Double-capacitance differential MEMS vacuum gauge

Abstract

The invention relates to the technical field of vacuum metering, in particular to a double-capacitance differential MEMS vacuum gauge, which comprises a glass substrate, a silicon substrate, a pressure sensing film, a silicon upper electrode, a metal lower electrode and a glass sealing cover, and is characterized in that the glass substrate is arranged at the lower part, and the metal lower electrode is arranged on the glass substrate; the silicon substrate is arranged on the glass substrate and is bonded with the glass substrate; the pressure sensing film and the silicon upper electrode are arranged on the silicon substrate; the pressure sensing film is arranged between the silicon upper electrode and the metal lower electrode; the pressure sensing film, the silicon upper electrode and a gap between the pressure sensing film and the silicon upper electrode form an upper sensitive capacitor; the pressure sensing film, the metal lower electrode and a gap between the two form a lower sensitive capacitor; and the glass sealing cover is arranged above the silicon substrate and is subjected to anodic bonding with the silicon substrate. The dual-capacitance differential structure is adopted, the influence of the environment temperature on the measurement result of the vacuum gauge is eliminated, the measurement precision is higher, the sensitivity is higher, and the temperature of the environment where the vacuum gauge is located can be monitored in real time.

Description

Technical Field

[0001] The present application relates to the field of vacuum measurement technology, and in particular to a dual-capacitance differential MEMS vacuum gauge. Background Art

[0002] Capacitive vacuum gauge has the characteristics of high precision, good linearity, good repeatability and good long-term stability. It can measure the total pressure of gas or steam. The measurement result is independent of the gas composition and type. However, temperature is one of the important factors affecting the measurement accuracy of capacitance film vacuum gauge.

[0003] In order to eliminate the influence of temperature on the measurement results, traditional mechanical capacitive thin film vacuum gauges usually use a temperature control system, which will greatly increase the size and power consumption of the capacitive thin film vacuum gauge. MEMS capacitive thin film vacuum gauges are manufactured using MEMS technology. The size of the entire vacuum gauge is in the millimeter range, so it is difficult to set up a separate temperature control system for it.

[0004] Therefore, in order to eliminate the influence of temperature on the MEMS capacitive thin film vacuum gauge, it is necessary to improve its structure. The original single capacitance sensitive capacitor of the MEMS capacitive thin film vacuum gauge is set to a dual capacitance differential structure, which is expected to eliminate the influence of temperature on the measurement results through differentiation. Summary of the invention

[0005] This application provides a dual-capacitance differential MEMS vacuum gauge that can achieve 1-10 5 The absolute vacuum degree can be measured in the Pa range, and the influence of ambient temperature on the measurement results can be eliminated.

[0006] In order to achieve the above-mentioned purpose, the present application provides a dual-capacitance differential MEMS vacuum gauge, including a glass substrate, a silicon substrate, a pressure-sensitive film, a silicon upper electrode, a metal lower electrode and a glass cover, wherein: the glass substrate is arranged at the bottom, and the metal lower electrode is arranged on the glass substrate; the silicon substrate is arranged on the glass substrate and bonded to the glass substrate; the pressure-sensitive film and the silicon upper electrode are arranged on the silicon substrate; the pressure-sensitive film is arranged between the silicon upper electrode and the metal lower electrode; the pressure-sensitive film and the silicon upper electrode and the gap therebetween constitute an upper sensitive capacitor; the pressure-sensitive film and the metal lower electrode and the gap therebetween constitute a lower sensitive capacitor; the glass cover is arranged above the silicon substrate and is anodically bonded to the silicon substrate.

[0007] Furthermore, it also includes a circuit board, which is arranged below the glass substrate and has a circuit board pad.

[0008] Furthermore, a thin film thermometer is arranged on the upper surface of the glass cover, and the thin film thermometer adopts a Pt thin film thermistor as a sensitive element.

[0009] Furthermore, a sealed reference cavity is formed between the glass cover and the silicon substrate, and the silicon upper electrode is arranged inside the sealed reference cavity and bonded to the glass cover by anodic bonding.

[0010] Furthermore, a first lead pad is provided on the silicon upper electrode and is connected to the circuit board pad through an aluminum wire.

[0011] Furthermore, a second lead pad is provided on the pressure-sensitive film and is connected to the circuit board pad via an aluminum wire.

[0012] Furthermore, a third lead pad is provided on the metal lower electrode and is connected to the circuit board pad via an aluminum wire.

[0013] Furthermore, the pressure-sensitive film is a square silicon film, and the four corners of the silicon film are rounded.

[0014] Furthermore, the silicon upper electrode is made of low-resistance silicon doped with concentrated boron; and the material used to prepare the metal lower electrode is aluminum.

[0015] Furthermore, the vacuum degree can be measured in the range of 1-10 5 Pa.

[0016] The dual-capacitance differential MEMS vacuum gauge provided in this application has the following beneficial effects:

[0017] The present application adopts a dual-capacitor differential structure to eliminate the influence of ambient temperature on the measurement results of the vacuum gauge, and the measurement accuracy is higher; the dual-capacitor differential structure is adopted to add anti-overload protection for the pressure-sensitive film, so that the size of the pressure-sensitive film in the vacuum gauge is larger than that of other MEMS vacuum gauges, and therefore has higher sensitivity; and a film thermometer is also provided, which is conducive to real-time monitoring of the ambient temperature of the vacuum gauge, and can provide indirect evidence for the measurement results of the vacuum gauge that are not affected by temperature. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings constituting a part of this application are used to provide a further understanding of this application, so that other features, purposes and advantages of this application become more obvious. The schematic embodiment drawings and their descriptions of this application are used to explain this application and do not constitute an improper limitation on this application. In the drawings:

[0019] Figure 1 is a schematic diagram of a dual-capacitance differential MEMS vacuum gauge provided according to an embodiment of the present application;

[0020] Figure 2 is a cross-sectional view of a dual-capacitance differential MEMS vacuum gauge provided according to an embodiment of the present application;

[0021] Figure 3 This is a comparison chart of the working principles of single-capacitor and double-capacitor differential vacuum gauges;

[0022] Figure 4 is a working principle diagram of a dual-capacitance differential MEMS vacuum gauge provided according to an embodiment of the present application;

[0023] In the figure: 1-glass cover, 2-silicon upper electrode, 3-thin film thermometer, 4-pressure sensitive film, 5-first lead pad, 6-sealed reference cavity, 7-circuit board pad, 8-circuit board, 9-second lead pad, 10-third lead pad, 11-metal lower electrode, 12-glass substrate, 13-silicon substrate, 14-aluminum wire. DETAILED DESCRIPTION

[0024] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present application.

[0025] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequential order. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present application described here. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device comprising a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0026] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0027] In addition, some of the above terms may be used to express other meanings in addition to indicating orientation or positional relationship. For example, the term "on" may also be used to express a certain dependency 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.

[0028] In addition, the term "plurality" shall mean two or more.

[0029] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0030] like Figure 1-2 As shown, the present application provides a dual-capacitance differential MEMS vacuum gauge, including a glass substrate 12, a silicon substrate 13, a pressure-sensitive film 4, a silicon upper electrode 2, a metal lower electrode 11 and a glass cover 1, wherein: the glass substrate 12 is arranged at the bottom, and the metal lower electrode 11 is arranged on the glass substrate 12; the silicon substrate 13 is arranged on the glass substrate 12 and bonded to the glass substrate 12; the pressure-sensitive film 4 and the silicon upper electrode 2 are arranged on the silicon substrate 13; the pressure-sensitive film 4 is arranged between the silicon upper electrode 2 and the metal lower electrode 11; the pressure-sensitive film 4 and the silicon upper electrode 2 and the gap therebetween constitute an upper sensitive capacitor; the pressure-sensitive film 4 and the metal lower electrode 11 and the gap therebetween constitute a lower sensitive capacitor; the glass cover 1 is arranged above the silicon substrate 13 and is anodically bonded to the silicon substrate 13.

[0031] Specifically, the dual-capacitance differential MEMS vacuum gauge provided in the embodiment of the present application is used for measuring the total pressure of gas under medium and low vacuum. The overall structure of glass-silicon-silicon-glass is adopted, and its sensitive capacitor is a dual-capacitance differential structure, that is, it has two sensitive capacitors, so that the output capacitance has the characteristics of not being affected by stray coupling capacitance and ambient temperature; the overall measurement accuracy of the vacuum gauge is high, the linearity is good, the output repeatability and long-term stability are good, and the influence of ambient temperature on the measurement results can also be eliminated. Among them, a pressure-sensitive film 4 is prepared on the silicon substrate 13, and the pressure-sensitive film 4 is used as a movable electrode, and the upper sensitive capacitor is formed with the silicon upper electrode 2 and the gap between the two. The capacitance signal is respectively led out by the first lead pad 5 and the second lead pad 9; similarly, the pressure-sensitive film 4 is used as a movable electrode, and the lower metal electrode 11 and the gap between the two form a lower sensitive capacitor, and the capacitance signal is respectively led out by the third lead pad 10 and the second lead pad 9. During measurement, the gas enters the gap of the lower sensitive capacitor from the third lead pad 10 of the metal lower electrode 11, causing the pressure-sensitive film 4 to deform, resulting in changes in the sensitive capacitor to achieve measurement, wherein the upper sensitive capacitor gap decreases and the output capacitor increases, while the lower sensitive capacitor gap increases and the output capacitor decreases, so that the overall output capacitance is a differential output, and its capacitance change is twice that of a single sensitive capacitor vacuum gauge. At the same time, since the output capacitance is the difference between the changes in the two sensitive capacitors, the influence of stray coupling capacitance and temperature on the measurement results can be eliminated.

[0032] Furthermore, it also includes a circuit board 8, which is arranged below the glass substrate 12, and is provided with a circuit board pad 7. The circuit board 8 is arranged as a whole below the glass substrate 12, and is provided with a circuit board pad 7, which is mainly used to connect with the lead-out pads of the silicon upper electrode 2, the pressure-sensitive film 4 and the metal lower electrode 11, and is used to collect and receive capacitance signals, and realize the measurement of vacuum degree according to the difference in capacitance change.

[0033] Furthermore, a thin film thermometer 3 is provided on the upper surface of the glass cover 1, and the thin film thermometer 3 uses a Pt thin film thermistor as a sensitive element. The thin film thermometer 3 is prepared on the upper surface of the glass cover 1 by magnetron sputtering, and preferably uses a Pt thin film thermistor as a sensitive element, with a thickness of preferably 250nm and a wire width of preferably 60μm, which can monitor the ambient temperature of the vacuum gauge in real time and verify the performance of the dual-capacitance differential MEMS vacuum gauge.

[0034] Furthermore, a sealed reference cavity 6 is formed between the glass cover 1 and the silicon substrate 13, and the silicon upper electrode 2 is arranged inside the sealed reference cavity 6 and bonded to the glass cover 1 by anodic bonding. The sealed reference cavity 6 is formed by anodic bonding of the glass cover 1 and the silicon substrate 13 in a high vacuum environment, providing a reference for absolute pressure measurement for the MEMS vacuum gauge.

[0035] Furthermore, a first lead pad 5 is provided on the silicon upper electrode 2 and is connected to the circuit board pad 7 via an aluminum wire 14 .

[0036] Furthermore, a second lead pad 9 is provided on the pressure-sensitive film 4 and is connected to the circuit board pad 7 via an aluminum wire 14 .

[0037] Furthermore, a third lead pad 10 is provided on the metal lower electrode 11 and is connected to the circuit board pad 7 via an aluminum wire 14 .

[0038] Specifically, lead pads are provided on the silicon upper electrode 2, the pressure-sensitive film 4 and the metal lower electrode 11, and the lead pads are connected to the circuit board pads 7 through aluminum wires 14 for leading out capacitance signals and transmitting them to the circuit board 8 for subsequent differential processing.

[0039] Furthermore, the pressure-sensitive film 4 is a square silicon film, and the four corners of the silicon film are rounded. In the embodiment of the present application, the film side length of the pressure-sensitive film 4 is preferably 4000 μm, the thickness is preferably 6 μm, and the fillet radius of the four corners is preferably 10 μm; wherein, the gap between the pressure-sensitive film 4 and the silicon upper electrode 2 is preferably 4 μm, and the gap between the pressure-sensitive film 4 and the metal lower electrode 11 is preferably 4 μm.

[0040] Furthermore, the silicon upper electrode 2 is made of low-resistance silicon doped with concentrated boron; and the metal lower electrode 11 is made of aluminum.

[0041] Specifically, the preparation process of the dual-capacitance differential MEMS vacuum gauge provided in the embodiment of the present application is as follows:

[0042] Step 1, select a 4-inch SOI wafer as a substrate, use photolithography to obtain the pattern of the pressure-sensitive film 4 on the back of the SOI, and then use dry etching to obtain the capacitance gap of the lower sensitive capacitor;

[0043] Step 2, select 4-inch BF33 glass as the glass substrate 12, and use photolithography to obtain the pattern of the metal bottom electrode 11, and use magnetron sputtering and electrode stripping technology to obtain the metal bottom electrode 11; use anodic bonding to bond the SOI wafer and the glass substrate 12, and then perform photolithography on the other side of the wafer after bonding to obtain the pattern of the sealed reference cavity 6, and obtain the sealed reference cavity 6 and the second lead pad 9 and the third lead pad 10 by etching;

[0044] Step 3, select 4-inch BF33 glass and use photolithography to obtain the pattern of the thin film thermometer 3, and use magnetron sputtering and electrode stripping technology to obtain the thin film thermometer 3;

[0045] Step 4, select a 4-inch boron-doped silicon wafer for cutting to make a silicon top electrode 2 and a first lead pad 5; laser punch a hole in the glass sheet obtained in the previous step according to the size of the silicon top electrode 2 to obtain a first lead pad 5 window; scribing the glass sheet obtained in the previous step according to the size of the silicon substrate 13 to obtain a glass cover 1; and perform anodically bonding the glass cover 1 to the silicon top electrode 2;

[0046] Step 5, in a high vacuum environment, the glass cover 1 obtained in the previous step is anodic bonded to the silicon substrate 13 to obtain a sealed reference cavity 6 with a high vacuum degree;

[0047] Step 6, lead each electrode of the vacuum gauge to the circuit board pad 7 of the circuit board 8 by aluminum wire pressure welding with aluminum wire 14, and complete the production of the dual-capacitance differential MEMS vacuum gauge.

[0048] Furthermore, the vacuum degree can be measured in the range of 1-10 5 Pa.

[0049] Specifically, Figure 3 As shown, the initial capacitance C0, sensitive output capacitance C, and capacitance change ΔC of the single capacitor MEMS vacuum gauge are:

[0050]

[0051] Among them, ε0(8.854×10 -12 F / m) is the vacuum dielectric constant, d is the electrode gap, A is the electrode area, and x is the electrode translation distance.

[0052] like Figure 3 As shown, the initial capacitance of the dual-capacitor plate capacitors C1 and C2, the sensitive output capacitor C 1b , C 2b And the capacitance changes ΔC are:

[0053]

[0054] It can be seen from this that the output capacitance change of the dual-capacitor differential MEMS vacuum gauge is twice that of the single-capacitor MEMS vacuum gauge.

[0055] And as Figure 4 As shown, the initial capacitance C0 of the dual-capacitor differential MEMS vacuum gauge provided in the present application example is obtained by formula (1), and the sensitive output capacitances C1, C2 and the capacitance change ΔC are:

[0056] Wherein, w is the deflection of the pressure-sensitive film, Ce is the stray capacitance caused by factors such as temperature. It can be seen from formula (8) that the dual-capacitance differential MEMS vacuum gauge provided in the embodiment of the present application can eliminate the influence of factors such as temperature on the measurement results, has high sensitivity and high measurement accuracy, and can achieve 1-10 5 Measurement of absolute vacuum in Pa range.

[0057] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A dual-capacitance differential MEMS vacuum gauge, characterized in that: It includes a glass substrate, a silicon substrate, a pressure-sensitive film, a silicon upper electrode, a metal lower electrode and a glass cover, wherein: The glass substrate is arranged at the bottom, and the metal bottom electrode is arranged on the glass substrate; The silicon substrate is disposed on the glass substrate and bonded to the glass substrate; The pressure-sensitive film and the silicon upper electrode are arranged on the silicon substrate; The pressure-sensitive film is arranged between the silicon upper electrode and the metal lower electrode; The pressure-sensitive film, the silicon upper electrode and the gap therebetween form an upper sensitive capacitor; The pressure-sensitive film, the metal lower electrode and the gap therebetween form a lower sensitive capacitor; The glass cover is arranged on the silicon substrate and is anodic bonded to the silicon substrate.

2. The dual-capacitance differential MEMS vacuum gauge according to claim 1, characterized in that: The invention also includes a circuit board, which is arranged below the glass substrate and has a circuit board pad arranged on the circuit board.

3. The dual-capacitance differential MEMS vacuum gauge according to claim 2, characterized in that: A thin film thermometer is arranged on the upper surface of the glass cover, and the thin film thermometer adopts a Pt thin film thermistor as a sensitive element.

4. The dual-capacitance differential MEMS vacuum gauge according to claim 3, characterized in that: A sealed reference cavity is formed between the glass cover and the silicon substrate. The silicon upper electrode is arranged inside the sealed reference cavity and is bonded to the glass cover by anodic bonding.

5. The dual-capacitance differential MEMS vacuum gauge according to claim 4, characterized in that: The silicon upper electrode is provided with a first lead pad, which is connected to the circuit board pad through an aluminum wire.

6. The dual-capacitance differential MEMS vacuum gauge according to claim 5, characterized in that: The pressure-sensitive film is provided with a second lead-out pad, which is connected to the circuit board pad via an aluminum wire.

7. The dual-capacitance differential MEMS vacuum gauge according to claim 6, characterized in that: The metal lower electrode is provided with a third lead pad, which is connected to the circuit board pad through an aluminum wire.

8. The dual-capacitance differential MEMS vacuum gauge according to claim 7, characterized in that: The pressure-sensitive film is a square silicon film, and the four corners of the silicon film are rounded.

9. The dual-capacitance differential MEMS vacuum gauge according to claim 8, characterized in that: The silicon upper electrode is made of low-resistance silicon doped with concentrated boron; the metal lower electrode is made of aluminum.

10. The dual-capacitance differential MEMS vacuum gauge according to claim 9, characterized in that: The measuring range of vacuum degree is 1-10 5 Pa.

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