CN117906801A

CN117906801A - MEMS three-dimensional force sensor and preparation method thereof

Info

Publication number: CN117906801A
Application number: CN202410093704.1A
Authority: CN
Inventors: 刘会聪; 李澳门; 李东升; 孙雨阳
Original assignee: Suzhou University
Current assignee: Suzhou University
Priority date: 2024-01-23
Filing date: 2024-01-23
Publication date: 2024-04-19

Abstract

The invention relates to a MEMS three-dimensional force sensor and a preparation method thereof, wherein the MEMS three-dimensional force sensor comprises: an elastic layer comprising a surface layer, a liquid metal layer and a first substrate; the liquid metal layer is arranged between the surface layer and the first substrate, and the liquid metal layer is provided with resistance wires; wherein, the Young modulus of the elastic layer is further controlled by controlling the phase state of the liquid metal layer; the force transmission layer comprises a second substrate which is attached to the first substrate, and the second substrate is provided with a plurality of microcontact units; the resistance wire is connected with the second substrate; the force sensitive layer comprises a third substrate which is attached to the second substrate, and the third substrate is provided with a plurality of cantilever beams; wherein the plurality of cantilevers Liang Zhishao and a portion of the microcontact units are disposed opposite to each other. The invention can be freely adjusted according to the requirements so as to adapt to different force measurement ranges and precision requirements.

Description

MEMS three-dimensional force sensor and preparation method thereof

Technical Field

The invention relates to the technical field of micro-electromechanical systems, in particular to a MEMS three-dimensional force sensor and a preparation method thereof.

Background

Microelectromechanical systems (Micro-Electro-MECHANICAL SYSTEMS, MEMS) are integrated technologies of mechanical and electronic components on the micrometer scale.

MEMS technology has found wide application in many fields including sensors, metrology instruments, biomedical and communication, and the like. In the field of force sensing, a MEMS force sensor consists of a micromechanical device and a sensitive circuit, so that accurate measurement of force can be realized.

However, the sensitivity requirements for force sensors may be different for different application scenarios. Traditional MEMS three-dimensional force sensors often have fixed sensitivity and cannot be adjusted according to actual needs.

Therefore, there is a need to develop a MEMS three-dimensional force sensor with adjustable sensitivity.

Disclosure of Invention

Aiming at the defects of the prior art, the invention discloses a MEMS three-dimensional force sensor and a preparation method thereof.

The technical scheme adopted by the invention is as follows:

a MEMS three-dimensional force sensor, comprising:

An elastic layer comprising a surface layer, a liquid metal layer and a first substrate; the liquid metal layer is arranged between the surface layer and the first substrate, and the liquid metal layer is provided with a resistance wire; wherein, the Young modulus of the elastic layer is further controlled by controlling the phase state of the liquid metal layer;

the force transmission layer comprises a second substrate which is attached to the first substrate, and the second substrate is provided with a plurality of microcontact units; and, the resistance wire extends along a first direction and is connected with the second substrate;

the force sensitive layer comprises a third substrate which is attached to the second substrate, and the third substrate is provided with a plurality of cantilever beams; wherein a plurality of the cantilevers Liang Zhishao and a part of the microcontact units are oppositely disposed;

When an external force is applied to the elastic layers with different Young's moduli, the elastic layers with high Young's moduli generate relatively smaller deformation, so that the phase change transferred to the force-sensitive layer is smaller, and the force-sensitive layer generates smaller signal output.

In an embodiment of the invention, a material of the surface layer of the elastic layer and the first substrate is polydimethylsiloxane.

In one embodiment of the present invention, the material of the second substrate of the force transmission layer is polydimethylsiloxane.

In one embodiment of the present invention, the plurality of microcontact units each extend in the thickness direction of the force transmission layer, and the distances by which the plurality of microcontact units extend are the same.

In one embodiment of the invention, the end of the microcontact unit contacting the cantilever beam is a tip contact.

In one embodiment of the present invention, the third substrate is provided with a plurality of cavities for installing the cantilever beams, one ends of the cantilever beams are abutted against the inner walls of the cavities, and the other ends of the cantilever beams are suspended in the cavities.

In one embodiment of the present invention, the third substrate is further provided with a plurality of electrode micro-channels in the same number as the cantilever beams, and the electrode micro-channels are covered with a conductive metal material.

In one embodiment of the present invention, the second substrate is provided with a positioning column, the third substrate is provided with a positioning hole, and the positioning column is inserted into the positioning hole.

The invention also provides a preparation method of the MEMS three-dimensional force sensor, which is used for preparing the MEMS three-dimensional force sensor and comprises the following steps of:

s1, manufacturing an elastic layer;

S11, dropwise adding a PDMS solution into a first die, and curing to obtain a surface layer;

S12, pouring the liquid metal solution into the first die in the step S11, and solidifying to obtain a liquid metal layer;

S13, placing resistance wires on the surface of the liquid metal layer obtained in the step S12;

S14, dropwise adding a PDMS solution into the second mold, and curing to obtain a first PDMS unit;

s15, dropwise adding a PDMS solution into a third mold, and curing to obtain a second PDMS unit;

s16, placing the liquid metal layer prepared in the step S13, the first PDMS unit prepared in the step S14 and the second PDMS unit prepared in the step S15 in a fourth mold, dripping a PDMS solution, and curing to obtain an elastic layer with a substrate;

s2, etching a microcontact unit on the surface of the second substrate, coating PDMS solution on the surface of the second substrate, and curing to obtain a force transmission layer;

and S3, etching a cantilever beam on the surface of the third substrate to obtain the force sensitive layer.

In one embodiment of the present invention, the first mold is square with a bottom surface of 320 μm×320 μm and a groove depth of 200 μm; the second die is square with the bottom surface of 400 mu m multiplied by 400 mu m, and the depth of the groove is 100 mu m; the third die is square with the bottom surface of 400 mu m multiplied by 400 mu m, and the depth of the groove is 300 mu m; the fourth die is square with the bottom surface of 400 mu m multiplied by 400 mu m, and the depth of the groove is 200 mu m.

Compared with the prior art, the technical scheme of the invention has the following advantages:

the MEMS three-dimensional force sensor can realize more accurate measurement in different measuring ranges by adjusting the sensitivity of the sensor, realize the adjustable sensitivity and measuring range of the sensor and improve the measuring precision.

The MEMS three-dimensional force sensor can cope with various working conditions, different application environments can have different noise levels, and the sensitivity of the sensor with variable sensitivity can be adjusted according to actual working conditions so as to cope with different signal intensities and noise levels, and accurate and reliable measurement is ensured.

The MEMS three-dimensional force sensor can avoid purchasing and maintaining a plurality of different sensors for different measuring ranges, and can realize a plurality of measuring requirements on the same sensor by adjusting the sensitivity of the sensor, thereby saving cost and resources.

Drawings

In order that the invention may be more readily understood, a more particular description of the invention will be rendered by reference to specific embodiments thereof that are illustrated in the appended drawings.

FIG. 1 is a schematic diagram of the structure of a MEMS three-dimensional force sensor in accordance with the present invention.

FIG. 2 is an exploded view of a first view of a MEMS three-dimensional force sensor of the present invention.

FIG. 3 is an exploded view of a second view of the MEMS three-dimensional force sensor of the present invention.

Fig. 4 is an exploded view of the elastic layer of the present invention.

Fig. 5 is a schematic structural view of a force transmission layer in the present invention.

Fig. 6 is a schematic structural diagram of a first view angle of a force sensitive layer according to the present invention.

Fig. 7 is a schematic structural diagram of a second view angle of the force sensitive layer in the present invention.

Description of the specification reference numerals: 100. an elastic layer; 101. a surface layer; 102. a liquid metal layer; 103. a resistance wire; 104. a first substrate; 200. a force transmission layer; 201. a second substrate; 202. a microcontact unit; 203. positioning columns; 300. a force sensitive layer; 301. a third substrate; 302. a cantilever beam; 303. and positioning holes.

Detailed Description

The present invention will be further described with reference to the accompanying drawings and specific examples, which are not intended to be limiting, so that those skilled in the art will better understand the invention and practice it.

The foregoing and other features, aspects and advantages of the present invention will become more apparent from the following detailed description of the embodiments, read in conjunction with the accompanying drawings. The directional terms mentioned in the following embodiments are, for example: upper, lower, left, right, front or rear, etc., are merely references to the directions of the drawings. Thus, directional terminology is used for the purpose of illustration and is not intended to be limiting of the invention, and furthermore, like reference numerals refer to like elements throughout the embodiments.

According to research, the traditional MEMS three-dimensional force sensor often has fixed sensitivity, can not be adjusted according to actual needs, the measuring range of the sensor can be limited, and the measuring range in certain application scenes can be too large or too small, so that the requirement of accurate measurement can not be met. To change the sensitivity of the sensor, it is often necessary to redesign the structure of the sensor and reassemble the individual modules of the sensor. This process requires careful assessment of the physical characteristics and measurement range of the sensor to ensure that the sensitivity of the sensor is properly adjusted while maintaining stability of other performance metrics. However, the process of redesigning and adjusting the sensor structure presents a number of problems, such as the need for time and money investments, which can increase manufacturing costs and extend the time to market for the product.

In order to solve the problems, the invention provides a MEMS three-dimensional force sensor and a preparation method thereof.

Referring to fig. 1 to 3, a MEMS three-dimensional force sensor includes:

An elastic layer 100 comprising a surface layer 101, a liquid metal layer 102 and a first substrate 104; the liquid metal layer 102 is arranged between the surface layer 101 and the first substrate 104, and the liquid metal layer 102 is provided with a resistance wire 103; wherein, the Young's modulus of the elastic layer 100 is further controlled by controlling the phase state of the liquid metal layer 102;

The force transmission layer 200 comprises a second substrate 201 attached to the first substrate 104, and the second substrate 201 is provided with a plurality of microcontact units 202; and, the resistance wire 103 extends in the first direction to be connected with the second substrate 201;

The force sensitive layer 300 comprises a third substrate 301 attached to the second substrate 201, and the third substrate 301 is provided with a plurality of cantilever beams 302; wherein the plurality of cantilever beams 302 are disposed at least opposite a portion of the microcontact unit 202;

When an external force is applied to the elastic layers 100 having different young's moduli, the deformation of the elastic layer 100 having a high young's modulus is relatively small, and thus the phase change transferred to the force sensitive layer 300 is small, so that the force sensitive layer 300 generates a small signal output.

As shown in fig. 4, the first direction specifically refers to the width direction of the liquid metal layer 102.

In this embodiment, the surface layer 101 of the elastic layer 100 and the first substrate 104 are made of Polydimethylsiloxane (PDMS).

In this embodiment, the material of the second substrate 201 of the force transmission layer 200 is Polydimethylsiloxane (PDMS).

In the present embodiment, the plurality of microcontact units 202 extend in the thickness direction of the force transmission layer 200, and the distances by which the plurality of microcontact units 202 extend are the same. Specifically, the end of the microcontact unit 202 contacting the cantilever beam 302 is a tip contact.

Further, the microcontact units 202 are arranged in a matrix of M N, M being 1 or more and N being 1 or more. Specifically, eight microcontact units 202 are arranged in an array as shown in fig. 5.

In this embodiment, referring to fig. 6 and 7, the third substrate 301 is provided with a plurality of cavities for installing the cantilever beams 302, one end of the cantilever beams 302 abuts against the inner wall of the cavity, and the other end of the cantilever beams 302 is suspended in the cavity. Specifically, the cantilever beams 302 have four, and an included angle of 90 ° is formed between two adjacent cantilever beams 302.

In this embodiment, the third substrate 301 is further provided with a plurality of electrode micro-channels as many as the cantilever beams 302, and the electrode micro-channels are covered with a conductive metal material, wherein the conductive metal material is selected from one of copper, aluminum, silver and gold.

As a modification, in order to facilitate rapid assembly and assembly of the subsequent force transmission layer 200 and the force sensitive layer 300, the second substrate 201 is provided with a positioning post 203, the third substrate 301 is provided with a positioning hole 303, and the positioning post 203 is inserted into the positioning hole 303. Preferably, the center of the positioning post 203 coincides with the center of the force transfer layer 200.

A preparation method of a MEMS three-dimensional force sensor comprises the following steps:

S1, manufacturing an elastic layer 100;

S11, designing a first die, wherein the bottom surface of the first die is a square with 320 mu m multiplied by 320 mu m, and the depth of a groove of the first die is 200 mu m. Preparing PDMS solution according to design requirements, dripping a proper amount of PDMS solution into a first die, scraping with a scraper, placing the die on a heating table, heating for 2 hours at 80 ℃, standing until the die is solidified, and demolding to obtain a surface layer 101;

S12, pouring the unset liquid metal into the first die in the step S1, scraping the liquid metal with a blade, cooling and waiting for forming, and demolding to obtain a liquid metal layer 102 with the surface area of 320 mu m multiplied by 320 mu m and the thickness of 200 mu m;

S13, placing a proper amount of resistance wires 103 on the surface of the liquid metal layer 102 obtained in the step S2;

s14, designing a second die, wherein the bottom surface of the second die is a square with the size of 400 mu m multiplied by 400 mu m, and the depth of a groove of the second die is 100 mu m. Dropwise adding a proper amount of PDMS solution prepared in the step S1 into a second mold, scraping with a scraper, placing the mixture on a heating table, heating the mixture for 2 hours at the temperature of 80 ℃, standing the mixture until the mixture is solidified, and demolding the mixture to obtain a first PDMS unit;

S15, designing a third die, wherein the bottom surface of the third die is a square with the size of 400 mu m multiplied by 400 mu m, and the depth of a groove of the third die is 300 mu m. Dropwise adding a proper amount of PDMS solution prepared in the step S1 into a third mold, scraping with a scraper, placing the mixture on a heating table, heating the mixture for 2 hours at the temperature of 80 ℃, standing the mixture until the mixture is solidified, and demolding the mixture to obtain a second PDMS unit;

s16, placing the liquid metal layer 102 prepared in the step S3, the first PDMS unit prepared in the step S4 and the second PDMS unit prepared in the step S5 in a fourth mold with a bottom area of 400 mu m multiplied by 400 mu m and a groove depth of 400 mu m, dripping a proper amount of PDMS solution prepared in the step S1, scraping the solution with a scraper, placing the solution on a heating table, heating the solution for 2 hours at a temperature of 80 ℃, standing the solution until the solution is solidified, and demolding the elastic layer 100 is obtained.

S2, manufacturing a force transmission layer 200; processing is based on a 4-inch N-type SOI wafer, wherein the thickness of a device layer, a buried oxide layer and a substrate layer is 5 mu m, 1 mu m and 300 mu m respectively;

S21, firstly growing a 100nm silicon nitride layer on the surface of the SOI by a Low Pressure Chemical Vapor Deposition (LPCVD) method for mask protection of wet etching; because the wet etching liquid has a relatively high etching rate on the silicon oxide mask layer, the process adopts silicon nitride as the mask layer for wet etching;

S22, etching a window to be corroded through Reactive Ion Etching (RIE) after photoetching and developing, wherein the process is used for etching LPCVD silicon nitride, and the etching rate is required to be tested because of higher compactness and slower etching rate, so that the over-etching of silicon is prevented;

And S23, wet etching to form the microcontact unit 202. Specifically, the KOH wet etching solution (potassium hydroxide etching solution) is adopted to etch the water bath, and the etching rate is related to the concentration degree of the KOH solution and the temperature of the water bath. The concentration of KOH corrosive liquid is 20%, and the complete microcontact unit 202 is obtained after corrosion for about 3 hours in a water bath environment at 80 ℃;

S24, back photoetching development; deep Reactive Ion Etching (DRIE) is used to etch the middle circular through hole. Because the round through holes are required to be etched through on the wafer, AZ4620 photoresist with higher viscosity is selected as the photoresist, and the photoresist homogenizing speed is determined by considering the etching rate ratio of silicon to the photoresist, so that the photoresist is kept to be reasonable in thickness. Before deep silicon etching, the silicon nitride of LPCVD in step S21 needs to be etched completely;

S25, after the mold preparation of the force transmission layer 200 is completed, preparing the force transmission layer 200 through reverse molding and demolding; pouring PDMS solution into a mould for preparing the force transmission layer 200, and curing to obtain the force transmission layer 200; wherein a mold-reverse tool is required as an aid in performing the heating-up of the mold-reverse casting of the PDMS solution to form the outer support region of the force-transmitting layer 200, and further, the thickness of the force-transmitting layer 200 may be controlled by controlling the depth of the mold-reverse tool.

As can be seen from the above, the force transmission layer 200 is manufactured by preparing a reverse mold, etching the front surface of the silicon wafer to form the microcontact unit 202 and the positioning posts 203 mainly by wet etching/dry etching, the microcontact unit 202 has a pyramid structure, spin-coating a PDMS solution with a certain thickness on the surface by spin-coating, and removing the PDMS after solidification to form the force transmission layer 200.

S3, manufacturing a force sensitive layer 300; the thickness of the device layer, the buried oxide layer and the substrate layer of the 4-inch n-type (100 crystal phase) SOI silicon wafer is 5 mu m, 1 mu m and 300 mu m respectively, and the processing process is as follows:

s31, forming on the front surface of the SOI silicon wafer by a thermal oxidation mode The silicon dioxide layer is used as a hard mask for the first ion implantation, and photoetching marks are made on the silicon dioxide layer through an etching process;

s32, spin-coating photoresist on the front surface of the SOI silicon wafer, wherein AZ5214 photoresist is selected as the photoresist, and is used as the positive photoresist, and hard mask protection is formed after a HDMS wafer pretreatment system, spin coating and pre-baking, wherein the thickness of the formed photoresist is about 2 mu m;

S33, photoetching and developing, and patterning photoresist on the front surface of the SOI silicon wafer; through a photoetching process, the positive photoresist is subjected to a crosslinking reaction under ultraviolet rays with certain intensity, and a pattern is provided for etching holes of silicon dioxide;

S34, etching (RIE) surface silicon oxide, and injecting boron ions to form lightly doped B+; etching surface silicon dioxide, wherein the thickness of the etched silicon oxide is 300nm, and performing ultrasonic cleaning on the surface photoresist after ion implantation is completed;

s35, rapid annealing (RTA); and after the annealing is finished, carrying out a test of the sheet-accompanying sheet resistance, and obtaining parameters of ion implantation dosage, implantation energy and annealing temperature. After the annealing is finished, a thin oxide layer is formed in the annealing process, and the oxide layer needs to be rinsed by a BOE solution;

S36, spin-coating photoresist on the front surface, and etching the silicon dioxide layer to form a window for the second ion implantation after photoetching and developing; then carrying out secondary boron ion implantation, completing rapid annealing, testing the sheet resistance, and determining parameters of the secondary boron ion implantation;

S37, sputtering 700nm aluminum, patterning and carrying out metallization treatment (annealing); 700nm aluminum is sputtered on the wafer surface by means of magnetron sputtering (FHR). And photoetching and developing, patterning the surface electrode to form an electrode micro-channel, corroding aluminum which is not protected by photoresist on the surface by using aluminum corrosive liquid in the patterning process, cleaning the photoresist on the surface after corrosion is finished, and carrying out metallization treatment on the aluminum to form ohmic contact. The piezoresistor is tested through a manual probe station;

S38, plasma Enhanced Chemical Vapor Deposition (PECVD) of 1 mu m silicon nitride; chemical vapor deposition is carried out to generate 1 mu m thick silicon nitride (SiNx) for surface protection;

s39, etching out a wire bonding hole; photoetching and developing a surface wire bonding hole window, etching silicon nitride, and checking whether the silicon nitride is etched or not, wherein the lead cannot be completed due to the fact that the etching is not completed;

S310, etching silicon nitride, silicon oxide and silicon on the front surface, and stopping at the buried oxide layer; patterning the surface, namely etching the thin film grown in the process and the device layer of the SOI wafer completely, and etching silicon of the intermediate layer of the SOI wafer by using deep silicon by using silicon nitride in the step S31 and silicon oxide in the step S32 respectively;

S311, etching silicon oxide on the back, etching monocrystalline silicon by deep silicon, and stopping at the buried oxide layer; in deep silicon etching, the etching time is controlled according to the actual etching condition until the silicon dioxide layer is stopped;

S312, etching the buried oxide layer in the middle of the SOI wafer to release the device. And (3) finishing the release, namely finishing the cutting of the sensor by laser cutting along the reserved cutting path.

The working principle of the invention is as follows:

The sensing principle of the MEMS three-dimensional force sensor with adjustable force sensitivity is realized based on a silicon-based piezoresistive effect and a cantilever structure. The piezoresistive effect is a physical phenomenon, which is a phenomenon in which when a semiconductor is subjected to stress, energy in an energy band changes due to the stress, and energy in an energy valley moves, so that the resistivity of the semiconductor changes. In the micro-elastic range, the piezoresistive effect of the semiconductor material is reversible. Based on the reversible piezoresistance effect, the invention builds a signal conversion bridge between the mechanical signals and the electric signals. When an external force is applied to the sensor, the cantilever beam 302 of the force sensitive layer 300 deforms, and stress concentration occurs at the end of the cantilever beam 302, i.e. the end far from the center of the force sensitive layer 300, so that the resistance value of the piezoresistive region at the end of the cantilever beam 302 changes. By measuring the change in the resistance value, pressure information can be obtained. And the Wheatstone bridge circuit is used as a detection circuit, and the stress is determined by detecting the output voltage signal of the bridge. When the MEMS three-dimensional force sensor is subjected to vertical load, namely when the MEMS three-dimensional force sensor is subjected to normal force, the normal force has consistent influence on the four cantilever beams 302, and the average resistance of the cantilever beams 302 can be used for detection; when the MEMS three-dimensional force sensor is subjected to horizontal load, namely when the MEMS three-dimensional force sensor is subjected to tangential force, the tangential force causes inconsistent resistance change of the cantilever beams 302, and the detection can be performed through the change difference of the resistance values of the cantilever beams 302 at two sides.

The principle of force sensitivity adjustment of the MEMS three-dimensional force sensor is as follows: the elastic layer 100 is composed of PDMS and liquid metal, and the phase states of the liquid metal of the elastic layer 100 are different at different temperatures, so that the whole equivalent Young modulus of the elastic layer 100 is changed, and the deformation generated during stress is different, so that the deformation of the cantilever beam 302 of the sensitive layer 300 is different, and the adjustment of the output signal of the sensor is realized. In the manufacturing of the elastic layer 100, a resistance wire is wound on the surface of the liquid metal layer 102 to control the phase state of the liquid metal, so as to further realize the adjustable sensitivity of the sensor.

From the above, the elastic layer 100 in the MEMS three-dimensional force sensor provided by the present invention is an important component of the induced force, and the change of young's modulus thereof directly affects the conduction and deformation of the force. By controlling the Young's modulus, the stiffness of the elastic layer 100 can be adjusted, thereby changing the sensitivity of the sensor to force. When the Young's modulus of the elastic layer 100 is higher, the sensor is more sensitive to external force and can detect smaller force changes; and when the Young's modulus of the elastic layer 100 is lower, the sensitivity of the sensor to force is lower to accommodate processing larger force signals.

When the MEMS three-dimensional force sensor is applied to palpation operation, a surgeon needs to identify early tumors or suspicious lesion areas in a small range by using a sensor with high sensitivity, and needs to identify subcutaneous deep nodules by using a sensor with a large range, so that the large range and the high sensitivity cannot be achieved, the sensitivity and the range of the probe are required to be intelligently adjustable, the MEMS three-dimensional force sensor with adjustable sensitivity is integrated into the palpation probe, and the sensitivity adjustment of the probe sensitivity and the range-adjustable surgical clamp is further critical to the enhancement of the safety of tissues by adjusting the sensitivity of the sensor. When the surgical clamp is used for a surgical suture needle, a wide range is preferable, when the surgical clamp is used for clamping tissues, a high-sensitivity smaller range is preferable, and similarly, a MEMS three-dimensional force sensor with adjustable sensitivity is integrated on the clamp, and the sensitivity of the surgical clamp is further adjustable by adjusting the sensitivity and the range of the sensor.

In the description of the embodiments of the present invention, it should also be noted that, unless explicitly specified and limited otherwise, the terms "disposed," "connected," and "connected" should be construed broadly, and may be, for example, fixedly connected, detachably connected, or integrally connected; can be mechanically or electrically connected; can be directly connected or indirectly connected through an intermediate medium, and can be communication between two elements. The specific meaning of the above terms in the present invention will be understood in specific cases by those of ordinary skill in the art.

It is apparent that the above examples are given by way of illustration only and are not limiting of the embodiments. Other variations and modifications of the present invention will be apparent to those of ordinary skill in the art in light of the foregoing description. It is not necessary here nor is it exhaustive of all embodiments. And obvious variations or modifications thereof are contemplated as falling within the scope of the present invention.

Claims

1.A MEMS three-dimensional force sensor, comprising:

An elastic layer (100) comprising a surface layer (101), a liquid metal layer (102) and a first substrate (104); the liquid metal layer (102) is arranged between the surface layer (101) and the first substrate (104), and the liquid metal layer (102) is provided with a resistance wire (103); wherein the Young's modulus of the elastic layer (100) is controlled by controlling the phase state of the liquid metal layer (102);

A force transmission layer (200) comprising a second substrate (201) attached to the first substrate (104), the second substrate (201) being provided with a plurality of microcontact units (202); and, the resistance wire (103) extends along a first direction and is connected with the second substrate (201);

A force sensitive layer (300) comprising a third substrate (301) attached to the second substrate (201), the third substrate (301) being provided with a plurality of cantilever beams (302); wherein a plurality of said cantilever beams (302) are arranged opposite at least part of said microcontact units (202);

When an external force is applied to the elastic layers (100) with different Young's moduli, the elastic layers (100) with high Young's moduli deform relatively less, and thus the phase change transferred to the force-sensitive layer (300) is smaller, so that the force-sensitive layer (300) generates a smaller signal output.

2. The MEMS three-dimensional force sensor of claim 1, wherein the material of the surface layer (101) of the elastic layer (100) and the first substrate (104) is polydimethylsiloxane.

3. The MEMS three-dimensional force sensor of claim 1, wherein the material of the second substrate (201) of the force transfer layer (200) is polydimethylsiloxane.

4. The MEMS three-dimensional force sensor of claim 1, wherein the plurality of microcontact units (202) each extend in a thickness direction of the force transmission layer (200), and the distances by which the plurality of microcontact units (202) extend are the same.

5. The MEMS three-dimensional force sensor of claim 1, wherein the end of the microcontact unit (202) contacting the cantilever beam (302) is a tip contact.

6. The MEMS three-dimensional force sensor of claim 1, wherein the third substrate (301) defines a plurality of cavities for mounting the cantilever beams (302), one end of the cantilever beams (302) abuts against an inner wall of the cavities, and the other end of the cantilever beams (302) is suspended in the cavities.

7. The MEMS three-dimensional force sensor of claim 6, wherein the third substrate (301) is further provided with a plurality of electrode micro-channels of the same number as the cantilever beams (302), the electrode micro-channels being covered with a conductive metal material.

8. The MEMS three-dimensional force sensor according to claim 1, wherein the second substrate (201) is provided with a positioning post (203), the third substrate (301) is provided with a positioning hole (303), and the positioning post (203) is inserted into the positioning hole (303).

9. A method for preparing a MEMS three-dimensional force sensor according to any one of claims 1-8, comprising the steps of:

s1, manufacturing an elastic layer (100);

S11, dropwise adding a PDMS solution into a first die, and curing to obtain a surface layer (101);

S12, pouring the liquid metal solution into the first die in the step S11, and solidifying to obtain a liquid metal layer (102);

s13, placing a resistance wire (103) on the surface of the liquid metal layer (102) obtained in the step S12;

s16, placing the liquid metal layer (102) prepared in the step S13, the first PDMS unit prepared in the step S14 and the second PDMS unit prepared in the step S15 in a fourth mold, dripping a PDMS solution, and curing to obtain the elastic layer (100) with the substrate (104);

S2, etching a microcontact unit (202) on the surface of a second substrate (201), coating PDMS solution on the surface of the second substrate (201), and curing to obtain a force transmission layer (200);

And S3, etching a cantilever beam (302) on the surface of the third substrate (301) to obtain the force sensitive layer (300).

10. The method of claim 9, wherein the first mold is a square with a bottom surface of 320 μm x 320 μm and a groove depth of 200 μm; the second die is square with the bottom surface of 400 mu m multiplied by 400 mu m, and the depth of the groove is 100 mu m; the third die is square with the bottom surface of 400 mu m multiplied by 400 mu m, and the depth of the groove is 300 mu m; the fourth die is square with the bottom surface of 400 mu m multiplied by 400 mu m, and the depth of the groove is 200 mu m.