CN101762356A - Vacuum micro-electronics pressure sensor - Google Patents

Abstract

A vacuum microelectronic pressure sensor, comprising: a silicon micro field emission cathode cone array, a vacuum microcavity, an insulating layer, an anode elastic film, an anode insulating protective film, an extraction electrode, an overload protection ring, a diamond film and an insulating substrate, It is characterized in that, in the middle part of the anode elastic membrane facing the vacuum microcavity, there is an anode piston membrane and its supporting pillars connected together, and the supporting pillars are opposite to the overload protection ring. According to the idea of functional separation, the present invention adopts a pressure sensor with a double-layer film structure. Compared with conventional vacuum microelectronic pressure sensors, the sensitivity of the vacuum microelectronic pressure sensor of the present invention is higher than that of conventional vacuum microelectronic pressure sensors. Increased by 100-300%. Moreover, due to the correspondence between the support column and the overload protection ring of the structure of the present invention, permanent deformation caused by contact between the anode piston film and the overload protection ring is prevented, which is very beneficial to the long-term stable operation of the sensor.

Description

Vacuum microelectronic pressure sensor

technical field

The invention relates to a pressure sensor, in particular to a vacuum microelectronic pressure sensor, and its applied field is pressure sensor manufacture in the field of micromechanical electronics (MEMS).

Background technique

The vacuum microelectronic pressure sensor was first proposed in 1991 at the Sixth International Conference on Solid-State Sensors, Actuators and Microsystems (International Conference on Solid-State Sensors, Actuators and Microsystems). The working principle of the vacuum microelectronic sensor is that the anode of the sensor applies a positive voltage relative to the cathode of the sensor, and an accelerating electric field is formed on the surface of the cathode. When the anode elastic film is compressed and deformed, the distance between the cathode and anode of the sensor changes, and the surface field strength of the cathode changes accordingly, resulting in a change in the cathode emission current.

Chinese patent document 1 (patent application number: 02204492, patent name: vacuum microelectronic pressure sensor) discloses a vacuum microelectronic pressure sensor, the structure of which is shown in FIG. 1 . The main features of the sensor are: by loading the overload protection ring 11a, the problems of overload protection and long-term stability of the sensor are solved. However, when its anode elastic membrane 3a is under pressure, the anode elastic membrane will produce arc-shaped deformation, that is, the middle part of the anode elastic membrane has the largest deformation, and the closer to the edge, the smaller the deformation, as shown in Figure 3, resulting in the sensitivity of the pressure sensor significantly reduce.

Contents of the invention

The purpose of the present invention is to provide a vacuum microelectronic pressure sensor, which overcomes the problem of greatly reduced sensitivity of the pressure sensor by adopting a new double-layer film structure.

The technical solution of the present invention to solve the above-mentioned technical problems is that a vacuum microelectronic pressure sensor includes: a silicon micro field emission cathode cone tip array 9, a vacuum microcavity 7, an insulating layer 6, an anode elastic film 3, and an anode insulating protective film 2, lead-out electrode 1, overload protection ring 11, diamond film 8 and insulating substrate 10, it is characterized in that, in the middle part of described anode elastic film 3 towards the vacuum microcavity 7 one side, there is the anode piston film 5 and the anode piston film that are connected as a whole. It supports the column 4 , and the support column 4 is opposite to the overload protection ring 11 .

There is a gap d between the anode piston membrane 5 and the inner wall of the vacuum microcavity 7 to allow the anode piston membrane 5 to move freely up and down.

The width of the anode piston film 5 completely covers the silicon micro field emission cathode cone array 9 opposite to it, and the initial gap between the anode piston film 5 and the silicon micro field emission cathode cone array 9 The distance X ₀ must be greater than the sum of the electrostatic attraction displacement value X _i and the desired emission distance X _q , that is, X ₀ >(X _i +X _q ).

The position of the support column 4 corresponds to the overload protection ring 11, that is, the upper and lower sides of the support column 4 are respectively connected to the center of the anode elastic film 3 and the anode piston film 5, and the overload protection ring 11 is located at the silicon micro field emission cathode cone Point the center of the array 9 .

The anode piston membrane 5 and its support column 4 are made of the same material as the anode elastic membrane 3 , both being silicon.

The thickness of the support column 4 is 5 μm±0.5 μm, the thickness of the anode piston film 5 is 10 μm±0.5 μm, and the gap d between the anode piston film 5 and the inner wall of the vacuum microcavity 7 is 5 μm±2 μm.

Beneficial effect:

According to the idea of functional separation, the present invention adopts a pressure sensor with a double-layer membrane structure. Compared with conventional vacuum microelectronic pressure sensors, the vacuum microelectronic pressure sensor of the present invention has the following characteristics:

1. The structure of the double membrane of the structure of the present invention makes the anode elastic film function of sensor be split, promptly it contains anode elastic film (reflects pressure change with the maximum deformation amount of its middle position) and anode piston film (with its whole body The amount of parallel movement changes the distance between the anode and the cathode, thereby changing the cathode emission current). Since the support column connecting the anode piston membrane and the anode elastic membrane is located in the middle of the anode elastic membrane, this is the position where the arc deformation of the anode elastic membrane is maximum when the anode elastic membrane is under pressure, so the effective value of the deformation of the anode elastic membrane at this time is the conventional pressure The maximum value of the deformation of the anode elastic film of the sensor, instead of the integral value of its arc deformation in the design of conventional vacuum microelectronic pressure sensors as the effective value. Field emission current J=AE ² e ^-B/E , where A, B, and e are constants, and E=V/D, it can be approximately considered that the field emission current and the distance between the anode piston film and the cathode cone array The distance is inversely proportional. If the distance between the anode piston film and the cathode cone array is changed from 50 μm to 20 μm, and the width of the anode piston film is 1000 μm, then it can be calculated that the output current variation of the structure of the present invention is 5 times that of the conventional structure. Therefore, the sensitivity of the vacuum microelectronic pressure sensor of the present invention is increased by 100-300% compared with the conventional vacuum microelectronic pressure sensor.

2. The supporting column of the structure of the present invention corresponds to the overload protection ring. When overloaded, the force point of the anode piston membrane is located at the part where the middle of the piston membrane is connected to the support column, and the force is transmitted to the anode elastic membrane, which prevents the permanent deformation caused by the contact between the anode piston membrane and the overload protection ring, so it is very effective It is beneficial to the long-term stable operation of the sensor.

Description of drawings

Fig. 1 is the transverse cross-sectional structure schematic diagram of conventional vacuum microelectronic pressure sensor;

FIG. 2 is a schematic diagram of a transverse cross-sectional structure of the vacuum pressure microelectronic sensor of the present invention.

Fig. 3 is a schematic diagram of the arc deformation of the anode elastic membrane when the conventional vacuum microelectronic pressure sensor is under pressure.

Fig. 4 is a schematic diagram of the parallel movement of the anode piston membrane when the vacuum pressure microelectronic sensor of the present invention is under pressure.

In Fig. 2, 1 is the lead-out electrode, 2 is the anode insulating protective film, 3 is the anode elastic film, 4 is the support column, 5 is the anode piston film, 6 is the insulating layer, 7 is the vacuum microcavity, 8 is the diamond film, 9 is the silicon micro field emission cathode cone tip array, 10 is the insulating substrate, 11 is the overload protection ring, 12 is the silicon substrate, and d is the anode piston film 5 that can be made between the inner wall of the vacuum microcavity 7 and the anode piston film 5. Gap for free movement up and down.

Detailed ways

Specific embodiments of the present invention are not limited to the following description. The method of the present invention will be further described below in conjunction with the accompanying drawings.

The schematic diagram of the lateral cross-sectional structure of the vacuum pressure microelectronic sensor of the present invention is shown in Figure 2, including silicon micro field emission cathode cone tip array 9, vacuum microcavity 7, insulating layer 6, anode elastic film 3, anode insulating protective film 2 , the anode piston film 5, the lead-out electrode 1, the overload protection ring 11 and the diamond film 8, wherein, a support column of the same silicon material as the anode elastic film 3 is integrally formed in the middle of the anode elastic film 3 facing the vacuum microcavity 7 4 and the anode piston membrane 5 connected to the top of the support column.

The anode piston film 5 is used as the anode receiving part of the sensor, and there is a movable gap d between the anode piston film 5 and the inner wall of the vacuum microcavity 7, and the width of the anode piston film 5 has covered the entire silicon micro field emission cathode opposite to it. The cone tip array 9, the initial distance X ₀ between the anode piston film and the silicon microfield emission cathode cone tip array 9 must be greater than the electrostatic attraction displacement X _i plus the expected emission distance X _q , that is, X ₀ >(X _i + _Xq ).

The working principle of this structure: the anode piston film 5 applies a certain positive voltage to the silicon micro field emission cathode cone array 9, and the cathode cone array 9 (i.e. the cathode of the sensor) and the anode piston membrane 5 (i.e. the anode of the sensor) An electric field will be formed between them, and when the electric field of the cathode cone array 9 reaches a certain strength, electrons will overcome the surface barrier and overflow, and will be collected by the anode piston film 5, thereby forming a current. When the voltage between the cathode and the anode is constant, a certain pressure is applied to the elastic membrane 3, and the elastic membrane will deform, causing the distance between the cathode cone tip and the anode piston membrane 5 to change, causing an electric field near the surface of the cone tip to occur. changes, so that the current between the cathode and anode changes. By measuring the change of the current of the cathode and the anode, the deformation of the elastic membrane 3 and the magnitude of the pressure received can be measured, and its direct output is a current signal.

Since the piston membrane support column 4 and the anode piston membrane 5 are integrally designed with the anode elastic membrane 3, when the anode elastic membrane 3 is subjected to a certain pressure, a certain deformation occurs, and the anode piston membrane 5 is driven downward as a whole by the piston membrane support column 4 The movement greatly increases the effective variation of the distance between the anode piston film 5 and the silicon micro-field emission cathode cone array 9, and thus greatly improves the sensitivity of the pressure sensor.

The vacuum microelectronic pressure sensor of the present invention adopts the MEMS process technology combining conventional IC process with deep groove etching and silicon/silicon bonding. The manufacturing process flow of the vacuum microelectronic sensor of the present invention is specifically as follows:

1. Fabrication of Silicon Micro Field Emission Cathode Taper Array 9

1) N-type (100) Si single crystal is selected, and the resistivity is 1-5Ω·cm;

2) Chemical cleaning and oxidation, the thickness of the oxide layer is 500nm±50nm;

3) Photolithographic cathode cone tip array area;

4) Dry etching of SiO ₂ and Si, the corrosion depth of Si is 2μm±0.1μm;

5) Degumming;

6) Cleaning and oxidation;

7) Deposit Si ₃ O ₄ ;

8) The overload protection ring 11 in the middle of photolithography;

8) Corrosion of Si ₃ O ₄ in the intercone region;

9) Photolithographic cathode cone tip array;

10) Dry etching of SiO ₂ to corrode the cone tip;

11) Combine dry etching and wet etching to form a cone tip with a thickness of 2 μm and a top area of less than 1×1 μm;

12) Cleaning→dry oxygen + wet oxygen + dry oxygen (950°C), further shrink the cone tip, remove the oxide layer, and obtain a silicon micro field emission cathode cone tip array 9 with a height of 2 μm and a tip of less than 0.3 μm;

13) Depositing a diamond film;

2. The preparation process of the anode piston membrane 5 and the support column 4

1) N-type (100) Si single crystal is selected, and the resistivity is 1-5Ω·cm;

2) Chemical cleaning and oxidation, the thickness of the oxide layer is 1 μm;

3) Photolithographic support columns;

4) Dry etching of SiO ₂ and Si to form Si support pillars 4 with a height of 5 μm;

5) LPCVD deposits polysilicon with a thickness of about 6 μm;

6) CMP polishing to obtain a flat surface;

7) performing silicon/silicon bonding on the N-type Si single crystal wafer with another N-type (100) Si single crystal (resistivity 1-5Ω·cm);

8) Thinning and polishing to obtain a silicon film (10 μm ± 0.5 μm) with the thickness of the anode piston film;

9) Photolithographic anode piston film area;

10) Dry etching of the silicon film to form the anode piston film 5;

11) Degumming;

12) Etching the sacrificial layer with a mixed solution of HF+HNO ₃ +H ₂ O (1:1:10) to obtain a movable anode piston membrane supported by supporting pillars.

3. Preparation process of vacuum microelectronic pressure sensor

1) Corrode the movable anode piston film 5 and cathode cone tip array 9 in HF solution (HF:H ₂ O = 1:20) for 2 minutes, and dehydrate with ethanol;

2) Immediately align the movable anode piston film 5 with the cathode cone tip array 9 up and down, and perform silicon/silicon bonding to form a vacuum microcavity of a vacuum microelectronic pressure sensor;

3) thinning and polishing to obtain the required stress film, that is, the anode elastic film 5 (thickness 10 μm);

4) Deposit SiO ₂ with a thickness of 1 μm, and photolithographic lead holes;

5) SiCrAu is sputtered on both sides, SiCr is used as the adhesion layer, and their thickness is SiCr/SiCrAu: 20nm/80nm;

6) Lithographic front leads;

5) alloy;

6) Dicing to obtain a vacuum microelectronic pressure sensor.

Oxidation, photolithography, corrosion, degumming, cleaning, deposition, etc. in the method of the present invention are all conventional techniques for those skilled in the art, and are not the subject of the method of the present invention, and will not be described in detail here.

Claims (6)

1. a vacuum microelectronic pressure sensor, comprising: silicon micro-field emission cathode cone-point array (9), vacuum microcavity (7), insulating layer (6), anode elastic film (3), anode insulating protection film ( 2), lead-out electrode (1), overload protection ring (11), diamond film (8) and insulating substrate (10), it is characterized in that, on described anode elastic film (3) towards vacuum microcavity (7) one side In the middle part, there is an anode piston membrane (5) and its support column (4) connected into one body, and the support column (4) is opposite to the overload protection ring (11). 2. vacuum microelectronic pressure sensor according to claim 1, is characterized in that: between described anode piston film (5) and the inwall of vacuum microcavity (7), there is a structure that can make anode piston film (5) move freely up and down. gap d. 3. vacuum microelectronic pressure sensor according to claim 1, it is characterized in that: the width of described anode piston film (5) completely covers the described silicon micro field emission cathode cone tip array (9) opposite to it, and The initial spacing X between the anode piston film (5) and the silicon micro-field emission cathode cone array ( ₉ ) must be greater than the sum of the electrostatic attraction displacement value X _i and the desired emission spacing X _q , i.e. X ₀ > (X _i +X _q ). 4. The vacuum microelectronic pressure sensor according to claim 1, characterized in that: the position of the support column (4) corresponds to the overload protection ring (11), that is, the upper and lower sides of the support column (4) are respectively connected. At the center of the anode elastic film (3) and the anode piston film (5), the overload protection ring (11) is located at the center of the silicon micro field emission cathode cone array (9). 5. The vacuum microelectronic pressure sensor according to claim 1, characterized in that: the anode piston membrane (5) and its support column (4) have the same material as the anode elastic membrane (3), both for silicon. 6. The vacuum microelectronic pressure sensor according to claim 1, characterized in that: the thickness of the support column (4) is 5 μm±0.5 μm, the thickness of the anode piston film (5) is 10 μm±0.5 μm, The gap d between the anode piston membrane (5) and the inner wall of the vacuum microcavity (7) is 5 μm±2 μm.

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