JP2020165896A - Mems-type semiconductor gas sensing element - Google Patents

Abstract

To provide an MEMS-type semiconductor gas sensing element capable of suppressing a decrease in sensitivity to gas to be detected even when a gas sensing unit is downsized.SOLUTION: An MEMS-type semiconductor gas sensing element 1 comprises a substrate 2, an electrode 3 provided on the substrate 2, and a gas sensing unit 4 provided on the substrate 2 so as to be electrically connected to the electrode 3. The electrode 3 comprises a first end region 31 including a first end part 3a, a second end part region 32 including a second end part 3b, and a main body region 33 connecting the first end part region 31 and the second end part region 32. The gas sensing unit 4 is provided so as to be electrically connected to the first end part region 31 and the second end part region 32, and so as not to be electrically connected to the main body region 33 over at least a part of length in a direction in which the main body region 33 extends.SELECTED DRAWING: Figure 1

Description

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

Conventionally, as a gas detection element for a gas detector, for example, as disclosed in Patent Document 1, a MEMS type semiconductor gas detection element provided with a gas sensitive unit for detecting a gas to be detected has been used. In the MEMS type semiconductor gas detection element, gas detection is provided in the upper layer of the gas sensitive portion, for example, a catalyst layer is provided to enhance gas selectivity, or a protective layer is provided to enhance siloxane poisoning resistance. A functional layer is provided to improve the characteristics.

Japanese Unexamined Patent Publication No. 2016-070704

In the MEMS type semiconductor gas detection element 100, as shown in FIG. 8, an electrode 102 is provided on the substrate 101, a gas sensitive portion 103 is formed on the electrode 102, and a functional layer 104 is formed on the upper layer of the gas sensitive portion 103. Is formed. At this time, the gas sensitive portion 103 and the functional layer 104 are formed by dropping and applying a paste-like material. In this method, as is often seen in FIG. 8, the gas-sensitive portion 103 may extend to the end portion of the substrate 101, and the functional layer 104 may become extremely thin on the end portion side of the gas-sensitive portion 103. There is sex. If the functional layer 104 is not formed at the end of the gas sensitive portion 103 to a required thickness, the functional layer 104 cannot fully exert its function as a whole, and the MEMS type semiconductor gas detection element 100 The expected gas detection characteristics may not be obtained.

As a method of forming a functional layer with a required thickness at the end of the gas-sensitive portion, for example, a method of forming a gas-sensitive portion on a part of electrodes on the substrate so as not to spread to the end of the substrate. Can be considered. By forming the gas-sensitive portion on a part of the electrodes on the substrate, the functional layer can be formed to a required thickness even at the end of the gas-sensitive portion, so that the functional layer has the expected function. Can be fully demonstrated.

However, if the size of the gas-sensitive portion is reduced with respect to the entire region of the electrode, the contact area of the gas-sensitive portion with the electrode is inevitably reduced, and as a result, the gas-sensitive portion when the detection target gas is detected. Since the change in the resistance value of the above is relatively small with respect to the combined resistance value of the electrode and the gas-sensitive portion, there arises a problem that the sensitivity to the detection target gas is lowered.

The present invention has been made in view of the above problems, and provides a MEMS type semiconductor gas detection element capable of suppressing a decrease in sensitivity to a detection target gas even if the size of the gas sensitive portion is reduced. The purpose.

The MEMS type semiconductor gas detection element of the present invention is provided with a substrate, an electrode provided on the substrate and connected between one lead wire and the other lead wire, and electrically connected to the electrode. A MEMS type semiconductor gas detection element including a gas-sensitive portion provided on the substrate, wherein the electrode is a first end region including a first end connected to the one lead wire. And a second end region including a second end connected to the other lead wire, and extending between the first end region and the second end region, the first The gas-sensitive portion is electrically connected to the first end region and the second end region so as to include a main body region connecting the end region of the above and the second end region. It is characterized in that it is provided so as not to be electrically connected to the main body region over at least a part of the length in the extending direction of the main body region.

Further, it is preferable that at least a part of the first end region and the second end region is provided inside the outer edge of the range on the substrate on which the main body region is provided.

Further, the gas-sensitive portion is electrically connected to an intermediate region at a position substantially intermediate in length in the extending direction of the main body region, and the first end region and the intermediate region are connected to each other. Over at least a portion of the length of the body region extending in between, and over at least a portion of the length of the body region between the intermediate region and the second end region. Therefore, it is preferable that the main body region is not electrically connected.

Further, the main body region is on one side in the direction perpendicular to the straight line connecting the first end portion and the second end portion on the substrate, and the first end portion and the said portion on the substrate. It preferably extends to the other side in the direction perpendicular to the straight line connecting the second end.

Further, it is preferable that the MEMS type semiconductor gas detection element includes a functional layer that covers the gas sensitive portion.

According to the present invention, it is possible to provide a MEMS type semiconductor gas detection element capable of suppressing a decrease in sensitivity to a detection target gas even if the size of the gas sensitive portion is reduced.

It is a top view of the MEMS type semiconductor type gas detection element which concerns on one Embodiment of this invention. It is explanatory drawing for demonstrating the cross-sectional structure of the MEMS type semiconductor type gas detection element of FIG. It is a conceptual diagram for demonstrating the circuit formed by the electrode and the gas sensitive part in the MEMS type semiconductor type gas detection element of FIG. It is a graph which shows the sensor output change with respect to the gas concentration change before performing the siloxane exposure test about the MEMS type semiconductor type gas detection element of an Example. It is a graph which shows the sensor output change with respect to the gas concentration change before performing the siloxane exposure test about the MEMS type semiconductor type gas detection element of the comparative example. It is a graph which shows the sensor output change at the time of performing a siloxane exposure test about the MEMS type semiconductor type gas detection element of an Example. It is a graph which shows the sensor output change at the time of performing a siloxane exposure test about the MEMS type semiconductor type gas detection element of the comparative example. It is sectional drawing of the conventional MEMS type semiconductor type gas detection element. It is a top view of (a) a conventional MEMS type semiconductor type gas detection element, and (b) is a conceptual diagram for explaining a circuit formed by an electrode and a gas sensitive part. It is a top view of (a) a conventional MEMS type semiconductor type gas detection element, and (b) is a conceptual diagram for explaining a circuit formed by an electrode and a gas sensitive part.

Hereinafter, the MEMS type semiconductor gas detection element according to the embodiment of the present invention will be described with reference to the accompanying drawings. However, the embodiment shown below is an example, and the MEMS type semiconductor gas detection element of the present invention is not limited to the following example.

The MEMS type semiconductor gas detection element of the present embodiment is used to detect a detection target gas contained in the environmental atmosphere in an environmental atmosphere such as the atmosphere. The MEMS type semiconductor gas detection element uses the fact that the resistance value (or electrical conductivity) changes with the chemical reaction between the oxygen adsorbed on the surface and the detection target gas in the environmental atmosphere to detect the detection target gas. Detect. The gas to be detected is not particularly limited, and examples thereof include hydrogen, methane, butane, isobutane, propane, carbon monoxide, and ethanol.

As shown in FIGS. 1 and 2, the MEMS type semiconductor type gas detection element 1 has a MEMS (Micro Electro Mechanical System) structure. The MEMS structure means a device structure in which at least a part of element components is integrated on a substrate such as a silicon substrate by microfabrication technology. Since the MEMS type semiconductor gas detection element 1 has a MEMS structure, it can be downsized and can be driven with low power consumption as compared with the coil type semiconductor gas detection element.

As shown in FIGS. 1 and 2, the MEMS type semiconductor gas detection element 1 is provided on the substrate 2 and the substrate 2, and is connected between one lead wire L1 and the other lead wire L2. It includes an electrode 3 and a gas-sensitive portion 4 provided on a substrate 2 so as to be electrically connected to the electrode 3. The MEMS type semiconductor gas detection element 1 may optionally include a functional layer (not shown) that covers the gas sensitive portion 4. Note that FIG. 2 is an explanatory view for explaining the cross-sectional structure of the MEMS type semiconductor gas detection element 1, and the wiring structure of the electrode 3 shown in FIG. 2 is the same as the wiring structure of the electrode 3 shown in FIG. Does not support.

The MEMS type semiconductor gas detection element 1 is incorporated into, for example, a known bridge circuit (not shown) and resists due to a chemical reaction between the adsorbed oxygen on the surface of the gas sensitive portion 4 and the gas to be detected in the environmental atmosphere. A change in value is detected. The MEMS type semiconductor gas detection element 1 is incorporated in a bridge circuit via an electrode 3 in order to detect a change in the resistance value of the gas sensitive unit 4. The bridge circuit measures the change in the potential difference in the circuit caused by the change in the resistance value in the MEMS type semiconductor gas detection element 1 with a potentiometer, and outputs the change in the potential difference as a detection signal of the detection target gas. 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 sensitive portion 4 and the gas to be detected. It may be used by being incorporated in a circuit different from the bridge circuit.

The substrate 2 is collectively referred to as an “integrated portion A” below, including the electrode 3 and the gas-sensitive portion 4 (including the functional layer if a functional layer is provided) so as to be electrically insulated from the substrate 2. ) Is a member that supports. The substrate 2 is not particularly limited as long as it can support the laminated body A in an electrically insulated state with respect to the substrate 2. In the present embodiment, the substrate 2 is located between the substrate main body 21, the insulating support film 22 supported by the substrate main body 21, and the substrate main body 21 and the insulating support film 22, as shown in FIGS. 1 and 2. It is provided with a cavity portion 23 to be provided.

The substrate main body 21 is a member that supports the insulating support film 22 and supports the integrated portion 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 (opposite the side where the integrated portion A is provided), and supports the insulating support film 22 from below. The substrate body 21 is formed with a recess 21a in order to form a cavity 23 with the insulating support film 22. The substrate main 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 integrated portion A so that the integrated portion A and the substrate main body 21 are electrically insulated from each other. As shown in FIG. 2, the insulating support film 22 is provided on the substrate main body 21 and is supported by the substrate main body 21. The insulating support film 22 is formed in a film shape by an insulating material. In the present embodiment, the insulating support film 22 is a silicon oxide film 22a connected to the substrate main 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 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 the insulating support film 22 from the substrate main body 21, and its layer structure, constituent material, and film thickness are not particularly limited. For example, the insulating support film 22 has a three-layer structure in the present embodiment, but may have a single-layer structure or a multi-layer structure other than the three-layer structure. Further, although the insulating support film 22 is formed of a silicon oxide film or a silicon nitride film in the present embodiment, it may be formed of another insulating material such as aluminum oxide. Further, the film thickness of the insulating support film 22 is not particularly limited, and can be appropriately set so that the integrated portion A can be supported by electrically insulating the film from the substrate main body 21.

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

The main body 221 is connected to the base 222 via the connecting portion 223, and is supported by the substrate main body 21 via the connecting portion 223 and the base 222. The main body portion 221 is provided apart from the substrate main body 21 via a hollow portion 23 formed between the main body portion 221 and the substrate main body 21. In the MEMS type semiconductor gas detection element 1, the integrated portion A is provided in the main body portion 221 provided apart from the substrate main body 21, thereby suppressing the heat applied to the integrated portion A from being conducted to the substrate main body 21. be able to. As a result, in the MEMS type semiconductor gas detection element 1, the integrated portion A can be heated more efficiently, and low power consumption can be driven. In the present embodiment, the main body portion 221 is formed in a substantially circular shape in a top view as shown in FIG. However, the main body portion 221 is not particularly limited as long as it is provided apart from the substrate main body 21 and can support the integrated portion A, and may be formed into another shape such as a substantially rectangular shape in a top view. Good.

The base 222 is provided on the substrate body 21 and is 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 the present embodiment, the base portion 222 is formed in a frame shape in which the central portion is hollowed out in a substantially rectangular shape, and the hollow portion 23 is formed in the frame. However, the base portion 222 is not particularly limited as long as it is provided on the substrate main body 21 and the main body portion 221 can be supported via the connecting portion 223, and is hollowed out in another shape such as a substantially circular shape. It may be formed in a frame shape.

As shown in FIG. 1, the connecting portion 223 is connected to the main body portion 221 and the base portion 222, and supports the main body portion 221 while being supported by the base portion 222. The connecting portion 223 is provided apart from the substrate main body 21 via a hollow portion 23 formed between the connecting portion 223 and the substrate main body 21. By providing the connecting portion 223 for connecting the main body portion 221 to the base portion 222 at a distance from the substrate main body 21, it is possible to suppress the heat applied to the integrated portion A from being conducted to the substrate main body 21. The connecting portion 223 is connected to the inner side surface of the frame of the base portion 222, and is formed so as to extend from the inner side surface of the frame of the base portion 222 toward the main body portion 221 located substantially at the center inside the frame of the base portion 222. In the present embodiment, the connecting portion 223 is connected to each of the four inner side surfaces of the frame of the base portion 222, and supports the main body portion 221 from four directions. Therefore, the connecting portion 223 can support the main body portion 221 in a well-balanced manner. However, the connecting portion 223 is not limited to the illustrated example as long as it can connect the main body portion 221 and the base portion 222 and support the main body portion 221.

The electrode 3 is a member for detecting a change in the resistance value of the gas sensitive portion 4. As shown in FIGS. 1 and 2, the electrode 3 is provided on the main body portion 221 of the insulating support film 22 of the substrate 2, and at least a part thereof is covered with the gas sensitive portion 4. In the electrode 3, the first end portion 3a is connected to one lead wire L1, and the second end portion 3b is connected to the other lead wire L2. The lead wires 1 and 2 are formed so as to have a lower electric 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 portion 4 can be measured. Then, by measuring the change in the combined resistance value between the electrode 3 and the gas-sensitive unit 4, the change in the resistance value of the gas-sensitive unit 4 can be detected.

As shown in FIG. 1, the electrode 3 has a first end region 31 including a first end 3a connected to one lead L1 and a second end region 31 connected to the other lead L2. A second end region 32 including the end 3b, extending between the first end region 31 and the second end region 32, the first end region 31 and the second end region 32. It is provided with a main body area 33 for connecting to. The electrode 3 includes a first end region 31, a second end region 32, and a body region 33, and is configured as a single electrode.

In the present embodiment, the electrode 3 also functions as a heater that generates heat by energization and heats the gas sensitive portion 4 (and the functional layer if a functional layer is provided). Therefore, the electrode 3 can heat the gas-sensitive portion 4 to a temperature suitable for detecting the detection target gas 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 unit 4, and may be provided separately from the heater for heating the gas-sensitive unit 4.

The electrode 3 is not particularly limited as long as it can detect a change in the resistance value of the gas sensitive portion 4. The electrode 3 can be formed of, for example, a precious metal such as platinum or a platinum-rhodium alloy. The electrode 3 can be formed by, for example, a known etching processing technique after forming a uniform film with the material for the electrode 3. As shown in FIG. 2, the electrode 3 optionally has an adhesive layer 5 formed of tantalum oxide or the like in order to improve the adhesion of the insulating support film 22 of the substrate 2 to the main body 221. It may be provided on the main body 221.

The first end region 31 is a partial region of the electrode 3 adjacent to the first end 3a, including the first end 3a. The first end region 31 is composed of a part of electrodes 3 in a predetermined length range from the first end 3a. In the present embodiment, as shown in FIG. 1, the first end region 31 includes a first end portion 3a arranged near the end portion of the substrate 2 (main body portion 221) and a first end portion. It is a region extending from 3a toward the center of the substrate 2 and between the first proximity portion 3c, which is the portion closest to the center of the substrate 2. In the present embodiment, the first end region 31 extends substantially linearly from the first end 3a toward the center of the substrate 2 at 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 so as to approach the center of the substrate 2 without moving away from at least the center of the substrate 2. It may be curved and extended. Further, the first end region 31 is a part of the electrode 3 in which the first end 3a is 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 composed of.

The first end region 31 may be composed of a part of the electrodes 3 having a predetermined length range from the first end 3a, and the length thereof is not particularly limited. The predetermined length of the first end region 31 is, for example, 15% or less of the length of the entire electrode 3 from the viewpoint of suppressing a decrease in sensitivity to the detection target gas, as will be described in detail later. It is more preferable, it is more preferably 10% or less of the total length of the electrode 3, and even more preferably 6% or less of the total length of the electrode 3. Alternatively, the predetermined length of the first end region 31 is, for example, preferably a length having an electric resistance value of 15% or less of the electric resistance value of the entire electrode 3, and the electric resistance of the entire electrode 3. It is more preferably a length having an electric resistance value of 10% or less of the value, and even more preferably a length having an electric resistance value of 6% or less of the electric resistance value of the entire electrode 3.

The second end region 32 is a partial region of the electrode 3 adjacent to the second end 3b, including the second end 3b. The second end region 32 is composed of a part of electrodes 3 in a predetermined length range from the second end 3b. In the present embodiment, the second end region 32 includes a second end 3b arranged near the end of the substrate 2 (main body 221) and a second end, as shown in FIG. It is a region extending from 3b toward the center of the substrate 2 and between the second proximity portion 3d, which is the portion closest to the center of the substrate 2. In the present embodiment, the second end region 32 extends substantially linearly from the second end 3b toward the center of the substrate 2 at a substantially shortest distance. However, the second end region 32 is limited to the present embodiment as long as it extends from the second end 3b so as to approach the center of the substrate 2 without moving away from at least the center of the substrate 2. It may be curved and extended. Further, in the present embodiment, the second end region 32 extends substantially parallel to and substantially in line with the first end region 31 and has substantially the same length as the first end region 31. However, it may be provided so as to be inclined with respect to the first end region 31, and may have a length different from that of the first end region 31. Further, the second end region 32 is a part of the electrode 3 in which the second end 3b is 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 composed of.

The second end region 32 may be composed of a part of the electrodes 3 having a predetermined length range from the second end 3b, and the length thereof is not particularly limited. The predetermined length of the second end region 32 is, for example, 15% or less of the total length of the electrode 3 from the viewpoint of suppressing a decrease in sensitivity to the detection target gas, as will be described in detail later. It is more preferable, it is more preferably 10% or less of the total length of the electrode 3, and even more preferably 6% or less of the total length of the electrode 3. Alternatively, the predetermined length of the second end region 32 is, for example, preferably a length having an electric resistance value of 15% or less of the electric resistance value of the entire electrode 3, and the electric resistance of the entire electrode 3. It is more preferably a length having an electric resistance value of 10% or less of the value, and even more preferably a length having an electric resistance value of 6% or less of the electric resistance value of the entire electrode 3.

The first end region 31 and the second end region 32 may be provided on the substrate 2 (main body portion 221), and their arrangement is not particularly limited. In the present embodiment, at least a part of the first end region 31 and the second end region 32 is larger than the outer edge E of the range on the substrate 2 where the main body region 33 is provided, as shown in FIG. It is provided on the inside. That is, at least a part of the first end region 31 and the second end region 32 is from the distance from the center of the substrate 2 of the portion of the main body region 33 arranged most distant from the center of the substrate 2. Is also provided within a short distance. Therefore, as will be described later, the gas-sensitive portion 4 provided so as to be electrically connected to the first end region 31 and the second end region 32 can be formed inside the outer edge E of the main body region 33. Therefore, the gas-sensitive portion 4 can be formed smaller than the size of the substrate 2. Further, as shown, the entire first end region 31 and the second end region 32 may be provided inside the outer edge E of the main body region 33. Thereby, the gas sensitive portion 4 can be formed to be smaller. However, at least a part of the first end region 31 and the second end region 32 may be provided inside the outer edge E of the main body region 33.

Further, the first end region 31 and the second end region 32 are provided close to each other in the present embodiment as shown in FIG. More specifically, in the first end region 31 and the second end region 32, the distance between the first end region 31 and the second end region 32 is from the center of the substrate 2. They are provided close to each other so as to be shorter than a distance of 1/2 of the distance to the outer edge E of the main body region 33. Therefore, the gas-sensitive portion 4 provided so as to be electrically connected to the first end region 31 and the second end region 32 can be formed smaller. From the viewpoint of forming the gas-sensitive portion 4 smaller, the distance between the first end region 31 and the second end region 32 is, for example, from the center of the substrate 2 to the outer edge E of the main body region 33. It is preferably 2/3 or less of the distance, more preferably 1/2 or less of the distance from the center of the substrate 2 to the outer edge E of the main body region 33, and from the center of the substrate 2 to the outer edge E of the main body region 33. It is even more preferable that the distance is 1/3 or less of the distance.

Further, in the present 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 approach the center of the substrate 2 to a distance closer than half the distance to the outer edge E of the main body region 33. And extend. Therefore, the gas-sensitive portion 4 can be formed smaller in the vicinity of the center of the substrate 2. Further, as shown in the drawing, since the gas-sensitive portion 4 is provided only near the center of the substrate 2, the protective layer can be formed with a sufficient thickness in the entire end portion of the gas-sensitive portion 4. The function of the functional layer can be further enhanced. From the viewpoint of providing the gas sensitive portion 4 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, the distance of the substrate 2. It is preferably 2/3 or less of the distance from the center to the outer edge E of the main body region 33, and more preferably 1/2 or less of the distance from the center of the substrate 2 to the outer edge E of the main body region 33. It is even more preferable that the distance from the center of the main body region 33 to the outer edge E of the main body region 33 is 1/3 or less.

The main body region 33 is a partial region 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 the present embodiment, the main body region 33 is in the direction perpendicular to the straight line S connecting the first end portion 3a and the second end portion 3b on the substrate 2 (main body portion 221) as shown in FIG. One side (first region 221a) and the other side (second region 221b) in the direction perpendicular to the straight line S connecting the first end portion 3a and the second end portion 3b on the substrate 2. 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 is raised to heat the gas sensitive portion 4, the substrate 2 becomes more stable. Since the substrate 2 is heated uniformly, the substrate 2 is prevented from being curved by heat.

In the present 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. A second main body region 332 provided in the above, and an intermediate region 333 between the first main body region 331 and the second main body region 332 are provided.

As shown in FIG. 1, the first main body region 331 is a first end portion on one side of the first end region 31 on the first region 221a of the substrate 2 (main body portion 221). It extends from the other end (first proximity 3c) on the opposite side of the end 3a to the intermediate region 333. More specifically, the first main body region 331 extends from the other end of the first end region 31 toward the first region 221a substantially perpendicular to the first end region 31. Then, it meanders toward the edge of the substrate 2 (upward in the figure), extends along the edge of the substrate 2, then extends toward the center of the substrate 2 and extends to the intermediate region 333. ing. As a result, the first main body region 331 is arranged at a high density in the first region 221a, so that a long wiring length can be secured and a high electric resistance value can be secured.

As shown in FIG. 1, the second main body region 332 is a second end portion on one side of the second end region 32 on the second region 221b of the substrate 2 (main body portion 221). It extends from the other end (second proximity 3d) on the opposite side of 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 second region 221b substantially perpendicular to the second end region 32. After that, it meanders toward the edge of the substrate 2 (downward in the figure), extends along the edge of the substrate 2, then extends toward the center of the substrate 2 and reaches the intermediate region 333. It is extending. As a result, the second main body region 332 is arranged at a high density in the second region 221b, so that a long wiring length can be secured and a high electric resistance value can be secured.

In this embodiment, the first main body region 331 and the second main 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. As a result, even if the temperature of the electrode 3 is raised to heat the gas-sensitive portion 4, the substrate 2 is heated more uniformly, so that the substrate 2 is prevented from being curved by heat. Further, the first main body region 331 and the second main body region 332 are arranged as point-finished objects with the center of the substrate 2 as a substantially center. As a result, when the temperature of the electrode 3 is raised, the substrate 2 is heated more uniformly, so that the substrate 2 is further suppressed from being curved by heat.

As shown in FIG. 1, the intermediate region 333 connects the first main body region 331 and the second main body region 332. The intermediate region 333 is a straight line S connecting the first end portion 3a and the second end portion 3b at the boundary between the first region 221a and the second region 221b of the substrate 2 (main body portion 221). It is provided so as to intersect (orthogonally in the illustrated example) and extend between the first region 221a and the second region 221b. In the present embodiment, since 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 as each other, the intermediate region 333 extends from the main body region 33. It is located at a length approximately intermediate in the main body region 33 in the direction. The intermediate region 333 is provided substantially in 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 the first main body region 331 and the second main body region 332.

The gas-sensitive unit 4 is a portion containing a metal oxide semiconductor as a main component and whose electrical resistance changes with a chemical reaction between the adsorbed oxygen on the surface and the gas to be detected. The gas sensitive portion 4 is provided on the substrate 2 so as to be electrically connected to the electrode 3 as shown in FIGS. 1 and 2. By providing the gas-sensitive unit 4 so as to be electrically connected to the electrode 3, it is possible to detect a change in the electrical resistance of the gas-sensitive unit 4 via the electrode 3. The detailed arrangement of the gas sensitive portion 4 on the substrate 2 will be described in detail below.

The gas-sensitive portion 4 may be provided on the substrate 2 so that the resistance change can be detected by the electrode 3, and the forming method thereof is not particularly limited. The gas-sensitive portion 4 can be formed, for example, by mixing fine powder of a metal oxide semiconductor with a solvent to form a paste, which is applied onto a substrate 2 provided with an electrode 3 in advance and dried. Is. Alternatively, the gas sensitive portion 4 can be formed by using a known film forming technique such as sputtering.

The metal oxide semiconductor of the gas sensitive portion 4 is not particularly limited as long as the electric resistance changes with the chemical reaction between the adsorbed oxygen and the gas to be detected. For example, as the metal oxide semiconductor of the gas sensitive portion 4, it is preferable to use an n-type semiconductor from the viewpoint of promoting oxygen adsorption and the chemical reaction between the adsorbed oxygen and the gas component and improving the 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.

The metal oxide semiconductor of the gas sensitive portion 4 may have a metal element added as a donor in order to adjust the electric resistance. The metal element to be added is not particularly limited as long as it can be added as a donor in the metal oxide semiconductor and the electrical resistance of the metal oxide semiconductor can be adjusted, but for example, antimony. , At least one selected from niobium and tungsten is exemplified. Further, in the metal oxide semiconductor of the gas sensitive portion 4, oxygen deficiency may be introduced into the metal oxide semiconductor in order to adjust the electric resistance. The metal element concentration and the oxygen deficiency concentration can be appropriately set according to the required electrical resistance.

As shown in FIG. 1, the gas-sensitive portion 4 is electrically connected to the first end region 31 and the second end region 32 of the electrode 3, and at least in the extending direction of the main body region 33 of the electrode 3. It is provided so as not to be electrically connected to the main body region 33 over a part of the length. The gas sensitive portion 4 is provided so as not to be electrically connected to at least a part of the main body region 33 of the electrode 3, and is provided on a part of the substrate 2 (main body portion 221) so as to be provided on the entire substrate 2. It is formed smaller than when it is used. And even in such a case, since the gas sensitive portion 4 is electrically connected to the first end region 31 and the second end region 32 of the electrode 3, as will be described in detail below, It is possible to suppress a decrease in sensitivity to the gas to be detected. Further, since the gas-sensitive portion 4 is provided on a part of the substrate 2, the functional layer is sufficiently thick even at the end of the gas-sensitive portion 4 even when the functional layer is provided so as to cover the gas-sensitive portion 4. Since it is formed by the water, it is possible to fully exert the function of the functional layer, which is to improve the gas detection characteristic of the gas sensitive portion 4.

The gas sensitive portion 4 is electrically connected to the first end region 31 and the second end region 32 of the electrode 3 for the purpose of suppressing a decrease in sensitivity to the gas to be detected. For that purpose, it does not necessarily have to be electrically connected to the entire first end region 31 and the second end region 32, and as shown in FIG. 1, the first end. It suffices to be electrically connected to at least a part of each of the partial region 31 and the second end region 32.

Here, as described above, the change in electrical resistance of the gas-sensitive unit 4 due to the chemical reaction between the adsorbed oxygen on the surface of the gas-sensitive unit 4 and the gas to be detected is detected via the electrode 3. At this time, the combined resistance value R between the first end portion 3a and the second end portion 3b of the electrode 3 is the electrical resistance value Rc of the electrode 3 and the gas sensitive portion 4 as shown in FIG. It is expressed as a combined resistance value with the electric resistance value Rv. The change in the electric resistance value Rv of the gas sensitive unit 4 is indirectly detected as the change in the combined resistance value R.

For example, as shown in FIG. 9, when the gas-sensitive portion is electrically connected to the entire electrode, the entire electrode and the entire gas-sensitive portion form a parallel circuit, and the combined resistance value R Is expressed as a parallel combined resistance value of the total electric resistance value Rc of the electrode and the total electric resistance value Rv of the gas sensitive portion. In this case, since the combined resistance value R changes greatly according to the change in the electric resistance value Rv of the gas-sensitive portion, high sensitivity to the detection target gas can be obtained.

On the other hand, as shown in FIG. 10, when the gas-sensitive part is electrically connected to only a part of the electrode, only a part of the electrode forms a parallel circuit with the whole gas-sensitive part and synthesizes. The resistance value R is a series-combined resistance value of the electric resistance value Rc of a part of the electrode and the electric resistance value Rv of the entire gas-sensitive part and the electric resistance value Rc of the other part of the electrode. Represented. In this case, the combined resistance value R does not change the resistance value between the ends of the other parts of the electrode to which the gas-sensitive part is not electrically connected even if the electric resistance value Rv of the gas-sensitive part changes. Since it does not change significantly as a whole, high sensitivity to the detection target gas cannot be obtained.

On the other hand, in the present embodiment, as shown in FIG. 1, the gas-sensitive portion 4 is not electrically connected to at least a part of the main body region 33 of the electrode 3, but the first end of the electrode 3 is not electrically connected. It is electrically connected to the part region 31 and the second end region 32. Therefore, as shown in FIG. 3, the combined resistance value R is expressed as a parallel combined resistance value of substantially the entire electrical resistance value Rc of the electrode 3 and the overall electrical resistance value Rv of the gas sensitive portion 4. In this case, the combined resistance value R is about the same as or close to the case where the gas-sensitive portion 4 is electrically connected to the entire electrode 3, and the electric resistance value Rv of the gas-sensitive portion 4 is It changes according to the change. Therefore, by reducing the size of the gas-sensitive portion 4, even if the gas-sensitive portion 4 is not electrically connected to a part of the main body region 33 of the electrode 3, the decrease in sensitivity to the detection target gas is suppressed. be able to.

The combined resistance value R between the end portions 3a and 3b of the electrodes 3 is the electricity of the gas sensitive portion 4 to the same extent as or close to the case where the gas sensitive portion 4 is electrically connected to the entire electrode 3. In order to change the resistance value Rv in response to the change, the gas sensitive portion 4 is electrically connected to a portion as close as possible to the first end portion 3a and the second end portion 3b of the electrode 3. Is preferable. The distance from the first end 3a and the second end 3b of the portion of the electrode 3 to which the gas sensitive portion 4 is electrically connected, or the first end region of the electrode 3 that defines the distance. The predetermined lengths of the 31 and the second end region 32 are not particularly limited as long as the decrease in sensitivity to the detection target gas can be suppressed, and the decrease in sensitivity to the detection target gas is suppressed. Can be appropriately determined according to the required level. The predetermined lengths of the first end region 31 and the second end region 32 are, for example, 15% or less of the total length of the electrode 3 from the viewpoint of suppressing a decrease in sensitivity to the detection target gas. It is more preferably 10% or less of the total length of the electrode 3, and even more preferably 6% or less of the total length of the electrode 3. Alternatively, the predetermined lengths of the first end region 31 and the second end region 32 may be, for example, a length having an electric resistance value of 15% or less of the electric resistance value of the entire electrode 3. More preferably, the length is such that the electric resistance value is 10% or less of the electric resistance value of the entire electrode 3, and the electric resistance value is 6% or less of the electric resistance value of the entire electrode 3. Is even more preferable.

In the present embodiment, as shown in FIG. 1, the gas-sensitive unit 4 is electrically connected to the intermediate region 333 located at a position substantially intermediate in length of the main body region 33 in the extending direction of the main body region 33. Over at least a portion of the length of the body region 33 (first body region 331) extending between the end region 31 of 1 and the intermediate region 333, and between the intermediate region 333 and the second end region. It is provided so as not to be electrically connected to the main body region 33 over at least a part of the length in the extending direction of the main body region 33 (second main body region 332) between the main body region 33 and the 32. In the illustrated example, the gas sensitive portion 4 is provided so as to be substantially electrically connected only to the first end region 31, the second end region 32, and the intermediate region 333.

Further, in the present embodiment, as shown in FIG. 1, at least a part of the first end region 31 and the second end region 32 of the electrode 3 is provided with the main body region 33 of the electrode 3. It is provided inside the outer edge E of the upper range. Therefore, since the gas-sensitive portion 4 can be formed inside the outer edge E of the main body region 33, it can be formed smaller than the size of the substrate 2.

Further, in the present embodiment, as shown in FIG. 1, the first end region 31 and the second end region 32 are provided close to each other. Therefore, the gas-sensitive portion 4 can be formed smaller than the size of the substrate 2.

Further, in the present embodiment, as shown in FIG. 1, 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). Therefore, the gas-sensitive portion 4 can be formed smaller in the vicinity of the center of the substrate 2.

The functional layer provided so as to optionally cover the gas-sensitive unit 4 has a function of improving the selectivity of the detection target gas in the gas-sensitive unit 4 and a function of suppressing deterioration of the gas-sensitive unit 4, and the like. It is a layer having a function of improving the gas detection characteristics of. The functional layer is provided on the gas-sensitive portion 4 so as to cover the gas-sensitive portion 4. In the MEMS type semiconductor gas detection element 1 of the present embodiment, the gas sensitive portion 4 is provided on a part of the substrate 2. As a result, the functional layer provided on the gas-sensitive portion 4 can be formed with a required thickness even in the end region of the gas-sensitive portion 4, so that deterioration of the function can be suppressed. Therefore, in the MEMS type semiconductor gas detection element 1 of the present embodiment, the overall function of the functional layer can be improved as compared with the case where the gas sensitive portion 4 is provided on the entire substrate 2.

In the present embodiment, as the functional layer, two types of layers having a function of suppressing deterioration of the gas sensitive portion 4 and protecting the gas sensitive portion 4 (hereinafter, referred to as a first functional layer and a second functional layer) are exemplified. To. However, the functional layer is not particularly limited as long as it has a function of improving the gas detection characteristics of the gas sensitive portion 4, and the semiconductor type gas detection element contains a metal oxide semiconductor as a main component. By covering the gas-sensitive portion, a known layer having a function of improving the gas detection characteristics of the gas-sensitive portion can be adopted.

The first functional layer, which is the first example, protects the gas-sensitive portion 4 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 portion 4. Improve. In the first functional layer, for example, the gas-sensitive portion 4 is poisoned by the adhesion of organic silicone gas (for example, hexamethyldisiloxane) contained in the environmental atmosphere to the gas-sensitive portion 4 (of the gas-sensitive portion 4). The detection sensitivity changes and the MEMS type semiconductor gas detection element 1 malfunctions) is suppressed.

The first functional layer is formed by supporting a metal oxide on a metal oxide semiconductor for the purpose of protecting the gas-sensitive portion 4 and improving the durability of the gas-sensitive portion 4. 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 portion 4 from a specific gas component, and is, for example, chromium oxide, palladium oxide, cobalt oxide, iron oxide, rhodium oxide, copper oxide, cerium oxide, and platinum oxide. , At least one selected from tungsten oxide and lanthanum oxide can be used. Among the metal oxides exemplified above, it is preferable that the metal oxide is at least one selected from chromium oxide and palladium oxide from the viewpoint of further suppressing the deterioration of the gas-sensitive portion 4.

The method for forming the first functional layer is not particularly limited as long as it can protect the gas-sensitive portion 4 from a specific gas component and improve the durability of the gas-sensitive portion 4. 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 with a solvent to form a paste, which is applied to the gas-sensitive portion 4 and dried. be able to.

The second functional layer, which is the second example, is composed of an insulating metal oxide for the same purpose as the first functional layer. The second functional layer protects the gas sensitive portion 4 by capturing a specific gas component with an insulating metal oxide. Further, since the second functional layer is composed of the insulating metal oxide, the current is suppressed from flowing through the second functional layer, and the influence on the resistance value change of the gas sensitive portion 4 at the time of detecting the detection target gas. Therefore, it is possible to suppress a decrease in the detection sensitivity of the detection target gas. The insulating metal oxide is not particularly limited, and examples thereof include at least one selected from aluminum oxide and silicon oxide.

The second functional layer may be formed by supporting a metal oxide having an oxidizing activity on an insulating metal oxide. The second functional layer is formed by supporting a metal oxide having an oxidizing activity on an insulating metal oxide, so that deterioration of the gas-sensitive portion 4 can be further suppressed. As the metal oxide having oxidative activity, for example, 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 metal oxides exemplified above, it is preferable that the metal oxide is at least one selected from chromium oxide and palladium oxide from the viewpoint of further suppressing the deterioration of the gas-sensitive portion 4.

The method for forming the second functional layer is not particularly limited as long as it can protect the gas-sensitive portion 4 from a specific gas component and improve the durability of the gas-sensitive portion 4. The second functional layer 5 is formed by, for example, mixing a mixture of a fine powder of an insulating metal oxide and a fine powder of a metal oxide with a solvent to form a paste, which is applied to the gas-sensitive portion 4 and dried. Can be formed.

Hereinafter, the excellent effects of the MEMS type semiconductor gas detection element of the present embodiment will be described based on the examples. However, the MEMS type semiconductor gas detection element of the present invention is not limited to the following examples.

(Example 1)
The MEMS type semiconductor gas detection element 1 shown in FIG. 1 was manufactured by the following procedure. First, a substrate 2 was prepared by a known microfabrication technique, and an electrode 3 was wired on the substrate 2. At that time, platinum was used as the electrode 3, and tantalum oxide was used as the adhesive layer 5. Next, a fine powder paste of tin oxide semiconductor to which 0.1 wt% of antimony was added as a donor was applied over a part of the electrode 3 on the substrate 2 so as to have a maximum thickness of 20 μm, and after drying. The gas-sensitive portion 4 was formed by heating in an electric furnace at 650 ° C. for 2 hours and sintering the mixture. At this time, the diameter of the gas sensitive portion 4 was 40 μm. Subsequently, in the produced MEMS type semiconductor type gas detection element 1, a functional layer was provided so as to cover the gas sensitive portion 4. The functional layer is coated with a fine powder paste of tin oxide semiconductor, which is a mixture of fine powders of chromium oxide and palladium oxide, coated on the gas-sensitive portion 4 so as to have a maximum thickness of 30 μm. It was formed by heating in a furnace at 650 ° C. for 2 hours and sintering.

(Comparative Example 1)
The MEMS type semiconductor gas detection element 100 shown in FIGS. 8 and 9 has a different electrode arrangement, and the gas-sensitive portion covers the entire substrate and extends to the edge of the substrate. It was prepared by the same method as in Example 1. At this time, the diameter of the gas-sensitive portion was 130 μm. Further, the electric resistance value of the electrode of Comparative Example 1 was adjusted so as to have the same electric resistance value as that of the electrode of Example 1.

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

(Siloxane exposure test)
The MEMS type semiconductor gas detection elements of Example 1 and Comparative Example 1 were evaluated for how the sensor output changed after being exposed to the atmosphere containing only 10 ppm of octamethylcyclotetrasiloxane (OMCTS). The sensor output was measured in an atmospheric environment not containing the detection target gas and in an atmospheric environment containing the detection target gas by the same method as the detection sensitivity test. As the detection target gas, methane (3000 ppm), ethanol (100 ppm), and hydrogen (1000 ppm) were used.

(Detection sensitivity test result)
The results of examining the changes in the sensor output when the concentrations of methane, ethanol, and hydrogen are changed in the MEMS type semiconductor gas detection elements of Example 1 and Comparative Example 1 are shown in FIGS. 4 and 5.

Looking at FIGS. 4 and 5, in both Example 1 and Comparative Example 1, the sensor output increases as the concentrations of methane, ethanol, and hydrogen increase. The sensor outputs of the respective concentrations of methane, ethanol, and hydrogen are not significantly different between Example 1 and Comparative Example 1. From this, in the MEMS type semiconductor gas detection element of Example 1, even if the size of the gas sensitive portion is smaller than that of the MEMS type semiconductor gas detection element of Comparative Example 1, the sensitivity to the detection target gas is lowered. Can be seen to be suppressed.

(Siloxane exposure test result 2)
6 and 7 show the results of examining the change in the sensor output after the siloxane exposure test was performed on the MEMS type semiconductor gas detection elements of Example 1 and Comparative Example 1. In FIGS. 6 and 7, the sensor output is standardized with the sensor output obtained in an atmospheric environment containing methane at a siloxane exposure time of 0 minutes as 100.

Looking at Comparative Example 1 of FIG. 7, the sensor outputs obtained in the atmospheric environment containing methane, ethanol, and hydrogen, including the atmospheric environment not containing the gas to be detected, are all the exposure times in the siloxane exposure test. It is increasing with the increase. From this, it can be seen that in Comparative Example 1, the gas-sensitive portion is deteriorated by the exposure to siloxane.

On the other hand, looking at Example 1 of FIG. 6, the change in the sensor output with the increase in the exposure time in the siloxane exposure test was slightly suppressed for ethanol as compared with the result of Comparative Example 1, and methane and hydrogen. And the atmosphere is greatly suppressed. From this, it can be seen that by reducing the gas-sensitive portion of the MEMS-type semiconductor gas detection element, the function of suppressing deterioration of the gas-sensitive portion due to exposure to siloxane can be improved.

1 MEMS type semiconductor gas detection element 2 Substrate 21 Substrate body 21a Recessed portion 22 Insulation support film 22a Silicon oxide film 22b Silicon nitride film 22c Silicon oxide film 221 Body part 221a First area 221b Second area 222 Base part 223 Connection part 23 Cavity 3 Electrode 3a 1st end 3b 2nd end 3c 1st proximity 3d 2nd proximity 31 1st end area 32 2nd end area 33 Body area 331 1st body Region 332 Second main body region 333 Intermediate region 4 Gas sensitive part 5 Adhesive layer A Integrated part E Outer edge of main body region of electrode L1 One lead wire L2 Another lead wire R Combined resistance value Rc Electrode electrical resistance value Rv Gas sensitive Electrical resistance value of the part S Straight line connecting the first end and the second end

Claims (5)

With the board
An electrode provided on the substrate and connected between one lead wire and the other lead wire,
A MEMS-type semiconductor gas detection element having a gas-sensitive portion provided on the substrate so as to be electrically connected to the electrode.
A first end region in which the electrode includes a first end connected to the 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.
The gas-sensitive portion is electrically connected to the first end region and the second end region, and electrically connects to the main body region over at least a part of the length in the extending direction of the main body region. It is provided so as not to connect
MEMS type semiconductor gas detection element. At least a portion of the first end region and the second end region is provided inside the outer edge of the range on the substrate on which the body region is provided.
The MEMS type semiconductor gas detection element according to claim 1. The gas-sensitive portion is electrically connected to an intermediate region located at a position approximately intermediate in length in the extending direction of the main body region, and is located between the first end region and the intermediate region. Over at least a portion of the length of the body region extending, and over at least a portion of the length of the body region between the intermediate region and the second end region. Provided so as not to be electrically connected to the main body area,
The MEMS type semiconductor gas detection element according to claim 1 or 2. The main body region is on one side in the direction perpendicular to the straight line connecting the first end portion and the second end portion on the substrate, and the first end portion and the second end portion on the substrate. Extends to the other side in the direction perpendicular to the straight line connecting the ends of
The MEMS type semiconductor gas detection element according to any one of claims 1 to 3. The MEMS type semiconductor gas detection element includes a functional layer that covers the gas sensitive portion.
The MEMS type semiconductor gas detection element according to any one of claims 1 to 4.

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