CN109231157B

CN109231157B - Integrated MEMS sensor for pressure and displacement combining four-beam circular membrane and coaxial cylinder

Info

Publication number: CN109231157B
Application number: CN201811318987.6A
Authority: CN
Inventors: 方续东; 吴晨; 蒋庄德
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2018-11-07
Filing date: 2018-11-07
Publication date: 2024-04-09
Anticipated expiration: 2038-11-07
Also published as: CN109231157A

Abstract

A pressure and displacement integrated MEMS sensor combining four-beam circular membrane and coaxial cylinder comprises an upper substrate and a lower substrate which is connected with the upper substrate in a matching way; the lower substrate comprises a lower substrate base layer, a lower substrate metal ohmic circuit layer is arranged on the lower substrate base layer, a lower solid cylinder is arranged in the middle of the lower substrate base layer, and a peripheral supporting structure is arranged at the peripheral edge above the lower substrate base layer; the upper substrate comprises an upper substrate base layer, an upper substrate insulating layer is arranged on the upper substrate base layer, an upper substrate metal ohmic contact circuit and an upper four-beam circular film structure consisting of four beams and an upper central circular film are arranged on the upper substrate insulating layer, and piezoresistive strips are arranged on the beams; a thin-wall cylinder is connected below the upper central circular film, the thin-wall cylinder is sleeved outside the lower solid cylinder, and the peripheral supporting structure is connected below the upper substrate base layer; the invention realizes the integrated measurement of pressure and displacement and has the advantages of good integration level, high measurement sensitivity and the like.

Description

Pressure and displacement integrated MEMS sensor combining four-beam circular membrane and coaxial cylinder

Technical Field

The invention belongs to the technical field of MEMS sensors, and particularly relates to a pressure and displacement integrated MEMS sensor with a four-beam circular membrane and a coaxial cylinder.

Background

In the aerospace, military, automotive and other industries and military fields, it is often necessary to measure parameters such as the pressure applied to a structure and the displacement caused by the pressure. In addition to accurately measuring these parameters in real time, the requirements for miniaturization, integration and versatility of the sensor are becoming more and more urgent. In the prior art structure, the MEMS pressure sensor and the displacement sensor are generally separated due to the difference of detection principles, thereby increasing the manufacturing cost and the space size of the chip. The integrated sensor based on the MEMS technology can realize the integrated measurement of multiple parameters such as pressure, displacement, temperature, acceleration and the like in a limited space, the types of the MEMS integrated sensors reported at present are few, and most of the MEMS integrated sensors belong to simple integration, namely, each physical quantity to be measured is independently designed into a structure according to a corresponding measurement principle, and then the independent functional units are processed at different positions on the same substrate. For example, the left half of the same sensor substrate is made into a pressure detection unit, the right half is made into an acceleration detection unit, and the simple integration can reduce the size and the manufacturing cost of the sensor to a certain extent, but does not fully utilize the cross relation among structures corresponding to each physical measurement principle, namely, does not utilize the structure relation corresponding to each detection principle, thus the sensor belongs to simple on-chip integration, and the integration level of the MEMS sensor needs to be further improved.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention aims to provide the pressure and displacement integrated MEMS sensor with the combination of the four-beam circular membrane and the coaxial cylinder, which realizes the integrated detection of the pressure and the displacement and has the advantages of small volume, low cost, good integration level, high measurement sensitivity and the like.

In order to achieve the above purpose, the invention adopts the following technical scheme:

a pressure and displacement integrated MEMS sensor combining four-beam circular membrane and coaxial cylinder comprises an upper substrate and a lower substrate which is connected with the upper substrate in a matching way;

the lower substrate comprises a lower substrate base layer 100, a lower substrate metal ohmic circuit layer 101 is arranged on the lower substrate base layer 100, a lower solid cylinder 102 is arranged in the middle of the lower substrate base layer 100, and a peripheral supporting structure 103 is also arranged at the peripheral edge above the lower substrate base layer 100;

the upper substrate comprises an upper substrate base layer 300, an upper substrate insulating layer 301 is arranged on the upper substrate base layer 300, an upper substrate metal ohmic contact circuit 303 and an upper four-beam circular film structure formed by four beams 400 and an upper center circular film 401 are arranged on the upper substrate insulating layer 301, piezoresistive strips 302 are arranged on the four beams 400, and a piezoresistive pressure sensor is formed by the piezoresistive strips 302, the upper substrate metal ohmic contact circuit 303 and the upper four-beam circular film structure;

the thin-walled cylinder 304 is connected below the middle part of the upper central circular film 401, the thin-walled cylinder 304 is sleeved outside the lower solid cylinder 102, the peripheral supporting structure 103 is connected below the upper substrate base layer 300, and the variable-area coaxial cylinder capacitive displacement sensor is formed by the axial relative movement of the thin-walled cylinder 304 and the lower solid cylinder 102.

The four piezoresistive strips 302 are designed at the root of the four beams 400 to obtain maximum pressure detection sensitivity.

The peripheral support structure 103 and the upper substrate base layer 300 are bonded below to form the upper and lower substrate connection layers 200.

On the upper substrate insulating layer 301, symmetrically distributed piezoresistive strips 302 are formed at the root parts of the four beams 400 through doping and etching processes, and wheatstone bridges of an upper substrate metal ohmic contact circuit 303 are formed on the upper surface of the upper substrate insulating layer 301 through electron beam evaporation or metal film sputtering processes, so that the piezoresistive strips 302 are connected with each other to form a complete signal output circuit.

The center of the thin-wall cylinder 304 and the center of the upper center circular film 401 need to be ensured to be centered and coincident.

The thin-walled cylinder 304 is processed by laser drilling with high precision, so that the thin-walled cylinder 304 is ensured to be as regular as possible.

The axial height H1 of the thin-walled cylinder 304 is slightly smaller than the axial height H2 of the lower solid cylinder 102, and the height difference dh=h2-H1 between the two is satisfied, and Dh is comprehensively determined according to the displacement and pressure measurement range and structural stress limit analysis of the designed sensor.

The beneficial effects of the invention are as follows: the MEMS pressure sensor and the MEMS displacement sensor are structurally integrated, so that the area of a chip can be reduced to the greatest extent, and the manufacturing cost of the chip is reduced; the whole chip can be packaged at one time, and the chip processing cost is obviously reduced. The upper four-beam circular membrane structure and the thin-wall cylinder of the cylindrical capacitor are concentric integrally, so that the symmetrical stability of the upper four-beam circular membrane structure ensures that the radial displacement of the thin-wall cylinder is minimum or even eliminated in the process of detecting displacement, thereby realizing the measurement of two physical quantities and simultaneously ensuring the linearity and the sensitivity of a displacement sensor. And the axial height difference Dh between the upper thin-wall cylinder and the lower cylinder of the sensor plays a role in natural limiting, has overload resistance more than 3 times, and avoids the sensor failure caused by overscan work.

Drawings

FIG. 1 is a schematic diagram of the overall structure of an embodiment of the present invention.

Fig. 2 is a schematic view of a lower substrate according to an embodiment of the present invention.

Fig. 3 is a schematic structural view of an upper substrate according to an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

Referring to fig. 1, 2 and 3, a pressure and displacement integrated MEMS sensor with a four-beam circular membrane combined with a coaxial cylinder has a cubic structure, and includes an upper substrate and a lower substrate cooperatively connected therewith;

a thin-walled cylinder 304 is connected below the middle part of the upper central circular membrane 401, the thin-walled cylinder 304 is sleeved outside the lower solid cylinder 102, the four-side supporting structure 103 and the lower part of the upper substrate base layer 300 are bonded to form an upper substrate connecting layer 200 and a lower substrate connecting layer, and the variable-area coaxial cylinder capacitive displacement sensor is formed by the axial relative movement of the thin-walled cylinder 304 and the lower solid cylinder 102.

For the present embodiment, as shown by finite element modeling analysis, when external pressure acts on the upper center circular membrane 401, the four beams 400 generate deflection, and simulation results indicate that root stress of the four beams 400 is maximum. Therefore, in this embodiment, according to the stress-strain direction of the four beams 400 when being pressed, the upper four piezoresistive strips 302 are symmetrically designed at the root portions of the four beams 400 by combining the principle of the variation of the transverse and longitudinal piezoresistive effects of the upper four piezoresistive strips 302, so as to obtain the maximum pressure detection sensitivity. When the four beams 400 are subjected to pressure to generate deflection, the resistance values of the four piezoresistive bars 302 positioned on the four beams are changed under the influence of the piezoresistive effect, so that the balance of the Wheatstone bridge of the upper substrate metal ohmic contact circuit 303 is broken, and the output voltage is used for completing the measurement of the pressure.

Through finite element modeling analysis, when external pressure acts on the upper center circular membrane 401, the four beams 400 generate deflection, and the upper center circular membrane 401 smoothly and uniformly generates displacement along the pressure direction, namely, the upper center circular membrane 401 does not generate obvious deflection. Based on this, the thin-walled cylinder 304 connected to the upper central circular membrane 401 will be axially displaced, creating an axial relative motion with the lower solid cylinder 102, producing a cylindrical capacitor output capacitance change, reflecting the displacement detected by the sensor.

On the upper substrate insulating layer 301, symmetrically distributed piezoresistive strips 302 are formed at the root parts of the four beams 400 through doping and etching processes, and wheatstone bridges of an upper substrate metal ohmic contact circuit 303 are formed on the upper surface of the upper substrate insulating layer 301 through electron beam evaporation or metal film sputtering processes, so that the piezoresistive strips are connected with each other to form a complete signal output circuit.

The center of the thin-wall cylinder 304 and the center of the upper center circular film 401 need to be ensured to be centered and coincident, so that the requirements on photoetching plate making and etching processes are high. The purpose of this design is to ensure that when the upper central circular membrane 401 is pressed, the deflection generated by the four beams 400 is uniform and equal, i.e. the upper central circular membrane 401 is kept not deflected in the horizontal XY plane and only generates axial displacement, so as to ensure that the existence of the thin-walled cylinder 304 has no or negligible influence on the piezoresistive structure of the beam membrane.

The thin-wall cylinder 304 adopts a laser drilling high-precision processing technology, so that the thin-wall cylinder 304 is ensured to be as regular as possible.

The axial height H1 of the thin-walled cylinder 304 should be slightly smaller than the axial height H2 of the lower solid cylinder 102, when the thin-walled cylinder 304 and the lower solid cylinder 102 are not subjected to pressure and displacement, the thin-walled cylinder 304 moves axially downwards, and when the displacement is applied, the lower solid cylinder 102 is stationary, so that the axial height H1 of the thin-walled cylinder 304 and the lower solid cylinder 102 should be slightly smaller than the axial height H2 of the lower solid cylinder 102 in the initial stage, and the height difference dh=h2-H1 and Δh of the two should be comprehensively determined according to the displacement and pressure measurement range and structural stress limit analysis of the designed sensor.

The working principle of the invention is as follows: the MEMS pressure sensor and the MEMS displacement sensor are structurally integrated, so that the area of a chip can be reduced to the greatest extent, and the manufacturing cost of the chip is reduced; the whole chip can be packaged by one-time packaging, so that the cost of chip packaging is reduced. When the environment where the sensor is located has pressure and displacement, the four beams 400 and the central circular membrane 401 form a piezoresistive pressure sensor structure together, the pressure is detected, and a corresponding voltage signal is output through the substrate metal ohmic contact circuit 303; meanwhile, the central circular membrane 401 can displace under the action of pressure and drives the thin-wall cylinder 304 to axially move, and forms a variable-area displacement sensor with the solid cylinder 102 of the substrate below, and as the upper part is of a four-beam circular membrane structure, the symmetrical stability of the structure ensures that the radial displacement of the thin-wall cylinder 304 is minimum or even eliminated in the axial displacement process, thereby realizing the measurement of two physical quantities and simultaneously ensuring the linearity and the sensitivity of the displacement sensor. Compared with the common structure, the piezoresistive pressure measurement structure on the upper part can generate larger stress concentration when the diaphragm is subjected to micro pressure, so that the sensor has higher sensitivity when the sensor is used for measuring the micro pressure, and the measurement nonlinearity generated by the film stress and the bending stress when the common diaphragm structure is very thin can be solved. The axial height difference deltah between the thin-walled cylinder 304 and the lower solid cylinder 102 serves as a limit to avoid sensor failure due to overscan operation.

The foregoing description of the preferred embodiments of the invention is not intended to be limiting, but rather is intended to cover all modifications, equivalents, and alternatives falling within the spirit and principles of the invention.

Claims

1. A pressure and displacement integrated MEMS sensor combining a four-beam circular membrane and a coaxial cylinder, comprising an upper substrate and a lower substrate connected thereto, characterized in that:

The lower substrate comprises a lower substrate base layer (100), a lower substrate metal ohmic circuit layer (101) is arranged on the lower substrate base layer (100), a lower solid cylinder (102) is arranged in the middle of the lower substrate base layer (100), and surrounding supporting structures (103) are also arranged on the surrounding edges above the lower substrate base layer (100);

The upper substrate comprises an upper substrate base layer (300), an upper substrate insulating layer (301) is arranged on the upper substrate base layer (300), an upper substrate metal ohmic contact circuit (303) and an upper four-beam circular membrane structure composed of four beams (400) and an upper central circular membrane (401) are arranged on the upper substrate insulating layer (301), piezoresistive strips (302) are arranged on the four beams (400), and the piezoresistive strips (302), the upper substrate metal ohmic contact circuit (303) and the upper four-beam circular membrane structure constitute a piezoresistive pressure sensor;

A thin-walled cylinder (304) is connected to the lower middle portion of the upper central circular membrane (401), the thin-walled cylinder (304) is sleeved outside the lower solid cylinder (102), and the surrounding supporting structure (103) is connected to the lower portion of the upper substrate base layer (300), and a variable area coaxial cylindrical capacitive displacement sensor is formed through the axial relative movement of the thin-walled cylinder (304) and the lower solid cylinder (102);

The surrounding supporting structure (103) and the lower part of the upper substrate base layer (300) are bonded to form an upper and lower substrate connection layer (200);

On the upper substrate insulating layer (301), symmetrically distributed piezoresistive strips (302) are formed at the roots of the four beams (400) through doping and etching processes, and a Wheatstone bridge of an upper substrate metal ohmic contact circuit (303) is formed on the upper surface of the upper substrate insulating layer (301) through electron beam evaporation or sputtering of a metal film, and the piezoresistive strips (302) are interconnected to form a complete signal output circuit.

2. According to claim 1, a pressure and displacement integrated MEMS sensor combining a four-beam circular membrane and a coaxial cylinder is characterized in that the four piezoresistive strips (302) are designed at the roots of the four beams (400) to obtain maximum pressure detection sensitivity.

3. The pressure and displacement integrated MEMS sensor combining four-beam circular membrane and coaxial cylinder according to claim 1 is characterized in that the axis of the thin-walled cylinder (304) and the axis of the upper circular membrane (401) must be aligned and coincident.

4. The pressure and displacement integrated MEMS sensor combining four-beam circular membrane and coaxial cylinder according to claim 1 is characterized in that: the thin-walled cylinder (304) is processed by laser drilling with high precision to ensure that the thin-walled cylinder (304) is as regular as possible.

5. According to claim 1, a pressure and displacement integrated MEMS sensor combining four-beam circular membrane and coaxial cylinder is characterized in that the axial height H1 of the thin-walled cylinder (304) should be slightly smaller than the axial height H2 of the lower solid cylinder (102), and the height difference between the two satisfies Δh=H2-H1, and the size of Δh is comprehensively determined based on the displacement and pressure measurement range of the designed sensor and the structural stress limit analysis.