CN116399481A

CN116399481A - A MEMS capacitive pressure sensor

Info

Publication number: CN116399481A
Application number: CN202310609407.3A
Authority: CN
Inventors: 聂少校; 孟凡瑞; 高成臣; 杨振川
Original assignee: Peking University
Current assignee: Peking University
Priority date: 2023-05-26
Filing date: 2023-05-26
Publication date: 2023-07-07

Abstract

The invention discloses an MEMS capacitive pressure sensor, which comprises a fixed electrode and a movable electrode, wherein a capacitive gap is formed between the fixed electrode and the movable electrode; the movable electrode consists of a back island structure, a flat membrane structure, a step structure, an insulating layer and an extraction electrode, wherein the back island structure is positioned below the flat membrane structure, the step structure is positioned above the flat membrane structure, the insulating layer is positioned between the back island structure and the flat membrane structure, and the extraction electrode is positioned on the step structure. The capacitive pressure sensor has good linearity, strong overload resistance, high sensitivity and low requirements on the interface circuit, and the 1/C output of the sensor and the pressure p form a linear relation, so that the calculation amount and the algorithm difficulty of the subsequent processing output of the interface circuit are greatly reduced.

Description

MEMS capacitive pressure sensor

Technical Field

The invention relates to the field of micro-electro-mechanical system (MEMS) sensors, in particular to an MEMS capacitive pressure sensor.

Background

The MEMS capacitive pressure sensor has the characteristics of low noise, low temperature drift, low power consumption and high impedance, and has wide application. MEMS capacitive pressure sensors can be divided into variable-pitch, variable-area and variable-medium, wherein the variable-pitch principle is simple, and the realization is convenient, so that the MEMS capacitive pressure sensor has the most wide application.

The capacitance calculation formula of the variable-spacing capacitance pressure sensor is

ε ₀ Represents the vacuum dielectric constant, ε _r Representing the relative permittivity, S representing the electrode area, d the capacitive gap, w (x, y) the deflection of the movable electrode around, from which it can be seen that a variable pitch capacitive pressure sensor has inherent non-linearity problems.

Disclosure of Invention

Aiming at the problems, the invention provides the MEMS capacitive pressure sensor and the preparation method thereof, which can solve the nonlinear problem and have the advantages of strong overload resistance, high sensitivity and low interface circuit requirement.

The technical scheme of the invention is as follows:

a MEMS capacitive pressure sensor comprises a fixed electrode and a movable electrode, wherein a capacitive gap is formed between the fixed electrode and the movable electrode; the movable electrode consists of a back island structure, a flat membrane structure, a step structure, an insulating layer and an extraction electrode, wherein the back island structure is positioned below the flat membrane structure, the step structure is positioned above the flat membrane structure, the insulating layer is positioned between the back island structure and the flat membrane structure, and the extraction electrode is positioned on the step structure.

The back island structure and the step structure are positioned at the center of the flat film structure.

The shape of the flat film structure includes, but is not limited to, circular, square or other polygonal shape, and the material of the flat film structure may be monocrystalline silicon, polycrystalline silicon, silicon oxide, silicon nitride, etc.

The shape of the back island structure includes, but is not limited to, a truncated cone, a quadrangular frustum (e.g., square frustum) or other polygonal frustum, and the material of the back island structure may be selected from monocrystalline silicon, polycrystalline silicon, silicon oxide, silicon nitride, etc.

The shape of the step structure includes, but is not limited to, circular, square or other polygonal shapes, and the material of the step structure may be selected from monocrystalline silicon, polycrystalline silicon, silicon oxide, silicon nitride, etc.

The outline range of the step structure is within the outline range of the back island structure.

The extraction electrode of the movable electrode can be Cr/Au or Ti/Pt electrodeWith a thickness of several hundred

Up to several thousand%>

All that is required.

The invention also provides a method for preparing the capacitive pressure sensor, which comprises the following steps:

1) Preparing a groove on the front side of an SOI silicon wafer through an etching process;

2) Further forming a step structure in the groove through an etching process;

3) Preparing an extraction electrode of the movable electrode on the step structure;

4) Preparing an extraction electrode of a fixed electrode on the surface of a glass sheet;

5) Leading the leading-out electrode of the movable electrode and the leading-out electrode of the fixed electrode face to face, bonding the SOI silicon chip and the glass chip together, and forming a capacitance gap between the SOI silicon chip and the glass chip;

6) And forming a back island structure on the back of the SOI silicon wafer through an etching process.

The etching process in the steps 1), 2) and 6) is dry etching or wet etching.

The extraction electrode may be prepared by sputtering and lift-off processes in steps 3) and 4) above.

The step 5) can adopt an anode bonding method to bond the silicon wafer and the glass sheet together.

Compared with the prior art, the capacitive pressure sensor with the movable electrode with the back island-flat membrane-step composite structure has the beneficial effects that:

first, the linearity is good. The deflection w (x, y) of each point of the traditional flat membrane structure is inconsistent when the traditional flat membrane structure is subjected to pressure, and the deflection w (x, y) of each point of the traditional flat membrane structure is inconsistent when the movable electrode of the capacitive pressure sensor is subjected to pressure on the lower surface of the movable electrode of the traditional flat membrane structure in a reasonably arranged measuring range through ANSYS software finite element simulation verification, and the deflection w (x, y) of each point of the step structure is consistent and is in direct proportion to the pressure, so that the capacitance calculation formula of the capacitive pressure sensor is as follows

I.e.

Wherein k is a constant, ε ₀ Represents the vacuum dielectric constant, ε _r Representing the relative dielectric constant, S representing the electrode area, d representing the capacitance gap, p representing the pressure, w (p) representing the deflection of each point of the movable electrode when the pressure is applied, so the 1/C output of the sensor is in linear relation with the pressure p.

And secondly, the overload resistance is strong. The back island structure can reduce the central deflection of the movable electrode under the action of pressure, and meanwhile, the step structure can be contacted with the fixed electrode when the movable electrode is under excessive pressure, so that the movable electrode stops moving, and the overload resistance of the sensor is improved.

Third, the sensitivity is high. The high-sensitivity capacitive sensor can be obtained by simulation optimization design of parameters such as flat film thickness, flat film area, back island area, step thickness, step area, capacitance gap and the like.

Fourth, the interface circuit requirements are low. The high sensitivity can relax the precision requirement of the interface circuit, and the linear relation between the 1/C output and the pressure p can greatly reduce the calculation amount and the algorithm difficulty of the subsequent processing output of the interface circuit.

Drawings

FIG. 1 is a schematic diagram of a capacitive pressure sensor with a movable electrode of a back island-flat membrane-step composite structure according to the present invention

Wherein 1 is a glass sheet, 2 is a first extraction electrode, 3 is a second extraction electrode, 4 is a step structure, 5 is a flat film structure, 6

And 7 is an oxygen buried layer of the SOI silicon wafer.

Fig. 2 (a) to 2 (h) are schematic views illustrating a main manufacturing process of a capacitive pressure sensor according to an embodiment of the present invention.

FIG. 3 is a graph of sensor 1/C output versus pressure p obtained by ANSYS simulation modeling of a capacitive pressure sensor of the present invention.

Detailed Description

The invention is further illustrated by the following examples, taken in conjunction with the accompanying drawings.

FIG. 1 is a schematic diagram of a capacitive pressure sensor with a back island-flat membrane-step composite structure movable electrode. The structure is integrally formed by bonding a glass part with a fixed electrode and a silicon part with a movable electrode, wherein the glass sheet 1 and the first extraction electrode 2 form the fixed electrode of the sensor, and the movable electrode comprises a second extraction electrode 3, a step structure 4, a flat film structure 5 and

back island structures

6 and 7 which are buried oxide layers of an SOI silicon wafer.

Fig. 2 (a) to 2 (h) are main manufacturing processes of the capacitive pressure sensor of the present embodiment, including:

1. preparing a silicon wafer: using silicon wafer as SOI silicon wafer, the thickness of device layer is 20 μm, the thickness of buried oxide layer is 7 μm, and the thickness of substrate layer is 480 μm, as shown in FIG. 2 (a);

2. preparing a capacitance gap: a wet etching method, such as TMAH etching silicon, can be adopted to prepare square grooves with the width of 1700 μm and the depth of 0.9 μm on the front surface of the SOI silicon wafer, as shown in FIG. 2 (b);

3. step structure preparation: a wet etching mode can be adopted to prepare square steps with the side length of 1000 mu m and the height of 2 mu m at the center of the groove, namely a step structure 4, as shown in fig. 2 (c);

4. preparing a movable electrode: can adopt sputtering and stripping processes to prepare Cr on the step structure

/Au

As the second extraction electrode 3, as shown in fig. 2 (d);

5. preparing a glass sheet: use of PYREX 7740 glass sheet 1 may be employed as shown in fig. 2 (e);

6. preparing a fixed electrode: cr can be prepared on the glass sheet 1 by adopting a sputtering and stripping process

/Au

As the first extraction electrode 2, a metal electrode is used as shown in fig. 2 (f);

7. anodic bonding of silicon glass: bonding the glass sheet 1 and the SOI silicon wafer with the first extraction electrode 2 and the second extraction electrode 3 facing each other to form a capacitance gap, as shown in FIG. 2 (g);

8. preparing a back island structure: a wet etching process may be used to prepare a square boss structure on the back surface of the SOI wafer, with a boss bottom surface width of 1200 μm, as shown in fig. 2 (h).

ANSYS simulation modeling is carried out on the capacitive pressure sensor, and when simulation parameters are 1700 mu m wide and 18 mu m thick in a flat film structure, 1000 mu m wide and 2 mu m thick in a square step structure, 1200 mu m wide in the bottom of a square boss back island structure, the capacitance gap of the sensor is 0.9 mu m, the simulation pressure range is 0-40kPa, the simulation result is shown in the following table (C is capacitance value, and p is pressure):

it can be seen that 1/C is linear with P, as shown in FIG. 3.

The scope of the invention is defined not by the detailed description but by the claims and their equivalents, and all modifications within the scope of the claims and their equivalents are to be construed as being included in the invention.

Claims

1. A MEMS capacitive pressure sensor comprises a fixed electrode and a movable electrode, wherein a capacitive gap is formed between the fixed electrode and the movable electrode; the movable electrode is characterized by comprising a back island structure, a flat membrane structure, a step structure, an insulating layer and an extraction electrode, wherein the back island structure is positioned below the flat membrane structure, the step structure is positioned above the flat membrane structure, the insulating layer is positioned between the back island structure and the flat membrane structure, and the extraction electrode is positioned on the step structure.

2. The MEMS capacitive pressure sensor of claim 1, wherein the back island structure and the step structure are centered on the flat membrane structure.

3. The MEMS capacitive pressure sensor of claim 1, wherein the shape of the flat membrane structure includes, but is not limited to, a circle, square, or other polygon.

4. The MEMS capacitive pressure sensor of claim 1, wherein the step structure is circular, square, or other polygonal in shape, and the back island structure is circular, quadrangular or other polygonal in shape, and the step structure has a contour range within the contour range of the back island structure.

5. The MEMS capacitive pressure sensor of claim 1, wherein the material of the back island structure, flat film structure, step structure is selected from the group consisting of single crystal silicon, polysilicon, silicon oxide, silicon nitride.

6. The MEMS capacitive pressure sensor of claim 1, wherein the extraction electrode of the movable electrode is a Cr/Au electrode or a Ti/Pt electrode.

7. The method for manufacturing the MEMS capacitive pressure sensor according to any one of claims 1 to 6, comprising the steps of:

2) Further forming a step structure in the groove through an etching process;

8. The method of claim 7, wherein the etching process in steps 1), 2) and 6) is dry etching or wet etching.

9. The method of claim 7, wherein the extraction electrode is prepared in steps 3) and 4) using a sputtering, stripping process.

10. The method of claim 7, wherein step 5) bonds the SOI wafer and the glass sheet together using anodic bonding.