JP7421441B2 - MEMS type semiconductor gas detection element - Google Patents

Description

The present invention relates to a MEMS type semiconductor gas sensing element.

BACKGROUND ART Conventionally, as a gas detection element for a gas detector, a MEMS type semiconductor gas detection element equipped with a gas sensitive part for detecting a gas to be detected has been used, for example, as disclosed in Patent Document 1. The MEMS type semiconductor gas sensing element of Patent Document 1 includes a substrate, an electrode and a heater provided on the substrate, and a gas sensing section electrically connected to the electrode and thermally connected to the heater. .

Japanese Patent Application Publication No. 2016-70704

In such a MEMS type semiconductor gas sensing element, the gas sensing portion is provided in direct contact with an electrode provided on a substrate, as disclosed in Patent Document 1. However, the adhesion of the gas sensitive part to the electrode is not necessarily sufficient, and it is difficult to ensure a good electrical connection between the gas sensitive part and the electrode. If a good electrical connection cannot be secured between the gas sensitive part and the electrode, it will not be possible to accurately detect changes in the resistance value of the gas sensitive part that occur when the gas to be detected comes into contact with the gas sensitive part. . Furthermore, low adhesion between the gas sensitive part and the electrode also causes changes in gas detection ability over time; for example, when exposed to high temperature and high humidity environments, gas detection sensitivity deteriorates over time. Such problems arise.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a MEMS type semiconductor gas sensing element with excellent adhesion of a gas sensitive part to an electrode.

The MEMS type semiconductor gas sensing element of the present invention includes a substrate, an electrode provided on the substrate, a heater provided on the substrate, electrically connected to the electrode, and thermally connected to the heater. A MEMS type semiconductor gas sensing element comprising a gas sensitive section provided on the substrate, the adhesiveness of which is higher with respect to the gas sensitive section compared to the electrode, and a conductive element that connects the electrode and the gas sensitive section. The conductive film is connected to the top surface of at least a portion of the electrode so as not to electrically short-circuit the electrode through a path different from the path of the electrode.

Further, it is preferable that the conductive film is formed mainly of a metal oxide semiconductor containing the same metal element as the metal element of the metal oxide semiconductor included in the gas sensitive part.

Further, the MEMS type semiconductor gas sensing element includes an insulating film having a higher electrical resistance than the electrode and the conductive film, and the insulating film has a path different from (shorter than) a path of the conductive film. It is preferable that the electrode be formed in a gap between two different points of the electrode so as not to electrically short-circuit the electrode along the path.

Further, it is preferable that at least a portion of the conductive film is provided on the insulating film.

Further, the electrode has a first end region including a first end connected to one lead wire, and a second end region including a second end connected to the other lead wire. and a main body region extending between the first end region and the second end region and connecting the first end region and the second end region, Preferably, a membrane is connected to said first end region and said second end region.

Further, the electrode also serves as the heater, the conductive film and the insulating film are denser than the gas sensitive part, and the conductive film and the insulating film are attached to the heater so as to cover the heater. Preferably, they are connected.

According to the present invention, it is possible to provide a MEMS type semiconductor gas sensing element with excellent adhesion of a gas sensitive part to an electrode.

FIG. 1 is a top view of a MEMS type semiconductor gas sensing element according to a first embodiment of the present invention. 2 is a sectional view taken along the line II-II in FIG. 1. FIG. FIG. 3 is a sectional view showing a modification of the MEMS type semiconductor gas sensing element shown in FIG. 2; FIG. 3 is a top view of a MEMS type semiconductor gas sensing element according to a second embodiment of the present invention. 5 is a sectional view taken along the line IV-IV in FIG. 4. FIG. FIG. 6 is a sectional view showing a modification of the MEMS type semiconductor gas sensing element shown in FIG. 5; 2 is a graph showing a change in sensor output with respect to a change in gas concentration of a MEMS type semiconductor gas sensing element according to an example, in which (a) is a graph for example 1, and (b) is a graph for example 3. It is a graph showing a sensor output change with respect to a gas concentration change of a MEMS type semiconductor type gas detection element of a comparative example. It is a graph showing the relationship between the number of days elapsed when the MEMS type semiconductor gas detection elements of Examples and Comparative Examples were left in a standard environment of 20 ° C. and 60% RH and the methane concentration at which the gas detector issues an alarm, (a) is a graph of Example 3, and (b) is a graph of Comparative Example 2. This is a graph showing the relationship between the number of days that have passed when the MEMS type semiconductor gas sensing elements of Examples and Comparative Examples were left in a high temperature and high humidity environment of 40°C and 85% RH, and the methane concentration at which the gas detector issues an alarm. (a) is a graph of Example 3, and (b) is a graph of Comparative Example 2. It is a graph showing the relationship between the power input to the electrode (heater) and the disconnection life until the electrode (heater) disconnects in samples of Examples and Comparative Examples.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, MEMS type semiconductor gas detection elements according to two embodiments of the present invention will be described with reference to the accompanying drawings. However, the embodiments shown below are merely examples, and the MEMS type semiconductor gas sensing element of the present invention is not limited to the following examples.

<First embodiment>
The MEMS type semiconductor gas detection element of this embodiment is used, for example, in an environment such as the atmosphere, to detect a gas to be detected contained in the environment. MEMS type semiconductor gas detection elements detect the target gas by utilizing the change in resistance (or electrical conductivity) caused by the chemical reaction between oxygen adsorbed on the surface and the target gas in the environment. Detect. The gas to be detected is not particularly limited, and examples include methane, butane, isobutane, propane, carbon monoxide, hydrogen, and ethanol.

The MEMS type semiconductor gas sensing element 1 has a MEMS (Micro Electro Mechanical System) structure, as shown in FIGS. 1 and 2. The MEMS structure refers to a device structure in which at least a portion of element components are integrated on a substrate such as a silicon substrate by microfabrication technology. Since the MEMS type semiconductor gas sensing element 1 has a MEMS structure, it can be made smaller and can be driven with lower power consumption than a coil type semiconductor gas sensing element.

As shown in FIGS. 1 and 2, the MEMS type semiconductor gas sensing element 1 includes a substrate 2, an electrode 3 provided on the substrate 2, a heater 4 provided on the substrate 2, and electrical connection to the electrode 3. It also includes a gas sensitive section 5 provided on the substrate 2 so as to be thermally connected to the heater 4, and a conductive film 6 that connects the electrode 3 and the gas sensitive section 5. The MEMS type semiconductor gas sensing element 1 may optionally include a functional layer 7 covering the gas sensitive section 5. Note that in FIG. 1 (also in FIG. 4), in order to make the arrangement of the electrodes 3 and heaters 4 easier to see, illustrations of the gas sensitive section 5 and functional layer 7 are omitted, and the conductive film 6 (in FIG. 4, an insulating Membrane 8) is also indicated by a chain double-dashed line.

The MEMS type semiconductor gas detection element 1 is incorporated into, for example, a known bridge circuit (not shown) to reduce resistance due to a chemical reaction between the adsorbed oxygen on the surface of the gas sensing section 5 and the detection target gas in the ambient atmosphere. A change in value is detected. The MEMS type semiconductor gas sensing element 1 is incorporated into a bridge circuit via an electrode 3 in order to detect a change in the resistance value of the gas sensing section 5. The bridge circuit uses a potentiometer to measure a change in potential difference within the circuit caused by a change in resistance value in the MEMS semiconductor gas detection element 1, and outputs the change in potential difference as a detection signal of the gas to be detected. However, the MEMS type semiconductor gas detection element 1 is limited to a bridge circuit as long as it can detect a change in resistance value that occurs due to a chemical reaction between the adsorbed oxygen on the surface of the gas sensing part 5 and the gas to be detected. Rather, it may be used by being incorporated into a circuit different from the bridge circuit.

The substrate 2 is a member that supports the electrode 3, the heater 4, the gas sensitive part 5, and the conductive film 6 so as to be electrically insulated from the substrate 2, and the functional layer 7 and the insulating layer in the second embodiment. When the membrane 8 and the adhesive layer 9 are provided, they are also included and supported. Hereinafter, the electrode 3, the heater 4, the gas sensitive part 5, and the conductive film 6 (including the functional layer 7, the insulating film 8 in the second embodiment, and the adhesive layer 9 if provided) will be collectively referred to as "integrated part A". Also called. The structure of the substrate 2 is not particularly limited as long as it can support the integrated section A in an electrically insulated state with respect to the substrate 2. In this embodiment, as shown in FIGS. 1 and 2, the substrate 2 includes a substrate body 21, an insulating support film 22 supported by the substrate body 21, and a structure between the substrate body 21 and the insulating support film 22. A cavity 23 is provided.

The substrate body 21 is a member that supports an insulating support film 22 and supports the integrated part A via the insulating support film 22. As shown in FIG. 2, the substrate main body 21 is provided below the insulating support film 22 (on the side opposite to the side where the integrated section A is provided), and supports the insulating support film 22 from below. A recess 21 a is formed in the substrate body 21 to form a cavity 23 between the substrate body 21 and the insulating support film 22 . However, the substrate main body 21 only needs to be formed so that a cavity 23 is provided between it and the insulating support film 22, for example, as shown in the modified example of FIG. 3 (the modified example of FIG. 6 is also the same). , without having the recessed portion 21a, it may have a structure in which the end portion of the insulating support film 22 is supported from below, but the substrate body 21 does not exist below the central portion of the insulating support film 22 at all. The substrate body 21 is not particularly limited as long as it can support the insulating support film 22, and is formed of, for example, silicon.

The insulating support film 22 is a member that supports the stacking section A so that the stacking section A and the substrate main body 21 are electrically insulated. The insulating support film 22 is provided on the substrate body 21 and supported by the substrate body 21, as shown in FIG. The insulating support film 22 is formed into a film shape of an insulator. In this embodiment, the insulating support film 22 includes a silicon oxide film 22a connected to the substrate body 21, a silicon nitride film 22b provided on the silicon oxide film 22a, and a silicon oxide film 22c provided on the silicon nitride film 22b. These three layers are laminated and formed. The insulating support film 22 can be formed, for example, by a known film forming technique such as CVD.

The insulating support film 22 only needs to be able to support the integrated portion A so as to electrically insulate it from the substrate body 21, and its layer structure, constituent material, and film thickness are not particularly limited. For example, although the insulating support film 22 has a three-layer structure in this embodiment, it may have a single-layer structure or a multi-layer structure other than three layers. Furthermore, although the insulating support film 22 is formed of a silicon oxide film or a silicon nitride film in this embodiment, it may be formed of other insulators such as aluminum oxide. Further, the thickness of the insulating support film 22 is not particularly limited, and can be appropriately set so as to be able to support the integrated portion A while electrically insulating it from the substrate body 21.

In this embodiment, as shown in FIGS. 1 and 2, the insulating support film 22 includes a main body part 221 that supports the integrated part A, a base part 222 provided on the substrate main body 21, and the main body part 221 and the base part 222. and a connecting portion 223 for connecting the two. The insulating support film 22 is supported by the substrate main body 21 via the base portion 222 and supports the integrated portion A via the main body portion 221. The main body portion 221, the base portion 222, and the connection portion 223 can be formed, for example, by a known etching technique after forming the uniform insulating support film 22 on the substrate main body 21.

The main body portion 221 is connected to the base portion 222 via the connecting portion 223 and is supported by the substrate body 21 via the connecting portion 223 and the base portion 222. The main body section 221 is provided apart from the substrate main body 21 via a cavity 23 formed between the main body section 221 and the substrate main body 21 . In the MEMS type semiconductor gas detection element 1, the accumulation part A is provided in the main body part 221 provided apart from the substrate main body 21, thereby suppressing heat applied to the accumulation part A from being conducted to the substrate main body 21. be able to. Thereby, in the MEMS type semiconductor gas detection element 1, the integrated portion A can be heated more efficiently, and driving with low power consumption becomes possible. In this embodiment, the main body portion 221 is formed into a substantially circular shape when viewed from above, as shown in FIG. However, the main body part 221 is not particularly limited as long as it is provided apart from the substrate main body 21 and can support the accumulation part A, and may be formed in other shapes such as a substantially rectangular shape when viewed from above. good.

The base 222 is provided on the substrate body 21 and supported by the substrate body 21, as shown in FIGS. 1 and 2. Further, the base portion 222 is connected to the main body portion 221 via the connecting portion 223 and supports the main body portion 221 via the connecting portion 223. In this embodiment, the base portion 222 is formed into a frame shape with a substantially rectangular hollowed out central portion, and the hollow portion 23 is formed within the frame. However, the base 222 is not particularly limited as long as it can be provided on the board main body 21 and support the main body 221 via the connection part 223, and the base 222 may be hollowed out in other shapes such as a substantially circular shape. It may be formed into a frame shape.

As shown in FIG. 1, the connecting portion 223 is connected to the main body 221 and the base 222, and supports the main body 221 while being supported by the base 222. The connecting portion 223 is provided apart from the substrate body 21 via a cavity 23 formed between the connecting portion 223 and the substrate body 21 . By providing the connecting portion 223 that connects the main body portion 221 to the base portion 222 at a distance from the substrate main body 21, conduction of heat applied to the integrated portion A to the substrate main body 21 can be suppressed. The connecting portion 223 is connected to the inner surface of the frame of the base 222 and is formed to extend from the inner surface of the frame of the base 222 toward the main body portion 221 located approximately at the center inside the frame of the base 222 . In this embodiment, the connecting portions 223 are connected to each of the four inner surfaces of the frame of the base portion 222, and extend from the main body with approximately equal lengths from four directions in which the angles between adjacent connecting portions 223 are approximately equal. 221 is supported. Therefore, the connecting portion 223 can support the main body portion 221 in a well-balanced manner. However, the connection part 223 is not limited to the illustrated example, as long as it can connect the main body part 221 and the base part 222 and support the main body part 221.

The electrode 3 is a member for detecting a change in resistance value of the gas sensitive section 5. As shown in FIGS. 1 and 2, the electrode 3 is provided on the main body 221 of the insulating support film 22 of the substrate 2, and at least a portion thereof is electrically connected to the gas sensitive section 5. The electrode 3 includes a first end 3a and a second end 3b, the first end 3a is connected to one lead wire L1, and the second end 3b is connected to the other lead wire L2. be done. The lead wires L1 and L2 are formed to have lower electrical resistance than the electrode 3. One and the other lead wires L1 and L2 are connected to, for example, a known bridge circuit (not shown), and the resistance value between the first end 3a and the second end 3b of the electrode 3 is measured. By doing so, the combined resistance value of the electrode 3 and the gas sensitive section 5 can be measured. Then, by measuring the change in the combined resistance value of the electrode 3 and the gas sensitive section 5, a change in the resistance value of the gas sensitive section 5 can be detected.

In this embodiment, the electrode 3 also functions as a heater 4 that generates heat when energized and heats the gas sensitive section 5 (and the functional layer 7 if the functional layer 7 is provided). That is, in the MEMS type semiconductor gas detection element 1 of this embodiment, the electrode 3 also serves as the heater 4, and conversely, the heater 4 also serves as the electrode 3. Therefore, the electrode 3 and the heater 4 can detect a change in the resistance value of the gas sensitive section 5, and can heat the gas sensitive section 5 to a temperature suitable for detecting the gas to be detected by energization. However, the electrode 3 only needs to be able to detect at least a change in the resistance value of the gas sensitive section 5, and may be provided separately from the heater 4 for heating the gas sensitive section 5. Further, the heater 4 only needs to be able to heat at least the gas sensitive section 5, and may be provided separately from the electrode 3 that detects a change in the resistance value of the gas sensitive section 5. In the following, detailed explanation of the heater 4 will be omitted by explaining the details of the electrode 3. When the electrode 3 and the heater 4 are provided separately, both the electrode 3 and the heater 4 can have the same configuration as described below, or one of the electrode 3 and the heater 4 can have the same configuration as described below. The electrode 3 and the heater 4 can have the same configuration as the configuration described below, and the other of the electrode 3 and the heater 4 can have a configuration different from the configuration described below, or both the electrode 3 and the heater 4 can have a configuration different from the configuration described below. can.

The electrode 3 only needs to be able to detect a change in the resistance value of the gas sensitive section 5, and its constituent material is not particularly limited. The electrode 3 can be made of, for example, a noble metal such as platinum or a platinum-rhodium alloy. The electrode 3 can be formed, for example, by a known etching technique after forming a uniform film using the material for the electrode 3. Note that, as shown in FIG. 2, for example, the electrode 3 may be optionally provided with a second electrode in order to increase the adhesion with the main body portion 221 of the insulating support film 22 of the substrate 2, and as shown in FIG. In order to improve the adhesion with the insulating film 8, which will be described later in connection with the MEMS type semiconductor gas sensing element 100 of the embodiment, the main body portion 221 and the insulating film 8 are bonded to each other through an adhesive layer 9 formed of tantalum oxide or the like. May be connected.

The electrode 3 may be arranged so as to be able to detect a change in the resistance value of the gas sensitive section 5, and its wiring route is not particularly limited. In this embodiment, as shown in FIG. 1, the electrode 3 has a first end region 31 including a first end 3a connected to one lead wire L1, and is connected to the other lead wire L2. a second end region 32 including a second end portion 3b which extends between the first end region 31 and the second end region 32; and a main body region 33 connecting the end region 32 of the main body region 32 to the end region 32 of the main body region 33 . The electrode 3 comprises a first end region 31, a second end region 32 and a body region 33 and is configured as a single electrode. However, the electrodes are not limited to this embodiment as long as they can detect a change in the resistance value of the gas sensitive section, and may be composed of two or more electrodes separated from each other.

The first end region 31 is a part of the electrode 3 including the first end 3a and adjacent to the first end 3a. The first end region 31 is constituted by a part of the electrode 3 within a predetermined length range from the first end 3a. In this embodiment, the first end region 31 includes a first end 3a disposed near the end of the substrate 2 (main body portion 221), and a first end region 31, as shown in FIG. This is a region extending from 3a toward the center of the substrate 2 and between the first proximal portion 3c, which is the portion closest to the center of the substrate 2. In this embodiment, the first end region 31 extends substantially linearly from the first end 3a toward the center of the substrate 2 over a substantially shortest distance. However, the first end region 31 is limited to the illustrated example as long as it extends from the first end 3a at least toward the center of the substrate 2 without moving away from the center. However, it may extend in a curved manner. The first end region 31 is a portion of the electrode 3 that has a first end 3a arranged near the center of the substrate 2 and extends from the first end 3a in a direction away from the center of the substrate 2. It may be configured by

The second end region 32 is a part of the electrode 3 including the second end 3b and adjacent to the second end 3b. The second end region 32 is constituted by a part of the electrode 3 within a predetermined length range from the second end 3b. In this embodiment, the second end region 32 includes a second end 3b disposed near the end of the substrate 2 (main body portion 221) and a second end, as shown in FIG. This is a region extending from 3b toward the center of the substrate 2 and between the second proximal portion 3d, which is the portion closest to the center of the substrate 2. In this embodiment, the second end region 32 extends substantially linearly from the second end 3b toward the center of the substrate 2 over a substantially shortest distance. However, the second end region 32 is not limited to this embodiment as long as it extends from the second end 3b at least toward the center of the substrate 2 without moving away from the center. Instead, it may extend in a curved manner. Further, in this embodiment, the second end region 32 extends substantially parallel to and in a straight line with the first end region 31 and has substantially the same length as the first end region 31. may be provided at an angle with respect to the first end region 31, and may have a different length from the first end region 31. The second end region 32 is a portion of the electrode 3 that has a second end 3b arranged near the center of the substrate 2 and extends from the second end 3b in a direction away from the center of the substrate 2. It may be configured by

In this embodiment, as shown in FIG. 1, the first end region 31 and the second end region 32 are The area is larger than the area per unit length of the main body region 33 (wider than the main body region 33). Therefore, as described below regarding the MEMS type semiconductor gas sensing element 100 of the second embodiment, the conductive film 6 can be easily provided in the first end region 31 and the second end region 32, and A wide connection area can be secured. Further, in this embodiment, the first end region 31 and the second end region 32 are provided close to each other, as shown in FIG. 1 . More specifically, the first end region 31 and the second end region 32 are such that the distance between the first end region 31 and the second end region 32 is the same as that of the substrate 2 (main body portion). 221), and are provided close to each other so that the distance is shorter than 1/2 of the distance from the center to the outer edge of 221). Therefore, the gas sensitive section 5 provided so as to be electrically connected to the first end region 31 and the second end region 32 can be formed smaller. Even if the gas sensitive part 5 is made small, the combined resistance value of the electrode 3 and the gas sensitive part 5 is the parallel combined resistance value of the almost entire electrical resistance value of the electrode 3 and the electrical resistance value of the gas sensitive part 5. Therefore, a slight change in the resistance value of the gas sensitive section 5 can be detected, and high detection sensitivity of the gas to be detected can be ensured. From the viewpoint of forming the gas sensitive part 5 smaller, the distance between the first end region 31 and the second end region 32 is, for example, 2/3 of the distance from the center to the outer edge of the substrate 2. The distance is preferably below, more preferably 1/2 or less of the distance from the center of the substrate 2 to the outer edge, and even more preferably 1/3 or less of the distance from the center of the substrate 2 to the outer edge.

Further, in this embodiment, the first end region 31 and the second end region 32 extend to the vicinity of the center of the substrate 2 (main body portion 221), as shown in FIG. More specifically, the first end region 31 and the second end region 32 are close to the center of the substrate 2 to a distance shorter than 1/2 of the distance to the outer edge of the substrate 2. It is extending. Therefore, the gas sensitive portion 5 can be formed smaller near the center of the substrate 2. Furthermore, by providing the gas sensitive section 5 only in the vicinity of the center of the substrate 2, the functional layer 7 can be formed with a sufficient thickness over the entire end of the gas sensitive section 5. can be further increased. From the viewpoint of providing the gas sensitive section 5 near the center of the substrate 2, the distance between each of the first end region 31 and the second end region 32 and the center of the substrate 2 is, for example, It is preferably 2/3 or less of the distance from the center to the outer edge, more preferably 1/2 or less of the distance from the center to the outer edge of the substrate 2, and 1/2 of the distance from the center to the outer edge of the substrate 2. It is even more preferable that it is 3 or less.

The main body region 33 is a part of the electrode 3 that connects the first end region 31 and the second end region 32 . If the main body region 33 extends between the first end region 31 and the second end region 32 so as to connect the first end region 31 and the second end region 32, The arrangement is not particularly limited. In this embodiment, as shown in FIG. 1, the main body region 33 extends in a direction perpendicular to a straight line S connecting the first end 3a and the second end 3b on the substrate 2 (main body 221). (first region 221a), and the other side (second region 221b) in the direction perpendicular to the straight line S connecting the first end 3a and second end 3b on the substrate 2. It extends to By providing the main body region 33 in the two opposing regions 221a and 221b on the substrate 2 (main body portion 221), even if the temperature of the electrode 3 (heater 4) is increased to heat the gas sensitive portion 5, Since the substrate 2 is heated more uniformly, bending of the substrate 2 due to heat is suppressed.

In this embodiment, the main body region 33 includes a first main body region 331 provided in the first region 221a of the substrate 2 (main body portion 221) and a second region 221b of the substrate 2, as shown in FIG. and an intermediate region 333 provided between the first body region 331 and the second body region 332.

As shown in FIG. 1, the first main body region 331 is located on the first region 221a of the substrate 2 (main body portion 221) at one end of the first end region 31. It extends from the other end (first proximal part 3c) opposite to the end 3a to the intermediate region 333. More specifically, the first main body region 331 extends in a meandering manner from the other end of the first end region 31 toward the end of the substrate 2 (upward in the figure), and After extending along the edge of the substrate 2 , it extends toward the center of the substrate 2 and extends to the intermediate region 333 . As a result, the first main body region 331 is arranged at a high density within the first region 221a, so that a long wiring length can be ensured and a high electrical resistance value can be ensured.

As shown in FIG. 1, the second main body region 332 is located on the second region 221b of the substrate 2 (main body portion 221), and is located at one end of the second end region 32. It extends from the other end (second proximal part 3d) opposite to the end 3b to the intermediate region 333. More specifically, the second main body region 332 extends from the other end of the second end region 32 toward the end of the substrate 2 (downward in the figure) while meandering, After extending along the edge of the substrate 2 , it extends toward the center of the substrate 2 and extends to the intermediate region 333 . Thereby, the second main body region 332 is arranged at a high density within the second region 221b, so that a long wiring length can be ensured and a high electrical resistance value can be ensured.

In this embodiment, the first body region 331 and the second body region 332 are formed to have substantially the same length and have substantially the same electrical resistance as each other, as shown in FIG. Thereby, even if the temperature of the electrode 3 (heater 4) is increased to heat the gas sensitive section 5, the substrate 2 is heated more uniformly, so that the substrate 2 is prevented from being bent due to heat. Further, the first main body region 331 and the second main body region 332 are arranged substantially point-symmetrically with respect to the substantially center of the substrate 2 . Thereby, when the temperature of the electrode 3 (heater 4) is raised, the substrate 2 is heated even more uniformly, so that the substrate 2 is further suppressed from being bent due to heat.

Intermediate region 333 connects first body region 331 and second body region 332, as shown in FIG. The intermediate region 333 is formed by a straight line S connecting the first end 3a and the second end 3b at the boundary between the first region 221a and the second region 221b of the substrate 2 (main body portion 221). They are provided so as to intersect (orthogonally in the illustrated example) and extend between the first region 221a and the second region 221b. In this embodiment, the first main body region 331 and the second main body region 332 provided on both sides of the intermediate region 333 are formed to have substantially the same length, so that the intermediate region 333 is It is located at approximately the mid-length position of the main body region 33 in the direction. The intermediate region 333 is provided approximately at the center of the substrate 2 between the first end region 31 and the second end region 32 . Between the first end region 31 and the second end region 32, only the intermediate region 333 is provided without providing the first main body region 331 and the second main body region 332.

The gas sensitive portion 5 is a portion whose electrical resistance changes due to a chemical reaction between the oxygen adsorbed on the surface and the gas to be detected. The gas sensitive section 5 is not particularly limited as long as it is made of a material whose electrical resistance changes upon contact with the gas to be detected, and can be made of, for example, a material whose main component is a metal oxide semiconductor. The gas sensitive section 5 is provided on the substrate 2 so as to be electrically connected to the electrode 3 and thermally connected to the heater 4, as shown in FIGS. 1 and 2. By providing the gas sensitive section 5 to be electrically connected to the electrode 3, a change in the electrical resistance of the gas sensitive section 5 can be detected via the electrode 3. Further, by providing the gas sensitive section 5 so as to be thermally connected to the heater 4, the gas sensitive section 5 can be heated to a temperature suitable for detecting the gas to be detected via the heater 4.

The metal oxide semiconductor of the gas sensing section 5 is not particularly limited as long as it has an electrical resistance that changes with the chemical reaction between the adsorbed oxygen and the gas to be detected. For example, it is preferable to use an n-type semiconductor as the metal oxide semiconductor of the gas sensing part 5 from the viewpoint of promoting oxygen adsorption and the chemical reaction between the adsorbed oxygen and gas components and improving gas detection sensitivity. It is more preferable to use a metal oxide semiconductor containing at least one selected from tin oxide, indium oxide, zinc oxide, and tungsten oxide, and a metal containing at least one selected from tin oxide and indium oxide. It is even more preferable to use an oxide semiconductor.

A metal element may be added as a donor to the metal oxide semiconductor of the gas sensitive portion 5 in order to adjust the electrical resistance. The metal element to be added is not particularly limited as long as it can be added to the metal oxide semiconductor as a donor and can adjust the electrical resistance of the metal oxide semiconductor, but for example, antimony , niobium, and tungsten. Furthermore, oxygen vacancies may be introduced into the metal oxide semiconductor of the gas sensitive portion 5 in order to adjust the electrical resistance. The metal element concentration and oxygen vacancy concentration can be appropriately set depending on the required electrical resistance.

The gas sensitive section 5 may be provided on the substrate 2 so that a change in resistance can be detected by the electrode 3 and may be heated by the heater 4, and the method of forming it is not particularly limited. The gas sensitive part 5 is formed, for example, by mixing fine powder of a metal oxide semiconductor in a solvent to form a paste and applying it onto the substrate 2 on which the electrodes 3 and the heater 4 have been previously provided and drying it. Is possible.

The functional layer 7, which is optionally provided to cover the gas sensitive section 5, has a function of improving the selectivity of the detection target gas in the gas sensitive section 5, a function of suppressing deterioration of the gas sensitive section 5, etc. This layer has the function of improving the gas detection characteristics of No. 5. The functional layer 7 is provided on the gas sensitive part 5 so as to cover the gas sensitive part 5. In the MEMS type semiconductor gas sensing element 1 of this embodiment, the gas sensitive section 5 is provided on a part of the substrate 2. Thereby, the functional layer 7 provided on the gas sensitive section 5 can be formed with a required thickness even in the end region of the gas sensitive section 5, so that deterioration in functionality can be suppressed. Therefore, in the MEMS type semiconductor gas sensing element 1 of this embodiment, the overall function of the functional layer 7 can be improved compared to the case where the gas sensitive section 5 is provided on the entire substrate 2.

In this embodiment, two types of layers (hereinafter referred to as a first functional layer and a second functional layer) having functions of suppressing deterioration of the gas sensitive section 5 and protecting the gas sensitive section 5 are exemplified as the functional layer 7. be done. However, the functional layer 7 is not particularly limited as long as it has the function of improving the gas detection characteristics of the gas sensitive part 5. A known layer having a function of improving the gas detection characteristics of the gas sensitive section can be employed.

The first functional layer, which is a first example, protects the gas sensitive section 5 from specific gas components (for example, organic silicone gas) other than the detection target gas contained in the environmental atmosphere, and improves the durability of the gas sensitive section 5. Improve. The first functional layer is formed by, for example, poisoning the gas sensitive part 5 when an organic silicone gas (for example, hexamethyldisiloxane, etc.) contained in the environmental atmosphere adheres to the gas sensitive part 5. This prevents the MEMS type semiconductor gas detection element 1 from malfunctioning due to a change in detection sensitivity.

The first functional layer is formed by supporting a metal oxide on a metal oxide semiconductor for the purpose of protecting the gas sensitive part 5 and improving the durability of the gas sensitive part 5. The metal oxide semiconductor is not particularly limited, and for example, a metal oxide semiconductor containing at least one selected from tin oxide, indium oxide, zinc oxide, and tungsten oxide can be used. The metal oxide is a metal oxide that can protect the gas sensitive part 5 from specific gas components, such as chromium oxide, palladium oxide, cobalt oxide, iron oxide, rhodium oxide, copper oxide, cerium oxide, platinum oxide. At least one selected from , tungsten oxide, and lanthanum oxide can be used. Among the examples listed above, the metal oxide is preferably at least one selected from chromium oxide and palladium oxide, from the viewpoint of further suppressing deterioration of the gas sensitive section 5.

The method of forming the first functional layer is not particularly limited as long as it can protect the gas sensitive section 5 from specific gas components and improve the durability of the gas sensitive section 5. The first functional layer is formed, for example, by mixing a mixture of a fine powder of a metal oxide semiconductor and a fine powder of a metal oxide in a solvent to form a paste, which is applied to the gas sensitive part 5 and dried. be able to.

The second functional layer, which is the second example, is made of an insulating oxide for the same purpose as the first functional layer. The second functional layer protects the gas sensitive section 5 by capturing specific gas components using an insulating oxide. In addition, since the second functional layer is made of an insulating oxide, the flow of current in the second functional layer is suppressed, and the influence on the resistance value change of the gas sensitive part 5 when detecting the gas to be detected is reduced. Therefore, it is possible to suppress a decrease in the detection sensitivity of the gas to be detected. The insulating oxide is not particularly limited, but for example, at least one selected from aluminum oxide and silicon oxide is exemplified.

The second functional layer may be formed by supporting an oxidizing active metal oxide on an insulating oxide. The second functional layer is formed by supporting a metal oxide having oxidation activity on an insulating oxide, so that deterioration of the gas sensitive section 5 can be further suppressed. Examples of the metal oxide having oxidizing activity include at least one selected from chromium oxide, palladium oxide, cobalt oxide, iron oxide, rhodium oxide, copper oxide, cerium oxide, platinum oxide, tungsten oxide, and lanthanum oxide. is exemplified. Among the examples listed above, the metal oxide is preferably at least one selected from chromium oxide and palladium oxide, from the viewpoint of further suppressing deterioration of the gas sensitive section 5.

The method of forming the second functional layer is not particularly limited as long as it can protect the gas sensitive section 5 from specific gas components and improve the durability of the gas sensitive section 5. The second functional layer is formed, for example, by mixing a mixture of insulating oxide fine powder and metal oxide fine powder with a solvent to form a paste, applying it to the gas sensitive part 5, and drying it. be able to.

The conductive film 6 has conductivity and electrically connects the electrode 3 and the gas sensitive part 5. The conductivity (or electrical resistance) of the conductive film 6 is not particularly limited as long as it allows the electrode 3 to detect a change in the resistance value of the gas sensitive part 5 through the conductive film 6; It is preferable that the conductivity is higher than that of the part 5 (or lower than the electrical resistance of the gas sensitive part 5). Further, the conductive film 6 has higher adhesion to the gas sensitive part 5 than the electrode 3, and preferably has higher adhesion to the electrode 3 compared to the gas sensitive part 5, It is interposed between the electrode 3 and the gas sensitive section 5 to connect the electrode 3 and the gas sensitive section 5 to each other. By connecting the electrode 3 and the gas sensitive part 5 through the conductive film 6, which has higher adhesion to the gas sensitive part 5 than the electrode 3, the adhesion of the gas sensitive part 5 to the electrode 3 can be increased. can. Thereby, a good electrical connection can be ensured between the electrode 3 and the gas sensitive part 5, and the change in the resistance value of the gas sensitive part 5 that occurs when the gas to be detected comes into contact with the gas sensitive part 5 can be further suppressed. Can be detected accurately. Furthermore, it is possible to suppress changes over time in the gas detection ability of the MEMS type semiconductor gas detection element 1, and to suppress deterioration in gas detection sensitivity over time that occurs when exposed to a high temperature and high humidity environment, for example. .

The conductive film 6 only needs to have conductivity and have higher adhesion to the gas sensitive part 5 than the electrode 3, and its constituent material is not particularly limited. In this embodiment, the conductive film 6 is formed mainly of a metal oxide semiconductor containing the same metal element as that of the metal oxide semiconductor contained in the gas sensitive section 5 . Specifically, for example, when the main component of the gas sensitive section 5 is tin oxide, the conductive film 6 contains tin oxide as the main component, and when the main component of the gas sensitive section 5 is indium oxide, the conductive film 6 contains tin oxide. Contains indium oxide as a main component. Since the conductive film 6 is formed mainly of a metal oxide semiconductor containing the same metal element as the metal element of the metal oxide semiconductor contained in the gas sensitive part 5, the gas sensitive part 5 and the conductive film 6 are mutually connected to each other. It is easy to fit in, and the adhesion between the gas sensitive part 5 and the conductive film 6 can be further improved. The thickness of the conductive film 6 is not particularly limited and can be set as appropriate so that the electrode 3 and the gas sensitive section 5 can be connected.

The method of forming the conductive film 6 is not particularly limited as long as it has conductivity and can be formed to have higher adhesion to the gas sensitive portion 5 than the electrode 3. In this embodiment, the conductive film 6 can be formed by sputtering or vacuum deposition. When the conductive film 6 is formed by sputtering or vacuum deposition, it is formed as a denser film than when it is formed by coating or the like. By forming the conductive film 6 as a denser film, it can further improve its adhesion to the gas sensitive part 5, and can also improve its adhesion to the electrode 3 on the opposite side of the gas sensitive part 5 and the insulating film 8, which will be described later. can be increased. The conductive film 6 is formed by, for example, sputtering a target metal oxide semiconductor such as tin oxide or indium oxide with argon ions while heating the substrate 2 at a high temperature such as 300°C. It can be formed as According to this method, it is possible to not only increase the adhesion to the gas sensitive part 5, but also increase the conductivity by creating oxygen vacancies in the metal oxide semiconductor, and further increase the adhesion to the electrode 3 and the insulating film 8. Can be done. Note that the conductivity of the conductive film 6 may be increased (or the electrical resistance may be decreased) by adding a donor such as antimony, niobium, or tungsten.

As shown in FIGS. 1 and 2, the conductive film 6 is formed on at least a portion of the upper surface of the electrode 3 so as not to electrically short-circuit the electrode 3 through a path different from (shorter than) the path of the electrode 3. Connected. In this case, the combined resistance value of the electrical resistance value of the electrode 3 and the electrical resistance value of the gas sensitive part 5 is the combined resistance value of the electrode 3 to which the gas sensitive part 5 is connected, since short circuiting of the electrode 3 by the conductive film 6 is suppressed. This becomes a parallel composite resistance value of the overall electrical resistance value and the electrical resistance value of the gas sensing section 5. As a result, even if the conductive film 6 is provided, the combined resistance value of the electrical resistance value of the electrode 3 and the electrical resistance value of the gas sensitive part 5 changes greatly in accordance with the change in the electrical resistance value of the gas sensitive part 5. , it is possible to obtain high sensitivity for the gas to be detected. Furthermore, in the case where the electrode 3 also serves as the heater 4 as in this embodiment, short-circuiting of the heater 4 by the conductive film 6 is suppressed, making it possible for the heater 4 to function normally or in a near-normal state. can.

Here, "short-circuiting the electrodes 3 by a route different from the route of the electrodes 3" means, for example, that the conductive film 6 is arranged in a route different from the wiring route of the electrodes 3 on the substrate 2, and the conductive film 6 is , which means short-circuiting some of the electrodes 3 by bridging them by a route different from the wiring route of the electrodes 3. Note that "not to electrically short-circuit the electrodes 3 in a path different from the path of the electrodes 3" means not to short-circuit the electrodes 3 over at least part of the path, and not necessarily in any of the paths of the electrodes 3. This does not mean that it will not be short-circuited. However, in order to obtain high detection sensitivity for the detection target gas, it is preferable not to short-circuit the entire path of the electrode 3. Further, in the case where the electrode 3 also serves as the heater 4 as in this embodiment, it is preferable not to short-circuit the entire path of the heater 4 (electrode 3) in order to allow the heater 4 to function properly.

As described above, the conductive film 6 only needs to be connected to the upper surface of at least a portion of the electrode 3 so as not to electrically short-circuit the electrode 3 through a path different from that of the electrode 3, and its arrangement is particularly determined. Not limited. In this embodiment, the conductive film 6 is connected only to the upper surface of the electrode 3, as shown in FIGS. 1 and 2. More specifically, the conductive film 6 is connected only to the upper surface of the electrode 3 over the entire length and width of the electrode 3. As a result, the conductive film 6 can be routed through a route different from the route of the electrode 3 while increasing the connection area with the gas-sensitive unit 5 to further increase the adhesion of the gas-sensitive unit 5 to the entire electrode 3. Do not electrically short-circuit the electrode 3. In the MEMS type semiconductor gas sensing element 1, by further increasing the adhesion of the gas sensitive part 5 to the entire electrode 3, it is possible to ensure a better electrical connection between the electrode 3 and the gas sensitive part 5. , it is possible to more accurately detect a change in the resistance value of the gas sensitive section 5 that occurs when the gas to be detected comes into contact with the gas sensitive section 5. Furthermore, it is possible to further suppress changes over time in the gas detection ability of the MEMS type semiconductor gas detection element 1, and to further suppress deterioration in gas detection sensitivity over time that occurs when exposed to a high temperature and high humidity environment, for example. Can be done. Note that the conductive film 6 only needs to be connected to at least a part of the upper surface of the electrode 3 by a route different from the route of the electrode 3 so as not to electrically short-circuit the electrode 3. It may be provided as follows.

<Second embodiment>
Next, a MEMS type semiconductor gas sensing element 100 according to a second embodiment will be described with reference to FIGS. 4 and 5. In the following, the structure different from the MEMS type semiconductor gas sensing element 1 according to the first embodiment (mainly the conductive film 6 and the insulating film 8) will be mainly explained, and the explanation of other common structures will be omitted. Furthermore, in FIGS. 4 and 5, components having the same functions as components of the MEMS type semiconductor gas sensing element 1 according to the first embodiment are indicated by the same reference numerals.

Similarly to the conductive film 6 in the first embodiment, the conductive film 6 of the MEMS type semiconductor gas detection element 100 of this embodiment also connects the electrode 3 with an electrical path different from (shorter than) the path of the electrode 3. The electrode 3 is connected to the top surface of at least a portion of the electrode 3 so as not to cause a short circuit. In this embodiment, the conductive film 6 is connected to the first end region 31 and the second end region 32 of the electrode 3, as shown in FIGS. 4 and 5. As a result, the gas sensitive section 5 is electrically connected to the first end region 31 and the second end region 32, and the combined resistance value of the electrode 3 and the gas sensitive section 5 is determined by the length of the electrode 3. It becomes a parallel composite resistance value of the overall electrical resistance value and the electrical resistance value of the gas sensing section 5 in the horizontal direction. Thereby, the combined resistance value of the electrode 3 and the gas sensitive section 5 changes greatly in accordance with the change in the electrical resistance value of the gas sensitive section 5, so that high sensitivity can be obtained for the gas to be detected. Note that, in the illustrated example, the conductive film 6 is connected only to the upper surfaces of the first end region 31 and the second end region 32 of the electrode 3. However, the conductive film 6 is not limited to the illustrated example as long as it is connected to the electrode 3 so as not to short-circuit the electrode 3. It may be provided so as to protrude from the.

To explain more specifically, in this embodiment, as shown in FIGS. 4 and 5, the conductive film 6 includes a first conductive film 61 connected to the first end region 31 and a second conductive film 61 connected to the first end region 31. A second conductive film 62 connected to the end region 32 is provided. The first conductive film 61 and the second conductive film 62 are provided so as to be electrically isolated from each other except that they are electrically connected to each other via the electrode 3. Thereby, the conductive film 6 does not electrically short-circuit the electrode 3 through a path different from the path of the electrode 3.

As shown in FIGS. 4 and 5, the first conductive film 61 and the second conductive film 62 have electrode connecting parts 61a and 62a connected to the electrode 3, and a gas sensitive part connected to the gas sensitive part 5, respectively. The connecting portions 61b and 62b are provided. The electrode connecting parts 61a and 62a are provided on the insulating film 8 and the adhesive layer 9, which will be described later, from the gas sensitive part 5 side toward the electrode 3 (first end region 31 and second end region 32). It is provided to extend through the through hole. One end of the electrode connection parts 61a, 62a is connected to the first end area 31 and the second end area 32 of the electrode 3, and the other end of the electrode connection part 61a, 62a is connected to the gas sensitive part connection part 61b, 62b. The gas sensitive part connecting parts 61b and 62b have an area larger than the connection area with the electrode 3 of the electrode connecting parts 61a and 62a and larger than the surface area of the electrode 3 along the surface of the substrate 2 (main body part 221). It is arranged so that it spreads out in a planar manner. One surface of the gas sensitive part connecting parts 61b, 62b is connected to the gas sensitive part 5, and the other surface of the gas sensitive part connecting parts 61b, 62b is connected to the electrode connecting parts 61a, 62a and an insulating film 8, which will be described later. be done. In this way, by providing at least a portion of the conductive film 6 on the insulating film 8, the conductive film 6 can be provided so as to spread planarly along the surface of the substrate 2 without shorting the electrodes 3. becomes possible. This increases the connection area between the gas sensitive part 5 and the conductive film 6, improves the adhesion between the gas sensitive part 5 and the conductive film 6, and as a result, the electrode 3 and the gas sensitive part 5 The adhesion between the two can be further improved. Furthermore, the gas sensing portion connecting portions 61b and 62b, which have a larger area than the electrode connecting portions 61a and 62a and a surface area of the electrode 3, are connected to the gas sensing portion 5, thereby providing conductivity. The conduction between the membrane 6 and the gas sensitive section 5, and further the conduction between the electrode 3 and the gas sensitive section 5, can be ensured more reliably, and the change in the resistance value of the gas sensitive section 5 can be detected more reliably. Furthermore, it is possible to further suppress changes over time in the gas detection ability of the MEMS type semiconductor gas detection element 100, and to further suppress deterioration in gas detection sensitivity over time that occurs when exposed to a high temperature and high humidity environment, for example. Can be done. Each of the gas sensing portion connecting portions 61b and 62b has an area approximately half that of the substrate 2 (main body portion 221), and is formed approximately in a semicircular shape. The gas sensing portion connecting portions 61b and 62b are arranged in substantially semicircular straight portions so as to face each other along the straight line S connecting the first end 3a and the second end 3b of the electrode 3. They are spaced apart from each other with a gap G provided between them.

The MEMS type semiconductor gas sensing element 100 includes an insulating film 8 having a higher electrical resistance than the electrode 3 and the conductive film 6, as shown in FIGS. 4 and 5. The insulating film 8 is formed in the gap between two different points of the electrode 3 so that the conductive film 6 does not electrically short-circuit the electrode 3 through a path different (shorter) than the path of the electrode 3. More specifically, the insulating film 8 is provided so as to fill a region on the substrate 2 (main body portion 221) where the electrode 3 is not provided. This makes it possible to more reliably suppress short-circuiting of the electrodes 3 due to the conductive film 6, thereby achieving higher sensitivity to the gas to be detected.

The constituent material of the insulating film 8 is not particularly limited as long as it is formed to have a higher electrical resistance than the electrode 3 and the conductive film 6; for example, silicon oxide, silicon nitride, aluminum oxide, tantalum oxide, etc. It can be constructed using an insulating material such as as a main component. In the present embodiment, the insulating film 8 is mainly composed of an insulating oxide containing the same metal element or semiconductor element as that of the insulating oxide contained in the substrate 2 (main body portion 221). Ru. Specifically, for example, when the insulating oxide contained in the substrate 2 is silicon oxide, the insulating film 8 is composed mainly of silicon oxide. Since the insulating film 8 is composed mainly of an insulating oxide containing the same metal element or semiconductor element as the insulating oxide metal element or semiconductor element contained in the substrate 2, the substrate 2 and the insulating film 8 are are easily adapted to each other, and the adhesion between the substrate 2 and the insulating film 8 can be improved. The thickness of the insulating film 8 is not particularly limited, and can ensure that the conductive film 6 does not electrically short-circuit the electrode 3 through a path different from the path of the electrode 3, and can ensure adhesion to the substrate 2. It can be set as appropriate.

The method of forming the insulating film 8 is not particularly limited as long as it can be formed to have a higher electrical resistance than the electrodes 3 and the conductive film 6. In this embodiment, the insulating film 8 can be formed by a known film forming technique such as CVD or sputtering. When the insulating film 8 is formed by CVD or sputtering, it is formed as a denser film than when it is formed by coating or the like.

As described above, the insulating film 8 may be formed in the gap between two different points of the electrode 3 so that the conductive film 6 does not electrically short-circuit the electrode 3 through a path different from that of the electrode 3. , the arrangement thereof is not particularly limited. In this embodiment, as shown in FIGS. 4 and 5, the insulating film 8 includes an inter-electrode insulating part 8a provided in the gap between the electrodes 3, and an electrode (via the adhesive layer 9 in this embodiment). The electrode surface insulating portion 8b is provided on the surface of the electrode 3. The interelectrode insulating section 8a is provided in the gap between the electrodes 3 so as to extend from the gas sensing section 5 side toward the substrate 2 (main body section 221). One end of the inter-electrode insulating section 8a is connected to the substrate 2, and the other end of the inter-electrode insulating section 8a is connected to the electrode surface insulating section 8b. The side surface of the interelectrode insulating section 8a in the direction along the surface of the substrate 2 is connected to the side surface of the adjacent electrode 3. Further, the electrode surface insulating portion 8b is provided so as to extend in a planar manner along the surface of the substrate 2. One surface of the electrode surface insulating section 8b is connected to the gas sensitive section 5 and the conductive film 6, and the other surface of the electrode surface insulating section 8b is connected to the electrode 3 and the conductive film 6 (in this embodiment, via the adhesive layer 9). It is connected to the interelectrode insulation part 8a. The electrode surface insulating portion 8b is provided with through holes through which the electrode connecting portions 61a and 62a of the conductive film 6 connected to the first end region 31 and the second end region 32 of the electrode 3 penetrate. Other than that, they are provided so as to spread over substantially the entire surface of the substrate 2 in a planar manner.

As shown above, in this embodiment, as shown in FIGS. 4 and 5, the conductive film 6 and the insulating film 8 are connected to the electrode 3 (in this embodiment, partially through the adhesive layer 9). It is connected to the electrode 3 so as to cover it. In this embodiment, since the electrode 3 also serves as the heater 4, the conductive film 6 and the insulating film 8 are also connected to the heater 4 so as to cover the heater 4. By forming the conductive film 6 and the insulating film 8 to be denser than the gas sensitive part 5, the heater 4 deteriorates more when the temperature rises compared to the case where the heater 4 is covered with the gas sensitive part 5. can be suppressed. This is considered to be because the occurrence of migration and the like is suppressed when the temperature of the heater 4 increases. By improving the thermal durability of the heater 4, the MEMS type semiconductor gas sensing element 100 can be used for a long period of time.

In the following, the excellent effects of the MEMS type semiconductor gas detection elements of two embodiments will be explained based on Examples. However, the MEMS type semiconductor gas sensing element of the present invention is not limited to the following embodiments.

(Example 1)
The MEMS type semiconductor gas sensing element 1 shown in FIGS. 1 and 2 was manufactured by the following procedure. First, a substrate 2 was created using a known microfabrication technique, and the conductive film 6/electrode 3 (heater 4)/adhesive layer 9 were wired on the substrate 2. At that time, tantalum oxide was used as the adhesive layer 9, platinum was used as the electrode 3 (heater 4), and tin oxide was used as the conductive film 6. Adhesive layer 9, electrode 3 (heater 4), and conductive film 6 were each formed by sputtering. The thicknesses of the adhesive layer 9, electrode 3 (heater 4), and conductive film 6 were 20 nm, 300 nm, and 100 nm, respectively. Next, a paste of fine powder of tin oxide semiconductor added with 0.1 wt% of antimony as a donor is applied to cover the adhesive layer 9/electrode 3 (heater 4)/conductive film 6 on the substrate 2 to a maximum thickness of 20 μm. The gas-sensitive portion 5 was formed by applying the coating so as to have the following properties, and after drying, heating and sintering in an electric furnace at 650° C. for 2 hours. Subsequently, a functional layer 7 was provided to cover the gas sensitive section 5. The functional layer 7 is formed by applying a paste of fine alumina powder mixed with fine powder of palladium oxide to cover the gas sensitive part 5 to a maximum thickness of 30 μm, and after drying, the paste is heated at 650° C. in an electric furnace. It was formed by heating and sintering for 2 hours. The above MEMS type semiconductor gas sensing element was subjected to a detection sensitivity test described below.

(Example 2)
In order to easily evaluate the thermal durability of the electrode 3 (heater 4) of the MEMS type semiconductor gas detection element 100 shown in FIGS. A sample excluding layer 7 was produced in the following procedure. First, a substrate 2 was created using a known microfabrication technique, and the adhesive layer 9/electrode 3 (heater 4)/adhesive layer 9 were wired on the substrate 2. At that time, tantalum oxide was used as the adhesive layer 9, and platinum was used as the electrode 3 (heater 4). Adhesive layer 9 and electrode 3 (heater 4) were each formed by sputtering. The film thicknesses of the adhesive layer 9 and the electrode 3 (heater 4) were 20 nm and 300 nm, respectively. Next, the conductive film 6/insulating film 8 was placed on the adhesive layer 9/electrode 3 (heater 4)/adhesive layer 9 using a known microfabrication technique. As the conductive film 6, tin oxide was used, and as the insulating film 8, silicon oxide was used. The conductive film 6 was formed by sputtering, and the insulating film 8 was formed by CVD. The thicknesses of the conductive film 6 and the insulating film 8 were 500 nm and 1000 nm, respectively. The above samples were subjected to a thermal durability test described below.

(Example 3)
A MEMS type semiconductor gas sensing element 100 shown in FIGS. 4 and 5 was manufactured by providing the gas sensing portion 5 and the functional layer 7 on the sample of Example 2 in the following procedure. A paste of fine powder of tin oxide semiconductor added with 0.1 wt% antimony as a donor was applied to cover the conductive film 6/insulating film 8 of the sample of Example 2 to a maximum thickness of 20 μm, and dried. Thereafter, the gas sensitive portion 5 was formed by heating and sintering at 650° C. for 2 hours in an electric furnace. Subsequently, a functional layer 7 was provided to cover the gas sensitive section 5. The functional layer 7 is formed by applying a paste of fine alumina powder mixed with fine powder of palladium oxide to cover the gas sensitive part 5 to a maximum thickness of 30 μm, and after drying, the paste is heated at 650° C. in an electric furnace. It was formed by heating and sintering for 2 hours. The above MEMS type semiconductor gas sensing element was subjected to a detection sensitivity test and a high temperature and high humidity durability test, which will be described later.

(Comparative example 1)
As a comparative example of thermal durability evaluation, a sample was prepared by removing the conductive film 6, gas sensitive portion 5, and functional layer 7 from the MEMS type semiconductor gas sensing element 1 shown in FIGS. 1 and 2 using the following procedure. First, a substrate 2 was created using a known microfabrication technique, and the electrode 3 (heater 4)/adhesive layer 9 was wired on the substrate 2. At that time, tantalum oxide was used as the adhesive layer 9, and platinum was used as the electrode 3 (heater 4). Adhesive layer 9 and electrode 3 (heater 4) were each formed by sputtering. The film thicknesses of the adhesive layer 9 and the electrode 3 (heater 4) were 20 nm and 300 nm, respectively. The above samples were subjected to a thermal durability test described below.

(Comparative example 2)
By providing the gas sensing portion 5 and the functional layer 7 in the sample of Comparative Example 1 in the following procedure, a MEMS type semiconductor type gas sensing element 1 obtained by removing the conductive film 6 from the MEMS type semiconductor type gas sensing element 1 shown in FIGS. 1 and 2 is obtained. A gas sensing element was fabricated. A paste of fine powder of tin oxide semiconductor to which 0.1 wt% of antimony was added as a donor was applied to cover the electrode 3 (heater 4)/adhesive layer 9 of the sample of Comparative Example 1 to a maximum thickness of 20 μm. After drying, the material was heated and sintered at 650° C. for 2 hours in an electric furnace, thereby forming the gas sensitive portion 5. Subsequently, a functional layer 7 was provided to cover the gas sensitive section 5. The functional layer 7 is formed by applying a paste of fine alumina powder mixed with fine powder of palladium oxide to cover the gas sensitive part 5 to a maximum thickness of 30 μm, and after drying, the paste is heated at 650° C. in an electric furnace. It was formed by heating and sintering for 2 hours. The above MEMS type semiconductor gas sensing element was subjected to a detection sensitivity test and a high temperature and high humidity durability test, which will be described later.

(Detection sensitivity test)
The MEMS type semiconductor gas detection elements of Examples 1 and 3 and Comparative Example 2 were incorporated into a known bridge circuit, and the sensor output was measured in an atmospheric environment containing a gas to be detected. Methane, ethanol, and hydrogen were used as detection target gases.

(High temperature and high humidity durability test)
The MEMS type semiconductor gas detection elements of Example 3 and Comparative Example 2 were incorporated into a known gas detector and tested in a standard environment of 20°C and 60% RH and in a high temperature and high humidity environment of 40°C and 85% RH. After standing, a gas detector, which was set to issue an alarm when a predetermined sensor output for methane was reached, measured the concentration of methane that would trigger an alarm.

(Thermal durability test)
A predetermined power was applied to the electrode 3 (heater 4) of the samples of Example 2 and Comparative Example 1, and the time until the electrode 3 (heater 4) was disconnected (disconnection life) was measured.

(Detection sensitivity test results)
FIGS. 7 and 8 show the results of examining changes in sensor output when changing the concentrations of methane, ethanol, and hydrogen for the MEMS type semiconductor gas sensing elements of Examples 1 and 3 and Comparative Example 2.

In the detection sensitivity test results of Comparative Example 2 shown in FIG. 8, the sensor outputs of each of methane, ethanol, and hydrogen increase as their respective concentrations increase. On the other hand, in the detection sensitivity test results of Example 1 shown in FIG. 7A, the sensor output increases at any gas concentration compared to the results of Comparative Example 2 shown in FIG. This is because the electrode 3 and the gas sensitive part 5 are connected through the conductive film 6, which has higher adhesion to the gas sensitive part 5 than the electrode 3, so that the adhesion of the gas sensitive part 5 to the electrode 3 is improved. It is thought that this is because a good electrical connection between the electrode 3 and the gas sensitive part 5 was secured. In this way, by improving the detection sensitivity of the gas sensitive section 5 to the gas to be detected, changes in the resistance value of the gas sensitive section 5 that occur when the gas to be detected comes into contact with the gas sensitive section 5 can be detected more accurately. , the gas to be detected can be detected more accurately. Furthermore, in the detection sensitivity test results of Example 3 in FIG. 7(b), compared with the results of Comparative Example 2 in FIG. 8, the detection sensitivity test results of Example 3 in FIG. Output is increasing. This is because the connection area between the gas sensitive part 5 and the conductive film 6 is larger than in Example 1, and the adhesion between the gas sensitive part 5 and the conductive film 6 is further improved, and as a result, the electrode This is considered to be because the adhesion between the electrode 3 and the gas sensitive section 5 was further improved, and a better electrical connection between the electrode 3 and the gas sensitive section 5 could be secured. In this way, by further improving the detection sensitivity of the gas sensitive section 5 to the gas to be detected, changes in the resistance value of the gas sensitive section 5 that occur when the gas to be detected comes into contact with the gas sensitive section 5 can be detected more accurately. However, the gas to be detected can be detected more accurately.

(High temperature and high humidity durability test)
The MEMS type semiconductor gas sensing elements of Example 3 and Comparative Example 2 incorporated into known gas detectors were tested in a standard environment of 20°C and 60% RH and in a high temperature and high humidity environment of 40°C and 85% RH. Figures 9 and 10 show the results of examining changes over time in the concentration of methane that causes the gas detector to issue an alarm when the gas detector is left unattended. The gas detector is set to issue an alarm when a predetermined sensor output is obtained, so the change over time in the methane concentration that causes the gas detector to issue an alarm is based on the methane concentration of the MEMS semiconductor gas detection element. It shows the change in detection sensitivity over time. For example, the higher the concentration of methane at which the gas detector issues an alarm, the lower the detection sensitivity of the MEMS semiconductor gas detection element to methane.

The results of leaving the MEMS type semiconductor gas sensing elements of Example 3 and Comparative Example 2 in a standard environment of 20°C and 60% RH (Fig. 9) show that Example 3 (Fig. 9(a)) and Comparative Example 2 ( In both cases (Figure 9(b)), there is a tendency for the methane concentration to slightly decrease (methane detection sensitivity increases) as the number of days elapsed, but the methane concentration (methane detection sensitivity) generally remains almost constant. . On the other hand, the results of leaving the MEMS type semiconductor gas sensing elements of Example 3 and Comparative Example 2 in a high temperature and high humidity environment of 40°C and 85% RH (Fig. 10) show that Comparative Example 2 (Fig. 10(b) ), the methane concentration increased significantly (methane detection sensitivity decreased significantly) as the number of days elapsed, whereas in Example 3 (Figure 10(a)), the methane concentration increased significantly as the number of days elapsed. Increase in concentration (decrease in methane detection sensitivity) is suppressed. In other words, in Example 3, deterioration in gas detection sensitivity over time that occurs when exposed to a high temperature and high humidity environment is suppressed. This is because the electrode 3 and the gas sensitive part 5 are connected through the conductive film 6, which has higher adhesion to the gas sensitive part 5 than the electrode 3, so that the adhesion of the gas sensitive part 5 to the electrode 3 is improved. It is thought that this is because a good electrical connection between the electrode 3 and the gas sensitive part 5 was secured.

(Thermal durability test results)
Figure 11 shows the results of measuring the time until the electrode 3 (heater 4) breaks (breakage life) by applying a predetermined power to the electrode 3 (heater 4) of the samples of Example 2 and Comparative Example 1. . In Figure 11, in both Example 2 and Comparative Example 1, the disconnection life becomes shorter as the input power increases, but the disconnection life is significantly longer in Example 2 than in Comparative Example 1. There is. This is considered to be because the dense conductive film 6 and insulating film 8 were connected to the heater 4 so as to cover the heater 4, thereby suppressing the occurrence of migration when the heater 4 was heated. In this way, by connecting the heater 4 so that the dense conductive film 6 and the insulating film 8 cover the heater 4 and improving the thermal durability of the heater 4, the MEMS semiconductor gas sensing element 100 can be used for a long time. becomes possible.

1, 100 MEMS semiconductor gas sensing element 2 Substrate 21 Substrate body 21a Recess 22 Insulating support film 22a Silicon oxide film 22b Silicon nitride film 22c Silicon oxide film 221 Main body 221a First region 221b Second region 222 Base 223 Connection Part 23 Cavity 3 Electrode 3a First end 3b Second end 3c First proximal part 3d Second proximal part 31 First end region 32 Second end region 33 Main body region 331 First Main body region 332 Second main body region 333 Intermediate region 4 Heater 5 Gas sensitive part 6 Conductive film 61 First conductive film 61a Electrode connection part 61b Gas sensitive part connection part 62 Second conductive film 62a Electrode connection part 62b Gas sensitive part Part connection part 7 Functional layer 8 Insulating film 8a Inter-electrode insulation part 8b Electrode surface insulation part 9 Adhesive layer A Integration part G Gap L1 One lead wire L2 Other lead wire S First end and second end straight line connecting

Claims (7)

A substrate and
an electrode provided on the substrate , the electrode extending along a path connecting a first end connected to one lead wire and a second end connected to the other lead wire;
a heater provided on the substrate;
A MEMS type semiconductor gas sensing element comprising a gas sensitive section provided on the substrate so as to be electrically connected to the electrode and thermally connected to the heater,
comprising a conductive film that has higher adhesion to the gas sensitive part than the electrode and connects the electrode and the gas sensitive part,
The conductive film is connected to an upper surface of at least a portion of the electrode so as not to electrically short-circuit the electrode through a path different from a path of the electrode ,
The conductive film is formed mainly of a metal oxide semiconductor containing the same metal element as the metal element of the metal oxide semiconductor included in the gas sensitive part.
MEMS type semiconductor gas detection element. The MEMS type semiconductor gas sensing element includes an insulating film having a higher electrical resistance than the electrode and the conductive film,
The insulating film is formed in a gap between two different points of the electrode so that the conductive film does not electrically short-circuit the electrode in a path different from the path of the electrode.
The MEMS type semiconductor gas sensing element according to claim 1 . at least a portion of the conductive film is provided on the insulating film;
The MEMS type semiconductor gas sensing element according to claim 2 . The electrode has a first end region including a first end connected to one lead wire, and a second end region including a second end connected to the other lead wire; a body region extending between the first end region and the second end region and connecting the first end region and the second end region;
the conductive film is connected to the first end region and the second end region;
The MEMS type semiconductor gas sensing element according to any one of claims 1 to 3 . The electrode also serves as the heater,
The conductive film and the insulating film are denser than the gas sensitive part,
the conductive film and the insulating film are connected to the heater so as to cover the heater;
The MEMS type semiconductor gas sensing element according to claim 2 or 3 . A substrate and
an electrode provided on the substrate, the electrode extending along a path connecting a first end connected to one lead wire and a second end connected to the other lead wire;
a heater provided on the substrate;
a gas sensitive section provided on the substrate so as to be electrically connected to the electrode and thermally connected to the heater;
A MEMS type semiconductor gas sensing element comprising:
comprising a conductive film that has higher adhesion to the gas sensitive part than the electrode and connects the electrode and the gas sensitive part,
The conductive film is connected to an upper surface of at least a portion of the electrode so as not to electrically short-circuit the electrode through a path different from a path of the electrode,
The MEMS type semiconductor gas sensing element includes an insulating film having a higher electrical resistance than the electrode and the conductive film,
The insulating film is formed in a gap between two different points of the electrode so that the conductive film does not electrically short-circuit the electrode in a path different from the path of the electrode.
MEMS type semiconductor gas detection element. A substrate and
an electrode provided on the substrate, the electrode extending along a path connecting a first end connected to one lead wire and a second end connected to the other lead wire;
a heater provided on the substrate;
a gas sensitive section provided on the substrate so as to be electrically connected to the electrode and thermally connected to the heater;
A MEMS type semiconductor gas sensing element comprising:
comprising a conductive film that has higher adhesion to the gas sensitive part than the electrode and connects the electrode and the gas sensitive part,
The conductive film is connected to the top surface of at least a portion of the electrode so as not to electrically short-circuit the electrode through a path different from the path of the electrode,
The electrode has a first end region including a first end connected to one lead wire, and a second end region including a second end connected to the other lead wire; a body region extending between the first end region and the second end region and connecting the first end region and the second end region;
the conductive film is connected to the first end region and the second end region;
MEMS type semiconductor gas detection element.

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