A wide-temperature high-precision optical acceleration sensing chip and an acceleration sensor based on microcavity interferometer principle

Abstract

A wide-temperature, high-precision optical acceleration sensing chip and acceleration sensor based on the principle of a microcavity interferometer are disclosed. The acceleration sensing chip includes a first substrate, a second substrate, and a third substrate. An optical fiber mounting base and a light-transmitting hole are formed on the first substrate. The chip is characterized by a single-mode optical fiber assembly fixed on the optical fiber mounting base. The end face of the single-mode optical fiber assembly is precision ground and perpendicular to the axis of the optical fiber core. The optical fiber mounting base is a stepped hole with a first stepped portion and a second stepped portion. The single-mode optical fiber assembly includes a glass sleeve disposed on the outer layer and a single-mode optical fiber disposed in the core. The first stepped portion, the second stepped portion, the end face of the glass sleeve, and the end face of the single-mode optical fiber are all perpendicular to the core axis of the single-mode optical fiber. The first stepped portion forms a first fit with the end face of the glass sleeve, and the second stepped portion forms a second fit with the end face of the single-mode optical fiber.

Description

Technical Field

[0001] This application is a divisional application of application number 2025100052678, with the original application date being January 3, 2025. The invention is entitled: A wide-temperature, high-precision optical acceleration sensing chip, sensor, and manufacturing method thereof based on the principle of microcavity interferometer.

[0002] This application relates generally to the field of optoelectronic technology, and in particular to a wide-temperature, high-precision optical acceleration sensing chip based on the principle of a microcavity interferometer and an acceleration sensor containing the chip, which is mainly used for the acceleration of objects and applied in the fields of inertial navigation, vibration and tilt measurement. Background Technology

[0003] Accelerometers are primarily used in inertial navigation, vibration, and tilt measurement. In the industrial sector, accelerometers are widely used to acquire vibration amplitude, frequency, and phase signals from large structures and electromechanical equipment. Combined with algorithms, they can be used to identify abnormal states and perform predictive health management. Industrial applications place increasingly stringent demands on accelerometers in terms of electrical insulation performance, resistance to lightning strikes and electromagnetic interference, ultra-low and ultra-high temperature operation capabilities, and wide-bandwidth response from ultra-low to mid-high frequencies. For example, in large equipment such as nuclear power units, wheel-rail systems and pantographs in rail transportation, mining machinery, wind turbine blades, ocean-going vessels, and power units, sensors are required to have electrical insulation, radiation resistance, electromagnetic interference resistance, tolerance to extreme high and low temperatures, ultra-high precision, and resistance to large acceleration impacts.

[0004] Commonly used accelerometers can be divided into electrical accelerometers and optical accelerometers. Electrical accelerometers measure the inertial force or displacement of a mass using electromechanical methods, while optical accelerometers measure the inertial force or displacement of a mass using optical signals. Compared with the former, optical accelerometers not only have the unique advantage of unparalleled resistance to electromagnetic interference, but also are small and lightweight, have a wide dynamic range, high accuracy, and can operate in harsh environments such as high temperature and high humidity. To improve transmission distance and resistance to electromagnetic interference, optical accelerometers typically use optical fiber as the signal transmission medium.

[0005] Traditional intrinsic fiber optic sensors use partially processed optical fibers or whole optical fibers as sensing and transmission elements, making them naturally suitable for harsh industrial environments. However, they are limited by many factors, such as the constant elasticity of the optical fiber and packaging materials, temperature drift and stress drift introduced by the temperature coefficient difference between the optical fiber and the packaging structure, and the available spectral range of the light source. In a wide temperature range, fiber optic sensors cannot achieve the accuracy of piezoelectric or even capacitive accelerometers. At the same time, existing fiber optic sensors are significantly affected by temperature cross-influence, resulting in poor measurement repeatability and consistency between sensors, making industrial-scale, mass production with consistent performance impossible.

[0006] Single-crystal silicon possesses excellent constant elasticity and a low coefficient of thermal expansion, making it an ideal material for fabricating mechanical structures and acceleration-sensitive structures composed of inertial mass blocks and elastic beams. Especially with the development of MEMS micro / nano manufacturing processes, the use of single-crystal silicon wafers to fabricate sensor chip structures and to integrate resistors, capacitors, or resonators for electrical signal readout has enabled the mass production of MEMS sensors for pressure, acceleration, sound, and other mechanical applications. Chinese patents CN115728512A and CN115728511A disclose a fiber optic accelerometer. A first reflective layer is deposited on an SOI silicon wafer, and a second reflective layer, polished from a glass sheet, is deposited on a third substrate. This accelerometer is a MEMS optical accelerometer based on a silicon-glass bonding structure. Sufficient gaps must be maintained to prevent the attraction between the silicon and glass at high bonding voltages from causing the inertial sensing structure to lose its relative displacement capability with the substrate, resulting in accelerometer failure. Therefore, it is difficult to adjust the damping characteristics of the MEMS optical accelerometer by reducing the gap between the inertial sensing structure and the substrate. Furthermore, the limited temperature resistance of glass further reduces the operating temperature range of the MEMS optical accelerometer. Additionally, using an SOI silicon wafer to fabricate an optical interference cavity or form an inertial sensing structure is costly. The bonding of the optical fiber to the MEMS sensor chip using adhesive or low-temperature glass welding makes it difficult to guarantee long-term reliability and high-temperature resistance. Summary of the Invention

[0007] To address the shortcomings of existing fiber optic accelerometer sensors, this application provides a wide-temperature, high-precision optical accelerometer-based chip based on the microcavity interferometer principle and its manufacturing method. The chip comprises a first substrate, a second substrate, and a third substrate. An optical fiber mounting base and a light-transmitting aperture are fabricated on the first substrate. A beam structure and an inertial mass block are fabricated on the second substrate. All three substrates are double-polished ultra-flat silicon wafers. A single-mode fiber assembly is fixed on the optical fiber mounting base. The end face of the single-mode fiber assembly is precision-ground and perpendicular to the fiber core axis. A first cavity mirror is formed on the end face of the inertial mass block facing the light-transmitting aperture, and a second cavity mirror is formed on the end face of the single-mode fiber assembly. The first and second cavity mirrors constitute an FP interferometer cavity. The first, second, and third substrates are connected using a silicon-silicon bonding process. The first cavity mirror is formed on the side of the inertial mass block facing the light-passing aperture. Utilizing the excellent surface finish and flatness of the double-polished ultra-flat silicon wafer and the high optical reflectivity of single-crystal silicon, the surface of the double-polished ultra-flat silicon wafer exhibits a laser reflectivity exceeding 25% for the 1500nm–1600nm range. It is directly used as the first cavity mirror of the FP optical interference cavity. The end face of a precision-ground single-mode fiber assembly perpendicular to the fiber core axis is used as the second cavity mirror of the FP optical interference cavity. Due to the divergence angle of the optical signal after leaving the end face of the single-mode fiber assembly, the laser emitted from the second cavity mirror of the FP optical interference cavity is... After reflection from the first cavity mirror of the FP optical interferometer, only a very small portion returns to the second cavity mirror and enters the single-mode fiber. This ensures that the two cavity mirrors of the FP optical interferometer are strictly parallel and aligned. Furthermore, it ensures that the FP optical interferometer not only satisfies the two-beam interference condition during the large displacement of the inertial mass, but also that its spectral characteristics, such as insertion loss and contrast, remain nearly constant. The measured acceleration can be converted into the inertial displacement of the mass, thereby changing the interference optical path length between the first and second cavity mirrors of the FP optical interferometer, and thus calculating the acceleration information. Three double-polished ultra-flat silicon wafers are used. Each wafer is patterned and etched, and then a silicon-silicon bonding process is used to mass-produce the optical acceleration-sensitive chip. This eliminates the thermal stress mismatch problem introduced by wafer heterogeneous aggregation, reduces the chip's temperature coefficient, and increases the overall high-temperature tolerance of the chip to over 500℃. Simultaneously, using double-polished ultra-flat silicon wafers instead of SOI silicon wafers significantly reduces the material cost of the sensor, reduces the amount of coating on the inertial mass, simplifies the sensor manufacturing process, and further saves on sensor production costs.

[0008] In a further embodiment, the end face of the single-mode fiber assembly is coated with an optical reflective film to modulate the spectral characteristics of the FP optical interferometer cavity. For example, an optical reflective film with a reflectivity of 1% to 20% is coated to improve the two-beam interference spectral characteristics. In a further preferred embodiment, the reflectivity of the optical reflective film is selected to be less than the reflectivity of the second substrate surface, so that the two interference beams reflected back into the fiber by the first cavity mirror and the second cavity mirror have the same light intensity and each light intensity is 12%, thereby obtaining the best two-beam interference effect.

[0009] In a further embodiment, the inertial mass block is connected to the second substrate via the beam structure. The beam structure is a double-layer elastic beam, which can employ the applicant's prior art or other beam structures in the prior art capable of achieving elastic connection of the inertial mass block. The double-layer elastic beam structure includes an upper elastic beam and a lower elastic beam. The upper surface of the upper elastic beam is flush with the upper surface of the second substrate, and the lower surface of the lower elastic beam is flush with the lower surface of the second substrate. This configuration simplifies the processing of the second substrate, as both sides of the second substrate are natural surfaces, improving the optical path effect. The beam structure surface requires no processing, increasing the symmetry between beam structures with the same surface and between beam structures on opposite surfaces, thus optimizing the paraxial suppression effect.

[0010] In a further preferred embodiment, the first and second cavity mirrors are parallel, and the two interference beams reflected back into the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same intensity, with each intensity being 5%-20% lower than the incident light intensity. This ensures that the optical acceleration sensing chip has good two-beam interference spectral characteristics, allowing for high-precision measurement of the interference optical path change between the first and second cavity mirrors of the FP optical interference cavity within the chip using the laser interference signal demodulation principle. Simultaneously, it also ensures that the FP optical interference cavity within the optical acceleration sensing chip has good stability and resistance to lateral vibration interference. Further preferably, according to simulation results, when the two interference beams reflected back into the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same intensity, with each intensity being less than or equal to 20% of the incident light intensity, the reflected light forms a good sinusoidal signal, facilitating demodulation by subsequent algorithms and enabling efficient calculation of acceleration information.

[0011] In a further preferred embodiment, an upper gap is etched on the side of the first substrate facing the second substrate; a lower gap is etched on the side of the third substrate facing the second substrate; the depth of the upper and lower gaps is 3μm-20μm. By controlling the etching depth of the upper and lower gaps, the damping characteristics of the optical accelerometer chip are adjusted and a limiting protection is provided for the inertial mass block, preventing excessive displacement of the inertial mass block under high impact that could lead to breakage of the elastic beam. Since the three gaps are bonded with silicon-silicon, there is no need to worry about the inertial mass block being too small and attracting to the surface of the upper gap while ensuring the bonding strength. Therefore, the depth of the gap can be freely adjusted to ensure that the optical accelerometer chip has an optimal damping ratio of approximately 0.707, thereby effectively suppressing nonlinear phenomena, reducing signal distortion, and helping system maintenance personnel understand the signal or channel status. At the same time, under high impact overload, the upper and lower gaps can provide limiting protection for the inertial mass block, preventing excessive displacement of the inertial mass block and irreversible deformation of the beam structure. The maximum free displacement of the inertial mass block can be adjusted by setting the upper and lower gaps to correspondingly improve the stiffness of the beam structure, maximizing the measurement sensitivity and dynamic range of the optical accelerometer chip without worrying about the breakage of the elastic beam under high impact overload. Taking a specific design parameter as an example, the first-order natural resonant frequency of the optical accelerometer chip is 16kHz. Under ±200g acceleration, the maximum displacement of the inertial mass block is ±0.2μm, which corresponds to a cavity length change of ±0.2μm in the FP optical interference cavity inside the chip. The minimum cavity length change of the FP optical interference cavity that can be measured using the laser interference signal demodulation principle is 10pm. Thus, the optical accelerometer chip can achieve a full-scale resolution of 0.05% and a linear accuracy of 0.01% when using laser interference signal demodulation.

[0012] In a further preferred embodiment, the fiber optic mounting base is a stepped hole with a first stepped portion and a second stepped portion. The single-mode fiber assembly includes a glass sleeve disposed on the outer layer and a single-mode fiber disposed in the core. The first stepped portion, the second stepped portion, the end face of the glass sleeve, and the end face of the single-mode fiber are all perpendicular to the core axis of the single-mode fiber. The first stepped portion forms a first fit with the end face of the glass sleeve, and the second stepped portion forms a second fit with the end face of the single-mode fiber. The single-mode fiber assembly is fixed on the fiber optic mounting base by glass solder. Further preferably, the distance between the end face of the glass sleeve and the end face of the single-mode fiber is set as a first distance, and the distance between the first stepped portion and the second stepped portion is set as a second distance. The first distance is less than the second distance, and the difference between the first distance and the second distance is 5-20 μm. Through the first fit and the second fit, the first cavity mirror and the second cavity mirror are strictly parallel, preventing the technical problem of non-parallelism of the first cavity mirror and the second cavity mirror caused by thermal stress due to temperature changes.

[0013] In a further preferred embodiment, a countersunk hole is formed on the side of the third substrate opposite to the second substrate. A diffuser hole penetrating the third substrate is formed at the bottom of the countersunk hole. An anti-reflection film is disposed on the second substrate at the position corresponding to the diffuser hole, thereby reducing specular reflection and preventing reflected light from returning to the FP optical interferometer cavity, thus avoiding the influence of multi-interface reflection light introduced by the third substrate on the optical performance of the FP optical interferometer cavity. Further preferably, an matting material is disposed within the countersunk hole, covering the bottom wall and side periphery of the countersunk hole, further reducing reflected light.

[0014] The wide-temperature, high-precision optical accelerometer chip based on the microcavity interferometer principle utilizes the Fabry-Perot (FP) interference principle: when three laser beams with wavelengths λ1, λ2, and λ3 are incident on the accelerometer chip, the reflected light from the first and second cavity mirrors, due to their identical reflection intensities and optical path difference, can form a two-beam interference corresponding to the three wavelengths. Under the influence of external acceleration or vibration, the relative distance between the first and second cavity mirrors changes, i.e., the optical path difference between the two beams in the two-beam interference changes, causing a corresponding change in the phase of the interference light returning to the collimator. Consequently, the three interference output signals are converted into voltage signals f1, f2, and f3 by photodiodes, and finally, the information of the acceleration to be measured is obtained through calculation.

[0015] This application also relates to an acceleration sensor comprising a wide-temperature, high-precision optical acceleration sensing chip based on the microcavity interferometer principle described above.

[0016] This application also relates to a method for manufacturing a wide-temperature, high-precision optical acceleration-sensitive chip based on the principle of a microcavity interferometer, comprising: S1 forming an inertial mass block and a beam structure on a second substrate through a processing technology, the processing technology including MEMS micro / nano processing technologies such as photolithography, dry etching, and wet etching; S2 fabricating an optical fiber mounting base, a light-transmitting hole, and an upper gap on a first substrate through a processing technology; S3 fabricating a lower gap, a countersunk hole, and a diffuser hole on a third substrate through a processing technology; the steps S1, S2, and S3 are not sequential and can be performed simultaneously or in an adjusted order.

[0017] More preferably, in step S2, the reverse side of the first substrate is fabricated with a fiber mounting base and a light-passing hole for fixing the single-mode fiber assembly using a combination of KOH etching and dry etching processes. The fiber mounting base provides angular guidance and limiting for the fiber, ensuring that the fiber end face and the first face of the inertial mass block have a certain spatial distance after encapsulation and fixation, thus ensuring batch consistency between the optical acceleration sensitive chip and the optical acceleration sensitive chip prepared by fiber encapsulation. Another function of the fiber mounting base is to provide guidance and shear protection for the solder and the glass sleeve protecting the fiber.

[0018] More preferably, in step S3, a countersunk hole and a diffuser hole are fabricated on the reverse side of the third substrate, i.e., the side opposite to the second substrate, by a combination of KOH etching and dry etching. The diffuser hole is used as a hard mask for patterning an optical antireflection film on the second surface of the inertial mass block, and at the same time, it serves as a light-transmitting hole to eliminate multi-interface reflection light that may be introduced into the FP optical interference cavity from the third double-polished ultra-flat silicon wafer.

[0019] Then, in step S4, the first substrate, the second substrate, and the third substrate are first bonded to silicon-silicon wafers; then, using the diffuser hole of the third substrate as a hard mask, an optical antireflection film is deposited on the lower surface of the second substrate at the position corresponding to the diffuser hole to form an optical antireflection film. Because the inertial mass block retains the complete thickness and original surface finish and flatness of the double-polished ultra-flat silicon wafer, and the refractive index of single-crystal silicon is approximately between 3.4 and 3.6, which is much higher than that of glass and silicon dioxide, the remaining transmitted light from the second cavity mirror of the FP optical interference cavity is further diverged after passing through the equivalent optical path of the thickness of the inertial mass block multiplied by the refractive index of single-crystal silicon. This greatly reduces the difficulty of patterning and fabricating the optical antireflection film on the second surface of the inertial mass block. Only after all the silicon-silicon bonding of the three double-polished ultra-flat silicon wafers is completed can the stepped hole of the third double-polished ultra-flat silicon wafer with silicon-silicon bonding be used as a hard mask to perform wafer-level optical antireflection film deposition. This allows for the patterning and fabrication of the optical antireflection film on the second surface of the inertial mass block for all optical acceleration-sensitive chips mass-produced on the wafer. Since the temperature of silicon-silicon bonding exceeds 1000℃, while the temperature resistance of optical films made of optical dielectric materials is usually only around 500℃, if optical films are prefabricated on silicon wafers, there is a risk of high-temperature damage and failure of silicon-silicon bonding. If a lower-temperature gold-silicon bonding process is used, the bonding strength and long-term reliability between multiple silicon wafers cannot be guaranteed, and the overall temperature resistance of the optical accelerometer chip will be directly reduced to below 400℃, which will further reduce the sealing temperature of the solder such as the encapsulation glass, introducing problems with the packaging reliability and operating temperature of the optical accelerometer chip.

[0020] After completing the above steps, the optical accelerometer chips can be diced and cut to mass-produce optical accelerometer chips that can withstand temperatures above 500℃. These chips are then welded to precision-ground single-mode optical fibers using a low-melting-point glass (with a glass transition temperature and softening temperature not lower than 400℃) with a sealing temperature between 500℃ and 580℃, thus completing the packaging of the optical accelerometer chips. This allows the optical accelerometer chips to operate over a wide temperature range, from ultra-low temperatures to temperatures above 400℃.

[0021] This application discloses an optical acceleration sensing chip and its manufacturing method, which integrates a MEMS structure with a high-precision optical FP cavity. Compared with existing technologies, it uses double-polished ultra-flat silicon wafers instead of SOI silicon wafers, which not only significantly reduces the material cost of the sensor but also reduces the amount of coating on the inertial mass block, simplifying the sensor manufacturing process and further saving sensor production costs. Using three double-polished ultra-flat silicon wafers, each wafer is patterned and etched, and then a silicon-silicon bonding process is used to achieve mass production of the optical acceleration sensing chip. This eliminates the thermal stress mismatch problem introduced by wafer heterogeneous aggregation, reduces the chip's temperature coefficient, and improves the overall chip's high tolerance. The temperature is increased to over 500℃; the adjustment of the upper and lower gap depths ensures that the optical acceleration sensitive chip has an optimal damping ratio of approximately 0.707, thereby effectively suppressing nonlinear phenomena, reducing signal distortion, and helping system maintenance personnel understand signal or channel conditions; at the same time, under high impact overload, the upper and lower gaps can provide limiting protection for the inertial mass block, preventing excessive displacement of the inertial mass block and causing irreversible deformation of the beam structure; through the cooperation of the stepped hole and the single-mode fiber assembly, the parallelism of the two cavity mirrors is ensured, while the bonding force between the single-mode fiber assembly and the first substrate is improved, preventing the single-mode fiber assembly from falling off in application scenarios with large vibrations. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the structure of the first embodiment of the optical acceleration sensitive chip of this application; Figure 2 This is a schematic diagram of the structure of the second embodiment of the optical acceleration sensitive chip of this application; Figure 3 This is a schematic diagram of the structure of the third embodiment of the optical acceleration sensitive chip of this application; Figure 4 This is a flowchart of the method in this application; Explanation of reference numerals in the attached figures: 1-First substrate; 11-Fiber optic mounting base; 12-Light transmission hole; 13-Upper gap; 14-First step; 15-Second step; 2-Second substrate; 21-Beam structure; 22-Inertial mass block; 3-Third substrate; 31-Diffusing hole; 32-Optical antireflection coating; 33-Extinction material; 34-Counterhole; 35-Lower gap; 4-Single-mode fiber assembly; 41-Glass sleeve; 42-Single-mode fiber; 43-Glass solder. Detailed Implementation

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] To keep the drawings concise, only the parts relevant to the invention are shown schematically in each figure, and they do not represent the actual structure of the product. Furthermore, for ease of understanding, in some figures, only one of components with the same structure or function is shown schematically, or only one is labeled. In this document, "one" can mean not only "only one" but also "more than one".

[0025] It should also be further understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0026] In this document, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to fixed connections, detachable connections, or integral connections; they can refer to mechanical connections or electrical connections; they can refer to direct connections or indirect connections through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] To address the shortcomings of existing fiber optic accelerometer sensors, this application provides a wide-temperature, high-precision optical accelerometer-based chip based on the microcavity interferometer principle and its manufacturing method. The wide-temperature, high-precision optical accelerometer-based chip includes a first substrate 1, a second substrate 2, and a third substrate 3. See details... Figure 1As shown, an optical fiber mounting base 11 and a light-transmitting hole 12 are formed on the first substrate 1, and a beam structure 21 and an inertial mass block 22 are formed on the second substrate 2. The first substrate 1, the second substrate 2, and the third substrate 3 are all made of double-polished ultra-flat silicon wafers. A single-mode optical fiber assembly 4 is fixed on the optical fiber mounting base 11. The end face of the single-mode optical fiber assembly 4 is precision ground and perpendicular to the axis of the optical fiber core. A first cavity mirror is formed on the end face of the inertial mass block 22 facing the light-transmitting hole 12, and a second cavity mirror is formed on the end face of the single-mode optical fiber assembly 4. The first cavity mirror and the second cavity mirror constitute an FP interference cavity. The first substrate 1, the second substrate 2, and the third substrate 3 are connected by silicon-silicon bonding technology. The inertial mass block 22 forms a first cavity mirror on the side facing the light-passing aperture 12. Utilizing the excellent surface finish and flatness of the double-polished ultra-flat silicon wafer and the high optical reflectivity of single-crystal silicon, the surface of the double-polished ultra-flat silicon wafer exhibits a laser reflectivity exceeding 25% for the 1500nm–1600nm range. It is directly used as the first cavity mirror of the FP optical interference cavity. The end face of the precision-ground single-mode fiber assembly 4, perpendicular to the fiber core axis, serves as the second cavity mirror of the FP optical interference cavity. Due to the divergence angle of the optical signal after leaving the end face of the single-mode fiber assembly 4, the laser emitted from the second cavity mirror of the FP optical interference cavity... After being reflected by the first cavity mirror of the FP optical interferometer, only a very small portion of the light can return to the second cavity mirror of the FP optical interferometer and enter the single-mode fiber. This ensures that the two cavity mirrors of the FP optical interferometer can be strictly parallel and aligned. It also ensures that the FP optical interferometer not only satisfies the two-beam interference condition during the large displacement of the inertial mass block 22, but also that its spectral characteristics, such as insertion loss and contrast, remain close to constant. The measured acceleration can be converted into the inertial displacement of the mass block, thereby changing the interference optical path change between the first and second cavity mirrors of the FP optical interferometer, and thus calculating the acceleration information. Three double-polished ultra-flat silicon wafers are used. Each wafer is patterned and etched, and then silicon-silicon bonding is used to mass-produce optical acceleration sensitive chips. This eliminates the thermal stress mismatch problem introduced by wafer heterogeneous aggregation, reduces the temperature coefficient of the chip, and increases the overall high temperature resistance of the chip to over 500℃. At the same time, using double-polished ultra-flat silicon wafers instead of SOI silicon wafers not only significantly reduces the material cost of the sensor, but also reduces the amount of coating on the inertial mass block 22, simplifies the sensor manufacturing process, and further saves on sensor production costs.

[0028] In a further embodiment, the end face of the single-mode fiber assembly 4 is coated with an optical reflective film to modulate the spectral characteristics of the FP optical interference cavity. For example, an optical reflective film with a reflectivity of 1% to 20% is coated to improve the two-beam interference spectral characteristics. In a further preferred embodiment, the reflectivity of the optical reflective film is selected to be less than the reflectivity of the surface of the second substrate 3, so that the two anti-interference beams reflected back to the fiber by the first cavity mirror and the second cavity mirror have the same light intensity, thereby obtaining the best two-beam interference effect.

[0029] In a further embodiment, the inertial mass block 22 is connected to the second substrate 2 via the beam structure 21. The beam structure 21 is a double-layer elastic beam. The structure of this double-layer elastic beam can adopt the applicant's prior art, or other beam structures 21 in the prior art that can achieve elastic connection of the inertial mass block 22. The double-layer elastic beam structure 21 includes an upper elastic beam and a lower elastic beam. The upper surface of the upper elastic beam is flush with the upper surface of the second substrate 2, and the lower surface of the lower elastic beam is flush with the lower surface of the second substrate 2. This configuration makes the processing of the second substrate simple and easy to implement. Both sides of the second substrate are natural surfaces, improving the optical path effect. The beam structure surface has no processing, improving the symmetry between beam structures with the same surface and between beam structures with opposite surfaces, thus optimizing the paraxial suppression effect.

[0030] In a further preferred embodiment, in order to avoid the impact of multi-interface reflection on the optical performance of the FP optical interference cavity, an optical antireflection film 32 is patterned on the lower surface of the inertial mass block 22. The purpose is to reduce its specular reflection and prevent its reflected light from returning to the FP optical interference cavity.

[0031] In a further preferred embodiment, the first and second cavity mirrors are parallel, and the two interference beams reflected back into the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same intensity, with each intensity being 5%-20% lower than the incident light intensity. This ensures that the optical acceleration sensing chip has good two-beam interference spectral characteristics, allowing for high-precision measurement of the interference optical path change between the first and second cavity mirrors of the FP optical interference cavity within the chip using the laser interference signal demodulation principle. Simultaneously, it also ensures that the FP optical interference cavity within the optical acceleration sensing chip has good stability and resistance to lateral vibration interference. Further preferably, according to simulation results, when the two interference beams reflected back into the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same intensity, with each intensity being 12% lower than the incident light intensity, the reflected light forms a good sinusoidal signal, facilitating demodulation by subsequent algorithms and enabling efficient calculation of acceleration information.

[0032] In a further preferred embodiment, an upper gap 13 is etched to form the side of the first substrate 1 facing the second substrate 2; a lower gap 35 is etched to form the side of the third substrate 3 facing the second substrate 2; the depths of the upper gap 13 and the lower gap 35 are 3μm-20μm. By controlling the etching depths of the upper gap 13 and the lower gap 35, the damping characteristics of the optical acceleration sensitive chip are adjusted, and the inertial mass block 22 is provided with limiting protection to prevent the inertial mass block 22 from displacing too much under high impact, which could cause the elastic beam to break; since the three are bonded by silicon-silicon bonds... The design ensures strong bonding without the risk of the inertial mass block 22 adhering to the surface of the upper gap 13 due to insufficient gap size. Therefore, the gap depth can be freely adjusted to ensure the optical accelerometer chip has an optimal damping ratio similar to 0.707, effectively suppressing nonlinear phenomena, reducing signal distortion, and helping system maintenance personnel understand signal or channel conditions. Simultaneously, under high impact overload, the upper gap 13 and lower gap 35 provide limiting protection for the inertial mass block 22, preventing excessive displacement and irreversible deformation of the beam structure 21. The maximum free displacement stroke of the inertial mass block 22 can be set by adjusting the upper gap 13 and lower gap 35 to adjust the stiffness of the beam structure 21, maximizing the measurement sensitivity and dynamic range of the optical accelerometer chip without worrying about the elastic beam breaking under high impact overload. Taking a specific design parameter as an example, the first-order natural resonant frequency of the optical acceleration sensing chip is 16KHz. Under the action of ±200g acceleration, the maximum displacement of the inertial mass block 22 is ±0.2μm, which corresponds to the cavity length change of the FP optical interference cavity inside the chip being ±0.2μm. The minimum cavity length change of the FP optical interference cavity that can be measured using the laser interference signal demodulation principle is 10pm. Thus, the optical acceleration sensing chip is guaranteed to achieve a full-scale high resolution of 0.05% and a linear accuracy of 0.01% when using the laser interference signal demodulation method.

[0033] In a further preferred embodiment, the fiber optic mounting base 11 is a stepped hole with a first step 14 and a second step 15. The single-mode fiber assembly 4 includes a glass sleeve 41 disposed on the outer layer and a single-mode fiber 42 disposed in the core. The first step 14, the second step 15, the end face of the glass sleeve 41, and the end face of the single-mode fiber are all perpendicular to the core axis of the single-mode fiber. The first step 14 forms a first fit with the end face of the glass sleeve 41, and the second step 15 forms a second fit with the end face of the single-mode fiber. The single-mode fiber is bonded together by glass solder 43. The single-mode fiber assembly 4 is fixed on the fiber mounting base 11. More preferably, the distance between the end face of the glass sleeve 41 and the end face of the single-mode fiber 42 is set as the first distance, and the distance between the first step 14 and the second step 15 is set as the second distance. The first distance is less than the second distance, and the difference between the first distance and the second distance is 5-20 μm. Through the first and second fits, the first cavity mirror and the second cavity mirror are strictly parallel, preventing the technical problem of non-parallelism of the first cavity mirror and the second cavity mirror caused by thermal stress due to temperature changes.

[0034] In another embodiment, see Figure 2 As shown, a diffuser hole 31 is provided through the third substrate 3 on the side opposite to the second substrate 2, and an optical antireflection film 32 is provided on the second substrate 2 at the position corresponding to the diffuser hole 31, thereby reducing its specular reflection and preventing its reflected light from returning to the FP optical interference cavity.

[0035] In a further preferred embodiment, see Figure 3As shown, a countersunk hole 34 is formed on the side of the third substrate 3 facing away from the second substrate 2. A diffuser hole 31 penetrating the third substrate 3 is formed at the bottom of the countersunk hole 34. An anti-reflection film 32 is provided on the second substrate 2 at the position corresponding to the diffuser hole 31, thereby reducing specular reflection and preventing reflected light from returning to the FP optical interferometer cavity, thus avoiding the influence of multi-interface reflected light introduced by the third substrate 3 on the optical performance of the FP optical interferometer cavity. More preferably, an exfoliating material 33 is arranged in the countersunk hole 34, covering the bottom wall and side periphery of the countersunk hole 34, further reducing reflected light. Other equivalent structures can also be provided for exfoliation, such as providing multiple reflective surfaces and controlling the angle of the reflective surfaces so that the reflected light is directed towards the outside or below the optical accelerometer. The wide-temperature, high-precision optical accelerometer chip based on the microcavity interferometer principle utilizes the Fabry-Perot (FP) interference principle: when three laser beams with wavelengths λ1, λ2, and λ3 are incident on the accelerometer chip, the reflected light returning from the first and second cavity mirrors into the optical fiber has the same intensity and an optical path difference, thus forming a two-beam interference corresponding to the three wavelengths. Under the action of external acceleration or vibration, the relative distance between the first and second cavity mirrors changes, that is, the optical path difference between the two beams in the two-beam interference changes, causing a corresponding change in the phase of the interference light returning to the collimator. As a result, the three interference output signals are converted into voltage signals f1, f2, and f3 by photodiodes, and finally, the information of the acceleration to be measured is obtained through calculation.

[0036] This application also relates to a method for manufacturing a wide-temperature, high-precision optical acceleration sensing chip based on the principle of a microcavity interferometer, see [link to relevant documentation]. Figure 4 The method flowchart includes: S1 forming an inertial mass block 22 and a beam structure 21 on the second substrate 2 through processing technology, the processing technology including MEMS micro-nano processing technology such as photolithography, dry etching, and wet etching; S2 fabricating an optical fiber mounting base 11, a light-transmitting hole 12, and an upper gap 13 on the first substrate 1 through processing technology; S3 fabricating a lower gap 35, a countersunk hole 34, and a diffuser hole 31 on the third substrate 3 through processing technology; the steps S1, S2, and S3 are not distinguished by a specific order and can be performed simultaneously or their order can be adjusted.

[0037] More preferably, in step S2, the reverse side of the first substrate 1 is fabricated with an optical fiber mounting base 11 and a light-passing hole 12 for fixing the single-mode optical fiber assembly 4 by a combination of KOH etching and dry etching processes. The function of the optical fiber mounting base 11 is to provide angular guidance and limiting for the optical fiber so that the end face of the optical fiber and the first face of the inertial mass block 22 have a certain spatial distance after encapsulation and fixation, ensuring that the optical acceleration sensitive chip and the optical acceleration sensitive chip prepared by optical fiber encapsulation have batch consistency. Another function of the optical fiber mounting base 11 is to provide guidance and shear protection for the solder and the glass sleeve 41 that protects the optical fiber.

[0038] More preferably, in step S3, a countersunk hole 34 and a diffuser hole 31 are fabricated on the reverse side of the third substrate 3, i.e., the side opposite to the second substrate 2, by a combination of KOH etching and dry etching. The diffuser hole 31 is used as a hard mask for patterning the optical antireflection film 32 on the second surface of the inertial mass block 22, and at the same time serves as a light-transmitting hole to eliminate the multi-interface reflection light that may be introduced into the FP optical interference cavity from the third double-polished ultra-flat silicon wafer.

[0039] Then, in step S4, the first substrate 1, the second substrate 2 and the third substrate 3 are first bonded to silicon-silicon wafers; then, using the diffuser hole 31 of the third substrate 3 as a hard mask, an optical antireflection film 32 is deposited on the lower surface of the second substrate 2 at the position corresponding to the diffuser hole 31 to form an optical antireflection film 32. Because the inertial mass block 22 retains the complete thickness and original surface finish and flatness of the double-polished ultra-flat silicon wafer, and the refractive index of single-crystal silicon is approximately between 3.4 and 3.6, which is much higher than that of glass and silicon dioxide, the remaining transmitted light from the laser emitted from the second cavity mirror of the FP optical interference cavity in the first cavity mirror (i.e., the upper surface of the inertial mass block 22) is further diverged after passing through the equivalent optical path of the thickness of the inertial mass block 22 multiplied by the refractive index of single-crystal silicon. This greatly reduces the difficulty of patterning and fabricating the optical antireflection film 32 on the second surface of the inertial mass block 22. Only after all the silicon-silicon bonding of the three double-polished ultra-flat silicon wafers is completed can the stepped hole of the third double-polished ultra-flat silicon wafer with silicon-silicon bonding be used as a hard mask to deposit the wafer-level optical antireflection film 32. This allows for the patterning and fabrication of the optical antireflection film 32 on the second surface of the inertial mass block 22 for all optical acceleration-sensitive chips mass-produced on the wafer. Since the temperature of silicon-silicon bonding exceeds 1000℃, while the temperature resistance of optical films made of optical dielectric materials is usually only around 500℃, if optical films are prefabricated on silicon wafers, there is a risk of high-temperature damage and failure of silicon-silicon bonding. If a lower-temperature gold-silicon bonding process is used, the bonding strength and long-term reliability between multiple silicon wafers cannot be guaranteed, and the overall temperature resistance of the optical accelerometer chip will be directly reduced to below 400℃, which will further reduce the sealing temperature of the solder such as the encapsulation glass, introducing problems with the packaging reliability and operating temperature of the optical accelerometer chip.

[0040] After completing the above steps, the optical accelerometer chips can be diced and cut to mass-produce optical accelerometer chips that can withstand temperatures above 500℃. These chips are then welded to precision-ground single-mode optical fibers using a low-melting-point glass (with a glass transition temperature and softening temperature not lower than 400℃) with a sealing temperature between 500℃ and 580℃, thus completing the packaging of the optical accelerometer chips. This allows the optical accelerometer chips to operate over a wide temperature range, from ultra-low temperatures to temperatures above 400℃.

Claims

1. A wide-temperature high-precision optical acceleration sensing chip based on microcavity interferometer principle, comprising a first substrate, a second substrate and a third substrate, a fiber mounting seat and a light hole are formed on the first substrate; characterized in that, The single-mode fiber assembly is fixed on the fiber mounting seat, the end face of the single-mode fiber assembly is precisely polished and perpendicular to the axial direction of the fiber core, the fiber mounting seat is a stepped hole with a first step portion and a second step portion, the single-mode fiber assembly includes a glass sleeve arranged on the outer layer and a single-mode fiber arranged on the core portion, the end face of the glass sleeve and the end face of the single-mode fiber are perpendicular to the core axis of the single-mode fiber, the first step portion and the end face of the glass sleeve form a first fit, and the second step portion and the end face of the single-mode fiber form a second fit.

2. The high-precision optical acceleration sensing chip based on the principle of the microcavity interferometer according to claim 1, characterized in that: The distance between the end face of the glass sleeve and the end face of the single-mode fiber is set as a first distance, the distance between the first step portion and the second step portion is set as a second distance, and the first distance is smaller than the second distance.

3. The high-precision optical acceleration sensing chip based on the principle of the microcavity interferometer according to claim 3, characterized in that: The difference between the first distance and the second distance is 5-20 μm.

4. The high-precision optical acceleration sensing chip based on the principle of microcavity interferometer according to any one of claims 1 to 3, characterized in that: The single-mode fiber assembly is fixed on the fiber mounting seat by a glass solder between the first step portion and the glass sleeve.

5. The high-precision optical acceleration sensing chip based on the principle of microcavity interferometer according to any one of claims 1 to 3, characterized in that: The first base, the second base and the third base are all double-polished ultra-flat silicon wafers, the single-mode fiber assembly is fixed on the fiber mounting seat, the end face of the single-mode fiber assembly is precisely polished and perpendicular to the axial direction of the fiber core, the first cavity mirror is formed on the side end face of the inertial mass block facing the through hole, the second cavity mirror is formed on the end face of the single-mode fiber assembly, the first cavity mirror and the second cavity mirror constitute an F-P interference cavity, and the first base, the second base and the third base are connected by a silicon-silicon bonding process.

6. The high-precision optical acceleration sensing chip based on the principle of the microcavity interferometer according to claim 5, characterized in that: The first cavity mirror and the second cavity mirror are parallel, and the two beams of interference light reflected back to the fiber by the F-P optical interference cavity have the same light intensity, and each light intensity is lower than 5%-20% of the incident light intensity.

7. The high-precision optical acceleration sensing chip based on the principle of the microcavity interferometer according to claim 5, characterized in that: A diffused light hole is arranged through the third base on the side of the third base away from the second base, and an optical anti-reflection film is arranged on the second base at a position corresponding to the diffused light hole.

8. The high-precision optical acceleration sensing chip based on the principle of the microcavity interferometer according to claim 1, characterized in that: A counterbore is formed on the side of the third base away from the second base, a diffused light hole is arranged through the third base on the bottom of the counterbore, and a light-absorbing material or an equivalent structure is arranged in the counterbore, covering the bottom wall and the side wall of the counterbore.

9. The high-precision optical acceleration sensing chip based on the principle of the microcavity interferometer according to claim 5, characterized in that: An optical reflection film is coated on the end face of the single-mode fiber assembly to regulate the spectral characteristics of the F-P optical interference cavity, and the reflectivity of the optical reflection film is set to be smaller than the reflectivity of the surface of the second base.

10. An acceleration sensor of a wide-temperature high-precision optical acceleration sensitive chip based on the principle of a microcavity interferometer according to any one of claims 1 to 9.

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