A wide-temperature, high-precision optical acceleration sensitive chip and sensor based on the principle of microcavity interferometer and a manufacturing method thereof

Abstract

A wide-temperature, high-precision optical acceleration sensitive chip and sensor based on the principle of a microcavity interferometer and a manufacturing method thereof, comprising a first substrate, a second substrate and a third substrate, wherein an optical fiber mounting seat and a light-through hole are formed on the first substrate, a beam structure and an inertial mass block are formed on the second substrate, the first substrate, the second substrate and the third substrate all adopt double-polished ultra-flat silicon wafers, a single-mode optical fiber assembly is fixed on the optical fiber mounting seat, the end face of the single-mode optical fiber assembly is precisely ground and perpendicular to the axial direction of the optical fiber core, a first cavity mirror is formed by using the end face of the inertial mass block facing the light-through hole, a second cavity mirror is formed by the end face of the single-mode optical fiber assembly, the first cavity mirror and the second cavity mirror constitute an F-P interferometer cavity, and the first substrate, the second substrate and the third substrate are connected by a silicon-silicon bonding process.

Description

Technical Field

[0001] The present application generally relates to the field of optoelectronic technology, and more particularly to a wide-temperature, high-precision optical acceleration sensitive chip based on the principle of a microcavity interferometer and a manufacturing method thereof, which is mainly used for the acceleration of an object and is applied to technical fields such as inertial navigation, vibration and inclination measurement. Background Art

[0002] Accelerometers are mainly used in inertial navigation, vibration and inclination measurement. In the industrial field, accelerometers can be widely used to collect signals such as vibration amplitude, frequency, phase, etc. of large structures and electromechanical equipment. Further combined with algorithms, abnormal state identification and predictive health management can be realized. In the industrial field, more stringent requirements are put forward for accelerometers in terms of electrical absolute pressure performance, lightning and electromagnetic interference resistance, ultra-low and ultra-high temperature working ability, and wide-band response capability from ultra-low frequency to medium and high frequency. For example, in large equipment such as nuclear power units, wheels, rails and pantographs in rail transit, mining machinery, fan blades, ocean-going ships and power units, sensors are required to be electrically insulated, radiation-resistant, anti-electromagnetic interference, extremely high and low temperature resistant, ultra-high precision, and resistant to large acceleration shocks.

[0003] Commonly used accelerometers can be divided into electrical detection accelerometers and optical detection accelerometers. Electrical detection accelerometers use electromechanical methods to measure the inertial force or displacement of the mass block, while optical detection accelerometers use optical signals to measure the inertial force or displacement of the mass block. Compared with the former, they not only have the unique advantage of unparalleled anti-electromagnetic interference, but also have small size and light weight, wide dynamic range, high accuracy, and can work in harsh environments such as high temperature and high humidity. In order to improve the transmission distance and anti-electromagnetic interference ability, optical detection accelerometers usually use optical fiber as a means of signal transmission.

[0004] Traditional intrinsic fiber optic sensors use partially processed optical fibers or entire optical fibers as sensing and transmission elements, and are naturally suitable for use in harsh industrial environments. However, they are restricted by many factors, such as the constant elastic properties of the optical fiber and packaging structure materials themselves, the 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, optical fiber sensors cannot achieve the accuracy of piezoelectric or even capacitive acceleration sensors. At the same time, existing optical fiber sensors are significantly affected by temperature cross-reaction, and have poor measurement repeatability and consistency between sensors, making them impossible to industrialize and mass-produce with consistency.

[0005] Single crystal silicon has excellent constant elasticity and low thermal expansion coefficient, and is an ideal material for making mechanical structures and inertial mass block-elastic beam combined acceleration sensitive structures. Especially with the development of MEMS micro-nano manufacturing technology, single crystal silicon wafers are used to make sensor sensitive chip structures and read out electrical signals through integrated manufacturing of resistors, capacitors or resonators, which has realized the consistent batch manufacturing of MEMS mechanical sensors such as pressure, acceleration, and sound. Chinese patents CN115728512A and CN115728511A disclose a fiber optic acceleration sensor, wherein a first reflection layer is deposited on an SOI silicon wafer, and a second reflection layer polished by a glass wafer is deposited on a third substrate. The acceleration sensor is a MEMS optical acceleration sensor made based on a silicon-glass bonding structure, and sufficient gaps must be reserved to avoid the attraction between silicon and glass under high bonding voltage, which causes the inertial sensitive structure and the substrate to lose relative displacement capability, causing the acceleration sensor to fail. Therefore, it is difficult to adjust the damping characteristics of the MEMS optical acceleration sensor by reducing the gap between the inertial sensitive structure and the substrate; and the temperature resistance of glass is limited, which further reduces the operating temperature range of the MEMS optical acceleration sensor; at the same time, the cost of using SOI silicon wafers to make optical interference cavities or form inertial sensitive structures is relatively high; it is difficult to ensure long-term reliability and high temperature resistance between the optical fiber in the sensor and the MEMS sensor sensitive chip by adhesive bonding or low-temperature glass welding. Summary of the invention

[0006] In view of the shortcomings of the fiber optic acceleration sensor in the prior art, the present application provides a wide temperature and high-precision optical acceleration sensitive chip based on the principle of microcavity interferometer and a manufacturing method thereof. The wide temperature and high-precision optical acceleration sensitive chip based on the principle of microcavity interferometer includes a first substrate, a second substrate and a third substrate. A fiber mounting seat and a light through hole are formed on the first substrate, and a beam structure and an inertial mass block are processed on the second substrate. The first substrate, the second substrate and the third substrate are all made of double-polished ultra-flat silicon wafers. A single-mode optical fiber assembly is fixed on the fiber mounting seat. The end face of the single-mode optical fiber assembly is precisely ground and perpendicular to the axial direction of the optical fiber core. A first cavity mirror is formed by using the end face of the inertial mass block facing the light through hole, and a second cavity mirror is formed by the end face of the single-mode optical fiber assembly. The first cavity mirror and the second cavity mirror constitute an FP interference cavity. The first substrate, the second substrate and the third substrate are connected by a silicon-silicon bonding process. The end face of the inertial mass block facing the light hole forms the first cavity mirror, which utilizes the good surface finish and flatness of the double-polished ultra-flat silicon wafer and the high optical reflectivity of single-crystal silicon. The surface reflectivity of the double-polished ultra-flat silicon wafer for lasers of 1500nm to 1600nm exceeds 25%. It is directly used as the first cavity mirror of the FP optical interferometer cavity, and the end face of the single-mode optical fiber component that is precisely ground and perpendicular to the axial direction of the optical fiber core is used as the second cavity mirror of the FP optical interferometer cavity; due to the divergence angle of the optical signal after leaving the end face of the single-mode optical fiber component, the laser emitted from the second cavity mirror of the FP optical interferometer cavity is After the reflection of the first cavity mirror of the FP optical interference cavity, only a very small part can return to the second cavity mirror of the FP optical interference cavity and enter the single-mode optical fiber, ensuring that the two cavity mirrors of the FP optical interference cavity can be strictly aligned in parallel and ensuring that the first cavity mirror not only meets the double-beam interference conditions during the large displacement of the inertial mass block, but also the spectral characteristics such as insertion loss and contrast can always be close to constant; the measured acceleration can be converted into the inertial displacement of the mass block to change the interference optical path change between the first cavity mirror and the second cavity mirror of the FP optical interference cavity, so as to calculate and obtain the acceleration information. Three double-polished ultra-flat silicon wafers are used. After each silicon wafer is processed by graphic etching, the silicon-silicon bonding process is used to realize the batch production of optical acceleration sensitive chips, eliminating the thermal stress mismatch problem introduced by the heterogeneous aggregation of wafers, reducing the temperature coefficient of the chip, and increasing the overall high temperature tolerance of the chip to above 500℃; at the same time, the use of 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 coating on the inertial mass block, simplifies the manufacturing process of the sensor, and further saves the production cost of the sensor.

[0007] In a further embodiment, the end face of the single-mode optical fiber assembly is coated with an optical reflective film to adjust 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 double-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 beams of interference light reflected back to the optical 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 double-beam interference effect.

[0008] In a further embodiment, the inertial mass block is connected to the second substrate through the beam structure, and the beam structure is a double-layer elastic beam. The structure of the double-layer elastic beam can adopt the applicant's previous existing technology, or other beam structures in the existing technology that can realize the 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 setting makes the processing of the second substrate simple and easy to implement, and the front and back surfaces of the second substrate are both natural surfaces, which improves the optical path effect; the beam structure surface has no process treatment, and the symmetry between the beam structures on the same surface and between the beam structures on the front and back surfaces is improved, which optimizes the effect of paraxial suppression.

[0009] In a further preferred embodiment, the first cavity mirror and the second cavity mirror are parallel, and the two beams of interference light reflected back to the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same light intensity and each light intensity is lower than 5%-20% of the incident light intensity, thereby ensuring that the optical acceleration sensitive chip has good double-beam interference spectrum characteristics, and the laser interference signal demodulation principle can be used to achieve a one-tenth of one-millionth high-precision measurement of the interference optical path change between the first cavity mirror and the second cavity mirror of the FP optical interference cavity inside the chip; at the same time, it also ensures that the FP optical interference cavity inside the optical acceleration sensitive chip has good stability and anti-lateral vibration interference ability. Further preferred, according to the simulation results, when the two beams of interference light reflected back to the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same light intensity and each light intensity is lower than or equal to 20% of the incident light intensity, the reflected light forms a good sinusoidal signal, which is convenient for the subsequent algorithm to demodulate, and the acceleration information can be efficiently calculated.

[0010] In a further preferred embodiment, an upper gap is etched on a side of the first substrate facing the second substrate; a lower gap is etched on a side of the third substrate facing the second substrate; the depth of the upper gap and the lower gap is 3 μm-20 μm, and by controlling the etching depth of the upper gap and the lower gap, the damping characteristics of the optical acceleration sensitive chip are adjusted and the inertial mass block is provided with limit protection, so as to avoid the elastic beam being broken due to excessive displacement of the inertial mass block under high impact; since the three are bonded by silicon-silicon, there is no need to worry about the inertial mass block being attracted to the surface of the upper gap due to the gap being too small while ensuring the bonding strength, so the depth of the gap can be freely adjusted to ensure that the optical acceleration sensitive chip has an optimal damping ratio similar to 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 gap and the lower gap can provide limit protection for the inertial mass block to prevent the inertial mass block from excessive displacement, resulting in irreversible deformation of the beam structure. The maximum free displacement of the inertial mass block can be adjusted by setting the upper gap and the lower gap, and the stiffness of the beam structure can be designed accordingly, which maximizes the measurement sensitivity and dynamic range of the optical acceleration sensitive chip, and there is no need to worry about the breakage of the elastic beam under high impact overload. Taking a specific design parameter as an example, the first-order natural resonance frequency of the optical acceleration sensitive chip is 16KHz, and the maximum displacement of the inertial mass block under the action of ±200g acceleration is ±0.2μm, which corresponds to the cavity length change of the FP optical interference cavity inside the chip is ±0.2μm. The minimum cavity length change of the FP optical interference cavity that can be measured by the laser interference signal demodulation principle is 10pm, thereby ensuring that the optical acceleration sensitive chip can achieve a high resolution of 500,000ths of the full scale and a linear accuracy of 1 / 10,000th of the full scale under the laser interference signal demodulation method.

[0011] In a further preferred embodiment, the optical fiber mounting seat is a stepped hole having a first step portion and a second step portion, the single-mode optical fiber assembly includes a glass sleeve arranged on the outer layer and a single-mode optical fiber arranged on the core, the first step portion, the second step 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 step portion forms a first fit with the end face of the glass sleeve, and the second step portion forms a second fit with the end face of the single-mode optical fiber, and the single-mode optical fiber assembly is fixed to the optical fiber mounting seat by glass solder; further preferably, the distance between the end face of the glass sleeve and the end face of the single-mode optical fiber is set to a first distance, and the distance between the first step portion and the second step portion is set to a second distance, the first distance is smaller than the second distance, and the difference between the first distance and the second distance is 5-20μm, and the strict parallelism of the first cavity mirror and the second cavity mirror is achieved through the first fit and the second fit, thereby preventing the technical problem of the first cavity mirror and the second cavity mirror being non-parallel due to thermal stress caused by temperature changes.

[0012] In a further preferred embodiment, a countersink is formed on the side of the third substrate away from the second substrate, a light diffusion hole penetrating the third substrate is opened at the bottom of the countersink, and an optical anti-reflection film is arranged at the position of the second substrate corresponding to the light diffusion hole, so as to reduce its specular reflection and prevent the reflected light from returning to the FP optical interference cavity, thereby preventing the multi-interface reflected light introduced by the third substrate from affecting the optical performance of the FP optical interference cavity. Further preferably, a matte material is arranged in the countersink, and the matte material covers the bottom wall and side periphery of the countersink to further reduce the reflected light.

[0013] The wide temperature and high precision optical acceleration sensitive chip based on the principle of microcavity interferometer uses the Fabry-Perot (FP) interference principle: when three lasers with wavelengths of λ1, λ2 and λ3 are incident on the acceleration sensor chip, the reflected light of the first cavity mirror and the second cavity mirror has the same reflection intensity and an optical path difference, so a double-beam interference corresponding to the three wavelengths can be formed. Under the action of external acceleration or vibration, the relative distance between the first cavity mirror and the second cavity mirror changes, that is, the optical path difference between the two beams of double-beam interference changes, so that the phase of the interference light returning to the collimator changes accordingly, and the three-way interference output signal is converted by the photodiode into voltage signals f1, f2, f3, and finally the information of the acceleration to be measured is obtained through calculation.

[0014] The present application also relates to an acceleration sensor, which includes a wide-temperature, high-precision optical acceleration sensitive chip based on the above-mentioned microcavity interferometer principle.

[0015] The present 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, including S1 forming an inertial mass block and a beam structure on the second substrate through a processing technology, and the processing technology includes MEMS micro-nano processing technologies such as lithography, dry etching, and wet etching; S2 making an optical fiber mounting seat, a light-through hole, and an upper gap on the first substrate through a processing technology; S3 making a lower gap, a countersunk hole, and a scattered light hole on the third substrate through a processing technology; the steps S1, S2, and S3 have no sequence distinction, and can be performed simultaneously or the sequence of steps S1, S2, and S3 can be adjusted.

[0016] Further preferably, in step S2, the reverse side of the first substrate is processed by a combined process of KOH etching and dry etching to produce a fiber mounting seat and a light hole for fixing the single-mode optical fiber assembly; the fiber mounting seat serves to provide angle guidance and positioning for the optical fiber so that after packaging and fixation, the end face of the optical fiber and the first face of the inertial mass block have a certain spatial distance, thereby ensuring batch consistency between the optical acceleration sensitive chip and the optical acceleration sensitive chip prepared by the optical fiber packaging; another function of the fiber mounting seat is to provide guidance and anti-shear protection for the solder and the glass sleeve for protecting the optical fiber.

[0017] Further preferably, in step S3, a countersunk hole and a scattered light hole are formed on the reverse side of the third substrate, i.e., the side away from the second substrate, by a combined process of KOH etching and dry etching. The scattered light hole is used for patterning a hard mask for forming an optical anti-reflection film on the second side of the inertial mass block, and at the same time serves as a light-transmitting hole to eliminate multi-interface reflected light that may be introduced into the FP optical interference cavity by the third double-polished ultra-flat silicon wafer.

[0018] Then in step S4, the first substrate, the second substrate and the third substrate are firstly bonded to silicon-silicon wafers; and then the light-scattering holes of the third substrate are used as a hard mask to form an optical anti-reflection film by wafer-level deposition on the lower surface of the second substrate corresponding to the position of the light-scattering holes. Since 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-crystalline silicon is roughly between 3.4 and 3.6, which is much higher than that of glass and silicon dioxide, the residual transmitted light of the laser emitted from the second cavity mirror of the FP optical interference cavity is further diverged after passing through the equivalent optical path of the inertial mass block thickness multiplied by the refractive index of single-crystalline silicon, which greatly reduces the difficulty of patterning the optical anti-reflection film on the second side of the inertial mass block. Only then can the optical anti-reflection film deposition at the wafer level be performed after all three double-polished ultra-flat silicon wafers are silicon-silicon bonded, and finally the stepped holes of the third double-polished ultra-flat silicon wafer bonded by silicon-silicon are used as a hard mask, so as to pattern the optical anti-reflection film on the second side of the inertial mass block of all optical acceleration sensitive chips mass-produced on the wafer. Since the temperature of silicon-silicon bonding exceeds 1000°C, and the temperature resistance of optical films made of optical dielectric materials is usually only more than 500°C, if the optical film is made on the silicon wafer in advance, the silicon-silicon bonding will be damaged and fail due to high temperature. If the lower temperature gold-silicon bonding process is used, the bonding strength and long-term reliability between the multi-layer silicon wafers cannot be guaranteed, and the overall tolerance temperature of the optical acceleration sensitive chip will be directly reduced to below 400°C, which will further reduce the sealing temperature of the packaging glass and other solders, introducing the optical acceleration sensitive chip packaging reliability and use temperature problems.

[0019] After completing the above steps, the chips can be cut and diced to produce optical acceleration sensitive chips that can withstand temperatures above 500°C in batches. The chips can be welded and fixed to the single-mode optical fiber with precision end grinding by means of low-melting glass with a sealing temperature between 500°C and 580°C (its glass transition temperature and softening temperature are not less than 400°C) to complete the packaging of the optical acceleration sensitive chips. In this way, the optical acceleration sensitive chips can have a wide operating temperature range from ultra-low temperatures to high temperatures above 400°C.

[0020] The optical acceleration sensitive chip and its manufacturing method of the present application integrate the MEMS structure with the high-precision optical FP cavity for manufacturing. Compared with the prior art, the use of 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 coating on the inertial mass block, simplifies the manufacturing process of the sensor, and further saves the production cost of the sensor; three double-polished ultra-flat silicon wafers are used, each of which is processed by graphic etching, and the silicon-silicon bonding process is used to realize the batch production of optical acceleration sensitive chips, which eliminates the thermal stress mismatch problem introduced by heterogeneous aggregation of wafers, reduces the temperature coefficient of the chip, and increases the overall tolerance of the chip to high The temperature is raised to above 500°C; the adjustment of the upper and lower gap depths ensures that the optical acceleration sensitive chip has an optimal damping ratio similar to 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 gap and the lower gap can provide limit protection for the inertial mass block to prevent the transitional displacement of the inertial mass block and cause irreversible deformation of the beam structure; through the cooperation of the stepped hole and the single-mode optical fiber assembly, the parallelism of the two cavity mirrors is guaranteed, and at the same time, the bonding force between the single-mode optical fiber assembly and the first substrate is improved to prevent the single-mode optical fiber assembly from falling off in application scenarios with large vibrations. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the structure of the first embodiment of the optical acceleration sensor chip of the present application;

[0022] Figure 2 This is a schematic diagram of the structure of the second embodiment of the optical acceleration sensor chip of the present application;

[0023] Figure 3 This is a schematic diagram of the structure of the third embodiment of the optical acceleration sensor chip of the present application;

[0024] Figure 4 This is a flow chart of the application method;

[0025] Description of reference numerals:

[0026] 1-first substrate; 11-fiber mounting seat; 12-light hole; 13-upper gap; 14-first step; 15-second step; 2-second substrate; 21-beam structure; 22-inertial mass block; 3-third substrate; 31-light diffusion hole; 32-optical anti-reflection film; 33-extinction material; 34-counterbore; 35-lower gap; 4-single-mode optical fiber assembly; 41-glass sleeve; 42-single-mode optical fiber; 43-glass solder. DETAILED DESCRIPTION

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] In order to simplify the drawings, only the parts related to the present invention are schematically shown in each figure, and they do not represent the actual structure of the product. In addition, in order to simplify the drawings and facilitate understanding, in some figures, only one of the parts with the same structure or function is schematically drawn or marked. In this article, "one" not only means "only one", but also means "more than one".

[0029] It should be further understood that the term “and / or” used in the specification and appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0030] In this document, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0031] In view of the shortcomings of the optical fiber acceleration sensor in the prior art, the present application provides a wide temperature and high precision optical acceleration sensitive chip based on the principle of microcavity interferometer and a manufacturing method thereof. The wide temperature and high precision optical acceleration sensitive chip based on the principle of microcavity interferometer comprises a first substrate 1, a second substrate 2 and a third substrate 3. Figure 1As shown in the figure, an optical fiber mounting seat 11 and a light through hole 12 are formed on the first substrate 1, 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 component 4 is fixed on the optical fiber mounting seat 11, the end face of the single-mode optical fiber component 4 is precisely ground and perpendicular to the axial direction of the optical fiber core, a first cavity mirror is formed by using the end face of the inertial mass block 22 facing the light through hole 12, and a second cavity mirror is formed by the end face of the single-mode optical fiber component 4, the first cavity mirror and the second cavity mirror constitute an FP interference cavity, and the first substrate 1, the second substrate 2 and the third substrate 3 are connected by a silicon-silicon bonding process. The end face of the inertial mass block 22 facing the light hole 12 forms a first cavity mirror, which utilizes the good surface finish and flatness of the double-polished ultra-flat silicon wafer and the high optical reflectivity of single-crystal silicon. The surface reflectivity of the double-polished ultra-flat silicon wafer for the laser of 1500nm to 1600nm exceeds 25%, and it is directly used as the first cavity mirror of the FP optical interference cavity. The end face of the single-mode optical fiber component 4 that is precisely ground and perpendicular to the axial direction of the optical fiber core 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 optical fiber component 4, the laser emitted from the second cavity mirror of the FP optical interference cavity After the light is reflected by the first mirror of the FP optical interference cavity, only a very small part of it can return to the second mirror of the FP optical interference cavity and enter the single-mode optical fiber, ensuring that the two mirrors of the FP optical interference cavity can be strictly aligned in parallel and that the FP optical interference cavity not only meets the double-beam interference condition during the large displacement of the inertial mass block 22, but also that the spectral characteristics such as insertion loss and contrast can always be 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 mirror and the second mirror of the FP optical interference cavity, thereby calculating and obtaining the acceleration information. Three double-polished ultra-flat silicon wafers are used. After each silicon wafer is processed by graphic etching, a silicon-silicon bonding process is used to realize batch production of optical acceleration sensitive chips, eliminating the thermal stress mismatch problem introduced by heterogeneous aggregation of wafers, reducing the temperature coefficient of the chip, and increasing the overall high temperature resistance of the chip to above 500°C. At the same time, the use of 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 coating on the inertial mass block 22, simplifies the manufacturing process of the sensor, and further saves the production cost of the sensor.

[0032] In a further embodiment, the end face of the single-mode optical fiber component 4 is coated with an optical reflective film to adjust 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 double-beam interference spectral characteristics. In a further preferred embodiment, the reflectivity of the optical reflective film is selected to be smaller than the reflectivity of the surface of the second substrate 3, so that the two anti-interference beams reflected back to the optical fiber by the first cavity mirror and the second cavity mirror have the same light intensity, and the best double-beam interference effect is obtained.

[0033] In a further embodiment, the inertial mass block 22 is connected to the second substrate 2 through the beam structure 21, and the beam structure 21 is a double-layer elastic beam. The structure of the double-layer elastic beam can adopt the prior art of the applicant, or other beam structures 21 in the prior art that can realize the 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 setting makes the processing of the second substrate simple and easy to achieve, and the front and back surfaces of the second substrate are both natural surfaces, which improves the optical path effect; the beam structure surface has no process treatment, and the symmetry between the beam structures on the same surface and between the beam structures on the front and back surfaces is improved, which optimizes the effect of paraxial suppression.

[0034] In a further preferred embodiment, in order to prevent multi-interface reflection from affecting the optical performance of the FP optical interference cavity, an optical anti-reflection film 32 is patterned on the lower surface of the inertial mass block 22 to reduce its mirror reflection and prevent the reflected light from returning to the FP optical interference cavity.

[0035] In a further preferred embodiment, the first cavity mirror and the second cavity mirror are parallel, and the two beams of interference light reflected back to the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same light intensity and each light intensity is lower than 5%-20% of the incident light intensity, thereby ensuring that the optical acceleration sensitive chip has good double-beam interference spectrum characteristics, and the laser interference signal demodulation principle can be used to achieve a one-tenth of one-millionth high-precision measurement of the interference optical path change between the first cavity mirror and the second cavity mirror of the FP optical interference cavity inside the chip; at the same time, it also ensures that the FP optical interference cavity inside the optical acceleration sensitive chip has good stability and anti-lateral vibration interference ability. Further preferred, according to the simulation results, when the two beams of interference light reflected back to the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same light intensity and each light intensity is lower than 12% of the incident light intensity, the reflected light forms a good sinusoidal signal, which is convenient for the subsequent algorithm to demodulate, and the acceleration information can be efficiently calculated.

[0036] In a further preferred embodiment, an upper gap 13 is etched on a side of the first substrate 1 facing the second substrate 2; a lower gap 35 is etched on a side of the third substrate 3 facing the second substrate 2; the depths of the upper gap 13 and the lower gap 35 are 3 μm-20 μm, and 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 avoid excessive displacement of the inertial mass block 22 under high impact, resulting in the breakage of the elastic beam; due to the three silicon-silicon bonds On the basis of ensuring the bonding strength, there is no need to worry about the gap being too small causing the inertial mass block 22 to be attracted to the surface of the upper gap 13. Therefore, the depth of the gap can be freely adjusted to ensure that the optical acceleration sensitive chip has an optimal damping ratio similar to 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 gap 13 and the lower gap 35 can provide limit protection for the inertial mass block 22 to prevent the transitional displacement of the inertial mass block 22, resulting in irreversible deformation of the beam structure 21. The maximum free displacement stroke of the inertial mass block 22 can be set by the upper gap 13 and the lower gap 35, and the stiffness of the beam structure 21 can be designed and adjusted accordingly, which maximizes the measurement sensitivity and dynamic range of the optical acceleration sensitive chip, and there is no need to worry about the breakage of the elastic beam under high impact overload. Taking a specific design parameter as an example, the first-order natural resonance frequency of the optical acceleration sensitive chip is 16KHz, and the maximum displacement of the inertial mass block 22 under the action of ±200g acceleration is ±0.2μm, that is, the cavity length change of the FP optical interference cavity inside the chip is ±0.2μm, and the minimum cavity length change of the FP optical interference cavity that can be measured by the laser interference signal demodulation principle is 10pm. Therefore, it is guaranteed that the optical acceleration sensitive chip can achieve a high resolution of 5 / 100,000 of the full scale and a linear accuracy of 1 / 10,000 when using the laser interference signal demodulation method.

[0037] In a further preferred embodiment, the optical fiber mounting seat 11 is a stepped hole having a first step 14 and a second step 15, the single-mode optical fiber assembly 4 comprises a glass sleeve 41 arranged on the outer layer and a single-mode optical fiber 42 arranged on 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 optical fiber are all perpendicular to the core axis of the single-mode optical fiber, the first step 14 forms a first match with the end face of the glass sleeve 41, the second step 15 forms a second match with the end face of the single-mode optical fiber, and the single-mode optical fiber is connected to the glass solder 43. The single-mode optical fiber assembly 4 is fixed on the optical fiber mounting seat 11; further preferably, the distance between the end face of the glass sleeve 41 and the end face of the single-mode optical fiber 42 is set as a first distance, and the distance between the first step 14 and the second step 15 is set as a second distance, the first distance is smaller than the second distance, and the difference between the first distance and the second distance is 5-20μm, and the strict parallelism of the first cavity mirror and the second cavity mirror is achieved through the first cooperation and the second cooperation, thereby preventing the technical problem of the first cavity mirror and the second cavity mirror being not parallel due to thermal stress caused by temperature changes.

[0038] In another embodiment, see Figure 2 As shown in the figure, a light diffusion hole 31 is provided through the third substrate 3 on the side of the third substrate 3 away from the second substrate 2, and an optical anti-reflection film 32 is provided at a position of the second substrate 2 corresponding to the light diffusion hole 31, so as to reduce its mirror reflection and prevent the reflected light from returning to the FP optical interference cavity.

[0039] In a further preferred embodiment, see Figure 3As shown in , a countersunk hole 34 is formed on the side of the third substrate 3 away from the second substrate 2, and a diffuse light hole 31 penetrating the third substrate 3 is opened at the bottom of the countersunk hole 34. An optical anti-reflection film 32 is arranged at the position of the second substrate 2 corresponding to the diffuse light hole 31, so as to reduce its mirror reflection and prevent its reflected light from returning to the FP optical interference cavity, thereby avoiding the multi-interface reflected light introduced by the third substrate 3 from affecting the optical performance of the FP optical interference cavity. Further preferably, an extinction material 33 is arranged in the countersunk hole 34, and the extinction material 33 covers the bottom wall and side periphery of the countersunk hole 34 to further reduce the reflected light. Other equivalent structures can also be set for extinction, such as setting multiple reflection surfaces, and controlling the angles of the reflection surfaces so that the reflected light is directed to the outside or below of the optical acceleration sensor. The wide temperature and high precision optical acceleration sensitive chip based on the principle of microcavity interferometer uses the Fabry-Perot (FP) interference principle: when three lasers with wavelengths of λ1, λ2 and λ3 are incident on the acceleration sensor chip, the reflected light returned by the first cavity mirror and the second cavity mirror into the optical fiber has the same intensity and an optical path difference, so a double-beam interference corresponding to the three wavelengths can be formed. Under the action of external acceleration or vibration, the relative distance between the first cavity mirror and the second cavity mirror changes, that is, the optical path difference between the two beams of double-beam interference changes, so that the phase of the interference light returning to the collimator changes accordingly, and the three-way interference output signal is converted by the photodiode into voltage signals f1, f2, f3, and finally the information of the acceleration to be measured is obtained through calculation.

[0040] The present application also relates to a method for manufacturing a wide temperature and high precision optical acceleration sensitive chip based on the principle of microcavity interferometer, see Figure 4 The method flow chart includes S1 forming an inertial mass block 22 and a beam structure 21 on the second substrate 2 by a processing technology, and the processing technology includes MEMS micro-nano processing technology such as photolithography, dry etching, and wet etching; S2 making an optical fiber mounting seat 11, a light-through hole 12, and an upper gap 13 on the first substrate 1 by a processing technology; S3 making a lower gap 35, a countersunk hole 34, and a scattered light hole 31 on the third substrate 3 by a processing technology; the steps S1, S2, and S3 have no sequence distinction, and can be performed simultaneously or the sequence of steps S1, S2, and S3 can be adjusted.

[0041] Further preferably, in step S2, the reverse side of the first substrate 1 is processed by a combined process of KOH etching and dry etching to produce a fiber mounting seat 11 and a light hole 12 for fixing the single-mode optical fiber assembly 4. The function of the fiber mounting seat 11 is to provide angle guidance and positioning for the optical fiber so that after packaging and fixing, the end face of the optical fiber and the first surface of the inertial mass block 22 have a certain spatial distance, thereby ensuring that the optical acceleration sensitive chip and the optical acceleration sensitive chip prepared by the optical fiber packaging have batch consistency. Another function of the fiber mounting seat 11 is to provide guidance and anti-shear protection for the solder and the glass sleeve 41 for protecting the optical fiber.

[0042] Further preferably, in step S3, a countersunk hole 34 and a light-scattering hole 31 are formed on the reverse side of the third substrate 3, i.e., the side away from the second substrate 2, by a combined process of KOH etching and dry etching. The light-scattering hole 31 is used for patterning a hard mask for forming an optical anti-reflection film 32 on the second side of the inertial mass block 22, and at the same time serves as a light-transmitting hole to eliminate multi-interface reflected light that may be introduced into the FP optical interference cavity by the third double-polished ultra-flat silicon wafer.

[0043] Then in step S4, the first substrate 1, the second substrate 2 and the third substrate 3 are firstly bonded to silicon-silicon wafers; then, the light-scattering holes 31 of the third substrate 3 are used as a hard mask, and an optical anti-reflection film 32 is formed by wafer-level deposition on the lower surface of the second substrate 2, i.e., at the position corresponding to the light-scattering holes 31. Since 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 roughly between 3.4 and 3.6, which is much higher than that of glass and silicon dioxide, the residual transmitted light of the laser emitted 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 22 multiplied by the refractive index of single-crystal silicon at the first cavity mirror (i.e., the upper surface of the inertial mass block 22), which greatly reduces the difficulty of patterning the optical anti-reflection film 32 on the second surface of the inertial mass block 22. Only then can the optical anti-reflection film 32 be deposited at the wafer level after all three double-polished ultra-flat silicon wafers are silicon-silicon bonded, and finally the stepped holes of the third double-polished ultra-flat silicon wafer bonded by silicon-silicon are used as a hard mask, so as to pattern the optical anti-reflection film 32 on the second surface of the inertial mass block 22 of all optical acceleration sensitive chips mass-produced on the wafer. Since the temperature of silicon-silicon bonding exceeds 1000°C, and the temperature resistance of optical films made of optical dielectric materials is usually only more than 500°C, if the optical film is made on the silicon wafer in advance, the silicon-silicon bonding will be damaged and fail due to high temperature. If the lower temperature gold-silicon bonding process is used, the bonding strength and long-term reliability between the multi-layer silicon wafers cannot be guaranteed, and the overall tolerance temperature of the optical acceleration sensitive chip will be directly reduced to below 400°C, which will further reduce the sealing temperature of the packaging glass and other solders, introducing the optical acceleration sensitive chip packaging reliability and use temperature problems.

[0044] After completing the above steps, the chips can be cut and diced to produce optical acceleration sensitive chips that can withstand temperatures above 500°C in batches. The chips can be welded and fixed to the single-mode optical fiber with precision end grinding by means of low-melting glass with a sealing temperature between 500°C and 580°C (its glass transition temperature and softening temperature are not less than 400°C) to complete the packaging of the optical acceleration sensitive chips. In this way, the optical acceleration sensitive chips can have a wide operating temperature range from ultra-low temperatures to high temperatures above 400°C.

Claims

1. A wide temperature and high precision optical acceleration sensitive chip based on the principle of microcavity interferometer, comprising a first substrate, a second substrate and a third substrate, wherein a fiber mounting seat and a light through hole are formed on the first substrate; characterized in that: A beam structure and an inertial mass block are processed on the second substrate; the first substrate, the second substrate and the third substrate are all made of double-polished ultra-flat silicon wafers; a single-mode optical fiber assembly is fixed on the optical fiber mounting seat; the end face of the single-mode optical fiber assembly is precisely ground and perpendicular to the axial direction of the optical fiber core; a first cavity mirror is formed by using the end face of the inertial mass block facing the light-through hole; a second cavity mirror is formed by the end face of the single-mode optical fiber assembly; the first cavity mirror and the second cavity mirror constitute an FP interferometer cavity; the first substrate, the second substrate and the third substrate are connected by a silicon-silicon bonding process; the upper surface and the lower surface of the second substrate are both natural surfaces; A light diffusion hole is provided on a side of the third substrate facing away from the second substrate, and an optical anti-reflection film is provided at a position of the second substrate corresponding to the light diffusion hole; after the first substrate, the second substrate and the third substrate are silicon-silicon wafer bonded; the light diffusion hole of the third substrate is used as a hard mask, and the optical anti-reflection film is formed on the lower surface of the second substrate corresponding to the position of the light diffusion hole.

2. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle described in claim 1 is characterized in that: The inertial mass block is connected to the second substrate through the beam structure, the beam structure is a double-layer elastic beam, and 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.

3. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to claim 1 or 2, characterized in that: The first cavity mirror and the second cavity mirror are parallel, and the two interference lights reflected back to the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same light intensity and each light intensity is lower than 5%-20% of the incident light intensity.

4. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle as described in claim 3, characterized in that: The two interference lights reflected back to the optical fiber by the two cavity mirrors of the FP optical interference cavity have the same light intensity and their respective light intensities are both lower than 20% of the incident light intensity.

5. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to claim 1 or 2, characterized in that: An upper gap is formed by etching on a side of the first substrate facing the second substrate; and a lower gap is formed by etching on a side of the third substrate facing the second substrate.

6. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle as described in claim 5, characterized in that: The depth of the upper gap and / or the lower gap is adjusted so that the optical acceleration sensitive chip has an optimal damping ratio of 0.

707.

7. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to claim 1 or 2, characterized in that: The optical fiber mounting seat is a stepped hole having a first step portion and a second step portion. The single-mode optical fiber assembly includes a glass sleeve arranged on the outer layer and a single-mode optical fiber arranged on the core. The first step portion, the second step 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 step portion forms a first fit with the end face of the glass sleeve, and the second step portion forms a second fit with the end face of the single-mode optical fiber.

8. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle as described in claim 7, characterized in that: The distance between the end face of the glass sleeve and the end face of the single-mode optical fiber is set as a first distance, and the distance between the first step portion and the second step portion is set as a second distance. The first distance is smaller than the second distance, and the difference between the first distance and the second distance is 5-20 μm.

9. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle as described in claim 1, characterized in that: A countersunk hole is formed on the side of the third substrate facing away from the second substrate, and a light-scattering hole penetrating the third substrate is opened at the bottom of the countersunk hole; a matte material or an equivalent structure is arranged in the countersunk hole, and the matte material or the equivalent structure covers the bottom wall and side periphery of the countersunk hole.

10. The wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to claim 1 or 2, characterized in that: An optical reflective film is plated on the end face of the single-mode optical fiber component to adjust the spectral characteristics of the FP optical interference cavity, and the reflectivity of the optical reflective film is set to be smaller than the reflectivity of the second substrate surface.

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

12. A method for manufacturing a wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to any one of claims 1 to 10, specifically comprising: S1. Forming an inertial mass block and a beam structure on the second substrate by a processing technique; S2. Manufacturing a fiber mounting seat, a light-through hole and an upper gap on the first substrate by a processing technology; S3. Manufacturing a lower gap, a countersunk hole and a light-scattering hole on the third substrate by a processing technology; the steps S1, S2 and S3 are not distinguished in order; S4. First, the first substrate, the second substrate and the third substrate are bonded to silicon-silicon wafers; then, the light diffusion holes of the third substrate are used as a hard mask to form an optical anti-reflection film on the lower surface of the second substrate at positions corresponding to the light diffusion holes.

13. The method for manufacturing a wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to claim 12, characterized in that: In the step S2, the reverse side of the first substrate is processed by a combination of KOH etching and dry etching to form an optical fiber mounting seat and a light hole for fixing the single-mode optical fiber assembly.

14. A method for manufacturing a wide temperature and high precision optical acceleration sensitive chip based on the microcavity interferometer principle according to claim 12 or 13, characterized in that: In the step S3, countersunk holes and scattered light holes are formed on the reverse side of the third substrate by a combined process of KOH etching and dry etching.

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