CN114217094B - MEMS high g value triaxial accelerometer - Google Patents
MEMS high g value triaxial accelerometer Download PDFInfo
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- CN114217094B CN114217094B CN202111531486.8A CN202111531486A CN114217094B CN 114217094 B CN114217094 B CN 114217094B CN 202111531486 A CN202111531486 A CN 202111531486A CN 114217094 B CN114217094 B CN 114217094B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P15/12—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values by alteration of electrical resistance
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01P—MEASURING LINEAR OR ANGULAR SPEED, ACCELERATION, DECELERATION, OR SHOCK; INDICATING PRESENCE, ABSENCE, OR DIRECTION, OF MOVEMENT
- G01P15/00—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration
- G01P15/02—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses
- G01P15/08—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values
- G01P2015/0862—Measuring acceleration; Measuring deceleration; Measuring shock, i.e. sudden change of acceleration by making use of inertia forces using solid seismic masses with conversion into electric or magnetic values being provided with particular means being integrated into a MEMS accelerometer structure for providing particular additional functionalities to those of a spring mass system
Abstract
The invention discloses a MEMS high g value triaxial accelerometer, which comprises: the outer rectangular frame, the mass block arranged in the center of the outer rectangular frame, the back beam arranged between the outer rectangular frame and the mass block; the two ends of the rectangular beam are connected with the mass block through a middle supporting beam; the external rectangular frame, the square beam and the mass block are connected through diagonal support beams at four corners; a sensitive micro-beam is connected between the external rectangular frame and the back-shaped beam, and a piezoresistor is arranged on the sensitive micro-beam. The triaxial accelerometer has the advantages of symmetrical structure center, low coupling degree between axes, high sensitivity without sacrificing natural frequency, and simple manufacturing process.
Description
Technical Field
The invention belongs to the field of acceleration sensors of micro-electromechanical systems, and particularly relates to a MEMS high g value triaxial accelerometer.
Background
Along with the development of micro-nano processing technology, the MEMS sensor is widely applied to various fields, such as industry, civil use and military use, and has higher sensitivity under the condition of lower acceleration value, such as wearable equipment, medical equipment and the like. However, in some special cases, especially in the field related to military and aerospace, acceleration sensors are required to have high sensitivity, high impact resistance and high bandwidth. The high-g-value piezoresistive acceleration sensor has the characteristics of small size, low mass production cost and large impact resistance and measurement range, and is mainly applied to the fields of penetration and penetration weapons, military explosion and impact measurement, automobile and aerospace and the like.
MEMS accelerometers are generally classified into piezoelectric, capacitive, piezoresistive, resonant, etc. types, each type of sensor having different characteristics and being used in different scenarios, piezoresistive accelerometers currently have the best high g-impact resistance, so piezoresistive accelerometers are generally used in developing high impact accelerometers. Since 1979, roylance et al developed the first piezoresistive accelerometer in the world, which developed as a spring bamboo shoot after rain for decades, and in which the U.S. Endevco company developed a high g value acceleration sensor 7270A, ranging up to 200000g, with a natural frequency up to 1MHZ, but which was expensive, less sensitive and limited by the united states. The Shanghai microsystem develops a high-g value acceleration sensor with a three-beam-double-island structure, the input voltage is 5V, the resonant frequency reaches 220kHz, and the sensitivity is 1.43 mu V/g (Wang Zuan, liu Deren. Influence of the natural frequency and damping of the sensor on impact acceleration detection [ J ]. Functional materials and devices school journal, 2003 (02): 161-164.). Four cantilever beams developed by university of North and middle Dan Yunbo and the like obtain higher natural frequencies at the expense of sensitivity (Y.Shi, X.Wen, Y.Zhao, R.Zhao, H.Cao and J.Liu, "Investigation and Experiment of High Shock Packaging Technology for High-G MEMS Accelerometer," in IEEE Sensors Journal, vol.20, no.16, pp.9029-9037,15Aug.15,2020, doi: 10.1109/JSEN.2020.2987971.). In order to improve sensitivity while securing high structural strength, the four-beam structure was improved by Kong Myeong Bae et al, korean still mountain national university, and a hinge-suspended piezoresistive structure was adopted, but the range was only 5000g (Bae, K.M., lee, J.M., kwon, K.B.et al, high-shock silicon accelerometer with suspended piezoresistive sensing bridges.J Mech Sci technology 28,1449-1454 (2014)). The Robert Kuells research team adopted a new idea, through a design method focusing on displacement rather than stress, and using a spring-mass system related parameter called "geometric constant", the first order natural frequency reached 3.7MHz, and the sensitivity was between 0.035 μV and 0.23 μV (Robert Kuells, siegfried Nau, manfred salt, klaus Thoma, novel piezoresistive high-g accelerometer geometry with very high sensitivity-bandwidth product, sensors and Actuators A: physical, volume 182,2012,Pages 41-48). A sensor is manufactured by adopting a hinge structure in the Western An university of transportation Zhao Libo and the like, the theoretical sensitivity is greater than 0.9mV/g/3V in the range of 0-100g, the theoretical resonance frequency is 25kHz, a plurality of different acceleration sensors are developed on the basis of the structure, and a triaxial integrated hinge High g acceleration sensor is published in the 14th institute of IEEE nanometer/micro engineering and molecular system International conference, the theoretical sensitivity is 1.2 mu V/g/3V, and the theoretical resonance frequency is 1.0MHz (M.Yu, L.Zhao, C.Jia, H.Wang, Y.Zhao and Z.Jiang, "A High-g Triaxial Piezoresistive Accelerometer with Sensing Beams in Pure Axial Deformation,"2019IEEE 14th International Conference on Nano/Micro Engineered and Molecular Systems (NEMS), 2019, pp.176-180, doi: 10.1109/NEMS.2019.8915619).
The traditional high-g-value piezoresistive accelerometer generally improves the natural frequency while sacrificing sensitivity, or adopts compromise treatment of the two, and then proposes a high-g-value accelerometer with pure axial deformation, but most of the acceleration sensors with pure axial deformation are single-axis measurement or independent integration of all directions of three axes, so that the process is complex and large in volume, and the single-block integrated high-g-value cantilever beam type has high inter-axis coupling degree and low sensitivity. A few monolithically integrated triaxial axially deformed accelerometers have a higher bandwidth, lower inter-axis coupling, but the sensitivity is still not satisfactory.
Therefore, it is of great importance to provide an accelerometer with higher sensitivity and simultaneously having higher bandwidth and low inter-axis coupling.
Disclosure of Invention
The invention aims to provide a MEMS high g value triaxial accelerometer to solve the problems of low sensitivity and large inter-axis coupling of the existing micromechanical high g acceleration sensor.
In order to achieve the above purpose, the present invention adopts the following technical scheme:
a MEMS high g-value triaxial accelerometer, comprising: the outer rectangular frame, the mass block arranged in the center of the outer rectangular frame, the back beam arranged between the outer rectangular frame and the mass block; the two ends of the rectangular beam are connected with the mass block through a middle supporting beam; the external rectangular frame, the back-shaped beam and the mass block are connected through diagonal support beams at four corners; a sensitive micro-beam is connected between the external rectangular frame and the back-shaped beam, and a piezoresistor is arranged on the sensitive micro-beam.
Further, the mass block is of an upper and lower double-layer structure formed by integrating an upper mass block and a lower mass block, the section of the upper mass block along the thickness direction is rectangular, and the section of the lower mass block along the thickness direction is inverted trapezoid.
Further, the four sensitive micro-beams are respectively a first sensitive micro-beam, a second sensitive micro-beam, a third sensitive micro-beam and a fourth sensitive micro-beam;
taking the center of the upper surface of the external rectangular frame as the origin of a plane coordinate system XOY, taking the plane of the upper surface of the external rectangular frame as the XOY plane, and arranging the first sensitive micro beam, the second sensitive micro beam, the third sensitive micro beam and the fourth sensitive micro beam along the X-axis negative direction, the Y-axis positive direction, the X-axis positive direction and the Y-axis negative direction respectively;
an X-direction detection resistor RX1 is arranged on the first sensitive micro-beam, an X-direction detection resistor RX2 is arranged on the third sensitive micro-beam, X-direction reference resistors RX3 and RX4 are arranged on a frame of an external rectangular frame positioned on one side of the third sensitive micro-beam, and RX1, RX2, RX3 and RX4 form a Wheatstone bridge in the X direction through metal connecting wires and bonding pads;
y-direction detection resistors RY1 are arranged on the second sensitive micro-beam, Y-direction detection resistors RY2 are arranged on the fourth sensitive micro-beam, Y-direction reference resistors RY3 and RY4 are arranged on a frame of an external rectangular frame positioned on one side of the second sensitive micro-beam, and RY1, RY2, RY3 and RY4 form a Wheatstone bridge in the Y direction through metal connecting wires and bonding pads;
z-direction detection resistors RZ3 and RZ2 are respectively arranged at the connection parts of the first sensitive micro beam and the external rectangular frame and the back-shaped beam; z-direction detection resistors RZ4 and RZ1 are respectively arranged at the connection part of the third sensitive micro beam and the external rectangular frame and the return beam; z-direction reference resistors RY5 and RY6 are arranged on a frame of the external rectangular frame, which is positioned at one side of the first sensitive micro-beam, and RZ1, RZ2, RZ3, RZ4, RZ5 and RZ6 form a Wheatstone bridge in the Z direction through metal connecting wires and bonding pads;
each detection resistor and each reference resistor are piezoresistors.
Further: the triaxial accelerometer is formed by processing (100) monocrystalline silicon wafers, and RX1, RX2, RZ1, RZ2, RZ3, RZ4, RY3 and RY4 are distributed in [011 ] _ ]Crystal orientation, RY1, RY2, RX3, RX4, RZ5, RZ6 are distributed in [011 ]]And (5) crystal orientation.
Further: the upper mass block, the return beam and the middle support beam are equal in thickness; the thickness of the sensitive micro beam is 70 mu m; the bottom surface of the lower mass block is positioned above the bottom surface of the external rectangular frame; the part of the diagonal support beam, which is connected with the external rectangular frame and the back-shaped beam, is equal in thickness to the back-shaped beam, and two sides of the diagonal support beam along the diagonal of the external rectangular frame are respectively provided with a side wing, and the thickness of each side wing is twice that of the sensitive micro-beam; the part of the diagonal support beam connected with the back-shaped beam and the mass block is a central wing, and the central wing is equal in thickness with the side wings.
Further: the three-axis accelerometer is centrally symmetrical in the whole structure.
Further: all parts of the high-g-value triaxial accelerometer are of an integrated structure and are processed based on (100) monocrystalline silicon wafers. The piezoresistor is formed in the corresponding region of the silicon chip through the processes of boron ion implantation and thermal diffusion.
The beneficial effects of the invention are as follows:
the MEMS high-g-value triaxial accelerometer mainly comprises an external rectangular frame, a double-layer mass block, eight supporting beams (four middle supporting beams and four diagonal supporting beams), four sensitive micro beams and a return beam, wherein the mass block is connected with the external rectangular frame and the return beam through the eight supporting beams, the sensitive micro beams are arranged between the external rectangular frame and the return beam, and piezoresistors on the sensitive micro beams are connected with a bonding pad through metal leads to form a Wheatstone bridge in three directions of XYZ. The arrangement of eight support beams ensures that the accelerometer has a sufficiently high natural frequency. The piezoresistor in the sensitive micro-beam is independent of the supporting beam, generates stress strain under the action of axial force, ensures extremely low coupling degree between shafts, and weakens the correlation between the measurement sensitivity and the resonant frequency. The triaxial accelerometer has the advantages of symmetrical structure center, low coupling degree between axes, high sensitivity without sacrificing natural frequency, and simple manufacturing process.
Drawings
FIG. 1 is a schematic diagram of the structure of a MEMS high g-value triaxial accelerometer of the present invention.
FIG. 2 is a cross-sectional view of the MEMS high g-value triaxial accelerometer of the present invention along AA' in FIG. 1.
FIG. 3 is a graph of the distribution of regions of a MEMS high g-value triaxial accelerometer according to the present invention.
FIG. 4 is a bottom oblique second isometric view of the MEMS high g-value triaxial accelerometer of the present invention.
FIG. 5 is a schematic diagram of the varistor according to the present invention.
Fig. 6 (a) is a schematic diagram of an X-direction wheatstone bridge of the present invention, fig. 6 (b) is a schematic diagram of a Y-direction wheatstone bridge of the present invention, and fig. 6 (c) is a schematic diagram of a Z-direction wheatstone bridge of the present invention.
Fig. 7 is a force acting diagram between Y positive beams according to the present invention.
Fig. 8 is a cloud graph of acceleration stress applied in the positive X direction by 4 thousand g according to the present invention.
Fig. 9 is a cloud plot of acceleration stress applied in the negative Z direction of the present invention at 4 thousand g.
FIG. 10 is a stress-strain diagram of an XY-direction sensitive microbeam with an acceleration applied in the X-direction of 4 thousand g according to the invention.
FIG. 11 is a schematic view of the processing technique of the present invention.
Reference numerals in the drawings: 1 is an external rectangular frame; 2 is a mass block; 2-1 is an upper mass block; 2-2 is a lower mass block; 3 is a middle support beam; 4-sensitive microbeams; 4-1 is a first sensitive microbeam; 4-2 is a second sensitive microbeam; 4-3 is a third sensitive micro beam; 4-4 is a fourth sensitive micro beam; 5 is a piezoresistor; 6 is a loop-shaped beam; 7 is a diagonal support beam; 7-1 is a side wing; 7-2 is a center wing; 8 is a silicon wafer; 9-1 is an upper surface thermal oxide silicon dioxide layer; 9-2 is a thermal oxide silicon dioxide layer 9-2 on the lower surface; 10 is a thin layer of silicon dioxide; 11 is a metal contact hole; 12 is a metal lead; 13 is a glass substrate.
Detailed Description
In order that the above objects, features and advantages of the invention will be readily understood, a more particular description of the invention will be rendered by reference to the appended drawings. The following is merely illustrative and explanatory of the principles of the invention, as it would be apparent to those skilled in this art that various modifications or additions may be made to the specific embodiments described or in a similar manner without departing from the principles of the invention or beyond the scope of the claims.
Referring to fig. 1 to 4, the MEMS high g-value triaxial accelerometer of the present embodiment has the following structure:
comprising the following steps: an outer rectangular frame 1, a mass block 2 arranged in the center of the outer rectangular frame 1, and a back beam 6 arranged between the outer rectangular frame 1 and the mass block 2; the two parts of the back-shaped beam 6 and the mass block 2 are connected through the middle supporting beam 3; the outer rectangular frame 1, the square beam 6 and the mass block 2 are connected at four corners through diagonal support beams 7; a sensitive micro-beam 4 is connected between the external rectangular frame 1 and the back-shaped beam 6, and a piezoresistor 5 is arranged on the sensitive micro-beam 4.
The mass block 2 is of an upper and lower double-layer structure formed by integrating an upper mass block 2-1 and a lower mass block 2-2, the section of the upper mass block 2-1 along the thickness direction is rectangular, and the section of the lower mass block 2-2 along the thickness direction is in an inverted trapezoid.
As shown in FIG. 5, the four sensitive microbeams 4 are a first sensitive microbeam 4-1, a second sensitive microbeam 4-2, a third sensitive microbeam 4-3 and a fourth sensitive microbeam 4-4 respectively.
The center of the upper surface of the outer rectangular frame 1 is taken as the origin of a plane coordinate system XOY, the plane of the upper surface of the outer rectangular frame 1 is taken as the XOY plane, and the first sensitive micro beam 4-1, the second sensitive micro beam 4-2, the third sensitive micro beam 4-3 and the fourth sensitive micro beam 4-4 are respectively arranged along the X-axis negative direction, the Y-axis positive direction, the X-axis positive direction and the Y-axis negative direction.
An X-direction detection resistor RX1 is arranged on the first sensitive micro-beam 4-1, an X-direction detection resistor RX2 is arranged on the third sensitive micro-beam 4-3, X-direction reference resistors RX3 and RX4 are arranged on a frame of an external rectangular frame positioned on one side of the third sensitive micro-beam, and the RX1, RX2, RX3 and RX4 form a Wheatstone bridge in the X direction through metal connecting wires and bonding pads, as shown in fig. 6 (a).
The second sensitive micro beam 4-2 is provided with a Y-direction detection resistor RY1, the fourth sensitive micro beam 4-4 is provided with a Y-direction detection resistor RY2, the frame of the external rectangular frame on one side of the second sensitive micro beam is provided with Y-direction reference resistors RY3 and RY4, and the RY1, RY2, RY3 and RY4 form a Wheatstone bridge in the Y direction through metal connection lines and bonding pads, as shown in fig. 6 (b).
Z-direction detection resistors RZ3 and RZ2 are respectively arranged at the connection parts of the first sensitive micro beam 4-1, the external rectangular frame 1 and the back-shaped beam 6; z-direction detection resistors RZ4 and RZ1 are respectively arranged at the connection parts of the third sensitive micro beam 4-3, the external rectangular frame 1 and the back-shaped beam 6; z-direction reference resistors RY5 and RY6 are arranged on the side frame of the external rectangular frame, which is positioned on one side of the first sensitive micro-beam, and RZ1, RZ2, RZ3, RZ4, RZ5 and RZ6 form a Wheatstone bridge in the Z direction through metal connecting wires and bonding pads, as shown in fig. 6 (c).
The detection resistors and the reference resistors are piezoresistors 5. The specific layout is as follows: RX1 is positioned on one side of the center of the first sensitive micro-beam, RZ3 and RZ2 are positioned on the other side, and the distances are equal; RX2 is located on one side of the center of the third sensitive micro-beam, RZ4 and RZ1 are located on the other side, and the distances are equal.
The triaxial accelerometer is formed by processing (100) monocrystalline silicon wafers, and RX1, RX2, RZ1, RZ2, RZ3, RZ4, RY3 and RY4 are distributed in [011 ] _ ]Crystal orientation, RY1, RY2, RX3, RX4, RZ5, RZ6 are distributed in [011 ]]And (5) crystal orientation. The three-axis accelerometer is centrally symmetrical in the whole structure. The four middle support beams 3 connecting the two beams 6 and the mass block are respectively arranged along the X-axis negative direction, the Y-axis positive direction, the X-axis positive direction and the Y-axis negative direction.
The thickness of the outer rectangular frame 1 is 500 μm of the silicon wafer. The thickness of the upper mass block 2-1, the back beam 6 and the middle support beam 3 is 300 mu m; the thickness of the sensitive microbeam 4 is 70 μm.
The part of the diagonal support beam 7, which is connected with the external rectangular frame 1 and the back-shaped beam 6, is equal in thickness to the back-shaped beam 6, and two sides of the diagonal support beam along the diagonal of the external rectangular frame are respectively provided with a side wing 7-1, wherein the thickness of the side wing is twice that of the sensitive micro-beam; the part of the diagonal support beam 7 connected with the back beam 6 and the mass block 2 is a central wing 7-2, and the central wing is equal in thickness with the side wings. The side wings, the center wings, the loop-shaped beam and the sensitive micro-beam form a certain leverage, and stress on the sensitive micro-beam is amplified, so that the sensitivity of the sensor is improved.
The bottom surface of the lower mass block 2-2 is located above the bottom surface of the outer rectangular frame 1, that is, a gap (10 μm may be set) exists between the lower mass block 2-2 and the bottom surface of the outer rectangular frame, so as to allow the mass block to move up and down.
Referring to fig. 7 to 10, the specific working principle of the accelerometer of the invention is as follows:
when acceleration along the positive direction of Y is applied to the accelerometer, the outer rectangular frame 1 is fixed, the mass block 2 generates tiny displacement along the positive direction of Y axis, direct acting force is generated on the four diagonal supporting beams 7 and the four middle supporting beams 3, and the stress on the sensitive micro-beams is amplified due to leverage generated by the two times of thickness on the diagonal supporting beams 7 on the side wings 7-1 of the sensitive micro-beams 4, and the main strain energy is absorbed by the supporting beams and the back beams and can not directly bring destructive impact force because of indirect acting on the sensitive micro-beams. When the Y-axis positive direction acceleration is applied, the piezoresistor RY1 receives axial tension to increase, the piezoresistor RY2 receives axial pressure to decrease, the Wheatstone bridge for detecting the Y direction is unbalanced, and for a half-bridge differential circuit, the bridge output voltage is as follows:
wherein: u (U) o -an output voltage; u (U) i -an input voltage; r is R Y1 、R Y2 、R Y3 、R Y4 -initial values of four piezoresistors RY1, RY2, RY3, RY4 of the Y-direction bridge; deltaR Y1 、ΔR Y2 -Y-direction bridge RY1, RY2 of two varistor variation values;
according to the standard piezoresistor silicon processing technology, all piezoresistors are arranged, the resistance values of all piezoresistors are equal under static placement, and according to the stressed characteristics of the RY1 and RY2 piezoresistors, the following can be assumed: deltaR Y1 ＝ΔR Y2 . At this time, the output voltage formula of the Y-direction bridge is simplified as:
when the accelerometer applies acceleration in the Y direction, the sensitivity formula in the Y direction is simplified as follows due to the pure axial stress:
wherein: a, a y -Y-direction acceleration; sigma-axial stress to which the varistor is subjected; Δl—axial strain length of the varistor; l-the initial length of the piezoresistor; pi 44 -shear piezoresistive coefficient; e-varistor Young's modulus; s is S Y -Y-direction sensitivity.
From the above, it can be seen that the output voltage, sensitivity, is mainly related to the piezoresistive strain, which is proportional to the stress. The sensor designed by the invention can better concentrate axial stress, so that higher sensitivity can be maintained while high natural frequency is maintained. The case of the X direction has symmetry with the case of the Y direction, so the output voltage formula of the X direction bridge is simplified as follows:
wherein: uo-output voltage; u (U) i -an input voltage; deltaR X1 -two piezoresistor variation values of the X-direction bridge; r is R X1 -varistor initial value of X-direction bridge.
The stress process of the X-direction piezoresistor is similar to that of the Y-axis, and in theory X, Y has the same sensitivity, referring to fig. 7 and 8, it can be seen that the X-direction sensitive micro-beam is stressed intensively, and the Y-direction sensitive micro-beam has micro-bending, but almost has small stress compared with the X-direction, so as to ensure extremely low coupling degree between the X, Y-direction axes.
When acceleration is applied in the negative Z direction (the direction from the upper surface to the lower surface of the external rectangular frame), the mass blocks descend to drive the eight support beams to directly displace, and indirectly, the cantilever beams stretch and bend, so that the sensitive micro beams deform axially, the stress directions of RZ3 and RZ2 are opposite, the stress directions of RZ4 and RZ1 are opposite, the resistance values of RZ3 and RZ4 are increased, and the resistance values of RZ1 and RZ2 are reduced. Also if it is assumed that:
ΔR Z1 ＝ΔR Z2 ；ΔR Z3 ＝ΔR Z4
wherein: uo-output voltage; ui—input voltage; deltaR Z1 、ΔR Z2 、ΔR Z3 、ΔR Z4 -the values of the changes of the voltage-dependent resistors RZ1, RZ2, RZ3 and RZ4 of the bridge in the Z direction; r is R Z1 、R Z2 、R Z3 、R Z4 -initial values of Z-direction bridge piezoresistors RZ1, RZ2, RZ3, RZ 4; r is R Z5 、R Z6 -Z-direction bridge references resistance values of piezoresistors RZ5 and RZ 6; due to DeltaR Z3 And DeltaR Z1 Different numbers, so the differential circuit is more than singleThe arm circuit performance is doubled.
The first-order natural frequency of the accelerometer designed by the invention is 209KHZ, the three-axis output sensitivity is Sy=Sx=15 mu v/g, sz=30 mu v/g, almost no inter-axis coupling exists, the accelerometer has better linearity below 10 ten thousand g, and the acceleration applied by the high overload impact resistance theory can reach 18 ten thousand g, so that the comprehensive performance of the accelerometer is superior to that of the existing acceleration sensor.
Referring to fig. 11, the MEMS high g-value triaxial accelerometer of the present invention is fabricated based on (100) monocrystalline silicon wafer, and the general flow is as follows:
(1) And (3) double-sided polishing is carried out on the silicon wafer 8, the surface of the pre-baked silicon wafer is cleaned, and the surface of the silicon wafer is an n-type (100) crystal face. The silicon wafer 8 was subjected to double-sided thermal oxidation at 1000 c to form an upper surface thermal oxide silicon dioxide layer 9-1 and a lower surface thermal oxide silicon dioxide layer 9-2 on the upper and lower surfaces of the silicon wafer, respectively, with a thickness of 1 μm.
(2) Photoetching of the varistor pattern, wet etching of the silicon dioxide layer, leakage of monocrystalline silicon wafer, boron ion implantation and thermal diffusion are sequentially carried out in combination to form the varistor 5, the doping concentration of the varistor 5 being 1.5X10 19 cm -3 . Rapid annealing followed by low pressure chemical deposition (LPECVD) of a new thin layer 10 of silicon dioxide with a thickness of 0.5 μm for protecting the varistor.
(3) The metal contact holes 11 of the varistor 5 are formed by reactive ion etching.
(4) And etching the bottom surface by utilizing potassium hydroxide anisotropic wet method to form the lower mass block 2-2.
(5) And then forming an upper mass block, a beam shape, a middle supporting beam, a diagonal supporting beam and a sensitive microbeam 4 with the thickness of 300 mu m by Deep Reactive Ion Etching (DRIE). A new thin layer 10 of silicon dioxide was deposited on the bottom surface using low pressure chemical deposition (LPECVD) to a thickness of 500nm.
(6) The first silicon dioxide thin layer 10 deposited on the upper surface is removed by reactive ion etching, so as to open a metal contact hole, the metal thin layer is sputtered on the top of the silicon wafer, patterning and sintering are performed to form a metal lead 12 and a bonding pad, and the redundant silicon dioxide thin layer 10 on the lower surface is etched by using HF solution.
(7) The HF solution is rinsed off and the bottom surface of the wafer is anodically bonded to the glass substrate 13.
The foregoing is merely a preferred embodiment of the present invention, and not all or only one, and any equivalent modifications of the technical solution of the present invention will be within the scope of the present invention by those skilled in the art after reading the present specification.
Claims (6)
1. A MEMS high g-value triaxial accelerometer, comprising: an outer rectangular frame (1), a mass block (2) arranged in the center of the outer rectangular frame (1), and a back beam (6) arranged between the outer rectangular frame (1) and the mass block (2);
the two ends of the U-shaped beam (6) are connected with the mass block (2) through an intermediate support beam (3); the outer rectangular frame (1), the back-shaped beam (6) and the mass block (2) are connected at four corners through diagonal support beams (7); a sensitive micro-beam (4) is connected between the external rectangular frame (1) and the back-shaped beam (6), and a piezoresistor (5) is arranged on the sensitive micro-beam (4);
the four sensitive micro beams (4) are respectively a first sensitive micro beam (4-1), a second sensitive micro beam (4-2), a third sensitive micro beam (4-3) and a fourth sensitive micro beam (4-4);
taking the center of the upper surface of the outer rectangular frame (1) as the origin of a plane coordinate system XOY, taking the plane of the upper surface of the outer rectangular frame (1) as the XOY plane, and arranging the first sensitive micro beam (4-1), the second sensitive micro beam (4-2), the third sensitive micro beam (4-3) and the fourth sensitive micro beam (4-4) along the X-axis negative direction, the Y-axis positive direction, the X-axis positive direction and the Y-axis negative direction respectively;
an X-direction detection resistor RX1 is arranged on the first sensitive micro-beam (4-1), an X-direction detection resistor RX2 is arranged on the third sensitive micro-beam (4-3), X-direction reference resistors RX3 and RX4 are arranged on a frame of an external rectangular frame positioned on one side of the third sensitive micro-beam, and the RX1, RX2, RX3 and RX4 form a Wheatstone bridge in the X direction through metal connecting wires and bonding pads;
a Y-direction detection resistor RY1 is arranged on the second sensitive micro-beam (4-2), a Y-direction detection resistor RY2 is arranged on the fourth sensitive micro-beam (4-4), Y-direction reference resistors RY3 and RY4 are arranged on a frame of an external rectangular frame positioned on one side of the second sensitive micro-beam, and RY1, RY2, RY3 and RY4 form a Wheatstone bridge in the Y direction through metal connection lines and bonding pads;
z-direction detection resistors RZ3 and RZ2 are respectively arranged at the connection parts of the first sensitive micro beam (4-1) and the external rectangular frame (1) and the return beam (6); z-direction detection resistors RZ4 and RZ1 are respectively arranged at the connection parts of the third sensitive micro beam (4-3) and the external rectangular frame (1) and the return beam (6); z-direction reference resistors RY5 and RY6 are arranged on a frame of the external rectangular frame, which is positioned at one side of the first sensitive micro-beam, and RZ1, RZ2, RZ3, RZ4, RZ5 and RZ6 form a Wheatstone bridge in the Z direction through metal connecting wires and bonding pads;
each detection resistor and each reference resistor are piezoresistors (5).
2. The MEMS high g-value triaxial accelerometer according to claim 1, characterized in that: the mass block (2) is of an upper-lower double-layer structure formed by integrating an upper-layer mass block (2-1) and a lower-layer mass block (2-2), the section of the upper-layer mass block (2-1) along the thickness direction is rectangular, and the section of the lower-layer mass block (2-2) along the thickness direction is inverted trapezoid.
3. The MEMS high g-value triaxial accelerometer according to claim 1, characterized in that: the triaxial accelerometer is formed by processing (100) monocrystalline silicon wafers, and RX1, RX2, RZ1, RZ2, RZ3, RZ4, RY3 and RY4 are distributed inCrystal orientation, RY1, RY2, RX3, RX4, RZ5, RZ6 are distributed in [011 ]]And (5) crystal orientation.
4. A MEMS high g-value triaxial accelerometer according to claim 2, characterized in that: the upper layer mass block (2-1), the back-shaped beam (6) and the middle supporting beam (3) are equal in thickness; the thickness of the sensitive micro beam (4) is 70 mu m; the bottom surface of the lower-layer mass block (2-2) is positioned above the bottom surface of the external rectangular frame (1);
the diagonal support beams (7) are connected with the external rectangular frame (1) and the part of the back-shaped beam (6) and have the same thickness as the back-shaped beam (6), and two sides of the diagonal support beams along the diagonal of the external rectangular frame are respectively provided with a side wing (7-1), and the thickness of each side wing is twice that of the sensitive micro-beam; the part of the diagonal support beam (7) connected with the back-shaped beam (6) and the mass block (2) is a central wing (7-2), and the central wing is equal in thickness with the side wings.
5. The MEMS high g-value triaxial accelerometer according to claim 1, characterized in that: the three-axis accelerometer is centrally symmetrical in the whole structure.
6. The MEMS high g-value triaxial accelerometer according to claim 1, characterized in that: the piezoresistor is formed in the corresponding region of the silicon chip through the processes of boron ion implantation and thermal diffusion.
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