Dual-Capacitor Differential MEMS Vacuum Gauge

Abstract

Dual-Capacitor Differential MEMS Vacuum Gauge The present application relates to a dual-capacitor differential MEMS vacuum gauge, including a glass substrate, a silicon substrate, a pressure-sensitive thin film, a silicon upper electrode, a metal lower electrode, and a glass lid, wherein: the glass substrate is arranged below, 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-sensitive thin film and the silicon upper electrode are arranged on the silicon substrate; the pressure-sensitive thin film is arranged between the silicon upper electrode and the metal lower electrode; the pressure-sensitive thin film and the silicon upper electrode and a gap therebetween constitute an upper sensitive capacitor; the pressure-sensitive thin film and the metal lower electrode and a gap therebetween constitute a lower sensitive capacitor; and the glass lid is arranged over and anodically bonded to the silicon substrate. Fig. 2

Description

l Dual-Capacitor Differential MEMS Vacuum Gauge TECHNICAL FIELD The present application relates to the technical eld of vacuum metrology, and in particular to a dual-capacitor differential MEMS vacuum gauge. BACKGROUND The capacitive vacuum gauges have the characteristics of high accuracy, good linearity, excellent repeatability, and long-term stability. They can measure the total pressure of gases or vapors, with measurement results independent of gas composition and type. However, temperature is one of the important factors that affect the measurement accuracy of capacitive thin lm vacuum gauges. Traditional mechanical capacitive thin lm vacuum gauges typically employ temperature control systems to eliminate the inuence of temperature on measurement results, which signicantly increases the size and power consumption of the gauges. MEMS capacitive thin lm vacuum gauges are fabricated using MEMS technology, with overall gauge dimensions on the order of millimeters, making it difcult to implement a separate temperature control system for them. Therefore, to eliminate the impact of temperature on MEMS capacitive diaphragm vacuum gauges, structural improvements are needed. One approach is to convert the original single sensitive capacitor of the MEMS capacitive thin lm vacuum gauge into a dual-capacitor differential structure, through which the effect of temperature on measurement results is expected to be eliminated. SUMMARY The present application provides a dual-capacitor differential MEMS vacuum gauge that enables measurement of absolute vacuum degree in the range of 1-105 Pa while eliminating the effect of ambient temperature on measurement results. To achieve the above objective, the present application provides a dual-capacitor differential MEMS vacuum gauge, including a glass substrate, a silicon substrate, a pressure-sensitive thin lm, a silicon upper electrode, a metal lower electrode and a glass lid, wherein: the glass substrate is arranged below, 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-sensitive thin lm and the silicon upper electrode are arranged on the silicon substrate; a pressure-sensitive thin lm is arranged between the silicon upper electrode and the metal lower electrode; the pressure-sensitive thin lm and the silicon upper electrode and the gap between the two compose an upper sensitive capacitance; the pressure-sensitive thin lm and the metal lower electrode and the gap between the two constitute a lower sensitive capacitance; a glass lid is arranged over and anodically bonded to the silicon substrate. Further, the dual-capacitor differential MEMS vacuum gauge includes a circuit board arranged beneath the glass substrate, the circuit board having circuit board pads arranged thereon. Further, an upper surface of the glass lid is provided with a thin lm thermometer, and the thin lm thermometer adopts a Pt thin lm thermistor as a sensitive element. Further, a sealed reference cavity is formed between the glass lid and the silicon substrate, the silicon upper electrode being arranged inside the sealed reference cavity and bonded to the glass lid by anodic bonding. Further, a rst lead-out pad is arranged on the silicon upper electrode, which is connected with the circuit board pad through an aluminum wire. Further, a second lead-out pad is arranged on the pressure-sensitive thin lm, which is connected with the circuit board pad through an aluminum wire. Further, a third lead-out pad is arranged on the metal lower electrode, which is connected with the circuit board pad through an aluminum wire. Further, the pressure-sensitive thin lm is a square silicon thin lm, and four comers of the silicon thin lm are subjected to comer rounding treatment. Further, the silicon upper electrode is made of low resistance silicon doped with concentrated boron; a preparation material of the metal lower electrode is aluminum. Further, the measurement range for vacuum degree is from 1 to 105 Pa. The present application provides a dual-capacitor differential MEMS vacuum gauge, which has the following advantageous effects: the present application adopts a dual-capacitor differential structure, which eliminates the inuence of ambient temperature on vacuum gauge measurement results, resulting in higher measurement accuracy. The dual-capacitor differential structure also provides overload protection for the pressure-sensitive thin lm, allowing the pressure-sensitive thin lm in the vacuum gauge to be larger in size compared to other MEMS vacuum gauges, thus achieving higher sensitivity. Additionally, a thin-lm thermometer is arranged, facilitating real-time monitoring of the ambient temperature surrounding the vacuum gauge. This provides indirect evidence for the temperature-independent measurement results of the vacuum gauge. BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which form a part of this application, are included to provide a further understanding of the application so that other features, objects, and advantages of the application will become apparent. The drawings and their description illustrate the present application and are not to be construed as unduly limiting the present application. In the drawings: FIG. 1 is a schematic diagram of a dual-capacitor differential MEMS vacuum gauge provided in accordance with an embodiment of the present application; FIG. 2 is a cross-sectional view of the dual-capacitor differential MEMS vacuum gauge provided in accordance with an embodiment of the present application; FIG. 3 is a diagram comparing the working principles of a single-capacitor vacuum gauge and a dual-capacitor differential vacuum gauge; and FIG. 4 is diagram of the working principle of the dual-capacitor differential MEMS vacuum gauge provided in accordance with an embodiment of the present application. In the drawings: 1-glass lid, 2-silicon upper electrode, 3-thin lm thermometer, 4-pressure-sensitive thin lm, 5-rst lead-out pad, 6-sealed reference cavity, 7-circuit board pad, 8-circuit board, 9-second lead-out pad, 10-third lead-out pad, 11-metal lower electrode, 12-glass substrate, 13-silicon substrate, 14-aluminum wire. DETAILED DESCRIPTION In order to make those skilled in the technical eld better understand the present application solutions, the technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the accompanying drawings in the embodiments of the present application, it is obvious that the embodiments described are only a part of the embodiments of the present application, but not all of them. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work should belong to the scope of protection of the present application. It should be noted that the terms "rst", "second" and the like in the description and claims of the present application and the gures described above are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It should be understood that data so used may be interchanged under appropriate circumstances in order to describe the embodiments of the present application herein. Furthermore, the terms comprising" and "having" and any variations thereof are intended to cover a non-exclusive inclusion, for example, a process, method, system, product, or apparatus including a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to such process, method, product, or apparatus. In this application, the terms "upper", "lower", "left", "right", "front", "rear", "top, "bottom", "inner", "outer", "center", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate an orientation or positional relationship based on that shown in the drawings. These terms are primarily for the purpose of better describing the present application and its embodiments, and are not intended to limit that the indicated device, element, or component must have a specic orientation, or be constructed and operated in a specic orientation. Moreover, some of the above terms may be used to mean other meanings in addition to orientation or positional relationships, for example, the term "on" may also be used to mean some kind of attachment or connection relationship in some cases. The specic meanings of these terms in the present application can be understood by those of ordinary skill in the art according to the specic circumstances. Further, the term "a plurality" should mean two or more. It should be noted that the embodiments and features in the embodiments in the present application may be combined with each other as long as there is no conict. Hereinafter, the present application will be described in detail with reference to the accompanying drawings in conjunction with embodiments. As shown in FIGS. 1-2, the present application provides a dual-capacitor differential MEMS vacuum gauge, including a glass substrate 12, a silicon substrate 13, a pressure-sensitive thin lm 4, a silicon upper electrode 2, a metal lower electrode 11 and a glass lid 1, wherein: the glass substrate 12 is arranged below, 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 is bonded with the glass substrate 12; the pressure-sensitive thin lm 4 and the silicon upper electrode 2 are arranged on the silicon substrate 13; the pressure-sensitive thin lm 4 is arranged between the silicon upper electrode 2 and the metal lower electrode 11; the pressure-sensitive thin lm 4 and the silicon upper electrode 2 and the gap therebetween constitute an upper sensitive capacitance; the pressure-sensitive thin lm 4 and the metal lower electrode 11 and the gap therebetween constitute a lower sensitive capacitance; the glass lid 1 is arranged over and anodically bonded to the silicon substrate 13. Specically, the dual-capacitor differential MEMS vacuum gauge provided by the embodiment of the present application is used for total gas pressure measurement in medium and low vacuum conditions. It adopts an overall glass-silicon-silicon-glass structure, with its sensitive capacitors being of a dual-capacitor differential structure, meaning it possesses two sensitive capacitors, which enables the output capacitance to be unaffected by stray coupling capacitance and ambient temperature. The vacuum gauge has high overall measurement accuracy, good linearity, excellent output repeatability and long-term stability, and can also eliminate the impact of ambient temperature on measurement results. In this structure, the pressure-sensitive thin lm 4 is fabricated on the silicon substrate 13, serving as a movable electrode to form an upper sensitive capacitor with the silicon upper electrode 2 and the gap between them. The capacitive signals are led out through a rst lead-out pad 5 and a second lead-out pad 9, respectively. Similarly, the pressure-sensitive thin lm 4, serving as a movable electrode, forms a lower sensitive capacitor with a metal lower electrode 11 and the gap between them, and the capacitive signals are led out through a third lead-out pad 10 and the second lead-out pad 9, respectively. During measurement, the gas enters the gap of the lower sensitive capacitor through the third lead-out pad 10 of the metal lower electrode 11, causing deformation of the pressure-sensitive thin lm 4, which results in changes in the sensitive capacitors and enables measurement. In this process, the capacitance gap of the upper sensitive capacitor decreases, increasing the output capacitance, while the capacitance gap of the lower sensitive capacitor increases, decreasing the output capacitance. Thus, the overall output capacitance is a differential output, with its capacitance change being twice that of a single-sensitive capacitor vacuum gauge. Meanwhile, since the output capacitance is the difference between the changes in the two sensitive capacitors, the impact of stray coupling capacitance and temperature on measurement results can be eliminated. Further, the dual-capacitor differential MEMS vacuum gauge includes a circuit board 8, which is arranged beneath the glass substrate 12, the circuit board 8 having circuit board pads 7 arranged thereon. The circuit board 8 is integrally arranged beneath the glass substrate 12, and is provided with circuit board pads 7, mainly for connecting with the lead-out pads of the silicon upper electrode 2, the pressure-sensitive thin lm 4, and the metal lower electrode 11, so as to collect and receive the capacitive signals, and implement the measurement of the vacuum degree according to the difference of the capacitance changes. Further, the upper surface of the glass lid 1 is provided with a thin lm thermometer 3, and the thin lm thermometer 3 employs a Pt thin lm thermistor as a sensitive element. The thin lm thermometer 3 is prepared on the upper surface of the glass lid 1 by magnetron sputtering, preferably, a Pt thin lm thermistor is used as a sensing element, with a thickness of 250 nm and a wire width of 60 um preferably. The thermistor can monitor the ambient temperature in which the vacuum gauge is placed in real time to verify the performance of the dual-capacitor differential MEMS vacuum gauge. Further, a sealed reference cavity 6 is formed between the glass lid 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 lid 1 by anodic bonding. The sealed reference cavity 6 is formed by anodic bonding of the glass lid 1 and the silicon substrate 13 in a high vacuum environment to provide a reference for absolute pressure measurement for the MEMS vacuum gauge. Further, a rst lead-out pad 5 is arranged on the silicon upper electrode 2, which is connected with the circuit board pad 7 through an aluminum wire 14. Further, a second lead-out pad 9 is arranged on the pressure-sensitive thin lm 4, which is connected with the circuit board pad 7 through an aluminum wire 14. Further, a third lead-out pad 10 is arranged on the metal lower electrode 11, which is connected with the circuit board pad 7 through an aluminum wire 14. Specically, the lead-out pads are provided on the silicon upper electrode 2, the pressure-sensitive thin lm 4 and the metal lower electrode 11, and the lead-out pad is connected to the circuit board pad 7 through the aluminum wire 14 for leading out a capacitive signal and transmitting to the circuit board 8 for subsequent differential processing. Further, the pressure-sensitive thin lm 4 is a square silicon thin lm, and four comers of the silicon thin lm are subjected to comer rounding treatment. In the embodiment of the present application, the thin lm side length of the pressure-sensitive thin lm 4 is preferably 4000 um, the thickness is preferably 6 um, and the llet radius of the four comers is preferably 10 um; wherein, a gap between the pressure-sensitive thin lm 4 and the silicon upper electrode 2 is preferably 4 um, and a gap between the pressure-sensitive thin lm 4 and the metal lower electrode 11 is preferably 4 um. Further, the silicon upper electrode 2 is made of low resistance silicon doped with concentrated boron; a preparation material of the metal lower electrode 11 is aluminum. Specically, the fabrication process of the dual-capacitor differential MEMS vacuum gauge provided by the embodiment of the preset application is as follows: Step 1, a 4-inch SOI wafer is selected as a substrate, photolithography is adopted to obtain a pattern of the pressure-sensitive thin lm 4 on the back surface of the SOI, and then dry etching is adopted to obtain a capacitor gap of the lower sensitive capacitor; Step 2, a 4-inch BF33 glass is selected as the glass substrate 12, and photolithography is adopted to obtain a pattern of the metal lower electrode 11, and magnetron sputtering and electrode stripping techniques are adopted to obtain the metal lower electrode 11; anodic bonding is used to bond the SOI wafer and the glass substrate 12; after bonding, photolithography is performed on the other side of the wafer to obtain the pattern of the sealed reference cavity 6; etching is then used to obtain the sealed reference cavity 6, as well as the second lead-out pad 9 and the third lead-out pad 10; Step 3, a 4-inch BF33 glass is selected to obtain a pattern of the thin lm thermometer 3 by photolithography, and magnetron sputtering and electrode stripping techniques are adopted to obtain the thin lm thermometer 3; Step 4, a 4-inch concentrated boron heavily doped silicon wafer is selected for cutting to make the silicon upper electrode 2 and the rst lead-out pad 5; laser drilling is performed on the glass sheet obtained in the previous step according to the size of the silicon upper electrode 2 to obtain a window for the rst lead-out pad 5; dicing is performed on the glass sheet obtained in the previous step according to the size of the silicon substrate 13 to obtain the glass lid 1; anodic bonding is used to bond the glass lid 1 and the silicon upper electrode 2; Step 5, in a high vacuum environment, anodic bonding is performed between the glass lid 1 obtained in the previous step and the silicon substrate 13 to obtain a sealed reference cavity 6 with a high vacuum degree; and Step 6, the respective electrodes of the vacuum gauge are led out to the circuit board pads 7 of the circuit board 8 with the aluminum wires 14 through aluminum wire bonding, thus completing the fabrication of the dual-capacitor differential MEMS vacuum gauge. Further, the measurement range for vacuum degree is from 1 to 105 Pa. Specically, as shown in FIG. 3, the initial capacitance Co, the sensitive output capacitance C, and the capacitance change AC of the single-capacitor MEMS vacuum gauge are respectively: A C 0 : O d (1) C = O A d x (2) 1 1 x AC : C CO : 0A() : eoAZ d x d d (3) wherein, 80 (8.854 ><10'12 F / m) is a vacuum dielectric constant, d is the electrode gap, A is the electrode area and x is the electrode translation distance. As shown in FIG. 3, the initial capacitances C1, C2, the sensitive output capacitances Cu C2b, and the capacitance change AC of the dual-capacitor plate capacitor are respectively: 8 A C 1 = C 2 = ° d (4) C = O A C : 0 A 1 b 2 b d x d + x (5) A 8 A 8 A A Aczq, +C C1 C2 =O°+°0 =2Agoï2 d d +x d x d d (6) It can be seen that the output capacitance change of the dual-capacitor differential MEMS vacuum gauge is twice that of the single-capacitor MEMS vacuum gauge. As shown in FIG. 4, the initial capacitance Co of the dual-capacitor differential MEMS vacuum gauge according to the present embodiment is given by Equation (1), the sensitive output capacitances C1, C2 and the capacitance change AC are: A A C1 = _gdxdy + Ce C2=8dxdy+Ce A d+W(XJ / ) , AdWÜCJ) (7) AC = C2C0 +C0 C1=2A8L;y)dxdy A d (8) wherein, w is the deection of the pressure-sensitive thin lm, and Ce is the stray capacitance caused by factors such as temperature, and it can be seen from Equation (8) that the dual-capacitor differential MEMS vacuum gauge provided by the embodiments of the present application can eliminate the inuence of factors such as temperature on the measurement results, has high sensitivity and high measurement accuracy, and can achieve the measurement of absolute vacuum degree in the range of 1-105 Pa. The above description has been given for the preferred embodiments of the present application and is not intended to limit the present application, and various modications and variations of the present application will be apparent to those skilled in the art. Any modication, equivalent substitution, improvement, etc. made within the spirit and principles of this application shall be included within the scope of protection of this application.

Claims

1. Double capacitor differential MEMS vacuum gauge, characterized in that it is a glass substrate, a silicone substrate, a pressure-sensitive thin film, an upper silicone contains an electrode, a lower metal electrode and a glass lid, whereby the glass substrate is applied at the bottom, the lower metal electrode on the glass substrate is installed; the silicone substrate is applied to the glass substrate and connected to the glass substrate; the pressure-sensitive thin lm and the top silicone electrode on the silicone substrate applied noun; the pressure-sensitive thin lm between the silicone upper electrode and the lower metal electrode is applied; the pressure-sensitive thin lm and the upper silicone electrode and an opening between them form a top sensitive capacitor; the pressure-sensitive thin lm and the lower metal electrode and an opening between them a lower sensitive capacitor forms; and the glass lid is applied over and forms an anode bond with the silicone substrate.

2. Double capacitor differential MEMS vacuum meter according to conclusion l, with the characteristic, that it further contains a switchboard mounted under the glass substrate, the switchboard switchboard has cushions mounted on it.

3. Double capacitor differential MEMS vacuum gauge according to claim 2, with the characteristic that an upper surface of the glass lid is provided with a thin film thermometer, and the thin lm thermometer a Pt thin lm thermistor as a sensitive element displays.

4. Double capacitor differential MEMS vacuum meter according to claim 3, with the characteristic, that a sealed reference cavity between the glass lid and the silicone substrate is formed, the upper silicone electrode being within the sealed reference cavity applied and connected to the glass lid by an anode bond.

5. Double capacitor differential MEMS vacuum gauge according to conclusion 4, with the characteristic that a first outflow cushion is applied to the upper silicone electrode, which is connected to the switchboard cushion by means of an aluminum wire.

6. Double capacitor differential MEMS vacuum gauge according to conclusion 5, with the characteristic that a second run-off cushion is fitted to the pressure-sensitive thin lm, which is connected to the switchboard cushion by means of an aluminum wire.

7. Double capacitor differential MEMS vacuum gauge according to conclusion 6, with the characteristic, that a third discharge cushion is fitted to the lower metal electrode, which is connected to the switchboard cushion by means of an aluminum wire.

8. Double capacitor differential MEMS vacuum gauge according to conclusion 7, with the feature, that the pressure-sensitive thin film is a square silicone thin film, and four corners of the silicone thin lm have been subjected to a corner rounding treatment.

9. Double capacitor differential MEMS vacuum gauge according to conclusion 8, with the characteristic, that the upper silicone electrode is made of low-resistance silicone doped with concentrated boron is manufactured; a preparatory material of the metal bearing electrode being aluminium.

10. Double capacitor differential MEMS vacuum gauge according to conclusion 9, with the characteristic that the measuring range for the vacuum degree is from 1 to 105 Pa. FIG. 1

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