阅读说明：本技术 一种爆炸场mems压阻式压力传感器 (Explosion field MEMS piezoresistive pressure sensor ) 是由 康昊 严家佳 陈君 何性顺 张俊峰 王丹 叶希洋 姬建荣 苏健军 于 2021-07-15 设计创作，主要内容包括：本发明公开了一种爆炸场MEMS压阻式压力传感器,包括了两个尺寸不同的敏感膜片,其中较小硅应变膜可以设计为灵敏度较小,量程较大的结构,具有较强的过载能力,满足冲击波压力峰值的测量；除此之外,其中较大硅应变膜的上方设置带有通孔的硅盖帽,盖帽与相应硅应变膜形成了空腔,通过合理设计气孔和空腔的体积可以滤除具有高频特征的冲击波压力信号,使具有低频、零频的准静态压力信号作用于相应硅应变膜；并且,两个敏感膜片的背面均设计有岛,当压力超过量程时,岛会与玻璃基底接触,具有一定的抗过载能力,进一步保护了具有高灵敏度、小量程的第一硅应变膜。(The invention discloses an explosion field MEMS piezoresistive pressure sensor, which comprises two sensitive membranes with different sizes, wherein a smaller silicon strain membrane can be designed into a structure with smaller sensitivity and larger measuring range, has stronger overload capacity and meets the measurement of a shock wave pressure peak value; in addition, a silicon cap with a through hole is arranged above the larger silicon strain film, the cap and the corresponding silicon strain film form a cavity, and shock wave pressure signals with high-frequency characteristics can be filtered out by reasonably designing the volume of the air hole and the cavity, so that quasi-static pressure signals with low frequency and zero frequency act on the corresponding silicon strain film; and moreover, the back surfaces of the two sensitive membranes are respectively provided with an island, when the pressure exceeds the measuring range, the islands can be contacted with the glass substrate, certain overload resistance is realized, and the first silicon strain membrane with high sensitivity and small measuring range is further protected.)

1. An explosion field MEMS piezoresistive pressure sensor, comprising:

the first piezoresistive pressure sensor comprises a first silicon strain film, a plurality of first piezoresistors, a first metal lead and a first glass substrate, wherein the first silicon strain film is a silicon film which is formed by etching the back surface of a first SOI (silicon on insulator) silicon wafer and is provided with a first island and a first cavity on the back surface, the first island is positioned in the first cavity, and the first glass substrate and the back surface of the first silicon wafer are bonded to seal the first cavity; the first piezoresistors and the first metal leads form a Wheatstone bridge and are positioned on the front surface of the first silicon strain film, and the first piezoresistors are positioned on the edge of the first silicon strain film;

the second piezoresistive pressure sensor comprises a second silicon strain film, a plurality of second piezoresistors, a second metal lead and a second glass substrate, wherein the second silicon strain film is a silicon film which is formed by etching the back surface of a second SOI silicon wafer and is provided with a second island and a second cavity on the back surface, and the second island is positioned in the second cavity; the second glass substrate is bonded with the back surface of the second silicon wafer to seal a second cavity; the plurality of second piezoresistors and the second metal leads form a Wheatstone bridge and are positioned on the front surface of the first silicon strain film, and meanwhile, the second piezoresistors are positioned on the inner edge of the second silicon strain film;

the thickness of the first silicon strain film is the same as that of the second silicon strain film, and the area of the first silicon strain film is larger than that of the second silicon strain film; the thickness of the first island is the same as that of the second island, and the cross-sectional area of the first island is larger than that of the second island;

the silicon cap is bonded with the front surface of the first silicon strain film and forms a containing cavity with the first silicon strain film, the first piezoresistors and the first metal lead are located at the bottom of the containing cavity, and at least one through hole is formed in the silicon cap at the top of the containing cavity.

2. The explosion field MEMS piezoresistive pressure sensor according to claim 1, wherein said cavity can filter out explosion field shock wave pressure signals with a frequency greater than f, where f satisfies formula (1);

in formula (1):

c is the speed of sound, m/s;

n is the number of the through holes, and n is more than or equal to 1;

r is the radius of the through hole, m;

a is the bottom area in the cavity, m²；

H₁Is the axial length of the through hole, m;

H₂m is the height from the bottom to the top in the cavity.

3. The detonation field MEMS piezoresistive pressure sensor of claim 1, wherein said first SOI silicon wafer is a unitary structure with said second SOI silicon wafer.

4. The detonation field MEMS piezoresistive pressure sensor of claim 1, wherein said first glass substrate and second glass substrate are of a unitary structure.

5. The detonation field MEMS piezoresistive pressure sensor according to claim 1, wherein said first silicon strained membrane is circular or rectangular and said second silicon strained membrane is circular or rectangular; the first island is a cylinder or a square column, and the second island is a cylinder or a square column.

6. The detonation field MEMS piezoresistive pressure sensor according to claim 1, wherein said plurality of first piezoresistors are distributed in parallel, with two piezoresistors disposed at the edge of the first silicon strained film; the plurality of second piezoresistors are distributed in parallel, wherein two piezoresistors are arranged at the edge of the second silicon strain film.

7. The detonation field MEMS piezoresistive pressure sensor according to claim 6 or 7, wherein said plurality of first piezoresistors is four; the number of the second piezoresistors is four.

8. The explosion field MEMS piezoresistive pressure sensor according to claim 1, wherein two through holes are provided on the silicon cap at the top of the cavity, and the two through holes are respectively provided along an outer edge of the first silicon strained film, and the first silicon strained film is located between the two through holes.

9. A method of making a detonation field MEMS piezoresistive pressure sensor according to any of claims 1 to 8, comprising:

(1) preparing a plurality of piezoresistors and metal wires on the front surface of the first silicon chip and the front surface of the second silicon chip respectively, and forming a Wheatstone bridge;

(2) photoetching and etching cavities and islands on the back of the first silicon wafer and the back of the second silicon wafer respectively to form silicon strain films;

(3) etching areas corresponding to the cavities on the front surface of the first glass substrate and the front surface of the second glass substrate respectively;

(4) bonding the front surface of the first glass substrate and the back surface of the first silicon wafer to form a first cavity, and bonding the front surface of the second glass substrate and the back surface of the second silicon wafer to form a second cavity;

(5) and etching a through hole on the silicon cap, and bonding the silicon cap with the front surface of the first silicon wafer.

10. The method for preparing a detonation field MEMS piezoresistive pressure sensor according to claim 9, wherein step (1) uses photolithography, etching, ion doping and LPCVD processes to prepare a plurality of piezoresistors and metal wires and form a wheatstone bridge.

Technical Field

The invention relates to the technical field of MEMS piezoresistive pressure sensors, in particular to an explosion field MEMS piezoresistive pressure sensor.

Background

When the explosive explodes in a closed environment, the explosive generates two effects of pressure, namely shock wave pressure and quasi-static pressure. Wherein: the shock wave pressure signal belongs to a typical non-stationary random signal and is characterized by large peak value, quick abrupt change and short duration; the quasi-static pressure is mainly pressure generated by gas thermal motion after the temperature is increased due to heat released by explosion, and has low quasi-static pressure peak value and long acting time.

Because the piezoelectric pressure sensor has better dynamic characteristics and overload capacity, the piezoelectric pressure sensor is commonly used for testing the overpressure peak value of the shock wave at present, but the low-frequency characteristic, particularly the zero-frequency characteristic, is poor, and is not suitable for measuring the quasi-static pressure.

The piezoresistive pressure sensor has good dynamic characteristics and low-frequency characteristics, but the overload capacity of the piezoresistive pressure sensor is generally 2-3 times of the range, which is far less than that of the piezoelectric pressure sensor with 10 times of the range, and the full-range output signal is only 100 mV. If the measurement of the overpressure peak value of the shock wave pressure is to be met and the sensor is not damaged, the sensitivity of the piezoresistive pressure sensor needs to be sacrificed to meet the requirement of the measuring range, and the quasi-static pressure is generally one tenth of the overpressure peak value of the shock wave.

Disclosure of Invention

In view of the shortcomings or drawbacks of the prior art, it is an object of the present invention to provide an explosion field MEMS piezoresistive pressure sensor.

In order to achieve the above object, the present invention provides an explosion field MEMS piezoresistive pressure sensor comprising:

the first piezoresistive pressure sensor comprises a first silicon strain film, a plurality of first piezoresistors, a first metal lead and a first glass substrate, wherein the first silicon strain film is a silicon film which is formed by etching the back surface of a first SOI (silicon on insulator) silicon wafer and is provided with a first island and a first cavity on the back surface, the first island is positioned in the first cavity, and the first glass substrate and the back surface of the first silicon wafer are bonded to seal the first cavity; the first piezoresistors and the first metal leads form a Wheatstone bridge and are positioned on the front surface of the first silicon strain film, and the first piezoresistors are positioned on the edge of the first silicon strain film;

the second piezoresistive pressure sensor comprises a second silicon strain film, a plurality of second piezoresistors, a second metal lead and a second glass substrate, wherein the second silicon strain film is a silicon film which is formed by etching the back surface of a second SOI silicon wafer and is provided with a second island and a second cavity on the back surface, and the second island is positioned in the second cavity; the second glass substrate is bonded with the back surface of the second silicon wafer to seal a second cavity; the plurality of second piezoresistors and the second metal leads form a Wheatstone bridge and are positioned on the front surface of the first silicon strain film, and meanwhile, the second piezoresistors are positioned on the inner edge of the second silicon strain film;

the thickness of the first silicon strain film is the same as that of the second silicon strain film, and the area of the first silicon strain film is larger than that of the second silicon strain film; the thickness of the first island is the same as that of the second island, and the cross-sectional area of the first island is larger than that of the second island;

the silicon cap is bonded with the front surface of the first silicon strain film and forms a containing cavity with the first silicon strain film, the first piezoresistors and the first metal lead are located at the bottom of the containing cavity, and at least one through hole is formed in the silicon cap at the top of the containing cavity.

In a preferable scheme, the cavity can filter an explosion field shock wave pressure signal with frequency greater than f, wherein f satisfies formula (1);

in formula (1):

c is the speed of sound, m/s;

n is the number of the through holes, and n is more than or equal to 1;

r is the radius of the through hole, m;

a is the bottom area in the cavity, m²；

H₁Is the axial length of the through hole, m;

H₂m is the height from the bottom to the top in the cavity.

Further, the first SOI silicon wafer and the second SOI silicon wafer are of an integrated structure.

Further, the first glass substrate and the second glass substrate are of an integrated structure.

Optionally, the first silicon strained film is circular or rectangular, and the second silicon strained film is circular or rectangular; the first island is a cylinder or a square column, and the second island is a cylinder or a square column.

Further, the plurality of first piezoresistors are distributed in parallel, wherein two piezoresistors are arranged at the edge of the first silicon strain film; the plurality of second piezoresistors are distributed in parallel, wherein two piezoresistors are arranged at the edge of the second silicon strain film.

Optionally, the number of the first piezoresistors is four; the number of the second piezoresistors is four.

Optionally, two through holes are formed in the silicon cap at the top of the cavity, the two through holes are respectively arranged along the outer edge of the first silicon strain film, and the first silicon strain film is located between the two through holes.

The invention also provides a preparation method of the explosion field MEMS piezoresistive pressure sensor. The provided method comprises the following steps:

(1) preparing a plurality of piezoresistors and metal wires on the front surface of the first silicon chip and the front surface of the second silicon chip respectively, and forming a Wheatstone bridge;

(2) photoetching and etching cavities and islands on the back of the first silicon wafer and the back of the second silicon wafer respectively to form silicon strain films;

(3) etching areas corresponding to the cavities on the front surface of the first glass substrate and the front surface of the second glass substrate respectively;

(4) bonding the front surface of the first glass substrate and the back surface of the first silicon wafer to form a first cavity, and bonding the front surface of the second glass substrate and the back surface of the second silicon wafer to form a second cavity;

(5) and etching a through hole on the silicon cap, and bonding the silicon cap with the front surface of the first silicon wafer.

Further, in the step (1), a plurality of piezoresistors and metal wires are prepared by adopting photoetching, etching, ion doping and LPCVD (low pressure chemical vapor deposition) processes, and a Wheatstone bridge is formed.

The pressure sensor comprises two sensitive membranes with different sizes, wherein the smaller silicon strain membrane can be designed into a structure with smaller sensitivity and larger measuring range, has stronger overload capacity and meets the measurement of the pressure peak value of the shock wave; in addition, a silicon cap with a through hole is arranged above the larger silicon strain film, the cap and the corresponding silicon strain film form a cavity, and shock wave pressure signals with high-frequency characteristics can be filtered out by reasonably designing the volume of the air hole and the cavity, so that quasi-static pressure signals with low frequency and zero frequency act on the corresponding silicon strain film; and moreover, the back surfaces of the two sensitive membranes are respectively provided with an island, when the pressure exceeds the measuring range, the islands can be contacted with the glass substrate, certain overload resistance is realized, and the first silicon strain membrane with high sensitivity and small measuring range is further protected.

Drawings

Fig. 1 is a schematic cross-sectional structure diagram of an explosion field MEMS piezoresistive pressure sensor according to the present invention.

Fig. 2 is a schematic structural diagram of a silicon cap of an embodiment.

Fig. 3 is a distribution diagram of the piezoresistors and the metal leads of the example.

FIG. 4 is a schematic diagram of the backside structure of the strained Si film of an embodiment.

Fig. 5 is a schematic three-dimensional structure of a glass substrate of an embodiment.

FIG. 6 is a schematic diagram of a reference process for manufacturing a sensor according to an embodiment, wherein (a) - (g) are schematic diagrams of results of intermediate steps in sequence.

FIG. 7 is a diagram showing simulation results of the sensor according to the embodiment.

Detailed Description

Unless otherwise indicated, the terms or methods herein are understood or implemented using established methods as recognized by one of ordinary skill in the relevant art.

Referring to the attached drawings, the explosion field MEMS piezoresistive pressure sensor comprises two piezoresistive pressure sensors with different silicon strain film areas and a silicon cap;

the two piezoresistive pressure sensors respectively comprise a silicon strain film (4-3; 4-4), a plurality of piezoresistors 2-2, a metal lead wire 2-1 and a glass substrate 5, wherein the silicon strain film is a silicon film which is formed by etching the back surface of an SOI (silicon on insulator) silicon wafer and is provided with an island (4-1; 4-2) and a cavity on the back surface, the island is positioned in the cavity 6, the glass substrate is bonded with the back surface of the silicon wafer to seal the cavity, the piezoresistors and the metal lead wire form a Wheatstone bridge and are positioned on the front surface of the silicon strain film, and when the silicon strain film is pressed, the edge position of the film is stressed maximally, so that the piezoresistors (2-2) are positioned on the edge of the silicon strain film and are parallel to the edge to ensure the maximum resistance change rate;

for the sake of clarity of describing the structural differences between the two piezoresistive pressure sensors, the term "first and second" difference is used herein before the corresponding characteristic or structural terms, on the basis of which the two piezoresistive pressure sensors are structurally different:

since the quasi-static pressure applied to the first silicon strained film 4-3 is much smaller than the shock wave pressure applied to the second silicon strained film 4-4, the area of the first silicon strained film is larger than that of the second silicon strained film; meanwhile, the first silicon strained film 4-3 and the second silicon strained film 4-4 have the same thickness for convenience of processing.

The first island 4-1 and the second island 4-2 have overload protection function, when the pressure applied to the silicon strain film is too large, the islands can be in contact with the glass substrate so as to avoid the excessive deformation of the sensitive diaphragm, and because the shock wave pressure applied to the second silicon strain film is far greater than the quasi-static pressure applied to the first silicon strain film, the cross section area of the second island 4-2 is larger than that of the first island 4-1 so as to ensure the firmness of the second silicon strain film, and the heights/thicknesses of the first island 4-1 and the second island 4-2 are the same;

the front surface of the first silicon strain film is bonded with a silicon cap 1-1, the silicon cap and the first strain film form a cavity, the first piezoresistors and the metal leads are positioned at the bottom of the cavity, at least one through hole 1-2 is formed in the silicon cap at the top of the cavity, two through holes 1-2 are formed in two sides of the top of the silicon cap and are respectively arranged along the outer edges of two sides of the first silicon strain film 4-3, the first silicon strain film is positioned between the two through holes, shock wave airflow can not directly act on the first silicon strain film, and the first silicon strain film can be protected.

When shock wave pressure acts on the sensor, after a shock wave pressure signal acting on the silicon cap 1-1 passes through the through hole 1-2 and the accommodating cavity 1-3, a high-frequency part with the frequency larger than f is filtered, so that only a low-frequency quasi-static pressure signal acts on the first silicon strain film 4-3, the first silicon strain film 4-3 deforms under the action of pressure, along with the strain of the diaphragm, the resistivity of the piezoresistor 2-2 arranged on the first silicon strain film 4-3 changes, the resistance value changes, and finally the output of the Wheatstone bridge changes, and the external quasi-static pressure can be determined by measuring the output of the Wheatstone bridge; the working principle of the second silicon strain film 4-4 is similar to that of the first silicon strain film 4-3, the shock wave pressure signal directly acts on the second silicon strain film 4-4, and finally the magnitude of the external shock wave pressure can be determined by measuring the output of the Steton bridge;

after the shock wave pressure passes through the through hole 1-2, due to the lumen effect, the shock wave pressure signal with high frequency characteristics is filtered, and the quasi-static pressure signal with low frequency is applied to the first silicon strained membrane 4-3. In the preferred scheme, the volume of the through hole 1-2 and the volume of the accommodating cavity 1-3 are reasonably designed to selectively filter and remove the blast field shock wave pressure signal larger than f, wherein f satisfies the formula (1);

wherein c is the sound velocity, m/s; n is the number of the through holes, and n is more than or equal to 1; r is the radius of the through hole, m; a is the bottom area in the cavity, m²；H₁Is the axial length of the through hole, m; h₂M is the height from the bottom to the top in the cavity.

In other schemes, the SOI silicon wafer of the piezoresistive pressure sensor in two of the above schemes is of an integral structure, and the two glass substrates are of an integral structure.

In a specific embodiment, the shape of the silicon strained film and the shape of the island may be selected according to the requirement, and are usually square or circular and cylindrical or square-column.

In a specific scheme, the number of the piezoresistors is multiple, and is generally 1-5.

Example (b):

in the embodiment, the first silicon wafer and the second silicon wafer are integrated silicon wafers, the first glass substrate and the second glass substrate are integrated glass substrates, wherein the SOI silicon wafer uses an N-type (100) crystal face double-sided polishing SOI silicon wafer, the silicon cap uses an N-type (100) crystal face double-sided polishing silicon wafer, and the glass substrate uses BF33 glass;

cleaning an SOI silicon wafer by using HF solution, wherein the SOI silicon wafer consists of an upper silicon layer 2-4, a buried silicon dioxide layer 3 and a silicon substrate 4, and the upper silicon layer 2-4 and the silicon substrate 4 are separated by the buried silicon dioxide layer 3;

the number n of the through holes on the silicon cap is 2, the through holes are round holes, and the radius r of the through holes is 2.5 mu m; the bottom area A in the cavity is 6.25 multiplied by 10^-6m²Axial length H of through hole₁120 μm, height H in the cavity₂280 μm, and f is 740Hz, and the frequency of the explosion shock wave pressure signal is more than 1kHz, so that the shock wave pressure signal of the high-frequency signal with the frequency more than 740Hz can be filtered.

In the embodiment, all the silicon strain films and the islands are square, the side length of the first silicon strain film is 1750 mu m from 4 to 3, and the thickness of the first silicon strain film is 50 mu m; the side length of the second silicon strain film 4-4 is 1000 mu m, and the thickness of the second silicon strain film is 50 mu m; the side length of the first island 4-1 is 500 μm, and the thickness is 400 μm; the side length of the second island 4-2 is 400 μm, and the thickness is 400 μm;

the distance between two adjacent edges of the first silicon strained film 4-3 and the second silicon strained film 4-4 in this embodiment is 1400 μm;

referring to fig. 6, the specific preparation method includes the following steps:

(1) preparing a plurality of piezoresistors and metal wires on the front surface of a silicon wafer, and forming a Wheatstone bridge of two piezoresistive sensors;

(1.1) growing a 300nm silicon dioxide layer 2-7 on the upper surface of the silicon upper layer 2-4 by thermal oxidation, photoetching to form a region needing doping, and Etching the silicon dioxide layer 2-7 which is not protected by photoresist by using an RIE (Reactive Ion Etching) process, as shown in FIG. 6 (a);

(1.2) carrying out boron ion light doping to form four piezoresistors 2-2, then carrying out annealing to ensure that the boron ion impurity concentration is uniformly distributed, and removing the silicon dioxide layer 2-7, as shown in fig. 6 (b);

(1.3) depositing silicon nitride 2-3 on the upper surface of the upper silicon layer 2-4 by using an LPCVD (Low Pressure Chemical Vapor Deposition) process, and photoetching and etching the silicon nitride to form ohmic contacts, metal leads and pad regions, as shown in fig. 6 (c);

(1.4) photoetching the surface of the silicon nitride layer 2-3 to form an ohmic contact, a metal lead and a pad area, sputtering titanium (Ti) -platinum (Pt) -gold (Au) three-layer metal, and forming the ohmic contact, the metal lead and the pad 2-5 by a stripping process to form a Wheatstone bridge, as shown in FIG. 6 (d);

(2) photoetching and etching cavities and islands on the back of the silicon wafer:

(2.1) spin-coating a photoresist 7 on the lower surface of the silicon substrate 4 and performing photoetching to form a pattern to be etched in the back cavity of the sensor, as shown in fig. 6 (e);

(2.2) Etching the back cavity by using a Deep Reactive Ion Etching (DRIE) process to form a first island 4-1, a second island 4-2, a first silicon strain film 4-3 and a second silicon strain film 4-4;

(3) etching the region of the front surface of the BF33 glass sheet 5 corresponding to the first silicon strain film 4-3 to a depth of 4.5 μm, and etching the region of the second silicon strain film 4-4 to a depth of 1 μm;

(4) bonding the front side of a BF33 glass sheet 5 with a silicon substrate 2-4 to form a vacuum chamber 6, as shown in FIG. 6 (f);

(5) and photoetching and etching the N-type (100) crystal face double-sided polished silicon wafer to form a through hole 1-2 and a cavity 1-3, and bonding the silicon cap 1-1 and the surface area 2-6 of the upper silicon layer 2-4, as shown in fig. 6(g), so as to prepare the explosion field MEMS piezoresistive pressure sensor of the embodiment.

The overload capability of the first silicon strained film (4-3) and the second silicon strained film (4-4) in the sensor of the above embodiment was simulated using a solid mechanics module in the COMSOL finite element software.

As shown in fig. 7, the graph (a) shows the relationship between the stress difference of the first silicon strained film 4-3 and the applied pressure, the design range of the first silicon strained film 4-3 in this embodiment is 1MPa, and in the case of overload protection in this embodiment, when the applied pressure is 4MPa, the stress difference of the diaphragm surface is 458MPa, which does not reach the rupture stress of the silicon material, and when overload protection is not performed, the stress difference of the diaphragm surface is 953MPa, which exceeds the rupture stress of the silicon material; fig. b shows the relationship between the stress difference of the second silicon strained film 4-4 and the applied pressure, the design range of the second silicon strained film 4-4 in this embodiment is 5MPa, and in the case of the overload protection in this embodiment, when the applied pressure is 15MPa, the stress difference on the surface of the diaphragm is 445MPa, which does not reach the fracture stress of the silicon material, and when the overload protection is not performed, the stress difference on the surface of the diaphragm is 937MPa, which exceeds the fracture stress of the silicon material.

Therefore, the overload capacity of the pressure sensor is effectively improved, the overload capacity of the first silicon strain film is 400% FS, and the overload capacity of the second silicon strain film is 300% FS.