Electrostatic and electrothermal driving combined two-degree-of-freedom micro gripper and preparation method thereof

Abstract

The invention discloses an electrostatic and electrothermal driving combined two-degree-of-freedom micro gripper and a preparation method thereof, and belongs to the field of micro electro mechanical systems. The electrostatic and electrothermal driving combined two-degree-of-freedom micro gripper mainly comprises an outer frame and an inner frame arranged on the inner side of the outer frame; the electric heating driving structure is connected between the outer frame and the inner frame; the electrostatic driving structure and the clamp holder body are arranged in the inner frame, and the electrostatic driving structure is connected with the clamp holder body; wherein the electric heating driving structure is used for controlling the inner frame comprising the holder body and the electrostatic driving structure to perform out-of-plane movement; the electrostatic driving structure is used for controlling the holder body to move in a plane, and in-plane and out-of-plane two-degree-of-freedom control over a tiny object is achieved.

Description

Technical Field

[0001] The present invention relates to the field of micro-electromechanical systems, and in particular to a two-degree-of-freedom micro-gripper combining electrostatic and electrothermal drive and a design and preparation method thereof. Background Art

[0002] In recent years, with the rapid development of the micro-electromechanical systems (MEMS) industry, micro-grippers, a key component of MEMS, have been widely used in the fields of biomedicine, aerospace, micro-assembly, and military. When using micro-grippers to clamp tiny objects such as cells and micro-machines, they usually need to be rotated, transferred, assembled, and other operations. These operations inevitably involve lifting and lowering the clamped objects, such as out-of-plane movements. However, existing two-degree-of-freedom micro-grippers can often only perform in-plane movements such as clamping and rubbing. Out-of-plane movements require the help of other micro-manipulation platforms, which leads to problems such as complex and inefficient operations on tiny objects. Therefore, it is very important to develop a micro-gripper that can perform both in-plane and out-of-plane operations. Summary of the invention

[0003] The purpose of the present invention is to overcome the problems existing in the prior art and to provide a two-degree-of-freedom micro-gripper combining electrostatic and electrothermal drive and a design and preparation method thereof, so as to realize in-plane and out-of-plane two-degree-of-freedom manipulation of tiny objects.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] In a first aspect, a two-degree-of-freedom micro-gripper combining electrostatic and electrothermal drive is provided, comprising:

[0006] An outer frame and an inner frame arranged inside the outer frame;

[0007] An electrothermal drive structure connected between the outer frame and the inner frame;

[0008] An electrostatic drive structure and a clamp body are arranged in the inner frame, and the electrostatic drive structure is connected to the clamp body;

[0009] The electrothermal drive structure is used to control the inner frame including the clamp body and the electrostatic drive structure to perform out-of-plane movement; and the electrostatic drive structure is used to control the clamp body to perform in-plane movement.

[0010] In some embodiments, an electrical insulation groove is provided on the inner frame.

[0011] In some embodiments, support structures are provided under the outer frame and the inner frame, wherein the thickness of the inner frame support structure is smaller than that of the outer frame support structure, so as to reserve space for the inner frame including the clamp body to move out of the plane.

[0012] In some embodiments, the electrothermal driving structure is a lateral shift free (LSF) type electrothermal driving structure, and the electrostatic driving structure is a comb-tooth type electrostatic driving structure.

[0013] In some embodiments, the electrothermal drive structure is composed of three driving arms and two straight arms, wherein the three driving arms are each composed of four Bimorph connecting arms of equal length and width, the length of the two driving arms close to the inner frame and the outer frame is 1 / 2 of the length of the middle driving arm, and the length of the two straight arms is equal. The materials of the Bimorph connecting arms are SiO2 / Pt (heating resistor) / SiO2 (upper insulating material) / Al) from bottom to top, and the materials of the straight arms are SiO2 / Pt / SiO2 from bottom to top.

[0014] In some embodiments, the electrostatic drive structure includes a support beam, fixed comb teeth and movable comb teeth, the fixed comb teeth are connected to the inner frame, and the movable comb teeth are connected to the clamp body through the support beam.

[0015] In some embodiments, the clamp body comprises a clamp arm and a jaw, wherein the clamp body is grounded via a wire when in a working state.

[0016] In a second aspect, a design method for a two-degree-of-freedom micro-gripper is provided, comprising:

[0017] The magnitude of the vertical and horizontal displacements generated by the electrothermal drive structure maintains a certain linear relationship with the magnitude of the input voltage, and the horizontal height of the clamp body is controlled by controlling the magnitude of the input voltage; the magnitude of the voltage input to the electrostatic drive structure is in a quadratic curve relationship with the magnitude of the displacement of the tip of the clamp body, and the magnitude of the input voltage is less than its pull-in voltage; the clamp body is grounded.

[0018] In the third aspect, a method for preparing a two-degree-of-freedom micro-gripper combining electrothermal and electrostatic drive is provided, which is prepared by SOI wafer, the device layer material is Si, the substrate layer material is Si, and the electrostatic comb teeth of the gripper body and the electrostatic drive structure are electrically insulated by the SiO2 buried oxide layer under the electrical insulation groove. Furthermore, a preparation process of the two-degree-of-freedom micro-gripper is given, which is as follows:

[0019] Step 1: On the front of the SOI substrate, a 2μm SiO2 thin layer is grown using a plasma enhanced chemical vapor deposition (PECVD) process as an insulating layer and the bottom layer of the Bimorph drive arm, and then RIE is used to etch away some areas for Al routing and through holes in the device layer Si;

[0020] Step 2: Based on the above, a 100nm thick Pt layer is sputtered by magnetron sputtering, which is peeled off to form the heating resistor of the Bimorph drive arm, and then a thin SiO2 layer is grown on the Pt resistor for electrical insulation;

[0021] Step 3: Then, a 2 μm thick Al layer is sputtered thereon by magnetron sputtering, and the Al layer and electrodes of the Bimorph drive arm are peeled off;

[0022] Step 4: Grow a 2μm SiO2 film on the bottom of the SOI substrate to act as a mask for DRIE etching, and then use RIE technology to etch a certain area to expose the bottom Si except the inner frame 5. Then use DRIE technology to etch the substrate Si until the buried oxide layer 11 is etched. At this time, the middle area forms a step of a certain height with its surroundings due to the blocking of the SiO2 film;

[0023] Step 5: Use DRIE isotropic technology to etch the device layer Si on the front side to release the device, and then slice it to obtain a single chip.

[0024] It should be further explained that the technical features corresponding to the above options can be combined or replaced with each other to form a new technical solution if there is no conflict.

[0025] Compared with the prior art, the present invention has the following beneficial effects:

[0026] (1) The present invention utilizes the electrothermal drive structure to control the inner frame including the clamp body and the electrostatic drive structure to perform out-of-plane movements such as lifting and lowering, and uses the electrostatic drive structure to control the clamp body to perform in-plane movements such as clamping and releasing, thereby realizing in-plane and out-of-plane two-degree-of-freedom control of tiny objects.

[0027] (2) The present invention performs grounding treatment on the clamping arm of the clamping body, which can lead out the charges on the clamping arm and the surface of the clamped object, effectively avoiding the adhesion problem caused by electrostatic force when operating microscopic objects.

[0028] (3) The thickness of the inner frame support structure of the present invention is smaller than that of the outer frame support structure, and a certain space is reserved for the drive outside the inner frame surface.

[0029] (4) The electrothermal drive structure of the micro-gripper proposed in the present invention adopts an LSF type drive structure, which can provide the inner frame with horizontal vertical displacement without lateral displacement. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A schematic diagram of the basic structure of a two-degree-of-freedom micro-gripper combining electrostatic and electrothermal drive according to an embodiment of the present invention;

[0031] Figure 2A schematic diagram of the electrostatic drive structure of a two-degree-of-freedom micro-gripper shown in an embodiment of the present invention;

[0032] Figure 3 A schematic diagram of the cross-sectional structure of a two-degree-of-freedom micro-gripper according to an embodiment of the present invention;

[0033] Figure 4 A schematic diagram of the electrothermal drive structure of a two-degree-of-freedom micro-gripper according to an embodiment of the present invention;

[0034] Figure 5 A schematic diagram of the back cavity structure of a two-degree-of-freedom micro-gripper according to an embodiment of the present invention;

[0035] Figure 6 A simplified schematic diagram of an electrostatic drive structure according to an embodiment of the present invention;

[0036] Figure 7 The relationship between the horizontal and vertical displacements of the clamp and the driving voltage is shown in the embodiment of the present invention;

[0037] Figure 8 The relationship between the displacement of the tip of the single-sided clamping arm and the driving voltage is shown in an embodiment of the present invention;

[0038] Fig. 9 The figure is a flow chart for preparing a two-degree-of-freedom micro-gripper according to an embodiment of the present invention.

[0039] In the figure: 1. Clamp body; 2. Support beam in electrostatic drive structure; 3. Electrostatic comb tooth structure; 3-1. Fixed comb teeth; 3-2. Moving comb teeth; 4. Electrical insulation grooves; 5. Inner frame; 6. Electrothermal drive structure; 6-1 / 6-2 / 6-3. Drive arms; 6-4 / 6-5. Straight arms; 7. Al leads; 8. Outer frame; 9. Outer frame support structure; 10. Inner frame support structure; 11. Buried oxide layer. DETAILED DESCRIPTION

[0040] The technical solution of the present invention is clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present application described and shown in the accompanying drawings can be arranged and designed in various configurations. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0041] It should be noted that the defects existing in the solutions in the above-mentioned prior art are the results obtained by the inventor after practice and careful research. Therefore, the discovery process of the above-mentioned problems and the solutions proposed in the embodiments of the present application for the above-mentioned problems below should all be the contributions made by the inventor to the present application in the process of invention and creation, and should not be understood as technical contents known to technical personnel in this field.

[0042] In view of the technical problems pointed out in the background technology, the embodiments provided by the present invention are as follows:

[0043] In an exemplary embodiment, referring to Figure 1-Figure 5 , a two-degree-of-freedom micro-gripper combining electrostatic and electrothermal drive is provided, wherein reference numeral 1 represents a gripper body, which is made of Si and includes a gripper arm and a jaw, and the gripper arm is a straight arm; reference numerals 2 and 3 constitute an electrostatic drive structure to control the closing and opening operations of the gripper body 1, reference numeral 2 is a support beam in the electrostatic drive structure, and reference numeral 3 is an electrostatic comb structure, Figure 2 3-1 is a fixed comb tooth, which is directly connected to the inner frame 5, and 3-2 is a movable comb tooth, which is connected to the clamp 1 through the support beam 2. During the electrostatic drive process, the electrostatic comb teeth 3 are driven by voltage, and the fixed comb teeth 3-1 and the movable comb teeth 3-2 are attracted by the electrostatic force, and the support beam 2 will bend with the attraction of the electrostatic comb teeth 3, thereby transmitting the force to the clamp body 1 to control the opening and closing of the clamp body 1. Among them, 4 is an electrical insulation groove distributed on the inner frame, the purpose of which is to achieve electrical insulation between the overall structure from the clamping arm 1 to the movable comb teeth 3-2 and the fixed comb teeth 3-1. The structure runs through the silicon device layer of SOI (Silicon-On-Insulator), the device layer material is Si, and electrical insulation is achieved below through the SOI buried oxide layer 11, the buried oxide layer material is SiO2, and rigid connection is achieved by the SOI substrate silicon, the substrate silicon material is Si, such as Figure 3 As shown; 5 is the inner frame of the micro-gripper, which is Si / SiO2 / Si / SiO2 from bottom to top, and plays a bearing role when the electrothermal drive structure 6 lifts the gripper body 1, so that the gripper body 1 and the electrostatic drive structure are maintained on a horizontal plane. Figure 4As shown, the electrothermal drive structure 6 connects the outer frame 8 and the inner frame 5 respectively, and is composed of three sections of drive arms 6-1, 6-2, and 6-3 and two sections of straight arms 6-4 and 6-5. The three sections of drive arms are each composed of four sections of Bimorph connecting arms with equal length and width. The three sections of Bimorph connecting arms are SiO2 / Pt / SiO2 / Al from bottom to top, and are used for electrothermal drive. The length of the drive arm 6-2 is twice that of the drive arms 6-1 and 6-3. The two sections of straight arms 6-4 and 6-5 are of equal length, and are Si / SiO2 / Pt / SiO2 from bottom to top. When the electrothermal drive structure 6 is working, the Bimorph drive arms are bent by the heat, causing the inner frame to perform horizontal and vertical movements without lateral displacement; reference numeral 7 is an Al lead; the outer frame 8 is Si / SiO2 / Si / SiO2 from bottom to top, providing support for the entire micro-gripper; Figure 5 It is a bottom view of the micro-gripper, wherein numbers 9 and 10 are support structures under the outer frame 8 and the inner frame 5 respectively, which are the substrate silicon layer in the SOI wafer. The thickness of the silicon layer under the inner frame is less than that under the outer frame, and a certain space is reserved for the driving of the inner frame 5.

[0044] Specifically, the basic principle of the micro-gripper is to use the LSF (Lateral Shift Free) type electrothermal drive structure 6 to control the inner frame 5 including the gripper body 1 and the electrostatic drive structure to perform out-of-plane movements such as lifting and lowering, and to control the micro-gripper to perform in-plane movements such as clamping and releasing through the comb-tooth type electrostatic drive structure, so as to realize the in-plane and out-of-plane two-degree-of-freedom manipulation of tiny objects.

[0045] Furthermore, the main function of the electrothermal drive structure 6 is to enable the gripper body 1 to perform out-of-plane movement, completing the lifting or lowering operation involved in the gripper operation. The basic principle of electrothermal drive is to generate Joule heat by applying voltage to the heating resistor Pt in the Bimorph drive arm. Due to the different thermal expansion coefficients of the SiO2 and Al layers in the Bimorph structure, the drive arm bends, thereby driving the micro gripper platform to lift or lower.

[0046] The driving angle formula of Bimorph is:

[0047]

[0048] Where L B and t b are the length and thickness of the Bimorph actuator arm, Δα is the difference in thermal expansion coefficients between the two layers of materials that make up the Bimorph actuator arm, ΔT is the temperature difference, and β is the curvature coefficient and the thickness of the two Bimorph materials, t i and the biaxial elastic modulus E i The expression is:

[0049]

[0050] Equivalent elastic modulus E i The expression is:

[0051]

[0052] Where E i is the Young's modulus of the material, v i is the Poisson’s ratio of the material.

[0053] The electrothermal drive structure 6 of the micro-gripper proposed in the present invention adopts an LSF type drive structure, which satisfies the length L of the two straight arms 6-4 and 6-5. Ri When the lengths of Bimorph 6-1 and Bimorph 6-3 are equal and half of the length of Bimorph 6-2 in the three-segment Bimorph, the bending angles Δθ1 and Δθ3 generated by Bimorph 6-1 and Bimorph 6-3 under the same temperature difference are the same, which is half of the bending angle Δθ2 generated by Bimorph 6-2. At this time, the LSF type drive structure can provide the inner frame 5 with horizontal vertical displacement without lateral displacement, and the vertical displacement output that can be achieved is:

[0054] ΔH LSF =L R1 ·sinΔθ1+L R2 ·sinΔθ3=2·L R ·sinΔθ 4)

[0055] Electrostatic drive structure such as Figure 2 As shown, in the working state, a positive voltage is applied to the fixed comb teeth 3-1, and the movable comb teeth 3-2 are grounded. Due to the Coulomb force, an attractive force is generated between the comb teeth, thereby driving the middle beam of the movable comb teeth 3-2 to move to the right, the support beam 2 is bent, and the clamping arm of the clamp body 1 is pushed to produce a clamping movement. A clamping arm of the micro-gripper proposed by the present invention is driven by two comb structures, each of which has n comb teeth. Therefore, the magnitude of the electrostatic force generated on a single clamping arm is:

[0056]

[0057] Where t is the thickness of each tooth, ε is the dielectric constant of air, d is the gap between two teeth, and V is the voltage applied between the teeth.

[0058] The electrostatic drive structure can be simplified as follows Figure 6 As shown, the Coulomb force generated by the electrostatic comb teeth during operation causes the four support beams 2 to bend, thereby driving the clamping arm to produce a clamping action. The total spring coefficient generated by the four support beams 2 can be equivalent to:

[0059]

[0060] where E is the Young's modulus of silicon, t is the thickness of the support beam, and w f is the width of the support beam, l f is the length of the support beam. The spring constant k of the clamping arm g for:

[0061]

[0062] Among them, w g and l b are the width and length of the support beam 2 below the clamping arm, l F is the distance from the connecting beam of the clamping arm and the comb structure to the supporting beam 2 below the clamping arm, w g is the width of the clamping arm, l u = l F -l b .

[0063] Therefore, the total spring constant produced by the four support beams 2 and the clamping arm is:

[0064] k=k f +k g (8)

[0065] According to Hooke's law, the total displacement x generated by the electrostatic drive at the tip of the single-sided clamping arm is:

[0066]

[0067] Combining equations (5) to (9), we can obtain:

[0068]

[0069] In the present design, the relationship between the vertical displacement of the electrothermal driven inner frame 5 and the input voltage and the relationship between the displacement of the tip of the clamping arm and the input voltage can be simulated by finite element analysis software.

[0070] In addition, the present invention grounds the clamp body 1, specifically, the clamping arm of the clamp body 1 is grounded, which can lead out the charges on the clamping arm and the surface of the clamped object, effectively avoiding adhesion problems caused by electrostatic force when operating microscopic objects.

[0071] In another exemplary embodiment, a design method of the above-mentioned two-degree-of-freedom micro-gripper is provided. Specifically, the present invention needs to meet three conditions in order to complete the two-degree-of-freedom clamping and release operation of the micro-object. First, the vertical horizontal displacement size generated by the electrothermal drive structure 6 needs to maintain a certain linear relationship with the size of the input voltage, so that the horizontal height of the micro-gripper can be controlled by controlling the size of the input voltage. Second, the voltage size input to the electrostatic comb structure 3 needs to be in a certain relationship with the displacement size of the tip of the clamping arm of the clamp, and the input voltage size needs to be less than its pull-in voltage, so as to prevent adhesion between the comb teeth. Third, the object clamped by the micro-gripper is usually in the micron and nanometer order. At this scale, due to the effects of van der Waals force, surface tension, and electrostatic force, adhesion will occur between the micro-objects, resulting in the failure of the clamping and release operations. Therefore, when designing the micro-gripper, it is necessary to ground the clamping arm to release the charge on the clamping arm and the clamped object to prevent the object from being adhered due to electrostatic action. The micro-gripper is prepared using an SOI wafer, and an electrically insulating groove 4 is etched between the clamping arm, the movable comb teeth 3-2, the support beam 2 and other structures of the inner frame 5 of the clamp body 1. This layer of groove is the device layer of the etched SOI wafer, and the device layer material is Si. The buried oxide layer material of the SOI wafer is SiO2, which has a good electrical insulation effect, so the SOI buried oxide layer 11 is selected for electrical isolation. At the same time, a certain thickness of the substrate silicon layer is retained below the connection between the movable comb tooth support beam 2 and the inner frame 5 as the connection between the clamping arm and the inner frame 5, and to ensure that the device has a certain rigidity.

[0072] The simulation curve results of the horizontal height of the clamp body 1 and the voltage of the input electric heating drive structure 6 are as follows: Figure 7 As shown, when the voltage input to the electrothermal drive structure 6 is greater than 1V, the horizontal and vertical displacements of the clamp are linearly related to the input voltage.

[0073] In order to simplify the calculation, when simulating the displacement of the clamping arm tip of the clamping body 1 with voltage change, the electrothermal drive part is removed and only the single-sided clamping arm including the electrostatic drive comb teeth 3 is simulated. The results are as follows: Figure 8 As shown, as expected, the displacement of the gripper arm tip has a quadratic relationship with the input voltage.

[0074] Furthermore, the preparation process of the two-degree-of-freedom micro-gripper combining electrothermal and electrostatic drive is given as follows:

[0075] Step 1: On the front of the SOI substrate, a 2μm SiO2 thin layer is grown using the plasma enhanced chemical vapor deposition (PECVD) process as an insulating layer and the bottom layer of the Bimorph drive arm. Then, RIE is used to etch away some areas for Al routing and through holes in the device layer Si, such as Fig. 9 (a) and Fig. 9 (b)

[0076] Step 2: Based on the above, a 100nm thick Pt layer is sputtered by magnetron sputtering, which is peeled off to form the heating resistor of the Bimorph drive arm, and then a thin SiO2 layer is grown on the Pt resistor for electrical insulation, such as Fig. 9 (c) Fig. 9 (d)

[0077] Step 3: Then, a 2 μm thick Al layer is sputtered thereon by magnetron sputtering, and the Al layer and electrodes forming the Bimorph drive arm are peeled off, as shown in FIG. Fig. 9 (e)

[0078] Step 4: Grow a 2μm SiO2 film on the bottom of the SOI substrate to act as a mask for DRIE etching, and then use RIE technology to etch a certain area to expose the bottom Si except the inner frame 5. Then use DRIE technology to etch the substrate Si until the buried oxide layer 11 is etched. At this time, the middle area forms a step of a certain height with its surroundings due to the blocking of the SiO2 film, such as Fig. 9 (f) Fig. 9 (g) Fig. 9 (h) and Fig. 9 (i) as shown;

[0079] Step 5: Use DRIE isotropic technology to etch the device layer Si on the front side to release the device, and then slice to obtain a single chip. Fig. 9 (j) as shown.

[0080] The above specific implementation methods are detailed descriptions of the present invention. It cannot be determined that the specific implementation methods of the present invention are limited to these descriptions. For ordinary technicians in the technical field to which the present invention belongs, several simple deductions and substitutions can be made without departing from the concept of the present invention, which should be regarded as belonging to the protection scope of the present invention.

Claims

1. A two-degree-of-freedom micro-gripper combining electrostatic and electrothermal drive, characterized in that: include: An outer frame and an inner frame arranged inside the outer frame; An electrothermal drive structure connected between the outer frame and the inner frame; An electrostatic drive structure and a clamp body are arranged in the inner frame, and the electrostatic drive structure is connected to the clamp body; The electrothermal drive structure is used to control the inner frame including the clamp body and the electrostatic drive structure to perform out-of-plane movement; and the electrostatic drive structure is used to control the clamp body to perform in-plane movement.

2. The two-degree-of-freedom micro-gripper according to claim 1, characterized in that: The inner frame is provided with an electrical insulation groove.

3. The two-degree-of-freedom micro-gripper according to claim 1, characterized in that: Support structures are provided under the outer frame and the inner frame, wherein the thickness of the inner frame support structure is smaller than that of the outer frame support structure, so as to reserve space for the inner frame including the clamp body to move out of the plane.

4. The two-degree-of-freedom micro-gripper according to claim 1, characterized in that: The electrothermal drive structure is a non-lateral displacement type electrothermal drive structure, and the electrostatic drive structure is a comb-tooth type electrostatic drive structure.

5. The two-degree-of-freedom micro-gripper according to claim 4, characterized in that: The electrothermal drive structure consists of three drive arms and two straight arms, wherein the three drive arms are each composed of four Bimorph connecting arms of equal length and width, the length of the two drive arms close to the inner frame and the outer frame is 1 / 2 of the length of the middle drive arm, and the length of the two straight arms is equal. The materials of the Bimorph connecting arms are SiO2 / Pt / SiO2 / Al) from bottom to top, and the materials of the straight arms are SiO2 / Pt / SiO2 from bottom to top.

6. The two-degree-of-freedom micro-gripper according to claim 4, characterized in that: The electrostatic drive structure comprises a support beam, fixed comb teeth and movable comb teeth, wherein the fixed comb teeth are connected to the inner frame, and the movable comb teeth are connected to the clamp body through the support beam.

7. The two-degree-of-freedom micro-gripper according to claim 1, characterized in that: The clamp body comprises a clamp arm and a jaw, wherein the clamp body is grounded through a wire in a working state.

8. The design method of a two-degree-of-freedom micro-gripper according to any one of claims 1 to 7, characterized in that: include: The magnitude of the vertical and horizontal displacements generated by the electrothermal drive structure maintains a certain linear relationship with the magnitude of the input voltage, and the horizontal height of the clamp body is controlled by controlling the magnitude of the input voltage; the magnitude of the voltage input to the electrostatic drive structure is in a quadratic curve relationship with the magnitude of the displacement of the tip of the clamp body, and the magnitude of the input voltage is less than its pull-in voltage; the clamp body is grounded.

9. A method for preparing a two-degree-of-freedom micro-gripper combining electrothermal and electrostatic drive as claimed in any one of claims 1 to 7, characterized in that: The device layer is made of Si and the substrate layer is made of Si. The electrostatic comb teeth of the gripper body and the electrostatic drive structure are electrically insulated by the SiO2 buried oxide layer under the electrical insulation groove. Furthermore, the preparation process of the two-degree-of-freedom micro gripper is given as follows: Step 1: On the front of the SOI substrate, a 2μm SiO2 thin layer is grown using a plasma enhanced chemical vapor deposition (PECVD) process as an insulating layer and the bottom layer of the Bimorph drive arm, and then RIE is used to etch away some areas for Al routing and through holes in the device layer Si; Step 2: Based on the above, a 100nm thick Pt layer is sputtered by magnetron sputtering, which is peeled off to form the heating resistor of the Bimorph drive arm, and then a thin SiO2 layer is grown on the Pt resistor for electrical insulation; Step 3: Then, a 2 μm thick Al layer is sputtered thereon by magnetron sputtering, and the Al layer and electrodes of the Bimorph drive arm are peeled off; Step 4: Grow a 2μm SiO2 film on the bottom of the SOI substrate to act as a mask for DRIE etching, and then use RIE technology to etch a certain area to expose the bottom Si except the inner frame 5. Then use DRIE technology to etch the substrate Si until the buried oxide layer 11 is etched. At this time, the middle area forms a step of a certain height with its surroundings due to the blocking of the SiO2 film; Step 5: Use DRIE isotropic technology to etch the device layer Si on the front side to release the device, and then slice it to obtain a single chip.

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