Silicon-based free-space optical MEMS accelerometer and method of manufacture

Abstract

The application provides a silicon-based free-space 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 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. The upper layer optical sensitive structure is composed of a pair of Michelson interferometers, a glass anchor point and a glass mass; the lower layer MEMS sensitive structure is composed of four groups of cantilever beams, a silicon anchor point and a silicon mass. The lower layer MEMS sensitive structure converts the horizontal axis input acceleration into the displacement of the silicon mass, the displacement is synchronously transmitted to the glass mass, and a pair of reversely arranged Michelson interferometers convert the displacement into the reverse transformation of the phase of the interference light, so that the high-precision differential detection of the acceleration is realized. The micro-optical accelerometer scheme provided by the application has the outstanding advantages of high detection sensitivity, strong anti-common-mode error capability and high integration.

Description

Technical Field

[0001] This invention relates to the fields of microelectromechanical systems (MEMS) technology and micro-inertial instruments, specifically to a silicon-based free-space optical MEMS accelerometer and its manufacturing method. Background Technology

[0002] Optical interference is a manifestation of the wave nature of light. Optical interferometers, based on the principle of optical interference, are classic high-precision measuring devices. Through the amplification effect of small optical path differences, they can convert weak physical disturbances into highly sensitive interference wave phase shifts, thereby enabling the detection of minute physical quantities. Among them, the Michelson interferometer, based on two-arm interference, is one type of interferometer commonly used for measuring displacement-type physical quantities. Currently, Michelson interferometers are generally implemented based on macroscopic free-space optical systems and are mainly used in the development of macroscopic measuring instruments.

[0003] Microelectromechanical systems (MEMS) technology is a field dedicated to the miniaturization of physical instruments and devices. MEMS accelerometers are a type of miniature sensor widely used in inertial navigation, attitude recognition, vibration monitoring, and other fields. Traditional MEMS accelerometers typically convert the displacement or deformation caused by acceleration into an electrical signal using electrical methods such as capacitance, piezoelectricity, and piezoresistive impedance. This method is susceptible to interface noise, limiting detection accuracy. Free-space optical MEMS accelerometers, achieved by miniaturizing a Michelson interferometer through microfabrication and combining it with a MEMS resonant sensing structure, can read out displacement through interferometric optical signals. This type of accelerometer shows promise for higher accuracy and is currently one of the key research directions in micro-inertial sensors. Summary of the Invention

[0004] Purpose of the invention: The technical problem to be solved by the present invention is to address the shortcomings of the prior art by providing a silicon-based free-space optical MEMS accelerometer and its manufacturing method. The accelerometer has the outstanding advantages of high detection sensitivity, strong anti-common-mode error capability, and high integration.

[0005] The accelerometer adopts a dual-layer bonding structure that combines an upper structure and a lower structure. The upper structure is a glass substrate free-space optical sensing structure, and the lower structure is a silicon-based horizontal axis MEMS sensing structure.

[0006] The free-space optical sensing structure on the glass substrate includes a first Michelson interferometer, a second Michelson interferometer, a glass anchor point, and a glass mass block;

[0007] The silicon-based horizontal axis MEMS sensing structure includes a first cantilever beam, a second cantilever beam, a third cantilever beam, a fourth cantilever beam, a silicon anchor point, and a silicon mass block.

[0008] The glass substrate free-space optical sensing structure is a rectangular structure, in which the glass mass block is located at the center of the upper structure and is used to convert acceleration measurement into displacement. The glass mass block is a rectangular structure, and rectangular grooves are opened on the lower left, lower right, upper left, and upper right of the glass mass block, respectively, for releasing the first cantilever beam, the second cantilever beam, the third cantilever beam, and the fourth cantilever beam.

[0009] The glass anchor point is ring-shaped and located on the periphery of the glass mass block.

[0010] The glass anchor point and the silicon anchor point are bonded together, and the glass mass block and the silicon mass block are bonded together.

[0011] The silicon mass block is connected to a fixed silicon anchor point via a first cantilever beam, a second cantilever beam, a third cantilever beam, and a fourth cantilever beam. When a horizontal acceleration signal a is input, the silicon mass block generates a horizontal displacement under the support of the first cantilever beam, the second cantilever beam, the third cantilever beam, and the fourth cantilever beam, and the glass mass block will generate the same displacement synchronously.

[0012] The first Michelson interferometer includes a first laser, a first beam splitter, a first reference mirror, a first detection mirror, and a first photodetector;

[0013] The second Michelson interferometer includes a second laser, a second beam splitter, a second reference mirror, a second detection mirror, and a second photodetector;

[0014] The first detection mirror and the second detection mirror are respectively arranged on the left and right sides of the glass mass block;

[0015] The first Michelson interferometer and the second Michelson interferometer are located on the upper left and lower right sides of the upper structure, respectively, in a reverse symmetrical arrangement, and are used to realize differential acceleration detection.

[0016] The first and second Michelson interferometers provide free-space laser sources through miniaturized free-space first and second lasers, respectively. The first and second Michelson interferometers detect the intensity of the interference light through miniaturized free-space first and second photodetectors, respectively, to realize the conversion of optical differential signals to electrical differential signals, and at the same time realize the integrated structure of the accelerometer.

[0017] The first incident light emitted by the first laser is split into a first reference incident light and a first detection incident light at the first beam splitter with equal power. The first reference incident light and the first detection incident light are reflected along their original paths when they reach the first reference mirror and the first detection mirror, respectively, to generate a first reference reflected light and a first detection reflected light. The first reference reflected light and the first detection reflected light merge at the first beam splitter and undergo optical interference, thereby generating a first interference light. The first interference light is received by the first photodetector and converted into an electrical signal.

[0018] The first detection mirror is used to convert the horizontal displacement of the glass mass block into a change in the length of the reference arm, and further into the optical path difference between the first detection incident light, the first detection reflected light, the first reference incident light, and the first reference reflected light, and finally couple the acceleration information into the phase of the first interference light;

[0019] The second detection mirror is arranged on the right side of the glass mass block, so that the second interference light generates phase information opposite to that of the first interference light, thus forming differential detection;

[0020] The optical paths of the first Michelson interferometer and the second Michelson interferometer are arranged within the glass anchor point, located on the left and right sides of the anchor point, respectively;

[0021] The first reference mirror, the second reference mirror, the first beam splitter, and the second beam splitter are arranged on the groove sidewall 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.

[0022] The first beam splitter and the second beam splitter are arranged at an angle, and the angle between the first beam splitter and the first reference mirror, and the angle between the second beam splitter and the second reference mirror are both 45°.

[0023] The center of the emitting surface of the first laser is aligned with the center of the front surface of the first beam splitter.

[0024] The center of the emitting surface of the second laser is aligned with the center of the front of the second beam splitter;

[0025] The first photodetector and the second photodetector are located on the upper left and lower right sides of the glass anchor point, respectively;

[0026] The center of the receiving surface of the first photodetector is aligned with the center of the back of the first beam splitter;

[0027] The center of the receiving surface of the second photodetector is aligned with the center of the back of the second beam splitter.

[0028] The displacement of the glass mass block will cause the first detection mirror to move to the right and the second detection mirror to move to the left, which in turn will cause the optical path length of the first detection incident light to decrease and the optical path length of the second detection incident light to increase, thereby realizing the inverse phase change of the interference light intensity of the first Michelson interferometer and the second Michelson interferometer, and finally completing the optical differential detection of the input acceleration.

[0029] The silicon-based horizontal axis MEMS sensing structure is a rectangular structure with the same length and width dimensions as the upper structure.

[0030] The silicon mass block is located at the center of the upper structure and has a rectangular structure. The length and width of the silicon mass block are the same as those of the glass mass block.

[0031] The silicon anchor point is ring-shaped and located on the periphery of the silicon mass block. The length and width of the silicon anchor point are the same as those of the glass anchor point, and it serves to fix and support the structure.

[0032] The glass mass block has through rectangular grooves at its lower left, lower right, upper left, and upper right.

[0033] The first cantilever beam, the second cantilever beam, the third cantilever beam, and the fourth cantilever beam are respectively arranged in the rectangular grooves at the lower left, lower right, upper left, and upper right of the silicon mass block, and are used to connect the silicon mass block and the silicon anchor point;

[0034] The first cantilever beam, the second cantilever beam, the third cantilever beam, and the fourth cantilever beam have the same structure, each consisting of two sets of folded beams and a T-shaped base. The T-shaped base is connected to the silicon anchor point and serves as a fixed support. The two sets of folded beams are connected to the inner wall of the rectangular groove of the silicon mass block and serve as an elastic support.

[0035] A gap is provided 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.

[0036] This invention also provides a method for manufacturing a silicon-based free-space optical MEMS accelerometer, comprising the following steps:

[0037] Step 1: Clean and prepare the glass substrate;

[0038] Step 2: Etch the glass substrate to form the glass mass block structure, optical path, and gap between the glass mass block and glass anchor point;

[0039] Step 3: Install the mirror shadow mask and deposit the metal mirror coating by electron beam evaporation or magnetron sputtering.

[0040] Step 4: Remove the mirror shadow mask to obtain the first reference mirror, the first detection mirror, the second reference mirror, and the second detection mirror element;

[0041] Step 5: Install the beam splitter shadow mask and deposit a dielectric beam splitter coating by electron beam evaporation or magnetron sputtering.

[0042] Step 6: Remove the shadow mask of the beam splitter to obtain the first beam splitter and the second beam splitter elements;

[0043] Step 7: Anodicly bond the glass substrate to the underlying silicon wafer;

[0044] Step 8: Etch the back of the glass substrate to release the gap between the glass mass block and the glass anchor point;

[0045] Step 9: Etch the silicon substrate to form a cantilever beam structure and release the silicon mass block structure;

[0046] Step 10: Obtain the complete MEMS accelerometer structure.

[0047] Beneficial effects: (1) This invention proposes to fabricate micro-optical paths and optical mirror substrates on optical glass substrates by etching, realize micro-optical mirror elements by sidewall coating, and finally realize an integrated free-space micro-interferometer on the glass substrate, thus realizing the miniaturization of macro-interferometers;

[0048] (2) This invention combines optical interferometer with MEMS technology to realize miniaturized optical MEMS accelerometer, which has the advantages of high detection accuracy and high detection sensitivity of optical interferometer, while also having the advantages of traditional MEMS technology such as high integration, high degree of integration and easy packaging.

[0049] (3) The present invention uses a pair of interferometers arranged in opposite directions as the acceleration detection mechanism. The phase of the interference light changes in the opposite direction with the input acceleration, realizing the optical differential detection method, which can effectively suppress the detection error caused by common mode interference and enhance the reliability of the device.

[0050] (4) The present invention adopts the method of processing the interferometer and the MEMS resonant structure separately on different substrates, and then bonding them together to release the structure to realize the main structure of the optical MEMS accelerometer. The process flow is reasonable and highly feasible, and the realized MEMS accelerometer structure has a high degree of integration. Attached Figure Description

[0051] Figure 1 This is a general structural diagram of the present invention.

[0052] Figure 2 This is the top view of the present invention.

[0053] Figure 3 This is a top view of the lower layer of the present invention.

[0054] Figure 4 This is a flowchart of the manufacturing process of the present invention.

[0055] Explanation of reference numerals in the attached figures: 1, glass anchor point; 2, glass mass block; 3, first Michelson interferometer; 4, second Michelson interferometer; 5, silicon anchor point; 6, silicon mass block; 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 Implementation

[0056] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments, and the advantages of the present invention in the above and / or other aspects will become clearer.

[0057] like Figure 1 As shown, in order to achieve the above-mentioned objective, the present invention proposes a two-layer structure: the upper layer is a glass substrate free space optical sensing structure and the lower layer is a silicon-based horizontal axis MEMS sensing structure, wherein the upper structure is bonded to the glass mass block 2 through glass anchor point 1 and to the silicon mass block 6 through silicon anchor point 5.

[0058] The upper glass substrate free-space optical sensing structure consists of a first Michelson interferometer 3, a second Michelson interferometer 4, a glass anchor point 1, and a glass mass block 2. The lower silicon-based horizontal axis MEMS sensing structure consists 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 block 6.

[0059] 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 undergoes 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. Furthermore, the glass mass block 2 is bonded to the silicon mass block 6, and therefore will generate the same displacement synchronously. The first Michelson interferometer 3 and the second Michelson interferometer 4 are arranged in a reverse symmetrical manner, wherein the first detection interferometer... The first detection mirror 3-9 and the second detection mirror 4-9 are respectively arranged on the left and right sides of the glass mass block 2. The above displacement will cause the first detection mirror 3-9 and the second detection mirror 4-9 to move to the right and to the left, respectively, which will cause the optical path of the first detection incident light 3-6 and the first detection reflected light 3-7 to decrease, and the optical path of the second detection incident light 4-6 and the second detection reflected light 4-7 to increase, thereby realizing the inverse phase change of 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.

[0060] The first Michelson interferometer 3 and the second Michelson interferometer 4 provide free-space laser sources through the miniaturized first laser 3-1 and second laser 4-1 in free space, and detect the intensity of interference light through the miniaturized first photodetector 3-11 and second photodetector 4-11 in free space, thereby realizing the conversion of optical differential signals to electrical differential signals, and at the same time realizing the integrated structure of MEMS accelerometer.

[0061] like Figure 2 As shown, the upper glass substrate free-space optical sensing structure is a rectangular structure, with glass mass block 2 located at the center of the upper structure to convert acceleration measurements into displacement. Glass mass block 2 is also rectangular, with through rectangular grooves on its lower left, lower right, upper left, and upper right sides to release the first cantilever beam 7, second cantilever beam 8, third cantilever beam 9, and fourth cantilever beam 10 of the lower structure. Glass mass block 2 is bonded to the lower silicon mass block 6, which helps reduce the overall mechanical and thermal noise of the MEMS accelerometer and increases its detection accuracy. Glass anchor point 1 is annular and located on the periphery of glass mass block 2, and is bonded to the lower silicon anchor point 5 to provide fixed support. The first Michelson interferometer 3 and the second Michelson interferometer 4 are located on the upper left and lower right sides of the upper structure, respectively, arranged in reverse symmetrical order, to achieve differential acceleration detection.

[0062] The first Michelson interferometer 3 comprises 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 split into a first reference incident light 3-4 and a first detection incident light 3-6 at the first beam splitter 3-3. Both incident lights are reflected along their original paths upon reaching the first reference mirror 3-8 and the first detection mirror 3-9, respectively, generating a first reference reflected light 3-5 and a first detection reflected light 3-7. These incident lights are then reflected by the first beam splitter 3-1. The light converges at point -3, causing optical interference and generating the first interference light 3-10. The first interference light 3-10 is received by the first photodetector 3-11 and converted into an electrical signal. The first detection reflector 3-9 is arranged on the left side of the glass mass block 2 to convert the horizontal displacement of the glass mass block 2 into a change in the length of the reference arm, and further into the optical path difference between the first detection incident light 3-6, the first detection reflected light 3-7, the first reference incident light 3-4, and the first reference reflected light 3-5. Finally, the acceleration information is coupled into the phase of the first interference light 3-10.

[0063] The second Michelson interferometer 4 consists 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 block 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 within the glass anchor point 1, located on the left and right sides of the glass anchor point 1, respectively.

[0064] 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 sidewall of the groove of the glass anchor point 1, located on the left and right sides of the glass anchor point 1, respectively.

[0065] The first beam splitter 3-3 and the second beam splitter 4-3 are arranged at an angle, and the angle between them and the first reference mirror 3-8 and the second reference mirror 4-8 is 45°.

[0066] The first laser 3-1 and the second laser 4-1 are located on the left and right sides of the glass anchor point 1, respectively, and the center of the emitting surface is aligned with the center of the front of the first beam splitter 3-3 and the second beam splitter 4-3.

[0067] The first photodetector 3-11 and the second photodetector 4-11 are located on the upper left and lower right sides of the glass anchor point 1, respectively, and the center of the receiving surface is aligned with the center of the back of the first beam splitter 3-3 and the second beam splitter 4-3.

[0068] like Figure 3 As shown, the lower silicon-based horizontal axis MEMS sensing structure is a rectangular structure with the same length and width as the upper structure. The silicon mass block 6 is located at the center of the upper structure and is also rectangular, with the same length and width as the upper glass mass block 2. The silicon anchor point 5 is annular and located around the silicon mass block 6, with the same length and width as the upper glass anchor point 1, serving 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 at the lower left, lower right, upper left, and upper right of the silicon mass block 6, connecting the silicon mass block 6 and the silicon anchor point 5. The four cantilever beams have identical structures, each consisting of two sets of folded beams (the first set consists of 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; the second set consists of the fifth folded beam 9-2, the sixth folded beam 9-3, and the fourth folded beam 8-3). 3. The structure consists of a seventh folded beam 10-2, an eighth folded beam 10-3, and a "T"-shaped base (including a first cantilever beam base 7-1, a second cantilever beam base 8-1, a third cantilever beam base 9-1, and a 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, serving 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 wall of the rectangular groove of the silicon mass block 6, serving as an elastic support. There is a gap 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.

[0069] like Figure 4 As shown, this embodiment also provides a method for manufacturing the silicon-based free-space optical MEMS accelerometer, comprising the following steps:

[0070] Step 1: Clean and prepare the optical glass substrate;

[0071] Step 2: Etch the glass substrate to form the structure of glass mass block 2, the optical path, and the gap between glass mass block 2 and glass anchor point 1;

[0072] Step 3: Install the mirror shadow mask and deposit the metal mirror coating by electron beam evaporation or magnetron sputtering.

[0073] Step 4: Remove the mirror shadow mask to obtain the first reference mirror 3-8, the first detection mirror 3-9, the second reference mirror 4-8, and the second detection mirror 4-9.

[0074] Step 5: Install the beam splitter shadow mask and deposit a dielectric beam splitter coating by electron beam evaporation or magnetron sputtering.

[0075] Step 6: Remove the shadow mask of the beam splitter to obtain the first beam splitter 3-3 and the second beam splitter 4-3 elements;

[0076] Step 7: Anodicly bond the glass substrate to the silicon substrate.

[0077] Step 8: Etch the back of the glass substrate to release the gap between the glass mass block 2 and the glass anchor point 1;

[0078] Step 9: Etch the silicon substrate to form a cantilever beam structure and release the silicon mass block 6 structure;

[0079] Step 10: Obtain the complete MEMS accelerometer structure.

[0080] This invention provides a silicon-based free-space optical MEMS accelerometer and its manufacturing method. Many methods and approaches exist for implementing this technical solution; the above description is merely a preferred embodiment of the invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention. All components not explicitly stated in this embodiment can be implemented using existing technologies.

Claims

1. A silicon-based free-space optical MEMS accelerometer, characterized in that, The accelerometer adopts a dual-layer bonding structure that combines an upper structure and a lower structure. The upper structure is a glass substrate free-space optical sensing structure, and the lower structure is a silicon-based horizontal axis MEMS sensing structure. The free-space optical sensing structure of the glass substrate includes a first Michelson interferometer (3), a second Michelson interferometer (4), a glass anchor point (1), and a glass mass block (2). The silicon-based horizontal axis MEMS sensing structure includes 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 block (6). The glass substrate free space optical sensitive structure is a rectangular structure in whole, wherein the glass mass block (2) is located at the center of the upper structure and is used to convert the acceleration measurement into the displacement. The glass mass block (2) is a rectangular structure, and rectangular grooves are opened on the lower left, lower right, upper left and upper right of the glass mass block (2) respectively, for releasing the first cantilever beam (7), the second cantilever beam (8), the third cantilever beam (9) and the fourth cantilever beam (10). The glass anchor point (1) is ring-shaped and located on the periphery of the glass mass block (2); 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; 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). The glass mass block (2) will generate the same displacement synchronously. The first Michelson interferometer (3) includes 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 second Michelson interferometer (4) includes 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 first detection mirror (3-9) and the second detection mirror (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 located on the upper left and lower right sides of the upper structure, respectively, and are arranged in opposite symmetrical manner to realize differential acceleration detection.

2. The silicon-based free-space optical MEMS accelerometer as described in claim 1, characterized in that, The first Michelson interferometer (3) and the second Michelson interferometer (4) provide free space laser sources through the first laser (3-1) and the second laser (4-1) in miniaturized free space, respectively. The first Michelson interferometer (3) and the second Michelson interferometer (4) detect the intensity of interference light through the first photodetector (3-11) and the second photodetector (4-11) in miniaturized free space, respectively, to realize the conversion of optical differential signal to electrical differential signal, and at the same time realize the integrated structure of the accelerometer.

3. A silicon-based free-space optical MEMS accelerometer as described in claim 2, characterized in that, The first incident light (3-2) emitted by the first laser (3-1) is split into a first reference incident light (3-4) and a first detection incident light (3-6) at the first beam splitter (3-3) with equal power. The first reference incident light (3-4) and the first detection incident light (3-6) are reflected along the original path when they reach the first reference reflector (3-8) and the first detection reflector (3-9), respectively, to generate 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 beam splitter (3-3) and undergo optical interference, thereby generating a first interference light (3-10). The first interference light (3-10) is received by the first photodetector (3-11) and converted into an electrical signal. The first detection mirror (3-9) is used to convert the horizontal displacement of the glass mass block (2) into a change in the length of the reference arm, and further into the optical path difference between the first detection incident light (3-6), the first detection reflected light (3-7), the first reference incident light (3-4), and 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 mirror (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), 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), located on the left and right sides of the glass anchor point (1), respectively. 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 side wall of the groove of the glass anchor point (1). The first reference mirror (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 mirror (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 at an angle, and the angle between the first beam splitter (3-3) and the first reference mirror (3-8) and the angle between the second beam splitter (4-3) and the second reference mirror (4-8) are both 45°. The center of the emitting surface of the first laser (3-1) is aligned with the center of the front of the first beam splitter (3-3); The center of the emitting surface of the second laser (4-1) is aligned with the center of the front of the second beam splitter (4-3); The first photodetector (3-11) and the second photodetector (4-11) are located on the upper left and lower right sides of the glass anchor point (1), respectively. 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 block (2) will cause the first detection mirror (3-9) to move to the right and the second detection mirror (4-9) to move to the left, which will in turn cause 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 respectively, thereby realizing the phase reversal of 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.

4. A silicon-based free-space optical MEMS accelerometer as described in claim 3, characterized in that, The silicon-based horizontal axis MEMS sensing structure is a rectangular structure with the same length and width dimensions as the upper structure. The silicon mass block (6) is located at the center of the upper structure and is 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 ring-shaped and located on the periphery of the silicon mass block (6). The length and width of the silicon anchor point (5) are the same as those of the glass anchor point (1), and it serves as a fixed support. The glass mass block (2) has through rectangular grooves on its lower left, lower right, upper left, and upper right sides 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) 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. They are all composed of two sets of folded beams and a T-shaped base. The T-shaped base is connected to the silicon anchor point (5) and plays a fixed support role. The two sets of folded beams are connected to the inner wall of the rectangular groove of the silicon mass block (6) and play an elastic support role. 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.

5. A method for manufacturing a silicon-based free-space optical MEMS accelerometer as described in any one of claims 1 to 4, characterized in that, Includes the following steps: Step 1: Clean and prepare the glass substrate; Step 2: Etch the glass substrate to form the structure of the glass mass block (2), the optical path, and the gap between the glass mass block (2) and the glass anchor point (1); Step 3: Install the mirror shadow mask and deposit the metal mirror coating by electron beam evaporation or magnetron sputtering. Step 4: Remove the mirror shadow mask to obtain the first reference mirror (3-8), the first detection mirror (3-9), the second reference mirror (4-8), and the second detection mirror (4-9) components; Step 5: Install the beam splitter shadow mask and deposit a dielectric beam splitter coating by electron beam evaporation or magnetron sputtering. Step 6: Remove the shadow mask of the beam splitter to obtain the first beam splitter (3-3) and the second beam splitter (4-3) elements; Step 7: Anodicly bond the glass substrate to the underlying silicon wafer; Step 8: Etch the back of the glass substrate to release the gap between the glass mass block (2) and the glass anchor point (1); Step 9: Etch the silicon substrate to form a cantilever beam structure and release the silicon mass block (6) structure; Step 10: Obtain the complete MEMS accelerometer structure.

Images