MEMS chip, preparation method thereof and gas sensor

Abstract

The invention provides an MEMS chip, a preparation method thereof and a gas sensor, and the preparation method comprises the steps: a first pole plate layer, a gap layer and a second pole plate layer are sequentially formed on the first side of a substrate, the gap layer is provided with a sacrifice part, and the sacrifice part is located between the first pole plate layer and the second pole plate layer; a vent hole is formed in the second polar plate layer, the first end of the vent hole is communicated with the outside, and the second end of the vent hole extends to the sacrificial part; and etching and removing the sacrificial part from the vent hole so as to form a gas detection cavity between the first polar plate layer and the second polar plate layer, thereby obtaining the MEMS chip.

Description

Technical Field

[0001] The present application relates to the technical field of gas sensors, and more specifically, to a MEMS chip and a preparation method thereof, and a gas sensor. Background Art

[0002] In related technologies, gas leakage from equipment can have an impact on our health, quality of life, life safety, and the operation of industrial processes. For example, some refrigerant gases are flammable and explosive, so real-time detection of such refrigerant leakage becomes extremely important.

[0003] The capacitive gas sensors currently used are mostly sensitive to the environment (humidity, temperature, pressure). Traditional capacitive gas sensors mostly use dielectric materials with selective gas adsorption characteristics (for example, high molecular polymers or metal oxides, etc.), and these dielectric materials easily adsorb water vapor in the air and change the capacitance, resulting in large detection errors. Moreover, this type of dielectric material is not only expensive, but also has a short lifespan, resulting in high cost of use. Summary of the invention

[0004] The present application provides a new technical solution for a method for preparing a MEMS chip, which can at least solve the problem of large detection errors of existing gas sensors.

[0005] The present application also provides a new technical solution for a MEMS chip.

[0006] The present application also provides a new technical solution for a gas sensor.

[0007] According to a first aspect of the present application, a method for preparing a MEMS chip is provided, comprising:

[0008] Forming a first electrode layer, a gap layer, and a second electrode layer in sequence on a first side of the substrate, wherein the gap layer has a sacrificial portion, and the sacrificial portion is located between the first electrode layer and the second electrode layer;

[0009] forming a vent hole on the second electrode layer, wherein a first end of the vent hole is connected to the outside, and a second end of the vent hole extends to the sacrificial portion;

[0010] The sacrificial portion is removed from the vent hole by etching to form a gas detection cavity between the first electrode layer and the second electrode layer to obtain a MEMS chip.

[0011] Optionally, the method of forming the first electrode layer on the first side of the substrate is:

[0012] N-type doping is performed on the first side of the substrate to obtain an N-type semiconductor, and the N-type semiconductor is formed as a first electrode layer.

[0013] Optionally, the preparation method further comprises:

[0014] The first side of the substrate is doped with P type to obtain a P type semiconductor, and the N type semiconductor and the P type semiconductor form a PN junction temperature sensing unit.

[0015] Optionally, the first electrode layer, the gap layer and the second electrode layer are formed by deposition.

[0016] Optionally, the preparation method comprises:

[0017] Before depositing the gap layer, a first insulating layer is deposited on the first side of the substrate, wherein the first insulating layer is provided with a through groove, and the through groove corresponds to the first electrode layer;

[0018] Depositing a first passivation layer on a side of the first insulating layer away from the first electrode layer;

[0019] The first passivation layer covers the first insulating layer, a deposition groove is formed at a position corresponding to the first passivation layer and the through groove, the gap layer is arranged in the deposition groove, and the gap layer is formed as a whole as the sacrificial portion.

[0020] Optionally, the gap layer is deposited on the first side surface of the substrate, and a portion of the gap layer is formed as the sacrificial portion.

[0021] Optionally, chemical mechanical polishing is performed on the first side surface of the substrate.

[0022] Optionally, the method of forming the first electrode layer and the gap layer on the first side of the substrate includes:

[0023] depositing a second insulating layer on the first side of the substrate;

[0024] Depositing a first electrode layer on a side of the second insulating layer facing away from the substrate;

[0025] Depositing a first passivation layer on a side of the first electrode layer away from the second insulating layer;

[0026] A gap layer is deposited on a side of the first passivation layer away from the first electrode layer, and the gap layer is entirely formed as the sacrificial portion.

[0027] Optionally, the second insulating layer has a through hole, and a portion of the first electrode layer is deposited in the through hole and contacts the substrate.

[0028] Optionally, before depositing the second electrode layer, a second passivation layer is deposited on a side of the gap layer facing away from the substrate.

[0029] Optionally, chemical mechanical polishing is performed on a side of the second passivation layer facing away from the gap layer.

[0030] Optionally, the first passivation layer and the second passivation layer are formed of a hydrophobic material.

[0031] Optionally, before forming the vent hole, a third insulating layer is deposited on a side of the second electrode plate away from the gap layer.

[0032] According to a second aspect of the present application, a MEMS chip is provided. The MEMS chip is manufactured by any one of the manufacturing methods described above.

[0033] According to a third aspect of the present application, a gas sensor is provided, comprising the above-mentioned MEMS chip.

[0034] According to the preparation method of the MEMS chip of the present application, a gas detection cavity connected to the vent is formed between the first electrode layer and the second electrode layer, so that the gas entering the gas detection cavity can be used as a dielectric. When the gas to be detected enters the gas detection cavity from the vent, the capacitance of the variable capacitor formed by the first electrode layer and the second electrode layer changes accordingly, thereby achieving high-sensitivity gas detection. Compared with the prior art, there is no need to set additional dielectric materials, thereby simplifying the preparation process and reducing production costs. Moreover, using gas as a dielectric can effectively reduce the capacitance change caused by the adsorption of water vapor by the solid dielectric material, thereby reducing detection errors and improving the detection sensitivity of the micro-electromechanical gas sensor using the MEMS chip prepared by the present application.

[0035] Other features and advantages of the present application will become apparent from the following detailed description of exemplary embodiments of the present application with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate embodiments of the application and, together with the description, serve to explain the principles of the application.

[0037] Figure 1 is a flow chart of a method for preparing a MEMS chip according to an embodiment of the present application;

[0038] Figure 2 is a schematic diagram of a method for preparing a MEMS chip after forming a gap layer according to an embodiment of the present application;

[0039] Figure 3 is a structural schematic diagram of a MEMS chip obtained according to a method for preparing a MEMS chip according to an embodiment of the present application;

[0040] Figure 4is a schematic diagram of a method for preparing a MEMS chip according to another embodiment of the present application after a gap layer is formed;

[0041] Figure 5 is a structural schematic diagram of a MEMS chip obtained according to a method for preparing a MEMS chip according to another embodiment of the present application;

[0042] Figure 6 is a schematic diagram of a method for preparing a MEMS chip according to another embodiment of the present application after a gap layer is formed;

[0043] Figure 7 is a schematic diagram of a method for preparing a MEMS chip according to another embodiment of the present application after forming a second electrode layer;

[0044] Figure 8 It is a schematic structural diagram of a MEMS chip obtained according to a method for preparing a MEMS chip according to another embodiment of the present application.

[0045] Reference numerals

[0046] 100.MEMS chip;

[0047] 10. Substrate; 11. First electrode layer; 12. P-type semiconductor; 20. Gap layer; 30. Second electrode layer; 31. Vent; 40. First insulating layer; 50. First passivation layer; 60. Second insulating layer; 70. Second passivation layer; 80. Third insulating layer; 90. Pad. DETAILED DESCRIPTION

[0048] Various exemplary embodiments of the present application will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present application.

[0049] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the present application, its application, or uses.

[0050] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered as part of the specification.

[0051] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0052] It should be noted that like reference numerals and letters refer to similar items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0053] like Figures 1 to 8 As shown, an embodiment of the present application provides a method for preparing a MEMS chip, and the method includes S100 to S300.

[0054] S100, forming a first electrode layer 11, a gap layer 20, and a second electrode layer 30 in sequence on a first side of a substrate 10, wherein the gap layer 20 has a sacrificial portion, and the sacrificial portion is located between the first electrode layer 11 and the second electrode layer 30;

[0055] Specifically, the substrate 10 is configured as a silicon substrate 10, and a first electrode layer 11, a gap layer 20 and a second electrode layer 30 are formed on a first side (for example, an upper side) of the substrate 10, wherein the gap layer 20 is located between the first electrode layer 11 and the second electrode layer 30, at least a portion of the gap layer 20 is formed as a sacrificial portion, and the first electrode layer 11 and the second electrode layer 30 form a capacitor.

[0056] S200, forming a vent hole 31 on the second electrode layer 30, wherein a first end of the vent hole 31 is connected to the outside, and a second end of the vent hole 31 extends to the sacrificial portion;

[0057] In detail, a vent hole 31 can be formed on the side of the second electrode layer 30 away from the gap layer 20 by an etching process. The position of the vent hole 31 corresponds to the position of the sacrificial part. The first end of the vent hole 31 is connected to the outside, and the second end of the vent hole 31 extends to the surface of the sacrificial part away from the first electrode layer 11, so that the vent hole 31 can be used as a release hole.

[0058] S300 , etching and removing the sacrificial portion from the vent hole 31 to form a gas detection cavity between the first electrode layer 11 and the second electrode layer 30 , thereby obtaining the MEMS chip 100 .

[0059] That is, after the release hole is formed, the sacrificial portion can be selectively removed by etching process, so that a gas detection cavity connected to the vent hole 31 is formed between the first electrode layer 11 and the first electrode layer 11, thereby obtaining the MEMS chip 100.

[0060] In this embodiment, the first electrode layer 11 and the second electrode layer 30 of the MEMS chip 100 prepared in this application form a variable capacitor, and the dielectric in the gas detection cavity of the variable capacitor is gas. When the gas to be detected enters the gas detection cavity from the vent 31, the capacitance of the variable capacitor changes, thereby realizing gas detection.

[0061] The MEMS chip 100 prepared in the present application can be used for micro-electromechanical sensors to detect gas. For example, it can be used to detect toxic and harmful gases leaking from certain equipment. For example, third-generation refrigerants (R32, R134a), fourth-generation refrigerants (R290, R1234yf, R1234ze), etc. When there is no gas leakage, the dielectric in the gas detection cavity is air. When the gas leaks, the gas can enter the gas detection cavity through the vent 31, thereby causing the dielectric in the gas detection cavity to change. The dielectric constant of the dielectric of the variable capacitor changes, so that the capacitance of the variable capacitor changes, and the MEMS chip 100 can transmit the signal to the ASIC chip for further processing, and transmit it to the control unit. Among them, the effective capacitance of the variable capacitor can be 2pF~4pF.

[0062] Therefore, according to the preparation method of the MEMS chip provided in this embodiment, a gas detection cavity connected to the vent 31 is formed between the first electrode layer 11 and the second electrode layer 30, so that the gas entering the gas detection cavity can be used as a dielectric. When the gas to be detected enters the gas detection cavity from the vent 31, the capacitance of the variable capacitor formed by the first electrode layer 11 and the second electrode layer 30 changes accordingly, thereby achieving high-sensitivity gas detection. Compared with the prior art, there is no need to set additional dielectric materials, thereby simplifying the preparation process and reducing production costs. Moreover, using gas as a dielectric can effectively reduce the capacitance change caused by the adsorption of water vapor by the solid dielectric material, thereby reducing detection errors and improving the detection sensitivity of the microelectromechanical gas sensor using the MEMS chip 100 prepared by the present application.

[0063] In some embodiments of the present application, the method for forming the first electrode layer 11 on the first side of the substrate 10 is: performing N-type doping on the first side of the substrate 10 to obtain an N-type semiconductor, and the N-type semiconductor is formed into the first electrode layer 11.

[0064] That is to say, Figures 2 to 5 As shown, during the formation of the first electrode layer 11, a mask technique can be used to perform high-concentration N-type doping (N++) in a specific area on the substrate 10, and the doping rate is controlled to be 1E19 / cm 3 ~1E20 / cm 3 By doping the region, an N-type semiconductor with a high doping concentration can be formed, and the N-type semiconductor can be used as the first electrode layer 11 to ensure the conductivity and capacitance performance of the first electrode layer 11.

[0065] In this example, the first electrode layer 11 is formed by doping the substrate 10 , which does not increase the size of the MEMS chip 100 in the thickness direction and has a compact structure.

[0066] According to an embodiment of the present application, the preparation method further includes: performing P-type doping on the first side of the substrate 10 to obtain a P-type semiconductor 12 , and the N-type semiconductor and the P-type semiconductor 12 form a PN junction temperature sensing unit.

[0067] Specifically, Figures 2 to 5 As shown, after the first electrode layer 11 is formed, a mask technique can be used to perform high-concentration P-type doping (P+) on a specific area on the substrate 10, and the doping rate is controlled to be 1E19 / cm 3 ~1E20 / cm 3 . By doping this area, a P-type semiconductor 12 with a high doping concentration can be formed. The P-type semiconductor 12 forms a PN junction with the N-type semiconductor (i.e., the first electrode layer 11). This PN junction can be used as a temperature sensing unit to detect the temperature change of the gas environment. At the same time, this structure can also effectively prevent leakage and ensure the stability and reliability of the MEMS chip 100. The micro-electromechanical gas sensor of the MEMS chip 100 prepared using this embodiment can compensate for the interference caused by environmental changes.

[0068] In some embodiments of the present application, the first electrode layer 11 , the gap layer 20 , and the second electrode layer 30 are formed by deposition.

[0069] That is to say, the first electrode layer 11, the gap layer 20 and the second electrode layer 30 can all be formed by a deposition process. Specifically, a polysilicon layer of a desired pattern is deposited on the substrate 10 by mask technology. The thickness of the polysilicon layer can be 100nm to 500nm, for example, 100nm, 200nm, 300nm, 400nm and 500nm, etc. The polysilicon layer is the first electrode layer 11; a silicon oxide layer of a desired pattern can be deposited on the first electrode layer 11 by mask technology. The silicon oxide layer is the gap layer 20. The thickness of the gap layer 20 can be 30nm~500nm, for example, 30nm, 100nm, 200nm, 300nm, 400nm and 500nm, etc.; a polysilicon layer of a desired pattern can be deposited above the gap layer 20 by mask technology, and the thickness of the polysilicon layer can be 500nm~1000nm, for example, 500nm, 600nm, 700nm, 800nm, 900nm and 1000nm, etc., and the polysilicon layer is the second electrode layer 30.

[0070] In some optional examples of the present application, tetraethoxysilane (TEOS) may be used as a raw material to form the silicon oxide layer through plasma enhanced chemical vapor deposition (PECVD) or low pressure chemical vapor deposition (LPCVD).

[0071] According to one embodiment of the present application, the preparation method includes:

[0072] Before depositing the gap layer 20, a first insulating layer 40 is deposited on the first side of the substrate 10, and the first insulating layer 40 is provided with a through groove, and the through groove corresponds to the first electrode layer 11;

[0073] Depositing a first passivation layer 50 on a side of the first insulating layer 40 away from the first electrode layer 11;

[0074] The first passivation layer 50 covers the first insulating layer 40 , and a deposition groove is formed at a position corresponding to the first passivation layer 50 and the through groove. The gap layer 20 is disposed in the deposition groove, and the gap layer 20 is formed as a sacrificial portion as a whole.

[0075] That is to say, Figure 2 and Figure 3 As shown, the method for sequentially forming a first electrode layer 11 and a gap layer 20 on a first side of a substrate 10 comprises: first, performing high-concentration N-type doping and P-type doping on the upper surface of the substrate 10, so as to form a first electrode layer 11 and a P-type semiconductor 12; then, depositing a first insulating layer 40 on the first side of the substrate 10 by mask technology, wherein the formed first insulating layer 40 has a through groove corresponding to the position of the first electrode layer 11, and the outer contour of the first insulating layer 40 is smaller than the substrate 10.

[0076] Then, a first passivation layer 50 is deposited on the side of the first insulating layer 40 away from the first electrode layer 11, and a deposition groove is formed at the position corresponding to the first passivation layer 50 and the through groove. Next, a silicon oxide layer is deposited in the deposition groove using a mask technique, and the silicon oxide layer is a sacrificial part, and the thickness of the sacrificial part is 50nm to 100nm, for example, 50nm, 60nm, 700nm, 80nm, 90nm and 100nm. Since the outer contour of the first insulating layer 40 is smaller than the substrate 10, the first passivation layer 50 can cover the side of the first insulating layer 40 away from the substrate 10, and at the same time, it can also cover the outer peripheral surface of the first insulating layer 40, so that the first passivation layer 50 can protect the first insulating layer 40, and can avoid damaging the first insulating layer 40 when dividing the MEMS chip 100, thereby ensuring the structural strength of the MEMS chip 100.

[0077] In this embodiment, the first insulating layer 40 can play a good insulating role between the first electrode layer 11 and the second electrode layer 30, which can ensure the performance of the variable capacitor; and the first passivation layer 50 can protect the first electrode layer 11 and the first insulating layer 40, and the first passivation layer 50 covering the surface of the first electrode layer 11 can play an insulating role, which can effectively reduce the risk of leakage.

[0078] In some embodiments of the present application, the gap layer 20 is deposited on the first side surface of the substrate 10 , and a portion of the gap layer 20 is formed as a sacrificial portion.

[0079] Specifically, if Figure 4 and Figure 5 As shown, when the first electrode layer 11 is formed by doping the substrate 10, the gap layer 20 can be directly deposited on the first side surface of the substrate 10. For example, the gap layer 20 can be deposited on the first side surface of the substrate 10 by mask technology, and a portion of the gap layer 20 covers the first electrode layer 11, and the portion covering the first electrode layer 11 can be used as a sacrificial portion.

[0080] In this embodiment, the thickness of the gap layer 20 is 30nm to 50nm, for example, 30nm, 35nm, 40nm, 45nm and 50nm, and the diameter of the vent hole 31 is 0.2um to 0.5um, for example, 0.2um, 0.3um, 0.4um and 0.5um, etc. Within this range, the influence of the edge effect on the variable capacitor can be reduced, the performance of the MEMS chip 100 can be improved, and the aperture of the vent hole 31 is relatively small, which can effectively reduce the risk of leakage.

[0081] In this embodiment, the sacrificial portion is directly formed on the surface of the first electrode layer 11, which can minimize the distance between the first electrode layer 11 and the second electrode layer 30, reduce the impact of the edge effect on the variable capacitor, and improve the performance of the MEMS chip 100; at the same time, the area of ​​the first electrode layer 11 and the second electrode layer 30 can be reduced, thereby reducing the size of the MEMS chip 100, and further reducing the production cost of the MEMS chip 100.

[0082] According to an embodiment of the present application, chemical mechanical polishing is performed on the first side surface of the substrate 10 .

[0083] In other words, when the first electrode layer 11 is formed by doping the substrate 10, before depositing the gap layer 20, for example, before or after doping the substrate 10, the first side surface of the substrate 10 may be subjected to chemical mechanical polishing (ie, CMP) so that the surface As a result, the surface of the growing sacrificial portion (i.e., the surface of the first electrode layer 11) has extremely low roughness, which is beneficial to minimizing the size of the gas detection cavity in the distribution direction of the first electrode layer 11 and the second electrode layer 30, reducing the influence of the edge effect on the variable capacitor, and improving the performance of the MEMS chip 100.

[0084] In some embodiments of the present application, a method for forming a first electrode layer 11 and a gap layer 20 on a first side of a substrate 10 includes:

[0085] Depositing a second insulating layer 60 on the first side of the substrate 10;

[0086] Depositing a first electrode layer 11 on a side of the second insulating layer 60 facing away from the substrate 10;

[0087] Depositing a first passivation layer 50 on a side of the first electrode layer 11 away from the second insulating layer 60;

[0088] The gap layer 20 is deposited on a side of the first passivation layer 50 away from the first electrode layer 11 , and the gap layer 20 is entirely formed as a sacrificial portion.

[0089] That is to say, Figures 6 to 8 As shown, the method for sequentially forming the first electrode layer 11 and the gap layer 20 on the first side of the substrate 10 includes: first, a dense and uniform silicon-rich oxide layer, i.e., a silicon thermal oxide layer, is deposited on the first side of the substrate 10 by a dry oxygen process using a mask technology, wherein the thickness of the thermal oxide layer is 30 nm to 200 nm, for example, 30 nm, 80 nm, 130 nm, 180 nm, and 200 nm, and the thermal oxide layer is the second insulating layer 60; then, a polysilicon layer is deposited on the side of the second insulating layer 60 away from the substrate 10 using a mask technology to form a desired pattern, and the polysilicon layer is the first electrode layer 11; then, a first passivation layer 50 is deposited on the side of the first electrode layer 11 away from the second insulating layer 60; finally, a silicon oxide layer is deposited on top of the first passivation layer 50 using a mask technology to form a desired pattern, and the silicon oxide layer is the sacrificial portion.

[0090] In this embodiment, the first passivation layer 50 covers the surface of the first electrode layer 11 away from the second insulating layer 60, which can protect the first electrode layer 11 and the second insulating layer 60, ensure the structural strength of the MEMS chip 100, and the first passivation layer 50 covering the surface of the first electrode layer 11 can play an insulating role, which can effectively reduce the risk of leakage.

[0091] In this embodiment, the aperture of the vent hole 31 is 0.5um to 5um, for example, 0.5um, 2um, 3.5um and 5um, etc. Within this range, the gas replacement rate in the gas detection cavity can be guaranteed, the response time of the MEMS can be shortened, and the detection sensitivity of the micro-electromechanical gas sensor using the MEMS chip 100 prepared by the present application can be improved.

[0092] In some optional examples of the present application, the second insulating layer 60 has a through hole, and a portion of the first electrode layer 11 is deposited in the through hole and contacts the substrate 10 .

[0093] Specifically, if Figures 6 to 8As shown, the second insulating layer 60 has one or more through holes extending through the second insulating layer 60 along its thickness direction. When depositing the first electrode layer 11, a portion of the first electrode layer 11 can be deposited in the through hole and contact the substrate 10, so that the first electrode layer and the substrate 10 can be at the same potential, thereby improving the performance of the MEMS chip 100.

[0094] According to an embodiment of the present application, before depositing the second electrode layer 30 , a second passivation layer 70 is deposited on a side of the gap layer 20 facing away from the substrate 10 .

[0095] In other words, in order to prevent the second electrode layer 30 from being damaged when etching the sacrificial portion, the second passivation layer 70 can be deposited on the side of the gap layer 20 away from the substrate 10, and then the second electrode layer 30 can be deposited on the side of the second passivation layer 70 away from the gap layer 20. Therefore, when etching the sacrificial portion, the second electrode layer 30 can be protected by the second passivation layer 70, the performance of the variable capacitor can be guaranteed, and the second passivation layer 70 can play an insulating role, which can effectively reduce the risk of leakage.

[0096] In some embodiments of the present application, chemical mechanical polishing is performed on a side of the second passivation layer 70 facing away from the spacer layer 20 .

[0097] That is, before depositing the second electrode layer, the surface of the second passivation layer 70 facing away from the gap layer 20 can be subjected to chemical mechanical polishing (ie, CMP) so that the Ra / Rq of the surface is As a result, the surface of the second electrode layer 30 has extremely low roughness, and the surface of the second electrode layer 30 close to the first electrode layer 11 has extremely low roughness, which can reduce the impact of the edge effect on the variable capacitor and improve the performance of the MEMS chip 100.

[0098] According to one embodiment of the present application, the first passivation layer 50 and the second passivation layer 70 are formed of a hydrophobic material.

[0099] Specifically, the materials forming the first passivation layer 50 and the second passivation layer 70 may be the same or different. In the present embodiment, the materials forming the first passivation layer 50 and the second passivation layer 70 are the same, and both may be hydrophobic materials, which may be one or more of silicon nitride and self-assembled monolayer polymers. For example, when forming the first passivation layer 50 and the second passivation layer 70, low stress silicon-rich silicon nitride (i.e., SiNx) may be formed by atomic layer deposition or low pressure chemical vapor deposition, with an atomic ratio x=0.9 to 1.1.

[0100] In this embodiment, the first passivation layer 50 and the second passivation layer 70 are formed of hydrophobic material, so that the inner wall surface of the gas detection cavity is hydrophobic material, thereby effectively preventing condensation of water vapor in the gas detection cavity and broadening the application range of the MEMS chip 100.

[0101] In some optional examples of the present application, the thickness of the first passivation layer 50 and the second passivation layer 70 can be 30nm to 200nm, for example, 30nm, 80nm, 130nm, 180nm and 200nm, etc. Within this range, the structural strength and product performance of the MEMS chip 100 can be guaranteed.

[0102] According to an embodiment of the present application, the MEMS chip 100 is formed with two variable capacitors and two fixed capacitors, and the two variable capacitors and the two fixed capacitors can form a Wheatstone full-bridge detection circuit.

[0103] In some embodiments of the present application, before forming the vent hole 31 , a third insulating layer 80 is deposited on a side of the second electrode plate facing away from the gap layer 20 .

[0104] That is to say, Figure 3 and Figure 5 As shown, the preparation method of the MEMS chip of the present application also includes: forming a low-stress silicon nitride layer by atomic layer deposition or low-pressure chemical vapor deposition on the side of the second electrode layer 30 away from the gap layer 20, and the silicon nitride layer is the third insulating layer 80. After the third insulating layer 80 is deposited, the third insulating layer 80, the second electrode layer 30 and the second passivation layer 70 are sequentially etched to form the vent 31.

[0105] In this embodiment, the third insulating layer 80 covers the surface of the second electrode layer 30, which can effectively prevent leakage and ensure the stability and reliability of the MEMS chip 100; and the third insulating layer 80 is formed before the vent hole 31 is formed, which is conducive to simplifying the subsequent process flow.

[0106] According to an embodiment of the present application, the method for preparing a MEMS chip further includes depositing a pad 90 .

[0107] Specifically, contact holes are etched above corresponding positions of the first electrode layer 11, the second electrode layer 30 and the P-type semiconductor 12, the contact hole corresponding to the first electrode layer 11 extends to the upper surface of the first electrode layer 11, the contact hole corresponding to the second electrode layer 30 extends to the upper surface of the second electrode layer 30, and the contact hole corresponding to the P-type semiconductor 12 extends to the upper surface of the P-type semiconductor 12; after the contact holes are formed, chromium-gold can be deposited in the contact holes using mask technology to form a pad 90.

[0108] In some embodiments of the present application, the method for preparing the MEMS chip further includes grinding and polishing the side of the substrate 10 facing away from the first electrode layer 11 to thin the MEMS chip 100 to a target thickness.

[0109] In summary, according to the preparation method of the MEMS chip provided in this embodiment, a gas detection cavity connected to the vent 31 is formed between the first electrode layer 11 and the second electrode layer 30, so that the gas entering the gas detection cavity can be used as a dielectric. When the gas to be detected enters the gas detection cavity from the vent 31, the capacitance of the variable capacitor formed by the first electrode layer 11 and the second electrode layer 30 changes accordingly, thereby achieving high-sensitivity gas detection. Compared with the prior art, there is no need to set additional dielectric materials, thereby simplifying the preparation process and reducing production costs. Moreover, using gas as a dielectric can effectively reduce the capacitance change caused by the adsorption of water vapor by the solid dielectric material, thereby reducing detection errors, and can improve the detection sensitivity of the microelectromechanical gas sensor using the MEMS chip 100 prepared by the present application.

[0110] The embodiment of the present application further provides a MEMS chip 100, which is made by the preparation method described in any of the above embodiments. Since the preparation method of the MEMS chip according to the embodiment of the present application has the above technical effects, the MEMS chip 100 according to the embodiment of the present application also has the corresponding technical effects, which will not be described in detail in this embodiment.

[0111] The embodiment of the present application also provides a gas sensor, including the above-mentioned MEMS chip 100. Since the method for preparing the MEMS chip according to the embodiment of the present application has the above-mentioned technical effects, the gas sensor according to the embodiment of the present application also has corresponding technical effects, which will not be described in detail in this embodiment.

[0112] In some embodiments of the present application, the gas sensor also includes an ASIC chip, the MEMS chip 100 is electrically connected to the ASIC chip, the mechanical resonance frequency of the first electrode layer 11 is f1, and the frequency of the voltage excitation sent by the ASIC chip to the ASIC chip is f0, f1>>f0. In this case, the first electrode layer 11 hardly vibrates relative to the second electrode layer 30, and the capacitance of the variable capacitor is changed only by changing the dielectric constant. This design does not need to consider acoustic or gas flow damping, and can ensure the detection sensitivity of the gas sensor.

[0113] According to one embodiment of the present application, the mechanical resonance frequency of the first plate layer 11 and the frequency at which the ASIC chip sends a voltage excitation to the MEMS chip 100 are both 60kHz to 100kHz. That is, the mechanical resonance frequency of the first plate layer 11 is 60kHz to 100kHz, the voltage excitation frequency sent by the ASIC chip to the MEMS chip 100 is 60kHz to 100kHz, and the mechanical resonance frequency f1 of the first plate layer 11 matches the voltage excitation frequency f0 sent by the ASIC chip to the MEMS chip 100. For example, f1 can be equal to f0, or f1 is close to f0. At this time, the ASIC chip sends a voltage excitation to the MEMS chip 100, which can cause the first plate layer 11 to mechanically resonate, and the vibration of the first plate layer 11 can change the distance from the second plate, thereby further increasing the change in capacitance, so as to further improve the sensitivity of the gas sensor.

[0114] In this example, the structural design of the MEMS chip 100 can reduce acoustic damping as much as possible to improve Q (quality factor), and the first electrode layer 11 can resonate more stably.

[0115] Although some specific embodiments of the present application have been described in detail by way of example, it should be understood by those skilled in the art that the above examples are only for illustration, not for limiting the scope of the present application. It should be understood by those skilled in the art that the above embodiments may be modified without departing from the scope and spirit of the present application. The scope of the present application is defined by the appended claims.

Claims

1. A method for preparing a MEMS chip, characterized in that: include: Forming a first electrode layer, a gap layer, and a second electrode layer in sequence on a first side of the substrate, wherein the gap layer has a sacrificial portion, and the sacrificial portion is located between the first electrode layer and the second electrode layer; forming a vent hole on the second electrode layer, wherein a first end of the vent hole is connected to the outside, and a second end of the vent hole extends to the sacrificial portion; The sacrificial portion is removed from the vent hole by etching to form a gas detection cavity between the first electrode layer and the second electrode layer to obtain a MEMS chip.

2. The method for preparing a MEMS chip according to claim 1, characterized in that: The method of forming a first electrode layer on a first side of a substrate is: N-type doping is performed on the first side of the substrate to obtain an N-type semiconductor, and the N-type semiconductor is formed as a first electrode layer.

3. The method for preparing a MEMS chip according to claim 2, characterized in that: The preparation method further comprises: The first side of the substrate is doped with P type to obtain a P type semiconductor, and the N type semiconductor and the P type semiconductor form a PN junction temperature sensing unit.

4. The method for preparing a MEMS chip according to claim 1, characterized in that: The first electrode layer, the gap layer and the second electrode layer are formed by deposition.

5. The method for preparing a MEMS chip according to claim 2, characterized in that: The preparation method comprises: Before depositing the gap layer, a first insulating layer is deposited on the first side of the substrate, wherein the first insulating layer is provided with a through groove, and the through groove corresponds to the first electrode layer; Depositing a first passivation layer on a side of the first insulating layer away from the first electrode layer; The first passivation layer covers the first insulating layer, a deposition groove is formed at a position corresponding to the first passivation layer and the through groove, the gap layer is arranged in the deposition groove, and the gap layer is formed as a whole as the sacrificial portion.

6. The method for preparing a MEMS chip according to claim 2, characterized in that: The gap layer is deposited on the first side surface of the substrate, and a portion of the gap layer is formed as the sacrificial portion.

7. The method for preparing a MEMS chip according to claim 2, characterized in that: The first side surface of the substrate is chemically mechanically polished.

8. The method for preparing a MEMS chip according to claim 3, characterized in that: The method of forming a first plate layer and a gap layer on a first side of a substrate comprises: depositing a second insulating layer on the first side of the substrate; Depositing a first electrode layer on a side of the second insulating layer facing away from the substrate; Depositing a first passivation layer on a side of the first electrode layer away from the second insulating layer; A gap layer is deposited on a side of the first passivation layer away from the first electrode layer, and the gap layer is entirely formed as the sacrificial portion. 9 . The method for preparing a MEMS chip according to claim 8 , wherein the second insulating layer has a through hole, and a portion of the first electrode layer is deposited in the through hole and in contact with the substrate.

10. The method for preparing a MEMS chip according to claim 5 or 8, characterized in that: Before depositing the second electrode layer, a second passivation layer is deposited on a side of the gap layer facing away from the substrate.

11. The method for preparing a MEMS chip according to claim 10, characterized in that: A chemical mechanical polishing is performed on a side of the second passivation layer facing away from the gap layer.

12. The method for preparing a MEMS chip according to claim 10, characterized in that: The first passivation layer and the second passivation layer are formed of a hydrophobic material.

13. The method for preparing a MEMS chip according to claim 1, characterized in that: Before forming the vent hole, a third insulating layer is deposited on a side of the second electrode plate away from the gap layer.

14. A MEMS chip, characterized in that: The MEMS chip is manufactured by the manufacturing method according to any one of claims 1 to 13.

15. A gas sensor, characterized in that: Comprising the MEMS chip as claimed in claim 14.

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