A double-sided MEMS thermal gas flow sensor and a manufacturing method thereof

Abstract

The present application relates to a double-sided MEMS thermal gas flow sensor, in which a heating resistor structure and a temperature measuring resistor structure are respectively formed on both sides of a middle bonding layer. The heating resistor and the temperature measuring resistor are separated to minimize the influence of the heating resistor on the temperature measuring resistor and improve the measurement accuracy.

Description

Technical Field

[0001] This application belongs to the field of sensor structure and manufacturing process technology, and in particular relates to a double-sided MEMS thermal gas flow sensor and its manufacturing method. Background Technology

[0002] Accurate measurement of wind speed and direction plays a crucial role in many aspects of social production and daily life. Therefore, wind speed and direction sensors are widely used in agriculture, transportation, equipment manufacturing, energy utilization, and weather forecasting. In recent years, with the development of MEMS and electronic technologies, the structure of thermal gas sensors has reached the micrometer level. MEMS features diverse manufacturing processes, device miniaturization, excellent performance, high integration, array capability, and mass production capacity. A complete MEMS system integrates many micro-devices onto a single chip, solving tasks that large-scale systems cannot accomplish, reducing costs, and achieving system multifunctionality and automation.

[0003] Thermostatic thermal gas flow meters represent the current main development direction, offering advantages such as: 1. Capability to measure extremely low flow rates. 2. High reliability with no moving parts. 3. Low pressure loss, almost negligible. 4. Direct flow measurement without pressure or temperature correction. 5. Large electrical signal output value. 6. Extremely high rangeability. 7. Good repeatability. However, they also suffer from the problem of the temperature sensing resistor being susceptible to thermal radiation from the heating resistor, thus affecting the accuracy of the sensor's velocity measurement. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a more accurate double-sided MEMS thermal gas flow sensor and its manufacturing method.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A double-sided MEMS thermal gas flow sensor, comprising:

[0007] The intermediate bonding layer is located in the middle, and the heating resistance structure and temperature measuring resistance structure are distributed on both sides of the intermediate bonding layer.

[0008] The heating resistor structure, from the direction near the intermediate bonding layer to the direction away from the bonding layer, includes, in sequence, a first silicon nitride layer, a first silicon layer, a second silicon nitride layer, a third silicon nitride layer encapsulating a first metal layer, and a first glass layer;

[0009] The temperature-sensing resistor structure, from the direction closest to the intermediate bonding layer to the direction furthest from the bonding layer, includes, in sequence, a fourth silicon nitride layer, a second silicon layer, a fifth silicon nitride layer, a sixth silicon nitride layer encapsulating a second metal layer, and a second glass layer.

[0010] The intermediate bonding layer, the first silicon nitride layer, the first silicon layer, the fourth silicon nitride layer, and the second silicon layer are hollow to form a cavity for air circulation;

[0011] The first metal layer includes a first metal frame and a heating resistor metal located inside the metal frame. The first metal frame is partially connected to the hollow second silicon nitride layer corresponding to the cavity, and is also connected to the second silicon nitride layer corresponding to the first silicon layer. The heating resistor metal has a bent reciprocating structure, and the two ends of the first metal layer have first terminals respectively.

[0012] The second metal layer includes a second metal frame and a temperature-sensing resistor metal located on both sides of the second metal frame and respectively connected to the second terminal.

[0013] In the cross-sectional projection, the first metal frame coincides with the second metal frame, the first terminal coincides with the second terminal, and the heating resistor metal completely covers the temperature measuring resistor metal.

[0014] Preferably, in the double-sided MEMS thermal gas flow sensor of the present invention, the first metal frame and the second metal frame are rectangular, and the diagonal has an opening for the first terminal or the second terminal to extend into the first metal frame or the second metal frame.

[0015] Preferably, in the double-sided MEMS thermal gas flow sensor of the present invention, the first metal frame and the second metal frame are two symmetrical L-shaped structures, including a first part parallel to the cavity and a second part perpendicular to the first part. Half of the first part is located above the cavity, and half is located above the first silicon layer and the second silicon layer. The second part spans the cavity and connects the first silicon layer and the second silicon layer on both sides of the cavity.

[0016] Preferably, in the double-sided MEMS thermal gas flow sensor of the present invention, the intermediate bonding layer is obtained by bonding a first silicon nitride layer and a fourth silicon nitride layer together using BCB adhesive.

[0017] Preferably, in the double-sided MEMS thermal gas flow sensor of the present invention, the first metal layer and the second metal layer are platinum.

[0018] The present invention also provides a method for manufacturing a double-sided MEMS thermal gas flow sensor, which is used to manufacture the above-mentioned double-sided MEMS thermal gas flow sensor, and includes the following steps:

[0019] S1. Take two silicon wafers, which are used as the first silicon layer and the second silicon layer, respectively. Perform low-pressure vapor deposition of SiN on the crystal orientation of both sides of the silicon wafers to form the first silicon nitride layer, the second silicon nitride layer, the fourth silicon nitride layer, and the fifth silicon nitride layer.

[0020] S2: Metal is deposited on the second silicon nitride layer and the fifth silicon nitride layer respectively to form a first metal layer and a second metal layer, so that the first metal layer and the second metal layer form the desired pattern, and finally the first metal layer and the second metal layer become a metallized heating resistor and a temperature measuring circuit respectively.

[0021] S3: Deposit silicon nitride on the surfaces of the first and second metal layers using low-pressure vapor deposition to form a third and a sixth silicon nitride layer to cover the first and second metal layers.

[0022] S4: Photolithography is used to form grooves between the first silicon nitride layer and the fourth silicon nitride layer to expose the first silicon layer and the second silicon layer;

[0023] S5: Etch the first and second silicon layers until the third and sixth silicon nitride layers are exposed, forming cavities in the heating resistor structure and the temperature measuring resistor structure, respectively.

[0024] S6: Using BCB photoresist bonding adhesive, the perforated glass is bonded to the third or sixth silicon nitride layer to form the first glass layer and the second glass layer.

[0025] S7: The first silicon nitride layer and the fourth silicon nitride layer are bonded together using BCB photoresist bonding adhesive, and the cavity is partially closed in the heating resistor structure and the temperature measuring resistor structure to form a cavity.

[0026] Preferably, in the manufacturing method of the double-sided MEMS thermal gas flow sensor of the present invention, the patterns in step S2 are as follows:

[0027] The first metal layer includes a first metal frame and a heating resistor metal located inside the metal frame. The first metal frame is partially connected to the hollow second silicon nitride layer corresponding to the cavity, and is also connected to the second silicon nitride layer corresponding to the first silicon layer. The heating resistor metal has a bent reciprocating structure, and the two ends of the first metal layer have first terminals respectively.

[0028] The second metal layer includes a second metal frame and a temperature-sensing resistor metal located on both sides of the second metal frame and respectively connected to the second terminal.

[0029] Preferably, in the manufacturing method of the double-sided MEMS thermal gas flow sensor of the present invention, the first metal frame and the second metal frame are two symmetrical L-shaped structures, including a first part parallel to the cavity and a second part perpendicular to the first part. Half of the first part is located above the cavity, and half is located above the first silicon layer and the second silicon layer. The second part spans the cavity and connects the first silicon layer and the second silicon layer on both sides of the cavity.

[0030] Preferably, in the manufacturing method of the double-sided MEMS thermal gas flow sensor of the present invention, the first metal frame and the second metal frame coincide in the cross-sectional projection, the first terminal and the second terminal coincide, and the heating resistor metal completely covers the temperature sensing resistor metal.

[0031] Preferably, in the manufacturing method of the double-sided MEMS thermal gas flow sensor of the present invention, step S5 uses 30% KOH + 85°C water bath etching of the first silicon layer and the second silicon layer.

[0032] The beneficial effects of this invention are:

[0033] 1. The double-sided MEMS thermal gas flow sensor of the present invention separates the heating resistor and the temperature measuring resistor through the double-sided structure of the intermediate bonding layer located in the middle, so as to minimize the influence of the heating resistor on the temperature measuring resistor and greatly reduce the measurement error by adopting a symmetrical structure.

[0034] 2. The double-sided MEMS thermal gas flow sensor of the present invention uses a metal outer frame to support the SiN film surface, which greatly improves the yield of the film surface and its reliability during use.

[0035] 3. The double-sided MEMS thermal gas flow sensor of the present invention uses BCB adhesive bonding to improve packaging reliability, integration, efficiency, and consistency.

[0036] 4. The double-sided MEMS thermal gas flow sensor of the present invention significantly improves temperature drift by fabricating the temperature sensing resistor and the heating resistor on the SiN film compared to on Si. Attached Figure Description

[0037] The technical solution of this application will be further described below with reference to the accompanying drawings and embodiments.

[0038] Figure 1 This is a side view of the double-sided MEMS thermal gas flow sensor of Embodiment 1 of this application;

[0039] Figure 2 This is a top view of the first metal layer in Embodiment 1 of this application;

[0040] Figure 3 This is a top view of the second metal layer in Embodiment 1 of this application;

[0041] Figure 4 This is a flowchart of the manufacturing method of the double-sided MEMS thermal gas flow sensor according to Embodiment 2 of this application. (Step S7, BCB adhesive bonding, is not included.)

[0042] The attached figures are labeled as follows:

[0043] 1. Bonding layer;

[0044] 2. Cavity;

[0045] 11 First silicon nitride layer;

[0046] 12 First silicon layer;

[0047] 13. Second silicon nitride layer;

[0048] 14 First metal layer;

[0049] 15. Third silicon nitride layer;

[0050] 17. First glass layer;

[0051] 21. Fourth silicon nitride layer;

[0052] 22 Second silicon layer;

[0053] 23. Fifth silicon nitride layer;

[0054] 24 Second metal layer;

[0055] 25. Sixth silicon nitride layer;

[0056] 27. Second glass layer;

[0057] 141 First metal frame;

[0058] 142 Heating resistance metal;

[0059] 143 First terminal;

[0060] 241 Second metal frame;

[0061] 242 Temperature sensing resistance metal;

[0062] 243 Second terminal. Detailed Implementation

[0063] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0064] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the scope of protection of this application. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0065] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art will understand the specific meaning of the above terms in this application based on the specific circumstances.

[0066] The technical solution of this application will now be described in detail with reference to the accompanying drawings and embodiments.

[0067] Example 1

[0068] This embodiment provides a double-sided MEMS thermal gas flow sensor, such as... Figure 1 Shown, including:

[0069] The intermediate bonding layer 1 is located in the middle, and the heating resistor structure and temperature measuring resistor structure are distributed on both sides of the intermediate bonding layer 1.

[0070] The heating resistor structure, from the direction near the intermediate bonding layer 1 to the direction away from the bonding layer 1, includes, in sequence, a first silicon nitride layer 11, a first silicon layer 12, a second silicon nitride layer 13, a third silicon nitride layer 15 encapsulating a first metal layer 14, and a first glass layer 17.

[0071] The temperature sensing resistor structure, from the direction close to the intermediate bonding layer 1 to the direction away from the bonding layer 1, includes, in sequence, a fourth silicon nitride layer 21, a second silicon layer 22, a fifth silicon nitride layer 23, a sixth silicon nitride layer 25 encapsulating the second metal layer 24, and a second glass layer 27.

[0072] The intermediate bonding layer 1, the first silicon nitride layer 11, the first silicon layer 12, the fourth silicon nitride layer 21, and the second silicon layer 22 are hollow to form a cavity 2 for air circulation;

[0073] The first metal layer 14, as Figure 2 and Figure 3 The device includes a first metal frame 141 and a heating resistor metal 142 located inside the metal frame. The first metal frame 141 is partially connected to the hollow second silicon nitride layer 13 corresponding to the cavity 2, and also connected to the second silicon nitride layer 13 corresponding to the first silicon layer 12. The connection between the two parts serves to support the SiN film surface of the second silicon nitride layer 13. The heating resistor metal 142 has a bent reciprocating structure, which makes the heating more uniform. The two ends of the heating resistor metal 142 each have a first terminal 143, which is connected to an external power supply to make the heating resistor metal heat up.

[0074] The second metal layer 24 includes a second metal frame 241 and a temperature-sensing resistor metal 242 located on both sides of the second metal frame 241 and connected to a second terminal 243 respectively. The second terminal 243 is connected to an external device to display physical quantities that can be read, such as resistance, voltage or current.

[0075] In the cross-sectional projection, the first metal frame 141 coincides with the second metal frame 241, the first terminal 143 coincides with the second terminal 243, and the heating resistor metal 142 completely covers the temperature measuring resistor metal 242.

[0076] The double-sided MEMS thermal gas flow sensor in this embodiment separates the heating resistor and the temperature sensing resistor through the double-sided structure of the middle bonding layer, minimizing the influence of the heating resistor on the temperature sensing resistor. The symmetrical structure ensures that the received thermal radiation is consistent with external interference, reducing measurement errors.

[0077] The double-sided MEMS thermal gas flow sensor in this embodiment uses a metal outer frame to support the SiN film, which greatly improves the yield and reliability of the film during use.

[0078] The double-sided MEMS thermal gas flow sensor in this embodiment uses BCB adhesive bonding to improve packaging reliability, integration, efficiency, and consistency.

[0079] The double-sided MEMS thermal gas flow sensor of this embodiment significantly improves temperature drift by fabricating the temperature sensing resistor and heating resistor on the SiN film compared to on Si.

[0080] Furthermore, the first metal layer 14 and the second metal layer 24 are platinum.

[0081] Furthermore, the first metal frame 141 and the second metal frame 241 are rectangular, and have openings at their diagonals for the first terminal 143 or the second terminal 243 to extend into the first metal frame 141 or the second metal frame 241.

[0082] Furthermore, the first metal frame 141 and the second metal frame 241 are two symmetrical L-shaped structures, including a first part parallel to the cavity 2 and a second part perpendicular to the first part. Half of the first part is located above the cavity 2, and the other half is located above the first silicon layer 12 and the second silicon layer 22. The second part spans across the cavity 2, connecting the first silicon layer 12 and the second silicon layer 22 on both sides of the cavity 2, thereby further strengthening the connection and support of the silicon nitride layer.

[0083] Furthermore, the intermediate bonding layer 1 is obtained by bonding the first silicon nitride layer 11 and the fourth silicon nitride layer 21 with BCB adhesive. BCB adhesive bonding improves packaging reliability, integration, efficiency, and consistency.

[0084] Example 2

[0085] This embodiment provides a method for manufacturing a double-sided MEMS thermal gas flow sensor, such as... Figure 4 As shown, it includes the following steps:

[0086] S1, take two silicon wafers (as the first silicon layer 12 and the second silicon layer 22 respectively), and perform low-pressure vapor deposition (i.e., lpcvd) SiN (the SiN thickness can be set to 1-10um) on the 100 crystal direction on both sides of the silicon wafers respectively to form the first silicon nitride layer 11, the second silicon nitride layer 13, the fourth silicon nitride layer 21, and the fifth silicon nitride layer 23.

[0087] S2: Metals are deposited on the second silicon nitride layer 13 and the fifth silicon nitride layer 23 respectively to form the first metal layer 14 and the second metal layer 24. The first metal layer 14 and the second metal layer 24 are formed into the desired pattern by photolithography and IBE etching. Finally, the first metal layer 14 and the second metal layer 24 become the metallized heating resistor (upper surface) and the temperature measuring circuit (lower surface) respectively.

[0088] S3: Deposit silicon nitride on the surfaces of the first metal layer 14 and the second metal layer 24 using low-pressure vapor deposition (LPCVD) to form a third silicon nitride layer 15 and a sixth silicon nitride layer 25 to cover the first metal layer 14 and the second metal layer 24.

[0089] S4: Photolithography is used to form grooves between the first silicon nitride layer 11 and the fourth silicon nitride layer 21 to expose the first silicon layer 12 and the second silicon layer 22;

[0090] S5: Use a 30% KOH + 85℃ water bath to etch the first silicon layer 12 and the second silicon layer 22 until the second silicon nitride layer 13 and the fifth silicon nitride layer 23 are exposed, forming cavities 2 in the heating resistor structure and the temperature measuring resistor structure, respectively.

[0091] S6: Using BCB photoresist bonding adhesive, the perforated glass is bonded to the third silicon nitride layer 15 or the sixth silicon nitride layer 25 to form the first glass layer 17 and the second glass layer 27.

[0092] S7: The first silicon nitride layer 11 and the fourth silicon nitride layer 21 are bonded together using BCB photoresist bonding adhesive, and the cavity 2 is partially closed in the heating resistor structure and the temperature measuring resistor structure to form the cavity 2.

[0093] Based on the above-described preferred embodiments according to this application, and through the foregoing description, those skilled in the art can make various changes and modifications without departing from the technical concept of this application. The technical scope of this application is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A double-sided MEMS thermal gas flow sensor, characterized in that: include: An intermediate bonding layer (1) located in the middle and a heating resistor structure and a temperature measuring resistor structure distributed on both sides of the intermediate bonding layer (1); The heating resistor structure comprises, in order from the direction close to the intermediate bonding layer (1) to the direction away from the bonding layer (1), a first silicon nitride layer (11), a first silicon layer (12), a second silicon nitride layer (13), a third silicon nitride layer (15) encapsulating the first metal layer (14), and a first glass layer (17); The temperature measuring resistor structure comprises, in order from the direction close to the intermediate bonding layer (1) to the direction away from the bonding layer (1), a fourth silicon nitride layer (21), a second silicon layer (22), a fifth silicon nitride layer (23), a sixth silicon nitride layer (25) encapsulating the second metal layer (24), and a second glass layer (27); The intermediate bonding layer (1), the first silicon nitride layer (11), the first silicon layer (12), the fourth silicon nitride layer (21), and the second silicon layer (22) are hollow to form a cavity (2) for air circulation; The first metal layer (14) comprises a first metal outer frame (141) and a heating resistor metal (142) located inside the metal outer frame; the first metal outer frame (141) is partially connected to the hollowed-out second silicon nitride layer (13) corresponding to the cavity (2), and is connected to the second silicon nitride layer (13) corresponding to the first silicon layer (12); the heating resistor metal (142) is a bent reciprocating structure, and the first metal layer (14) has first wiring terminals (143) at both ends; The second metal layer (24) comprises a second metal outer frame (241) and a temperature measuring resistor metal (242) located in the second metal outer frame (241); the temperature measuring resistor metal (242) is located on both sides of the second metal outer frame (241) and is respectively connected to a second wiring terminal (243); In cross-sectional projection, the first metal outer frame (141) overlaps with the second metal outer frame (241), the first terminal (143) overlaps with the second terminal (243), and the heating resistor metal (142) completely covers the temperature measuring resistor metal (242).

2. The double-sided MEMS thermal gas flow sensor according to claim 1, characterized in that: The first metal outer frame (141) and the second metal outer frame (241) are rectangular, and have openings at the diagonals for the first wiring terminal (143) or the second wiring terminal (243) to extend into the first metal outer frame (141) or the second metal outer frame (241).

3. The double-sided MEMS thermal gas flow sensor according to claim 2, characterized in that: The first metal outer frame (141) and the second metal outer frame (241) are two symmetrical L-shaped structures, comprising a first part parallel to the cavity (2) and a second part perpendicular to the first part, half of the first part is located above the cavity (2), and half is located above the first silicon layer (12) and the second silicon layer (22), and the second part spans the cavity (2) and connects the first silicon layer on both sides of the cavity (2). (12) and above the second silicon layer (22).

4. The double-sided MEMS thermal gas flow sensor according to any one of claims 1 to 3, characterized in that: The intermediate bonding layer (1) is obtained by bonding the first silicon nitride layer (11) and the fourth silicon nitride layer (21) by means of BCB adhesive.

5. The double-sided MEMS thermal gas flow sensor according to any one of claims 1 to 3, characterized in that: The first metal layer (14) and the second metal layer (24) are made of platinum.

6. A method for manufacturing a double-sided MEMS thermal gas flow sensor, used to manufacture the double-sided MEMS thermal gas flow sensor according to any one of claims 1 to 5, characterized in that: The following steps are involved: S1, taking two silicon wafers, respectively serving as a first silicon layer (12) and a second silicon layer (22), and performing low-pressure vapor deposition of SiN on both sides of the silicon wafers in the (100) crystal direction to form a first silicon nitride layer (11), a second silicon nitride layer (13), a fourth silicon nitride layer (21), and a fifth silicon nitride layer (23); S2: Metal is plated on the second silicon nitride layer (13) and the fifth silicon nitride layer (23) to form a first metal layer (14) and a second metal layer (24), respectively, so that the first metal layer (14) and the second metal layer (24) form a desired pattern, and finally the first metal layer (14) and the second metal layer (24) become a metallized heating resistor and a temperature measuring circuit respectively; S3: depositing silicon nitride on the surfaces of the first metal layer (14) and the second metal layer (24) using a low-pressure vapor deposition method to form a third silicon nitride layer (15) and a sixth silicon nitride layer (25) to cover the first metal layer (14) and the second metal layer (24); S4: using photolithography to form grooves in the first silicon nitride layer (11) and the fourth silicon nitride layer (21) to expose the first silicon layer (12) and the second silicon layer (22); S5: etching the first silicon layer (12) and the second silicon layer (22) until the second silicon nitride layer (13) and the fifth silicon nitride layer (23) are exposed, thereby forming the cavity (2) in the heating resistor structure and the temperature measuring resistor structure respectively; S6: using BCB photoresist bonding adhesive to bond the perforated glass to the third silicon nitride layer (15) or the sixth silicon nitride layer (25) to form a first glass layer (17) and a second glass layer (27); S7: using BCB photoresist bonding glue to perform BCB glue bonding on the first silicon nitride layer (11) and the fourth silicon nitride layer (21), and the cavity (2) is partially sealed at the heating resistor structure and the temperature measuring resistor structure to form the cavity (2).

7. The method for manufacturing a double-sided MEMS thermal gas flow sensor according to claim 6, characterized in that: The patterns in step S2 are: The first metal layer (14) comprises a first metal outer frame (141) and a heating resistor metal (142) located inside the metal outer frame; the first metal outer frame (141) is partially connected to the hollowed-out second silicon nitride layer (13) corresponding to the cavity (2), and is connected to the second silicon nitride layer (13) corresponding to the first silicon layer (12); the heating resistor metal (142) is a bent reciprocating structure, and the first metal layer (14) has first wiring terminals (143) at both ends; The second metal layer (24) comprises a second metal outer frame (241) and the temperature measuring resistor metal (242), wherein the temperature measuring resistor metal (242) is located on both sides of the second metal outer frame (241) and is respectively connected to the second wiring terminal (243).

8. The method for manufacturing a double-sided MEMS thermal gas flow sensor according to claim 7, characterized in that: The first metal outer frame (141) and the second metal outer frame (241) are two symmetrical L-shaped structures, comprising a first part parallel to the cavity (2) and a second part perpendicular to the first part, wherein half of the first part is located above the cavity (2) and the other half is located above the first silicon layer (12) and the second silicon layer (22), and the second part spans the cavity (2) and connects the first silicon layer (12) and the second silicon layer (22) on both sides of the cavity (2).

9. The method for manufacturing a double-sided MEMS thermal gas flow sensor according to claim 7 or 8, characterized in that: In cross-sectional projection, the first metal outer frame (141) overlaps with the second metal outer frame (241), the first terminal (143) overlaps with the second terminal (243), and the heating resistor metal (142) completely covers the temperature measuring resistor metal (242).

10. The method for manufacturing a double-sided MEMS thermal gas flow sensor according to claim 6, characterized in that: In step S5, 30% KOH + 85°C water bath is used to etch the first silicon layer (12) and the second silicon layer (22).

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