CN118392945B - MEMS gas sensor and method for manufacturing the same - Google Patents

Abstract

The application provides an MEMS gas sensor, which comprises a silicon substrate, a supporting layer, a heating element, an isolating layer, a testing element and a gas sensitive element, wherein the silicon substrate comprises a front surface and a back surface deviating from the front surface; the supporting layer is connected between the first cavity wall and the second cavity wall and is positioned in the heat insulation cavity, and the supporting layer isolates the heat insulation cavity from the heat collection cavity; the heating element is arranged on the supporting layer and positioned in the heat insulation cavity; the isolating layer covers the supporting layer and the heating element; the test element is arranged on one surface of the isolation layer, which is away from the heating element; the gas sensor is arranged in the test the side of the element facing away from the barrier layer. In addition, the application also provides a manufacturing method of the MEMS gas sensor.

Description

MEMS gas sensor and method for manufacturing the same

Technical Field

The present application relates to the field of semiconductor technology, and in particular to a MEMS gas sensor and a manufacturing method thereof.

Background Art

Medical testing often uses human exhaled gas to detect corresponding indicators to perform non-invasive and safe testing on the human body. In the prior art, semiconductor metal oxide MEMS gas sensors are often used to detect human exhaled gas. Semiconductor metal oxide MEMS gas sensors require a micro-heating platform to allow sensitive materials to work at a suitable temperature. The micro-heating platform can be divided into suspended membrane type and closed membrane type according to the different types of supporting membrane structures.

However, suspended membrane type MEMS gas sensors require the support of support beams, so they have low mechanical strength, are easy to break, and have low stability. In addition, the manufacturing process from silicon wafers to gas sensors is complex, and the yield of finished products is low. In addition, suspended membrane type MEMS gas sensors require the production of additional masks when making cavities, which increases the cost of MEMS gas sensors. When making cavities, silicon islands are easily left under the support beams due to corrosion angles, which increases power consumption. The micro-thermal platform of closed membrane type MEMS gas sensors increases the power loss of MEMS gas sensors due to excessive heat dissipation.

Summary of the invention

The present application provides a MEMS gas sensor and a manufacturing method thereof, which can improve the mechanical strength of the MEMS gas sensor, reduce its power loss, and reduce the volume of the equipment therein.

In a first aspect, an embodiment of the present application provides a MEMS gas sensor, which includes a silicon substrate, a supporting layer, a heating element, an isolation layer, a test element, and a gas sensitive element. The silicon substrate includes a front side and a back side facing away from the front side, the front side is provided with a heat insulation cavity, the back side is provided with a heat collection cavity, the heat insulation cavity and the heat collection cavity are connected, and the silicon substrate also includes a first cavity wall and a second cavity wall arranged opposite to the heat insulation cavity; the supporting layer is connected between the first cavity wall and the second cavity wall and is located in the heat insulation cavity, and the supporting layer isolates the heat insulation cavity from the heat collection cavity; the heating element is arranged on the supporting layer and is located in the heat insulation cavity; the isolation layer covers the supporting layer and covers the heating element; the test element is arranged on a side of the isolation layer facing away from the heating element; and the gas sensitive element is arranged on a side of the test element facing away from the isolation layer.

In a second aspect, an embodiment of the present application provides a method for manufacturing a MEMS gas sensor, the method for manufacturing the MEMS gas sensor comprising: etching from the front side of the silicon substrate to the back side facing away from the front side to form an insulating cavity, the insulating cavity comprising a first cavity wall and a second cavity wall arranged opposite to each other; alternately depositing silicon oxide films and silicon nitride films in the insulating cavity to sequentially form silicon oxide layers and silicon nitride layers to form a supporting layer, and connecting the supporting layer to the first cavity wall and the second cavity wall; preparing a heating element in the insulating cavity and arranging it on the supporting layer; depositing a silicon nitride film on a side of the supporting layer facing the front side and a side of the heating element facing the front side to form an isolation layer, so that the isolation layer covers the supporting layer and covers the heating element; preparing a test element on a side of the isolation layer facing away from the heating element; preparing a gas sensitive element on a side of the test element facing away from the isolation layer; etching from the back side to the front side to form a heat collecting cavity, so that the support layer isolates the insulating cavity from the heat collecting cavity.

The above-mentioned MEMS gas sensor and its manufacturing method are provided with a heat-insulating cavity and a heat-collecting cavity on the front and back of the silicon substrate respectively, and a support layer connected to the wall of the heat-insulating cavity is provided in the heat-insulating cavity to connect to the silicon substrate, and a heating element, an isolation layer, a test element and a gas-sensitive element are arranged in sequence in the direction of the support layer toward the front, so that other components of the MEMS gas sensor can be stably arranged in the heat-insulating cavity, and the mechanical strength of the MEMS gas sensor is improved. At the same time, the heat-insulating cavity can slow down the heat loss generated by the heating element due to heat convection, and the heat-collecting cavity can collect more heat generated by the heating element on the support layer, thereby reducing the power loss of the MEMS gas sensor. In addition, the heat-insulating cavity and the heat-collecting cavity are manufactured by deep silicon etching process and inductively coupled plasma etching process, which saves manufacturing costs, and the volume of the device is reduced by the arrangement of the heating element electrode and the test element electrode, thereby reducing the space occupied by the electrode.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

FIG1 is a cross-sectional view of a MEMS gas sensor provided in an embodiment of the present application.

FIG. 2 is a three-dimensional diagram of a MEMS gas sensor provided in an embodiment of the present application.

FIG3 is a flow chart of a method for manufacturing a MEMS gas sensor provided in an embodiment of the present application.

The realization of the purpose, functional features and advantages of this application will be further explained in conjunction with embodiments and with reference to the accompanying drawings.

DETAILED DESCRIPTION

In order to make the purpose, technical solutions and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not intended to limit the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without making creative work are within the scope of protection of the present application.

The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of this application and the above-mentioned drawings are used to distinguish similar planning objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate. In other words, the described embodiments are implemented according to an order other than that illustrated or described herein. In addition, the terms "including" and "having" and any of their variations may also include other content. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to only those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

It should be noted that the descriptions involving "first", "second", etc. in this application are only for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in this field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

Please refer to Figure 1, which is a cross-sectional view of a MEMS gas sensor provided in an embodiment of the present application. The present application provides a MEMS gas sensor 10, which can improve the mechanical strength of the MEMS gas sensor 10, reduce the power loss of the MEMS gas sensor 10, and reduce the volume of the equipment in the MEMS gas sensor 10. The specific features of each component in the MEMS gas sensor 10 will be described in detail below.

Please refer to Figures 1 and 2. The MEMS gas sensor 10 is a gas sensor based on semiconductor metal oxide. The MEMS gas sensor 10 includes a silicon substrate 1, a support layer 2, a heating element 3, an isolation layer 4, a test element 5 and a gas sensitive element 6. The silicon substrate 1 is in the shape of a rectangular parallelepiped as a whole. The silicon substrate 1 includes a front side 13 and a back side 14 facing away from the front side 13. Among them, the front side 13 is provided with an insulating cavity 11, and the insulating cavity 11 is used to reduce the loss of heat convection. The back side 14 is provided with a hollow heat collection cavity 12, and the heat collection cavity 12 is used to collect the heat lost by heat conduction in the MEMS gas sensor 10. The insulating cavity 11 is connected to the heat collection cavity 12. The silicon substrate 1 also includes a first cavity wall 111 and a second cavity wall 112 arranged opposite to the insulating cavity 11. The present application reduces the power loss of the MEMS gas sensor 10 during operation by using the insulating cavity 11 and the heat collection cavity 12.

In this embodiment, the support layer 2 is connected between the first cavity wall 111 and the second cavity wall 112 and is located in the heat-insulating cavity 11, so as to support the MEMS gas sensor 10 while enhancing the mechanical strength of the MEMS gas sensor 10. The support layer 2 isolates the heat-insulating cavity 11 from the heat-collecting cavity 12. Among them, the support layer 2 is composed of a silicon oxide layer 21 and a silicon nitride layer 22 obtained by depositing a silicon oxide film and a silicon nitride film respectively. The silicon oxide layer 21 is close to the heat-collecting cavity 12. The silicon nitride layer 22 is located on the side of the silicon oxide layer 21 away from the heat-collecting cavity 12. Among them, the thickness of the silicon oxide layer 21 is 500-700nm. The thickness of the silicon nitride layer 22 is 1300-1500nm. In this application, the depth of the heat-insulating cavity 11 is formed from the front side 13 to the side of the support layer 2 facing the front side 13, and the depth of the heat-collecting cavity 12 is formed from the back side 14 to the side of the support layer 2 facing the back side 14. The depth of the heat-insulating cavity 11 is less than the depth of the heat-collecting cavity 12. Preferably, the depth of the heat insulation cavity 11 is 5-20 um, and the depth of the heat collection cavity 12 is 300-600 um.

Furthermore, the silicon substrate 1 further includes a third cavity wall 113 and a fourth cavity wall 114 which are arranged between the first cavity wall 111 and the second cavity wall 112. The support layer 2 is also connected between the third cavity wall 113 and the fourth cavity wall 114, that is, the first cavity wall 111, the third cavity wall 113, the second cavity wall 112 and the fourth cavity wall 114 are sequentially connected to form the thermal insulation cavity 11.

In some feasible embodiments, the support layer 2 is further composed of a silicon oxide layer 21 and two silicon nitride layers 22 obtained by depositing a silicon oxide film and a silicon nitride film. The silicon oxide layer 21 is located between the two silicon nitride layers 22. One of the two silicon nitride layers 22 is located on the side of the silicon oxide layer 21 facing the heating element 3, and the other is located on the side of the silicon oxide layer 21 facing the heat collecting chamber 12.

In other feasible embodiments, the support layer 2 may also be made of other materials with low thermal conductivity, such as polyimide, to reduce heat loss in the MEMS gas sensor 10 due to heat conduction.

In this embodiment, the heating element 3 is disposed on the support layer 2 and located in the heat insulation cavity 11, that is, the heating element 3 is disposed on the side of the silicon nitride layer 22 away from the silicon oxide layer 21. The material of the heating element 3 includes but is not limited to tungsten, polysilicon, platinum, etc. The heating element 3 of the heating wire includes but is not limited to round, S-shaped, round-shaped, etc. Preferably, the thickness of the heating element 3 is 100-500nm.

In this embodiment, the isolation layer 4 is formed by depositing a silicon nitride film. The isolation layer 4 covers the support layer 2 and covers the heating element 3. In the present application, the support layer 2 and the isolation layer 4 are arranged in parallel. The test element 5 is arranged on the side of the isolation layer 4 away from the heating element 3. The test element 5 is used to obtain corresponding preset indicators according to the gas sensed by the gas sensor 6, such as the composition of the exhaled gas, the respiratory spectrum reflected by the exhaled gas, etc. The material of the test element 5 includes but is not limited to platinum, palladium, etc. The shape of the test element 5 includes but is not limited to forked electrodes, strips, forked three electrodes, etc. The thickness of the test element 5 is 100-500nm, that is, the thickness of the heating element 3 and the test element 5 can be equal or unequal. The gas sensor 6 is used to sense gas. The gas sensor 6 is arranged on the side of the test element 5 away from the isolation layer 4.

In this embodiment, the support layer 2 includes a first support portion 23 for supporting the heating element 3, and a second support portion 24 and a third support portion 25 respectively connected to both sides of the first support portion 23 close to the first cavity wall 111 and the second cavity wall 112. The MEMS gas sensor 10 is provided with an electrode 7 for providing energy for the normal operation of the MEMS gas sensor 10. The second support portion 24 and the third support portion 25 are provided with electrodes 7 on one side away from the first support portion 23. The second support portion 24 and the third support portion 25 are also connected between the third cavity wall 113 and the fourth cavity wall 114 and are located in the thermal insulation cavity 11. When the electrode 7 is provided on one side of the second support portion 24 and the third support portion 25 away from the first support portion 23, the electrode 7 does not protrude from the front side 13 to reduce the size of the MEMS gas sensor 10.

Further, the isolation layer 4 has a certain gap with the second support portion 24 and the third support portion 25 respectively. The electrode 7 includes a heating element electrode 71 and a test element electrode 72. Among them, the heating element electrode 71 is provided with an electrode connecting portion 711 accommodated in the gap, so that the heating element electrode 71 is electrically connected to the heating element 3 through the electrode connecting portion 711. The test element electrode 72 is sleeved on the electrode connecting portion 711 and is electrically connected to the test element 5 to reduce the equipment size of the MEMS gas sensor 10. The test element 5 obtains a preset index according to the gas under the energy provided by the test element electrode 72. The heating element 3 generates heat under the energy provided by the heating element electrode 71 so that the gas sensitive element 6 and the test element 5 have a certain temperature, so as to improve the sensitivity of the gas sensitive element 6 and the test element 5, thereby improving the sensing efficiency of the MEMS gas sensor 10.

Please refer to FIG. 3, which is a flow chart of a method for manufacturing a MEMS gas sensor provided in an embodiment of the present application. The present application also provides a method for manufacturing a MEMS gas sensor, which is used to manufacture a MEMS gas sensor 10. The MEMS gas sensor 10 has been described in detail above and will not be described here. The method for manufacturing a MEMS gas sensor includes steps S101-S107.

Step S101, etching from the front side of the silicon substrate to the back side facing away from the front side to form a heat-insulating cavity.

In step S101, an inductively coupled plasma-reactive ion etching (ICP-RIE) process is used to etch from the front side 13 to the back side 14 to form an insulating cavity 11. The depth of the insulating cavity 11 is 5-20um. The present application can also use silicon-on-insulator (SOI), that is, SOI wafer to replace the silicon substrate 1 to etch the insulating cavity 11, so as to reduce the silicon dioxide manufacturing process in the ICP-RIE process. Among them, the insulating cavity 11 includes a first cavity wall 111 and a second cavity wall 112 arranged opposite to each other. The insulating cavity 11 also includes a third cavity wall 113 and a fourth cavity wall 114 arranged opposite to each other between the first cavity wall 111 and the second cavity wall 112. While the insulation cavity 11 is being etched on the front side 13 of the silicon substrate 1, a receiving member (not shown) for receiving the electrode 7 is also etched outside the insulation cavity 11 and on both sides of the first cavity wall 111 and the second cavity wall 112, respectively, so that the electrode 7 does not protrude from the front side 13 in the MEMS gas sensor 10, thereby reducing the size of the MEMS gas sensor 10.

Step S102 , alternately depositing silicon oxide films and silicon nitride films in the heat-insulating cavity to sequentially form a silicon oxide layer and a silicon nitride layer to form a support layer, and connecting the support layer to the first cavity wall and the second cavity wall.

In step S102, a silicon oxide film and a silicon nitride film are alternately deposited in the insulation cavity 11 by a plasma enhanced chemical vapor deposition (PECVD) process and a low pressure chemical vapor deposition (LPCVD) process to form a support layer 2. The silicon nitride layer 22 is located on the side of the insulation cavity 11 facing the front surface 13, and the silicon oxide layer 21 is located on the side of the silicon nitride layer 22 away from the front surface 13, that is, the support layer 2 is a silicon oxide layer 21 and a silicon nitride layer 22 from the insulation cavity 11 to the front surface 13. The thickness of the silicon oxide layer 21 is 500-700nm. The thickness of the silicon nitride layer 22 is 1300-1500nm. The present application also alternately deposits silicon oxide films and silicon nitride films in the insulation cavity 11 and the accommodating member to form a first support portion 23 located in the insulation cavity 11, and a second support portion 24 and a third support portion 25 respectively connected to the first support portion 23 on both sides close to the first cavity wall 111 and the second cavity wall 112. The second supporting portion 24 and the third supporting portion 25 are used to place the electrode 7 .

Step S103, preparing a heating element in the heat-insulating cavity and setting it on the support layer.

In step S103, a heating element 3 is prepared on the support layer 2 by a magnetron sputtering process and a stripping process. The thickness of the heating element 3 is 100-500 nm. The material of the heating element 3 includes but is not limited to gold, platinum, tungsten, polysilicon, etc. The shape of the heating element 3 includes but is not limited to S-shaped, round, circular, elliptical, etc. At the same time, corresponding heating element electrodes 71 are respectively provided on the second support portion 24 and the third support portion 25, and the heating element 3 is electrically connected to the heating element electrode 71.

Step S104, depositing a silicon nitride film on a side of the support layer facing the front surface and a side of the heating element facing the front surface to form an isolation layer, so that the isolation layer covers the support layer and the heating element.

In step S104, a silicon nitride film is deposited on one side of the support layer 2 facing the front surface 13 and one side of the heating element 3 facing the front surface 13 by a PECVD process to form an isolation layer 4. The thickness of the isolation layer 4 is 300-500 nm. The isolation layer 4 has a certain gap with the second support portion 24 and the third support portion 25 respectively. The heating element electrode 71 is provided with an electrode connecting portion 711 accommodated in the gap, so that the heating element 3 is electrically connected to the heating element electrode 71 through the electrode connecting portion 711. There is a certain height difference between the heating element 3 and the heating element electrode 71, which can reduce the vertical height when the isolation layer 4 covers the heating element 3, thereby reducing the material loss of the MEMS gas sensor 10.

Step S105 , preparing a test element on a side of the isolation layer facing away from the heating element.

In step S105, a test element 5 is prepared on the side of the isolation layer 4 away from the heating element 3 by using a magnetron sputtering process and a stripping technology process. The material of the test element 5 includes but is not limited to gold, platinum, palladium, etc. The thickness of the test element 5 is 100-500nm. Preferably, the thickness of the test element 5 is 100-300nm. The shape of the test element 5 includes but is not limited to a forked electrode, a single electrode, a forked electrode of a three-electrode structure, etc. At the same time, corresponding test element electrodes 72 are respectively provided on the second support portion 24 and the third support portion 25, and the test element 5 is electrically connected to the test element electrode 72. The test element electrode 72 is sleeved on the electrode connecting portion 711.

Step S106, preparing a gas sensor on a side of the test element facing away from the isolation layer.

In step S106, a gas sensor 6 is prepared on the side of the test element 5 away from the isolation layer 4 by magnetron sputtering process, so that the gas sensor 6 covers the test element 5. The material of the gas sensor 6 includes but is not limited to tin dioxide, zinc oxide and the like.

Step S107, etching from the back side to the front side to form a heat collecting cavity, so that the support layer isolates the heat insulating cavity and the heat collecting cavity.

In step S107 , a deep silicon etching process is used to etch from the back surface 14 to the front surface 13 to form a heat collection cavity 12 . The depth of the heat collection cavity 12 is 300-600 um, that is, the depth of the heat collection cavity 12 is greater than the depth of the heat insulation cavity 11 .

In the above embodiment, by providing an insulation cavity and a heat collection cavity on the front and back of the silicon substrate respectively, providing a support layer connected to the insulation cavity wall in the insulation cavity to connect to the silicon substrate, and sequentially arranging the heating element, the isolation layer, the test element and the gas-sensitive element in the direction of the support layer toward the front, the other components of the MEMS gas sensor can be stably arranged in the insulation cavity, and the mechanical strength of the MEMS gas sensor can be improved. The insulation cavity can slow down the heat loss caused by the heating element due to heat convection, and the heat collection cavity can gather more heat generated by the heating element on the support layer, thereby reducing the power loss of the MEMS gas sensor. In addition, the insulation cavity and the heat collection cavity are made by deep silicon etching process and inductively coupled plasma etching process, which saves the production cost, and the volume of the device is reduced by the arrangement of the heating element electrode and the test element electrode, thereby reducing the space occupied by the electrode.

Obviously, those skilled in the art can make various changes and modifications to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

It should be understood that, although the steps in the flowchart of the accompanying drawings are displayed in sequence as indicated by the arrows, these steps are not necessarily executed in sequence in the order indicated by the arrows. Unless otherwise specified herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least a part of the steps in the flowchart of the accompanying drawings may include multiple sub-steps or multiple stages, and these sub-steps or stages are not necessarily executed at the same time, but can be executed at different times, and their execution order is not necessarily sequential, but can be executed in turn or alternately with other steps or at least a part of the sub-steps or stages of other steps.

The above examples are only preferred embodiments of the present application, and certainly cannot be used to limit the scope of rights of the present application. Therefore, equivalent changes made according to the claims of the present application still fall within the scope covered by the present application.

Claims (4)

1. A MEMS gas sensor, characterized in that the MEMS gas sensor comprises: A silicon substrate, comprising a front side and a back side facing away from the front side, wherein the front side is provided with a heat-insulating cavity, the back side is provided with a heat-collecting cavity, the heat-insulating cavity and the heat-collecting cavity are connected, and the silicon substrate further comprises a first cavity wall and a second cavity wall arranged opposite to the heat-insulating cavity, the first cavity wall and the second cavity wall are respectively perpendicular to the front side; A support layer, connected between the first cavity wall and the second cavity wall and located in the heat-insulating cavity, and the support layer isolates the heat-insulating cavity from the heat-collecting cavity; A heating element, disposed on the support layer and located in the heat insulation cavity; An isolation layer, covering the support layer and the heating element, wherein the isolation layer is formed by depositing a silicon nitride film; a test element, disposed on a side of the isolation layer facing away from the heating element; and A gas sensor is arranged on a side of the test element away from the isolation layer; Wherein, the silicon substrate also includes a third cavity wall and a fourth cavity wall which are arranged between the first cavity wall and the second cavity wall relative to the thermal insulation cavity, and the support layer is also connected between the third cavity wall and the fourth cavity wall; the MEMS gas sensor is provided with an electrode for providing energy for the normal operation of the MEMS gas sensor, and the support layer includes a first support portion for supporting the heating element, and a second support portion and a third support portion which are respectively connected to both sides of the first support portion close to the first cavity wall and the second cavity wall, and the second support portion and the third support portion are provided with the electrode on one side facing away from the first support portion; The second support part and the third support part are also connected between the third cavity wall and the fourth cavity wall and are located in the heat-insulating cavity; when the electrode is arranged on the side of the second support part and the third support part facing away from the first support part, the electrode does not protrude from the front side; the isolation layer has a certain gap with the second support part and the third support part respectively, and the electrode includes a heating element electrode and a test element electrode, and the heating element electrode is provided with an electrode connecting part accommodated in the gap so that the heating element electrode is electrically connected to the heating element through the electrode connecting part, and the test element electrode is sleeved on the electrode connecting part and electrically connected to the test element. 2 . The MEMS gas sensor according to claim 1 , wherein the depth of the thermal insulation cavity is smaller than the depth of the heat focusing cavity. 3. The MEMS gas sensor as described in claim 1 is characterized in that the supporting layer is composed of a silicon oxide layer and a silicon nitride layer obtained by depositing a silicon oxide film and a silicon nitride film respectively, the silicon oxide layer is close to the heat focusing cavity, the silicon nitride layer is located on a side of the silicon oxide layer away from the heat focusing cavity, and the heating element is arranged on a side of the silicon nitride layer away from the silicon oxide layer. 4. A method for manufacturing a MEMS gas sensor according to any one of claims 1 to 3, characterized in that the method for manufacturing the MEMS gas sensor comprises: Using an inductively coupled plasma-reactive ion etching process, etching from the front side of the silicon substrate to the back side away from the front side to form a heat-insulating cavity, wherein the heat-insulating cavity includes a first cavity wall and a second cavity wall that are arranged opposite to each other; Alternately depositing a silicon oxide film and a silicon nitride film in the heat-insulating cavity to sequentially form a silicon oxide layer and a silicon nitride layer to form a support layer, and connecting the support layer to the first cavity wall and the second cavity wall, wherein the first cavity wall and the second cavity wall are respectively perpendicular to the front surface; A heating element is prepared in the heat-insulating cavity and arranged on the supporting layer; Depositing a silicon nitride film on a side of the support layer facing the front surface and a side of the heating element facing the front surface to form an isolation layer, so that the isolation layer covers the support layer and the heating element; Prepare a test element on a side of the isolation layer facing away from the heating element; Preparing a gas sensor on a side of the test element facing away from the isolation layer; and A deep silicon etching process is adopted to etch from the back side to the front side to form a heat collecting cavity, so that the support layer isolates the heat insulating cavity from the heat collecting cavity.