Dual-capacitor differential MEMS vacuum gauge

Abstract

The present application relates to the technical field of vacuum metrology, and in particular to a dual-capacitor differential MEMS vacuum gauge, comprising a glass substrate, a silicon substrate, a pressure-sensitive diaphragm, a silicon upper electrode, a metal lower electrode, and a glass cover. The glass substrate is arranged at the lower position, 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 diaphragm and the silicon upper electrode are arranged on the silicon substrate; the pressure-sensitive diaphragm is arranged between the silicon upper electrode and the metal lower electrode; the pressure-sensitive diaphragm, the silicon upper electrode, and a gap therebetween form an upper sensitive capacitor; the pressure-sensitive diaphragm, the metal lower electrode, and a gap therebetween form a lower sensitive capacitor; and the glass cover is arranged above the silicon substrate and anodically bonded to the silicon substrate. The present application employs a dual-capacitor differential structure, eliminating the impact of ambient temperature on a measurement result of the vacuum gauge, achieving higher measurement accuracy and higher sensitivity, and also enabling real-time monitoring of the ambient temperature of the vacuum gauge.

Description

A dual-capacitor differential MEMS vacuum gauge Technical Field

[0001] This application relates to the field of vacuum measurement technology, and more specifically, to a dual-capacitor differential MEMS vacuum gauge. Background Technology

[0002] Capacitive vacuum gauges are characterized by high accuracy, good linearity, good repeatability, and good long-term stability. They can measure the total pressure of gases or vapors, and the measurement results are independent of the gas composition and type. However, temperature is one of the important factors affecting the measurement accuracy of capacitive thin-film vacuum gauges.

[0003] Traditional mechanical capacitive thin-film vacuum gauges typically employ temperature control systems to eliminate the influence of temperature on measurement results, which significantly increases the size and power consumption of the gauge. MEMS capacitive thin-film vacuum gauges, fabricated using MEMS technology, have dimensions on the millimeter scale, making it difficult to implement a separate temperature control system for them.

[0004] Therefore, in order to eliminate the influence of temperature on MEMS capacitive thin film vacuum gauges, structural improvements are needed. The original single-capacitor sensitive capacitor of the MEMS capacitive thin film vacuum gauge can be replaced with a dual-capacitor differential structure. The differential structure is expected to eliminate the influence of temperature on the measurement results. Summary of the Invention

[0005] This application provides a dual-capacitor differential MEMS vacuum gauge capable of achieving 1-10 5 It measures absolute vacuum within the Pa range and can eliminate the influence of ambient temperature on the measurement results.

[0006] To achieve the above objectives, this application provides a dual-capacitor differential MEMS vacuum gauge, comprising a glass substrate, a silicon substrate, a pressure-sensitive film, a silicon upper electrode, a metal lower electrode, and a glass cap, wherein: the glass substrate is disposed below, and the metal lower electrode is disposed 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 disposed on the silicon substrate; the pressure-sensitive film is disposed between the silicon upper electrode and the metal lower electrode; the pressure-sensitive film, the silicon upper electrode, and the gap between them constitute the upper sensitive capacitor; the pressure-sensitive film, the metal lower electrode, and the gap between them constitute the lower sensitive capacitor; and the glass cap is disposed above the silicon substrate and anoly bonded to the silicon substrate.

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

[0008] Furthermore, a thin-film thermometer is installed on the upper surface of the glass cover, and the thin-film thermometer uses a Pt thin-film thermistor as the sensing element.

[0009] Furthermore, a sealed reference cavity is formed between the glass cap and the silicon substrate, and the silicon on-electrode is disposed inside the sealed reference cavity and bonded to the glass cap by anodic bonding.

[0010] Furthermore, a first lead-out pad is provided on the silicon electrode, which is connected to the circuit board pad via an aluminum wire.

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

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

[0013] Furthermore, the pressure-sensitive film is a square silicon film with rounded corners.

[0014] Furthermore, the silicon upper electrode is made of low-resistivity silicon doped with concentrated boron; the metal lower electrode is made of aluminum.

[0015] Furthermore, the vacuum degree measurement range is 1-10. 5 Pa.

[0016] The dual-capacitor differential MEMS vacuum gauge provided in this application has the following advantages:

[0017] This application employs a dual-capacitor differential structure, eliminating the influence of ambient temperature on the measurement results of the vacuum gauge, resulting in higher measurement accuracy. The dual-capacitor differential structure also adds overload protection to the pressure-sensitive film, making the pressure-sensitive film in the vacuum gauge larger than that of other MEMS vacuum gauges, thus providing higher sensitivity. Furthermore, a film thermometer is also included, which facilitates real-time monitoring of the ambient temperature of the vacuum gauge, providing indirect evidence that the measurement results of the vacuum gauge are unaffected by temperature. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of the application and to make other features, objects, and advantages of the application more apparent. The illustrative embodiments and descriptions of this application are used to explain the application and do not constitute an undue limitation of the application. In the drawings:

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

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

[0021] Figure 3 is a comparison diagram of the working principles of single-capacitor and dual-capacitor differential vacuum gauges.

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

[0023] In the figure: 1-glass cap, 2-silicon top 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 bottom electrode, 12-glass substrate, 13-silicon substrate, 14-aluminum wire. Detailed Implementation

[0024] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort 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, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate for the embodiments of this application described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

[0026] In this application, the terms "upper," "lower," "left," "right," "front," "rear," "top," "bottom," "inner," "outer," "middle," "vertical," "horizontal," "lateral," and "longitudinal" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. These terms are primarily for the purpose of better describing this application and its embodiments, and are not intended to limit the indicated device, element, or component to having a specific orientation, or to be constructed and operated in a specific orientation.

[0027] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0028] In addition, the term "multiple" should mean two or more.

[0029] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. This application will now be described in detail with reference to the accompanying drawings and embodiments.

[0030] As shown in Figures 1-2, this application provides a dual-capacitor 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 disposed below, and the metal lower electrode 11 is disposed on the glass substrate 12; the silicon substrate 13 is disposed on the glass substrate 12 and bonded to the glass substrate 12; the pressure-sensitive film 4 and the silicon upper electrode 2 are disposed on the silicon substrate 13; the pressure-sensitive film 4 is disposed between the silicon upper electrode 2 and the metal lower electrode 11; the pressure-sensitive film 4, the silicon upper electrode 2, and the gap between them form an upper sensitive capacitor; the pressure-sensitive film 4, the metal lower electrode 11, and the gap between them form a lower sensitive capacitor; the glass cover 1 is disposed above the silicon substrate 13 and is anoly bonded to the silicon substrate 13.

[0031] Specifically, the dual-capacitor differential MEMS vacuum gauge provided in this application embodiment is used for gas pressure measurement under medium and low vacuum conditions. It adopts a glass-silicon-silicon-glass structure, and its sensitive capacitor is a dual-capacitor differential structure, meaning it has two sensitive capacitors. This allows the output capacitance to be unaffected by stray coupling capacitance and ambient temperature. The vacuum gauge exhibits high overall measurement accuracy, good linearity, good output repeatability and long-term stability, and can also eliminate the influence of ambient temperature on the measurement results. Specifically, a pressure-sensitive film 4 is fabricated on a silicon substrate 13. The pressure-sensitive film 4 serves as a movable electrode, forming an upper sensitive capacitor with the silicon upper electrode 2 and the gap between them. The capacitance signal is extracted from the first lead-out pad 5 and the second lead-out pad 9, respectively. Similarly, the pressure-sensitive film 4 serves as a movable electrode, forming a lower sensitive capacitor with the metal lower electrode 11 and the gap between them. The capacitance signal is extracted from the third lead-out pad 10 and the second lead-out pad 9, respectively. During measurement, gas enters the gap of the lower sensitive capacitor through the third lead-out pad 10 of the lower metal electrode 11, causing deformation of the pressure-sensitive film 4. This results in a change in the sensitive capacitance, thus achieving the measurement. The gap of the upper sensitive capacitor decreases, increasing the output capacitance, while the gap of the lower sensitive capacitor increases, decreasing the output capacitance. As a result, the overall output capacitance is differential, and its capacitance change is twice that of a single sensitive capacitor vacuum gauge. Furthermore, 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 disposed below the glass substrate 12, and has circuit board pads 7. The circuit board 8 is disposed entirely below the glass substrate 12 and has circuit board pads 7, which are 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, for collecting and receiving capacitance signals, and measuring the vacuum degree based on the difference in capacitance change.

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

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

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

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

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

[0038] Specifically, lead-out pads are provided on the silicon upper electrode 2, the pressure-sensitive film 4, and the metal lower electrode 11. The lead-out pads are connected to the circuit board pads 7 via aluminum wires 14 to lead out the capacitor signal and transmit it to the circuit board 8 for subsequent differential processing.

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

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

[0041] Specifically, the fabrication process of the dual-capacitor differential MEMS vacuum gauge provided in this application embodiment is as follows:

[0042] Step 1: Select a 4-inch SOI wafer as the 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 capacitor gap of the lower sensitive capacitor.

[0043] Step 2: Select 4-inch BF33 glass as the glass substrate 12, and obtain the pattern of the lower metal electrode 11 by photolithography. Obtain the lower metal electrode 11 by magnetron sputtering and electrode lift-off technology. Bond the SOI wafer and the glass substrate 12 by anodic bonding. After bonding, perform photolithography on the other side of the wafer to obtain the pattern of the sealed reference cavity 6. Obtain the sealed reference cavity 6, the second lead-out pad 9, and the third lead-out pad 10 by etching.

[0044] Step 3: Select 4-inch BF33 glass and obtain the pattern of thin film thermometer 3 by photolithography. Then, use magnetron sputtering and electrode stripping technology to obtain thin film thermometer 3.

[0045] Step 4: Select a 4-inch heavily boron-doped silicon wafer and cut it to fabricate the silicon top electrode 2 and the first lead-out pad 5; according to the size of the silicon top electrode 2, laser-drill holes in the glass sheet obtained in the previous step to obtain the window of the first lead-out pad 5; according to the size of the silicon substrate 13, scribing the glass sheet obtained in the previous step to obtain the glass cap 1; anodic bonding of the glass cap 1 and the silicon top electrode 2.

[0046] Step 5: Under a high vacuum environment, the glass cap 1 obtained in the previous step is anodicly bonded to the silicon substrate 13 to obtain a sealed reference cavity 6 with a high vacuum degree.

[0047] Step 6: The electrodes of the vacuum gauge are led out to the circuit board pads 7 of the circuit board 8 by aluminum wire 14 for aluminum wire bonding, thus completing the fabrication of the dual-capacitor differential MEMS vacuum gauge.

[0048] Furthermore, the vacuum degree measurement range is 1-10. 5 Pa.

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

[0050] Wherein, 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.

[0051] As shown in Figure 3, the initial capacitances C1 and C2 of the dual-capacitor parallel plate capacitor, and the sensitive output capacitance C...1b C 2b And the capacitance change ΔC are respectively:

[0052] This shows that the output capacitance change of the dual-capacitor differential MEMS vacuum gauge is twice that of the single-capacitor MEMS vacuum gauge.

[0053] As shown in Figure 4, the initial capacitance C0 of the dual-capacitor differential MEMS vacuum gauge provided in this application example is obtained by formula (1), and the sensitive output capacitances C1, C2 and capacitance change ΔC are:

[0054] Where w is the deflection of the pressure-sensitive film and Ce is the stray capacitance caused by factors such as temperature. As can be seen from formula (8), the dual-capacitor differential MEMS vacuum gauge provided in this application embodiment can eliminate the influence of factors such as temperature on the measurement results, and has high sensitivity and high measurement accuracy, and can achieve 1-10 5 Measurement of absolute vacuum within the Pa range.

[0055] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A dual-capacitor differential MEMS vacuum gauge, characterized in that, It includes a glass substrate, a silicon substrate, a pressure-sensitive thin film, a silicon upper electrode, a metal lower electrode, and a glass cap, wherein: The glass substrate is disposed below, and the metal lower electrode is disposed 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 electrode are disposed on the silicon substrate; The pressure-sensitive film is disposed between the silicon upper electrode and the metal lower electrode; The pressure-sensitive film, the silicon upper electrode, and the gap between them constitute an upper-sensitive capacitor; The pressure-sensitive film, the lower metal electrode, and the gap between them constitute a lower sensitive capacitor. The glass cap is disposed above the silicon substrate and is anoly bonded to the silicon substrate.

2. The dual-capacitor differential MEMS vacuum gauge according to claim 1, characterized in that, It also includes a circuit board disposed below the glass substrate, and the circuit board has circuit board pads.

3. The dual-capacitor differential MEMS vacuum gauge according to claim 2, characterized in that, A thin-film thermometer is provided on the upper surface of the glass cover, and the thin-film thermometer uses a Pt thin-film thermistor as the sensing element.

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

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

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

8. The dual-capacitor differential MEMS vacuum gauge according to claim 7, characterized in that, The pressure-sensitive film is a square silicon film with rounded corners.

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

10. The dual-capacitor differential MEMS vacuum gauge according to claim 9, characterized in that, The vacuum degree measurement range is 1-10. 5 Pa.

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