A step-type FP sensor based on MEMS technology and its preparation method

Abstract

The present invention discloses a step-type FP sensor based on MEMS technology and a preparation method thereof, belonging to the field of acoustic sensor technology. The sensor includes a diaphragm, a substrate, a capillary tube, and an optical fiber; a plurality of steps of different heights arranged in sequence are provided in the middle area of the sensing input end of the diaphragm device layer, and a reflective layer is provided on the other side of the device layer; a step-type through-hole is provided in the axial center of the substrate, and the periphery of the diaphragm is fixedly connected to the substrate; the step-type through-hole includes a first through-fixing hole and a second fixing hole, which are respectively adapted to the optical fiber and the capillary tube; the capillary tube is inserted and fixed in the second fixing hole; the optical fiber passes through the capillary tube and is inserted into the first fixing hole and fixed therein, the axial projection of the optical fiber toward the diaphragm is located in the center area of the diaphragm, and there is a light transmission gap between the end of the optical fiber and the reflective layer. The present invention can achieve multiple resonant frequencies of the sensor, as well as high sensitivity and signal stability in each frequency response range, and reduce the production cost of the multi-resonant frequency sensor.

Description

Technical Field

[0001] The present invention relates to the field of acoustic sensing technology, in particular to a step-type FP sensor based on MEMS technology and a preparation method thereof. Background Art

[0002] In recent years, with the continuous advancement of MEMS (microelectromechanical systems) technology and optical sensors, sensors based on the Fabry-Perot (FP) interferometry principle have been widely used in a variety of fields, such as environmental monitoring, pressure sensing, smart healthcare, and structural health monitoring. FP sensors, with their high sensitivity and high precision, are an ideal choice for many precision measurement systems. However, despite the impressive achievements of these sensors, significant technical bottlenecks still exist, limiting their widespread application in complex environments.

[0003] First, despite some innovative FP sensors in design and materials, they mostly rely on a single resonant frequency or interference peak to sense changes in physical quantities. This makes them inflexible when faced with complex multi-quantity measurement tasks. Many FP sensors currently on the market can only measure a specific physical quantity (such as pressure, temperature, or displacement), and often lack sufficient responsiveness in applications requiring simultaneous monitoring of multiple parameters. This limitation of a single frequency response makes FP sensors unable to adapt to rapidly changing operating conditions in multivariable environments and complex sensing requirements, limiting their application in some demanding fields.

[0004] Secondly, the signal stability and sensitivity of FP sensors remain prominent issues. Although researchers have recently improved sensor sensitivity by improving diaphragm materials and structural designs, existing sensors are still significantly affected by factors such as temperature fluctuations, environmental noise, and mechanical vibration. Especially in high-precision applications such as industrial testing and biomedical fields, the sensitivity and stability of FP sensors often struggle to meet stringent requirements. Environmental interference (such as temperature fluctuations and vibration) can cause offsets in the interference signal, thereby affecting measurement accuracy. Signal instability remains a significant challenge, especially in applications with high dynamic range and long-term stability.

[0005] Furthermore, while some researchers have made design improvements, attempting to address temperature and environmental interference issues by optimizing diaphragm shape and adding compensation mechanisms, these solutions often face complex fabrication processes and high production costs in practical applications. FP sensors require extremely high microstructure design and optical control, making their production process cumbersome and placing extremely stringent demands on equipment precision. Consequently, existing technologies remain challenging to achieve large-scale and cost-effective manufacturing. Summary of the Invention

[0006] The present invention aims to provide a MEMS-based stepped FP sensor and its fabrication method, enabling the sensor to achieve multiple resonant frequencies, while maintaining high sensitivity and signal stability across all frequency response ranges, while also reducing the production cost of the multi-resonant frequency sensor. The present invention employs the following technical solutions.

[0007] In one aspect, the present invention provides a step-type FP sensor based on MEMS technology, comprising a diaphragm, a substrate, a capillary tube, and an optical fiber;

[0008] The diaphragm includes a device layer, one side of the device layer is a sensing input end, and a plurality of steps of different heights are arranged in sequence in the middle area of the device layer, and the other side of the device layer is a plane with a reflective layer provided thereon;

[0009] The substrate is a column with a stepped through hole formed in its axial center. The periphery of the diaphragm is fixedly connected to the periphery of one end surface of the substrate, and the reflective layer faces the substrate. The stepped through hole includes a first through fixing hole close to the diaphragm and a second fixing hole away from the diaphragm. The first fixing hole and the second fixing hole are adapted to the optical fiber and the capillary, respectively.

[0010] One end of the capillary tube is inserted into and fixed in the second fixing hole;

[0011] The optical fiber passes through and is fixed to the capillary, and one end thereof is inserted into the first fixing hole and fixed. The axial projection of the optical fiber toward the diaphragm is located in the central area of the diaphragm, and there is a light transmission gap between the end of the optical fiber and the reflective layer.

[0012] In the above technical solution, multiple steps of varying heights provided on the diaphragm constitute a multi-resonant structure of the sensor, forming a Fabry-Perot interferometer cavity between the optical fiber and the diaphragm's reflective layer. The optical fiber emits incident light toward the reflective layer and receives reflected light from the Fabry-Perot interferometer cavity. When sound pressure acts on the diaphragm surface, the diaphragm deforms, while the optical fiber attached to the capillary tube does not shift. As a result, the length of the FP cavity changes, and the optical path difference of the reflected light caused by the change in the length of the Fabry-Perot interferometer cavity can be used to calculate the ultrasonic sound pressure value. In this process, since the thickness of each step region of the diaphragm in the present invention is different, their respective maximum deformations also occur at different frequencies, resulting in multiple resonance peaks.

[0013] Optionally, the area on the diaphragm sensing input end where the multiple steps are arranged is a circular area centered on the diaphragm center, and the diameter of the capillary is adapted to the diameter of the circular area, so that the circular area is projected onto the interior of the capillary. In this embodiment, the FP cavity can better sense deformation caused by external input signals in different resonant regions of the diaphragm, ensuring that each of the multiple resonant regions has good sensitivity.

[0014] Optionally, the ratio of the area of the circular region where the multiple steps are located to the total area of the diaphragm on the sensing input end of the diaphragm, and the diaphragm thickness values corresponding to the multiple step regions are designed in coordination with each other according to the resonance peak required for each step region:

[0015] The larger the desired resonance peak, the smaller the circular area of the multiple steps and the greater the step thickness. Based on this rule, a reasonable combination of sensitive area and step height ensures a wider frequency response range for the FP sensor, and within the frequency response range corresponding to each resonance zone, the FP sensor exhibits higher sensitivity.

[0016] Optionally, the surface height of the largest step among the multiple steps at the sensing input end of the diaphragm is equal to or less than the surface height of the diaphragm's peripheral region. This design not only takes into account the convenience of the diaphragm etching process, but also realizes a multi-resonant structure with higher sensitivity in the central region of the diaphragm.

[0017] Optionally, the number of steps on the diaphragm sensing input end is designed according to the number of required resonance peaks. The more resonance peaks required, the greater the number of steps.

[0018] Optionally, the width of each step on the diaphragm sensing input end is designed according to the required sensitivity of the corresponding frequency range. For the frequency range corresponding to any step area, the greater the required sensitivity, the wider the width of the step area.

[0019] Optionally, the widths of the steps on the diaphragm sensing input end are equal.

[0020] Optionally, on the sensing input end of the diaphragm, the heights of the multiple steps from one side of the diaphragm to the other side increase or decrease sequentially.

[0021] Furthermore, on the sensing input end of the diaphragm, the heights of the multiple steps from one side of the diaphragm to the other side increase or decrease by the same value in sequence.

[0022] The above designs can reduce the computational complexity during sensor design and actual application, and facilitate simulation analysis in the sensor design stage.

[0023] In addition to the above design, as another implementation method of multiple steps at the sensing input end: on the sensing input end of the diaphragm, the heights of the multiple steps are symmetrically distributed from one side of the diaphragm to the other side.

[0024] Preferably, it can be designed that the step on one diameter is the highest or the lowest, and the step heights on both sides of the step decrease or increase successively.

[0025] Optionally, the diaphragm also includes a supporting layer and a connecting layer, which are annular and connected to the periphery of the reflective end of the device layer and projected onto the periphery of multiple step areas, wherein the upper and lower surfaces of the connecting layer are fixedly connected to the supporting layer and the device layer respectively; the end face of one end of the substrate is fixedly connected to the supporting layer.

[0026] Optionally, the optical fiber is a single-mode optical fiber, and the reflective layer is a gold material that is vacuum ion sputtered on the reflective end surface of the diaphragm. The reflective layer can also be made of other metal materials with high reflective properties.

[0027] In the above technical solution, the provision of the support layer can achieve mechanical support for the diaphragm device layer and form an FP cavity between the diaphragm and the optical fiber.

[0028] In a second aspect, the present invention provides a method for preparing the stepped FP sensor based on MEMS technology according to the first aspect, comprising preparing the diaphragm. The diaphragm preparation process includes:

[0029] Coating a photoresist layer on the cleaned SOI wafer and performing a baking process;

[0030] The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which are respectively used to etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the surface shape of the sensing input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the area to be etched at the reflective end of the diaphragm;

[0031] For the exposed area of the silicon base layer of the SOI wafer, deep reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is further etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is metal-coated to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used to etch, and according to the different heights of the multiple steps, the etching is carried out layer by layer until the multiple step areas are obtained, thereby completing the preparation of the diaphragm.

[0032] The above-mentioned layer-by-layer etching can be layer-by-layer etching from shallow to deep, or layer-by-layer etching from deep to shallow.

[0033] As an etching operation implementation mode, optionally, there are multiple upper mask plates, each of which is made according to the shape of multiple step regions;

[0034] The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the different heights of the multiple steps to obtain the multiple step regions, including:

[0035] According to the different heights of the multiple steps, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0036] In the order of the heights of the multiple step surfaces from high to low or from low to high, the corresponding mask plates are sequentially used to perform etching operation processes of each height level on the silicon substrate layer of the SOI crystal to sequentially obtain multiple step areas;

[0037] Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, using the mask plate corresponding to the current height level to transfer the pattern to be etched to the photoresist layer, and controlling the etching depth according to the surface height difference between the step area to be etched and the adjacent surface height step area to complete the etching of the current height level and obtain the corresponding step area.

[0038] Optionally, the preparation method further includes assembling the sensor, specifically including:

[0039] Cut the required length of optical fiber, remove the coating and clean the bare fiber;

[0040] Etching a step-type through hole in the substrate;

[0041] Insert the capillary into the second fixing hole of the stepped through hole of the substrate, and fix the capillary to the substrate with UV glue;

[0042] Insert the optical fiber into the capillary tube and then pass it through the capillary tube to the first fixing hole of the stepped through hole until the end of the optical fiber slightly protrudes from the first fixing hole, and fix the optical fiber to the capillary tube and the first fixing hole with UV glue;

[0043] Laser cutting and cleaning the end of the optical fiber protruding from the first fixing hole so that the plane of the optical fiber end is flush with the surface of the substrate;

[0044] The prepared diaphragm reflective end is directed toward the substrate and fixed to the substrate by UV glue, so that the center of the region where the multiple steps on the diaphragm are located is located on the axial extension line of the optical fiber, thereby obtaining the step-type FP sensor based on MEMS technology.

[0045] Beneficial effects

[0046] This MEMS-based stepped FP sensor utilizes a stepped structure to achieve multi-band measurement performance by gradually varying the height or thickness of the diaphragm's sensing input end. This broadens the sensor's operating frequency range, avoiding the limitations of traditional sensors that rely on a single resonant frequency. It also improves the sensor's overall sensitivity and sensitivity across various frequency bands, significantly enhancing its flexibility, accuracy, response speed, and applicability in complex environments. It has broad applications in the fields of mechanics, optics, and sensors, promoting the development of fiber optic sensor technology in a wider range of application scenarios.

[0047] Furthermore, the structural design of the present invention not only improves sensor performance but also simplifies the manufacturing process and reduces costs. The fabrication method designs the etching process based on the structural characteristics of the diaphragm. By using different mask plates, the multi-level step area is etched layer by layer, ensuring the sensor's high sensitivity and wide frequency response range. Furthermore, the nested protective design of the substrate, optical fiber, and capillary tube enables the fabrication method to ensure accurate centering and assembly of the sensor diaphragm. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 FIG2 is a schematic diagram of the structure of a stepped FP sensor according to an embodiment of the present invention;

[0049] Figure 2 FIG2 is a schematic diagram of the three-dimensional structure of the diaphragm in the multi-step region of the stepped FP sensor according to an embodiment of the present invention;

[0050] Figure 3 FIG2 is a schematic diagram of the diaphragm structure of the stepped FP sensor according to an embodiment of the present invention;

[0051] Figure 4 FIG2 is a schematic diagram of a process for preparing a membrane in a stepped FP sensor according to an embodiment of the present invention, which includes steps (a), (b), (c), (d), and (e);

[0052] Figure 5 FIG. 4 is a frequency response characteristic curve diagram of the stepped FP sensor according to an embodiment of the present invention.

[0053] In the figure, 1-diaphragm, 11-device layer, 12-connecting layer, 13-support layer, 14-reflection layer, 2-substrate, 3-capillary, 4-optical fiber, 5-step-shaped resonant induction area. DETAILED DESCRIPTION

[0054] The following is further described in conjunction with the accompanying drawings and specific embodiments. The embodiments mentioned are merely exemplary descriptions of the present invention, used to illustrate the present invention, and should not be understood as limiting the present invention. In the absence of any conflict, the various embodiments of the present invention and their technical features may be combined with each other.

[0055] Example 1

[0056] This embodiment introduces a step-type Fabry-Perot sensor based on MEMS technology. Figure 1 As shown, it includes a diaphragm 1, a substrate 2, a capillary 3 and an optical fiber 4;

[0057] refer to Figures 1 to 5 The diaphragm 1 includes a device layer 11, which can be processed from a silicon substrate layer of an SOI crystal. One side of the device layer 11 is a sensing input end, and a plurality of steps of different heights arranged in sequence are provided in the middle area of the sensing input end; the other side of the device layer is a reflective end, and the end face of the reflective end is a plane and is provided with a reflective layer 14;

[0058] The substrate 2 is a column with a stepped through hole at its axial center. The periphery of the diaphragm 1 is fixedly connected to the periphery of one end surface of the substrate 2, and the reflective layer 14 faces the substrate. The stepped through hole includes a first through fixing hole close to the diaphragm and a second fixing hole away from the diaphragm. The first fixing hole and the second fixing hole are respectively adapted to the optical fiber 4 and the capillary 3.

[0059] One end of the capillary tube 3 is inserted into and fixed in the second fixing hole;

[0060] The optical fiber 4 passes through and is fixed to the capillary 3, and one end thereof is inserted into the first fixing hole and fixed. The axial projection of the optical fiber toward the diaphragm is located in the central area of the diaphragm, and there is a light transmission gap between the end of the optical fiber and the reflective layer.

[0061] In this embodiment, multiple steps of varying heights are arranged on the diaphragm, forming a multi-resonant Fabry-Perot structure. The substrate is used to mount and position the capillary tube and optical fiber. The capillary tube protects and positions the optical fiber passing through it, ensuring alignment between the optical fiber and the center of the diaphragm, achieving an accurate fiber interferometry measurement path. The end face of the optical fiber and the reflective layer surface at the center of the diaphragm form a Fabry-Perot interferometer cavity, which is used to detect acoustic signals.

[0062] When sound pressure acts on the surface of the diaphragm, the diaphragm will deform. Since the thickness of the resonance zone corresponding to each step area of the diaphragm is different, the maximum deformation of each resonance zone also occurs at a different frequency. The frequency response of the diaphragm will have multiple resonance peaks. The stepped sensing input end composed of these steps can effectively enhance the optical signal detection capability of the sensor, making the sensor as a whole have a higher sensitivity.

[0063] During detection, when the optical fiber emits incident light, the cavity length of the Fabry-Perot interferometer cavity changes as the diaphragm deforms. This change in cavity length causes the optical path difference of the reflected light to change. By detecting the optical path difference of the reflected light in the interferometer cavity, the sound pressure values at different frequencies can be calculated, thereby achieving high-precision measurement of multi-band acoustic signals.

[0064] In the stepped structure of the diaphragm sensing input end, the number and width of the steps can be adjusted as needed. The adjustment rules include:

[0065] If the number of resonance peaks required by the sensor is greater, the number of steps will be greater;

[0066] For the frequency range corresponding to any step region, if the required sensitivity is greater, the width of the step region is wider.

[0067] Example 2

[0068] Based on Example 1, Figures 2 to 4 In the stepped Fabry-Perot sensor of this embodiment, the area on the sensing input end of the diaphragm for arranging the multiple steps is a circular area centered on the center of the diaphragm, i.e., the stepped resonant sensing area 5. The diameter of the capillary is adapted to the diameter of the circular area, so that the circular area is projected onto the interior of the capillary. This allows the FP cavity to better sense the deformation of the resonant areas corresponding to different steps of the diaphragm caused by external input signals, thereby ensuring that the multiple resonant areas each have good sensitivity.

[0069] The ratio of the circular area of the steps to the total diaphragm area, as well as the corresponding diaphragm thickness, can be designed based on the desired resonance peak values for each step region. Specifically, the larger the desired resonance peak, the smaller the circular area of the steps and the thicker the steps. Based on this rule, a reasonable combination of sensitive area and step height ensures a wider frequency response range for the FP sensor and higher sensitivity within the frequency response range of each resonance region.

[0070] In this embodiment, Figure 3 and Figure 4 At the sensing input end of the diaphragm, the surface height of the largest step among the multiple steps is equal to or less than the height of the diaphragm's outer periphery. This design not only takes into account the convenience of the diaphragm etching process, but also realizes a multi-resonant structure with high sensitivity in the center of the diaphragm.

[0071] The number, width, and height of the steps on the diaphragm can be designed according to the design rules introduced in Example 1 and actual application needs, such as:

[0072] The widths of the steps on the sensing input end of the diaphragm are equal or unequal;

[0073] Alternatively, the heights of the multiple steps from one side of the diaphragm to the other side may increase or decrease sequentially, or may be arranged at intervals as needed; in the case where the heights increase or decrease sequentially, the design may be to increase or decrease the same height value sequentially, thereby facilitating calculations in the design and application stages;

[0074] Alternatively, the heights of the multiple steps are symmetrically distributed from one side to the other side of the diaphragm, such as being designed such that the step on a diameter of the circular area where the multiple steps are located is the highest or lowest, and the step heights on both sides of the step decrease or increase in sequence.

[0075] refer to Figure 2 In this embodiment, the diaphragm sensing input end has four steps, which are arranged in sequence according to height. The height difference between any two adjacent steps is equal, and the widths of all steps are also equal.

[0076] The shape of the area where the multiple steps are located can also be set to other shapes such as squares, but a circular shape is more friendly to the consistency of the deformation response of multiple resonant zones, which facilitates logical operations during simulation and detection. The number of multiple resonant zones can also be adjusted as needed to meet the detection requirements of scenarios with different frequency bands.

[0077] Example 3

[0078] To facilitate assembly of the stepped Fabry-Perot sensor, stabilize the overall structure, implement the Fabry-Perot interferometer cavity, and enhance the resonant response of the diaphragm, this embodiment includes an extension of the device layer around the circular area where the multiple steps are located. The diaphragm also includes a connecting layer and a support layer. The diaphragm can be designed as a circle or other shape.

[0079] Specifically, based on Example 1 or Example 2, combined with Figure 1 、 Figure 3 and Figure 4 The stepped Fabry-Perot sensor of this embodiment includes a diaphragm, a substrate, a capillary, and an optical fiber. The diaphragm includes a device layer 11, a connection layer 12, and a support layer 13. The support layer and the connection layer are annular and connected to the periphery of the reflective end of the device layer, projecting onto the periphery of the stepped region. The upper and lower surfaces of the connection layer are fixedly connected to the support layer and the device layer, respectively. The end surface of one end of the substrate is fixedly connected to the support layer. The provision of the support layer provides mechanical support for the diaphragm device layer and forms an FP cavity between the diaphragm and the optical fiber.

[0080] The entire membrane 1 in this embodiment can be made based on SOI crystal, and the device layer, the connection layer and the support layer correspond to the silicon substrate layer, the silicon oxide layer and the silicon base layer of the SOI crystal respectively.

[0081] The optical fiber adopts a single-mode optical fiber, and the reflective layer is a gold material that is vacuum ion sputtered on the reflective end surface of the diaphragm. The reflective layer can also be made of other metal materials with high reflective properties.

[0082] Example 4

[0083] refer to Figure 4 As shown, this embodiment introduces a method for preparing the stepped structure Fabry-Perot sensor in Examples 1 to 3. The method includes preparing the diaphragm. The preparation process of the diaphragm includes:

[0084] Coating a photoresist layer on the cleaned SOI wafer and performing a baking process;

[0085] The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which are respectively used to etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the surface shape of the sensing input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the area to be etched at the reflective end of the diaphragm;

[0086] For the exposed area of the silicon base layer of the SOI wafer, reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is further etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is metal-coated to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used to etch, and according to the different heights of the multiple steps, the etching is carried out layer by layer until the multiple step areas are obtained, thereby completing the preparation of the diaphragm.

[0087] Since multiple step areas of different thicknesses need to be prepared on the silicon substrate layer, when etching the silicon substrate layer of the SOI wafer, the number of upper mask plates required should adapt to the number of steps of the stair structure, and each mask plate is designed according to the width and shape of different steps.

[0088] The above-mentioned layer-by-layer etching can be from deep to shallow layer-by-layer etching, or from shallow to deep layer-by-layer etching. Specifically:

[0089] The exposed area of the silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the different heights of the multiple steps to obtain the multiple step areas, including:

[0090] According to the different heights of the multiple steps, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels;

[0091] In the order of the heights of the multiple step surfaces from high to low or from low to high, the corresponding mask plates are sequentially used to perform etching operation processes of each height level on the silicon substrate layer of the SOI crystal to sequentially obtain multiple step areas;

[0092] Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, using the mask plate corresponding to the current height level to transfer the pattern to be etched to the photoresist layer, and controlling the etching depth according to the surface height difference between the step area to be etched and the adjacent surface height step area to complete the etching of the current height level and obtain the corresponding step area.

[0093] After the membrane is prepared, the membrane is assembled with the substrate, capillary tube and optical fiber according to the sensor structure described in Examples 1 to 3 to obtain a stepped structure FP sensor.

[0094] Example 5

[0095] Based on Example 4, Figure 1 The ladder-type Fabry-Perot sensor shown is the preparation target, refer to Figure 4 The preparation process of this embodiment includes the following steps:

[0096] S1, select or prepare a SOI crystal of appropriate size and shape, such as Figure 4 The circular SOI wafer substrate shown in step (a);

[0097] S2, making a mask for etching steps of different thicknesses;

[0098] S3, such as Figure 4 In step (a), the SOI crystal is cleaned to remove surface dirt and ensure that there are no impurities on the wafer surface. In this process, the wafer is usually cleaned with deionized water and chemical solutions, and then placed in an oven for drying. The SOI wafer is then placed on a spin coater, and a photoresist layer is evenly coated on the silicon base layer. The photoresist layer is pre-baked at 90-100°C for 1-2 minutes to remove the solvent in the photoresist and enhance its stability during the exposure process.

[0099] S4, after precisely aligning the silicon base layer of the wafer covered with photoresist with the lower mask, the wafer is placed into an exposure machine, and ultraviolet light is irradiated on the transparent area of the mask to cause a photochemical reaction on the surface of the photoresist, thereby forming a projection of the mask pattern. After exposure, a developer is used to remove the reacted photoresist area, while retaining the pattern structure of the unexposed area. Post-baking is then performed to enhance the adhesion and tolerance of the developed photoresist layer, thereby ensuring that it effectively protects the desired pattern area during the deep etching process;

[0100] S5, such as Figure 4In step (b), for the silicon base layer of the SOI wafer, deep reactive ion etching (DRIE) technology is used to gradually etch until the silicon oxide layer is exposed, and then continue as shown in the following example. Figure 4 In step (c), the silicon oxide layer is etched and cleaned. After the silicon oxide layer is cleaned, the required pattern structure of the sensor reflective end can be accurately transferred to the wafer, forming the target microstructure of the diaphragm reflective end;

[0101] S6, such as Figure 4 In step (d), the silicon substrate layer of the SOI crystal is finely processed using the multiple deep reactive ion etching (DRIE) processes described in Example 4. Accurate structures of different thicknesses are achieved through step-by-step photolithography and etching. For example, photoresist is first coated on the surface of the silicon substrate layer and photolithography is performed using an upper mask pattern to define the etching area for each layer. Subsequently, by controlling the etching depth, peripheral regions of decreasing thickness are sequentially formed. After each layer is etched, the upper mask is replaced and photolithography is performed again to define the etching depth of the next layer. Finally, a stepped structure with multiple steps is formed in the center area of the device layer.

[0102] S7, such as Figure 4 In step (e), vacuum sputtering is used to metallize the bottom surface of the silicon substrate, i.e., the surface of the silicon substrate exposed at the reflective end of the diaphragm. By sputtering a metal target in a vacuum environment, gold atoms are uniformly deposited on the diaphragm surface to form a highly reflective gold film, thus achieving precise processing of the asymmetric multi-resonant structure diaphragm.

[0103] S8, cut the required length of optical fiber, remove its coating, and then use a dust-free paper soaked in alcohol to gently wipe the optical fiber to thoroughly remove the coating residue;

[0104] Insert the capillary into the second fixing hole of the stepped through hole of the substrate, and fix the capillary to the substrate with UV glue;

[0105] Insert the bare fiber into the capillary tube, and then pass the capillary tube through the first fixing hole of the stepped through hole until the end of the fiber slightly protrudes outside the first fixing hole. Secure the fiber to the capillary tube and the first fixing hole with UV glue. Use a precision cutting tool to cut the fiber end face flat to ensure it is smooth and defect-free, providing a good optical interface for subsequent assembly. Ensure that the fiber end face is flush with the substrate surface, completing the initial fixation of the fiber, capillary tube, and substrate.

[0106] S9, using a three-dimensional adjustment frame and a microscope to ensure precise alignment of all components for an effective acoustic transmission path, forms a Fabry-Perot interferometer cavity between the end face of the single-mode fiber and the gold-plated surface of the diaphragm. The diaphragm is bonded to the end face of the substrate, with the reflective end facing the substrate. A UV curing lamp is used to irradiate the diaphragm 360° for 10 minutes to secure the diaphragm to the substrate, completing the step-shaped FP sensor.

[0107] like Figure 5 Experiments have shown that the stepped Fabry-Perot sensor fabricated according to this invention can effectively improve the frequency response and sensitivity of signal detection. In particular, in scenarios requiring simultaneous detection of signals in multiple frequency bands, the sensor offers greater flexibility and high precision, overcoming the limitations of traditional fiber optic sensors that rely solely on a single resonant frequency.

[0108] The embodiments of the present invention are described above in conjunction with the accompanying drawings, but the present invention is not limited to the above-mentioned specific implementation methods. The above-mentioned specific implementation methods are merely illustrative and not restrictive. Under the guidance of the present invention, ordinary technicians in this field can also make many forms without departing from the scope of protection of the purpose of the present invention and the claims, which are all protected by the present invention.

Claims

1. A step-type FP sensor based on MEMS technology, characterized in that: Including diaphragm, substrate, capillary and optical fiber; The diaphragm includes a device layer, one side of the device layer is a sensing input end, and a plurality of steps of different heights are arranged in sequence in the middle area of the device layer, and the other side of the device layer is a plane with a reflective layer provided thereon; The substrate is a column with a stepped through hole formed in its axial center. The periphery of the diaphragm is fixedly connected to the periphery of one end surface of the substrate, and the reflective layer faces the substrate. The stepped through hole includes a first fixing hole close to the diaphragm and a second fixing hole away from the diaphragm. The first fixing hole and the second fixing hole are adapted to the optical fiber and the capillary, respectively. One end of the capillary tube is inserted into and fixed in the second fixing hole; The optical fiber passes through and is fixed to the capillary, and one end thereof is inserted into the first fixing hole and fixed. The axial projection of the optical fiber toward the diaphragm is located in the central area of the diaphragm, and there is a light transmission gap between the end of the optical fiber and the reflective layer.

2. The MEMS-based stepped FP sensor according to claim 1, wherein: The area on the diaphragm sensing input end for arranging multiple steps is a circular area with the center of the diaphragm as the center. The diameter of the capillary is adapted to the diameter of the circular area, so that the circular area is projected inside the capillary.

3. The MEMS-based stepped FP sensor according to claim 2, wherein: On the diaphragm sensing input end, the ratio of the area of the circular region where the multiple steps are located to the total area of the diaphragm, and the diaphragm thickness values corresponding to the multiple step regions are designed in coordination with each other according to the resonance peak required for each step region: The larger the required resonance peak value is, the smaller the area of the circular region where the multiple steps are located is, and the greater the step thickness is.

4. The MEMS-based stepped FP sensor according to claim 2, wherein: On the sensing input end of the diaphragm, the surface height of the step with the largest height value among the multiple steps is equal to or less than the surface height of the peripheral area of the diaphragm.

5. The step-type FP sensor based on MEMS technology according to claim 1, characterized in that: The number of steps on the diaphragm sensing input end is designed according to the number of required resonance peaks: the more resonance peaks required, the greater the number of steps.

6. The MEMS-based stepped FP sensor according to claim 1, wherein: The width of each step on the diaphragm sensing input end is designed according to the required sensitivity of the corresponding frequency range: for the frequency range corresponding to any step area, the greater the required sensitivity, the wider the width of the step area.

7. The MEMS-based stepped FP sensor according to claim 1, wherein: The widths of the steps on the sensing input end of the diaphragm are equal.

8. The MEMS-based stepped FP sensor according to claim 1, wherein: On the sensing input end of the diaphragm, the heights of the multiple steps from one side of the diaphragm to the other side increase or decrease in sequence.

9. The MEMS-based stepped FP sensor according to claim 8, characterized in that: On the sensing input end of the diaphragm, the heights of the multiple steps from one side of the diaphragm to the other side increase or decrease by the same value in sequence.

10. The MEMS-based stepped FP sensor according to claim 1, wherein: On the sensing input end of the diaphragm, the heights of the multiple steps are symmetrically distributed from one side of the diaphragm to the other side.

11. The MEMS-based stepped FP sensor according to claim 1, wherein: The diaphragm also includes a supporting layer and a connecting layer. The supporting layer and the connecting layer are annular and connected to the periphery of the reflective end of the device layer and projected onto the periphery of multiple step areas. The upper and lower surfaces of the connecting layer are respectively fixedly connected to the supporting layer and the device layer; the end surface of one end of the substrate is fixedly connected to the supporting layer.

12. The MEMS-based stepped FP sensor according to any one of claims 1 to 11, characterized in that: The optical fiber is a single-mode optical fiber, and the reflective layer is a gold material that is sputtered on the reflective end surface of the diaphragm by vacuum ions.

13. A method for preparing a step-type FP sensor based on MEMS technology according to any one of claims 1 to 12, characterized in that: The process of preparing the diaphragm includes: Coating a photoresist layer on the cleaned SOI wafer and performing a baking process; The SOI wafer coated with a photoresist layer and baked is aligned with a mask plate and then placed in an exposure machine for exposure and development processing, and then the SOI wafer after exposure and development is post-baked; wherein the mask plate includes an upper mask plate and a lower mask plate, which are respectively used to etch the silicon substrate layer and the silicon base layer of the SOI wafer, and the pattern on the upper mask plate corresponds to the surface shape of the sensing input end of the diaphragm, and the pattern on the lower mask plate corresponds to the shape of the area to be etched at the reflective end of the diaphragm; For the exposed area of the silicon base layer of the SOI wafer, deep reactive ion etching is used to etch until the silicon oxide layer is exposed, and the silicon oxide layer is further etched and cleaned. After the silicon oxide layer is cleaned, the exposed area is metal-coated to obtain the reflective layer; for the silicon substrate layer of the SOI wafer, multiple deep reactive ion etching processes are used to etch, and according to the different heights of the multiple steps, the etching is carried out layer by layer until the multiple step areas are obtained, thereby completing the preparation of the diaphragm.

14. The preparation method according to claim 13, characterized in that: There are multiple upper mask plates, each made according to the shape of the multiple step regions; The silicon substrate layer of the SOI wafer is etched by multiple deep reactive ion etching processes, and etching layer by layer according to the different heights of the multiple steps to obtain the multiple step regions, including: According to the different heights of the multiple steps, the etching process of the silicon substrate layer is divided into etching operation processes of multiple height levels; In the order of the heights of the multiple step surfaces from high to low or from low to high, the corresponding mask plates are sequentially used to perform etching operation processes of each height level on the silicon substrate layer of the SOI crystal to sequentially obtain multiple step areas; Among them, for each height level, the etching operation process includes: coating the surface of the current silicon substrate layer with photoresist, using the mask plate corresponding to the current height level to transfer the pattern to be etched to the photoresist layer, and controlling the etching depth according to the surface height difference between the step area to be etched and the adjacent surface height step area to complete the etching of the current height level and obtain the corresponding step area.

15. The preparation method according to claim 14, characterized in that: It also includes the assembly of sensors, including: Cut the required length of optical fiber, remove the coating and clean the bare fiber; Etching a step-type through hole in the substrate; Insert the capillary into the second fixing hole of the stepped through hole of the substrate, and fix the capillary to the substrate with UV glue; Insert the optical fiber into the capillary tube and then pass it through the capillary tube to the first fixing hole of the stepped through hole until the end of the optical fiber slightly protrudes from the first fixing hole, and fix the optical fiber to the capillary tube and the first fixing hole with UV glue; Laser cutting and cleaning the end of the optical fiber protruding from the first fixing hole so that the plane of the optical fiber end is flush with the surface of the substrate; The prepared diaphragm reflective end is directed toward the substrate and fixed to the substrate by UV glue, so that the center of the region where the multiple steps on the diaphragm are located is located on the axial extension line of the optical fiber, thereby obtaining the step-type FP sensor based on MEMS technology.

Images