Differential MEMS optical fiber differential pressure sensor chip and manufacturing method therefor

Abstract

A differential MEMS optical fiber differential pressure sensor chip (100), comprising: a first pressure-sensitive structure (10), a second pressure-sensitive structure (20), an intermediate sensitive layer structure (30), a first optical fiber collimator pair (60), and a second optical fiber collimator pair (70), wherein the intermediate sensitive layer structure (30) is arranged between the bottom surface of the first pressure-sensitive structure (10) and the bottom surface of the second pressure-sensitive structure (20); and the intermediate sensitive layer structure (30) is configured to separate the first optical fiber collimator pair (60) from the second optical fiber collimator pair (70), and is constructed to support the first pressure-sensitive structure (10) and the second pressure-sensitive structure (20) and reduce the stiffness of the intermediate sensitive layer structure (30). The chip has an ingenious structure, can be mass-produced, and has the advantages of a passive probe, resistance to electromagnetic interference, capability for long-distance transmission, capability of operating in severe environments, etc. The present application further relates to a manufacturing method for a differential MEMS optical fiber differential pressure sensor chip.

Description

Differential MEMS fiber optic differential pressure sensor chip and manufacturing method thereof TECHNICAL FIELD

[0001] The present application relates to the technical field of optical fiber sensing detection, and particularly relates to a differential MEMS fiber optic differential pressure sensor chip and a manufacturing method thereof. BACKGROUND

[0002] The present disclosure aims to support the construction of high-level research institutions, accelerate the independent research and development of key scientific research instruments and standard construction, focus on the key core technology and domestic components of high-end general scientific instrument equipment and major scientific instrument equipment, enhance the independent research and development and professional supply of large-scale scientific instruments and research devices, and innovate and break through to form an optical fiber sensing detection technology with independent intellectual property rights.

[0003] Specifically, the present application relates to the technical field of optical fiber sensing detection, and to the micro-electro-mechanical system (MEMS) technology. MEMS is a micro-mechanical or micro-electromechanical element manufactured by means of semiconductor technology, with a size ranging from nanometers to millimeters, and typical features of small size, low power consumption and batch production. Common MEMS devices include acceleration sensors, pressure sensors, oscillators, microphones, etc. MEMS pressure sensors have been widely used in consumer electronics, automobiles, rail transportation, aerospace and other industrial internet applications. MEMS differential pressure sensors, as an important branch of MEMS pressure sensors, have also been widely used. However, traditional piezoresistive differential pressure sensors have the following problems: low detection accuracy, large temperature coefficient, susceptibility to fluctuation interference, and inability to measure small pressure difference changes; and thermal MEMS differential pressure sensors have the disadvantages of long response time and high power consumption, which are not conducive to the widespread application of MEMS differential pressure sensors. Moreover, the current technical approach lacks a simple and batch production method, hindering the industrial application of fiber optic differential pressure sensors. In particular, in some high-temperature and strong electromagnetic interference environments, the differential pressure sensor cannot be used, and there is an urgent need for a passive, electromagnetic interference-resistant and high-precision differential pressure sensor.

[0004] Therefore, the prior art still needs to be improved and enhanced.

[0005] SUMMARY

[0006] To solve one or more of the above technical problems, the present disclosure provides a differential MEMS fiber optic differential pressure sensor chip and a manufacturing method thereof.

[0007] In a first aspect of the present disclosure, a differential MEMS fiber optic differential pressure sensor chip is provided, comprising: a first pressure sensitive structure, a second pressure sensitive structure, an intermediate sensitive layer structure, a first fiber collimator pair, and a second fiber collimator pair; the first pressure sensitive structure is configured as a membrane-island structure with a bottom surface and a side surface surrounding the membrane-island structure, the bottom of the first pressure sensitive structure is provided with a first collimating groove, and the first collimating groove cooperates with the intermediate sensitive layer structure to form a first collimating through hole; the second pressure sensitive structure is configured as a membrane-island structure with a bottom surface and a side surface surrounding the membrane-island structure, and the second pressure sensitive structure is configured to be mirror-symmetric to the first pressure sensitive structure with respect to the intermediate plane of the intermediate sensitive layer structure, the bottom of the second pressure sensitive structure is provided with a second collimating groove, and the second collimating groove cooperates with the intermediate sensitive layer structure to form a second collimating through hole; the first fiber collimator pair is symmetrically arranged and fixed in the first collimating through hole between the bottom surface of the first pressure sensitive structure and the intermediate sensitive layer structure, and the two fiber collimators in the first fiber collimator pair are arranged in alignment; the second fiber collimator pair is symmetrically arranged and fixed in the second collimating through hole between the bottom surface of the second pressure sensitive structure and the intermediate sensitive layer structure, and the two fiber collimators in the second fiber collimator pair are arranged in alignment; the intermediate sensitive layer structure is arranged between the bottom surface of the first pressure sensitive structure and the bottom surface of the second pressure sensitive structure; the intermediate sensitive layer structure is arranged to separate the first fiber collimator pair and the second fiber collimator pair, and the intermediate sensitive layer structure is configured to support the first pressure sensitive structure and the second pressure sensitive structure and reduce the rigidity of the intermediate sensitive layer structure.

[0008] Further, in some embodiments, the intermediate sensitive layer structure is configured as a hollow structure or a grid structure, and the grid structure is arranged as a grid structure composed of parallel and equidistant strips or frames.

[0009] Further, in some embodiments, the distance between the end faces of the two fiber collimators in the first fiber collimator pair is equal to the distance between the end faces of the two fiber collimators in the second fiber collimator pair; the distance from the end face of one fiber collimator in the first fiber collimator pair to the central axis of the first pressure sensitive structure is equal to the distance from the end face of the other fiber collimator in the first fiber collimator pair to the central axis of the first pressure sensitive structure; the distance from the end face of one fiber collimator in the second fiber collimator pair to the central axis of the second pressure sensitive structure is equal to the distance from the end face of the other fiber collimator in the second fiber collimator pair to the central axis of the second pressure sensitive structure.

[0010] Further, in some embodiments, the distance from the end face of any fiber collimator in the first fiber collimator pair to the central axis of the first pressure sensitive structure is equal to the distance from the end face of any fiber collimator in the second fiber collimator pair to the central axis of the second pressure sensitive structure.

[0011] Further, in some embodiments, the differential MEMS fiber differential pressure sensor chip further comprises: a first side via hole arranged on the first pressure sensitive structure close to the side surface of the first pressure sensitive structure; a second side via hole arranged on the second pressure sensitive structure close to the side surface of the second pressure sensitive structure; the first fiber collimator pair is arranged to be welded to the first pressure sensitive structure through the first side via hole, and the second fiber collimator pair is arranged to be welded to the second pressure sensitive structure through the second side via hole.

[0012] In a second aspect of the present disclosure, a preparation method of a fiber differential pressure sensor chip is provided, which comprises: S1, forming a film-island structure on a first polished surface of a silicon wafer with a given thickness by photolithography, dry etching or wet etching; S2, forming a collimating groove on a second polished surface of the silicon wafer by photolithography, dry etching or wet etching, the second polished surface being another polished surface away from the first polished surface of the silicon wafer; S3, forming two fiber welding via holes on the silicon wafer between the film-island structure side and the outer side of the silicon wafer by photolithography, dry etching or wet etching, thereby obtaining the first pressure sensitive structure; S4, repeating S1-S3 to obtain the second pressure sensitive structure; S5, performing photolithography on the top layer silicon of an SOI silicon wafer, and then forming a hollow structure or a grid structure on the top layer silicon by dry etching or wet etching; S6, performing silicon-silicon bonding between the first pressure sensitive structure and the SOI silicon wafer, the corresponding bonding surface being the second polished surface of the first pressure sensitive structure and the top layer silicon of the SOI silicon wafer, and the collimating groove of the first pressure sensitive structure and the top layer silicon of the SOI silicon wafer forming the first collimating via hole; S7, thinning and etching the substrate silicon and buried oxygen layer of the SOI silicon wafer to expose the top layer silicon, to form the intermediate sensitive layer structure; S8, performing silicon-silicon bonding between the second pressure sensitive structure and the intermediate sensitive layer structure, the corresponding bonding surface being the side of the intermediate sensitive layer structure away from the first pressure sensitive structure and the side of the second pressure sensitive structure formed with the collimating groove, and the collimating groove of the second pressure sensitive structure and the intermediate sensitive layer structure forming the second collimating via hole; S9, arranging the first fiber collimator pair and the second fiber collimator pair in the first collimating via hole and the second collimating via hole respectively and aligning.

[0013] Further, in some embodiments, the preparation method is in S1, the silicon wafer is a double-polished silicon wafer, and the double-polished silicon wafer refers to that polishing processing is performed on both sides of the silicon wafer.

[0014] Further, in some embodiments, the preparation method is in S5, and the etching depth of the top layer silicon is the thickness of the top layer silicon.

[0015] Further, in some embodiments, the preparation method is in S7, and the thinning and etching of the substrate silicon and the buried oxygen layer of the SOI silicon wafer to expose the top layer silicon refer to that the substrate silicon of the SOI silicon wafer is thinned by dry etching or wet etching to expose the buried oxygen layer of the SOI silicon wafer, and then the buried oxygen layer of the SOI silicon wafer is etched by dry etching or wet etching to expose the top layer silicon, so as to form the intermediate sensitive layer structure.

[0016] Further, in some embodiments, the preparation method is in S9, and after the first fiber collimator pair and the second fiber collimator pair are respectively aligned, the first fiber collimator pair and the second fiber collimator pair are respectively welded and fixed in the first collimating through hole and the second collimating through hole by applying solder through the fiber welding through hole.

[0017] The beneficial effects of the present disclosure are that:

[0018] 1) In some embodiments, the first pressure sensitive structure and the second pressure sensitive structure are distributed in mirror symmetry with respect to the intermediate plane of the intermediate sensitive layer structure (i.e., the plane in the middle position where the distance to the upper surface and the lower surface of the intermediate sensitive layer structure is equal), and when the differential pressure exists, one generates stretching and the other generates compression, therefore, the two F-P cavities formed by the two collimator pairs have one cavity length becoming longer and the other cavity length becoming shorter, and the change amount is consistent, at this time, the output wavelength change of the two F-P cavities is subtracted and will not be 0, therefore, the information of the external differential pressure can be obtained, and the output signal will be twice as large as the signal when only the first pressure sensitive structure or the second pressure sensitive structure exists, thereby making the fiber differential pressure sensor with the structure have the advantages of anti-interference and signal amplification at the same time;

[0019] 2) In some embodiments, the intermediate sensitive layer structure reduces the original stiffness of the intermediate sensitive layer structure under the condition of guaranteeing that the partition is in the first fiber collimator pair in the first pressure sensitive structure and the second fiber collimator pair in the second pressure sensitive structure, supporting the first pressure sensitive structure and the second pressure sensitive structure under pressure (so as not to be crushed when the first pressure sensitive structure and the second pressure sensitive structure are under pressure during measurement), forming the corresponding mirror image F-P cavity, and facilitating the alignment and fixation of the first fiber collimator pair and the second fiber collimator pair.

[0020] 3) In some embodiments of the preparation process of the intermediate sensitive layer structure, by gradually thinning the substrate silicon of the SOI silicon wafer, then gradually etching the buried oxide layer to gradually expose the top layer silicon, the surface properties of the top layer silicon and the side of the buried oxide layer can be effectively protected, which is conducive to the formation of the intermediate sensitive layer structure, and without damaging the intermediate sensitive layer structure, another pressure sensitive structure layer (for example, a second pressure sensitive structure) can be effectively re-bonded;

[0021] 4) In some embodiments, the intermediate sensitive layer structure with a grid structure is made of the top layer silicon of the SOI silicon wafer, which not only can adjust the thickness of the grid structure by customizing the thickness of the top layer silicon (the conventional way is to use etching or corrosion to obtain the required thickness, but etching or corrosion will cause the silicon surface flatness to deteriorate greatly and thus cannot be bonded), but also the top layer silicon of the SOI silicon wafer is a natural polished surface of silicon on both sides, which is not subjected to any thinning treatment. This natural polished surface is an ideal bonding interface, thereby greatly reducing the bonding difficulty in the present application.

[0022] 5) In some embodiments, after the first fiber collimator pair and the second fiber collimator pair are respectively aligned, the first fiber collimator pair and the second fiber collimator pair are respectively welded and fixed in the first collimating through hole and the second collimating through hole by applying solder through the fiber welding through hole. It can be seen that the fiber welding through hole arrangement can facilitate the fixation of the fiber collimator pair in the collimating through hole. BRIEF DESCRIPTION OF DRAWINGS

[0023] The above and other features, advantages, and aspects of embodiments of the present disclosure will become more apparent upon consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which:

[0024] FIG. 1 shows a cross-sectional schematic view of a differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure;

[0025] FIG. 2 shows a schematic view of a differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure;

[0026] FIG. 3 shows another cross-sectional schematic view of a differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure;

[0027] FIG. 4 shows a schematic view of an intermediate sensitive layer structure of a differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure;

[0028] FIG. 5 shows a graph of the relationship between the thickness of a solid structure intermediate sensitive layer structure and the wavelength differential output according to an embodiment of the present disclosure;

[0029] FIG. 6 shows a diagram of the thickness of the middle sensing layer structure of the grid structure versus the full-scale wavelength differential output according to an embodiment of the present disclosure;

[0030] FIG. 7 shows a flowchart of a preparation method of the differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure;

[0031] FIG. 8 shows a schematic diagram of a preparation process of the differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure; and

[0032] In the various drawings, the same or corresponding reference signs represent the same or corresponding parts. DETAILED DESCRIPTION

[0033] Embodiments of the present disclosure will be described in more detail with reference to the drawings. Although certain embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure can be implemented in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that the present disclosure can be more thoroughly and completely understood. It should be understood that the drawings and embodiments of the present disclosure are for exemplary purposes only and are not intended to limit the scope of protection of the present disclosure.

[0034] In the description of embodiments of the present disclosure, the term "comprising" and its conjugations should be understood to encompass the meanings of "consisting of" and "consisting essentially of". The term "based on" should be understood as "based at least in part on". The term "one embodiment" or "the embodiment" should be understood as "at least one embodiment". The terms "first", "second", etc. can refer to different or identical objects. Other explicit and implicit definitions can also be included below.

[0035] It should be noted that the conventional piezoresistive differential pressure sensor has the disadvantages of low detection accuracy, large temperature coefficient, susceptibility to fluctuation interference, and inability to measure smile pressure difference changes. Correspondingly, the thermal MEMS differential pressure sensor has the disadvantages of long response time, high power consumption, and the like, which is not conducive to the wide application of the MEMS differential pressure sensor. In contrast, the fiber pressure sensor uses the coupling of the optical fiber and the mechanical pressure-sensitive diaphragm to measure the pressure difference, has a series of advantages such as passive probe, anti-electromagnetic interference, long-distance transmission, and work in harsh environments, so the fiber differential pressure sensor has a wider range of applications, but the corresponding technical means lacks a simple and batch production method, thus hindering the industrial application of the fiber differential pressure sensor.

[0036] To this end, the present disclosure proposes a differential MEMS fiber differential pressure sensor chip, which will be described in detail below in conjunction with the drawings.

[0037] Figure 1 shows a schematic cross-sectional view of a differential MEMS fiber optic differential pressure sensor chip according to an embodiment of the present disclosure. In this example embodiment, a differential MEMS fiber optic differential pressure sensor chip 100 is shown, which comprises: a first pressure sensitive structure 10, a second pressure sensitive structure 20, an intermediate sensitive layer structure 30, a first fiber collimator pair 60, a second fiber collimator pair 70; in the first pressure sensitive structure 10, its bottom surface and side surface surround a membrane-island structure 40; further, a first collimating groove (not shown) is provided at the bottom of the first pressure sensitive structure 10, which cooperates with the intermediate sensitive layer structure 30 to form a first collimating through-hole (not shown); correspondingly, the bottom surface of the second pressure sensitive structure 20 and its side surface surround another membrane-island structure, and the second pressure sensitive structure 20 can be configured in an upside-down mirror-symmetrical relationship with the first pressure sensitive structure 10 relative to the intermediate plane of the intermediate sensitive layer structure 30 (the so-called intermediate plane of the intermediate sensitive layer structure 30 refers to the plane in the middle of the thickness direction of the intermediate sensitive layer structure 30, which is equidistant from the upper surface and the lower surface, so that the upper and lower surfaces can also be mirror-symmetric relative to this intermediate plane), correspondingly, a second collimating groove (not shown) is provided at the bottom of the second pressure sensitive structure 20, which cooperates with the intermediate sensitive layer structure 30 to form a second collimating through-hole (not shown); it should be noted that the first fiber collimator pair 60 is symmetrically arranged and fixed in the first collimating through-hole (not shown) between the bottom surface of the first pressure sensitive structure 10 and the intermediate sensitive layer structure 30, and the two fiber collimators in the first fiber collimator pair 60 are arranged in alignment, so that the incident light realizes alignment into the F-P cavity after passing through the fiber collimators; correspondingly, the second fiber collimator pair 70 is symmetrically arranged and fixed in the second collimating through-hole (not shown) between the bottom surface of the second pressure sensitive structure 20 and the intermediate sensitive layer structure 30, and the two fiber collimators in the second fiber collimator pair 70 are arranged in alignment, so that the incident light realizes alignment into the F-P cavity after passing through the fiber collimators; for the intermediate sensitive layer structure 30, it is provided between the bottom surface of the first pressure sensitive structure 10 and the bottom surface of the second pressure sensitive structure 20, correspondingly, the intermediate sensitive layer structure 30 is used to separate the first fiber collimator pair 60 and the second fiber collimator pair 70, and the intermediate sensitive layer structure 30 is configured to support the first pressure sensitive structure 10 and the second pressure sensitive structure 20, and when the intermediate sensitive layer structure 30 is subjected to pressure changes, its deformation causes the F-P cavity to change, thereby realizing pressure measurement or differential pressure measurement, correspondingly, if the stiffness of the intermediate sensitive layer structure 30 is reduced, the intermediate sensitive layer structure 30 is more likely to produce greater deformation due to pressure, thereby causing greater F-P cavity changes, thereby improving the sensitivity of the corresponding differential MEMS fiber optic differential pressure sensor chip.Preferably, in some embodiments, the intermediate sensing layer structure 30 can be configured as a hollow structure, which not only reduces the stiffness of the intermediate sensing layer structure 30, but also ensures that the first pressure sensing structure 10 and the second pressure sensing structure 20 are supported; more preferably, in some embodiments, the intermediate sensing layer structure 30 can be configured as a grid structure, which can be provided as a grid structure composed of parallel and equidistant long strips or frames. In the illustrated embodiment, a grid structure in the form of parallel and equidistant long strips; such a grid structure not only facilitates machining processing, but also facilitates the support of the intermediate sensing layer structure 30 to the upper and lower layers (the first pressure sensing structure 10 and the second pressure sensing structure 20), and also completely separates the first fiber collimator pair 60 and the second fiber collimator pair 70; it should be noted that such separation must ensure that the fiber collimator end faces of the first fiber collimator pair 60 and the second fiber collimator pair 70 must abut against the long strip solid sections of the grid, rather than the groove gap sections, as shown in FIG. 1.

[0038] Preferably, in some embodiments, the distance from the end face of one fiber collimator in the first fiber collimator pair 60 to the central axis of the first pressure sensitive structure 10 is equal to the distance from the end face of the other fiber collimator in the first fiber collimator pair 60 to the central axis of the first pressure sensitive structure 10; correspondingly, the distance from the end face of one fiber collimator in the second fiber collimator pair 70 to the central axis of the second pressure sensitive structure 20 is equal to the distance from the end face of the other fiber collimator in the second fiber collimator pair 70 to the central axis of the second pressure sensitive structure 20. It should be understood that the first fiber collimator pair 60 includes two fiber collimators, in the illustration, the left and right fiber collimators, and the two end faces are opposite to each other at the central position of the bottom of the first pressure sensitive structure 10, and the first pressure sensitive structure 10 can be regarded as a disc, and the disc central axis can be the central axis from the top of the paper to the bottom of the paper, and thus arranged, the two fiber collimators in the first fiber collimator pair 60 can be aligned and arranged. Correspondingly, the distance from the end face of one fiber collimator in the second fiber collimator pair 70 to the central axis of the second pressure sensitive structure 20 is equal to the distance from the end face of the other fiber collimator in the second fiber collimator pair 70 to the central axis of the second pressure sensitive structure 20, which is similar to the relative arrangement of the two fiber collimators in the first fiber collimator pair 60, and thus facilitates the alignment and arrangement of the two fiber collimators in the second fiber collimator pair 70. It should be noted that the central axis of the island structure also needs to have a relatively equal position, because the deformation of the structure at the central axis is the largest; the upper and lower fiber end faces need to fall on the solid part of the grid structure to reduce the torsion of the fiber end faces (the F-P cavity requires the two end faces of the fiber to be as parallel as possible), and a six-dimensional adjustment frame is used in packaging to cooperate with an infrared microscope (seeing the fiber collimator through the silicon structure) to accurately position the fiber collimator, so that the center of the F-P cavity is exactly at the central axis position of the island structure of the membrane island structure.

[0039] More preferably, in some embodiments, the distance from the end face of any fiber collimator in the first fiber collimator pair 60 to the central axis of the first pressure sensitive structure 10 is equal to the distance from the end face of any fiber collimator in the second fiber collimator pair 70 to the central axis of the second pressure sensitive structure 20. In this way, the arrangement and alignment position of the first fiber collimator pair 60 and the arrangement and alignment position of the second fiber collimator pair 70 are mirror images of each other with respect to the intermediate sensitive layer structure 30, so that the upper and lower F-P cavities tend to be consistent, which is more conducive to forming a differential MEMS fiber differential pressure sensor chip 100, and also makes the anti-common mode interference performance better and the measurement accuracy higher.

[0040] Preferably, in some embodiments, the differential MEMS fiber differential pressure sensor chip 100 further comprises: first side vias 50-1, 50-2 disposed on the first pressure sensitive structure 10 close to the side surface of the first pressure sensitive structure 10; second side vias 50-3, 50-4 disposed on the second pressure sensitive structure 20 close to the side surface of the second pressure sensitive structure 20; the first fiber collimator pair 60 is disposed to be weldedly connected with the first pressure sensitive structure 10 through the first side vias 50-1, 50-2, and the second fiber collimator pair 70 is disposed to be weldedly connected with the second pressure sensitive structure 20 through the second side vias 50-3, 50-4. Due to the provision of the corresponding first side vias 50-1, 50-2, it is convenient to weld and fix the first fiber collimator pair 60 on the differential MEMS fiber differential pressure sensor chip 100. Similarly, due to the provision of the corresponding second side vias 50-3, 50-4, it is convenient to weld and fix the second fiber collimator pair 70 on the differential MEMS fiber differential pressure sensor chip 100, so as to prevent the deviated original position of the aligned fiber collimator caused by internal and external factors.

[0041] Fig. 2 shows a schematic diagram of a differential MEMS fiber optic differential pressure sensor chip according to an embodiment of the present disclosure. In the illustrated embodiment, the first pressure sensitive structure 10 corresponds to a disc-like recessed structure excavated near the center of the upper surface of a cuboid silicon wafer, and the center of the disc-like recess further includes a circular protrusion (similar to an island in the recessed area), thereby forming a membrane-island structure of the differential MEMS fiber optic differential pressure sensor chip 200. It should be understood that, as shown in Fig. 2, the disc-like structure formed by the membrane-island structure 40 has a central axis, i.e., the disc structure has a similar cylindrical structure extending from the island structure, and the central axis of the disc structure must coincide with the central axis of the cylindrical structure of the island structure. Further, in the illustrated embodiment, an intermediate sensitive layer structure 30 is provided between the first pressure sensitive structure 10 and the second pressure sensitive structure 20, and the intermediate sensitive layer structure 30 is a grid structure, wherein the parallel and equidistant long strips of the grid structure are perpendicular to the direction of the first fiber collimator pair 60 (or the first fiber collimator pair 70), and it can be understood that the end face of the fiber collimator can be abutted against the side of the long strips of the grid structure of the intermediate sensitive layer structure 30 facing the first pressure sensitive structure 10 (or the second pressure sensitive structure 20) when aligned, so that the F-P cavity is formed therein. It should be understood that if the end face of the fiber collimator falls within the gap of the grid structure when aligned, the upper and lower F-P cavities cannot be formed, and the differential MEMS fiber optic differential pressure sensor chip loses its original pressure differential measurement function. Further, as shown in the illustrated embodiment, the first side through holes 50-1, 50-2 are provided in the silicon wafer region between the central membrane-island structure of the silicon wafer and the side of the collimating through hole, so that the first side through holes 50-1, 50-2 can pass through the surface of the silicon wafer and the collimating through hole, so that the fiber collimator arranged in the collimating through hole can be welded and fixed or fixed in other ways through the first side through holes 50-1, 50-2. Similarly, in the illustrated embodiment, the second pressure sensitive structure 20 faces the direction below the paper and cannot be seen, and there are similar, not shown membrane-island structures, second side through holes, and mirror-symmetric structures relative to the middle plane of the intermediate sensitive layer structure. It should be understood that the first pressure sensitive structure 10 and the second pressure sensitive structure 20 are in a mirror-symmetric relationship relative to the middle plane of the intermediate sensitive layer structure 30.It should be noted that in the illustrated embodiment, a protruding ridge 45 is formed along the direction of the fiber collimator pair (e.g. the first fiber collimator pair 60 or the first fiber collimator pair 70) to protect the fiber collimator pair (to protect the inner fiber 60-1, 70-1), which is achieved by multiple etching in the manufacturing process, since in order to improve the sensitivity of the first pressure sensitive structure 10 and the second pressure sensitive structure 20 to pressure, the membrane part of the membrane-island structure 40 needs to be made thin enough, and the overall thickness of the membrane can be smaller than the diameter of the fiber; however, the membrane part of the membrane-island structure 40 is too thin, which introduces a new technical problem: it will cause the fiber to be exposed and cause the device to fail, therefore, the protruding ridge 45 is to add a "fiber wrapping" channel to the fiber 60-1, 70-1, as shown in FIG. 3.

[0042] FIG. 3 shows another cross-sectional schematic view of a differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure, i.e. rotated by 90° around the center axis of the disc structure formed by the membrane-island structure relative to FIG. 1. In the embodiment of the differential MEMS fiber differential pressure sensor chip shown in FIG. 3, in order to cover the first fiber collimator pair 60, fiber 60-1 in the first collimator groove inside the membrane part of the membrane-island structure 40, the membrane part of the membrane-island structure 40 is structured as a protruding ridge 45 structure to protect the first fiber collimator pair 60, fiber 60-1 with an inner diameter larger than the membrane thickness of the remaining membrane part of the membrane-island structure 40; correspondingly, in the illustrated embodiment, in order to cover the second fiber collimator pair 70, fiber 70-1 in the second collimator groove inside the membrane part of the lower membrane-island structure, the membrane part of the lower membrane-island structure is structured as a lower protruding ridge structure to protect the second fiber collimator pair 70, fiber 70-1 with an inner diameter larger than the membrane thickness of the remaining membrane part of the membrane-island structure; such a design of the protruding ridge 45 structure allows the membrane thickness of the part around the fiber to be arbitrarily adjusted according to the sensitivity requirement, without being restricted by the diameter of the fiber. In the illustrated embodiment, the fiber 60-1, 70-1 is circular from the cross-sectional perspective, and the through hole for accommodating the fiber 60-1, 70-1 can be a circular structure, or a square structure as shown, or other structures that can accommodate the fiber 60-1, 70-1, and further, the corresponding protruding ridge 45 structure should also correspond to the through hole structure, for example, also square in the illustrated embodiment.

[0043] This design allows the membrane thickness of the part around the fiber to be arbitrarily adjusted according to the sensitivity requirement, without being restricted by the diameter of the fiber.

[0044] It should be understood that the principle of the signal output of the differential pressure sensor of the differential MEMS optical fiber differential pressure sensor chip employing some embodiments of the present disclosure is that the presence of external pressure causes the deformation of the MEMS mechanical structure, thereby causing the displacement of the optical fiber collimator, i.e., the change of the cavity length of the F-P cavity, and finally the change of the F-P cavity length can be obtained from the change of the wavelength, thereby obtaining the information of the external pressure. On the structure, a pair of optical fiber collimators are arranged on the first pressure sensitive structure 10 and the second pressure sensitive structure 20 to form an F-P cavity, i.e., there are two F-P cavities, and the final output signal is the result of the subtraction of the wavelengths output by the two F-P cavities. When external interference such as environmental temperature change exists, the MEMS mechanical structure will also deform due to thermal expansion and contraction, and the cavity length of the F-P cavity will also change, but since the structural parameters of the first pressure sensitive structure 10 and the second pressure sensitive structure 20 are exactly the same, the cavity length changes of the two F-P cavities are also exactly the same, and the final output signal is 0, i.e., it can resist interference. When the first pressure sensitive structure 10 and the second pressure sensitive structure 20 are subjected to the same pressure, the output is also similar, i.e., the output is 0. However, when the first pressure sensitive structure 10 and the second pressure sensitive structure 20 are subjected to different pressures, i.e., when a differential pressure exists, the entire MEMS mechanical structure will bend, and there is a neutral layer that neither elongates nor shortens when the mechanical structure bends. In some embodiments of the present disclosure, due to the symmetrical structure above and below, the neutral layer is located in the middle of the middle sensitive layer structure 30, and correspondingly, when a differential pressure exists, the first pressure sensitive structure 10 and the second pressure sensitive structure 20 will be stretched on one side and compressed on the other side due to the symmetrical distribution on both sides of the neutral layer, so that the cavity length of one F-P cavity becomes longer and the cavity length of the other F-P cavity becomes shorter, and the change amounts are consistent. At this time, the output wavelength changes of the two F-P cavities will not be 0 when subtracted, and therefore the information of the external differential pressure can be obtained, and the output signal will be twice as large as that when only the first pressure sensitive structure 10 or only the second pressure sensitive structure 20 exists. Therefore, the differential MEMS optical fiber differential pressure sensor chip employing the above structure has the advantages of anti-interference and signal amplification of the corresponding differential MEMS optical fiber differential pressure sensor.

[0045] Figure 4 shows a schematic diagram of the intermediate sensing layer structure of the differential MEMS fiber optic differential pressure sensor chip according to embodiments of the present disclosure. In this diagrammatic example, the intermediate sensing layer structure 30 is configured as a grid structure, which is shown as a spaced structure of parallel and equidistant long strips or frames. Since the intermediate sensing layer structure 30 is sandwiched (bonded) between the first pressure sensitive structure 10 and the second pressure sensitive structure 20, it should be understood that the grid structure maintains its shape not by the intermediate sensing layer structure 30 itself, but by the first pressure sensitive structure 10 and the second pressure sensitive structure 20. As shown, the fiber collimator arrangement is oriented in a preferential orthogonal relationship to the long strip direction of the grid structure, so that both end faces of the fiber collimator pair are arranged on the side of the long strips of the grid structure close to the first pressure sensitive structure 10 or the second pressure sensitive structure 20, which facilitates not only the arrangement of the corresponding F-P cavities, but also the alignment of the two fiber collimators in the fiber collimator pair. It should also be understood that the intermediate sensing layer structure 30 adopts a grid structure because the grid structure has lower stiffness than a flat plate solid structure, so that the deformation of the structure under the same pressure is greater, and the cavity change of the F-P cavity after stress is also greater, thereby the sensitivity of the output signal is also higher. Alternatively, in other embodiments, in addition to adopting a grid structure, the intermediate sensing layer structure can also adopt other hollow structures, as long as it simultaneously functions to: 1) reduce the original stiffness of the intermediate sensing layer structure; 2) separate the first fiber collimator pair in the first pressure sensitive structure and the second fiber collimator pair in the second pressure sensitive structure; 3) support the first pressure sensitive structure and the second pressure sensitive structure under pressure through the intermediate sensing layer structure (so that the intermediate sensing layer structure is not crushed when the first pressure sensitive structure and the second pressure sensitive structure are under pressure during measurement); 4) form corresponding mirror F-P cavities, and facilitate the alignment and fixation of the first fiber collimator pair and the second fiber collimator pair.

[0046] In addition, it should be noted that there is a trade-off between stiffness and support capacity in the thickness of the intermediate sensing layer structure (for example, which can be referred to as the intermediate layer in some embodiments). Figure 5 shows the relationship between the thickness of the intermediate sensing layer structure (shown as the intermediate layer) and the wavelength differential output (i.e., the sensitivity of the device) of the F-P cavity of the differential MEMS fiber optic differential pressure sensor chip according to embodiments of the present disclosure, where the intermediate sensing layer structure is a solid structure of the top layer of silicon of an SOI silicon wafer. Although it is possible to pursue a thinner and better intermediate sensing layer structure, in order to maintain the inherent structure of the differential MEMS fiber optic differential pressure sensor chip, which is arranged to be crushed by the first pressure sensitive structure and / or the second pressure sensitive structure when it is under external force during measurement, the intermediate sensing layer structure also needs to have sufficient mechanical strength to support the first pressure sensitive structure and the second pressure sensitive structure above and below.

[0047] Further, in order to correspond to the top layer silicon of the intermediate sensitive layer structure being configured as a grid structure after the SOI silicon wafer, FIG. 6 shows the relationship between the thickness of the intermediate sensitive layer structure (illustrated as the intermediate layer) of the differential MEMS fiber differential pressure sensor chip and the wavelength differential output of the F-P cavity according to an embodiment of the present disclosure. Obviously, when the intermediate sensitive layer structure is configured as a grid structure, the wavelength differential output of the F-P cavity is significantly improved under the same thickness. This is of great significance to the field which requires high accuracy but does not need to withstand particularly large pressure.

[0048] FIG. 7 shows a preparation flowchart of a differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure. In the illustrated example, a preparation method of a fiber differential pressure sensor chip is shown, which comprises: S1, forming a film-island structure on a first polished surface of a silicon wafer of a given thickness by photolithography, dry etching or wet etching; S2, forming a collimating groove on a second polished surface of the above-mentioned silicon wafer by photolithography, dry etching or wet etching, the second polished surface being the other polished surface away from the first polished surface of the silicon wafer; S3, forming two fiber welding through holes on the silicon wafer between the film-island structure side and the outer side of the silicon wafer by photolithography, dry etching or wet etching, thereby obtaining the first pressure sensitive structure; S4, repeating S1-S3 to obtain the second pressure sensitive structure; S5, performing photolithography on the top layer silicon of the SOI silicon wafer, and then forming a hollow structure or a grid structure on the top layer silicon by dry etching or wet etching; S6, silicon-silicon bonding the first pressure sensitive structure and the SOI silicon wafer, the corresponding bonding surface being the second polished surface of the first pressure sensitive structure and the top layer silicon of the SOI silicon wafer, and the collimating groove of the first pressure sensitive structure and the top layer silicon of the SOI silicon wafer forming the first collimating through hole; S7, thinning and etching the substrate silicon and buried oxygen layer of the SOI silicon wafer to expose the top layer silicon to form the intermediate sensitive layer structure; S8, silicon-silicon bonding the second pressure sensitive structure and the intermediate sensitive layer structure, the corresponding bonding surface being the side of the intermediate sensitive layer structure away from the first pressure sensitive structure and the side of the second pressure sensitive structure having the collimating groove, and the collimating groove of the second pressure sensitive structure and the intermediate sensitive layer structure forming the second collimating through hole; S9, arranging the first fiber collimator pair and the second fiber collimator pair in the first collimating through hole and the second collimating through hole respectively and aligning. Preferably, in some embodiments, in S1, the silicon wafer can adopt a double-polished silicon wafer, which means that the polishing process is performed on both sides of the silicon wafer.

[0049] In a preferred embodiment, the preparation method forms, in S1, a film-island structure and a protruding ridge structure on the first polished surface of the silicon wafer of a given thickness by photolithography, dry etching or wet etching, the protruding ridge structure being a groove wall covering the collimating groove in S2, the groove wall forming a protruding structure on the film portion of the film-island structure.

[0050] Preferably, in some embodiments, the preparation method etches the top layer silicon to a depth of the thickness of the top layer silicon, i.e. the top layer silicon, when not being thinned and etching the buried oxide layer and the substrate silicon, can still retain the grid structure without disintegration, and after the top layer silicon of the grid structure is bonded to the first pressure sensitive structure and thus constrained by the first pressure sensitive structure, even if the buried oxide layer and the substrate silicon are thinned and etched, the top layer silicon can still retain the grid structure without disintegration.

[0051] Preferably, in some embodiments, the preparation method thins and etches the substrate silicon and the buried oxide layer of the SOI silicon wafer to expose the top layer silicon in S7 means that the substrate silicon of the SOI silicon wafer is thinned by dry etching or wet etching to expose the buried oxide layer of the SOI silicon wafer, and then the buried oxide layer of the SOI silicon wafer is etched by dry etching or wet etching to expose the top layer silicon to form the intermediate sensitive layer structure. Therefore, in order to adapt to the thinning and etching of the buried oxide layer and the substrate silicon when the top layer silicon of the SOI silicon wafer is a grid structure, the corresponding thinning and etching of the buried oxide layer and the substrate silicon cannot be arbitrarily changed or omitted or arbitrarily changed.

[0052] Preferably, in some embodiments, the preparation method aligns the first pair of fiber collimators and the second pair of fiber collimators in S9, and then applies solder through the fiber soldering through holes to respectively weld and fix the first pair of fiber collimators and the second pair of fiber collimators in the first collimating through hole and the second collimating through hole. It can be seen that the fiber soldering through hole can facilitate the fixation of the pair of fiber collimators in the collimating through hole.

[0053] It should be noted that the differential MEMS fiber differential pressure sensor chip prepared by the above preparation method is based on the Fabry-Perot (F-P) interference principle. When a coherent light beam is incident on the F-P pressure sensitive chip along the collimator, multiple reflections between the high reflection end faces of the two fiber collimators of the fiber collimator pair form multiple beam interference, and can be output along the original path or the other fiber collimator. The interference output signal of the fiber collimator pair is related to the distance between the end faces of the two fiber collimators forming the fiber collimator pair. Under the action of the pressure at the upper and lower ends, the MEMS pressure sensitive structure will be deformed, thereby causing the distance between the two fiber collimators of the collimator pair to change, so that the wavelength or phase of the interference output signal of the collimator pair changes accordingly. When the pressures at the upper and lower ends are equal, the changes of the interference outputs of the two fiber collimator pairs are the same, and the difference between the two interference output signals is 0. When an additional pressure is applied at any one of the upper and lower ends, the changes of the interference outputs of the two fiber collimator pairs are different, and the precise measurement of the pressure difference can be realized by subtracting the two interference output signals. When interference signals such as temperature changes exist, the influence on the interference outputs of the two collimator pairs is consistent, so subtracting the two interference output signals can offset the influence of external interference on the sensor output.

[0054] In order to further show the preparation process, FIG. 8 shows a schematic diagram of the preparation process of the differential MEMS fiber differential pressure sensor chip according to an embodiment of the present disclosure. In FIG. 8, subgraphs (a)-(j) correspond to the manufacturing process of the first pressure sensitive structure, the second pressure sensitive structure formed by double-throwing a silicon wafer, and the intermediate sensitive layer structure formed by an SOI silicon wafer in the entire preparation process.

[0055] In the illustrated embodiment, in the (a) diagram of FIG. 8, a groove is formed on the surface of a double- polished silicon wafer by photolithography, dry etching or wet etching; in the (b) diagram of FIG. 8, a film-island structure is formed at the bottom of the groove by photolithography, dry etching or wet etching; in the (c) diagram of FIG. 8, a fiber collimator through-hole is formed on the other side of the double-polished silicon wafer by photolithography, dry etching or wet etching; in the (d) diagram of FIG. 8, two fiber welding through-holes are etched outside the film-island structure by photolithography, dry etching or wet etching, thereby forming a first pressure-sensitive structure; in the (e) diagram of FIG. 8, a second pressure-sensitive structure is formed using the process steps shown in (a)-(d); in the (f) diagram of FIG. 8, after photolithography is performed on the top layer of silicon of an SOI wafer, a grid structure (or other hollow structure in other embodiments) is formed on the top layer of silicon by dry etching or wet etching; in the illustrated embodiment, the etching depth is the thickness of the top layer of silicon; in the (g) diagram of FIG. 8, the first pressure-sensitive structure and the SOI wafer are bonded by silicon-silicon bonding, the bonding surface being the side of the first pressure-sensitive structure on which the fiber collimator through-hole is formed and the top layer of silicon of the SOI wafer; in the (h) diagram of FIG. 8, the substrate silicon of the SOI wafer is thinned by dry etching or wet etching until the buried oxygen layer of the SOI wafer stops, and then the exposed buried oxygen layer is etched clean by dry etching or wet etching, thereby exposing the intermediate sensitive layer structure; in the (i) diagram of FIG. 8, the second pressure-sensitive structure and the intermediate sensitive layer structure are bonded by silicon-silicon bonding, the bonding surface being the side of the intermediate sensitive layer structure away from the first pressure-sensitive structure and the side of the second pressure-sensitive structure on which the fiber collimator through-hole is formed; in the (j) diagram of FIG. 8, after the first fiber collimator pair and the second fiber collimator pair are respectively aligned in the first fiber collimator through-hole and the second fiber collimator through-hole, the fiber welding through-holes are filled with solder to weld the MEMS structure as a whole.

[0056] In an alternative embodiment, another method for preparing a differential MEMS fiber optic differential pressure sensor chip is proposed, which comprises the following steps: S101, forming a groove on the surface of a double-etched silicon wafer by photolithography, dry etching or wet etching; S102, forming a membrane-island structure at the bottom of the groove by photolithography, dry etching or wet etching; S103, forming a fiber collimation through hole on the other side of the double-etched silicon wafer by photolithography, dry etching or wet etching; S104, etching two fiber welding through holes outside the membrane-island structure by photolithography, dry etching or wet etching, thereby forming a first pressure sensitive structure; S105, using the process steps and process parameters of S101-104 to form a second pressure sensitive structure; S106, silicon-silicon bonding the first pressure sensitive structure with another double-etched silicon wafer, the bonding surface being the side of the first pressure sensitive structure on which the fiber collimation through hole is formed and any side of the double-etched silicon wafer; S107, forming an intermediate sensitive layer structure on the bonded double-etched silicon wafer by photolithography and dry etching, the etching depth being the thickness of the double-etched silicon wafer; S108, silicon-silicon bonding the second pressure sensitive structure with the intermediate sensitive layer structure, the bonding surface being the side of the intermediate sensitive layer structure away from the first pressure sensitive structure and the side of the intermediate sensitive layer structure on which the fiber collimation through hole is formed; S109, aligning the first fiber collimator pair and the second fiber collimator pair in the first fiber collimation through hole and the second fiber collimation through hole respectively, and then welding the MEMS structure with the fiber collimation through hole by applying solder. The above method does not use SOI silicon wafer, but still uses double-etched silicon wafer for the intermediate sensitive layer structure, which has relatively reduced cost and process complexity, but in order to better performance and robustness (sensitivity, support and bonding), the SOI silicon wafer scheme for the intermediate sensitive layer structure is superior to the double-etched silicon wafer scheme.

[0057] It should be noted that the general bonding is usually only two sides, and the bonding area that can be used for bonding is usually large. In some embodiments of the present disclosure, the bonding is not only a three-layer bonding, but also the middle layer is a grid structure, and the bonding area is small. The conventional bonding processing method is prone to bonding failure or insufficient bonding force. To solve this problem (difficulty), the middle grid structure adopted in some embodiments of the present disclosure is made of the top layer of silicon of the SOI silicon wafer. It not only can adjust the thickness of the grid structure by customizing the thickness of the top layer of silicon (the conventional method is to use etching or corrosion to obtain the required thickness, but etching or corrosion will cause the silicon surface flatness to deteriorate extremely and thus cannot be bonded), but also the top layer of silicon of the SOI is a natural polished surface of silicon on both sides, which is not subjected to any thinning process. This natural polished surface is the ideal interface for bonding, thereby greatly reducing the bonding difficulty in the present application. By gradually thinning the substrate silicon, gradually etching the buried oxygen layer, and gradually exposing the top layer of silicon, the surface properties of the top layer of silicon and the buried oxygen layer on one side can be effectively protected, which is beneficial to the re-bonding of another pressure-sensitive structure layer (for example, a second pressure-sensitive structure) without damaging the intermediate sensitive layer structure after forming the intermediate sensitive layer structure.

[0058] It should be noted that the SOI silicon wafer, i.e. the Silicon On Insulator silicon wafer, is a special silicon-based material. The SOI silicon wafer is a sandwiched structure similar to a sandwich, which is composed of three layers: the top layer is a device layer for making circuit elements; the middle is a buried oxygen layer as an insulating silicon dioxide layer; and the bottom layer is a substrate, which is usually composed of bulk silicon. The three layers of the present disclosure are referred to as top layer of silicon, buried oxygen layer and substrate silicon.

[0059] It should be noted that in the above-mentioned illustrated embodiments, the display of each figure does not strictly follow the center symmetry or other symmetry, and is only used to illustrate the approximate relative position between the components. Some embodiments of the present disclosure do not strictly measure the drawings according to the picture display of the present disclosure, and the protection scope of the present disclosure is not limited to the measurement results of the drawings.

[0060] In some embodiments, the first pressure sensitive structure and the second pressure sensitive structure are distributed in mirror symmetry relative to the middle plane of the middle sensitive layer structure (i.e. the plane in the middle position where the distance to the upper surface and the lower surface of the middle sensitive layer structure is equal), when a differential pressure exists, one will produce stretching and the other will produce compression, therefore, the two F-P cavities formed by the two collimators respectively, one cavity length becomes longer and one cavity length becomes shorter, and the change is consistent, at this time the output wavelength change of the two F-P cavities is subtracted and will not be 0, therefore the information of the external differential pressure can be obtained, and the output signal will be twice as large as the signal when only the first pressure sensitive structure or the second pressure sensitive structure exists, thereby making the fiber differential pressure sensor with the structure have the advantages of anti-interference and signal amplification.

[0061] It should also be noted that in the above corresponding embodiments, six-dimensional adjustment frame is needed to cooperate with an infrared microscope (seeing the fiber collimator through the silicon structure) to accurately position the fiber collimator when packaging, so that the center of the F-P cavity passes through the central axis (center axis) of the island structure of the film island structure.

[0062] It should be understood that making the middle sensitive layer structure into a grid structure does indeed increase the deformation ability of the middle sensitive layer structure, which in turn brings benefits to the measurement of the appropriate pressure range, however, the grid structure inevitably leads to the stiffness of the middle sensitive layer structure, which in turn affects the measured range (cannot be too large), but the differential MEMS fiber differential pressure sensor chip in the present disclosure is designed for harsh magnetic and high temperature environments, not for extreme pressure differential environments.

[0063] It should be noted that the grid structure of the middle sensitive layer structure is perpendicular to the fiber in principle, when the grid structure of the middle sensitive layer structure is not perpendicular to the fiber, the grid spacing must be smaller than the fiber diameter, otherwise the fiber may fall into the gap between the grids, which in turn leads to the failure to form the F-P cavity or causes the upper and lower fibers to contact. When the grid structure of the middle sensitive layer structure is perpendicular to the fiber direction, the grid spacing can be easily adjusted. The output schematic of the middle sensitive layer structure as a flat (solid) structure (see Fig. 5) and the grid structure (see Fig. 6) can be seen that the sensitivity of the grid structure is significantly improved relative to the flat structure under the same middle layer thickness, almost an order of magnitude.

[0064] Embodiments of the present disclosure have been described above, with the understanding that these embodiments are exemplary only and are not exhaustive of overall disclosure. Many modifications and variations will be apparent to those of ordinary skill in the art. The scope of the disclosure, therefore, is to be determined from the following claims, which are to be accorded the full breadth of equivalents to which they are entitled under the law. The selection of the terms to be used in the description herein is intended to best explain the principles of the embodiments, the practical application of the embodiments, or the technical improvements over the prior art, or to enable other of ordinary skill in the art to understand the embodiments disclosed herein.

[0065] The above description is merely illustrative of the embodiments of the present disclosure and is not intended to limit the scope of the present disclosure. It is obvious to those skilled in the art that various modifications and changes can be made to the present disclosure without departing from the spirit and principle of the present disclosure. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims

A differential MEMS fiber optic differential pressure sensor chip, characterized in that, Comprising: a first pressure sensitive structure, a second pressure sensitive structure, an intermediate sensitive layer structure, a first pair of fiber collimators, a second pair of fiber collimators; the first pressure sensitive structure is configured as a membrane-island structure with a bottom surface and a side surface surrounding, the bottom of the first pressure sensitive structure is provided with a first collimating groove, the first collimating groove cooperates with the intermediate sensitive layer structure to form a first collimating through hole; the second pressure sensitive structure is configured as a membrane-island structure with a bottom surface and a side surface surrounding, and the second pressure sensitive structure is configured to be mirror-symmetric to the first pressure sensitive structure relative to the intermediate plane of the intermediate sensitive layer structure, the bottom of the second pressure sensitive structure is provided with a second collimating groove, the second collimating groove cooperates with the intermediate sensitive layer structure to form a second collimating through hole; the first pair of fiber collimators is fixed in the first collimating through hole, and the two fiber collimators in the first pair of fiber collimators are arranged in alignment; the second pair of fiber collimators is fixed in the second collimating through hole, and the two fiber collimators in the second pair of fiber collimators are arranged in alignment; the intermediate sensitive layer structure is arranged between the bottom surface of the first pressure sensitive structure and the bottom surface of the second pressure sensitive structure; the intermediate sensitive layer structure is arranged to separate the first pair of fiber collimators and the second pair of fiber collimators, and the intermediate sensitive layer structure is configured to support the first pressure sensitive structure and the second pressure sensitive structure and reduce the rigidity of the intermediate sensitive layer structure. According to the differential MEMS fiber differential pressure sensor chip of claim 1, wherein the intermediate sensitive layer structure is configured as a hollow structure or a grid structure, and the grid structure is arranged as a grid structure composed of parallel and equidistant strips or frames. According to the differential MEMS fiber differential pressure sensor chip of claim 1, wherein the distance between the end faces of the two fiber collimators in the first pair of fiber collimators is equal to the distance between the end faces of the two fiber collimators in the second pair of fiber collimators; the distance from the end face of one fiber collimator in the first pair of fiber collimators to the central axis of the first pressure sensitive structure is equal to the distance from the end face of the other fiber collimator in the first pair of fiber collimators to the central axis of the first pressure sensitive structure; the distance from the end face of one fiber collimator in the second pair of fiber collimators to the central axis of the second pressure sensitive structure is equal to the distance from the end face of the other fiber collimator in the second pair of fiber collimators to the central axis of the second pressure sensitive structure. According to the differential MEMS fiber differential pressure sensor chip of claim 3, wherein the distance from the end face of any fiber collimator in the first pair of fiber collimators to the central axis of the first pressure sensitive structure is equal to the distance from the end face of any fiber collimator in the second pair of fiber collimators to the central axis of the second pressure sensitive structure. Further comprising: The differential MEMS fiber optic pressure sensor chip according to claim 1, wherein, a first side through hole arranged on the first pressure sensitive structure close to the side surface of the first pressure sensitive structure; ​ A second side through hole is arranged on the second pressure sensitive structure close to the side surface of the second pressure sensitive structure; The first fiber collimator pair is arranged to be welded with the first pressure sensitive structure through the first side through hole, and the second fiber collimator pair is arranged to be welded with the second pressure sensitive structure through the second side through hole. A method of manufacturing an optical fiber differential pressure sensor chip according to any one of claims 1-5, characterized in that, Comprise: S1, a film-island structure is formed on a first polished surface of a silicon wafer with a given thickness by photolithography, dry etching or wet etching; S2, a collimating groove is formed on a second polished surface of the silicon wafer by photolithography, dry etching or wet etching, the second polished surface being the other polished surface away from the first polished surface of the silicon wafer; S3, two fiber welding through holes are formed on the silicon wafer between the film-island structure side and the outer side of the silicon wafer by photolithography, dry etching or wet etching, so as to obtain the first pressure sensitive structure; S4, repeating S1-S3 to obtain the second pressure sensitive structure; S5, photolithography is performed on the top layer silicon of the SOI silicon wafer, and then a hollow structure or a grid structure is formed on the top layer silicon by dry etching or wet etching; S6, the first pressure sensitive structure is bonded with the SOI silicon wafer by silicon-silicon bonding, and the corresponding bonding surface is the second polished surface of the first pressure sensitive structure and the top layer silicon of the SOI silicon wafer, and the collimating groove of the first pressure sensitive structure and the top layer silicon of the SOI silicon wafer form the first collimating through hole; S7, the substrate silicon and buried oxygen layer of the SOI silicon wafer are thinned and etched to expose the top layer silicon to form the intermediate sensitive layer structure; S8, the second pressure sensitive structure is bonded with the intermediate sensitive layer structure by silicon-silicon bonding, and the corresponding bonding surface is the side of the intermediate sensitive layer structure away from the first pressure sensitive structure and the side of the second pressure sensitive structure formed with the collimating groove, and the collimating groove of the second pressure sensitive structure and the intermediate sensitive layer structure form the second collimating through hole; S9, the first fiber collimator pair and the second fiber collimator pair are respectively arranged in the first collimating through hole and the second collimating through hole and aligned. The preparation method according to claim 6, wherein In S1, the silicon wafer is a double-polished silicon wafer, which means that the two sides of the silicon wafer have been polished. The preparation method according to claim 6, wherein In S5, the etching depth of the top layer silicon is the thickness of the top layer silicon. The preparation method according to claim 6, wherein In S7, the thinning and etching of the substrate silicon and buried oxygen layer of the SOI silicon wafer to expose the top layer silicon means that the substrate silicon of the SOI silicon wafer is thinned by dry etching or wet etching to expose the buried oxygen layer of the SOI, and then the buried oxygen layer of the SOI silicon wafer is etched by dry etching or wet etching to expose the top layer silicon, so as to form the intermediate sensitive layer structure. The preparation method according to claim 6, wherein In S9, after the first fiber collimator pair and the second fiber collimator pair are respectively aligned, the first fiber collimator pair and the second fiber collimator pair are respectively fixed in the first collimation through hole and the second collimation through hole by applying solder through the optical fiber welding through hole.

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