JP2019158358A - Sensor element and gas sensor including the same - Google Patents

Abstract

To enhance heat resistance of a membrane part while securing mechanical strength of beam parts.SOLUTION: A sensor element includes: a substrate 10 having a cavity part 11; a membrane part 20M positioned on the cavity part 11 of the substrate 10 and supported by beam parts 20B-20Bextending from a front surface of the substrate 10; a heater resistance 30 formed on the membrane part 20M. A rib extending in a longitudinal direction is arranged on front surfaces of the beam parts 20B-20B. Since the rib is arranged in the beam parts 20B-20Bfor supporting the membrane part 20M, a cross sectional area required for securing mechanical strength being the same as that in a case where the rib is not arranged can be reduced. Thus, while preventing damage in the beam parts, heat resistance of the membrane part can be enhanced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a sensor element and a gas sensor including the sensor element, and more particularly to a sensor element having a membrane structure and a gas sensor including the sensor element.

  As a gas sensor for measuring the concentration of the detection target gas, a gas sensor having a membrane structure is known. A gas sensor having a membrane structure can increase the thermal resistance of the membrane portion by forming a heater resistance in the membrane portion supported by the substrate, thereby reducing power consumption. For example, Patent Document 1 discloses a structure in which a membrane portion in which a heater resistor is formed is supported by four beam portions.

  Most of the heat released from the membrane is due to heat conduction through the beam. Therefore, in order to increase the thermal resistance of the membrane portion, it is desirable to increase the length of the beam portion or reduce the cross-sectional area of the beam portion.

Japanese Patent Laid-Open No. 6-118047

  However, when the length of the beam portion is simply increased or the cross-sectional area of the beam portion is reduced, the mechanical strength of the beam portion is insufficient and the beam portion may be damaged by slight vibration.

  Accordingly, an object of the present invention is to provide a sensor element capable of increasing the thermal resistance of the membrane portion while securing the mechanical strength of the beam portion, and a gas sensor including the sensor element.

  A sensor element according to the present invention includes a substrate having a cavity, a membrane portion positioned on the cavity of the substrate and supported by a beam extending from the surface of the substrate, and a heater resistor formed in the membrane portion. And a rib extending in the length direction connecting the substrate and the membrane portion is provided on the surface of the beam portion.

  According to the present invention, since the ribs are provided on the beam part that supports the membrane part, the cross-sectional area required to ensure the same mechanical strength is reduced as compared with the case where the ribs are not provided. be able to. As a result, it is possible to increase the thermal resistance of the membrane portion while preventing damage to the beam portion.

  In the present invention, the ribs may be provided on both sides in the width direction of the beam portion, or may be provided in the center portion in the width direction of the beam portion. In any of these, it is possible to increase the mechanical strength of the beam portion.

  In the present invention, the membrane part and the beam part are formed of a part of the insulating film covering the surface of the substrate, and the insulating film located on the cavity part is formed with a plurality of cutout parts. You may divide into a beam part. According to this, the cavity can be formed by removing a part of the substrate on which the insulating film is formed, and the membrane portion and the beam can be formed by forming a plurality of notches in the insulating film on the cavity. The part can be formed.

  In the present invention, the beam portion includes a main body portion made of an insulating film, a rib, and a stopper film that is located between the main body portion and the rib and made of a material different from the insulating film constituting the main body portion. It doesn't matter. According to this, since the stopper film functions as an etching stopper when the rib is formed on the beam portion, the beam portion can be processed with high accuracy and easily.

  A gas sensor according to the present invention includes the above-described sensor element, a thermistor formed on a membrane portion so as to overlap with a heater resistance, and a pair of thermistor electrodes connected via the thermistor. According to this, it becomes possible to provide a heat conduction type gas sensor.

  The gas sensor according to the present invention may further include a catalyst that is formed on the membrane portion so as to overlap with the heater resistance and the thermistor and that promotes the combustion of the detection target gas. According to this, it becomes possible to provide a contact combustion type gas sensor.

  As described above, according to the present invention, it is possible to provide a sensor element capable of increasing the thermal resistance of the membrane portion while ensuring the mechanical strength of the beam portion, and a gas sensor including the sensor element. Thereby, the reliability of the sensor element and the gas sensor can be improved, and the power consumption can be reduced.

FIG. 1 is a schematic perspective view for explaining the appearance of the sensor element 1 according to the first embodiment of the present invention. FIG. 2 is a schematic top view of the sensor element 1. FIG. 3 is a schematic cross-sectional view along the line AA shown in FIG. Figure 4 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ of the comparative example. FIG. 5 is a schematic cross-sectional view taken along the line BB shown in FIG. 2, and shows a cross-sectional shape of the beam portion 20B ₁ according to the first specific example. Figure 6 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ of the second embodiment. Figure 7 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ of the third embodiment. Figure 8 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ of the fourth embodiment. Figure 9 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ of the fifth embodiment. Figure 10 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ according to an embodiment of the sixth. Figure 11 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ according to the seventh embodiment of. Figure 12 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ according to an embodiment of the eighth. FIG. 13 is a schematic top view for explaining the configuration of the gas sensor 2 according to the second embodiment of the present invention. FIG. 14 is a schematic cross-sectional view along the line CC shown in FIG. FIG. 15 is a schematic top view for explaining the configuration of the gas sensor 3 according to the third embodiment of the present invention. FIG. 16 is a schematic cross-sectional view along the line DD shown in FIG. FIG. 17 is a schematic cross-sectional view showing a modified example of the gas sensor 2.

  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 perspective view for explaining the appearance of the sensor element 1 according to the first embodiment of the present invention. FIG. 2 is a schematic top view of the sensor element 1.

  The sensor element 1 according to the present embodiment functions as a temperature sensor or a gas sensor, and includes a substrate 10, an insulating film 20 formed on the surface of the substrate 10, and a heater resistor 30 as shown in FIGS. 1 and 2. .

  The substrate 10 is not particularly limited as long as it has a suitable mechanical strength and is suitable for fine processing such as etching. A silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, and a quartz substrate are not limited. A glass substrate or the like can be used. In the substrate 10, the cavity 11 is provided at a position overlapping the heater resistor 30 in plan view in order to suppress conduction of heat from the heater resistor 30 to the substrate 10.

The insulating film 20 is formed on the surface of the substrate 10 and also on the portion covering the cavity 11. Portion covering the cavity 11 of the insulating film 20, and a membrane portion 20M which is located at a substantially central portion comprises four beam portions _20B 1 _{~20B 4} for supporting the membrane portion 20M. That is, the insulating film 20, in addition to the portion covering the surface of the substrate 10, the beam portion _20B 1 _{~20B 4} extending from the surface of the substrate 10, the membrane portion 20M which is supported by the beam portion _20B 1 _{~20B 4} These are configured integrally. The portion covering the cavity 11 of the insulating film 20 is provided with four notches 20a, thereby being divided into the membrane unit 20M and the beam portion _20B 1 _{~20B 4.}

  The heater resistor 30 is made of a conductive material whose resistivity varies with temperature, and is a metal material made of a material having a relatively high melting point, such as molybdenum (Mo), platinum (Pt), gold (Au), tungsten (W). Tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing any two or more thereof is preferable. Moreover, it is preferable that the conductive material be capable of high-precision dry etching such as ion milling, and it is more preferable that platinum (Pt) having high corrosion resistance is the main component. Further, in order to improve the adhesion to the insulating film 20, an adhesion layer such as titanium (Ti) may be formed on the base of Pt.

The heater resistor 30 meanders in the membrane part 20M, thereby increasing the resistance value and improving the heat uniformity in the surface direction of the membrane part 20M. One end of the heater resistor 30 is connected to the terminal electrode 41 through the drawn-out conductor portions 31 formed on the beam portion 20B _1, the other end of the heater resistor 30, the drawn-out conductor portions 32 formed on the beam portion 20B ₃ To the terminal electrode 42. The lead conductor portions 31 and 32 and the terminal electrodes 41 and 42 may be made of the same metal material as that of the heater resistor 30, or may be made of a different metal material.

  FIG. 3 is a schematic cross-sectional view along the line AA shown in FIG.

  As shown in FIG. 3, the membrane part 20M has a configuration in which a lower insulating film 21 and an upper insulating film 22 are laminated, and a heater resistor 30 is formed between them. The lower insulating film 21 and the upper insulating film 22 are made of an insulating material such as silicon oxide or silicon nitride. When silicon oxide is used as the material of the lower insulating film 21 and the upper insulating film 22, for example, a film forming method such as a thermal oxidation method or a CVD (Chemical Vapor Deposition) method may be used. In order to prevent delamination due to thermal stress, the lower insulating film 21 and the upper insulating film 22 are preferably made of the same insulating material.

  Thus, in this embodiment, since the heater resistance 30 is formed in the membrane part 20M, the heat generated by the heater resistance 30 is difficult to escape to the substrate 10. That is, since the thermal resistance of the membrane portion 20M is increased, it is possible to perform heating with less power consumption. For example, the environmental temperature and the gas concentration can be measured based on a change in resistance value obtained when a constant current is passed through the heater resistor 30.

Figure 4 is a schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ of the comparative example.

As shown in FIG. 4, the cross section of the beam portion 20B ₁ of the comparative example it is rectangular, thus, the upper and lower surfaces is flat. If the cross section of the beam portion 20B ₁ is such a rectangular shape, reducing the cross-sectional area in order to increase the thermal resistance of the beam portion 20B _1, the mechanical strength of the beam portion 20B ₁ is insufficient, the beam portion 20B ₁ Will be easily damaged. In consideration of this point, in the present embodiment, ribs are provided in the beam portions 20B _{1 to} 20B ₄ .

5 to 12 are schematic cross-sectional view taken along the line B-B shown in FIG. 2 shows a cross-sectional shape of the beam portion 20B ₁ by the respective specific example of the first to eighth. It has the same cross-sectional shape as the beam portion 20B ₁ for the other of the beam portion _20B 2 _{~20B 4.}

In a first embodiment shown in FIG. 5, the ribs R are provided on both sides in the width direction of the upper insulating film 22 constituting the beam portion 20B _1. Rib R is a protrusion extending in the longitudinal direction for connecting the substrate 10 and the membrane portion 20M, thickness of the beam portion 20B ₁ is selectively increased at the portion where the ribs R are present. Ribs R serves to increase the mechanical strength of the beam portion 20B _1, as compared with the absence of the rib R as in the comparative example shown in FIG. 4, to obtain a greater mechanical strength in the same cross-sectional area be able to. Conversely, it is possible to further reduce the cross-sectional area to achieve the same mechanical strength, while securing the mechanical strength, it is possible to increase the thermal resistance of the beam portion 20B _1. The rib R shown in FIG. 5 can be formed by etching a substantially central portion in the width direction of the upper insulating film 22 through a mask.

Rib R, the length direction of the beam portion 20B _1, that is, it is necessary to extend in a direction connecting the substrate 10 and the membrane portion 20M. This is because the stress applied to the beam portion 20B ₁ is due to the displacement in the z direction of the membrane portion 20M, it is necessary to increase the flexural strength in the z-direction.

In a second embodiment shown in FIG. 6, the rib R is provided in a central portion in the width direction of the upper insulating film 22 constituting the beam portion 20B _1. Even with such a shape, while ensuring the mechanical strength, it is possible to increase the thermal resistance of the beam portion 20B _1. The rib R shown in FIG. 6 can be formed by etching both sides in the width direction of the upper insulating film 22 through a mask.

In a third embodiment shown in FIG. 7, that are further provided ribs R on both sides in the width direction of the lower insulating film 21 constituting the beam portion 20B ₁ is different from the first embodiment. With such a shape, it is possible to obtain higher mechanical strength than in the first specific example. The rib R shown in FIG. 7 can be formed by etching a substantially central portion in the width direction of the lower insulating film 21 and the upper insulating film 22 through a mask.

In the fourth embodiment shown in FIG. 8, a point that the ribs R are further provided in the central portion in the width direction of the lower insulating film 21 constituting the beam portion 20B ₁ is different from the second embodiment. With such a shape, it is possible to obtain higher mechanical strength than that of the second specific example. The rib R shown in FIG. 8 can be formed by etching both sides of the lower insulating film 21 and the upper insulating film 22 in the width direction through a mask.

Specific examples of the fifth and sixth 9 and 10 is a modification of the first and second embodiment, respectively, the beam portion 20B ₁ is lower insulating film 21, upper insulating film 22 and the ribs insulating film 23, and is different from the first and second specific examples in that a stopper film 50 is interposed between the upper insulating film 22 and the rib insulating film 23. The stopper film 50 is made of an insulating material different from that of the upper insulating film 22 and functions as an etching stopper when the rib insulating film 23 is patterned. That is, if the lower insulating film 21, the upper insulating film 22, the stopper film 50, and the rib insulating film 23 are stacked in this order, then the upper insulating film 22 is etched using the stopper film 50 as an etching stopper through the mask, the rib R Can be processed with high accuracy and ease. As an example, when the upper insulating film 22 is made of silicon oxide, the stopper film 50 can be made of a material having an etching rate different from that of silicon oxide, such as silicon nitride or aluminum oxide.

  The seventh and eighth specific examples shown in FIGS. 11 and 12 are modifications of the third and fourth specific examples, respectively, and not only between the upper insulating film 22 and the rib insulating film 23 but also the lower insulating film. A stopper film 50 is also interposed between the rib 21 and the rib insulating film 23. Thus, if the lower insulating film 21 is etched using the stopper film 50 as an etching stopper, the beam portion of the rib R can be processed with high accuracy and ease.

As described above, in the sensor element 1 according to the present embodiment, since the heater resistor 30 is formed in the membrane portion 20M, the heat generated by the heater resistor 30 is difficult to escape to the substrate 10. Since the heat dissipation path from the membrane unit 20M is a path that mostly through the beam portion _20B 1 _{~20B 4,} which in the present embodiment, the ribs R are provided on the beam portion _20B 1 _{~20B 4} The cross-sectional area for obtaining the same mechanical strength can be further reduced. Accordingly, while securing a sufficient mechanical strength, since the thermal resistance of the beam portion 20B ₁ ~20B ₄ is enhanced, it is possible to perform heating with less power consumption.

<Second Embodiment>
FIG. 13 is a schematic top view for explaining the configuration of the gas sensor 2 according to the second embodiment of the present invention. FIG. 14 is a schematic cross-sectional view along the line CC shown in FIG.

  As shown in FIGS. 13 and 14, the gas sensor 2 according to the present embodiment includes a thermistor 60 provided on the membrane portion 20 </ b> M so as to overlap the heater resistor 30, and a pair of thermistor electrodes 61 and 62 connected via the thermistor 60. Terminal electrodes 63 and 64 connected to the thermistor electrodes 61 and 62, respectively, and a thermistor protective film 24 covering the thermistor 60 and the thermistor electrodes 61 and 62. Since other basic configurations are the same as those of the sensor element 1 according to the first embodiment, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  The thermistor 60 is made of a material having a negative resistance temperature coefficient, such as a composite metal oxide, amorphous silicon, polysilicon, germanium, etc., and can be formed using a thin film process such as sputtering or CVD. The film thickness of the thermistor 60 may be adjusted according to the target resistance value. For example, if the resistance value (R25) at room temperature is set to about 2 MΩ using a MnNiCo-based oxide, a pair of thermistor electrodes is used. Depending on the distance between 61 and 62, the film thickness may be set to about 0.2 to 1 μm.

  The thermistor electrodes 61 and 62 are a pair of electrodes arranged at a predetermined interval so as to be in contact with the thermistor 60, whereby the resistance value between the pair of thermistor electrodes 61 and 62 is determined by the resistance value of the thermistor 60. . The material of the thermistor electrodes 61 and 62 is a conductive substance that can withstand processes such as the film formation process and heat treatment process of the thermistor 60 and has a relatively high melting point, such as molybdenum (Mo), platinum (Pt). Gold (Au), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing any two or more thereof is preferable.

  The thermistor 60 and the thermistor electrodes 61 and 62 are covered with the thermistor protective film 24. When the thermistor 60 and a reducing material are brought into contact with each other and brought to a high temperature state, oxygen is taken from the thermistor to cause reduction, which affects the thermistor characteristics. In order to prevent this, it is desirable to use a non-reducing insulating oxide film such as a silicon oxide film as the material of the thermistor protective film 24.

  As shown in FIG. 13, the end portions of the thermistor electrodes 61 and 62 are connected to terminal electrodes 63 and 64, respectively.

The gas sensor 2 according to the present embodiment can be used as a heat conduction type gas sensor. The heat conduction type gas sensor detects a gas having a thermal conductivity different from that of air, such as CO ₂ . That is, by utilizing the fact that the heat dissipation characteristic of the thermistor 60 changes depending on the concentration of the detection target gas in the atmosphere, heating by the heater resistor 30 and measuring the resistance value between the thermistor electrodes 61 and 62, The concentration of the detection target gas (for example, CO ₂ gas) in can be detected.

  As illustrated in the present embodiment, the sensor element according to the present invention can be applied to a heat conduction type gas sensor.

<Third Embodiment>
FIG. 15 is a schematic top view for explaining the configuration of the gas sensor 3 according to the third embodiment of the present invention. FIG. 16 is a schematic cross-sectional view taken along the line DD shown in FIG.

  As shown in FIGS. 15 and 16, the gas sensor 3 according to the present embodiment is different from the gas sensor 2 according to the second embodiment in that the gas sensor 3 includes a catalyst 70 provided in the membrane portion 20 </ b> M so as to overlap the heater resistor 30 and the thermistor 60. It is different. Since the other basic configuration is the same as that of the gas sensor 2 according to the second embodiment, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  As the catalyst 70, a material obtained by supporting platinum (Pt) on γ-alumina or the like into a paste form together with a binder, and applying and baking can be used. The material to be supported may be a catalyst metal such as gold (Au) or palladium (Pd).

When the catalyst 70 is heated to a predetermined temperature by the heater resistor 30, the catalyst 70 promotes the reaction (combustion) between the combustible gas to be detected such as CO gas and the O ₂ gas in the atmosphere. The reaction heat generated at that time is conducted to the thermistor 60 and changes its resistance value. For this reason, if the resistance value between the thermistor electrodes 61 and 62 is measured while heating by the heater resistor 30, the concentration of the detection target gas (for example, CO gas) in the atmosphere can be detected.

  As illustrated in this embodiment, the sensor element according to the present invention can be applied to a catalytic combustion type gas sensor.

  The preferred embodiments of the present invention have been described above, but the present invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of the present invention. Needless to say, it is included in the range.

  For example, in each of the embodiments described above, the cavity 11 penetrates the substrate 10 in the z direction, but this point is not essential in the present invention. Therefore, as illustrated in FIG. 17 as a modification of the gas sensor 2, the hollow portion 11 may be configured by a non-penetrating recess provided in the substrate 10. Although not shown, it is not essential that the membrane portion 20M is made only of the insulating film 20, and a part of the substrate 10 may remain thin on the membrane portion 20M.

1 sensor elements 2 gas sensor 10 substrate 11 cavity 20 insulating film _20B 1 _{~20B 4} beam portions 20M membrane portion 20a notch 21 the lower insulating film 22 upper insulating film 23 rib insulating film 24 thermistor protective film 30 heater resistor 31 , 32 Lead conductor portions 41, 42 Terminal electrode 50 Stopper film 60 Thermistor 61, 62 Thermistor electrode 63, 64 Terminal electrode 70 Catalyst R Rib

Claims (7)

A substrate having a cavity,
A membrane portion located on a cavity portion of the substrate and supported by a beam portion extending from the surface of the substrate;
A heater resistor formed on the membrane part,
A sensor element, wherein a rib extending in a length direction connecting the substrate and the membrane portion is provided on a surface of the beam portion.   The sensor element according to claim 1, wherein the rib is provided on both sides in the width direction of the beam portion.   The sensor element according to claim 1, wherein the rib is provided at a central portion in the width direction of the beam portion. The membrane part and the beam part are composed of a part of an insulating film covering the surface of the substrate,
4. The insulating film located on the hollow portion has a plurality of cutout portions, and is thereby partitioned into the membrane portion and the beam portion. The sensor element according to item.   The beam portion includes a main body portion made of the insulating film, the rib, and a stopper film located between the main body portion and the rib and made of a material different from the insulating film. Item 5. The sensor element according to Item 4. The sensor element according to any one of claims 1 to 5,
A thermistor formed on the membrane part so as to overlap the heater resistance;
A gas sensor comprising: a pair of thermistor electrodes connected via the thermistor.   The gas sensor according to claim 6, further comprising a catalyst that is formed on the membrane portion so as to overlap the heater resistance and the thermistor, and that promotes combustion of the detection target gas.

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