Double-layer absolute pressure type MEMS capacitor film vacuum gauge

Abstract

The invention relates to the technical field of vacuum measurement, in particular to a double-layer absolute pressure type MEMS capacitor film vacuum gauge, which comprises a silicon substrate, a glass substrate and a PCB, and is characterized in that the silicon substrate comprises a thick silicon layer, a silicon oxide layer and a thin silicon layer from bottom to top; obtaining a reference cavity and a film extraction electrode window on the thick silicon layer, and obtaining a pressure sensing film and a film extraction electrode on the thin silicon layer; the glass substrate comprises a silicon electrode and glass; a silicon electrode lead-out hole is formed in the center of the glass; the lower surface of the silicon electrode is bonded with the upper surface of the glass through anodic bonding; an insulating layer is arranged on the upper surface of the silicon electrode; performing secondary anodic bonding on the upper surface of the glass and the lower surface of the thick silicon layer; and the combination body of the silicon substrate and the glass substrate is welded with the PCB through a bonding pad and soldering tin. The double-layer structure of the silicon substrate and the glass substrate is adopted, the preparation process flow is simplified, the sensitivity is high, the stability is good, and the absolute vacuum degree in the range of 1 * 10 <-2 > Pa to 1 * 10 < 5 > Pa can be measured.

Description

Technical Field

[0001] The present application relates to the technical field of vacuum measurement, and in particular, to a double-layer absolute pressure type MEMS capacitive thin film vacuum gauge. Background Art

[0002] As a medium and low vacuum measurement instrument, the absolute pressure type capacitive thin film vacuum gauge has the characteristics of high accuracy, good stability, and measurement results independent of gas composition, and is widely used in fields such as aerospace, semiconductor industry, and vacuum metrology; with the increasing demand for in-situ vacuum measurement in technologies such as space exploration and intelligent manufacturing, the micro-miniaturized absolute pressure type capacitive thin film vacuum gauge has become a research hotspot.

[0003] Microelectromechanical system (MEMS) technology is one of the main ways to miniaturize the absolute pressure type capacitive thin film vacuum gauge. The absolute pressure type MEMS capacitive thin film vacuum gauge is fabricated based on semiconductor materials such as single crystal silicon and glass, with light weight (gram level), small volume (less than 1 cm 3 ), and low power consumption (milliwatt level), and the corresponding parameters are reduced by three orders of magnitude compared with the traditional metal capacitive thin film vacuum gauge. In addition, the manufacturing process compatible with integrated circuits enables it to have the potential for large-scale batch production, can reduce production costs while maintaining good performance, and is expected to replace the traditional metal capacitive thin film vacuum gauge.

[0004] However, the existing absolute pressure type MEMS capacitive thin film vacuum gauges have problems such as the pressure-sensitive film being prone to breakage, low sensitivity, and complex preparation processes, which lead to difficulties in preparing the absolute pressure MEMS capacitive thin film vacuum gauge and low yield, and cannot well meet the current market demand. Therefore, an absolute pressure type MEMS capacitive thin film vacuum gauge with a simple and reliable preparation process, high yield, low cost, high sensitivity, and good stability has broad application prospects, but there is no similar product currently. Summary of the Invention

[0005] The present application provides a double-layer absolute pressure type MEMS capacitive thin film vacuum gauge, with a simple and reliable preparation process, high sensitivity, and good stability.

[0006] To achieve the above object, the present application provides a double-layer absolute pressure type MEMS capacitive thin-film vacuum gauge, including a silicon substrate, a glass substrate and a PCB circuit board, wherein: the silicon substrate is made of an SOI wafer, and includes a thick silicon layer, a silicon oxide layer and a thin silicon layer from bottom to top; a reference cavity and a thin-film lead-out electrode window are formed on the thick silicon layer by photolithography and wet etching, and after removing the silicon oxide layer, a pressure-sensitive thin film and a thin-film lead-out electrode are formed on the thin silicon layer; the glass substrate includes a silicon electrode and glass; a silicon electrode lead-out hole is formed at the center of the glass by laser ablation; the silicon electrode is located inside the reference cavity, and its lower surface is bonded to the upper surface of the glass by anodic bonding, and the lower surface of the silicon electrode completely covers the silicon electrode lead-out hole; an insulating layer is provided on the upper surface of the silicon electrode; the upper surface of the glass and the lower surface of the thick silicon layer are secondarily anodically bonded to realize the bonding of the silicon substrate and the glass substrate and the sealing of the reference cavity; the combination of the silicon substrate and the glass substrate is welded to the PCB circuit board through pads and solder.

[0007] Further, the pressure-sensitive thin film is a square thin film made of single-crystalline silicon, with a side length of 5 mm and a thickness of 6 μm.

[0008] Further, the silicon oxide layer is a self-stopping layer for wet etching, and the thickness of the silicon oxide layer > 1 μm.

[0009] Further, the insulating layer is deposited on the upper surface of the silicon electrode by chemical vapor deposition. The material of the insulating layer is silicon dioxide, and the thickness of the insulating layer is 300 nm.

[0010] Further, the silicon electrode is cut from a low-resistivity silicon wafer. The length and width of the silicon electrode are equal and the same as the side length of the pressure-sensitive thin film. The thickness of the silicon electrode is 4 - 20 μm less than the depth of the reference cavity.

[0011] Further, the silicon electrode lead-out hole is a square hole, and the side length of the silicon electrode lead-out hole is 1 / 2 of the length of the silicon electrode. The silicon electrode lead-out hole coincides with the central axis of the silicon electrode.

[0012] Further, the reference cavity is sealed in a high-vacuum environment, and the vacuum pressure of the bonding environment during the secondary anodic bonding < 10 -4 Pa.

[0013] Further, thin-film electrode pads and silicon electrode pads are provided on the lower surface of the glass. The thin-film lead-out electrode is connected to the thin-film electrode pad by aluminum wire pressure welding, and the silicon electrode is connected to the silicon electrode pad by aluminum wire pressure welding.

[0014] Further, a thin-film electrode circuit pad, a silicon electrode circuit pad, and a capacitance measurement circuit are provided on the upper surface of the PCB circuit board, where: the thin-film electrode pad is fixedly connected to the thin-film electrode circuit pad by soldering; the silicon electrode pad is fixedly connected to the silicon electrode circuit pad by soldering; both the thin-film electrode circuit pad and the silicon electrode circuit pad are connected to the capacitance measurement circuit through wires on the PCB circuit board.

[0015] Further, by setting the thickness of the thin silicon layer on the silicon substrate or adjusting the parameters of the secondary anodic bonding, the measurement within the vacuum pressure range of 1×10 -2 Pa to 1×10 5 Pa can be achieved.

[0016] A double-layer absolute pressure type MEMS capacitive thin-film vacuum gauge provided by the present application has the following beneficial effects: (1) The present application has a double-layer structure of a silicon substrate and a glass substrate, and the sensitive capacitive electrodes are all made of silicon material. Metal is no longer used as the fixed electrode, and only one etching is required for the preparation of the pressure-sensitive film, which simplifies the preparation process flow and improves the yield of preparation.

[0017] (2) The present application uses silicon electrode and punched glass anodic bonding and the combination body and the silicon substrate secondary anodic bonding, which not only ensures the sealing performance of the reference cavity, but also simplifies the lead-out process of the fixed electrode; it ensures the acquisition and maintenance of a high vacuum degree in the reference cavity, and can extend the lower limit of the vacuum gauge measurement to 10 -2 Pa high vacuum.

[0018] (3) The length and width of the silicon electrode lead-out hole in the present application are half of the length and width of the silicon electrode, and the center axis of the silicon electrode lead-out hole coincides with that of the silicon electrode. This design enables the silicon electrode and the glass to have a wide enough bonding surface, ensuring the sealing performance of the reference cavity and making the through-hole size large enough to facilitate the lead-out of electrical signals.

[0019] (4) The present application uses a low-resistivity silicon block with an insulating layer on the upper surface as the fixed electrode, which prevents the pressure-sensitive film from contacting and short-circuiting with the fixed electrode, ensuring the transmission of electrical signals; it also provides good limit protection for the pressure-sensitive film, avoiding the risk of the pressure-sensitive film breaking due to exceeding the deformation limit. This design improves the anti-overload ability and reliability of the vacuum gauge on the one hand, and on the other hand, under the limit protection, the aspect ratio of the pressure-sensitive film can be increased, thereby improving the sensitivity of the vacuum gauge.

[0020] (5) In the double-layer structure of the present application, the pressure-sensitive film deforms towards the fixed electrode side under the action of external pressure, and the sensitive capacitance increases with the increase of pressure. After the film contacts the insulating layer, the capacitance output shows a segmented linearity, improving the linearity of the vacuum gauge within the measurement range.

[0021] (6) The double-layer structure of this application is directly sealed on the PCB circuit board by means of flip-chip bonding, which integrates the vacuum gauge and the measurement circuit closely, reduces the influence of stray capacitance on the measurement result, reduces the difficulty of the whole package, simplifies the packaging and testing process, and is conducive to large-scale production. Description of the Drawings

[0022] The drawings forming a part of this application are used to provide a further understanding of this application, making other features, purposes, and advantages of this application more obvious. The schematic embodiments and their descriptions of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings: Figure 1 is a schematic structural diagram of a double-layer absolute pressure type MEMS capacitive thin-film vacuum gauge provided by an embodiment of this application; Figure 2 is a schematic diagram of the glass substrate of a double-layer absolute pressure type MEMS capacitive thin-film vacuum gauge provided by an embodiment of this application; Figure 3 is a schematic diagram of the silicon substrate of a double-layer absolute pressure type MEMS capacitive thin-film vacuum gauge provided by an embodiment of this application; In the figure: 1-thin silicon layer, 2-silicon oxide layer, 3-thick silicon layer, 4-reference cavity, 5-pressure-sensitive thin film, 6-thin film lead electrode, 7-thin film lead electrode window, 8-insulating layer, 9-silicon electrode, 10-glass, 11-silicon electrode lead hole, 12-thin film electrode pad, 13-silicon electrode pad, 14-aluminum wire, 15-PCB circuit board, 16-silicon electrode circuit pad, 17-thin film electrode circuit pad, 18-capacitance measurement circuit, 19-solder. Detailed Embodiments

[0023] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0024] It should be noted that the terms "first", "second", etc. in the description, claims and the above-mentioned drawings of this application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so as to implement the embodiments of the present application described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0025] In this application, the orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", etc. is based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe this application and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation, or be constructed and operated in a specific orientation.

[0026] Moreover, in addition to being used to represent an orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in this application can be understood according to specific circumstances.

[0027] In addition, the meaning of the term "plurality" should be two or more.

[0028] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will describe this application in detail with reference to the drawings and in combination with the embodiments.

[0029] Such as Figures 1-3As shown in the figure, the present application provides a double-layer absolute pressure MEMS capacitive thin-film vacuum gauge, which includes a silicon substrate, a glass substrate, and a PCB circuit board 15, where: the silicon substrate is made of an SOI wafer, and from bottom to top are a thick silicon layer 3, a silicon oxide layer 2, and a thin silicon layer 1; a reference cavity 4 and a thin-film lead-out electrode window 7 are obtained on the thick silicon layer 3 by means of photolithography and wet etching, and after removing the silicon oxide layer 2, a pressure-sensitive thin film 5 and a thin-film lead-out electrode 6 are directly obtained on the thin silicon layer 1; the glass substrate includes a silicon electrode 9 and glass 10; a silicon electrode lead-out hole 11 is formed at the center of the glass 10 by laser ablation; the silicon electrode 9 is located inside the reference cavity 4, and its lower surface is bonded to the upper surface of the glass 10 by anodic bonding, and the lower surface of the silicon electrode 9 completely covers the silicon electrode lead-out hole 11; an insulating layer 8 is provided on the upper surface of the silicon electrode 9; the upper surface of the glass 10 and the lower surface of the thick silicon layer 3 are subjected to secondary anodic bonding to achieve the bonding of the silicon substrate and the glass substrate and the sealing of the reference cavity 4; the combination of the silicon substrate and the glass substrate is welded to the PCB circuit board 15 through pads and solder 19.

[0030] Specifically, the double-layer absolute pressure MEMS capacitive thin-film vacuum gauge provided in the embodiment of the present application is made by MEMS technology, and is a double-layer structure of silicon-glass, and can be used for measuring the total gas pressure from high vacuum to medium-low vacuum (1×10 -2 Pa~1×10 5 Pa), the preparation process is simple and reliable, has high sensitivity, good anti-overload performance, and can be applied in fields such as deep space exploration, wind tunnel experiments, and biomedicine that have requirements for miniaturization of vacuum measurement instruments.

[0031] More specifically, in the embodiment of the present application, the silicon substrate is preferably made of a 4-inch SOI wafer, including a thick silicon layer 3, a silicon oxide layer 2, and a thin silicon layer 1. The reference cavity 4 and the thin-film lead-out electrode window 7 are obtained by wet etching the thick silicon layer 3. The pressure-sensitive thin film 5 is located on the thin silicon layer 1. After the wet etching is completed, the silicon oxide layer 2 is directly removed using a BOE solution, and the pressure-sensitive thin film 5 and the thin-film lead-out electrode 6 made of single-crystalline silicon material can be directly obtained. The thickness of the thin silicon layer 1 is the thickness of the pressure-sensitive thin film 5. The shape, size, and thickness of the pressure-sensitive thin film 5 can be designed according to the measurement range requirements of the vacuum gauge, and the shape is square or circular, and the size is between 1mm 2 to 25mm 2Between 6 μm and 20 μm in thickness. The silicon electrode 9 is disposed inside the reference cavity 4 and forms a sensitive capacitor of the vacuum gauge together with the insulating layer 8 and the pressure-sensitive film 5. The pressure-sensitive film 5 is a movable electrode, and the silicon electrode 9 is a fixed electrode. During measurement, the pressure-sensitive film 5 deforms in the direction of the silicon electrode 9 under the action of pressure, causing a change in the plate gap of the sensitive capacitor and an increase in the sensitive capacitor. The insulating layer 8 prevents the pressure-sensitive film 5 from contacting and short-circuiting with the silicon electrode 9. The silicon electrode lead hole 11 on the glass 10 corresponds to the silicon electrode 9, and the thin film lead electrode window 7 corresponds to the thin film lead electrode 6. The capacitive signal of the sensitive capacitor is connected to the thin film electrode pad 12 and the silicon electrode pad 13 respectively by the aluminum wire 14 for pressure welding through the silicon electrode lead hole 11 and the thin film lead electrode window 7. Then, the thin film electrode pad 12 and the silicon electrode pad 13 are welded to the thin film electrode circuit pad 17 and the silicon electrode circuit pad 16 on the PCB circuit board 15 respectively by solder 19. The capacitance measurement circuit 18 on the PCB circuit board 15 measures the capacitance value of the received capacitive signal to achieve the measurement of the vacuum pressure.

[0032] Further, the pressure-sensitive film 5 is a square film made of single-crystalline silicon, with a side length of 5 mm and a thickness of 6 μm. The pressure-sensitive film 5 is formed on the thin silicon layer 1, preferably a square film, with a preferred side length of 5 mm and a preferred thickness of 6 μm.

[0033] Further, the silicon oxide layer 2 is a self-stopping layer for wet etching, and the thickness of the silicon oxide layer 2 > 1 μm. The silicon oxide layer 2 is a self-stopping layer for wet etching, mainly serving to protect the pressure-sensitive film 5.

[0034] Further, the insulating layer 8 is deposited on the upper surface of the silicon electrode 9 by chemical vapor deposition. The material of the insulating layer 8 is silicon dioxide, and the thickness of the insulating layer 8 is 300 nm.

[0035] Further, the silicon electrode 9 is cut from a low-resistivity silicon wafer. The length and width of the silicon electrode 9 are equal and the same as the side length of the pressure-sensitive film 5. The thickness of the silicon electrode 9 is 4 - 20 μm less than the depth of the reference cavity 4.

[0036] Further, the silicon electrode lead hole 11 is a square hole, and the side length of the silicon electrode lead hole 11 is 1 / 2 of the length of the silicon electrode 9. The silicon electrode lead hole 11 coincides with the central axis of the silicon electrode 9.

[0037] Specifically, the silicon electrode 9 is preferably made of a 4-inch silicon wafer with a resistivity < 0.1 Ω·m and is formed by dicing and cutting. A 300-nm-thick silicon dioxide is deposited on the upper surface of the silicon electrode 9 by chemical vapor deposition as the insulating layer 8 to prevent the pressure-sensitive film 5 from contacting the silicon electrode 9 and forming a short circuit. The glass 10 is preferably a 4-inch BF33 glass, and the silicon electrode lead hole 11 is obtained by laser ablation drilling. The silicon electrode lead hole 11 is preferably a square through-hole. The length and width of the silicon electrode 9 are the same as the side length of the pressure-sensitive film 5 and are twice the length and width of the silicon electrode lead hole 11. The lower surface of the silicon electrode 9 is bonded to the glass 10 by anodic bonding, and the central axes of the silicon electrode 9 and the silicon electrode lead hole 11 coincide. At this time, the silicon electrode lead hole 11 is completely and well sealed by the silicon electrode 9. The thickness of the silicon electrode 9 is 4 μm to 20 μm less than the depth of the reference cavity 4, so that there is a certain gap between the pressure-sensitive film 5 and the silicon electrode 9, that is, to ensure a certain distance between the two plates of the sensitive capacitor.

[0038] Furthermore, the reference cavity 4 is sealed in a high-vacuum environment, and the vacuum pressure in the bonding environment during the secondary anodic bonding process < 10 -4 Pa. The upper surface of the glass 10 bonded to the silicon electrode 9 and the lower surface of the thick silicon layer 3 will undergo secondary anodic bonding. When bonding, the silicon electrode 9 is placed inside the reference cavity 4, and the environmental vacuum degree is better than 10 -4 Pa, and the preheating time for bonding can be selected between 1 hour and 4 hours according to the measurement range of the vacuum gauge.

[0039] Furthermore, a thin-film electrode pad 12 and a silicon electrode pad 13 are provided on the lower surface of the glass 10. The thin-film lead electrode 6 is connected to the thin-film electrode pad 12 by pressure welding with an aluminum wire 14, and the silicon electrode 9 is connected to the silicon electrode pad 13 by pressure welding with an aluminum wire 14.

[0040] Furthermore, a thin-film electrode circuit pad 17, a silicon electrode circuit pad 16, and a capacitance measurement circuit 18 are provided on the upper surface of the PCB circuit board 15. Among them: the thin-film electrode pad 12 is fixedly connected to the thin-film electrode circuit pad 17 by soldering 19; the silicon electrode pad 13 is fixedly connected to the silicon electrode circuit pad 16 by soldering 19; both the thin-film electrode circuit pad 17 and the silicon electrode circuit pad 16 are connected to the capacitance measurement circuit 18 through the wires on the PCB circuit board 15.

[0041] Specifically, the electrical signal of the thin-film lead electrode 6 is led out to the thin-film electrode pad 12 by the aluminum wire 14 formed by pressure welding, and then led to the thin-film electrode circuit pad 17 on the PCB circuit board 15 by the solder 19; the electrical signal of the silicon electrode 9 is led out to the silicon electrode pad 13 by the aluminum wire 14 formed by pressure welding, and then led to the silicon electrode circuit pad 16 on the PCB circuit board 15 by the solder 19; the thin-film electrode circuit pad 17 and the silicon electrode circuit pad 16 are connected to the capacitance measurement circuit 18 through the internal wires of the PCB circuit board 15; the vacuum gauge as a whole is directly encapsulated on the PCB circuit board 15 together with the measurement circuit through the above process.

[0042] Further, by setting the thickness of the thin silicon layer 1 of the silicon substrate or adjusting the parameters of the secondary anodic bonding, the measurement within the vacuum pressure range of 1×10 -2 Pa to 1×10 5 Pa is achieved.

[0043] Specifically, the sensitive capacitance of the vacuum gauge is composed of the pressure-sensitive thin film 5, the silicon electrode 9, and the insulating layer 8. The pressure-sensitive thin film 5 and the silicon electrode 9 are the moving electrode and the fixed electrode of the sensitive capacitance respectively. The insulating layer 8 and the vacuum in the gap between the pressure-sensitive thin film 5 and the silicon electrode 9 are the dielectrics of the sensitive capacitance. The internal vacuum pressure of the reference cavity 4 is less than the lower limit of the vacuum gauge measurement, which is 10 -2 Pa. During measurement, the external vacuum pressure received by the pressure-sensitive thin film 5 is greater than the internal vacuum pressure of the reference cavity 4. The pressure-sensitive thin film 5 deforms towards the silicon electrode 9. As the external vacuum pressure increases, the distance between the pressure-sensitive thin film 5 and the silicon electrode 9 decreases, and the output capacitance of the sensitive capacitance increases. By measuring the capacitance value, the relationship curve between the vacuum pressure and the capacitance is obtained, and the vacuum pressure measurement is realized.

[0044] More specifically, the embodiment of the present application as a whole adopts a double-layer structure of a silicon substrate and a glass substrate. First, the silicon electrode 9 and the perforated glass 10 are anodically bonded to form a glass substrate, which not only ensures the sealing between the silicon electrode 9 and the glass 10, but also facilitates the extraction of the electrical signal of the silicon electrode 9; then the silicon substrate and the glass substrate are secondarily anodically bonded to form a silicon-glass 10 double-layer structure. The design of the double-layer structure enables the pressure-sensitive thin film 5 to deform towards the silicon electrode 9 side under the action of an external pressure. The pressure-sensitive thin film 5 will contact the insulating layer 8 on the upper surface of the silicon electrode 9 at a certain pressure, avoiding the risk of the pressure-sensitive thin film 5 breaking due to exceeding the deformation limit. On this basis, the aspect ratio of the pressure-sensitive thin film 5 can be increased, thereby improving the sensitivity of the vacuum gauge; while the silicon substrate and the glass substrate are secondarily anodically bonded to form a silicon-glass 10 double-layer structure, the high vacuum degree in the reference cavity 4 is obtained and maintained, reducing the difficulty of the overall encapsulation.

[0045] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, various modifications and changes can be made to the present application. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A double-layer absolute pressure MEMS capacitive thin film vacuum gauge, characterized in that: It includes a silicon substrate, a glass substrate and a PCB circuit board, wherein: The silicon substrate is made of an SOI wafer, and comprises a thick silicon layer, a silicon oxide layer and a thin silicon layer from bottom to top; A reference cavity and a thin film lead-out electrode window are obtained on the thick silicon layer by photolithography and wet etching, and a pressure-sensitive film and a thin film lead-out electrode are obtained on the thin silicon layer after removing the silicon oxide layer; The glass substrate comprises a silicon electrode and glass; Forming a silicon electrode lead-out hole at the center of the glass by laser ablation; The silicon electrode is located inside the reference cavity, and its lower surface is bonded to the upper surface of the glass by anodic bonding, and the lower surface of the silicon electrode completely covers the silicon electrode lead-out hole; An insulating layer is provided on the upper surface of the silicon electrode; The upper surface of the glass and the lower surface of the thick silicon layer are subjected to secondary anodic bonding to achieve bonding of the silicon substrate and the glass substrate and sealing of the reference cavity; The combination of the silicon substrate and the glass substrate is welded to the PCB circuit board via a welding pad and solder.

2. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 1, characterized in that: The pressure-sensitive film is a square film made of single-crystal silicon, with a side length of 5 mm and a thickness of 6 μm.

3. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 2, characterized in that: The silicon oxide layer is a self-stop layer for wet etching, and the thickness of the silicon oxide layer is greater than 1 μm.

4. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 3, characterized in that: The insulating layer is deposited on the upper surface of the silicon electrode by chemical vapor deposition. The material of the insulating layer is silicon dioxide and the thickness of the insulating layer is 300 nm.

5. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 4, characterized in that: The silicon electrode is cut from a low-resistivity silicon wafer, the length and width of the silicon electrode are equal and the same as the side length of the pressure-sensitive film, and the thickness of the silicon electrode is 4-20 μm less than the depth of the reference cavity.

6. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 5, characterized in that: The silicon electrode lead-out hole is a square hole, the side length of the silicon electrode lead-out hole is 1 / 2 of the length of the silicon electrode, and the silicon electrode lead-out hole coincides with the central axis of the silicon electrode.

7. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 6, characterized in that: The reference cavity is sealed in a high vacuum environment, and the vacuum pressure of the bonding environment during the secondary anodic bonding process is less than 10 -4 Pa.

8. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 7, characterized in that: A thin film electrode pad and a silicon electrode pad are provided on the lower surface of the glass, the thin film lead-out electrode is connected to the thin film electrode pad by aluminum wire pressure welding, and the silicon electrode is connected to the silicon electrode pad by aluminum wire pressure welding.

9. The double-layer absolute pressure MEMS capacitive thin film vacuum gauge according to claim 8, characterized in that: The upper surface of the PCB circuit board is provided with a thin film electrode circuit pad, a silicon electrode circuit pad and a capacitance measurement circuit, wherein: The thin film electrode pad and the thin film electrode circuit pad are connected and fixed by soldering; The silicon electrode pad is connected and fixed to the silicon electrode circuit pad by soldering; The thin film electrode circuit pad and the silicon electrode circuit pad are both connected to the capacitance measurement circuit through wires on the PCB circuit board.

10. The double-layer absolute pressure MEMS capacitance thin film vacuum gauge according to claim 9, characterized in that: By setting the thickness of the thin silicon layer of the silicon substrate or adjusting the parameters of the secondary anodic bonding, 1×10 -2 Pa~1×10 5 Measurements in the Pa vacuum pressure range.

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