different manner of change in heat generation over time due to power supply from the power source from the first resistor;
The thermal sensor comprises:

According to the present invention, even if the resistance value of the first resistor changes over time due to repeated heating, the presence of the second resistor can mitigate the effect of the change in the resistance value of the first resistor. This can suppress the change in the amount of heat generated by the first resistor. As a result, the deterioration of the measurement accuracy of the thermal sensor can also be suppressed. For example, when measuring the gas composition of an ambient gas using a thermal sensor having only the first resistor, the amount of heat generated decreases as the resistance value of the first resistor increases, causing a measurement error in the thermal conductivity of the ambient gas, and therefore a correction of the measured value is required. In contrast, adding the second resistor suppresses the decrease in the amount of heat generated by the first resistor, making correction of the measured value unnecessary.

In addition, in the present invention,
A plurality of resistors that generate heat when supplied with power from a power source;
A substrate having an opening in a cavity area on a surface thereof;
a thin film portion formed so as to cover an opening of the cavity area;
a temperature detector for detecting a temperature of at least one of the plurality of resistors or a temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors include
A first resistor disposed on the thin film portion;
a second resistor disposed in the thin film portion or the substrate near the first resistor, the second resistor having a resistance value between 1 and 1.5 times the resistance value of the first resistor;
With this, even if the resistance value of the first resistor changes over time due to repeated heat generation, the influence of the change in the resistance value of the first resistor can be mitigated by the presence of the second resistor.

In addition, in the present invention, the temperature detector may be a thermal sensor characterized in that it is two or more thermopiles arranged in pairs facing each other in the thin film portion, and the first resistor is installed between the pair of thermopiles in the thin film portion. This allows the temperature around the resistor to be detected with high accuracy.

In the present invention, the second resistor may be disposed in a location that has higher heat dissipation than the first resistor, making it possible to form a thermal sensor. With this, heat generated in the second resistor is more easily diffused than heat generated in the first resistor, and changes in the resistance value of the second resistor over time can be suppressed. An example of a location that has high heat dissipation is a substrate with high thermal conductivity.

The present invention may also provide a thermal sensor characterized in that the initial resistance value of the first resistor is equal to the initial resistance value of the second resistor. This allows the second resistor to be constructed from the same component as the first resistor, reducing component costs and component management costs. In addition, when the second resistor is added, the formula for calculating the change in heat generation due to the change in the resistance value of the first resistor can be simplified, making it possible to reduce the management and design burden.

In addition, the present invention may be a thermal sensor characterized in that the power supply is a constant voltage source, and the second resistor is connected in series with the first resistor on the substrate. With this, for example, when the resistance value of the first resistor increases over time, the resistance value of the second resistor does not change, so that the voltage division in the first resistor increases. This makes it possible to suppress a decrease in the amount of heat generated in the first resistor.

The present invention may also be a thermal sensor characterized in that the power supply is a constant current source, and the second resistor is connected in parallel with the first resistor on the substrate. With this, for example, when the resistance value of the first resistor increases over time, the resistance value of the second resistor does not change, and the current flowing through the first resistor decreases. This makes it possible to suppress an increase in the amount of heat generated in the first resistor.

In addition, the present invention may be a thermal sensor characterized in that the first resistor is supplied with power from a constant voltage source, the second resistor is supplied with power from a constant current source, the second resistor is installed between a pair of the thermopiles on the thin film portion, and the first resistor and the second resistor are arranged in parallel independently of each other. In this way, the resistance values of the two resistors both change over time, but the amounts of heat generated at each resistance change over time in opposite directions. Due to the canceling effect of these opposite changes, the change over time in the amount of heat generated by both resistors combined is suppressed.

The present invention may also provide a thermal sensor, characterized in that the power supply is a constant voltage source, the second resistor is connected in series with the first resistor at the thin film portion, and a resistance value of the second resistor changes over time in the opposite direction to that of the first resistor by passing a current through it. According to this, by appropriately selecting the rate of change in resistance of the first resistor and the second resistor due to temperature, it is possible to offset the change in power over time in the first resistor and the second resistor.

The present invention may also be a thermal sensor, characterized in that the power supply is a constant current source, the second resistor is connected in parallel with the first resistor at the thin film portion, and the resistance value of the second resistor changes over time in the opposite direction to that of the first resistor by passing a current through it. In this way, it is possible to offset the change in power over time in the first resistor and the second resistor by appropriately selecting the rate of change in resistance due to temperature of the first resistor and the second resistor. The same effect can be obtained when a constant current is applied in an arrangement in which the second resistor is connected in parallel with the first resistor and when a constant voltage is applied in an arrangement in which the second resistor is connected in series with the first resistor.

The means for solving the above problems can be used in combination with each other whenever possible.

According to the present invention, when the resistance value of the heater resistor increases, the change in the amount of heat generated in the heater resistor can be suppressed. As a result, the life of the heater resistor is extended, and the deterioration of the measurement accuracy of the thermal sensor as a measurement device of the present invention can be suppressed.

FIG. 1 is a schematic diagram showing an example of a sensor element constituting a conventional thermal gas sensor. FIG. 2 is a plan view showing an example of a sensor element constituting the thermal type gas sensor in the first embodiment. FIG. 2 is a block diagram showing a functional configuration of the thermal gas sensor when measuring the gas composition of an atmospheric gas. 4 is a flowchart showing a process performed when measuring the gas composition of an atmospheric gas by a thermal gas sensor. FIG. 11 is a plan view showing an example of a sensor element constituting a thermal type gas sensor in Modification 1. FIG. 11 is a plan view showing an example of a sensor element constituting a thermal type gas sensor in Modification 2. FIG. 11 is a plan view showing an example of a sensor element constituting a thermal type gas sensor in Modification 3.

[Application example]
In this application example, a case will be described where the thermal sensor is a thermal gas sensor. The thermal gas sensor according to this application example has a configuration in which a compensation resistor is additionally disposed in addition to a heater resistor that generates heat when a current flows through it. In other words, the thermal gas sensor includes a plurality of resistors.

Figure 2 is a plan view showing an example of a sensor element 2 constituting a thermal gas sensor 1 to which the present invention can be applied. The sensor element 2 includes a heater resistor 3, a thermopile (temperature detection unit) 4 arranged symmetrically on either side of the heater resistor 3, and a compensation resistor 13 that generates heat when a current is passed through it like the heater resistor 3 and is connected in series to the heater resistor 3. Note that although two thermopiles 4 are shown in Figure 2, there is no limit to the number of thermopiles 4 as long as there are two or more. The heater resistor 3 is a resistor made of, for example, polysilicon. The shape of the thermopile 4 is approximately rectangular in a plan view. The heater resistor 3, the thermopile 4, and the compensation resistor 13 are provided in an insulating thin film 5 formed on a silicon substrate 6.

Although shown in a simplified manner in Figure 2, each thermopile 4 is composed of multiple thermocouples 7 (see Figure 1(b)) arranged in a row at a specified interval within the insulating thin film 5. Of these, the point connected on the same side as the heater resistor 3 is the hot junction 8 (see Figure 1(b)), and the point connected on the opposite side to the heater resistor 3 is the cold junction 9 (see Figure 1(b)).

In addition, a cavity area 10, which is a recess, is provided in the silicon substrate 6 below the heater resistor 3 and thermopile 4 in the insulating thin film 5. A cross-sectional view of the cavity area 10 is shown in FIG. 1(b). Here, the heater resistor 3 is arranged so as to cross the opening of the cavity area 10, while the compensation resistor 13 is arranged in contact with the silicon substrate 6. Therefore, compared to the heat released into the cavity area 10 in the heater resistor 3, the heat generated in the compensation resistor 13 is transmitted through the silicon substrate 6 and diffuses quickly. In other words, the compensation resistor 13 is arranged in a location with higher heat dissipation properties than the heater resistor 3.

The constant voltage source 11 is disposed outside the sensor element 2, and a conductor is connected to an electrode 12 that is conductive to the heater resistor 3 and the compensation resistor 13. When a constant voltage is applied from the constant voltage source 11 to the sensor element 2, the heater resistor 3 and the compensation resistor 13 generate heat. Here, the heater resistor 3 is disposed in the insulating thin film 5 on the cavity 10, and is in a state of relatively low heat dissipation, whereas the compensation resistor 13 is disposed in the insulating thin film 5 on the silicon substrate 6, and is in a state of high heat dissipation. In other words, the compensation resistor 13 is disposed in a place having high heat dissipation compared to the heater resistor 3. Therefore, the temperature of the heater resistor 3 rises due to the current from the constant voltage source 11, but the temperature of the compensation resistor 13 does not rise like the heater resistor 3. As a result, the resistance value of the heater resistor 3 increases over time due to repeated current from the constant voltage source 11. On the other hand, the resistance value of the compensation resistor 13 hardly changes over time.

The thermal gas sensor according to this application example has a function of suppressing a decrease in the amount of heat generated in the heater resistor 3 when the resistance value of the heater resistor 3 increases over time, by additionally disposing the compensating resistor 13 in relation to the heater resistor 3. Details will be described later (see formula (2) in Example 1).

Example 1
A thermal sensor according to a first embodiment of the present invention will be described in detail below with reference to the drawings. In the following embodiment, an example in which the present invention is applied to a thermal gas sensor will be described, but the present invention may also be applied to other devices such as an oxygen concentrator or a gas flow meter. The thermal gas sensor according to the present invention is not intended to be limited to the following configuration.

<Device Configuration>
Fig. 1 is a schematic diagram showing an example of a sensor element 2 constituting a conventional thermal gas sensor 1. Fig. 1(a) is a plan view of the sensor element 2 constituting the conventional thermal gas sensor 1, and Fig. 1(b) is a cross-sectional view taken along the line X-X of Fig. 1(a). The thermal gas sensor 1 is a type of MEMS (Micro Electro Mechanical Systems), and is used, for example, to measure the gas composition (concentration ratio) of an atmospheric gas.

A conventional thermal gas sensor 1 does not have any resistors other than the heater resistor 3. The sensor element 2 has the heater resistor 3 and a thermopile 4 arranged symmetrically on either side of the heater resistor 3. The heater resistor 3 and the thermopile 4 are formed in an insulating thin film 5, which is provided on a silicon substrate 6. Here, the heater resistor 3 corresponds to the first resistor in the present invention. The insulating thin film 5 and the silicon substrate 6 correspond to the thin film portion and the substrate, respectively, in the present invention.

As shown in FIG. 1(b), when the hot junction 8 of the thermocouple 7 constituting the thermopile 4 detects heat generation in the heater resistor 3, an electromotive force is generated due to the temperature difference with the cold junction 9 due to the Seebeck effect. The hot junctions 8 are located next to each other on the top of the cavity area 10, and the cold junctions 9 are located in an area of the silicon substrate 6 other than the cavity area 10. Since the heat generated in the heater resistor 3 is released to the cavity area 10, the diffusion of heat to the silicon substrate 6 is suppressed. Therefore, the temperature of the cold junctions 9 located in areas of the silicon substrate 6 other than the cavity area 10 hardly increases, and a temperature difference with the hot junctions 8 located around the heater resistor 3 is more likely to occur.

The heater resistor 3 generates heat when a constant voltage is applied from the constant voltage source 11 to the sensor element 2 via the electrode 12. The temperature of the heat generated in the heater resistor 3 is measured by the thermopile 4, so that the thermal conductivity of the ambient gas that has flowed into the sensor element 2 can be measured.

Since thermal conductivity is a specific value depending on the type of gas, the gas composition of the ambient gas can be measured by measuring the thermal conductivity of the ambient gas that has flowed into the sensor element 2. For example, if the ambient gas is air, it is also possible to measure the oxygen concentration in the air. However, if the amount of heat generated in the heater resistor 3 is not always constant, the measurement accuracy of the thermal gas sensor 1 decreases. This causes measurement errors in the thermal conductivity of the ambient gas.

In the case of a flow meter, the ambient gas flows along the heater resistor 3 and the pair of thermocouples 7 in FIG. 1B. The longitudinal direction of the heater resistor 3 and the thermopile 4 is perpendicular to the flow direction of the ambient gas. Therefore, when the ambient gas flows into the sensor element 2, the heat of the heater resistor 3 does not diffuse symmetrically around the heater resistor 3, but diffuses asymmetrically along the direction in which the ambient gas flows. At that time, a temperature difference occurs between the hot junctions 8 on both sides of the heater resistor 3. Then, an output voltage is generated from the thermopile 4 in proportion to the temperature difference. In addition, since the temperature difference increases according to the flow velocity, the magnitude of the flow velocity can be detected based on the electromotive force of the thermopile 4. In this case, if the amount of heat generated in the heater resistor 3 is not always constant, the measurement accuracy of the flow meter decreases. Therefore, a measurement error occurs in the flow rate of the ambient gas.

なお、Ｖは定電圧源１１の電圧値である。 When a constant voltage is applied from the constant voltage source 11 to the sensor element 2, the resistance value of the heater resistor 3 increases over time due to repeated heating of the heater resistor 3, and the power of the heater resistor 3 decreases. Here, the life of the heater resistor 3 is defined as the time when the initial resistance value Rh of the heater resistor 3 increases over time and becomes a times (a>1). In this case, if the initial power of the heater resistor 3 is _W0 and the power at the end of the life is _W1 , the ratio of _W0 to _W1 is expressed by the following formula (1).

Here, V is the voltage value of the constant voltage source 11.

ここで、Ｒｈ＝Ｒ１とすると、ａ＞１より、式（２）におけるＷ_１／Ｗ_０の値は、式（１）におけるＷ_１／Ｗ_０の値より大きい。すなわち、ヒータ抵抗３に対して付加的に補償抵抗１３を配置することで、ヒータ抵抗３における抵抗値が経時的に増加した際の、ヒータ抵抗３における電力の減少を抑制できる。ここで、補償抵抗１３は、本発明における第２抵抗に相当する。 Here, we return to the explanation of FIG. 2. As described above, when a constant voltage is applied from the constant voltage source 11 to the sensor element 2, the resistance value of the heater resistor 3 increases over time, whereas the resistance value of the compensation resistor 13 hardly increases. When considering a case where thermal conductivity is repeatedly measured using the thermal gas sensor 1, the rate of increase in the resistance value of the compensation resistor 13 is extremely small compared to the rate of increase in the resistance value of the heater resistor 3, so it can be considered that the resistance value of the compensation resistor 13 does not change even if a constant voltage is applied. Then, when thermal conductivity is repeatedly measured, the resistance value of the heater resistor 3 increases over time, and at the same time, the partial pressure across the heater resistor 3 increases. Therefore, the decrease in power (approximately equivalent to the amount of heat generated) in the heater resistor 3 is suppressed. At this time, similar to formula (1), the ratio of _W0 to _W1 is expressed by the following formula (2).

Here, if Rh=R1, then because a>1, the value of _W1 / _W0 in formula (2) is greater than the value of _W1 / _W0 in formula (1). In other words, by additionally disposing the compensating resistor 13 on the heater resistor 3, it is possible to suppress a decrease in power in the heater resistor 3 when the resistance value of the heater resistor 3 increases over time. Here, the compensating resistor 13 corresponds to the second resistor in the present invention.

Ｗ_１／Ｗ_０の値を１とするｋとして、第３行目のようなｋが求まる。すなわち、ヒータ抵抗３における初期抵抗値Ｒｈが経時的に増加してａ倍になった時をヒータ抵抗３の寿命とすると、補償抵抗１３における初期抵抗値Ｒ１をヒータ抵抗３における初期抵抗値Ｒｈの√ａ倍とすることで、ヒータ抵抗３における電力の減少率を最小に抑制することができる。その結果、ヒータ抵抗３の寿命を延ばすことができる。なお、√ａの値は、例えば１以上１．５以下としてもよい。 Furthermore, in equation (2), consider the resistance value of compensation resistor 13 for reducing the rate of decrease when the power decreases from _W0 to _W1 . When the rate of decrease from _W0 to _W1 is 0, that is, when the value of _W1 / _W0 is 1, the rate of decrease from _W0 to _W1 is minimum. In this case, if the resistance value R1 of compensation resistor 13 is kRh, the following equation (3) is established.

With k set to 1 for the value of _W1 / _W0 , k is calculated as shown in the third row. In other words, if the life of the heater resistor 3 is defined as the time when the initial resistance value Rh of the heater resistor 3 increases over time to a times, the rate of decrease in power in the heater resistor 3 can be minimized by setting the initial resistance value R1 of the compensation resistor 13 to √a times the initial resistance value Rh of the heater resistor 3. As a result, the life of the heater resistor 3 can be extended. The value of √a may be, for example, 1 to 1.5.

Figure 3 is a block diagram showing the functional configuration of the thermal gas sensor 1 when measuring the gas composition of the atmospheric gas. The thermal gas sensor 1 includes a control unit 14, and an input unit 15, a measurement unit 16, a memory unit 17, and an output unit 18, each of which is connected to the control unit 14 wirelessly or by wire.

The control unit 14 includes a CPU, ROM, RAM, etc., and stores information on thermal conductivity, which has a unique value depending on the type of gas, for example. As described above, the thermal conductivity of the ambient gas flowing into the sensor element 2 is measured, and the gas composition of the ambient gas can be measured based on the information on the thermal conductivity, which has a unique value depending on the type of gas.

The input unit 15 has a function for inputting in advance, for example, the type of gas contained in the gas to be measured. This makes it possible to measure the gas composition of each input gas in the atmospheric gas by measuring the thermal conductivity of the atmospheric gas that has flowed into the sensor element 2.

The measurement unit 16 includes a gas flow path (not shown), heater resistor 3, compensation resistor 13, thermopile 4, etc., and measures parameters such as the power of the heater resistor 3 and the temperature of heat generated in the heater resistor 3. The measured parameters are stored in the memory unit 17.

The control unit 14 calculates the gas composition of the atmospheric gas based on the output of the thermopile 4 in the measurement unit 16 and the parameters stored in the memory unit 17. The measured gas composition is displayed on the output unit 18. The output unit 18 is, for example, an LCD monitor.

FIG. 4 is a flowchart showing the process of measuring the gas composition of the ambient gas by the thermal gas sensor 1. The flow of the process will be described below with reference to FIG. 4. In this flowchart, first, the ambient gas, the type of which is specified by the input unit 15, is flowed into the sensor element 2 constituting the thermal gas sensor 1 (S101). In the case of a flow meter, the ambient gas flows into the heater resistor 3 along the short side direction of the thermopile 4 in FIG. 2. The ambient gas that flows into the heater resistor 3 is heated by the heat generated by the heater resistor 3 (S102). In this embodiment, the heater resistor 3 is heated by applying a constant voltage from the constant voltage source 11 to the sensor element 2, but depending on the connection between the heater resistor 3 and the compensation resistor 13, a constant current may be driven. Next, the control unit 14 calculates the gas composition of the ambient gas based on the output of the thermopile 4 and the parameters stored in the memory unit 17 (S103). The parameters of the measured gas composition of the ambient gas are newly stored in the memory unit 17. Finally, the gas composition of the atmospheric gas is displayed on the output unit 18 (S104). This allows the purity of a specific gas in the atmospheric gas to be known, for example.

In the following modified examples, the functional configuration of the thermal gas sensor when measuring the gas composition of the atmospheric gas, and the processing performed by the thermal gas sensor when measuring the gas composition of the atmospheric gas, are as shown in Figures 3 and 4, similar to Example 1.

[Modification 1]
Next, a first modified example of the present invention will be described. Fig. 5 is a plan view showing an example of a sensor element 2a constituting a thermal gas sensor 1a in the first modified example. The first modified example differs from the first embodiment in that a compensation resistor 13a is connected in parallel to the heater resistor 3a, and that a constant current is applied from the constant current source 19 to the sensor element 2a via the electrode 12a using a constant current source 19 as a power source. When a constant current is applied, the compensation resistor 13a is connected in parallel to the heater resistor 3a, thereby obtaining the same effect as the first embodiment. That is, an effect of suppressing a decrease in power in the heater resistor 3a when the resistance value of the heater resistor 3a increases over time is obtained.

なお、Ｉは定電流源１９の電流値である。また、Ｒｈ＝Ｒ１である。ここで、同条件下で式（４）におけるＷ_１／Ｗ_０の値は、式（２）におけるＷ_１／Ｗ_０の値と等しい。よって、センサ素子２ａにおいて、補償抵抗１３ａがヒータ抵抗３ａに対して並列に接続される配置で、センサ素子２ａに定電流を印加する場合と、補償抵抗１３ａがヒータ抵抗３ａに対して直列に接続される配置で、センサ素子２ａに定電圧を印加する場合とで、同様の効果が得られる。 Here, the time when the initial resistance value Rh of the heater resistor 3a increases over time and becomes a times as large as a (a>1) is defined as the end of the heater resistor 3a's life. In this case, if the initial resistance value of the compensation resistor 13a is R1, the initial power of the heater resistor 3a is _W0 , and the power at the end of the life is _W1 , the ratio of _W0 to _W1 is expressed by the following formula (4).

Here, I is the current value of the constant current source 19. Also, Rh=R1. Here, under the same conditions, the value of _W1 / _W0 in formula (4) is equal to the value of _W1 / _W0 in formula (2). Therefore, in the sensor element 2a, the compensation resistor 13a is connected in parallel to the heater resistor 3a, and a constant current is applied to the sensor element 2a, and the compensation resistor 13a is connected in series to the heater resistor 3a, and a constant voltage is applied to the sensor element 2a.

[Modification 2]
Next, a second modified example of the present invention will be described. FIG. 6 is a plan view showing an example of a sensor element 2b constituting a thermal gas sensor 1b in the second modified example. The second modified example differs from the first embodiment in that the heater resistor 3b and the compensation resistor 13b are arranged in parallel independently of each other, and the compensation resistor 13b is also arranged to cross the opening of the cavity area 10b between a pair of thermopiles 4b, as with the heater resistor 3b, and that two power sources are arranged outside the sensor element 2b, the constant voltage source 11b has a conductor connected to the electrode 12b conducting to the heater resistor 3b, and the constant current source 19b has a conductor connected to the electrode 12b conducting to the compensation resistor 13b. When the heater resistor 3b and the compensation resistor 13b generate heat, a constant voltage and a constant current are applied to the sensor element 2b so that the two resistors generate the same power at the initial point. At this time, the resistance values of the two resistors increase over time, but the powers change in the opposite directions, so that they cancel each other out and suppress the increase in the resistance value. Specifically, as the resistance value of the heater resistor 3b to which a constant voltage is applied increases over time, the power in the heater resistor 3b decreases over time, whereas as the resistance value of the compensation resistor 13b to which a constant current is applied increases over time, the power in the compensation resistor 13b increases over time.

なお、Ｖは定電圧源１１ｂの電圧値であり、Ｉは定電流源１９ｂの電流値である。また、Ｒｈ＝Ｒ１である。ここで、同条件下で式（５）におけるＷ_１／Ｗ_０の値は、式（１）におけるＷ_１／Ｗ_０の値より大きいので、変形例２の構成によっても、充分に、ヒータ抵抗における発熱量の変化を抑制することが可能である。 Here, the time when the initial resistance value Rh of the heater resistor 3b and the initial resistance value R1 of the compensation resistor 13b increase over time to a times (a>1) is defined as the end of the lives of the heater resistor 3b and the compensation resistor 13b. If the total initial power of the heater resistor 3b and the compensation resistor 13b is _W0 and the total power at the end of the lives is _W1 , the ratio of _W0 to _W1 is expressed by the following equation (5).

Here, V is the voltage value of the constant voltage source 11b, and I is the current value of the constant current source 19b. Also, Rh=R1. Here, under the same conditions, the value of _W1 / _W0 in formula (5) is greater than the value of _W1 / _W0 in formula (1), so even with the configuration of modified example 2, it is possible to sufficiently suppress the change in the heat generation amount in the heater resistor.

[Modification 3]
Next, a third modification of the present invention will be described. Fig. 7 is a plan view showing an example of a sensor element 2c constituting a thermal gas sensor 1c in the third modification. The third modification differs from the first embodiment in that in the sensor element 2c, a compensation resistor 13c is arranged across the opening of a cavity area 100c in addition to a cavity area 10c in which a heater resistor 3c is arranged, and that while the resistance value of the heater resistor 3c increases over time due to heat generation, the resistance value of the compensation resistor 13c decreases over time.

ここで、Ｒｈ＝Ｒ１とすると、第２行目が成立する。結果として、第３行目に示すように、β＝２√α－αのとき、ヒータ抵抗３ｃ及び補償抵抗１３ｃにおける電力は経時変化しないことが分かる。また、キャビティエリア１００ｃの開口サイズを調整し、定電圧源１１ｃからセンサ素子２ｃに定電圧を印加することにより、式（６）を成立させることが可能である。 Here, the rate of increase of the initial resistance value Rh of the heater resistor 3c is α (α>1), and the rate of decrease of the initial resistance value R1 of the compensation resistor 13c is β (0<β<1). The condition for no change in power over time in the heater resistor 3c and the compensation resistor 13c is expressed by the first line of the following equation (6).

Here, if Rh=R1, the second line is established. As a result, as shown in the third line, when β=2√α-α, the power in the heater resistor 3c and the compensation resistor 13c does not change over time. In addition, by adjusting the opening size of the cavity area 100c and applying a constant voltage from the constant voltage source 11c to the sensor element 2c, it is possible to establish equation (6).

In addition, in the third modification, when a constant current is applied using a constant current source 19c (not shown) instead of applying a constant voltage using a constant voltage source 11c, the same effect can be obtained by connecting the compensation resistor 13c in parallel to the heater resistor 3c. In other words, when β=2√α-α holds, the power in the heater resistor 3c and the compensation resistor 13c does not change over time, and by adjusting the opening size of the cavity area 100c and applying a constant current from the constant voltage source 11c to the sensor element 2c, it is possible to hold formula (6).

In addition, in the above embodiment and modified example, a case has been described in which the resistance value of the heater resistor increases over time due to repeated heat generation. However, the technical concept of the present invention is also applicable to a case in which the resistance value of the heater resistor decreases over time due to repeated heat generation. By adding a configuration equivalent to the above embodiment and modified example, it is possible to suppress the increase or decrease in the amount of heat generated over time.

In the above embodiment, a thermopile-type sensor using a thermopile 4 as a temperature detector has been described as an example, but the sensors to which the present invention is applicable are not limited to thermopile-type sensors. For example, the present invention can be applied to sensors having temperature sensors other than thermopiles, and gas sensors that do not have a thermopile but supply power to a heater to raise the temperature of the heater and detect the temperature by the change in the resistance value of the heater itself.

In the following, the components of the present invention will be described with reference to the reference numerals in the drawings in order to make it possible to compare the components of the present invention with the configurations of the embodiments.
<Invention 1>
a plurality of resistors (3, 3a, 3b, 3c, 13, 13a, 13b, 13c) that generate heat when supplied with power from a power source (11, 11b, 11c, 19, 19b, 19c);
A substrate (6) having an opening of a cavity area (10, 10a, 10b, 10c, 100c) on a surface thereof;
A thin film portion (5, 5a, 5b, 5c) formed so as to cover the opening of the cavity area;
a temperature detector (4, 4a, 4b, 4c) for detecting a temperature of at least one of the plurality of resistors or a temperature around the resistor;
A thermal sensor (1, 1a, 1b, 1c) comprising:
The plurality of resistors include
a first resistor (3, 3a, 3b, 3c) provided on the thin film portion and indicating a change over time in the amount of heat generated by the power supply from a power source based on a change over time in the resistance value;
a second resistor (13, 13a, 13b, 13c) whose resistance value changes over time or whose heat generation amount changes over time due to power supply from the power source is different from that of the first resistor;
A thermal sensor comprising:

1: Thermal gas sensor 2: Sensor element 3: Heater resistor 4: Thermopile 5: Insulating thin film 6: Silicon substrate 7: Thermocouple 8: Hot junction 9: Cold junction 10: Cavity area 11: Constant voltage source 12: Electrode 13: Compensating resistor 14: Control unit 15: Input unit 16: Measuring unit 17: Memory unit 18: Output unit 19: Constant current source

Claims (8)

A plurality of resistors that generate heat when supplied with power from a constant voltage source ;
A substrate having an opening in a cavity area on a surface thereof;
a thin film portion formed so as to cover an opening of the cavity area;
a temperature detector for detecting a temperature of at least one of the plurality of resistors or a temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors include
a first resistor provided on the thin film portion, the first resistor indicating a change over time in a heat generation amount caused by the supply of power from the constant voltage source based on a change over time in a resistance value;
a second resistor having a different manner of change over time in resistance value or a different manner of change over time in heat generation due to power supply from the constant voltage source from the first resistor;
Including,
The thermal sensor according to claim 1, wherein the second resistor is connected in series with the first resistor on the substrate . A plurality of resistors that generate heat when power is supplied from a constant current source;
a substrate having an opening in a cavity area on a surface thereof;
a thin film portion formed so as to cover an opening of the cavity area;
a temperature detector for detecting a temperature of at least one of the plurality of resistors or a temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors include
a first resistor provided on the thin film portion, the first resistor indicating a change over time in a heat generation amount caused by the power supply from the constant current source based on a change over time in a resistance value;
a second resistor having a different manner of change over time in resistance value or a different manner of change over time in heat generation due to power supply from the constant current source than the first resistor;
Including,
The thermal sensor according to claim 1, wherein the second resistor is connected in parallel with the first resistor on the substrate. A plurality of resistors that generate heat when supplied with power from a constant voltage source or a constant current source;
a substrate having an opening in a cavity area on a surface thereof;
a thin film portion formed so as to cover an opening of the cavity area;
a temperature detector for detecting a temperature of at least one of the plurality of resistors or a temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors include
a first resistor provided on the thin film portion, the first resistor indicating a change over time in a heat generation amount caused by the supply of power from the constant voltage source based on a change over time in a resistance value;
a second resistor having a different manner of change over time in resistance value or a different manner of change over time in heat generation due to power supply from the constant current source than the first resistor;
Including,
the temperature detector is two or more thermopiles arranged in pairs facing each other in the thin film portion,
the first resistor is disposed between the pair of thermopiles in the thin film portion,
A thermal sensor, characterized in that the first resistor and the second resistor are arranged in parallel independently of each other on the thin film portion. The temperature detector includes:
In the thin film portion, a pair of two or more thermopiles are arranged opposite each other,
3. The thermal sensor according to claim 1, wherein the first resistor is disposed between the pair of thermopiles in the thin film portion. 3. The thermal sensor according to claim 1, wherein the second resistor is disposed at a location having a higher heat dissipation property than the first resistor. The thermal sensor according to any one of claims 1 to 4, characterized in that the initial resistance value of the first resistor is equal to the initial resistance value of the second resistor. 2. The thermal sensor according to claim 1, wherein the second resistor is connected in series with the first resistor in the thin film portion, and a resistance value of the second resistor changes over time in a direction opposite to that of the first resistor when a current is passed through the second resistor. 3. The thermal sensor according to claim 2, wherein the second resistor is connected in parallel with the first resistor in the thin film portion, and a resistance value of the second resistor changes over time in a direction opposite to that of the first resistor when a current is passed through the second resistor.

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