A MEMS gas sensor

Abstract

The present disclosure relates to the field of gas sensors, and specifically provides a MEMS gas sensor. The MEMS gas sensor comprises a substrate and at least one sensing structure for sensing the same or different gases; the sensing structure comprises an electrode structure, a catalyst layer and a filter layer; the electrode structure comprises an end portion and a middle portion, the middle portion is supported by the end portion to form a gap between the middle portion and the substrate, the middle portion has a hollow portion, the hollow portion prevents the catalyst layer formed on the middle portion of the electrode structure from falling onto the substrate, and the filter layer covers the catalyst layer and the end portion of the electrode structure, and together with the substrate, seals the gap to form a cavity. In the MEMS gas sensor of the present disclosure, the electrode structure can simultaneously satisfy the functions of heating the catalyst layer, testing the resistance of the catalyst layer and bearing the catalyst layer, and an additional support structure is not needed to bear the catalyst layer, thereby reducing the volume of the gas sensor.

Description

Technical Field

[0001] This disclosure relates to the field of semiconductor devices, and more particularly to a MEMS (Micro-Electro-Mechanical System) gas sensor. Background Technology

[0002] MEMS gas sensors, with their advantages of miniaturization, high sensitivity, and low power consumption, are widely used in industrial safety, environmental monitoring, and smart home applications. To achieve even more compact device dimensions, the size of MEMS gas sensors needs to be further reduced. Summary of the Invention

[0003] To address the aforementioned issues, this disclosure provides a MEMS gas sensor.

[0004] The MEMS gas sensor disclosed herein includes: a substrate and at least one sensing structure, the sensing structure being used to sense a specific gas, the gases sensed by the sensing structure may be the same or different, the sensing structure including an electrode structure, a catalyst layer and a filter layer, the electrode structure including an end portion and a middle portion, the middle portion being supported by the end portion to form a gap between the middle portion and the substrate, the middle portion having a cutout, the cutout ensuring that the catalyst layer formed thereon cannot fall onto the substrate, the filter layer covering the catalyst layer and the end portion of the electrode structure, together with the substrate sealing the gap between the middle portion and the substrate to form a cavity, the height of the cavity being greater than 0.5 μm.

[0005] In some embodiments, the size of the cutout ranges from 1 μm to 100 μm. In some embodiments, the size of the cutout ranges from 1 μm to 30 μm. In some embodiments, the size of the cutout ranges from 1 μm to 20 μm.

[0006] In some embodiments, the electrode structure includes a test electrode and a heating electrode, the test electrode being used to obtain the resistance of the catalyst layer, and the heating electrode being used to heat the catalyst layer, wherein the width of the test electrode is less than or equal to the width of the heating electrode.

[0007] In some embodiments, the thickness of the test electrode and the heating electrode ranges from 1 μm to 100 μm; the width of the test electrode and the heating electrode ranges from 1 μm to 100 μm. In some embodiments, the thickness of the test electrode and the heating electrode ranges from 1 μm to 30 μm; the width of the test electrode and the heating electrode ranges from 1 μm to 30 μm. In some embodiments, the thickness of the test electrode and the heating electrode ranges from 1 μm to 20 μm; the width of the test electrode and the heating electrode ranges from 1 μm to 20 μm.

[0008] In some embodiments, the test electrode and the heating electrode are formed in the same process.

[0009] In some embodiments, the test electrode and the heating electrode are formed on two separate planes.

[0010] According to one embodiment of this disclosure, the MEMS gas sensor further includes: a test conductive pad adapted to apply a test electrical signal; and a heating conductive pad adapted to apply a heating electrical signal; the test conductive pad and the heating conductive pad are formed on the substrate and located at the periphery of the end.

[0011] According to one embodiment of this disclosure, the MEMS gas sensor further includes: a first grounding pad adapted to apply a grounding signal, the first grounding pad being formed on the substrate and located at the periphery of the end.

[0012] In some embodiments, the test electrode includes a first test end, a second test end, and a test intermediate portion located between the first test end and the second test end. The first test end of the test electrode is adapted to be electrically connected to a test conductive pad, and the second test end is adapted to be electrically connected to a first ground pad. The first test end and the second test end of the test electrode are adapted to suspend and support the test intermediate portion of the test electrode, forming a gap between them and the substrate.

[0013] In some embodiments, the test middle portion of the test electrode includes a first comb-shaped test electrode and a second comb-shaped test electrode. The first and second comb-shaped test electrodes are comb-shaped. The first comb-shaped test electrode includes a first comb handle and a plurality of parallel first comb teeth. The interval between two adjacent first comb teeth is 10 μm to 100 μm. One end of the plurality of parallel first comb teeth is electrically connected to the first comb handle, and the other end is a free end. The second comb-shaped test electrode includes a second comb handle and a plurality of parallel second comb teeth. The interval between two adjacent second comb teeth is 10 μm to 100 μm. One end of the plurality of parallel second comb teeth is electrically connected to the second comb handle, and the other end is a free end. The first and second comb teeth are arranged alternately.

[0014] According to one embodiment of this disclosure, the MEMS gas sensor further includes: a second grounding pad adapted to apply a grounding signal, the second grounding pad being formed on the substrate and located at the periphery of the end.

[0015] In some embodiments, the heating electrode includes a first heating end, a second heating end, and a heating intermediate portion located between the first heating end and the second heating end. The first heating end of the heating electrode is adapted to be electrically connected to a heating conductive pad, and the second heating end is adapted to be electrically connected to a second grounding pad. The first heating end and the second heating end of the heating electrode are adapted to suspend and support the heating intermediate portion of the heating electrode, forming a gap between them and the substrate.

[0016] In some embodiments, the heating middle portion of the heating electrode is curved or zigzag-shaped; the heating middle portion is interposed between the corresponding staggered first and second comb teeth of the test electrode.

[0017] In some embodiments, the first grounding pad and the second grounding pad are the same grounding pad.

[0018] In some embodiments, the catalyst layer includes a metal oxide material, the surface of which is coated with palladium, platinum and gold atoms, and the metal oxide material includes one or more of SnO2, WO3, Nb2O5, Y2O3, ZrO2, CeO2, La2O3, HfO2, Ta2O5, In2O3, CuO, Fe2O3, NiO and Cu2O.

[0019] In some embodiments, the catalyst layer further includes a porous material, wherein palladium, platinum and gold atoms are fixed in the pores of the porous material, and the porous material includes one or more of carbon black, graphite and zeolite.

[0020] In some embodiments, the catalyst layer further includes a filter layer for absorbing interfering gases and moisture in the air. The filter layer is made of materials including SnO2 and / or WO3, as well as one or more of carbon black, graphite, and zeolite.

[0021] In some embodiments, the substrate is made of aluminum oxide, quartz, glass, silicon carbide, or silicon.

[0022] In some embodiments, the test electrode or the heating electrode is composed of a single metal, the single metal material including gold, platinum or copper; or the test electrode or the heating electrode is composed of two or more layers of metal, the outer layer material of the two or more layers of metal being platinum or gold.

[0023] This disclosure also provides a method for fabricating a MEMS gas sensor, comprising: providing a substrate, the substrate including a first region and a second region; forming an electrode structure in the first region of the substrate, the electrode structure having an end and a middle portion, the end supporting the middle portion and forming a gap between the middle portion and the substrate, the middle portion having a cutout; forming a catalyst layer, the catalyst layer being formed in the middle portion of the electrode structure, the catalyst layer being unable to fall onto the substrate from the cutout; forming a filter layer, the filter layer covering the catalyst layer and the end of the electrode structure, and sealing the gap between the middle portion and the substrate together with the substrate to form a cavity.

[0024] In some embodiments, forming the electrode structure includes: forming a sacrificial layer on a substrate, the sacrificial layer covering a first region of the substrate and exposing a second region of the substrate; forming a metal layer covering the second region of the substrate and the surface of the sacrificial layer; and forming a mask layer located above the metal layer, covering portions where the test electrode and the heating electrode do not need to be fabricated.

[0025] In some embodiments, the formation of the electrode structure further includes: electroplating, wherein the metal layer is used as a cathode for electroplating, and the portion of the metal layer covered by the mask layer cannot contact the electroplating solution and cannot be electroplated.

[0026] In some embodiments, the electroplating bath temperature is 20℃-60℃, and the electroplating current density is 1A / dm³. 2 -5A / dm 2 The electroplating solution contains Au or Pt metal ions. After electroplating, the thickness of the test electrode and the heating electrode ranges from 1 μm to 100 μm. In some embodiments, the thickness of the test electrode and the heating electrode after electroplating ranges from 1 μm to 30 μm. In some embodiments, the thickness of the test electrode and the heating electrode after electroplating ranges from 1 μm to 10 μm.

[0027] In some embodiments, forming the electrode structure further includes removing the mask layer and the metal layer covered by the mask layer.

[0028] In some embodiments, the electrode structure includes a test electrode and a heating electrode. The test electrode includes a test intermediate portion, which includes a first comb-shaped test electrode and a second comb-shaped test electrode. The first and second comb-shaped test electrodes are comb-shaped, and the first teeth of the first comb-shaped test electrode and the second teeth of the second comb-shaped test electrode are arranged alternately. The heating electrode includes a heating intermediate portion, which is curved or zigzag-shaped and interspersed between the corresponding alternately arranged first and second comb teeth of the test electrode.

[0029] In some embodiments, the electrode structure further includes a first test end and a second test end of the test electrode, wherein a test middle portion of the test electrode is located between the first test end and the second test end. In some embodiments, a test conductive pad and a first grounding pad are also formed in a second region of the substrate, wherein the first test end of the test electrode is electrically connected to the test conductive pad, and the second test end is electrically connected to the first grounding pad.

[0030] In some embodiments, the electrode structure further includes a first heating end and a second heating end of a heating electrode, wherein a heating middle portion of the heating electrode is located between the first heating end and the second heating end. In some embodiments, a heating conductive pad and a second grounding pad are also formed in a second region of the substrate, wherein the first heating end of the heating electrode is electrically connected to the heating conductive pad, and the second heating end is electrically connected to the second grounding pad.

[0031] In some embodiments, the metal layer material includes Au, Pt, Ti, or Cu, with a thickness of 20 angstroms to 200 angstroms, and the metal layer is fabricated by methods including vapor deposition and sputtering.

[0032] In some embodiments, the formation of the electrode structure further includes: removing the sacrificial layer by immersion in a solution to remove the sacrificial layer; after removal, the first test end and the second test end of the test electrode suspend and support the test middle portion of the test electrode, forming a gap between them and the substrate; the first heating end and the second heating end of the heating electrode suspend and support the heating middle portion of the heating electrode, forming a gap between them and the substrate.

[0033] In some embodiments, the sacrificial layer material is magnesium oxide, the thickness of the sacrificial layer ranges from 1 μm to 20 μm, and the solution for removing the sacrificial layer includes a phosphoric acid solution.

[0034] The MEMS gas sensor disclosed herein has the advantage that, within the MEMS gas sensor, the electrode structure can simultaneously fulfill the functions of heating the catalyst layer, testing the resistance of the catalyst layer, and supporting the catalyst layer, eliminating the need for an additional support structure to support the catalyst layer and reducing the size of the gas sensor. Furthermore, the catalyst layer of the MEMS gas sensor disclosed herein is in direct contact with air of low thermal conductivity, thus providing better heat preservation.

[0035] To more clearly illustrate the technical solution of this disclosure, the disclosure will be further described below in conjunction with the accompanying drawings. Attached Figure Description

[0036] Figure 1 This is a schematic cross-sectional view of a MEMS gas sensor disclosed herein.

[0037] Figure 2 for Figure 1 The diagram shows a top view of the MEMS gas sensor.

[0038] Figure 3 for Figure 1 The diagram shows a top view of the test electrode of a MEMS gas sensor.

[0039] Figure 4 for Figure 1 The diagram shows a top view of the heating electrode of a MEMS gas sensor.

[0040] Figure 5 This is a schematic cross-sectional view of another MEMS gas sensor disclosed herein.

[0041] Figure 6 for Figure 1 The diagram shows a flowchart of the fabrication process for a MEMS gas sensor.

[0042] Figures 7-15 for Figure 1 The diagram shows a cross-sectional view of the MEMS gas sensor during its fabrication process.

[0043] Figure 7 for Figure 1 The diagram shows a cross-sectional view of the substrate during the fabrication of the MEMS gas sensor.

[0044] Figure 8 for Figure 1 The diagram shows a cross-sectional view of the MEMS gas sensor after the formation of the sacrificial layer.

[0045] Figure 9 for Figure 1 The diagram shows a cross-sectional view of the MEMS gas sensor after the metal layer has been formed.

[0046] Figure 10 for Figure 1 The diagram shows a cross-sectional view of the MEMS gas sensor after the mask layer has been formed.

[0047] Figure 11 for Figure 1 The diagram shows a cross-sectional view of the electroplated MEMS gas sensor.

[0048] Figure 12 for Figure 1 The diagram shows a cross-section of the MEMS gas sensor after the mask layer has been removed.

[0049] Figure 13 for Figure 1 The diagram shows a cross-sectional view of the MEMS gas sensor after the electrode structure has been formed.

[0050] Figure 14 for Figure 1 The diagram shows a cross-sectional view of a MEMS gas sensor with the sacrificial layer removed.

[0051] Figure 15 for Figure 1 The diagram shows a cross-sectional view of the MEMS gas sensor after the formation of the catalyst layer and filter layer. Detailed Implementation

[0052] This disclosure discloses a MEMS gas sensor, including a substrate and a sensing structure for sensing a specific gas. The sensing structure includes an electrode structure, a catalyst layer, and a filter layer. The electrode structure comprises an end portion and a middle portion, with the middle portion supported by the end portion to form a gap between the middle portion and the substrate. The middle portion has a cutout, which prevents the catalyst layer formed thereon from falling onto the substrate. The filter layer covers the catalyst layer and the end portion of the electrode structure, sealing the gap between the middle portion and the substrate together with the substrate to form a cavity. This MEMS gas sensor's electrode structure can simultaneously perform the functions of heating the catalyst layer, testing the catalyst layer's resistance, and supporting the catalyst layer. Therefore, this MEMS gas sensor does not require an additional support structure, reducing the sensor's size.

[0053] Furthermore, the catalyst layer of the MEMS gas sensor disclosed herein is in direct contact with air with low thermal conductivity, thus the MEMS gas sensor disclosed herein has a better heat preservation effect.

[0054] The technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this disclosure, and not all of them. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0055] The step numbers in the following embodiments are for ease of explanation only, and the order of the steps is not limited. The execution order of each step in the embodiments can be adaptively adjusted according to the understanding of those skilled in the art. In the description of this disclosure, "first" and "second" are only used to distinguish technical features and should not be construed as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the sequential relationship of the known technical features.

[0056] Figure 1 This is a schematic diagram of a cross-section of a MEMS gas sensor disclosed herein. Figure 1 As shown, a MEMS gas sensor disclosed herein includes a substrate 10 and a sensing structure 20. The sensing structure 20 is used to sense a specific gas. The sensing structure 20 includes an electrode structure 21, a catalyst layer 22, and a filter layer 23. The electrode structure 21 includes a test electrode 211 and a heating electrode 212, which are formed in the same process and located on the same plane. The electrode structure 21 includes an end portion and a middle portion. The middle portion is supported by the end portion to form a gap between the middle portion and the substrate. The middle portion has a cutout 40. The size of the cutout 40 ranges from 1 μm to 100 μm. In some embodiments, the more preferred size range of the cutout 40 is from 1 μm to 30 μm. In some embodiments, the more preferred size range of the cutout 40 is 1 μm. Within a size range of -20μm, the perforations can accommodate various ratios of catalyst layers 22, preventing the catalyst layers 22 formed thereon from falling onto the substrate 10. The filter layer 23 covers the catalyst layer 22 and the ends of the electrode structure, and together with the substrate 10, seals the gap between the middle part and the substrate 10, forming a cavity 30 to prevent the catalyst layer 22 from directly contacting interfering gases and moisture.

[0057] In some embodiments, the catalyst layer 22 is used to sense the target detection gas. When the target detection gas comes into contact with the catalyst layer 22, the resistance of the catalyst layer 22 changes. The catalyst layer 22 includes a metal oxide material, and the surface of the metal oxide material molecules is coated with metal atoms of palladium, platinum, and gold. The metal oxide material includes one or more of SnO2, WO3, Nb2O5, Y2O3, ZrO2, CeO2, La2O3, HfO2, Ta2O5, In2O3, CuO, Fe2O3, NiO, and Cu2O.

[0058] In some embodiments, the catalyst layer 22 further includes a porous material, wherein palladium, platinum and gold metal atoms are fixed in the pores of the porous material, and the porous material includes one or more of carbon black, graphite and zeolite.

[0059] In some embodiments, the filter layer 23 is used to absorb interfering gases and water vapor in the air, and the material of the filter layer includes SnO2 and / or WO3, as well as one or more of carbon black, graphite, and zeolite.

[0060] In some embodiments, the substrate 10 is made of aluminum oxide, quartz, glass, silicon carbide, or silicon.

[0061] Figure 2 This is a top view schematic diagram of a MEMS gas sensor disclosed herein. Figure 2 As shown, the electrode structure 21 includes a test electrode 211 and a heating electrode 212. In some embodiments, the test electrode 211 and the heating electrode 212 are electrically insulated from each other. In some embodiments, the test electrode 211 and the heating electrode 212 are in the same layer. A test conductive pad 101, a heating conductive pad 102, a first ground pad 103, and a second ground pad 104 are formed on the substrate 10. In some embodiments, the first ground pad 103 and the second ground pad 104 may be the same.

[0062] In some embodiments, the test electrode 211 and the heating electrode 212 are composed of a single metal, the single metal material including gold, platinum or copper, or the test electrode 211 and the heating electrode 212 are composed of two or more layers of metal, the outer layer material of the two or more layers of metal being platinum or gold.

[0063] Figure 3 This is a schematic diagram of the test electrode 211 of the MEMS gas sensor disclosed herein. Figure 3As shown, the test electrode 211 includes a first test end 111, a second test end 112, and a test intermediate portion 110 located between the first test end and the second test end. The first test end 111 of the test electrode 211 is adapted to be electrically connected to the test conductive pad 101, and the second test end 112 is adapted to be electrically connected to the first ground pad 103. The first test end 111 and the second test end 112 of the test electrode 211 are adapted to suspend and support the test intermediate portion 110 of the test electrode 211, forming a gap with the substrate 10.

[0064] In some embodiments, the test middle portion 110 of the test electrode 211 includes a first comb-shaped test electrode 211A and a second comb-shaped test electrode 211B. The first comb-shaped test electrode 211A and the second comb-shaped test electrode 211B are comb-shaped. The first comb-shaped test electrode 211A includes a first comb handle and a plurality of parallel first comb teeth. The interval W1 between two adjacent first comb teeth is 80 μm. One end of the plurality of parallel first comb teeth is electrically connected to the first comb handle, and the other end is a free end. The second comb-shaped test electrode 211B includes a second comb handle and a plurality of parallel second comb teeth. The interval W2 between two adjacent second comb teeth is 80 μm. One end of the plurality of parallel second comb teeth is electrically connected to the second comb handle, and the other end is a free end. The first comb teeth and the second comb teeth are arranged alternately.

[0065] Figure 4 This is a schematic diagram of the heating electrode 212 of the MEMS gas sensor disclosed herein. Figure 4 As shown, the heating electrode 212 includes a first heating end 121, a second heating end 122, and a heating intermediate portion 120 located between the first heating end and the second heating end. The first heating end 121 of the heating electrode 212 is adapted to be electrically connected to the heating conductive pad 102, and the second heating end 122 is adapted to be electrically connected to the second grounding pad 104. The first heating end 121 and the second heating end 122 of the heating electrode 212 are adapted to suspend and support the heating intermediate portion 120 of the heating electrode, forming a gap with the substrate 10.

[0066] In some embodiments, the heating middle portion 120 of the heating electrode 212 is curved or zigzag-shaped; the heating middle portion 120 is inserted between the corresponding staggered first comb teeth and second comb teeth of the test electrode 211.

[0067] According to the distribution of the electrode structure 21 in this embodiment, the interval between two adjacent first comb teeth and between two adjacent second comb teeth in the test electrode 211 is 80μm, so the size of the formed hollow is 20μm.

[0068] Figure 5 This is a schematic diagram of a cross-section of another MEMS gas sensor disclosed herein. (As shown...) Figure 5 As shown, another MEMS gas sensor disclosed herein, compared with... Figure 2 The difference in the MEMS gas sensor shown is that the test electrode 211 and the heating electrode 212 in the electrode structure 21 are located on two planes respectively. In this case, the projections of the test electrode 211 and the heating electrode 212 on the substrate may or may not overlap. Figure 5 The other parts of the MEMS gas sensor shown are similar to Figure 2 The MEMS gas sensor shown is the same and will not be described in detail here.

[0069] This disclosure provides a method for fabricating a MEMS gas sensor. Figure 6 A flowchart illustrating the manufacturing method is shown.

[0070] like Figure 6 As shown, the manufacturing method includes the following steps: S101, providing a substrate, the substrate including a first region and a second region; S102, forming a sacrificial layer on the first region of the substrate; S103, forming a metal layer, the metal layer covering the surface of the sacrificial layer and the second region of the substrate; S104, forming a mask layer, the mask layer located on the surface of the metal layer, covering the portion where the test electrode and the heating electrode do not need to be fabricated; S105, performing electroplating with the metal layer as a cathode; S106, removing the mask layer and the metal layer covered by the mask layer; S107, removing the sacrificial layer by solution immersion; S108, forming a catalyst layer and a filter layer.

[0071] The following is combined Figures 7-15 A schematic diagram of the cross-section of the intermediate process, with detailed explanation. Figure 6 Each step in the described manufacturing method.

[0072] like Figure 7 As shown, a substrate 10 is provided, the substrate 10 including a first region 11 and a second region 12.

[0073] like Figure 8 As shown, a sacrificial layer 50 is formed on a first region 11 of the substrate 10, exposing a second region 12 of the substrate 10. The thickness of the sacrificial layer 50 is 20 μm, and the material of the sacrificial layer 50 includes magnesium oxide.

[0074] In some embodiments, the method for fabricating the sacrificial layer 50 includes: completely depositing the sacrificial layer 50 on the substrate 10; coating the sacrificial layer 50 with photoresist; selectively exposing the substrate using a patterned mask to remove the photoresist at positions corresponding to the second region 12; removing the sacrificial layer 50 at positions corresponding to the second region 12; and finally removing the photoresist at positions corresponding to the first region 11 to obtain the desired result. Figure 8 The structure shown.

[0075] like Figure 9 As shown, a metal layer 60 is formed on the surface of the second region 12 of the substrate 10 and on the surface of the sacrificial layer 50. The material of the metal layer includes Ti or Cu, and the thickness of the metal layer is 100 angstroms.

[0076] like Figure 10 As shown, a mask layer 70 is formed on the metal layer 60, and the mask layer 70 covers the portion where electrodes do not need to be fabricated. In some embodiments, the method for fabricating the mask layer 70 includes: coating a complete photoresist layer on the surface of the metal layer 60; selectively exposing the mask layer using a patterned mask; and removing the photoresist layer outside the mask layer 70 to obtain the desired result. Figure 10 The mask layer 70 is shown.

[0077] like Figure 11 As shown, the completed structure is placed in the electroplating solution 80, and the metal layer 60 is connected to the cathode 90 for electroplating to form an electroplated layer 61. In some embodiments, the temperature of the electroplating solution is 20°C, and the electroplating current density is 5A / dm³. 2 The electroplating solution contains Au or Pt metal ions.

[0078] like Figure 12 , Figure 13 As shown, after electroplating, the mask layer is removed, and the metal layer covered by the mask layer is further removed to form a layer as shown. Figure 13 The electrode structure 21 shown is a stacked structure of the metal layer 60 and the electroplated layer 61.

[0079] In some embodiments, the width of the electrode structure 21 ranges from 1 μm to 100 μm, and the thickness also ranges from 1 μm to 100 μm. The thickness and width ranges of the electrode structure 21 are related to the catalyst layer 22 formed on the electrode structure 21. In some embodiments, the width of the electrode structure 21 ranges from 1 μm to 30 μm, and the thickness also ranges from 1 μm to 30 μm. Electrode structures within this range can accommodate catalyst layers 22 with various ratios.

[0080] The electrode structure 21 includes a test electrode 211 and a heating electrode 212. Figure 13 (a) and Figure 13 (b) Cross-sectional schematic diagrams of the test electrode 211 and the heating electrode 212 are provided respectively. In fact, in the embodiment, the test electrode 211 and the heating electrode 212 are formed in the same process and located on the same plane. For ease of illustration, they are shown separately. Figure 13 (a) and Figure 13 (b) A cross-sectional schematic diagram of the test electrode after the mask layer has been removed and a cross-sectional schematic diagram of the heating electrode are shown respectively.

[0081] like Figure 13 As shown in (a), the test electrode 211 includes a test middle portion 110, which includes a first comb-shaped test electrode 211A and a second comb-shaped test electrode 211B. The first comb-shaped test electrode 211A and the second comb-shaped test electrode 211B are comb-shaped. The first comb teeth of the first comb-shaped test electrode 211A and the second comb teeth of the second comb-shaped test electrode 211B are arranged alternately and correspondingly. The test middle portion 110 of the test electrode 211 is located on the sacrificial layer 50.

[0082] like Figure 13 As shown in (b), the heating electrode 212 includes a heating middle portion 120. The heating middle portion 120 of the heating electrode 212 is curved or zigzag-shaped and is inserted between the corresponding staggered first comb teeth and second comb teeth of the test electrode 211. The heating middle portion 120 of the heating electrode 212 is also located on the sacrificial layer 50.

[0083] Continue to refer to Figure 13 (a) The test electrode 211 further includes a first test end 111 and a second test end 112, with the test middle portion 110 of the test electrode 211 located between the first test end 111 and the second test end 112. In some embodiments, a test conductive pad 101 and a first ground pad 103 are also formed on the substrate 10. The test conductive pad 101 and the first ground pad 103 are formed in the same process as the test electrode 211. The first test end 111 of the test electrode 211 is electrically connected to the test conductive pad 101, and the second test end 112 is electrically connected to the first ground pad 103. The first test end 111 and the second test end 112 of the test electrode 211 are located on the sidewall of the sacrificial layer 50.

[0084] Continue to refer to Figure 13(b) The heating electrode 212 further includes a first heating end 121 and a second heating end 122. The heating middle portion 120 of the heating electrode 212 is located between the first heating end 121 and the second heating end 122. In some embodiments, a heating conductive pad 102 and a second grounding pad 104 are also formed on the substrate 10. The heating conductive pad 102 and the second grounding pad 104 are formed in the same process as the heating electrode 212. The first heating end 121 of the heating electrode 212 is electrically connected to the heating conductive pad 102, and the second heating end 122 is electrically connected to the second grounding pad 104. The first heating end 121 and the second heating end 122 of the heating electrode 212 are located on the sidewall of the sacrificial layer 50.

[0085] like Figure 14 As shown, the entire structure fabricated in the above steps is placed in solution 91 to remove the sacrificial layer 50. After removal, a gap is formed between the electrode structure 21 and the substrate 10. The solution 91 is a phosphoric acid solution, which does not damage other materials during the removal of the sacrificial layer 50.

[0086] like Figure 15 As shown, a catalyst layer 22 and a filter layer 23 are formed on the electrode structure 21. The catalyst layer 22 cannot fall from the cutout 40 of the electrode structure 21 onto the substrate 10. The filter layer 23 covers the catalyst layer 22 and the end of the electrode structure 21, and together with the substrate 10, seals the gap between the middle part and the substrate 10 to form a cavity 30. The height of the cavity 30 is 0.5 μm.

[0087] This disclosure discloses a MEMS gas sensor, including a substrate and a sensing structure for sensing a specific gas. The sensing structure includes an electrode structure, a catalyst layer, and a filter layer. The electrode structure comprises an end portion and a middle portion, with the middle portion supported by the end portion to form a gap between the middle portion and the substrate. The middle portion has a cutout with a size ranging from 10 to 100 μm, ensuring that the catalyst layer formed thereon cannot fall onto the substrate. The filter layer covers the catalyst layer and the end portion of the electrode structure, sealing the gap between the middle portion and the substrate together with the substrate to form a cavity. This MEMS gas sensor's electrode structure can simultaneously perform the functions of heating the catalyst layer, testing the catalyst layer's resistance, and supporting the catalyst layer. Therefore, this MEMS gas sensor eliminates the need for an additional support structure, reducing the sensor's size.

[0088] The various specific embodiments described above and shown in the accompanying drawings are for illustrative purposes only and are not exhaustive. Any modifications made by those skilled in the art within the scope of the basic technical concept of this disclosure are within the protection scope of this disclosure.

Claims

1. A MEMS gas sensor, characterized in that, include: substrate; as well as At least one sensing structure for sensing a specific gas, wherein each of the sensing structures can sense the same or different gases; The sensing structure includes an electrode structure, a catalyst layer, and a filter layer. The electrode structure includes an end portion and a middle portion. The middle portion is supported by the end portion to form a gap between the middle portion and the substrate. The middle portion has a cutout, which prevents the catalyst layer formed thereon from falling onto the substrate. The filter layer covers the catalyst layer and the end portion of the electrode structure, and together with the substrate, seals the gap between the middle portion and the substrate to form a cavity. The cavity height is greater than 0.5 μm.

2. The MEMS gas sensor according to claim 1, characterized in that, The size of the cutout is within the range of 1μm to 30μm.

3. The MEMS gas sensor according to claim 2, characterized in that, The electrode structure includes a test electrode and a heating electrode. The test electrode is used to obtain the resistance of the catalyst layer, and the heating electrode is used to heat the catalyst layer. The width of the test electrode is less than or equal to the width of the heating electrode.

4. The MEMS gas sensor according to claim 3, characterized in that, The thickness of the test electrode and the heating electrode is within the range of 1 μm to 30 μm; the width of the test electrode and the heating electrode is within the range of 1 μm to 30 μm.

5. The MEMS gas sensor according to claim 4, characterized in that, The test electrode and the heating electrode are formed in the same process step.

6. The MEMS gas sensor according to claim 5, characterized in that, The test electrode and the heating electrode are respectively formed on two planes.

7. The MEMS gas sensor according to claim 6, characterized in that, Also includes: Test conductive pad, suitable for applying test electrical signals; A heating conductive pad, suitable for applying heating electrical signals; A first grounding pad and a second grounding pad, the first grounding pad and the second grounding pad being adapted to apply a grounding signal; The test conductive pad, the heating conductive pad, the first ground pad, and the second ground pad are formed on the substrate and located around the end of the electrode structure.

8. The MEMS gas sensor according to claim 7, characterized in that, The test electrode includes a first test end, a second test end, and a test intermediate portion located between the first test end and the second test end. The first test end of the test electrode is adapted to be electrically connected to the test conductive pad, and the second test end of the test electrode is adapted to be electrically connected to the first grounding pad. The first test end and the second test end of the test electrode are adapted to suspend and support the test intermediate portion of the test electrode.

9. The MEMS gas sensor according to claim 8, characterized in that, The test middle portion of the test electrode includes a first comb-shaped test electrode and a second comb-shaped test electrode. The first comb-shaped test electrode and the second comb-shaped test electrode are comb-shaped. The first comb-shaped test electrode includes a first comb handle and a plurality of parallel first comb teeth. One end of the plurality of parallel first comb teeth is electrically connected to the first comb handle, and the other end is a free end. The second comb-shaped test electrode includes a second comb handle and a plurality of parallel second comb teeth. One end of the plurality of parallel second comb teeth is electrically connected to the second comb handle, and the other end is a free end. The first comb teeth and the second comb teeth are arranged alternately.

10. The MEMS gas sensor according to claim 9, characterized in that, The heating electrode includes a first heating end, a second heating end, and a heating intermediate portion located between the first heating end and the second heating end. The first heating end of the heating electrode is adapted to be electrically connected to the heating conductive pad, and the second heating end of the heating electrode is adapted to be electrically connected to the second grounding pad. The first heating end and the second heating end of the heating electrode are adapted to suspend and support the heating intermediate portion of the heating electrode.

11. The MEMS gas sensor according to claim 10, characterized in that, The heating middle portion of the heating electrode is curved or zigzag-shaped; the heating middle portion of the heating electrode is inserted between the corresponding staggered first comb teeth and the second comb teeth of the test electrode.

12. The MEMS gas sensor according to claim 11, characterized in that, The first grounding pad and the second grounding pad are the same grounding pad.

13. The MEMS gas sensor according to any one of claims 1-12, characterized in that, The catalyst layer includes a metal oxide material, and the surface of the metal oxide material molecules is coated with metal atoms of palladium, platinum and gold. The metal oxide material includes one or more of SnO2, WO3, Nb2O5, Y2O3, ZrO2, CeO2, La2O3, HfO2, Ta2O5, In2O3, CuO, Fe2O3, NiO and Cu2O.

14. The MEMS gas sensor according to claim 13, characterized in that, The catalyst layer also includes a porous material, in which palladium, platinum and gold atoms are fixed in the pores of the porous material. The porous material includes one or more of carbon black, graphite and zeolite.

15. The MEMS gas sensor according to any one of claims 1-12, characterized in that, The filter layer is used to absorb interfering gases and water vapor in the air; The filter layer is made of SnO2 and / or WO3, as well as one or more of carbon black, graphite, and zeolite.

16. The MEMS gas sensor according to claim 1, characterized in that, The substrate material includes aluminum oxide, quartz, glass, silicon carbide, or silicon.

17. The MEMS gas sensor according to any one of claims 3-6, characterized in that, The test electrode or the heating electrode is composed of a single metal, including gold, platinum or copper; or the test electrode or the heating electrode is composed of two or more layers of metal, with the outer layer of the two or more layers of metal being platinum or gold.

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