CN117783587A - Array mass block type MEMS accelerometer and preparation method thereof - Google Patents

Abstract

The invention provides an array mass block type MEMS accelerometer and a preparation method thereof, wherein the MEMS accelerometer comprises: a plurality of sensor units and an outer frame; the outer frame is used for packaging the plurality of sensor units; each sensor unit comprises: the mass block, at least one first capacitor comb tooth, at least one second capacitor comb tooth, an inner frame, a second spring beam and a first anchor point; one end of the second spring beam is provided with a first anchor point, and the other end of the second spring beam is connected with the inner side of the mass block; the outer side of the mass block is connected with the first capacitance comb teeth, the inner side of the inner frame is connected with the second capacitance comb teeth, and the inner side of the inner frame is opposite to the outer side of the mass block, so that the first capacitance comb teeth and the second capacitance comb teeth are distributed in a staggered manner; the first anchor point is used for connecting one end of a second spring beam with the outer frame; the plurality of sensor units are arranged in an array, and the mass blocks of the adjacent sensor units are connected through a first spring beam. The invention improves the zero bias stability of the MEMS accelerometer.

Description

Array mass block type MEMS accelerometer and preparation method thereof

Technical Field

The invention belongs to the field of micro-electronics and machinery, and particularly relates to an array mass block type MEMS accelerometer and a preparation method thereof.

Background

Microelectromechanical systems (Micro-Electro-Mechanical System, MEMS) are leading edge technologies that involve multiple disciplines of electronics, mechanics, physics, photonics, chemistry, materials, and the like. Generally refers to a system with sensors, readout circuits, control circuits, interfaces integrated on micro-nano silicon chips. The integrated circuit technology is adopted to manufacture the required components, and the materials such as silicon and the like are subjected to oxidation corrosion, deposition and the like to manufacture the corresponding structural layers, so that the corresponding mechanical elements are obtained. MEMS has the advantages of integration, intelligence, microminiaturization and extremely high reliability, and is the microminiaturization system integration.

MEMS capacitive accelerometers are widely used in the fields of aerospace, inertial navigation, electronic consumption, medical treatment, navigation guidance and the like due to the advantages of small volume, low cost, high precision and the like. With the progress and development of the MEMS technology, the MEMS capacitive accelerometer is continuously optimized and improved in terms of precision, volume and the like, but the improvement and the stress reduction of the zero bias stability are the problems which we pay attention to for a long time and need to be solved.

Disclosure of Invention

Aiming at the defects of the prior art, the invention aims to provide an array mass block type MEMS accelerometer and a preparation method thereof, and aims to solve the problems of poor zero deflection stability and high stress of the existing MEMS accelerometer.

To achieve the above object, in a first aspect, the present invention provides an array mass MEMS accelerometer, comprising: a plurality of sensor units and an outer frame;

each sensor unit comprises: the mass block, at least one first capacitor comb tooth, at least one second capacitor comb tooth, an inner frame, a second spring beam and a first anchor point; one end of the second spring beam is provided with a first anchor point, and the other end of the second spring beam is connected with the inner side of the mass block; the outer side of the mass block is connected with the first capacitance comb teeth, the inner side of the inner frame is connected with the second capacitance comb teeth, and the inner side of the inner frame is opposite to the outer side of the mass block, so that the first capacitance comb teeth and the second capacitance comb teeth are distributed in a staggered manner; the first anchor point is used for connecting one end of a second spring beam with the outer frame;

the sensor units are arranged in an array, and the mass blocks of the adjacent sensor units are connected through a first spring beam.

Optionally, each sensor unit further comprises: at least one second anchor point;

the second anchor point is arranged on the outer frame and is used for connecting the inner frame with the outer frame.

Optionally, the zero offset error of the MEMS accelerometer is equal to the average of the zero offset errors of the plurality of sensor units.

Optionally, the first anchor point and the second anchor point are interconnected with the outer frame by way of Jin Jinjian.

Optionally, in the sensor unit:

the mass block is a hollow square, and the first anchor point is arranged in the middle of the mass block;

the second spring Liang Weirao is arranged at a first anchor point and is used for connecting the first anchor point with the inner side of the mass block;

the inner frame is arranged on two sides of the outer part of the mass block, and at least one of the other two sides of the outer part of the mass block is connected with the mass blocks of other adjacent sensor units through a first spring beam.

In a second aspect, the invention provides a method for manufacturing an array mass type MEMS accelerometer, comprising the following steps:

step 1, etching a lower cover plate with a plurality of first anchor points and a plurality of second anchor points;

step 2, forming an oxide layer on the lower cover plate through thermal oxidation, and forming an electric connection hole at a preset position of the lower cover plate;

step 3, depositing metal on the oxide layers of the first anchor points and the second anchor points of the lower cover plate and the edges of the lower cover plate, and depositing metal wires on the oxide layers of the lower cover plate;

step 4, depositing metal bonded with the metal of the plurality of first anchor points and the plurality of second anchor points on the thin silicon layer of the SOI wafer;

step 5, etching a plurality of device layers on the thin silicon layer of the SOI wafer; each device layer includes: the device comprises a mass block, a first spring beam, at least one first capacitor comb tooth, at least one second capacitor comb tooth and an inner frame; the mass blocks of the adjacent device layers are connected through a second spring beam; one end of the first spring beam is connected with the inner side of the mass block, the other end of the first spring beam is provided with a first anchor point, and the inner frame is provided with a second anchor point;

the first capacitor comb teeth are movable comb teeth, and the second capacitor comb teeth are fixed comb teeth.

Step 6, combining the device layers obtained in the step 5 with the lower cover plate obtained in the step 3 through a first anchor point and a second anchor point Jin Jinjian;

step 7, etching the thick silicon layer and the oxide layer of the SOI wafer of the device layer;

step 8, depositing bond metal on the upper cover plate, and etching a concave cavity;

and 9, bonding the upper cover plate and the lower cover plate bonded with the device layer to Jin Jinjian, thereby obtaining the MEMS accelerometer.

The first anchor point on the lower cover plate is combined with hollow metal Jin Jinjian of the mass block of the device layer, and the hollow metal refers to the first anchor point arranged on the other end of the first spring beam; the second anchor point on the lower cover plate is combined with the metal Jin Jinjian on the fixed comb teeth of the device layer, and the metal on the fixed comb teeth refers to the second anchor point arranged on the inner frame.

Optionally, the lower cover plate and the upper cover plate serve as an outer frame.

Optionally, the lower cover plate and the upper cover plate are both obtained by processing monocrystalline silicon.

In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

the invention provides an array mass block type MEMS accelerometer and a preparation method thereof. The signals of the mass blocks are subjected to average deviation reduction by adjusting the relative positions among the mass blocks and the rigidity of the elastic structure, so that the zero-bias stability of the MEMS capacitive accelerometer is improved. The invention adopts a single anchor point design method in a small-unit sensor. The movable structure of each inertial sensing unit is connected with the substrate through only one anchor point, and compared with a multi-anchor point technology, the stress generated by packaging, temperature and the like of the substrate can be effectively reduced and transferred to the movable structure, so that the stress isolation between the movable mass and the substrate is realized, and the zero bias stability of the MEMS accelerometer is improved. The invention adopts gold-gold bonding method, the process difficulty is low, metal interconnection can be realized, and the bonding temperature is 100 ℃ to 450 ℃.

Drawings

FIG. 1 is a basic schematic diagram of a MEMS capacitive accelerometer provided by an embodiment of the invention;

FIG. 2 is a plan view of the overall structure of a MEMS capacitive accelerometer provided by an embodiment of the invention;

fig. 3 is a schematic diagram of an m×n multi-mass block structure according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of a small cell sensor structure provided by an embodiment of the present invention;

FIG. 5 is a top view of an anchor point of a MEMS capacitive accelerometer provided by an embodiment of the invention;

FIG. 6 is a process flow diagram of a MEMS capacitive accelerometer provided by an embodiment of the invention;

the same reference numbers are used throughout the drawings to reference like elements or structures, wherein: 1 is a single anchor point, 2 is a spring beam, 3 is a sensing comb, 4 is a frame anchor point, 5 is a connecting beam, 6 is a pick-up electrode pad point, 7 is a drive electrode pad point, 8 is a lower cover silicon grounding pad point, 9 is a packaging outer frame, 10 is a metal wiring, 11 is a small unit sensor, 12 is a metal bonded with a lower cover, 13 is a metal bonded with an upper cover plate, 14 is an electrical connecting hole, 15 is a silicon structure, 16 is a bottom silicon layer, 17 is a mass block, 18 is a spring, 19 is an oxide layer, 20 is an upper cover plate, 21 is a device layer, and 22 is a lower cover plate.

Detailed Description

For convenience of understanding, the following explains and describes english abbreviations and related technical terms related to the embodiments of the invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings in the embodiments of the present invention.

The invention aims to improve zero bias stability and facilitate stress release, and provides a high-precision MEMS acceleration sensor chip design and a manufacturing method thereof, wherein the manufactured sensor achieves the requirements.

The MEMS capacitive acceleration sensor is a sensor for measuring acceleration by using a MEMS manufacturing technology. Compared with sensors of other measuring methods, the sensor has the advantages of high precision, easiness in integration and the like. However, the method also has the problems of poor zero deflection stability, easiness in stress influence, precision and the like.

Furthermore, the invention provides a structural design and a process flow manufacturing method of the array type mass block MEMS capacitive acceleration sensor. The method specifically comprises the following steps: acceleration sensor structure, jin Jinjian of this design structure.

The acceleration sensor structure comprises: and (3) designing a m-n structural design, namely designing an acceleration sensor with a small unit, and constructing the acceleration sensor into m-n array arrangement. The acceleration sensor of the small unit comprises an elastic beam, a mass block, a capacitor polar plate and a single anchor point.

The Jin Jinjian combined process flow comprises the following steps:

1) Manufacturing a lower cover plate of the MEMS sensing device: and etching an anchor point on the silicon by taking monocrystalline silicon, forming an oxide layer on the surface of the silicon by thermal oxidation, and patterning after depositing metal on the electrical wiring, the anchor point and the bonding periphery on the oxide layer.

2) Device layers of MEMS sensing devices are fabricated: and (3) taking an SOI silicon wafer, depositing bonding metal on the surface of the thin silicon layer, etching a device layer structure on the thin silicon layer, bonding the etched device layer with a lower cover plate, and then releasing the device structure.

3) Manufacturing an upper cover plate of the MEMS sensing device: and 2) taking monocrystalline silicon, depositing metal at the bonding position of the silicon wafer, etching a groove on the silicon wafer to form a cavity, bonding the upper cover plate with the bonded structure in the step 2), and finally scribing the bonded device.

The design principle of the invention is as follows: the basic mechanical model of the linear acceleration sensor is a mass-spring-damping system, and the acceleration sensor consists of a spring vibrator, a mass block, capacitance comb teeth and an inner frame structure. Wherein the capacitive comb teeth typically comprise movable comb teeth and fixed comb teeth. When no acceleration acts on the accelerometer, the mass block does not move, namely the area between the capacitor comb teeth does not change; when acceleration acts on the accelerometer, the mass block connected with the spring and the movable comb teeth can be displaced up and down, so that the area between the fixed comb teeth and the movable comb teeth is changed, and the area between the comb teeth of the upper part and the comb teeth of the lower part is changed to form a differential capacitor. The schematic diagram is shown in fig. 1.

In order to further explain the MEMS capacitive accelerometer with m×n mass block array arrangement according to the embodiments of the present invention, the present invention will be further described in detail with reference to the accompanying drawings.

The embodiment of the invention provides an array type mass block MEMS uniaxial capacitive acceleration sensor device, which is designed to be in m-by-n mass block array arrangement and single anchor point stress isolation. A structural plan view of the device is shown in fig. 2. Comprising an upper cover plate 20, a device layer 21, and a lower cover plate 22. The upper cover plate 20 comprises a silicon structure 15 and a bond metal 13. The device layer 21 includes the mass 17, springs 18, and metal 12 bonded to the lower cap. The lower cover plate 22 includes the metal 13 bonded to the device layer, the oxide layer 19, the electrical connection holes 14, the metal traces 10, and the bottom silicon layer 16.

Further, the upper cover plate 20 and the lower cover plate 22 may be combined into an outer frame.

Fig. 3 is a schematic diagram of a small-cell sensor structure according to an embodiment of the present invention. The structure comprises a single anchor point 1, a spring beam 2, sensing comb teeth 3, a frame anchor point 4 and a connecting beam 5 between two small-unit sensors.

Fig. 4 is a schematic structural diagram of an m×n multi-mass accelerometer according to an embodiment of the invention. Comprises a pick-up electrode pad point 6, a drive electrode pad point 7, a lower cover silicon grounding pad point 8, a packaging outer frame 9, a metal wire 10 and a small-unit sensor 11.

Fig. 5 is a single anchor arrangement. Comprises a single anchor point 1 and a frame anchor point 4 on the mass block, wherein the anchor point 4 is a shared anchor point of small unit sensors which are distributed left and right. As shown in the drawing of fig. 3.

Fig. 6 is a process flow diagram of a MEMS capacitive accelerometer according to an embodiment of the invention. Firstly, taking a monocrystalline silicon piece, etching an anchor point to be the bottom silicon 16 of a lower cover plate, as shown in (a) of fig. 6; thermal oxidation to form an oxide layer and open electrical connection holes, respectively, the oxide layer 19 and the electrical connection holes 14 of the lower cover plate, as shown in fig. 6 (b); depositing metal on the oxide layer to form metal and metal traces bonded to the device layer and the upper cover plate, and respectively metal 13 and metal trace 10 bonded to the lower cover plate and the upper cover plate of metal 12 bonded to the device layer and the lower cover plate, as shown in fig. 6 (c); taking an SOI wafer, depositing and bonding metal 12 on a thin silicon layer of the SOI wafer, as shown in (d) of FIG. 6; etching the device layer on the thin silicon layer of the SOI wafer to obtain a mass 17 and a spring beam 18, as shown in (e) of FIG. 6; combining the device layer with the lower cap plate Jin Jinjian to form (f) in fig. 6; etching away the thick silicon layer and oxide layer of the SOI wafer of the device layer after bonding, as in FIG. 6 (g); manufacturing an upper cover plate, namely taking monocrystalline silicon, and depositing metal 13 bonded with the lower cover plate, as shown in (h) of fig. 6; etching the cavity, i.e. the silicon 15 of the upper cover plate, as shown in fig. 6 (i); jin Jinjian the upper cover plate and the lower cover plate bonded with the device layer are combined as shown in (j) of fig. 6; dicing this to form the device shown in fig. 6 (k), the final device is shown in fig. 2.

It should be noted that MEMS devices are typically fabricated by mass production, and dicing is the division of mass produced MEMS devices into individual MEMS devices, it being understood that expressions such as "include" and "may include" as may be used in the present invention denote the presence of the disclosed functions, operations or constituent elements, and do not limit one or more additional functions, operations and constituent elements. In the present invention, terms such as "comprising" and/or "having" may be construed to mean a particular feature, number, operation, constituent element, component, or combination thereof, but may not be construed to exclude the presence or addition of one or more other features, numbers, operations, constituent elements, components, or combination thereof.

Furthermore, in the present invention, the expression "and/or" includes any and all combinations of the words listed in association. For example, the expression "a and/or B" may include a, may include B, or may include both a and B.

In describing embodiments of the present invention, it should be noted that the term "coupled" should be interpreted broadly, unless otherwise explicitly stated and defined, for example, the term "coupled" may be either detachably coupled or non-detachably coupled; may be directly connected or indirectly connected through an intermediate medium. Wherein, "fixedly connected" means that the relative positional relationship is unchanged after being connected with each other. "rotationally coupled" means coupled to each other and capable of relative rotation after coupling. "slidingly coupled" means coupled to each other and capable of sliding relative to each other after being coupled. References to directional terms in the embodiments of the present invention, such as "top", "bottom", "inner", "outer", "left", "right", etc., are merely with reference to the directions of the drawings, and thus are used in order to better and more clearly illustrate and understand the embodiments of the present invention, rather than to indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the embodiments of the present invention.

In addition, in embodiments of the present invention, the mathematical concepts mentioned are symmetrical, equal, parallel, perpendicular, etc. These definitions are all for the state of the art and not strictly defined in a mathematical sense, allowing for minor deviations, approximately symmetrical, approximately equal, approximately parallel, approximately perpendicular, etc. For example, a is parallel to B, meaning that a is parallel or approximately parallel to B, and the angle between a and B may be between 0 degrees and 10 degrees. A and B are perpendicular, which means that the angle between A and B is between 80 degrees and 100 degrees.

The foregoing is merely illustrative of the present invention, and the present invention is not limited thereto, and any person skilled in the art will readily recognize that variations or substitutions are within the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (8)

1. An array-mass MEMS accelerometer, comprising: a plurality of sensor units and an outer frame;

each sensor unit comprises: the mass block, at least one first capacitor comb tooth, at least one second capacitor comb tooth, an inner frame, a second spring beam and a first anchor point; one end of the second spring beam is provided with a first anchor point, and the other end of the second spring beam is connected with the inner side of the mass block; the outer side of the mass block is connected with the first capacitance comb teeth, the inner side of the inner frame is connected with the second capacitance comb teeth, and the inner side of the inner frame is opposite to the outer side of the mass block, so that the first capacitance comb teeth and the second capacitance comb teeth are distributed in a staggered manner; the first anchor point is used for connecting one end of a second spring beam with the outer frame;

the sensor units are arranged in an array, and the mass blocks of the adjacent sensor units are connected through a first spring beam.

2. The MEMS accelerometer of claim 1, wherein each sensor unit further comprises: at least one second anchor point;

the second anchor point is arranged on the outer frame and is used for connecting the inner frame with the outer frame.

3. The MEMS accelerometer of claim 1, wherein a zero offset error of the MEMS accelerometer is equal to a mean value of zero offset errors of the plurality of sensor units.

4. The MEMS accelerometer of claim 1, wherein the first anchor point and the second anchor point are interconnected with the outer frame by way of a Jin Jinjian bond.

5. The MEMS accelerometer of claim 1, wherein in the sensor unit:

the mass block is a hollow square, and the first anchor point is arranged in the middle of the mass block;

the second spring Liang Weirao is arranged at a first anchor point and is used for connecting the first anchor point with the inner side of the mass block;

the inner frame is arranged on two sides of the outer part of the mass block, and at least one of the other two sides of the outer part of the mass block is connected with the mass blocks of other adjacent sensor units through a first spring beam.

6. The preparation method of the array mass block type MEMS accelerometer is characterized by comprising the following steps of:

step 1, etching a lower cover plate with a plurality of first anchor points and a plurality of second anchor points;

step 2, forming an oxide layer on the lower cover plate through thermal oxidation, and forming an electric connection hole at a preset position of the lower cover plate;

step 3, depositing metal on the oxide layers of the first anchor points and the second anchor points of the lower cover plate and the edges of the lower cover plate, and depositing metal wires on the oxide layers of the lower cover plate;

step 4, depositing metal bonded with the metal of the plurality of first anchor points and the plurality of second anchor points on the thin silicon layer of the SOI wafer;

step 5, etching a plurality of device layers on the thin silicon layer of the SOI wafer; each device layer includes: the device comprises a mass block, a first spring beam, at least one first capacitor comb tooth, at least one second capacitor comb tooth and an inner frame; the mass blocks of the adjacent device layers are connected through a second spring beam; one end of the first spring beam is connected with the inner side of the mass block, the other end of the first spring beam is provided with a first anchor point, and the inner frame is provided with a second anchor point;

step 6, combining the device layers obtained in the step 5 with the lower cover plate obtained in the step 3 through a first anchor point and a second anchor point Jin Jinjian;

step 7, etching the thick silicon layer and the oxide layer of the SOI wafer of the device layer;

step 8, depositing bond metal on the upper cover plate, and etching a concave cavity;

and 9, bonding the upper cover plate and the lower cover plate bonded with the device layer to Jin Jinjian, thereby obtaining the MEMS accelerometer.

7. The method of manufacturing according to claim 6, wherein the lower cover plate and the upper cover plate are used as the outer frame.

8. The method of claim 6, wherein the lower cover plate and the upper cover plate are each obtained by processing monocrystalline silicon.