Thermoelectric gas sensor

Abstract

This invention provides a thermoelectric gas sensor that can increase the amount of heat generated by the catalytic reaction and improve detection sensitivity without increasing the size of the catalyst material. [Solution] This thermoelectric gas sensor comprises a substrate 11, a membrane 12 formed on the substrate 11, a catalyst material 13 positioned above the membrane 12 and in contact with the gas to be detected to produce a catalytic reaction, and a thermocouple layer 14 that converts the heat produced by the catalytic reaction into an electrical signal. The substrate 11 and the membrane 12 have a cavity C3 below the catalyst material 13 that exposes the lower surface of the catalyst material 13. This makes it possible to supply the gas to be detected to the back surface of the catalyst material 13, thereby improving the detection sensitivity of the gas to be detected by the sensor.

Description

Technical Field

[0001] The present invention relates to a thermoelectric conversion type gas sensor that uses heat generated by a catalytic reaction as a detection signal by means of a thermoelectric conversion effect.

Background Art

[0002] A thermoelectric conversion type gas sensor has a catalyst material that comes into contact with a gas to be detected to cause a catalytic reaction, and detects the gas by detecting the heat generated by the catalytic reaction with a thermocouple (see, for example, Patent Document 1). The catalyst material is formed on a membrane for heat shielding via a substrate. In order to improve the detection sensitivity of the sensor, it is necessary to increase the heat of the catalytic reaction. For this purpose, it is required to increase the area (contact area) where the catalyst comes into contact with the gas to be detected.

[0003] However, if an attempt is made to increase the contact area of the catalyst, both the catalyst material and the membrane become larger, resulting in insufficient strength of the sensor and an overall increase in the size of the sensor. Further, if the membrane is thinned to reduce the size of the hot junction portion, the same problem of insufficient strength occurs.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In view of the above problems, an object of the present invention is to provide a thermoelectric conversion type gas sensor that can increase the amount of heat generated by a catalytic reaction and improve detection sensitivity without increasing the size of the catalyst material.

Means for Solving the Problems

[0006] The thermoelectric gas sensor according to the present invention comprises a substrate, a membrane formed on the substrate, a catalytic material disposed above the membrane and in contact with the gas to be detected to produce a catalytic reaction, and a thermocouple layer that converts the heat produced by the catalytic reaction into an electrical signal. The substrate and the membrane are provided with a cavity below the catalytic material that exposes the lower surface of the catalytic material. [Effects of the Invention]

[0007] This invention makes it possible to provide a thermoelectric gas sensor that can increase the amount of heat generated by the catalytic reaction and improve detection sensitivity without increasing the size of the catalyst material. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic perspective view of the thermoelectric gas sensor 1 according to the first embodiment. [Figure 2] This is a plan view of the thermoelectric gas sensor 1 according to the first embodiment. [Figure 3] This is a cross-sectional view AA in Figure 2. [Figure 4] Figure 2 is a cross-sectional view of BB. [Figure 5] This is a plan view of the thermoelectric gas sensor 1 according to the second embodiment. [Figure 6] This is a cross-sectional view AA of Figure 5. [Figure 7] This is a cross-sectional view AA of the thermoelectric gas sensor 1 according to the third embodiment. [Figure 8] This is a cross-sectional view of BB of the thermoelectric gas sensor 1 according to the third embodiment. [Modes for carrying out the invention]

[0009] This embodiment will be described below with reference to the attached drawings. In the attached drawings, functionally identical elements may be indicated by the same number. The attached drawings show embodiments and implementation examples in accordance with the principles of this disclosure, but these are for the purpose of understanding this disclosure and are not to be used in any way to restrict the interpretation of this disclosure. The descriptions in this specification are merely typical examples and do not limit the claims or applications of this disclosure in any way. In each drawing, identical or substantially equivalent elements, members and parts are given the same reference numerals. Also, the dimensions and proportions in the drawings are exaggerated for illustrative purposes and may differ from actual proportions.

[0010] While this embodiment is described in sufficient detail for those skilled in the art to implement the disclosure, it is important to understand that other implementations and forms are possible, and that the configuration and structure can be modified and various elements replaced without departing from the scope and spirit of the technical idea of ​​this disclosure. Therefore, the following description should not be construed as limiting to this.

[0011] [First Embodiment] First, the thermoelectric gas sensor 1 according to the first embodiment will be described with reference to Figures 1 to 3. Figure 1 is a schematic perspective view of the thermoelectric gas sensor 1, Figure 2 is a plan view, and Figures 3 and 4 are cross-sectional views AA and BB of Figure 2, respectively.

[0012] This thermoelectric gas sensor 1 comprises a substrate 11, a membrane 12, a catalyst material 13, and a thermocouple layer 14. Although not shown in Figure 1, an insulating layer 15 made of silicon oxide film (SiO2) is formed between the membrane 12 and the catalyst material 13. The thermocouple layer 14 is embedded in the insulating layer 15. The membrane 12 and the insulating layer 15 constitute a membrane in the broad sense.

[0013] The substrate 11 is, for example, silicon (Si substrate). The membrane 12 is a silicon nitride thin film or silicon oxide thin film formed by MEMS processing on the surface of the substrate 11, and is formed to a thickness of, for example, about 1 μm. A thermocouple layer 14 is wired on the surface of the membrane 12 so as to contact the back surface of the catalyst layer 12 via an electrode layer. The thermocouple layer 14 and the catalyst material 13 are configured to be in contact in all areas except for the third cavity C3, which will be described later. The catalyst material 13 is a catalyst that produces a catalytic reaction when in contact with the gas to be detected, and is made of, for example, platinum (Pt). The thermocouple layer 14 converts the heat from the catalytic reaction into an electrical signal, and is formed using, for example, p-type polysilicon and n-type polysilicon as materials.

[0014] A first cavity C1 is formed in the substrate 11 below the membrane 12. The first cavity C1 is formed to a depth that does not reach (penetrate) the back surface of the substrate 11, and functions as a passage for the gas to be detected. The first cavity C1 is provided so as to encompass substantially the entire catalyst material 13, including the outer circumference of the catalyst material 13. The cross-sectional shape of the first cavity C1 may be rectangular, tapered as shown in Figures 3 and 4, or inversely tapered.

[0015] Furthermore, a second cavity C2 (through-hole) through which air can pass is formed in a portion of the membrane 12 and insulating layer 15 (membrane in a broad sense) on the outer periphery of the catalyst material 13, and a third cavity C3 (through-hole) is formed directly beneath the catalyst material 13, reaching the back surface of the catalyst material 13 and communicating with the first cavity C1 below. The region where the first cavity C1 to the third cavity C3 are formed constitutes the hot junction portion of the sensor, and the remaining portion constitutes the cold junction portion of the sensor. The first cavity C1 can be formed, for example, by forming a hole corresponding to the first cavity C1 in a substrate 11 made of silicon (Si) by anisotropic etching, embedding a polysilicon film as a sacrificial film in the hole, and then removing it by etching. After forming the membrane 12 and insulating layer 15 on the substrate 11 including the polysilicon film, the second cavity C2 and the third cavity C3 are formed by penetrating the membrane 12 and insulating layer 15 using photolithography and etching. Subsequently, by removing the aforementioned sacrificial film using an etching solution such as KOH, the first cavity C1 is formed and communicates with the second cavity C2 and the third cavity C3.

[0016] The catalyst material 13 can be formed on the surface of the membrane 12 obtained by MEMS processing by sputter deposition. A heater for heating the catalyst material 13 may be provided near the catalyst material 13. However, as will be described later, in the gas sensor 1 of this embodiment, the gas to be detected can be guided to both the front and back surfaces of the catalyst material 13, making it easy to raise the temperature of the hot junction, so the heater can often be omitted.

[0017] As shown in Fig. 3, a third cavity C3 is formed in the membrane 12 and the insulating layer 15 on the lower surface of the catalyst material 13. This third cavity C3 is continuous with the first cavity C1 and the second cavity C2, and the gas to be detected can reach the back surface of the catalyst material 13 from the outside. The gas to be detected can also reach the surface of the catalyst material 13. Thus, the gas to be detected can be detected on both the front and back surfaces of the catalyst material 13. As a result of being able to detect on both the front and back surfaces, the catalyst material 13 can enhance the gas detection sensitivity compared to a sensor that can only detect on the surface. Since the amount of heat generated in the catalyst material 13 also increases, a heater for heating the catalyst material 13 can be made unnecessary. Further, since the catalyst material 13 is held by the membrane 12 and the insulating layer 15 in regions excluding the second cavity C2, even if the thickness of the catalyst material 13 is reduced, it is possible to hold the catalyst material 13 while preventing bending and breakage.

[0018] [Second Embodiment] Next, the thermoelectric conversion type gas sensor 1 according to the second embodiment will be described with reference to Figs. 5 to 6. Since the schematic perspective view of the thermoelectric conversion type gas sensor 1 of this second embodiment is substantially the same as that of the first embodiment, the illustration thereof is omitted. Fig. 5 is a plan view of the thermoelectric conversion type gas sensor 1 of the second embodiment, and Fig. 6 is a cross-sectional view taken along the line A - A of Fig. 5.

[0019] This second embodiment is different from the first embodiment in that the third cavity C3 is not arranged as one directly below the catalyst material 13, but is divided and arranged in a plurality of regions (two in Fig. 5). By increasing the number of the third cavities C3 to a plurality, the strength of the membrane 12 can be enhanced, and the detection sensitivity of the sensor itself can be appropriately adjusted. The larger the exposed area of the back surface of the catalyst material 13, the higher the sensitivity as a sensor. However, depending on the purpose of use of the sensor and the gas to be detected, there may be a case where it is desired to set the detection sensitivity to an appropriate magnitude. In this case, according to the second embodiment, by appropriately adjusting the number, arrangement, and individual area of the third cavities C3, it becomes possible to adjust the detection sensitivity of the sensor.

[0020] [Third Embodiment] Next, a thermoelectric gas sensor 1 according to the third embodiment will be described with reference to Figures 7 and 8. The schematic perspective view and plan view of the thermoelectric gas sensor 1 of this third embodiment are substantially the same as those of the first embodiment, so they are omitted from the illustration. Figures 7 and 8 are cross-sectional views AA and BB of the thermoelectric gas sensor 1 of the third embodiment.

[0021] The thermoelectric gas sensor 1 of this third embodiment differs from the previously described embodiment in that the first cavity C1 formed in the substrate 11 extends to the back surface of the substrate 11 and penetrates the substrate 11 from front to back. In the previously described embodiment, the gas to be detected reaches the first cavity C1 from the front side of the sensor 1 via the second cavity C2, and then reaches the back surface of the catalyst material 13. In contrast, in the gas sensor 1 of this third embodiment, the gas to be detected can reach the back surface of the catalyst material 13 directly via the first cavity C1 not only from the front side but also from the back side of the sensor 1. Therefore, according to this third embodiment, it is possible to provide a gas sensor 1 with higher detection sensitivity.

[0022] This disclosure is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail for the purpose of explaining this disclosure clearly, and are not necessarily limited to having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of Symbols]

[0023] 1. Thermoelectric gas sensor 11 circuit boards 12 Membrane 13 Catalyst material 14 Thermocouple layer 15. Insulating layer C1~C3 Cavity

Claims

1. circuit board and A membrane formed on the substrate, A catalyst material is positioned above the membrane and comes into contact with the gas to be detected to produce a catalytic reaction, A thermocouple layer that converts the heat generated by the catalytic reaction into an electrical signal, Equipped with, The substrate and the membrane are provided with a cavity below the catalyst material that exposes the lower surface of the catalyst material. A thermoelectric gas sensor characterized by the following features.

2. The substrate has a first cavity portion that includes the outer periphery of the catalyst material as the cavity portion, The thermoelectric gas sensor according to claim 1, wherein the membrane comprises a second cavity formed on the outer circumference of the catalyst material and a third cavity formed directly below the lower surface of the catalyst material.

3. The thermoelectric gas sensor according to claim 2, wherein the thermocouple layer is configured to be in contact with the catalyst material in portions excluding the third cavity.

4. The thermoelectric gas sensor according to claim 2, wherein the third cavity is formed by dividing it into multiple regions below the catalyst material.

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