Silicon-based free space type optical MEMS accelerometer and manufacturing method thereof

Abstract

The invention provides a silicon-based free space type optical MEMS accelerometer and a manufacturing method, the upper layer of the accelerometer is a glass substrate free space optical sensitive structure, the lower layer of the accelerometer is a silicon-based horizontal axis MEMS sensitive structure, and the upper layer structure is fixed on the lower layer structure through a bonding process. Wherein the upper-layer optical sensitive structure consists of a pair of Michelson interferometers, a glass anchor point and a glass mass block; and the lower-layer MEMS sensitive structure consists of four groups of cantilever beams, a silicon anchor point and a silicon mass block. The lower layer MEMS sensitive structure converts the horizontal shaft input acceleration into the displacement of the silicon mass block, the displacement is synchronously transmitted to the glass mass block, and the pair of oppositely arranged Michelson interferometers converts the displacement into the reverse transformation of an interference light phase, so that the high-precision differential detection of the acceleration is realized. The micro-optical accelerometer scheme provided by the invention has the outstanding advantages of high detection sensitivity, strong common-mode error resistance and high integration level.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of micro-electro-mechanical system (MEMS) and micro-inertial instrument, and particularly relates to a silicon-based free-space optical MEMS accelerometer and a manufacturing method. BACKGROUND

[0002] Optical interference is a manifestation of light wave nature, and an optical interferometer based on the optical interference principle is one of classical high-precision measuring devices. Through the amplification effect of a small optical path difference, the optical interferometer can convert weak physical disturbance into high-sensitivity interference wave phase drift, so that the weak physical quantity can be detected. The Michelson interferometer based on double-arm interference is one of the types of interferometers commonly used for displacement physical quantity measurement. At present, the Michelson interferometer is generally realized based on a macro free-space optical system and is mainly used for the development of macro measuring instruments.

[0003] Micro-electro-mechanical system (MEMS) is a technology specially used for the miniaturization of physical instrument devices, and a MEMS accelerometer is a kind of micro sensor widely used in the fields of inertial navigation, attitude recognition, vibration monitoring and the like. The traditional MEMS accelerometer usually converts the displacement or deformation caused by acceleration into an electrical signal through a capacitive, piezoelectric or piezoresistive electrical method. This method is easily affected by interface noise, thereby limiting the detection precision. The free-space optical MEMS accelerometer realized by miniaturizing the Michelson interferometer through a micro-processing technology and combining the Michelson interferometer with a MEMS resonant sensitive structure can read out the displacement through an interference optical signal and has higher precision development prospects. Therefore, the free-space optical MEMS accelerometer is one of the key research directions of the current micro-inertial sensor. SUMMARY

[0004] The application aims to solve the technical problems of the prior art and provides a silicon-based free-space optical MEMS accelerometer and a manufacturing method.

[0005] The accelerometer adopts a double-layer bonding structure scheme combining an upper structure and a lower structure, wherein the upper structure is a glass substrate free-space optical sensitive structure, and the lower structure is a silicon-based horizontal axis MEMS sensitive structure.

[0006] The glass substrate free-space optical sensitive structure comprises a first Michelson interferometer, a second Michelson interferometer, a glass anchor point and a glass mass. The silicon-based horizontal axis MEMS sensitive structure comprises a first cantilever beam, a second cantilever beam, a third cantilever beam, a fourth cantilever beam, a silicon anchor point and a silicon mass.

[0007] The glass substrate free-space optical sensitive structure is a whole rectangular structure, wherein the glass mass is located at the center of the upper structure and is used to convert the acceleration into displacement; the glass mass is a rectangular structure, and rectangular grooves are formed at the lower left, lower right, upper left and upper right of the glass mass respectively for releasing the first, second, third and fourth cantilever beams; The glass anchor point is annular and located at the periphery of the glass mass.

[0008] The glass anchor point and the silicon anchor point are bonded, and the glass mass and the silicon mass are bonded.

[0009] The silicon mass is connected to the fixed silicon anchor point through the first, second, third and fourth cantilever beams, and when a horizontal acceleration signal a is input, the silicon mass generates horizontal displacement under the support of the first, second, third and fourth cantilever beams, and the glass mass synchronously generates the same displacement; The first Michelson interferometer comprises a first laser, a first beam splitter, a first reference mirror, a first detection mirror and a first photodetector; The second Michelson interferometer comprises a second laser, a second beam splitter, a second reference mirror, a second detection mirror and a second photodetector; The first and second detection mirrors are arranged on the left and right sides of the glass mass respectively; The first and second Michelson interferometers are arranged in reverse symmetry on the left upper part and right lower part of the upper structure respectively, so as to realize differential detection of acceleration.

[0010] The first and second Michelson interferometers provide free-space laser sources through the first and second lasers in the miniaturized free space respectively, and detect the intensity of interference light through the first and second photodetectors in the miniaturized free space respectively, so as to realize conversion of optical differential signals into electrical differential signals and realize integrated structure of the accelerometer.

[0011] The first incident light emitted by the first laser is equally divided into first reference incident light and first detection incident light at the first beam splitter, and the first reference incident light and the first detection incident light are reflected back when reaching the first reference mirror and the first detection mirror respectively, to generate first reference reflected light and first detection reflected light, the first reference reflected light and the first detection reflected light converge at the first beam splitter, optical interference occurs, and then first interference light is generated, which is received by the first photodetector and converted into an electrical signal; The first detection mirror is used for converting the horizontal displacement of the glass mass into the change of the reference arm length, further converting the optical path difference between the first detection incident light, the first detection reflected light and the first reference incident light, the first reference reflected light, and finally coupling the acceleration information into the phase of the first interference light; The second detection mirror is arranged on the right side of the glass mass, so that the second interference light generates the opposite phase information to the first interference light, forming differential detection; The optical paths of the first Michelson interferometer and the second Michelson interferometer are arranged in the glass anchor point, and are located on the left side and the right side of the anchor point, respectively; The first reference mirror, the second reference mirror, the first beam splitter and the second beam splitter are arranged on the groove side wall of the glass anchor point, the first reference mirror and the first beam splitter are located on the left side of the glass anchor point, and the second reference mirror and the second beam splitter are located on the right side of the glass anchor point; The first beam splitter and the second beam splitter are arranged obliquely, and the included angle between the first beam splitter and the first reference mirror and the included angle between the second beam splitter and the second reference mirror are both 45°; The center of the emission surface of the first laser is aligned with the center of the front surface of the first beam splitter; The center of the emission surface of the second laser is aligned with the center of the front surface of the second beam splitter; The first photodetector and the second photodetector are located on the upper left side and the lower right side of the glass anchor point, respectively; The center of the receiving surface of the first photodetector is aligned with the center of the back surface of the first beam splitter; The center of the receiving surface of the second photodetector is aligned with the center of the back surface of the second beam splitter.

[0012] The displacement of the glass mass will cause the right movement of the first detection mirror and the left movement of the second detection mirror, respectively, and further cause the decrease and increase of the first detection incident light path and the second detection incident light path, respectively, so as to realize the opposite change of the interference light intensity of the first Michelson interferometer and the second Michelson interferometer, and finally complete the optical differential detection of the input acceleration.

[0013] The silicon-based horizontal axis MEMS sensitive structure is a rectangular structure, and the length and width dimensions are the same as those of the upper layer structure; The silicon mass is located at the center of the upper layer structure and is a rectangular structure, and the length and width dimensions of the silicon mass are the same as those of the glass mass; The silicon anchor point is annular and located at the periphery of the silicon mass, and the length and width dimensions of the silicon anchor point are consistent with those of the glass anchor point, and the silicon anchor point plays a role of fixing and supporting; Rectangular grooves are formed in the lower right, lower left, upper left and upper right of the glass mass, respectively; The first cantilever beam, the second cantilever beam, the third cantilever beam and the fourth cantilever beam are arranged in rectangular grooves below the left, the right, the top left and the top right of the silicon mass block respectively, and are used for connecting the silicon mass block and the silicon anchor point; The first cantilever beam, the second cantilever beam, the third cantilever beam and the fourth cantilever beam are of the same structure and are each composed of two groups of folded beams and a T-shaped base, wherein the T-shaped base is connected with the silicon anchor point and serves as a fixed support, and the two groups of folded beams are connected to the inner side walls of the rectangular grooves of the silicon mass block and serve as elastic supports. A gap is arranged between the silicon mass block and the silicon anchor point, and the gap is greater than the displacement of the silicon mass block under the maximum acceleration.

[0014] The application further provides a manufacturing method of the silicon-based free-space optical MEMS accelerometer. Step 1, cleaning and preparing a glass substrate; Step 2, etching the glass substrate to form a glass mass block structure, an optical path and a gap between the glass mass block and the glass anchor point; Step 3, installing a mirror shadow mask and depositing a metal mirror coating layer by an electron beam evaporation or a magnetron sputtering process; Step 4, removing the mirror shadow mask to obtain a first reference mirror, a first detection mirror, a second reference mirror and a second detection mirror element; Step 5, installing a beamsplitter shadow mask and depositing a dielectric beamsplitter coating layer by an electron beam evaporation or a magnetron sputtering process; Step 6, removing the beamsplitter shadow mask to obtain a first beamsplitter and a second beamsplitter element; Step 7, anodically bonding the glass substrate with a lower structure silicon wafer; Step 8, etching the back of the glass substrate to release the gap between the glass mass block and the glass anchor point; Step 9, etching the silicon substrate to form a cantilever beam structure and release the silicon mass block structure; Step 10, obtaining a complete MEMS accelerometer structure.

[0015] Beneficial effects: (1) The application proposes to manufacture a micro optical path and an optical mirror substrate on an optical glass substrate by etching, to realize a micro optical mirror element by means of side wall coating, and to finally realize an integrated free-space micro interferometer on the glass substrate, thereby realizing the miniaturization of a macro interferometer; (2) The application combines an optical interferometer with MEMS technology to realize a miniaturized optical MEMS accelerometer, which has the advantages of high detection precision and high detection sensitivity of optical interference, and the advantages of high integration degree, high integration level and easy packaging of traditional MEMS technology; (3) The application adopts a pair of reverse symmetrical interferometers as acceleration detection mechanism, the interference light phase changes reversely with input acceleration, realizes optical differential detection mode, can effectively inhibit detection error caused by common mode interference, and enhances the reliability of the device; (4) The application adopts the mode that the interferometer and the MEMS resonant structure are independently processed on different substrates, then are integrally bonded, and then are released to realize the main structure of the optical MEMS accelerometer, the process flow is reasonable, the implementability is strong, and the realized MEMS accelerometer structure has high integration. BRIEF DESCRIPTION OF DRAWINGS

[0016] Figure 1 It is the overall structural diagram of the application.

[0017] Figure 2 It is the upper layer bottom view of the application.

[0018] Figure 3 It is the lower layer top view of the application.

[0019] Figure 4 It is the manufacturing process flow diagram of the application.

[0020] BRIEF DESCRIPTION OF DRAWINGS: 1, glass anchor point; 2, glass mass; 3, first Michelson interferometer; 4, second Michelson interferometer; 5, silicon anchor point; 6, silicon mass; 7, first cantilever beam; 8, second cantilever beam; 9, third cantilever beam; 10, fourth cantilever beam; 3-1, first laser; 3-2, first incident light; 3-3, first beam splitter; 3-4, first reference incident light; 3-5, first reference reflected light; 3-6, first detection incident light; 3-7, first detection reflected light; 3-8, first reference mirror; 3-9, first detection mirror; 3-10, first interference light; 3-11, first photodetector; 4-1, second laser; 4-2, second incident light; 4-3, second beam splitter; 4-4, second reference incident light; 4-5, second reference reflected light; 4-6, second detection incident light; 4-7, second detection reflected light; 4-8, second reference mirror; 4-9, second detection mirror; 4-10, second interference light; 4-11, second photodetector; 7-1, first cantilever beam base; 7-2, first folded beam; 7-3, second folded beam; 8-1, second cantilever beam base; 8-2, third folded beam; 8-3, fourth folded beam; 9-1, third cantilever beam base; 9-2, fifth folded beam; 9-3, sixth folded beam; 10-1, fourth cantilever beam base; 10-2, seventh folded beam; 10-3, eighth folded beam. DETAILED DESCRIPTION

[0021] The above and / or other aspects of the present application will become apparent and more readily appreciated from the following description, taken in conjunction with the accompanying drawings in which:

[0022] As shown in Figure 1 To achieve the above object, the present application provides a double-layer structure, wherein the upper layer is a glass substrate free-space optical sensing structure, and the lower layer is a silicon substrate horizontal-axis MEMS sensing structure, and the upper layer structure is bonded to the glass mass 2 through the glass anchor point 1 and to the silicon mass 6 through the silicon anchor point 5.

[0023] The upper layer glass substrate free-space optical sensing structure is composed of a first Michelson interferometer 3, a second Michelson interferometer 4, a glass anchor point 1 and a glass mass 2. The lower layer silicon substrate horizontal-axis MEMS sensing structure is composed of a first cantilever beam 7, a second cantilever beam 8, a third cantilever beam 9, a fourth cantilever beam 10, a silicon anchor point 5 and a silicon mass 6.

[0024] The silicon mass 6 is connected to the fixed silicon anchor point 5 through the first cantilever beam 7, the second cantilever beam 8, the third cantilever beam 9 and the fourth cantilever beam 10. When a horizontal-direction acceleration signal a is input, the silicon mass 6 generates a horizontal displacement under the support of the first cantilever beam 7, the second cantilever beam 8, the third cantilever beam 9 and the fourth cantilever beam 10. Further, the glass mass 2 is bonded on the silicon mass 6, and thus the same displacement is generated synchronously. The first Michelson interferometer 3 and the second Michelson interferometer 4 are arranged in reverse symmetry, wherein a first detection mirror 3-9 and a second detection mirror 4-9 are arranged on the left side and the right side of the glass mass 2 respectively. The above displacement will cause the right shift and the left shift of the first detection mirror 3-9 and the second detection mirror 4-9 respectively, and further cause the decrease of the optical path of the first detection incident light 3-6 and the first detection reflected light 3-7 and the increase of the optical path of the second detection incident light 4-6 and the second detection reflected light 4-7 respectively, so as to realize the reverse change of the interference light intensity of the first Michelson interferometer 3 and the second Michelson interferometer 4, and finally complete the optical differential detection of the input acceleration. The first Michelson interferometer 3 and the second Michelson interferometer 4 provide a free-space laser source through a miniaturized free-space first laser 3-1 and a second laser 4-1, and detect the interference light intensity through a miniaturized free-space first photoelectric detector 3-11 and a second photoelectric detector 4-11, so as to realize the conversion from the optical differential signal to the electrical differential signal, and realize the integrated structure of the MEMS accelerometer.

[0025] As shown in Figure 2As shown, the upper layer glass substrate free space optical sensitive structure is a whole rectangular structure, wherein the glass mass 2 is located at the center position of the upper layer structure, for converting the acceleration quantity into displacement quantity; the glass mass 2 is also a rectangular structure, and rectangular grooves are respectively opened at the lower left, lower right, upper left and upper right of the glass mass 2, for releasing the first cantilever beam 7, the second cantilever beam 8, the third cantilever beam 9 and the fourth cantilever beam 10 of the lower layer structure; the glass mass 2 is bonded with the lower layer silicon mass 6 as a whole, which is conducive to reducing the overall mechanical thermal noise of the MEMS accelerometer and increasing the detection accuracy of the MEMS accelerometer; the glass anchor point 1 is annular and located at the periphery of the glass mass 2, which is bonded with the lower layer silicon anchor point 5 as a whole, and plays a role of fixing support; the first Michelson interferometer 3 and the second Michelson interferometer 4 are respectively located at the upper left and lower right of the upper layer structure, and are arranged in reverse symmetry, for realizing differential detection of acceleration.

[0026] The first Michelson interferometer 3 is composed of a first laser 3-1, a first beam splitter 3-3, a first reference mirror 3-8, a first detection mirror 3-9 and a first photodetector 3-11; the first incident light 3-2 emitted by the first laser 3-1 is equally divided into the first reference incident light 3-4 and the first detection incident light 3-6 at the first beam splitter 3-3, and the two are reflected back when reaching the first reference mirror 3-8 and the first detection mirror 3-9 respectively, to generate the first reference reflected light 3-5 and the first detection reflected light 3-7, which are combined at the first beam splitter 3-3 to produce the first interference light 3-10, which is received by the first photodetector 3-11 and converted into an electrical signal; wherein the first detection mirror 3-9 is arranged on the left side of the glass mass 2, for converting the horizontal displacement of the glass mass 2 into the change of the reference arm length, and further converting it into the optical path difference between the first detection incident light 3-6, the first detection reflected light 3-7 and the first reference incident light 3-4, the first reference reflected light 3-5, and finally coupling the acceleration information into the phase of the first interference light 3-10.

[0027] The second Michelson interferometer 4 is composed of a second laser 4-1, a second beam splitter 4-3, a second reference mirror 4-8, a second detection mirror 4-9 and a second photodetector 4-11; the detection process of the second Michelson interferometer 4 is similar to that of the first Michelson interferometer 3; the second detection mirror 4-9 is arranged on the right side of the glass mass 2, so that the second interference light 4-10 generates phase information opposite to that of the first interference light 3-10, forming differential detection; the optical paths of the first Michelson interferometer 3 and the second Michelson interferometer 4 are arranged in the glass anchor point 1, respectively on the left side and the right side of the glass anchor point 1.

[0028] The first reference mirror 3-8, the second reference mirror 4-8, the first beam splitter 3-3 and the second beam splitter 4-3 are arranged on the groove side wall of the glass anchor point 1, and are respectively located on the left side and the right side of the glass anchor point 1; The first beam splitter 3-3 and the second beam splitter 4-3 are arranged obliquely, and the included angle between the first beam splitter 3-3 and the second reference mirror 3-8 and the second beam splitter 4-3 and the second reference mirror 4-8 is 45°. The first laser 3-1 and the second laser 4-1 are respectively located on the left side and the right side of the glass anchor point 1, and the center of the emitting surface is aligned with the center of the front surface of the first beam splitter 3-3 and the second beam splitter 4-3. The first photodetector 3-11 and the second photodetector 4-11 are respectively located on the upper left side and the lower right side of the glass anchor point 1, and the center of the receiving surface is aligned with the center of the back surface of the first beam splitter 3-3 and the second beam splitter 4-3.

[0029] As shown in Figure 3 The lower silicon-based horizontal axis MEMS sensitive structure is a rectangular structure as a whole, and the length and width dimensions are consistent with those of the upper structure. The silicon mass block 6 is located at the center of the upper structure and is also a rectangular structure, and the length and width dimensions are consistent with those of the upper glass mass block 2. The silicon anchor point 5 is annular and is located at the periphery of the silicon mass block 6, and the length and width dimensions are consistent with those of the upper glass anchor point 1, which serves as a fixed support. The first cantilever beam 7, the second cantilever beam 8, the third cantilever beam 9 and the fourth cantilever beam 10 are respectively arranged in the rectangular grooves on the lower left, lower right, upper left and upper right of the silicon mass block 6, and are used to connect the silicon mass block 6 and the silicon anchor point 5. The four groups of cantilever beam structures are completely consistent, and each group is composed of two groups of folded beams (the first group is the first folded beam 7-2, the second folded beam 7-3, the third folded beam 8-2 and the fourth folded beam 8-3, and the second group is the fifth folded beam 9-2, the sixth folded beam 9-3, the seventh folded beam 10-2 and the eighth folded beam 10-3) and a “T” type base (including the first cantilever beam base 7-1, the second cantilever beam base 8-1, the third cantilever beam base 9-1 and the fourth cantilever beam base 10-1). The first cantilever beam base 7-1, the second cantilever beam base 8-1, the third cantilever beam base 9-1 and the fourth cantilever beam base 10-1 are connected to the silicon anchor point 5 and serve as a fixed support. The first folded beam 7-2, the second folded beam 7-3, the third folded beam 8-2, the fourth folded beam 8-3, the fifth folded beam 9-2, the sixth folded beam 9-3, the seventh folded beam 10-2 and the eighth folded beam 10-3 are connected to the inner side wall of the rectangular groove of the silicon mass block 6 and serve as an elastic support. A gap is provided between the silicon mass block 6 and the silicon anchor point 5, and the gap is greater than the displacement of the silicon mass block 6 under the maximum acceleration.

[0030] As shown in Figure 4 The embodiment also provides a manufacturing method of the silicon-based free-space optical MEMS accelerometer, and the manufacturing method comprises the following steps: Step 1, cleaning and preparing the optical glass substrate; Step 2, etching the glass substrate to form the glass mass 2 structure, optical path, and gap between the glass mass 2 and the glass anchor 1; Step 3, installing a mirror shadow mask and depositing a metal mirror coating through an electron beam evaporation or magnetron sputtering process; Step 4, removing the mirror shadow mask to obtain the first reference mirror 3-8, first detection mirror 3-9, second reference mirror 4-8, and second detection mirror 4-9 elements; Step 5, installing a beamsplitter shadow mask and depositing a dielectric beamsplitter coating through an electron beam evaporation or magnetron sputtering process; Step 6, removing the beamsplitter shadow mask to obtain the first beamsplitter 3-3 and second beamsplitter 4-3 elements; Step 7, anodically bonding the above glass substrate to a silicon substrate; Step 8, etching the back of the glass substrate to release the gap between the glass mass 2 and the glass anchor 1; Step 9, etching the silicon substrate to form a cantilever beam structure and release the silicon mass 6 structure; Step 10, obtaining a complete MEMS accelerometer structure.

[0031] The present application provides a silicon-based free-space optical MEMS accelerometer and a manufacturing method. There are many methods and approaches to achieve the technical solution. The above description is only the preferred embodiment of the present application. It should be noted that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application. These improvements and refinements should also be considered within the scope of protection of the present application. The components not explicitly described in the embodiments can be implemented using existing technology.

Claims

1. A silicon-based free-space optical MEMS accelerometer, characterized in that: The accelerometer adopts a double-layer bonding structure scheme combining an upper structure and a lower structure, wherein the upper structure is a glass substrate free space optical sensitive structure, and the lower structure is a silicon-based horizontal axis MEMS sensitive structure.

2. The silicon-based free-space optical MEMS accelerometer according to claim 1, wherein: The glass substrate free-space optical sensitive structure comprises a first Michelson interferometer (3), a second Michelson interferometer (4), a glass anchor point (1) and a glass proof block (2); The silicon-based horizontal-axis MEMS sensitive structure comprises a first cantilever beam (7), a second cantilever beam (8), a third cantilever beam (9), a fourth cantilever beam (10), a silicon anchor point (5), and a silicon proof block (6).

3. The silicon-based free-space optical MEMS accelerometer according to claim 2, wherein: The glass substrate free space optical sensitive structure is a rectangular structure as a whole, wherein a glass mass block (2) is located at the center of the upper structure and is used to convert acceleration into displacement; the glass mass block (2) is a rectangular structure, and rectangular grooves are respectively provided at the lower left, lower right, upper left, and upper right of the glass mass block (2) for releasing the first cantilever beam (7), the second cantilever beam (8), the third cantilever beam (9), and the fourth cantilever beam (10).

4. The silicon-based free-space optical MEMS accelerometer according to claim 3, wherein: The glass anchor point (1) is annular and is located on the periphery of the glass mass block (2).

5. The silicon-based free-space optical MEMS accelerometer according to claim 4, wherein: The glass anchor point (1) and the silicon anchor point (5) are bonded together, and the glass mass block (2) and the silicon mass block (6) are bonded together.

6. The silicon-based free-space optical MEMS accelerometer according to claim 5, wherein: The silicon mass block (6) is connected to a fixed silicon anchor point (5) via a first cantilever beam (7), a second cantilever beam (8), a third cantilever beam (9), and a fourth cantilever beam (10). When a horizontal acceleration signal a is input, the silicon mass block (6) generates a horizontal displacement under the support of the first cantilever beam (7), the second cantilever beam (8), the third cantilever beam (9), and the fourth cantilever beam (10), and the glass mass block (2) will generate the same displacement synchronously. The first Michelson interferometer (3) comprises a first laser (3-1), a first beam splitter (3-3), a first reference reflector (3-8), a first detection reflector (3-9) and a first photodetector (3-11); The second Michelson interferometer (4) comprises a second laser (4-1), a second beam splitter (4-3), a second reference reflector (4-8), a second detection reflector (4-9) and a second photodetector (4-11); The first detection reflector (3-9) and the second detection reflector (4-9) are respectively arranged on the left and right sides of the glass mass block (2); The first Michelson interferometer (3) and the second Michelson interferometer (4) are respectively located at the upper left side and the lower right side of the superstructure, and are arranged in reverse symmetry, for realizing acceleration differential detection.

7. The silicon-based free-space optical MEMS accelerometer according to claim 6, wherein: The first Michelson interferometer (3) and the second Michelson interferometer (4) respectively provide a free-space laser source through a first laser (3-1) and a second laser (4-1) in a miniaturized free space. The first Michelson interferometer (3) and the second Michelson interferometer (4) respectively detect the intensity of interference light through a first photodetector (3-11) and a second photodetector (4-11) in a miniaturized free space, thereby realizing the conversion of optical differential signals into electrical differential signals and realizing the integrated and integrated structure of the accelerometer.

8. The silicon-based free-space optical MEMS accelerometer according to claim 7, wherein: The first incident light (3-2) emitted by the first laser (3-1) is equally split into a first reference incident light (3-4) and a first detection incident light (3-6) at the first spectroscope (3-3); the first reference incident light (3-4) and the first detection incident light (3-6) are respectively reflected along their original paths when reaching the first reference reflector (3-8) and the first detection reflector (3-9), thereby generating a first reference reflected light (3-5) and a first detection reflected light (3-7); the first reference reflected light (3-5) and the first detection reflected light (3-7) converge at the first spectroscope (3-3), causing optical interference, thereby generating a first interference light (3-10); the first interference light (3-10) is received by a first photodetector (3-11) and converted into an electrical signal; The first detection reflector (3-9) is used to convert the horizontal displacement of the glass mass (2) into a change in the length of the reference arm, and further convert it into an optical path difference between the first detection incident light (3-6), the first detection reflected light (3-7) and the first reference incident light (3-4), the first reference reflected light (3-5), and finally couple the acceleration information into the phase of the first interference light (3-10); The second detection reflector (4-9) is arranged on the right side of the glass mass block (2), so that the second interference light (4-10) generates phase information opposite to that of the first interference light (3-10), thereby forming differential detection; The optical paths of the first Michelson interferometer (3) and the second Michelson interferometer (4) are arranged within the glass anchor point (1), and are located on the left and right sides of the glass anchor point (1), respectively; The first reference reflector (3-8), the second reference reflector (4-8), the first beam splitter (3-3), and the second beam splitter (4-3) are arranged on the side wall of the groove of the glass anchor point (1); the first reference reflector (3-8) and the first beam splitter (3-3) are located on the left side of the glass anchor point (1), and the second reference reflector (4-8) and the second beam splitter (4-3) are located on the right side of the glass anchor point; The first beam splitter (3-3) and the second beam splitter (4-3) are arranged tilted, and the angle between the first beam splitter (3-3) and the first reference reflector (3-8), and the angle between the second beam splitter (4-3) and the second reference reflector (4-8) are both 45°; The center of the emission surface of the first laser (3-1) is aligned with the center of the front surface of the first beam splitter (3-3); The center of the emission surface of the second laser (4-1) is aligned with the center of the front surface of the second beam splitter (4-3); The first photodetector (3-11) and the second photodetector (4-11) are respectively located on the upper left side and the lower right side of the glass anchor point (1); The center of the receiving surface of the first photodetector (3-11) is aligned with the center of the back surface of the first beam splitter (3-3); The center of the receiving surface of the second photodetector (4-11) is aligned with the center of the back surface of the second beam splitter (4-3); The displacement of the glass mass (2) will respectively cause the first detection reflector (3-9) to move rightward and the second detection reflector (4-9) to move leftward, thereby respectively causing the optical path of the first detection incident light (3-6) and the optical path of the second detection incident light (4-6) to decrease and increase, thereby achieving anti-phase changes in the interference light intensity of the first Michelson interferometer (3) and the second Michelson interferometer (4), and finally completing the optical differential detection of the input acceleration.

9. The silicon-based free-space optical MEMS accelerometer according to claim 8, wherein: The silicon-based horizontal-axis MEMS sensitive structure is a rectangular structure as a whole, and its length and width are the same as those of the upper structure; The silicon mass block (6) is located at the center of the upper structure and has a rectangular structure. The length and width of the silicon mass block (6) are the same as those of the glass mass block (2); The silicon anchor point (5) is annular and is located on the periphery of the silicon mass block (6). The length and width of the silicon anchor point (5) are consistent with those of the glass anchor point (1), and plays a role of fixed support. The glass mass block (2) is provided with through rectangular grooves at the lower left, lower right, upper left and upper right respectively; The first cantilever beam (7), the second cantilever beam (8), the third cantilever beam (9), and the fourth cantilever beam (10) are respectively arranged in the rectangular grooves at the lower left, lower right, upper left, and upper right of the silicon mass block (6), and are used to connect the silicon mass block (6) and the silicon anchor point (5); The first cantilever beam (7), the second cantilever beam (8), the third cantilever beam (9), and the fourth cantilever beam (10) have the same structure, and are all composed of two groups of folded beams and a T-shaped base, wherein the T-shaped base is connected to the silicon anchor point (5) and plays a role of fixed support, and the two groups of folded beams are connected to the inner side wall of the rectangular groove of the silicon mass block (6) and play a role of elastic support; A gap is provided between the silicon mass block (6) and the silicon anchor point (5), and the gap is larger than the displacement of the silicon mass block (6) under the action of maximum acceleration.

10. The method for manufacturing a silicon-based free-space optical MEMS accelerometer according to any one of claims 1 to 9, wherein: The following steps are involved: Step 1, cleaning and preparing the glass substrate; Step 2, etching the glass substrate to form the glass mass block (2) structure, the optical path, and the gap between the glass mass block (2) and the glass anchor point (1); Step 3: Install the reflector shadow mask and deposit the metal reflector coating by electron beam evaporation or magnetron sputtering process; Step 4, removing the reflector shadow mask to obtain the first reference reflector (3-8), the first detection reflector (3-9), the second reference reflector (4-8), and the second detection reflector (4-9) components; Step 5: Install the beam splitter shadow mask and deposit the dielectric beam splitter coating by electron beam evaporation or magnetron sputtering. Step 6, removing the beam splitter shadow mask to obtain the first beam splitter (3-3) and the second beam splitter (4-3) components; Step 7, performing anodic bonding on the glass substrate and the underlying silicon wafer; Step 8, etching the back of the glass substrate to release the gap between the glass mass (2) and the glass anchor point (1); Step 9, etching the silicon substrate to form a cantilever beam structure and releasing the silicon mass block (6) structure; Step 10: Obtain a complete MEMS accelerometer structure.

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