JP2022129947A - thermal sensor - Google Patents

Abstract

To provide a thermal sensor capable of suppressing the change in a calorific value in a heater resistor and suppressing the decrease in measurement accuracy as a measuring device, even when a resistance value in a resistor generating heat by energization increases due to repeated heat generation.SOLUTION: A thermal sensor includes a plurality of resistors which generates heat by power supply from a power source. The plurality of resistors includes: a first resistor which is installed in a thin film part and whose calorific value by the power supply from the power source shows temporal changes due to a change over time of a resistance value; and a second resistor different from the first resistor in a mode of the change over time of the resistance value or in a mode of the change over time of the calorific value by the power supply from the power source.SELECTED DRAWING: Figure 2

Description

The present invention relates to thermal sensors.

Conventionally, there has been proposed a flow sensor capable of performing highly accurate temperature compensation over a long period of time and allowing simplification of the circuit. The flow sensor consists of a heater (3) that generates heat when an electric current is applied, temperature sensors (4a, 4b) arranged near the heater, a temperature measuring resistor (5) that measures the ambient temperature, and a heating resistor. A control circuit is provided to control the current flowing through the body, and the temperature sensor detects the state of the temperature distribution due to the heat from the heater, which changes according to the flow rate or flow velocity of the fluid. The control circuit has a first branch in which a temperature measuring resistor and a first fixed resistor (8a) are connected in series and a second branch in which a heating resistor and a second fixed resistor (8b) are connected in series in parallel. A connected bridge circuit is provided, and the bridge circuit is formed on the same semiconductor substrate (1) (see, for example, Patent Document 1).

Also, even if chip resistors arranged on the surface of the insulating substrate (5) are used as the heating resistor (2) and the temperature compensating resistor (3), the deterioration of the responsiveness and sensitivity to fluid flow can be suppressed. A sensor (1) was also proposed. The flow sensor has a signal processing section that processes signals from the heat generating resistor and the temperature compensating resistor. The temperature compensating resistor is a chip resistor placed on the back surface (5b) of the insulating substrate. A temperature compensating resistor is placed in the heat dissipation path of the heat generating resistor via the insulating substrate, and the insulating substrate provides more opportunities for the temperature compensating resistor and the fluid to contact than the heat generating resistor and the fluid. (see Patent Document 2, for example).

In the above two inventions, the resistance value of the resistor that generates heat when energized increases with time, and as a result, the amount of heat generated by the energization of the resistor may change gradually. As a result, the accuracy of the measuring device may deteriorate.

Japanese Patent Application Laid-Open No. 2002-310762 JP 2017-067724 A JP 2011-174814 A

The present invention has been made in view of the problems described above. However, the final object is to provide a thermal sensor capable of suppressing changes in the amount of heat generated by the heater resistance and suppressing deterioration in measurement accuracy as a measuring device.

The present invention for solving the above problems is
a plurality of resistors that generate heat when supplied with power from a power source;
a substrate having a cavity area opening on its surface;
a thin film portion formed to cover the opening of the cavity area;
a temperature detector that detects the temperature of at least one of the plurality of resistors or the temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors are
a first resistor that is installed in the thin film portion and exhibits a change in the amount of heat generated by power supply from a power supply over time due to a change in resistance value over time;
a second resistor that differs from the first resistor in the mode of increase in resistance value over time or in the mode of change over time in the amount of heat generated by power supply from the power supply;
A thermal sensor comprising:

According to the present invention, even if the resistance value of the first resistor changes over time due to repeated heat generation, the existence of the second resistor can mitigate the influence of the change in the resistance value of the first resistor. can. By doing so, it is possible to suppress a change in the amount of heat generated by the first resistor due to this. As a result, 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, and the thermal conductivity of the ambient gas decreases. Since measurement errors occur, the measured values need to be corrected. On the other hand, by adding the second resistor to suppress the decrease in the amount of heat generated by the first resistor, correction of the measured value becomes unnecessary.

Moreover, in the present invention,
a plurality of resistors that generate heat when supplied with power from a power source;
a substrate having a cavity area opening on its surface;
a thin film portion formed to cover the opening of the cavity area;
a temperature detector that detects the temperature of at least one of the plurality of resistors or the temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors are
a first resistor installed in the thin film portion;
a second resistor disposed near the first resistor in the thin film portion or the substrate and having a resistance value of 1 to 1.5 times the resistance value of the first resistor;
It may be a thermal sensor characterized by including Thus, even if the resistance value of the first resistor changes over time due to repeated heat generation, the existence of the second resistor can mitigate the influence of the change in the resistance value of the first resistor.

Further, in the present invention, the temperature detector is two or more thermopiles arranged facing each other in the thin film portion, and the first resistor is located between the pair of thermopiles in the thin film portion. It may be a thermal sensor, characterized in that it is installed in the According to this, the temperature around the resistor can be detected with high accuracy.

Further, in the present invention, the thermal sensor may be characterized in that the second resistor is arranged at a location having higher heat dissipation than the first resistor. According to this, the heat generated in the second resistor diffuses more easily than the heat generated in the first resistor, and the change in the resistance value of the second resistor over time can be suppressed. Note that the location with high heat dissipation is, for example, a substrate with high thermal conductivity.

Further, in the present invention, the thermal sensor may be characterized in that the initial resistance value of the first resistor is equal to the initial resistance value of the second resistor. According to this, the second resistor can be configured with the same parts as the first resistor, and the parts cost and parts management cost can be reduced. In addition, when the second resistor is added, it is possible to simplify the formula for calculating the change in the amount of heat generated due to the change in the resistance value of the first resistor, and it is possible to reduce the management and design load.

Further, in the present invention, the power source may be a constant voltage source, and the second resistor may be connected in series with the first resistor on the substrate. . According to 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 the divided voltage of the first resistor increases. This makes it possible to suppress a decrease in the amount of heat generated by the first resistor.

Further, in the present invention, the power source may be a constant current source, and the second resistor may be connected in parallel with the first resistor on the substrate. . According to this, for example, when the resistance value of the first resistor increases over time, the current flowing through the first resistor decreases because the resistance value of the second resistor does not change. This can suppress an increase in the amount of heat generated in the first resistor.

Further, in the present invention, power is supplied to the first resistor from a constant voltage source, power is supplied to the second resistor from a constant current source, and the second resistor is a pair of resistors on the thin film portion. A thermal sensor may be provided between the thermopiles, wherein the first resistor and the second resistor are arranged in parallel independently of each other. According to this, the resistance values of the two resistors both change with time, but the amounts of heat generated at the resistance values change with time in opposite directions to each other. Due to the effect of canceling each other due to the change in the opposite direction, the change over time of the amount of heat generated by both resistances is suppressed.

Further, in the present invention, the power source is a constant voltage source, the second resistor is connected in series with the first resistor in the thin film portion, and the resistance value of the second resistor is It may be a thermal sensor characterized in that it changes with time in a direction opposite to that of the first resistance. According to this, by appropriately selecting the rate of change in resistance depending on the temperature of the first resistor and the second resistor, it is possible to cancel out the change in power over time in the first resistor and the second resistor.

Further, in the present invention, the power source is a constant current source, the second resistor is connected in parallel with the first resistor in the thin film portion, and the resistance value of the second resistor is changed by passing current. It may be a thermal sensor characterized in that it changes with time in a direction opposite to that of the first resistance. According to this, by appropriately selecting the rate of change in resistance depending on the temperature of the first resistor and the second resistor, it is possible to cancel out the change in power over time in the first resistor and the second resistor. When the second resistor is connected in parallel with the first resistor and a constant current is applied, and when the second resistor is connected in series with the first resistor and a constant voltage is applied A similar effect can be obtained with

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

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

FIG. 2 is a schematic diagram showing an example of a sensor element that constitutes a conventional thermal gas sensor; 2 is a plan view showing an example of a sensor element that constitutes the thermal gas sensor in Example 1. FIG. FIG. 4 is a block diagram showing the functional configuration of the thermal gas sensor when measuring the gas composition of the atmospheric gas; 4 is a flow chart showing a process when measuring the gas composition of atmospheric gas with a thermal gas sensor. FIG. 10 is a plan view showing an example of a sensor element that constitutes a thermal gas sensor according to modification 1; FIG. 11 is a plan view showing an example of a sensor element that constitutes a thermal gas sensor according to modification 2; FIG. 11 is a plan view showing an example of a sensor element that constitutes a thermal gas sensor according to modification 3;

[Example of application]
In this application example, a case where the thermal sensor is a thermal gas sensor will be described. The thermal gas sensor according to this application example has a configuration in which a compensating resistor is additionally arranged with respect to the heater resistor, which is a resistor that generates heat when an electric current is applied. That is, it has a plurality of resistors.

FIG. 2 is a plan view showing an example of the sensor element 2 forming the thermal gas sensor 1 to which the present invention is applicable. The sensor element 2 includes a heater resistor 3 and a thermopile (temperature detection unit) 4 provided symmetrically with the heater resistor 3 interposed therebetween. and a compensating resistor 13 connected in series. Although two thermopiles 4 are shown in FIG. 2, the number of thermopiles 4 is not limited as long as it is two or more. The heater resistor 3 is a resistor made of polysilicon, for example. Each of the thermopiles 4 has a substantially rectangular shape in plan view. The heater resistor 3 , thermopile 4 and compensating resistor 13 are provided in an insulating thin film 5 formed on a silicon substrate 6 .

Although shown in a simplified manner in FIG. 2, each of the thermopiles 4 is constructed by arranging a plurality of thermocouples 7 (see FIG. 1(b)) in the insulating thin film 5 at predetermined intervals. . Of these, the point connected on the same side as the heater resistor 3 is the hot junction 8 (see FIG. 1(b)), and the point connected on the opposite side to the heater resistor 3 is the cold junction 9 (see FIG. 1 ( b) see).

In the insulating thin film 5, the silicon substrate 6 below the heater resistor 3 and the thermopile 4 is provided with a cavity area 10 which is a concave portion. A cross-sectional view of the cavity area 10 is shown in FIG. 1(b). Here, the heater resistor 3 is arranged across the opening of the cavity area 10 , whereas the compensating resistor 13 is arranged on the silicon substrate 6 in contact therewith. Therefore, the heat generated in the compensating resistor 13 is transmitted through the silicon substrate 6 and diffused more quickly than the heat generated in the heater resistor 3 radiates to the cavity area 10 . That is, the compensating resistor 13 is arranged at a location having higher heat dissipation than the heater resistor 3 .

A constant voltage source 11 is located outside the sensor element 2 and is connected to an electrode 12 that conducts to the heater resistor 3 and the compensating 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 compensating resistor 13 generate heat. Here, the heater resistor 3 is placed in the insulating thin film 5 on the cavity 10 and has relatively low heat dissipation, whereas the compensating resistor 13 is placed in the insulating thin film 5 on the silicon substrate 6. It is in a state of high heat dissipation. In other words, the compensating resistor 13 is arranged at a location having a higher heat dissipation than the heater resistor 3 . Therefore, the temperature of the heater resistor 3 rises due to the energization from the constant voltage source 11 , but the temperature of the compensating resistor 13 does not rise like the heater resistor 3 . As a result, the resistance value of the heater resistor 3 increases with time due to repeated energization from the constant voltage source 11 . On the other hand, the resistance value of the compensation resistor 13 hardly changes with time.

In the thermal gas sensor according to this application example, by disposing the compensation resistor 13 in addition to the heater resistor 3, the amount of heat generated by the heater resistor 3 can be reduced when the resistance value of the heater resistor 3 increases with time. It has the function of suppressing the decrease. Details will be described later (see formula (2) in Example 1).

[Example 1]
A thermal sensor according to Example 1 of the present invention will be described in detail below with reference to the drawings. In the following embodiments, an example in which the present invention is applied to a thermal gas sensor will be described, but the present invention may be applied to other devices such as oxygen concentrators and gas flow meters. Note that 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 that constitutes a conventional thermal gas sensor 1. As shown in FIG. FIG. 1(a) is a plan view of a sensor element 2 constituting a conventional thermal gas sensor 1, and FIG. 1(b) is a sectional view taken along the line XX of FIG. 1(a). The thermal gas sensor 1 is a kind of MEMS (Micro Electro Mechanical Systems) and is used, for example, to measure the gas composition (concentration ratio) of atmospheric gas.

The conventional thermal gas sensor 1 has no resistance other than the heater resistance 3 . The sensor element 2 includes a heater resistor 3 and a thermopile 4 provided symmetrically with the heater resistor 3 interposed therebetween. A heater resistor 3 and a 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. Also, the insulating thin film 5 and the silicon substrate 6 correspond to the thin film portion and the substrate in the present invention, respectively.

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

By applying a constant voltage from the constant voltage source 11 to the sensor element 2 via the electrode 12, the heater resistor 3 generates heat. By measuring the temperature of the heat generated in the heater resistor 3 with the thermopile 4, the thermal conductivity of the atmospheric gas flowing into the sensor element 2 can be measured.

Since the thermal conductivity is a specific value depending on the type of gas, measuring the thermal conductivity of the atmospheric gas that has flowed into the sensor element 2 enables measurement of the gas composition of the atmospheric gas. For example, when the atmospheric gas is air, it is also possible to measure the oxygen concentration in the air. However, if the amount of heat generated by the heater resistor 3 is not always constant, the measurement accuracy of the thermal gas sensor 1 is degraded. Therefore, a measurement error occurs in the thermal conductivity of the ambient gas.

In the case of a flow meter, ambient gas flows along the heater resistor 3 and the pair of thermocouples 7 in FIG. 1(b). The longitudinal directions of the heater resistor 3 and the thermopile 4 are 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. A temperature difference then occurs between the hot junctions 8 on both sides of the heater resistor 3 . An output voltage is generated from the thermopile 4 in proportion to the temperature difference. Moreover, 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 . Also in this case, if the amount of heat generated by the heater resistor 3 is not always constant, the measurement accuracy of the flow meter will deteriorate. Therefore, a measurement error occurs in the flow rate of the atmospheric 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 with time due to repeated heat generation of the heater resistor 3, and the electric power of the heater resistor 3 decreases. rice field. Here, it is assumed that the life of the heater resistor 3 is defined as the time when the initial resistance value Rh of the heater resistor 3 increases with time and becomes a times (a>1). At this time, assuming that the initial power in the heater resistor 3 is W ₀ and the power at the end of its life is W ₁ , the ratio between W ₀ and W ₁ is expressed by the following equation (1).

Note that 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。 Now, return to the description of FIG. 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 with time, while the resistance value of the compensation resistor 13 hardly increases. When considering the case of repeatedly measuring the thermal conductivity 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. 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 the thermal conductivity is repeatedly measured, the resistance value of the heater resistor 3 increases with time, and simultaneously the partial pressure across the heater resistor 3 increases. Therefore, the decrease in electric power (substantially equivalent to the amount of heat generated) in the heater resistor 3 is suppressed. At this time, the ratio of W ₀ and W ₁ is expressed by the following formula (2) as in formula (1).

Here, if Rh=R1, the value of W ₁ /W ₀ in formula (2) is greater than the value of W ₁ /W ₀ in formula (1) from a>1. That is, by disposing the compensating resistor 13 in addition to 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 with 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。 Also, in equation (2), consider the resistance value of the compensating resistor ₁₃ for reducing the rate of decrease when the power decreases from _W0 to W1. If the rate of decrease from W ₀ to W ₁ is 0, ie the value of W ₁ /W ₀ is 1, then the rate of decrease from W ₀ to W ₁ is minimal. At this time, assuming that the resistance value R1 of the compensation resistor 13 is kRh, the following equation (3) holds.

Assuming that the value of W ₁ /W ₀ is 1, k is obtained as in the third row. That is, assuming that the life of the heater resistor 3 is the time when the initial resistance value Rh of the heater resistor 3 increases over time and becomes a times as large as the initial resistance value Rh of the heater resistor 3, the initial resistance value R1 of the compensation resistor 13 is the initial resistance value Rh of the heater resistor 3. By multiplying by √a, the rate of decrease in power in the heater resistor 3 can be minimized. As a result, the life of the heater resistor 3 can be extended. Note that the value of √a may be, for example, 1 or more and 1.5 or less.

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

The control unit 14 includes a CPU, a ROM, a 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 atmospheric gas that has flowed into the sensor element 2 is measured, and the gas composition of the atmospheric gas can be measured based on the thermal conductivity information, which has a unique value depending on the type of gas.

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

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

The control unit 14 calculates the gas composition of the atmosphere gas based on the output of the thermopile 4 in the measurement unit 16 and the parameters accumulated in the storage unit 17 . The measured gas composition is displayed on the output section 18 . The output unit 18 is, for example, a liquid crystal monitor.

FIG. 4 is a flow chart showing the process when the thermal gas sensor 1 measures the gas composition of the ambient gas. The flow of processing will be described below with reference to FIG. In this flowchart, first, an ambient gas whose type is specified by the input unit 15 is introduced into the sensor element 2 constituting the thermal gas sensor 1 (S101). In the case of a flow meter, it flows into the heater resistor 3 along the lateral direction of the thermopile 4 in FIG. The ambient gas that has flowed into the heater resistor 3 is heated by the heat generated in the heater resistor 3 (S102). In this embodiment, the heater resistor 3 generates heat by applying a constant voltage from the constant voltage source 11 to the sensor element 2. Depending on the connection mode between the heater resistor 3 and the compensation resistor 13, a constant current is driven. In some cases. Next, in the control unit 14, the gas composition of the atmosphere gas is calculated based on the output of the thermopile 4 and the parameters accumulated in the storage unit 17 (S103). The measured parameters of the gas composition of the ambient gas are newly stored in the storage unit 17 . Finally, the output section 18 displays the gas composition of the ambient gas (S104). According to this, it is possible to grasp the purity of a specific gas in the atmospheric gas, 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 of the thermal gas sensor when measuring the gas composition of the atmospheric gas are the same as in Example 1. It is as shown in FIG.3 and FIG.4.

[Modification 1]
Next, Modification 1 of the present invention will be described. FIG. 5 is a plan view showing an example of the sensor element 2a that constitutes the thermal gas sensor 1a in Modification 1. As shown in FIG. Modification 1 differs from Example 1 in that the compensating resistor 13a is connected in parallel to the heater resistor 3a, and that the constant current source 19 is used as a power supply, and the constant current source 19 supplies the current through the electrode 12a. The point is that a constant current is applied to the sensor element 2a. When a constant current is applied, the compensation resistor 13a is connected in parallel with the heater resistor 3a, thereby obtaining the same effect as in the first embodiment. That is, it is possible to obtain an effect of suppressing a decrease in electric power in the heater resistor 3a when the resistance value of the heater resistor 3a increases with time.

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 life of the heater resistor 3a is defined as the time when the initial resistance value Rh of the heater resistor 3a increases over time and becomes a times (a>1). At this time, assuming that the initial resistance value of the compensating resistor 13a is _R1 , the initial power of the heater resistor 3a is _W0 , and the power at the end of its life is W1, the _ratio of _W0 to W1 is expressed by the following formula: (4).

Note that I is the current value of the constant current source 19 . Also, Rh=R1. Here, under the same conditions, the value of W ₁ /W ₀ in equation (4) is equal to the value of W ₁ /W ₀ in equation (2). Therefore, in the sensor element 2a, when the compensating resistor 13a is connected in parallel to the heater resistor 3a and a constant current is applied to the sensor element 2a, the compensating resistor 13a is connected in series with the heater resistor 3a. The same effect can be obtained by applying a constant voltage to the sensor element 2a in such an arrangement.

[Modification 2]
Next, Modification 2 of the present invention will be described. FIG. 6 is a plan view showing an example of the sensor element 2b that constitutes the thermal gas sensor 1b in Modification 2. As shown in FIG. The difference of Modification 2 from Embodiment 1 is that the heater resistor 3b and the compensating resistor 13b are arranged independently of each other in parallel. and two power supplies are located external to the sensor element 2b, a constant voltage source 11b being wire-connected to an electrode 12b conducting to the heater resistor 3b. The point is that the constant current source 19b is connected to the electrode 12b that conducts to the compensating resistor 13b. When the heater resistor 3b and the compensating 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 electric power at the initial time. At this time, the resistance values of the two resistors increase with time, but the electric powers change in opposite directions, so that they cancel each other out and the effect of suppressing the increase in resistance value is obtained. Specifically, as the resistance value of the heater resistor 3b to which a constant voltage is applied increases over time, the power of the heater resistor 3b decreases over time, whereas the power of the heater resistor 3b to which a constant current is applied decreases over time. The power at the compensating resistor 13b increases with time as the resistance value of .

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 life of the heater resistor 3b and the compensation resistor 13b is defined as 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). Define. At this time, assuming that the total power of the heater resistor 3b and the compensating resistor 13b at the initial stage is W ₀ and the total power of the power when reaching the end of life is W ₁ , the ratio between W ₀ and W ₁ is given by the following formula (5 ).

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 W ₁ /W ₀ in equation (5) is greater than the value of W ₁ /W ₀ in equation (1). It is possible to suppress the change in the calorific value in

[Modification 3]
Next, Modified Example 3 of the present invention will be described. FIG. 7 is a plan view showing an example of a sensor element 2c that constitutes a thermal gas sensor 1c according to Modification 3. As shown in FIG. The difference of Modification 3 from Embodiment 1 is that, in sensor element 2c, compensating resistor 13c is arranged so as to cross the opening of cavity area 100c separately from cavity area 10c where heater resistor 3c is arranged. , and the resistance value of the heater resistor 3c increases with time due to heat generation, while the resistance value of the compensating resistor 13c decreases with 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 increasing speed of the initial resistance value Rh of the heater resistor 3c is α (α>1), and the decreasing speed of the initial resistance value R1 of the compensating resistor 13c is β (0<β<1). The condition that the electric power in the heater resistor 3c and the compensating resistor 13c does not change with time is represented 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 row, it can be seen that when β=2√α−α, the power in heater resistor 3c and compensating resistor 13c does not change with time. Also, 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, the equation (6) can be established.

In modification 3, when a constant current is applied using a constant current source 19c (not shown) instead of applying a constant voltage using the constant voltage source 11c, the compensating resistor 13c is connected to the heater resistor 3c. A similar effect can be obtained by connecting in parallel. That is, when β=2√α−α is established, the electric power in the heater resistor 3c and the compensation resistor 13c does not change with time, and by adjusting the opening size of the cavity area 100c, the voltage from the constant voltage source 11c to the sensor element 2c is maintained. Equation (6) can be established by applying a constant current to .

Further, in the above embodiment and modified example, the case where the resistance value of the heater resistor increases with time due to repeated heat generation has been described. However, the technical idea of the present invention can also be applied to the case where the resistance value of the heater resistor decreases with time due to repeated heat generation. By adding a configuration equivalent to that of the above-described embodiment and modified example, it is possible to suppress an increase or decrease in the amount of heat generation over time.

In the above embodiment, the thermopile type sensor using the thermopile 4 as the temperature detector has been described as an example, but the sensor to which the present invention is applied is not limited to the thermopile type sensor. For example, it can be applied to a sensor that has a temperature sensor other than a thermopile, or a gas sensor that does not have a thermopile, supplies power to a heater to increase the temperature of the heater, and detects the temperature from the change in the resistance value of the heater itself. is.

In order to allow comparison between the constituent elements of the present invention and the configurations of the embodiments, the constituent elements of the present invention will be described below with reference numerals in the drawings.
<Invention 1>
a plurality of resistors (3, 3a, 3b, 3c, 13, 13a, 13b, 13c) that generate heat by power supply (11, 11b, 11c, 19, 19b, 19c);
a substrate (6) having openings for cavity areas (10, 10a, 10b, 10c, 100c) on its surface;
a thin film portion (5, 5a, 5b, 5c) formed to cover the opening of the cavity area;
a temperature detector (4, 4a, 4b, 4c) for detecting the temperature of or around at least one of said plurality of resistors;
A thermal sensor (1, 1a, 1b, 1c) comprising:
The plurality of resistors are
first resistors (3, 3a, 3b, 3c) that are installed in the thin film portion and show temporal changes in the amount of heat generated by power supply from a power source due to temporal changes in resistance values;
second resistors (13, 13a, 13b, 13c) different from the first resistor in terms of the change over time of the resistance value or the change over time of the amount of heat generated by the power supply from the power supply;
A thermal sensor, comprising:

Reference Signs List 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: Compensation resistor 14 : control unit 15 : input unit 16 : measurement unit 17 : storage unit 18 : output unit 19 : constant current source

Claims (10)

a plurality of resistors that generate heat when supplied with power from a power source;
a substrate having a cavity area opening on its surface;
a thin film portion formed to cover the opening of the cavity area;
a temperature detector that detects the temperature of at least one of the plurality of resistors or the temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors are
a first resistor that is installed in the thin film portion and exhibits a change in the amount of heat generated by power supply from a power supply over time due to a change in resistance value over time;
a second resistor that differs from the first resistor in the mode of change over time in the resistance value or the mode of change over time in the amount of heat generated by power supply from the power supply;
A thermal sensor, comprising: a plurality of resistors that generate heat when supplied with power from a power source;
a substrate having a cavity area opening on its surface;
a thin film portion formed to cover the opening of the cavity area;
a temperature detector that detects the temperature of at least one of the plurality of resistors or the temperature around the resistor;
A thermal sensor comprising:
The plurality of resistors are
a first resistor installed in the thin film portion;
a second resistor disposed near the first resistor in the thin film portion or the substrate and having a resistance value of 1 to 1.5 times the resistance value of the first resistor;
A thermal sensor, comprising: The temperature detector is
In the thin film portion, two or more thermopiles arranged in pairs facing each other,
3. The thermal sensor according to claim 1, wherein said first resistor is installed between said pair of said thermopiles in said thin film portion. 4. The thermal sensor according to any one of claims 1 to 3, wherein said second resistor is arranged at a location having higher heat dissipation than said first resistor. 5. The thermal sensor according to claim 1, wherein the initial resistance value of the first resistor is equal to the initial resistance value of the second resistor. the power source is a constant voltage source;
5. The thermal sensor according to claim 1, wherein said second resistor is connected in series with said first resistor on said substrate. the power source is a constant current source;
5. The thermal sensor according to claim 1, wherein said second resistor is connected in parallel with said first resistor on said substrate. supplying power to the first resistor from a constant voltage source;
supplying power to the second resistor from a constant current source;
4. The thermal sensor according to claim 3, wherein said first resistor and said second resistor are arranged independently in parallel on said thin film portion. the power source is a constant voltage source;
The second resistor is connected in series with the first resistor in the thin film portion, and the resistance value of the second resistor changes with time in a direction opposite to that of the first resistor by flowing a current. 4. A thermal sensor according to any one of claims 1 to 3. the power source is a constant current source;
The second resistor is connected in parallel with the first resistor in the thin film portion, and the resistance value of the second resistor changes over time in a direction opposite to that of the first resistor by flowing a current. 4. A thermal sensor according to any one of claims 1 to 3.

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