JP2020106310A - Gas sensor - Google Patents

Abstract

To provide a gas sensor provided with a heater resistor for heating a thermistor, in which the in-plane temperature distribution of the thermistor is further equalized.SOLUTION: A gas sensor 10A comprises a thermistor Rd having a thermistor film 30, and a heater resistor MH for heating the thermistor film 30. The thermistor film 30 has a first and a second region 30a, 30b, and the heater resistor MH includes a first section MHz for heating the first region 30a and a second section MH2 for heating the second region 30b. A current is supplied to at least the first section MH1 in a first period, and more current is supplied to the second section MH2 than to the first section MH1 in a second period. According to this, as the degree of freedom of a heating profile increases, it is possible to further equalize the in-plane temperature distribution of the thermistor.SELECTED DRAWING: Figure 3

Description

The present invention relates to a gas sensor for detecting gas contained in an atmosphere, and more particularly to a gas sensor having a heater resistance for heating a thermistor.

The gas sensor detects the concentration of the gas to be measured contained in the atmosphere. Above all, the gas sensor of the type that heats the thermistor by the heater resistance is excellent in miniaturization. For example, Patent Document 1 discloses a gas sensor having a structure in which a meandering heater resistance and a thermistor are stacked. In the gas sensor described in Patent Document 1, the pattern width of the meander-shaped heater resistance is widened in the central portion to make the in-plane temperature distribution of the thermistor uniform.

JP, 2016-134246, A

However, it is difficult to make the in-plane temperature distribution of the thermistor sufficiently uniform because the amount of current flowing through the heater resistance does not change simply by adjusting the pattern width of the heater resistance.

Therefore, it is an object of the present invention to make the in-plane temperature distribution of the thermistor more uniform in a gas sensor having a heater resistance for heating the thermistor.

A gas sensor according to the present invention includes a thermistor, a heater resistance that heats the thermistor, a heater control circuit that controls the heater resistance, and a detection circuit that generates an output signal based on the resistance value of the thermistor. The heater resistance has a second region, the heater resistance includes a first period for heating the first region and a second period for heating the second region, and the heater control circuit has a second period in the first period. It is characterized in that a current is supplied to at least the first section and more current is supplied to the second section than to the first section in the second period.

According to the present invention, the heater resistance is divided into the first and second sections, and the current flowing in the first and second sections is controlled by the heater control circuit, so that the degree of freedom of the heating profile is increased. This makes it possible to make the in-plane temperature distribution of the thermistor more uniform.

In the present invention, the heater control circuit may supply more current to the first section than to the second section in the first period. According to this, the heat generation amount of the first section can be increased in the first period, and the heat generation amount of the second section can be increased in the second period.

In the present invention, the heater control circuit supplies the current to the first section without supplying the current to the second section in the first period and supplies the current to the first section in the second period. The current may be supplied to the second section without doing so. According to this, in the first period, the first section is heated without heating the second section, and in the second period, the second section is heated without heating the first section. be able to.

In the present invention, the first region may be sandwiched by the second region from at least one direction, or may be surrounded by the second region. In this case, heat tends to accumulate in the first region, but in the second control state, the amount of heat generated in the second section increases, so that the in-plane temperature distribution of the thermistor can be made more uniform. Become.

In the present invention, the heater control circuit may alternately repeat the first period and the second period. According to this, the in-plane temperature distribution of the thermistor can be made more uniform by adjusting the ratio between the first period and the second period. In this case, the second period may be longer than the first period. According to this, it is possible to suppress a phenomenon in which the first region where heat easily accumulates locally becomes high in temperature.

As described above, according to the present invention, in the gas sensor having the heater resistance for heating the thermistor, the in-plane temperature distribution of the thermistor can be made more uniform.

FIG. 1 is a schematic plan view transparently showing the structure of a gas sensor 10A according to the first embodiment of the present invention. FIG. 2 is a schematic cross-sectional view showing a state in which the gas sensor 10A is housed in the ceramic package 21, and corresponds to the cross section taken along the line AA shown in FIG. FIG. 3 is a circuit diagram showing a part of an external circuit connected to the terminal electrodes E1 to E4. FIG. 4 is a circuit diagram of the gas sensor 10A. FIG. 5 is a timing chart for explaining the operation of the gas sensor 10A. 6A and 6B are schematic diagrams showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10A. FIG. 6A shows the in-plane temperature distribution in the period T1, and FIG. 6B shows the in-plane temperature distribution in the period T2. There is. FIG. 7 is a schematic plan view transparently showing the structure of the gas sensor 10B according to the second embodiment. FIG. 8 is a circuit diagram of the gas sensor 10B. FIG. 9 is a timing chart for explaining the operation of the gas sensor 10B. 10A and 10B are schematic diagrams showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10B. FIG. 10A shows the in-plane temperature distribution in the period T1, and FIG. 10B shows the in-plane temperature distribution in the period T2. There is. FIG. 11 is a schematic plan view transparently showing the structure of the gas sensor 10C according to the third embodiment. FIG. 12 is a circuit diagram of the gas sensor 10C. FIG. 13 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10C, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature distribution in the period T2. There is. FIG. 14 is a schematic plan view transparently showing the structure of the gas sensor 10D according to the fourth embodiment. FIG. 15 is a circuit diagram of the gas sensor 10D. FIG. 16 is a timing chart for explaining the operation of the gas sensor 10D. FIG. 17 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10D, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature distribution in the period T2. There is. FIG. 18 is a schematic plan view transparently showing the structure of the gas sensor 10E according to the fifth embodiment. FIG. 19 is a circuit diagram of the gas sensor 10E. FIG. 20 is a timing chart for explaining the operation of the gas sensor 10E. FIG. 21 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10E, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature distribution in the period T2. There is. FIG. 22 is a schematic plan view transparently showing the structure of the gas sensor 10F according to the sixth embodiment. 23A and 23B are schematic diagrams showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10F. FIG. 23A shows the in-plane temperature distribution in the period T1, and FIG. 23B shows the in-plane temperature distribution in the period T2. There is.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

<First Embodiment>
FIG. 1 is a schematic plan view transparently showing the structure of a gas sensor 10A according to the first embodiment of the present invention. 2 is a schematic cross-sectional view showing a state in which the gas sensor 10A is housed in the ceramic package 21, and corresponds to the cross section taken along the line AA shown in FIG.

As shown in FIGS. 1 and 2, the gas sensor 10A according to the present embodiment includes a substrate 11, a heater resistance MH and a thermistor Rd formed on the substrate 11. The gas sensor 10A according to the present embodiment can be housed and used in the ceramic package 21 shown in FIG. The ceramic package 21 is a box-shaped case having an open top, and a lid 22 is provided on the top. The lid 22 has a plurality of ventilation holes 23, which allows a measurement target gas (for example, CO ₂ gas or CO gas) in the atmosphere to flow into the ceramic package 21. The gas sensor 10A according to the present embodiment further includes an external circuit connected to the terminal electrodes E1 to E6. The circuit configuration of the external circuit will be described later.

The substrate 11 is not particularly limited as long as it is a material having appropriate mechanical strength and suitable for fine processing such as etching, and may be a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, a quartz substrate. Alternatively, a glass substrate or the like can be used. The substrate 11 is provided with a cavity 11 a at a position overlapping with the heater resistance MH in a plan view in order to suppress heat generated by the heater resistance MH from being conducted to the substrate 11. The portion where the substrate 11 is removed by the cavity 11a is called a membrane. If the membrane is configured, the heat capacity is reduced by the amount of the thinned substrate 11, and thus heating can be performed with less power consumption.

Insulating films 12 and 13 made of an insulating material such as silicon oxide or silicon nitride are formed on the lower surface and the upper surface of the substrate 11, respectively. When, for example, silicon oxide is used as the insulating films 12 and 13, a film forming method such as a thermal oxidation method or a CVD (Chemical Vapor Deposition) method may be used. The thickness of the insulating films 12 and 13 is not particularly limited as long as the insulating property is secured, and may be, for example, about 0.1 to 1.0 μm. In particular, since the insulating film 13 is also used as an etching stop layer when the cavity 11a is formed in the substrate 11, the insulating film 13 may have a film thickness suitable for fulfilling the function.

The heater resistance MH is formed on the insulating film 13. The planar shape of the heater resistance MH is as shown in FIG. 1, and is composed of one meander-shaped conductor pattern that can be written with one stroke. One end and the other end of the heater resistance MH are connected to the terminal electrodes E1 and E2 provided on the substrate 11, respectively. The two internal nodes of the heater resistance MH are connected to the terminal electrodes E3 and E4, respectively. In the heater resistance MH, the section connected between the terminal electrode E3 and the terminal electrode E4 constitutes a first section MH1, and the section connected between the terminal electrode E1 and the terminal electrode E3 and the terminal The section connected between the electrode E2 and the terminal electrode E4 constitutes a second section MH2.

The heater resistance MH is made of a conductive material whose resistivity changes with temperature, and is a metal material having a relatively high melting point, for example, molybdenum (Mo), platinum (Pt), gold (Au), tungsten (W). , Tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing any two or more of these is preferable. Further, it is preferably a conductive material capable of highly accurate dry etching such as ion milling, and more preferably platinum (Pt) having high corrosion resistance as a main component. Further, in order to improve the adhesion with the insulating film 13, it is preferable to form an adhesion layer of titanium (Ti) or the like under the Pt.

The heater protection film 14 is formed on the heater resistance MH. As the material of the heater protective film 14, it is desirable to use the same material as the insulating film 13. Since the heater resistance MH repeatedly rises from room temperature to, for example, 150° C. or 300° C. and then drops to room temperature again, a large amount of thermal change is repeatedly generated. Therefore, the insulating film 13 and the heater protective film 14 are also subjected to a strong thermal stress. If continuously received, it will lead to destruction such as delamination and cracks. However, if the insulating film 13 and the heater protection film 14 are made of the same material, the material properties of both are the same and the adhesion is strong. Breakage such as cracks and cracks is less likely to occur. When silicon oxide is used as the material of the heater protection film 14, it may be formed by a method such as a thermal oxidation method or a CVD method. The film thickness of the heater protection film 14 is not particularly limited as long as insulation with the thermistor Rd is ensured, and may be, for example, about 0.1 to 3.0 μm.

A thermistor Rd is provided on the heater protection film 14. The thermistor Rd is composed of the thermistor film 30 and a pair of thermistor electrodes 31 and 32 in contact with the thermistor film 30. The planar shape of the thermistor electrodes 31 and 32 is as shown in FIG.

The thermistor film 30 is made of a material having a negative temperature coefficient of resistance such as composite metal oxide, amorphous silicon, polysilicon, or germanium, and can be formed by using a thin film process such as sputtering or CVD. The film thickness of the thermistor film 30 may be adjusted according to the target resistance value, and if the resistance value (R25) at room temperature is set to about 2 MΩ using MnNiCo-based oxide, for example, 0.2. The thickness may be set to about 1 μm. Here, the reason why the thermistor film 30 is used as the temperature-sensitive resistance element is that a large detection sensitivity can be obtained because the resistance temperature coefficient is larger than that of a platinum temperature sensing element or the like. Further, because of the thin film structure, it is possible to efficiently detect the heat generation of the heater resistance MH.

The thermistor electrodes 31 and 32 are conductive materials that can withstand processes such as a film forming process of the thermistor film 30 and a heat treatment process, and have a relatively high melting point such as molybdenum (Mo), platinum (Pt), or gold. (Au), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing any two or more of these. As shown in FIG. 1, one ends of the thermistor electrodes 31 and 32 are connected to the terminal electrodes E5 and E6, respectively, and the other ends of the thermistor electrodes 31 and 32 are both open.

The thermistor electrodes 31 and 32 extend in the y direction on the thermistor film 30 while maintaining their parallel state. That is, the distance between the thermistor electrodes 31 and 32 in the x direction is substantially constant. As a result, the resistance value between the terminal electrodes E5 and E6 changes depending on the temperature. In the present embodiment, each of the thermistor electrodes 31 and 32 has an overlap with the portion of the heater resistance MH extending in the x direction.

The thermistor Rd is covered with the thermistor protective film 15. If the thermistor film 30 is brought into contact with a reducing material to reach a high temperature state, oxygen is taken from the thermistor film 30 to cause reduction, which affects the thermistor characteristics. In order to prevent this, the material of the thermistor protective film 15 is preferably an insulating oxide film having no reducing property such as a silicon oxide film.

The terminal electrodes E1 to E6 are connected to the package electrodes 17 provided on the ceramic package 21 via the bonding wires 16. The package electrode 17 is connected to an external circuit via an external terminal 18 provided on the back surface of the ceramic package 21.

As described above, since the gas sensor 10A according to the present embodiment has a configuration in which the heater resistance MH and the thermistor Rd are stacked on the substrate 11, the heat generated by the heater resistance MH is efficiently transmitted to the thermistor Rd.

FIG. 3 is a circuit diagram showing a part of an external circuit connected to the terminal electrodes E1 to E4.

As shown in FIG. 3, the constant voltage source 42 is connected between the terminal electrodes E1 and E2, and the switch circuit SW1 is connected between the terminal electrodes E3 and E4. With this configuration, the same current flows in the first section MH1 and the second section MH2 while the switch circuit SW1 is off. On the other hand, while the switch circuit SW1 is on, the first section MH1 is bypassed by the switch circuit SW1, so that the current flowing in the first section MH1 is significantly reduced.

The thermistor film 30 has a first region 30a that overlaps the first section MH1 of the heater resistance MH, and a second region 30b that overlaps the second section MH2 of the heater resistance MH. Therefore, while the switch circuit SW1 is off, both the first and second regions 30a and 30b of the thermistor film 30 are heated, while while the switch circuit SW1 is on, the thermistor film 30 is heated. The second region 30b of the film 30 is heated, while the first region 30a of the thermistor film 30 is barely heated. The first region 30a is sandwiched by the second regions 30b from the y direction. The y direction is a direction orthogonal to the direction (x direction) in which the thermistor electrode 31 and the thermistor electrode 32 face each other. As shown in FIG. 3, the terminal electrode E5 corresponding to the thermistor electrode 31 is connected to the connection node N, and the terminal electrode E6 corresponding to the thermistor electrode 32 is given a ground potential.

FIG. 4 is a circuit diagram of the gas sensor 10A according to the present embodiment.

As shown in FIG. 4, connection node N is connected to power supply Vcc via reference resistance 41. The detection level Vdet appearing at the connection node N is supplied to the comparator 43 that is a detection circuit. The comparator 43 compares the detection level Vdet with the reference level Vref and generates an output signal Vout based on the difference. The switch circuit SW1 is switched on/off by the heater control circuit 40. The heater control circuit 40 may switch activation/deactivation of the constant voltage source 42 itself.

FIG. 5 is a timing chart for explaining the operation of the gas sensor 10A according to the present embodiment.

As shown in FIG. 5, the gas sensor 10A according to the present embodiment operates such that a period T1 in which the switch circuit SW1 is off and a period T2 in which the switch circuit SW1 is on are alternately repeated. The period T1 in which the switch circuit SW1 is turned off is the first control state in which the same current flows in the first and second sections MH1 and MH2 of the heater resistance MH. The period T2 in which the switch circuit SW1 is turned on is the second control state in which the current flowing in the first section MH1 of the heater resistance MH is significantly reduced. In the example shown in FIG. 5, the period T2 is set longer than the period T1.

6A and 6B are schematic diagrams showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10A according to the present embodiment, where FIG. 6A shows the in-plane temperature distribution in the period T1 during which the switch circuit SW1 is off, and FIG. The in-plane temperature distribution in the period T2 during which the switch circuit SW1 is turned on is shown. The broken line in the graph shown in FIG. 6A shows the in-plane temperature distribution in the period T2, and the broken line in the graph shown in FIG. 6B shows the in-plane temperature distribution in the period T1.

As shown in FIG. 6A, during the period T1 in which the switch circuit SW1 is off, the same current flows in the first and second sections MH1 and MH2 of the heater resistance MH, so that the first and second sections of the thermistor film 30 are Both the second regions 30a and 30b are heated. However, the in-plane temperature distribution of the thermistor film 30 is not uniform, the temperature of the central portion is high and the temperature of the peripheral portion is low. This is because the central portion of the thermistor film 30 is more likely to accumulate heat than the peripheral portion.

On the other hand, as shown in FIG. 6B, during the period T2 in which the switch circuit SW1 is turned on, the current flowing in the first section MH1 of the heater resistance MH is significantly reduced, so that the second resistance of the thermistor film 30 is reduced. The region 30b is heated, while the first region 30a of the thermistor film 30 is hardly heated. As a result, the temperature of the second region 30b of the thermistor film 30 rises and the temperature of the first region 30a of the thermistor film 30 falls.

Therefore, by repeating the period T1 and the period T2 alternately, the temperature of the central portion of the thermistor film 30 where heat is likely to accumulate is lowered, and the temperature distribution of the thermistor film 30 in the y direction is made more uniform. The y direction is a direction orthogonal to the direction (x direction) where the thermistor electrode 31 and the thermistor electrode 32 face each other, so that the current density of the current flowing from the thermistor electrode 31 to the thermistor electrode 32 is more uniform.

As described above, in the gas sensor 10A according to the present embodiment, by turning on the switch circuit SW1 in the period T2, the current flowing in the first section MH1 of the heater resistance MH is significantly reduced. By repeating T2 alternately, it becomes possible to make the temperature distribution of the thermistor film 30 in the y direction more uniform. In particular, if the period T2 is set longer than the period T1 as shown in FIG. 5, heat is less likely to be accumulated in the central portion of the thermistor film 30, so that the temperature distribution becomes more uniform.

In the operation shown in FIG. 5, there is no interval between the period T1 and the period T2, but in actuality, by providing the interval period during which the heater resistance MH is not heated between the period T1 and the period T2, the power consumption is reduced. Is preferably reduced. In this case, the constant voltage source 42 may be deactivated by the heater control circuit 40 during the interval period.

<Second Embodiment>

7 and 8 are a schematic plan view and a circuit diagram transparently showing the structure of the gas sensor 10B according to the second embodiment, respectively.

As shown in FIG. 7, the gas sensor 10B according to the present embodiment has a configuration in which a switch circuit SW2 is further connected between the terminal electrode E1 and the terminal electrode E3 and between the terminal electrode E2 and the terminal electrode E4. There is. The switch circuit SW1 and the switch circuit SW2 are exclusively turned on by the heater control circuit 40 shown in FIG. Since the other basic configuration is the same as that of the gas sensor 10A according to the first embodiment, the same reference numerals are given to the same elements, and duplicate description will be omitted.

With this configuration, while the switch circuit SW1 is off and the switch circuit SW2 is on, the second section MH2 is bypassed by the switch circuit SW2, so that the current flowing in the second section MH2 is significantly reduced. On the other hand, during the period in which the switch circuit SW1 is on and the switch circuit SW2 is off, the first section MH1 is bypassed by the switch circuit SW1, so that the current flowing in the first section MH1 is significantly reduced.

FIG. 9 is a timing chart for explaining the operation of the gas sensor 10B according to the present embodiment.

As shown in FIG. 9, in the gas sensor 10B according to the present embodiment, a period T1 in which the switch circuit SW1 is off and the switch circuit SW2 is on, and a period T2 in which the switch circuit SW1 is on and the switch circuit SW2 is off are alternated. Works to repeat. As described above, the current flowing in the second section MH2 of the heater resistance MH is significantly reduced in the period T1, and the current flowing in the first section MH1 of the heater resistance MH is significantly reduced in the period T2. In the example shown in FIG. 9, the period T2 is set longer than the period T1. Also in this embodiment, it is preferable to reduce the power consumption by providing an interval period during which the heater resistance MH is not heated between the period T1 and the period T2.

FIG. 10 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10B according to the present embodiment, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature in the period T2. The distribution is shown. The broken line in the graph shown in FIG. 10A shows the in-plane temperature distribution in the period T2, and the broken line in the graph shown in FIG. 10B shows the in-plane temperature distribution in the period T1.

As shown in FIG. 10A, in the period T1, the current flowing in the second section MH2 of the heater resistance MH is significantly reduced, so that the first region 30a of the thermistor film 30 is heated, The second region 30b of the thermistor film 30 is hardly heated. As a result, the temperature of the first region 30a of the thermistor film 30 rises and the temperature of the second region 30b of the thermistor film 30 falls.

On the other hand, as shown in FIG. 10B, in the period T2, the current flowing in the first section MH1 of the heater resistance MH is significantly reduced, so that the second region 30b of the thermistor film 30 is heated. On the other hand, the first region 30a of the thermistor film 30 is hardly heated. As a result, the temperature of the second region 30b of the thermistor film 30 rises and the temperature of the first region 30a of the thermistor film 30 falls.

Therefore, by alternately repeating the period T1 and the period T2 and setting the period T2 longer than the period T1, the temperature of the central portion of the thermistor film 30 where heat is likely to accumulate is lowered, and the thermistor film 30 in the y direction is reduced. The temperature distribution is made more uniform.

As described above, the gas sensor 10B according to the present embodiment can alternately heat the first region 30a and the second region 30b of the thermistor film 30, so that the period T1 and the period T2 are alternately repeated, and If the period T2 is set to be longer than the period T1, heat is less likely to be accumulated in the central portion of the thermistor film 30, and the temperature distribution can be made more uniform.

<Third Embodiment>
11 and 12 are a schematic plan view and a circuit diagram transparently showing the structure of the gas sensor 10C according to the third embodiment, respectively.

As shown in FIG. 11, in the present embodiment, the heater resistance MH is not meandering, the first section MH1 is located at the center in the x direction and the y direction, and the second section MH2 surrounds the center. It has a shape located on the outer peripheral portion. Correspondingly, the first region 30a of the thermistor film 30 that overlaps the first section MH1 of the heater resistance MH is located at the center, and the second area that overlaps the second section MH2 of the heater resistance MH. 30b is located in the outer peripheral portion. That is, the first region 30a is surrounded by the second region 30b.

One end and the other end of the heater resistance MH are connected to the terminal electrodes E1 and E2, respectively. Here, the terminal electrode E1 is located on the first section MH1 side, and the terminal electrode E2 is located on the second section MH2 side. Further, a portion which is an intermediate point of the heater resistance MH and is located at a boundary between the first section MH1 and the second section MH2 is connected to the terminal electrode E7. The constant voltage source 42 is connected between the terminal electrodes E1 and E2, and the switch circuit SW1 is connected between the terminal electrodes E1 and E7. Since the other basic configuration is the same as that of the gas sensor 10A according to the first embodiment, the same reference numerals are given to the same elements, and duplicate description will be omitted.

The operation of the gas sensor 10C according to the present embodiment is the same as the operation of the gas sensor 10A according to the first embodiment shown in FIG. Therefore, during the first period when the switch circuit SW1 is off, the same current flows in the first section MH1 and the second section MH2. On the other hand, during the second period in which the switch circuit SW1 is on, the first section MH1 is bypassed by the switch circuit SW1, so that the current flowing in the first section MH1 is significantly reduced. As a result, the entire thermistor film 30 is heated during the first period when the switch circuit SW1 is off, whereas the outer peripheral portion of the thermistor film 30 is during the second period when the switch circuit SW1 is on. Is heated, the central portion of the thermistor film 30 is hardly heated.

13A and 13B are schematic diagrams showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10C according to the present embodiment, where FIG. 13A shows the in-plane temperature distribution in the period T1 and FIG. 13B shows the in-plane temperature in the period T2. The distribution is shown. The broken line in the graph shown in FIG. 13A shows the in-plane temperature distribution in the period T2, and the broken line in the graph shown in FIG. 13B shows the in-plane temperature distribution in the period T1.

As shown in FIG. 13A, during the period T1 in which the switch circuit SW1 is turned off, the same current flows in the first and second sections MH1 and MH2 of the heater resistance MH, so that the first and second sections of the thermistor film 30 are formed. Both the second regions 30a and 30b are heated. However, the in-plane temperature distribution of the thermistor film 30 is not uniform, the temperature of the central portion is high and the temperature of the peripheral portion is low. This is because the central portion of the thermistor film 30 is more likely to accumulate heat than the peripheral portion.

On the other hand, as shown in FIG. 13B, during the period T2 in which the switch circuit SW1 is turned on, the current flowing in the first section MH1 of the heater resistance MH is significantly reduced, so that the second resistance of the thermistor film 30 is reduced. The region 30b is heated, while the first region 30a of the thermistor film 30 is hardly heated. As a result, the temperature of the second region 30b of the thermistor film 30 rises and the temperature of the first region 30a of the thermistor film 30 falls.

Therefore, by alternately repeating the period T1 and the period T2 and setting the period T2 longer than the period T1, the temperature of the central portion of the thermistor film 30 where heat easily accumulates is lowered, and the temperature of the thermistor film 30 in the x direction and The temperature distribution in the y direction is made more uniform.

As described above, in the gas sensor 10C according to the present embodiment, the first section MH1 of the heater resistance MH is located in the central portion, and the second section MH2 is located in the outer peripheral portion. Not only the temperature distribution in the y direction but also the temperature distribution in the x direction can be made uniform.

<Fourth Embodiment>
14 and 15 are a schematic plan view and a circuit diagram transparently showing the structure of the gas sensor 10D according to the fourth embodiment, respectively.

As shown in FIG. 14, in the present embodiment, the constant voltage source 42 is connected to the terminal electrode E7, and one of the terminal electrodes E1 and E2 is grounded via the switch circuit SW1. This is different from the gas sensor 10C according to the embodiment. Since the other basic configuration is the same as that of the gas sensor 10C according to the third embodiment, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

FIG. 16 is a timing chart for explaining the operation of the gas sensor 10D according to the present embodiment.

As shown in FIG. 16, the gas sensor 10D according to the present embodiment operates such that a period T1 in which the switch circuit SW1 is connected to the node a side and a period T2 in which the switch circuit SW1 is connected to the node b side are alternately repeated. .. In the period T1 in which the switch circuit SW1 is connected to the node a side, current flows in the first section MH1 of the heater resistance MH, but no current flows in the second section MH2. On the contrary, in the period T2 in which the switch circuit SW1 is connected to the node b side, the current flows in the second section MH2 of the heater resistance MH, while the current does not flow in the first section MH1.

FIG. 17 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10D according to the present embodiment, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature in the period T2. The distribution is shown. The broken line in the graph shown in FIG. 17A shows the in-plane temperature distribution in the period T2, and the broken line in the graph shown in FIG. 17B shows the in-plane temperature distribution in the period T1.

As shown in FIG. 17A, in the period T1, the current flows only in the first section MH1 of the heater resistance MH, and the current does not flow in the second section MH2. Therefore, in the first section of the thermistor film 30, While the region 30a of 30 is heated, the second region 30b of the thermistor film 30 is not heated. As a result, the temperature of the first region 30a of the thermistor film 30 rises and the temperature of the second region 30b of the thermistor film 30 falls.

On the other hand, as shown in FIG. 17B, in the period T2, the current flows only in the second section MH2 of the heater resistance MH, and the current does not flow in the first section MH1. The second region 30b is heated, while the first region 30a of the thermistor film 30 is no longer heated. As a result, the temperature of the second region 30b of the thermistor film 30 rises and the temperature of the first region 30a of the thermistor film 30 falls.

Therefore, by alternately repeating the period T1 and the period T2 and setting the period T2 longer than the period T1, the temperature of the central portion of the thermistor film 30 where heat easily accumulates is lowered, and the temperature of the thermistor film 30 in the x direction and The temperature distribution in the y direction is made more uniform.

As described above, the gas sensor 10D according to the present embodiment can heat the first region 30a and the second region 30b of the thermistor film 30 alternately, like the gas sensor 10B according to the second embodiment. If the period T1 and the period T2 are alternately repeated and the period T2 is set longer than the period T1, heat is less likely to be accumulated in the central portion of the thermistor film 30, and the temperature distribution can be made more uniform. Moreover, in the gas sensor 10D according to the present embodiment, as in the gas sensor 10C according to the third embodiment, the first section MH1 of the heater resistance MH is located in the central portion and the second section MH2 is located in the outer peripheral portion. Therefore, not only the temperature distribution in the y direction of the thermistor film 30 but also the temperature distribution in the x direction can be made uniform.

<Fifth Embodiment>
18 and 19 are a schematic plan view and a circuit diagram transparently showing the structure of the gas sensor 10E according to the fifth embodiment, respectively.

As shown in FIG. 18, in the present embodiment, the heater resistance MH is completely separated into the first section MH1 and the second section MH2. One end of the first section MH1 is connected to the terminal electrode E3, and the other end of the first section MH1 is connected to the terminal electrode E4. Further, one end of the second section MH2 is connected to the terminal electrode E1, and the other end of the second section MH2 is connected to the terminal electrode E2. The constant voltage source 42 and the switch circuit SW1 are connected in series between the terminal electrode E1 and the terminal electrode E2, and the constant voltage source 44 and the switch circuit SW2 are connected in series between the terminal electrode E3 and the terminal electrode E4. It is connected. The switch circuit SW1 and the switch circuit SW2 are exclusively turned on by the heater control circuit 40 shown in FIG. Therefore, the constant voltage source 42 and the constant voltage source 44 may be common. Since the other basic configuration is the same as that of the gas sensor 10B according to the second embodiment, the same reference numerals are given to the same elements, and duplicate description will be omitted.

With such a configuration, while the switch circuit SW1 is on and the switch circuit SW2 is off, current flows only in the first section MH1 of the heater resistance MH, and no current flows in the second section MH2. On the contrary, during the period in which the switch circuit SW1 is off and the switch circuit SW2 is on, the current flows only in the first section MH1 of the heater resistance MH, and the current does not flow in the second section MH2.

FIG. 20 is a timing chart for explaining the operation of the gas sensor 10E according to the present embodiment.

As shown in FIG. 20, in the gas sensor 10E according to the present embodiment, a period T1 in which the switch circuit SW1 is on and the switch circuit SW2 is off, and a period T2 in which the switch circuit SW1 is off and the switch circuit SW2 is on are alternated. Works to repeat. As described above, in the period T1, the current flows only in the first section MH1 of the heater resistance MH, and in the period T2, the current flows only in the second section MH2 of the heater resistance MH. In the example shown in FIG. 20, the period T2 is set longer than the period T1. Also in the present embodiment, it is preferable to reduce the power consumption by providing an interval period during which both the switch circuits SW1 and SW2 are turned off between the periods T1 and T2.

FIG. 21 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10E according to the present embodiment, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature in the period T2. The distribution is shown. The broken line of the graph shown in FIG. 21A shows the in-plane temperature distribution in the period T2, and the broken line of the graph shown in FIG. 21B shows the in-plane temperature distribution in the period T1.

As shown in FIG. 21A, in the period T1, the current flows only in the first section MH1 of the heater resistance MH, and the current does not flow in the second section MH2. Therefore, in the first section of the thermistor film 30, While the region 30a of 30 is heated, the second region 30b of the thermistor film 30 is not heated. As a result, the temperature of the first region 30a of the thermistor film 30 rises and the temperature of the second region 30b of the thermistor film 30 falls.

On the other hand, as shown in FIG. 21B, in the period T2, the current flows only in the second section MH2 of the heater resistance MH, and the current does not flow in the first section MH1. The second region 30b is heated, while the first region 30a of the thermistor film 30 is no longer heated. As a result, the temperature of the second region 30b of the thermistor film 30 rises and the temperature of the first region 30a of the thermistor film 30 falls.

Therefore, by alternately repeating the period T1 and the period T2 and setting the period T2 longer than the period T1, the temperature of the central portion of the thermistor film 30 where heat is likely to accumulate is lowered, and the thermistor film 30 in the y direction is reduced. The temperature distribution is made more uniform.

As described above, the gas sensor 10E according to the present embodiment can control the first section MH1 and the second section MH2 of the heater resistance MH independently, so that more accurate control is possible. Further, in the above example, the periods T1 and T2 are alternately repeated, but a third period for turning on both the switch circuit SW1 and the switch circuit SW2 may be inserted if necessary.

<Sixth Embodiment>
FIG. 22 is a schematic plan view transparently showing the structure of the gas sensor 10F according to the sixth embodiment. The circuit diagram of the gas sensor 10F according to the sixth embodiment is the same as FIG.

As shown in FIG. 22, in the gas sensor 10F according to the present embodiment, like the gas sensor 10C according to the third embodiment, the first section MH1 of the heater resistance MH is located in the central portion, and the second section MH2 is the outer peripheral portion. Is located in. Further, as in the gas sensor 10E according to the fifth embodiment, the heater resistance MH is completely separated into the first section MH1 and the second section MH2. One end of the first section MH1 is connected to the terminal electrode E1, and the other end of the first section MH1 is connected to the terminal electrode E9. Further, one end of the second section MH2 is connected to the terminal electrode E2, and the other end of the second section MH2 is connected to the terminal electrode E8.

The constant voltage source 42 and the switch circuit SW1 are connected in series between the terminal electrode E1 and the terminal electrode E9, and the constant voltage source 44 and the switch circuit SW2 are connected in series between the terminal electrode E2 and the terminal electrode E8. It is connected. The switch circuit SW1 and the switch circuit SW2 are exclusively turned on by the heater control circuit 40 shown in FIG. Therefore, the constant voltage source 42 and the constant voltage source 44 may be common. Since the other basic configuration is the same as that of the gas sensor 10E according to the fifth embodiment, the same elements are designated by the same reference numerals, and duplicate description will be omitted.

With such a configuration, while the switch circuit SW1 is on and the switch circuit SW2 is off, current flows only in the first section MH1 of the heater resistance MH and no current flows in the second section MH2. On the contrary, while the switch circuit SW1 is off and the switch circuit SW2 is on, the current flows only in the first section MH1 of the heater resistance MH, and the current does not flow in the second section MH2.

The operation of the gas sensor 10F according to the present embodiment is the same as the operation of the gas sensor 10E according to the fifth embodiment shown in FIG. Therefore, in the period T1, the current flows only in the first section MH1 of the heater resistance MH, and in the period T2, the current flows only in the second section MH2 of the heater resistance MH.

FIG. 23 is a schematic diagram showing the in-plane temperature distribution of the thermistor film 30 in the gas sensor 10F according to the present embodiment, where (a) shows the in-plane temperature distribution in the period T1 and (b) shows the in-plane temperature in the period T2. The distribution is shown. The broken line in the graph shown in FIG. 23A shows the in-plane temperature distribution in the period T2, and the broken line in the graph shown in FIG. 23B shows the in-plane temperature distribution in the period T1.

As shown in FIG. 23A, in the period T1, the current flows only in the first section MH1 of the heater resistance MH, and the current does not flow in the second section MH2. While the region 30a of 30 is heated, the second region 30b of the thermistor film 30 is not heated. As a result, the temperature of the first region 30a of the thermistor film 30 rises and the temperature of the second region 30b of the thermistor film 30 falls.

On the other hand, as shown in FIG. 23B, in the period T2, the current flows only in the second section MH2 of the heater resistance MH, and the current does not flow in the first section MH1. The second region 30b is heated, while the first region 30a of the thermistor film 30 is no longer heated. As a result, the temperature of the second region 30b of the thermistor film 30 rises and the temperature of the first region 30a of the thermistor film 30 falls.

Therefore, by alternately repeating the period T1 and the period T2 and setting the period T2 longer than the period T1, the temperature of the central portion of the thermistor film 30 where heat is likely to accumulate is lowered, and the thermistor film 30 in the y direction is reduced. The temperature distribution is made more uniform.

As described above, the gas sensor 10F according to the present embodiment, like the gas sensor 10E according to the fifth embodiment, can control the first section MH1 and the second section MH2 of the heater resistance MH independently. Precise control is possible. Moreover, in the gas sensor 10F according to the present embodiment, like the gas sensor 10C according to the third embodiment, the first section MH1 of the heater resistance MH is located in the central portion and the second section MH2 is located in the outer peripheral portion. Therefore, not only the temperature distribution in the y direction of the thermistor film 30 but also the temperature distribution in the x direction can be made uniform.

Although the preferred embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist of the present invention. It goes without saying that it is included in the range.

10A to 10F Gas sensor 11 Substrate 11a Cavities 12 and 13 Insulating film 14 Heater protective film 15 Thermistor protective film 16 Bonding wire 17 Package electrode 18 External terminal 21 Ceramic package 22 Lid 23 Vent hole 30 Thermistor film 30a First region 30b Second region Regions 31 and 32 Thermistor electrode 40 Heater control circuit 41 Reference resistance 42 Constant voltage source 43 Comparator 44 Constant voltage source E1 Terminal electrodes E1 to E9 Terminal electrode MH Heater resistance MH1 First section MH2 Second section N Connection node Rd Thermistor SW1 , SW2 switch circuits a and b nodes

Claims (7)

A thermistor, a heater resistance that heats the thermistor, a heater control circuit that controls the heater resistance, and a detection circuit that generates an output signal based on the resistance value of the thermistor,
The thermistor has first and second regions,
The heater resistance includes a first section that heats the first area and a second section that heats the second area,
The heater control circuit supplies a current to at least the first section in a first period, and supplies a larger amount of current to the second section than in the first section in a second period. Gas sensor characterized by. The gas sensor according to claim 1, wherein the heater control circuit supplies more current to the first section than to the second section during the first period. The heater control circuit supplies current to the first section without supplying current to the second section during the first period, and supplies current to the first section during the second period. The gas sensor according to claim 2, wherein the current is supplied to the second section without supplying the gas. The gas sensor according to claim 1, wherein the first region is sandwiched by the second region from at least one direction. The gas sensor according to claim 4, wherein the first region is surrounded by the second region. The gas sensor according to claim 4 or 5, wherein the heater control circuit alternately repeats the first period and the second period. The gas sensor according to claim 6, wherein the second period is longer than the first period.

Images