An absolute pressure contact type MEMS capacitive thin film vacuum sensor

Abstract

The present invention discloses an absolute pressure contact type MEMS capacitive thin film vacuum sensor, including a sensor chip, a housing for mounting the sensor chip, and an upper shell for encapsulating the sensor chip in the housing; the sensor chip includes a borosilicate pressure-sensitive film, a silicon substrate and a glass substrate, which are connected in sequence from top to bottom; a cavity is provided on one side of the silicon substrate, and the silicon substrate is directly bonded to the borosilicate pressure-sensitive film on the side provided with the cavity to form a vacuum reference cavity; an air extraction hole is provided in the vacuum reference cavity, and the air extraction hole is sealed by anodically bonding the other side of the silicon substrate to the glass substrate, so that the vacuum reference cavity forms a high vacuum. The present invention simplifies the process flow and reduces the lower limit of measurement of the vacuum sensor by providing an air extraction hole inside the vacuum reference cavity, converting the technology of forming the vacuum reference cavity into a combination of silicon-silicon direct bonding and silicon-glass anode bonding; a protective ring is provided on the borosilicate pressure-sensitive film to reduce the influence of the sensor sensitivity and improve the resolution of the vacuum sensor.

Description

Technical Field

[0001] The invention belongs to the field of MEMS micro-machining and vacuum measurement technology, and in particular relates to an absolute pressure contact type MEMS capacitance film vacuum sensor. Background Art

[0002] As one of the fastest growing pressure sensor devices today, pressure sensors based on micro-electromechanical systems (MEMS) have gradually replaced traditional mechanical pressure sensors in some fields due to their advantages such as small size, light weight, low cost, easy integration and mass production. As a member of MEMS pressure sensors, MEMS capacitive vacuum sensors are mainly used for testing pressures below atmospheric pressure. They have the characteristics of high sensitivity, low temperature drift, good DC response and low power consumption. Therefore, they are attracting more and more attention from researchers in the research of various MEMS pressure sensors.

[0003] Since small-range pressure testing has high requirements for sensitivity, there is little research on MEMS capacitive thin film vacuum sensors. While improving the pressure sensitivity, it still faces problems such as a measurement limit greater than 1000Pa, low resolution, and easy damage to the pressure-sensitive membrane when using a large range of pressure. Summary of the invention

[0004] In view of the above-mentioned deficiencies, the present invention provides an absolute pressure contact type MEMS capacitive thin film vacuum sensor with high resolution and high sensitivity.

[0005] The object of the present invention is achieved as follows: an absolute pressure contact type MEMS capacitive thin film vacuum sensor, comprising a sensor chip, a housing for mounting the sensor chip, and an upper shell for encapsulating the sensor chip in the housing; characterized in that: the sensor chip comprises a borosilicate pressure-sensitive film, a silicon substrate and a glass substrate, which are connected in sequence from top to bottom;

[0006] A cavity is provided on one side of the silicon substrate, and the silicon substrate directly bonds the side provided with the cavity to the borosilicate pressure-sensitive film to form a vacuum reference cavity;

[0007] The vacuum reference cavity is provided with an exhaust hole, and the exhaust hole is sealed by anodically bonding the other side of the silicon substrate to the glass substrate, so that the vacuum reference cavity forms a high vacuum;

[0008] A lower electrode is provided on the lower end surface of the vacuum reference cavity, and an insulating layer is provided on the lower end surface of the borosilicate pressure-sensitive film; the insulating layer, the lower electrode and the borosilicate pressure-sensitive film form a capacitor structure;

[0009] An upper lead electrode is arranged on the borosilicate pressure-sensitive film; and a lower lead electrode is arranged on the silicon substrate.

[0010] Preferably, a protective ring is provided on the borosilicate pressure-sensitive film, and the protective ring separates the borosilicate pressure-sensitive film from the silicon substrate. The protective ring separates the borosilicate pressure-sensitive film from the silicon substrate, which can reduce the influence of the bypass capacitance on the sensitivity of the vacuum sensor and improve the resolution of the vacuum sensor.

[0011] Preferably, a lower electrode is provided on the lower end surface of the vacuum reference cavity, and an insulating layer is provided on the lower end surface of the borosilicate pressure-sensitive film; the insulating layer, the lower electrode and the borosilicate pressure-sensitive film form a capacitor structure. The insulating layer insulates the borosilicate pressure-sensitive film from the lower electrode in the vacuum reference cavity, thereby preventing the borosilicate pressure-sensitive film from directly contacting the lower electrode and causing a short circuit during testing.

[0012] Preferably, the base material of the borosilicate pressure-sensitive film is boron-doped wafer-level P-type silicon with a resistivity of less than 0.006Ω·cm.

[0013] Preferably, the borosilicate pressure-sensitive film is provided with an upper lead electrode groove and a lower lead electrode groove;

[0014] The upper lead electrode is led out through the upper lead electrode groove, and the lower lead electrode is led out through the lower lead electrode groove; the upper lead electrode and the lower lead electrode are used to lead out a pressure detection signal.

[0015] Preferably, the depth of the vacuum reference cavity is less than the maximum deflection of the borosilicate pressure-sensitive film within the measurement range, and a lower electrode smaller than the cavity bottom area is sputtered on the bottom surface of the vacuum reference cavity, and the sputtered electrode material is aluminum. The depth of the vacuum reference cavity is less than the maximum deflection of the borosilicate pressure-sensitive film within the measurement range, and the external environmental pressure is greater than a certain value, and the borosilicate pressure-sensitive film contacts the lower electrode, ensuring that the borosilicate pressure-sensitive film will not be damaged due to excessive pressure.

[0016] Preferably, the vacuum reference cavity is circular with a diameter of 2500 μm.

[0017] Preferably, the air extraction hole is made by wet etching, and the air extraction hole structure is trapezoidal; the upper surface of the air extraction hole is connected to the vacuum reference cavity, and the lower surface is connected to the glass substrate. The added trapezoidal air extraction hole can transform the technology of forming the vacuum reference cavity from the existing silicon-silicon bonding process technology to a combination of silicon-silicon direct bonding and silicon-glass anodic bonding, thereby improving the bonding rate of direct bonding, and at the same time improving the vacuum degree in the cavity, thereby reducing the measurement lower limit of the vacuum sensor.

[0018] Preferably, a front-stage circuit board and a support column for fixing the front-stage circuit board in the housing are provided in the housing; the sensor chip is welded to the front-stage circuit board by aluminum wire;

[0019] The shell is provided with an electrode lead hole for leading out the electrode, and the electrode lead hole is arranged on the side of the shell.

[0020] Preferably, the upper shell is provided with an air inlet hole for measurement. The air inlet hole is provided to facilitate the vacuum measurement system to measure the vacuum sensor. When the vacuum measurement system measures, the air enters the vacuum sensor through the air inlet hole for measurement.

[0021] The beneficial effects of the present invention are as follows: 1. By arranging an exhaust hole inside the vacuum reference cavity, the technology for forming the vacuum reference cavity is transformed from the existing silicon-silicon bonding process technology to a combination of silicon-silicon direct bonding and silicon-glass anode bonding, which does not require multiple standard cleaning and activation processes, simplifies the process flow, improves the bonding rate, reduces the measurement limit of the sensor, and improves the resolution of the sensor; at the same time, a protective ring is processed on the borosilicate pressure-sensitive film to separate the borosilicate pressure-sensitive film from the silicon substrate, which can reduce the influence of the parasitic capacitance on the sensitivity of the sensor and improve the resolution of the sensor.

[0022] 2. By adopting a contact structure for the borosilicate pressure-sensitive film, silicon substrate and glass substrate, the pressure-sensitive film is prevented from being damaged under high pressure, the compromise between sensitivity and linearity is improved, and the output repeatability and stability are improved; at the same time, a pressure measurement range of 10Pa to 80,000Pa can be achieved.

[0023] 3. By setting the present invention into a three-layer packaging structure, the problem of the need to lead out the electrode wires in the vacuum reference cavity is solved, and the process complexity and production cost of the electrode wire leading out are reduced; at the same time, the advantages of the present invention such as high sensitivity, low temperature drift, small size, low energy consumption, high accuracy and high measurement value are increased.

[0024] 4. By using boron-doped wafer-level P-type silicon material for the borosilicate pressure-sensitive film, the conductive properties of the semiconductor are changed, the electronic transmission performance of the pressure-sensitive film is effectively improved, and the performance of the sensor is further improved; the borosilicate pressure-sensitive film has the characteristic of self-stopping corrosion, and the thickness of the pressure-sensitive film can be accurately controlled; the large aspect ratio pressure-sensitive film can increase sensitivity and increase basic capacitance. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a schematic diagram of the hierarchical structure of the present invention.

[0026] Figure 2 for Figure 1 Cross-sectional view along the AA direction.

[0027] Figure 3 It is a schematic diagram of the overall structure of the present invention.

[0028] Figure 4 It is a cross-sectional view of the overall structural schematic diagram of the present invention.

[0029] Figure 5 This is a data chart of the performance test of the absolute pressure contact MEMS capacitive thin film vacuum sensor of the present invention.

[0030] Figure 6 This is a data chart of the overload resistance test of the absolute pressure contact MEMS capacitive thin film vacuum sensor of the present invention.

[0031] Among them, 1-sensor chip; 11-boron silicon pressure-sensitive film; 111-lower lead electrode groove; 112-upper lead electrode; 113-protective ring; 114-insulating layer; 12-silicon substrate; 121-exhaust hole; 122-lower lead electrode; 123-vacuum reference cavity; 124-lower electrode; 13-glass substrate; 400-upper shell; 401-air inlet; 500-outer shell; 501-electrode lead hole; 502-support column; 700-front stage circuit board. DETAILED DESCRIPTION

[0032] The present invention is further summarized below with reference to the accompanying drawings.

[0033] like Figure 1 As shown, an absolute pressure contact type MEMS capacitive thin film vacuum sensor includes a sensor chip 1, a housing 500 for mounting the sensor chip 1, and an upper housing 400 for encapsulating the sensor chip 1 in the housing 500; the housing 500 includes a front-stage circuit board 700 and a support column 502, the support column 502 fixes the front-stage circuit board 700 in the housing 500, and four support columns 502 are respectively arranged around the front-stage circuit board 700. The sensor chip 1 is connected to the front-stage circuit board 700, and the sensitive capacitor is electrically connected to the front-stage circuit board 700 by aluminum wire pressure welding; the side of the housing 500 is provided with an electrode lead hole 501, the output signal line of the front-stage circuit board 700 is led out through the electrode lead hole 501 on the side of the housing 500, and the housing 500 and the upper housing 400 are sealed by glue sealing, and the upper housing 400 is provided with an air inlet 401, which is connected to the ambient pressure through the air inlet 401 of the upper housing 400 to realize the external environmental pressure test.

[0034] Further, if Figure 2As shown, the sensor chip 1 includes a borosilicate pressure-sensitive film 11, a silicon substrate 12 and a glass substrate 13, which are connected in sequence from top to bottom; a cavity is provided on one side of the silicon substrate 12, and the side provided with the cavity is directly bonded to the borosilicate pressure-sensitive film 11 to form a vacuum reference cavity 123; an exhaust hole 121 is provided in the vacuum reference cavity 123, and the exhaust hole 121 is made by a wet etching method. According to the anisotropy of the wet etching, the exhaust hole 121 forms a trapezoid with an upper surface of 50 μm and a lower surface of 475 μm; the upper surface of the exhaust hole 121 is provided in the vacuum reference cavity 123, and the lower surface is connected to the glass substrate 13; the exhaust hole 121 can transform the technology of forming the vacuum cavity from the existing silicon-silicon bonding process technology to a combination of silicon-silicon direct bonding and silicon-glass anode bonding, thereby improving the bonding rate of direct bonding, while improving the vacuum degree of the cavity, and reducing the measurement lower limit of the vacuum sensor. The other side of the silicon substrate 12 is anodically bonded to the glass substrate 13 to block the exhaust hole 121 and form a high vacuum in the vacuum reference cavity 123 .

[0035] Furthermore, an insulating layer 114 is provided on the lower end surface of the borosilicate pressure-sensitive film 11, and a lower electrode 124 is provided in the vacuum reference cavity 123. The lower electrode 124 in the vacuum reference cavity 123, the insulating layer 114 and the borosilicate pressure-sensitive film 11 constitute a capacitor structure; the insulating layer 114 insulates the borosilicate pressure-sensitive film 11 from the lower electrode 124 in the vacuum reference cavity 123, so as to avoid direct contact and short circuit between the borosilicate pressure-sensitive film 11 and the lower electrode 124 during testing.

[0036] Furthermore, the borosilicate pressure-sensitive film 11 is made by the method of concentrated boron diffusion and self-stopping silicon corrosion. The thickness of the borosilicate pressure-sensitive film 11 is 6μm, and the width-to-thickness ratio is greater than 400. A protective ring 113 is provided on the borosilicate pressure-sensitive film 11 to separate the borosilicate pressure-sensitive film 11 from the silicon substrate 12, which can reduce the influence of the parasitic capacitance on the sensitivity of the sensor and improve the resolution of the sensor. The depth of the vacuum reference cavity 123 is less than the maximum deflection of the borosilicate pressure-sensitive film in the measurement range. When the external environmental pressure is greater than a certain value, the borosilicate pressure-sensitive film 11 contacts the lower electrode 124, ensuring that the borosilicate pressure-sensitive film 11 will not be damaged due to excessive pressure.

[0037] Furthermore, an upper lead electrode 112 groove and a lower lead electrode 122 groove 111 are provided on the borosilicate pressure-sensitive film 11, and the upper lead electrode 112 is provided at the position where the upper lead electrode 112 groove is provided on the borosilicate pressure-sensitive film 11; a lower lead electrode 122 is provided at the position where the lower lead electrode 122 groove 111 is provided on the silicon substrate 12; the upper lead electrode 112 is led out through the upper lead electrode 112 groove, and the lower lead electrode 122 is led out through the lower lead electrode 122 groove 111; the upper lead electrode 112 and the lower lead electrode 122 are used to lead out pressure detection signals.

[0038] The present invention tests the performance of the absolute pressure contact MEMS capacitive film vacuum sensor through a vacuum measurement system. The vacuum measurement system includes a pump group, an air inlet needle valve, a set of commercial capacitive film gauges and a cold cathode ionization gauge. The pump group maintains the vacuum degree of the system at 10 -2 The magnitude of Pa. The vacuum degree in the intake needle valve control system changes at a certain rate. Commercial capacitance film gauges are used to detect the low vacuum degree of the test system vacuum chamber, while cold cathode ionization gauges are used to measure the high vacuum degree.

[0039] During the test, the vacuum degree of the vacuum chamber is adjusted by slowly adjusting the air inlet valve to complete the vacuum degree test within the range of (10-80000) Pa, and the capacitance change is measured using a precision LCR capacitance meter. The performance experiments of the sensor are all carried out under a certain temperature (25°C) and humidity (24% RH) environment.

[0040] The performance of the present invention is measured by measuring the capacitance-pressure curve. The measurement results are as follows: Figure 5 As shown in the figure, the absolute pressure contact type MEMS capacitive thin film vacuum sensor, hereinafter referred to as the vacuum sensor, has a measurement range of (10~80000) Pa and a capacitance change of 12.455 pF-33.241 pF. Figure 5 It can be seen that when the measurement lower limit is less than 200 Pa, the capacitance-pressure characteristic curve of the vacuum sensor has good linearity, and the sensitivity of the vacuum sensor (10~110)Pa is 11.75 fF / Pa.

[0041] Overload resistance test: Figure 6As shown in the figure, the vacuum sensor is divided into three stages within the full-scale measurement range of (10~100000)Pa. The first stage is the normal working stage of the vacuum sensor, and the pressure range of the vacuum sensor is (10~720)Pa. In this stage, due to the small pressure on the borosilicate pressure-sensitive film 11, the borosilicate pressure-sensitive film 11 and the vacuum chamber are in non-contact mode, and the maximum sensitivity is 35.45fF / Pa. The second stage is the main working stage of the vacuum sensor, in which the output capacitance is mainly contact capacitance. In this working stage, the pressure test range is (720~38300)Pa, and the borosilicate pressure-sensitive film 11 changes from a non-contact state to a contact state. When the borosilicate pressure-sensitive film 11 just contacts the vacuum chamber, the capacitance rises rapidly, and as the contact area gradually increases, the capacitance rises slowly. The maximum sensitivity of the vacuum sensor before and after the optimization of the contact stage is 69.49 fF / Pa. The third stage is the saturation stage. The pressure test range is (38300~100000)Pa. Due to the size limitation of the borosilicate pressure-sensitive film 11, the contact area between the borosilicate pressure-sensitive film 11 and the vacuum chamber gradually reaches saturation, and the capacitance changes slowly until it reaches saturation. In this stage, the sensitivity is 5.96fF / Pa. By testing the vacuum sensor in the measurement range of (10~100000)Pa, it is verified that the pressure-sensitive film has good overload resistance.

[0042] Working principle: A high vacuum reference cavity 123 is formed between the borosilicate pressure-sensitive film 11 and the lower electrode 124, and the external environmental pressure directly acts on the borosilicate pressure-sensitive film 11. When the external pressure is different from the pressure in the reference cavity 123, a pressure difference is formed on both sides of the borosilicate pressure-sensitive film 11, and the borosilicate pressure-sensitive film 11 is deformed due to the pressure difference on both sides. When the external pressure is greater than the pressure in the vacuum reference cavity 123, the borosilicate pressure-sensitive film 11 is deformed toward the lower electrode 124, resulting in a change in the effective distance between the borosilicate pressure-sensitive film 11 and the lower electrode 124, thereby causing a change in capacitance. As the external pressure continues to increase, the distance between the borosilicate pressure-sensitive film 11 and the lower electrode 124 continues to decrease. When the borosilicate pressure-sensitive film 11 contacts the lower electrode 124, the capacitance value is reflected by the displacement change between the borosilicate pressure-sensitive film 11 and the lower electrode 124 and the contact area between the borosilicate pressure-sensitive film 11 and the dielectric, and the relative vacuum value is obtained by measuring the capacitance.

[0043] The above description is only an embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent substitution, improvement, etc. made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. An absolute pressure contact type MEMS capacitive thin film vacuum sensor, comprising a sensor chip (1), a housing (500) for mounting the sensor chip, and an upper housing (400) for encapsulating the sensor chip (1) in the housing; characterized in that: The sensor chip (1) comprises a borosilicate pressure-sensitive film (11), a silicon substrate (12) and a glass substrate (13), which are connected in sequence from top to bottom; A cavity is provided on one side of the silicon substrate (12), and the silicon substrate (12) is directly bonded with the side provided with the cavity to the borosilicate pressure-sensitive film (11) to form a vacuum reference cavity (123); The vacuum reference cavity (123) is provided with an exhaust hole (121), and the exhaust hole (121) is sealed by anodically bonding the other side of the silicon substrate (12) with the glass substrate (13), so that a high vacuum is formed in the vacuum reference cavity (123); A lower electrode (124) is provided on the lower end surface of the vacuum reference cavity (123), and an insulating layer (114) is provided on the lower end surface of the borosilicate pressure-sensitive film (11); the insulating layer (114), the lower electrode (124) and the borosilicate pressure-sensitive film (11) form a capacitor structure; An upper lead electrode (112) is provided on the borosilicate pressure-sensitive film (11); and a lower lead electrode (122) is provided on the silicon substrate (12).

2. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: A protective ring (113) is provided on the borosilicate pressure-sensitive film (11), and the protective ring (113) separates the borosilicate pressure-sensitive film (11) from the silicon substrate (12).

3. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: The base material of the borosilicate pressure-sensitive film (11) is boron-doped wafer-level P-type silicon, with a resistivity of less than 0.006Ω·cm.

4. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: The borosilicate pressure-sensitive film (11) is provided with an upper lead electrode groove and a lower lead electrode groove (111); The upper lead electrode (112) is led out through the upper lead electrode groove, and the lower lead electrode (122) is led out through the lower lead electrode groove (111); the upper lead electrode (112) and the lower lead electrode (122) are used to lead out pressure detection signals.

5. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: The depth of the vacuum reference cavity (123) is smaller than the maximum deflection of the measurement range of the borosilicate pressure-sensitive film (11), and a lower electrode (124) smaller than the cavity bottom area is sputtered on the bottom surface of the vacuum reference cavity (123), and the sputtered electrode material is aluminum.

6. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: The vacuum reference cavity (123) is circular and has a diameter of 2500 μm.

7. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: The air pumping hole (121) is manufactured by wet etching, and the structure of the air pumping hole (121) is trapezoidal; the upper surface of the air pumping hole (121) is connected to the vacuum reference cavity (123), and the lower surface is connected to the glass substrate (13).

8. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: A front-stage circuit board (700) and a support column (502) for fixing the front-stage circuit board (700) in the housing are provided in the housing; the sensor chip (1) is welded to the front-stage circuit board (700) by aluminum wire pressure welding; The outer shell (500) is provided with an electrode lead hole (501) for leading out the electrode, and the electrode lead hole (501) is arranged on a side surface of the outer shell (500).

9. The absolute pressure contact type MEMS capacitive thin film vacuum sensor according to claim 1, characterized in that: The upper shell (400) is provided with an air inlet hole (401) for measuring.

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