Piezoelectric hydrophone suitable for deep sea high-pressure environment and preparation method thereof

Abstract

The invention discloses a piezoelectric hydrophone suitable for a deep sea high-pressure environment and a preparation method thereof, and belongs to the technical field of sound wave sensing. The piezoelectric hydrophone comprises an electrode layer, a piezoelectric layer, a structural layer, a supporting layer, a bonding layer and a substrate which are stacked in sequence, a cavity is formed in the supporting layer in the stacking direction in a penetrating mode. The piezoelectric layer is a single crystal piezoelectric material film; the structural layer, the supporting layer and the bonding layer are all photosensitive dry films; and the electrode layer is a patterned coplanar metal electrode. According to the technical scheme, the photosensitive dry film is used as the structural layer, the supporting layer and the bonding layer, and the electrodes adopt a transverse plane infield structure, so that high-sensitivity conversion between an acoustic signal and an electric signal is realized through the piezoelectric effect of the piezoelectric layer.

Description

TECHNICAL FIELD

[0001] The application relates to a piezoelectric hydrophone suitable for a deep-sea high-pressure environment and a preparation method thereof, and belongs to the technical field of acoustic wave sensing. BACKGROUND

[0002] With the rapid development of Underwater Wireless Sensor Networks (UWSNs) and Underwater Internet of Things (UIoT), reliable communication and efficient data interaction between underwater nodes have become key challenges for realizing intelligent underwater monitoring and autonomous networking. Given the severe attenuation of electromagnetic waves and light waves in seawater, sound waves have become the only viable means for long-distance underwater information transmission. In this context, the sensitivity, pressure resistance and stability of hydrophones, as the core detection devices of sonar systems, directly affect the performance of underwater communication, target detection and environmental monitoring.

[0003] In recent years, micro hydrophones based on Micro Electromechanical System (MEMS) technology have become a research hotspot in the field of underwater sensing due to their outstanding miniaturization and integration advantages. Sensor arrays prepared by advanced micro-nano processing technology not only achieve significant reduction in device size (typical size can reach millimeter level), but also simultaneously improve spatial resolution and environmental adaptability of the device, providing key technical support for high-density deployment of large-scale underwater sensor networks. Among various MEMS hydrophones, piezoelectric MEMS hydrophones have significantly outperformed traditional capacitive and resistive sensing mechanisms due to their inherent characteristics, including high sensitivity, wide frequency response and unique advantage of not requiring direct current bias, and have gradually developed into the preferred solution for modern underwater sensing systems.

[0004] To meet the needs of intelligent ocean development, the new generation of hydrophones not only need to meet the basic indicators of miniaturization, low power consumption and high sensitivity, but also need to have pressure resistance, long-term environmental stability and modular deployment capability to meet the stringent requirements of deep-sea monitoring, seafloor observation network and other application scenarios. However, existing piezoelectric MEMS hydrophones are usually only suitable for 200-500 meter shallow sea environment (0.2-5 MPa), and their piezoelectric sensitive structure and packaging system are prone to performance degradation and structural failure under deep-sea high pressure (>30 MPa). SUMMARY

[0005] In order to solve the problem that the piezoelectric sensitive structure and the packaging system in the prior art of hydrophone are prone to performance attenuation and structural failure under deep-sea high pressure (> 30MPa), a technical solution of a piezoelectric hydrophone suitable for deep-sea high pressure environment is provided, which adopts a MEMS device structure, uses a photosensitive dry film as a structure layer, a support layer and a bonding layer at the same time, adopts a transverse in-plane field structure for the electrode, and then realizes high-sensitivity conversion of sound wave signals and electric signals through piezoelectric effect.

[0006] The technical solution adopted by the present application is as follows: According to the first aspect of the present application, a piezoelectric hydrophone suitable for deep-sea high pressure environment is provided, which comprises an electrode layer, a piezoelectric layer, a structure layer, a support layer, a bonding layer and a substrate which are sequentially stacked. A cavity is provided through the support layer in the stacking direction; The piezoelectric layer is a single crystal piezoelectric material film; The structure layer, the support layer and the bonding layer are all photosensitive dry films; The electrode layer is a patterned coplanar metal electrode.

[0007] Optionally, the photosensitive dry film is a positive dry film.

[0008] Optionally, the thickness of the electrode layer is 0.01-2 μm.

[0009] Optionally, the thickness of the piezoelectric layer is 1-20 μm.

[0010] Optionally, the thickness of the structure layer is 5-50 μm.

[0011] Optionally, the thickness of the support layer is 5-50 μm.

[0012] Optionally, the thickness of the bonding layer is 5-50 μm.

[0013] According to the second aspect of the present application, a preparation method of the above-mentioned piezoelectric hydrophone suitable for deep-sea high pressure environment is provided, which comprises: Providing a clean single crystal piezoelectric wafer, and sequentially attaching a first photosensitive dry film, a second photosensitive dry film and a third photosensitive dry film to one side of the single crystal piezoelectric wafer as a structure layer, a support layer and a bonding layer respectively, wherein after attaching the second photosensitive dry film, the second photosensitive dry film is etched to form a through cavity; Attaching the third photosensitive dry film away from one side of the single crystal piezoelectric wafer to the surface of the substrate; Thinning the side of the single crystal piezoelectric wafer away from the substrate to form a single crystal piezoelectric material film as a piezoelectric layer; A patterned coplanar metal electrode is deposited as an electrode layer on the side of the single-crystal piezoelectric material film facing away from the substrate.

[0014] Optionally, the first photosensitive dry film may be softened before the second photosensitive dry film is applied. And / or, before attaching the third photosensitive dry film, the process further includes hard baking the second photosensitive dry film through which the cavity is opened; And / or, before attaching the side of the third photosensitive dry film away from the single-crystal piezoelectric wafer to the substrate surface, the third photosensitive dry film is further subjected to hard baking.

[0015] Optionally, the thinning of the side of the single-crystal piezoelectric wafer facing away from the substrate includes: The single-crystal piezoelectric wafer is thinned in multiple steps using a thinning solution containing particles to gradually reduce its thickness. After the multi-step thinning process, a first fine polishing is performed using a polishing slurry to remove the surface damage layer; After the first fine polishing, a second fine polishing is performed using deionized water to improve surface smoothness and gloss.

[0016] The beneficial effects of this application include: (1) The piezoelectric hydrophone provided in this application, suitable for deep-sea high-pressure environments, uses a photosensitive dry film as the structural layer, support layer, and bonding layer. The photosensitive dry film can be directly formed into a uniform film with a thickness of tens or even hundreds of micrometers by coating or lamination. The process is simple and does not require complex thinning, etching, or high-temperature treatment. At the same time, the photosensitive dry film material itself is inexpensive and supports mass production, which greatly reduces the manufacturing cost of the hydrophone.

[0017] (2) In the fabrication process of the piezoelectric hydrophone suitable for deep-sea high-pressure environments provided in this application, the photosensitive dry film with a thickness of tens of micrometers has strong mechanical strength and good flexibility after curing. Under external force, the photosensitive dry film is more likely to deform rather than break, which can effectively release stress and improve the reliability and durability of the hydrophone under high-pressure environments.

[0018] (3) The electrodes of the piezoelectric hydrophone suitable for deep-sea high-pressure environments provided in this application adopt a transverse in-plane field structure, which simplifies the double-layer electrodes required by traditional piezoelectric hydrophones to a single-layer electrode, effectively reducing process steps and manufacturing costs. At the same time, it reduces the equivalent capacitance and improves the receiving performance of the hydrophone. Attached Figure Description

[0019] Figure 1 The attached diagram is a three-dimensional structural schematic of a piezoelectric hydrophone suitable for deep-sea high-pressure environments provided in this application. The diagram is only for process illustration and has no product size or scale limitation. Figure 2 The attached diagram is a structural schematic of a piezoelectric hydrophone suitable for deep-sea high-pressure environments, provided for this application. The diagram is only a schematic of one product form at one size scale.

[0020] Attached Figure Labels 1. Electrode layer; 2. Piezoelectric layer; 3. Structural layer; 4. Support layer; 5. Bonding layer; 6. Substrate. Detailed Implementation

[0021] The present application is described in detail below with reference to the embodiments, but the present application is not limited to these embodiments.

[0022] Unless otherwise specified, all raw materials used in the embodiments of this application were purchased through commercial channels.

[0023] Unless otherwise specified, all test methods are standard and all instrument settings are those recommended by the manufacturer.

[0024] The core component of a hydrophone is the diaphragm, which vibrates mechanically under external sound pressure and converts mechanical energy into electrical signals through the piezoelectric effect. Currently, the cavity corresponding to the diaphragm mainly adopts a closed structure to achieve high-sensitivity sound pressure response. One side of the diaphragm is subjected to water pressure, while the other side is under air pressure or vacuum. This cavity structure is prone to diaphragm rupture when the pressure difference across the diaphragm is too large, leading to device failure and making it unsuitable for the high-pressure environment of the deep sea. An open cavity structure avoids device failure under high water pressure by balancing the water pressure on both sides of the diaphragm. However, this structure also makes it difficult for the diaphragm to deform effectively with external sound waves, thus significantly degrading the device's sound pressure response sensitivity. In contrast, using a closed cavity structure and strengthening it by increasing the diaphragm thickness is expected to synergistically resolve the contradiction between pressure resistance and high sensitivity, thereby meeting the application requirements of deep-sea exploration.

[0025] Traditional piezoelectric hydrophones typically use silicon-on-insulator (SOI) wafers as the substrate and are fabricated by depositing a piezoelectric layer. To withstand the high-pressure environment of the deep sea (below 3000 meters), the SOI silicon structure layer needs to be at least 20 μm thick, and the piezoelectric layer also needs to be over 5 μm thick. However, this requirement significantly increases manufacturing costs and presents numerous technical challenges: firstly, the high cost of SOI wafers limits the low-cost mass production of hydrophones; secondly, most existing thin-film deposition processes can only achieve piezoelectric films with a thickness of 1-2 μm, which is insufficient for fabrication requirements exceeding 5 μm. To address the aforementioned technical problems in existing technologies, this application provides a MEMS device solution for a piezoelectric hydrophone suitable for deep-sea high-pressure environments. The device employs a vertical structure, consisting of an electrode layer, a piezoelectric layer, a structural layer, a cavity-supported layer, a bonding layer, and a substrate, arranged from top to bottom. The electrodes utilize a coplanar electrode structure, which, compared to traditional top-and-bottom electrode structures, reduces process steps and effectively lowers the device's equivalent capacitance, thus facilitating electrical signal output. The piezoelectric layer is composed of a piezoelectric single-crystal thin film prepared by a thinning process. This not only allows for a thicker piezoelectric layer but also avoids interface defects such as lattice mismatch and stress concentration commonly encountered in heteroepitaxial growth on silicon substrates, while reducing reliance on high-cost deposition equipment. The structural layer, the core of the hydrophone—the diaphragm—is prepared using a photosensitive dry film material with controllable thickness, ensuring structural stability and pressure resistance in the high-pressure environment of the deep sea. The cavity-containing support layer and bonding layer both use the same photosensitive dry film material as the structural layer, together forming a sealed back cavity structure. The substrate is integrated with the back cavity of the device through the bonding layer to improve the stability of the back cavity. During device operation, a significant pressure difference is generated between the front and back sides of the diaphragm under sound pressure, causing significant deformation of the diaphragm. This, in turn, enables highly sensitive conversion between acoustic and electrical signals through the piezoelectric effect.

[0026] According to one embodiment of this application, a piezoelectric hydrophone suitable for deep-sea high-pressure environments has the following structure: Figure 1 As shown, it includes an electrode layer, a piezoelectric layer, a structural layer, a support layer, a bonding layer, and a substrate stacked in sequence. A cavity is provided through the support layer along the stacking direction; The piezoelectric layer is a single-crystal piezoelectric material thin film; The structural layer, the support layer, and the bonding layer are all photosensitive dry films; The electrode layer is a patterned coplanar metal electrode.

[0027] In one embodiment, the shape of the cavity can be selected and prepared as needed; for example, the shape of the cavity is rectangular.

[0028] In one embodiment, the photosensitive dry film is a positive dry film. Positive dry films exhibit lower lateral diffusion and less over-crosslinking during curing.

[0029] In one embodiment, the photosensitive dry film is selected from a positive dry film of the type PVT-MX3000, PVT-MX3030, PVT-MX3050 or Per3050.

[0030] In one embodiment, one side of the photosensitive dry film is a polyester adhesive layer for attachment.

[0031] In one embodiment, the thickness of the electrode layer is 0.01~2 μm. When the electrode layer thickness is too low, it is prone to breakage and poor contact; when the electrode layer thickness is too high, electrode layer patterning is difficult to achieve, and thick film deposition is prone to generating high residual stress, affecting the sensitivity of the device.

[0032] In one embodiment, the material of the coplanar metal electrode is selected from metals with high conductivity and low ohmic loss. For example, the material of the coplanar metal electrode is selected from at least one of gold (Au), aluminum (Al), platinum (Pt), chromium (Cr) or molybdenum (Mo).

[0033] In one embodiment, the electrode layer is a coplanar metal electrode formed by at least one pair of first electrodes and second electrodes.

[0034] In one embodiment, the thickness of the piezoelectric layer is 1~20 μm. If the piezoelectric layer thickness is too low, it will result in low receiver sensitivity and poor device stability; if the piezoelectric layer thickness is too high, the deposition process will find it difficult to simultaneously increase the mass load and reduce the resonant frequency.

[0035] For example, the single-crystal piezoelectric material may be selected from lithium niobate (LiNbO3), lithium tantalate (LiTaO3), aluminum nitride (AlN), or lead zirconate titanate (PZT).

[0036] In one embodiment, the piezoelectric layer is obtained by thinning a single-crystal piezoelectric material.

[0037] In one embodiment, the thickness of the structural layer is 5-50 μm. The structural layer is a first photosensitive dry film, serving as part of the vibrating film.

[0038] In one embodiment, the thickness of the support layer is 5~50 μm. The support layer is a second photosensitive dry film with an internal cavity, the cavity structure of which can be circular, square, or polygonal.

[0039] In one embodiment, the thickness of the bonding layer is 5~50 μm. The bonding layer is a third photosensitive dry film layer used to achieve a reliable connection between the support layer and the substrate.

[0040] In one embodiment, the thickness of the substrate is 1-2 mm. The substrate is made of glass and serves as a supporting base, providing good mechanical stability.

[0041] According to another embodiment of this application, the method for manufacturing the above-mentioned piezoelectric hydrophone suitable for deep-sea high-pressure environments includes: A clean single-crystal piezoelectric wafer is provided, and a first photosensitive dry film, a second photosensitive dry film, and a third photosensitive dry film are sequentially attached to one side of the single-crystal piezoelectric wafer as a structural layer, a support layer, and a bonding layer, respectively. After attaching the second photosensitive dry film, the second photosensitive dry film is further etched to form a through cavity. The side of the third photosensitive dry film facing away from the single crystal piezoelectric wafer is attached to the surface of the substrate; The side of the single-crystal piezoelectric wafer facing away from the substrate is thinned to form a single-crystal piezoelectric material thin film as a piezoelectric layer; A patterned coplanar metal electrode is deposited as an electrode layer on the side of the single-crystal piezoelectric material film facing away from the substrate.

[0042] In one embodiment, the first photosensitive dry film is further softened before the second photosensitive dry film is attached. And / or, before attaching the third photosensitive dry film, the process further includes hard baking the second photosensitive dry film through which the cavity is opened; And / or, before attaching the side of the third photosensitive dry film away from the single-crystal piezoelectric wafer to the substrate surface, the third photosensitive dry film is further subjected to hard baking.

[0043] In one embodiment, thinning the side of the single-crystal piezoelectric wafer away from the substrate includes: The single-crystal piezoelectric wafer is thinned in multiple steps using a thinning solution containing particles to gradually reduce its thickness. After the multi-step thinning process, a first fine polishing is performed using a polishing slurry to remove the surface damage layer; After the first fine polishing, a second fine polishing is performed using deionized water to improve surface smoothness and gloss.

[0044] In one embodiment, the particle-containing thinning liquid contains particles with a particle size of 1 to 20 μm. For example, the particles may be alumina.

[0045] In one embodiment, attaching the first photosensitive dry film, the second photosensitive dry film, and the third photosensitive dry film includes: Before being applied, the upper and lower surfaces of the photosensitive dry film are respectively covered with a polyester protective film and a polyester support film, and at least one side of the surface of the photosensitive dry film is a polyester adhesive layer. During the application process, the polyester protective film on one side of the photosensitive dry film is removed first to allow the resin adhesive side of the photosensitive dry film to adhere. The polyester support film is removed before applying the next layer of photosensitive dry film.

[0046] According to another embodiment of this application, the process is as follows: Figure 2 As shown, the method for fabricating a piezoelectric hydrophone for use in deep-sea high-pressure environments includes: Step 1: Take a single-crystal piezoelectric wafer and use alcohol and water for ultrasonic cleaning to remove surface particulate impurities and organic contaminants. After cleaning, purge with high-purity nitrogen gas to ensure it is dry and clean.

[0047] In one embodiment, the thickness of the single-crystal piezoelectric wafer is 300-500 μm.

[0048] In one embodiment, ultrasonic cleaning using alcohol and water includes ultrasonic cleaning sequentially with deionized water (DI water), propanol, isopropanol (IPA), and DI water.

[0049] In one embodiment, ultrasonic cleaning using alcohol and water involves first rinsing with flowing distilled water for 1-2 minutes to remove surface particulate matter. This is followed by ultrasonic cleaning with propanol and IPA for 6-10 minutes to remove organic contaminants.

[0050] In one embodiment, the ambient temperature for high-purity nitrogen convection purging is 60-80°C.

[0051] Step 2: Transfer the clean and dry single-crystal piezoelectric wafer to a coating machine. Take a first layer of photosensitive dry film of a certain thickness, remove its polyethylene (PE) protective film, and attach it to the surface of the single-crystal piezoelectric wafer with the resin adhesive layer facing down. Remove the polyester (PET) support film of the first dry film, and then perform soft baking. This process can optimize the adhesion and uniformity between the dry film and the wafer substrate by controlling the roller speed, pressure, and temperature of the coating machine.

[0052] In one embodiment, during the process of attaching the resin adhesive layer face down to the surface of the single-crystal piezoelectric wafer, the roller speed of the coating machine is controlled to be 0.3~1.0 m / min, the pressure to be 0.5~1.5 bar, and the temperature to be 40~100°C, in order to ensure good adhesion and uniformity between the photosensitive dry film and the wafer substrate.

[0053] In one embodiment, to prevent the resin adhesive layer of the first photosensitive dry film from becoming rough, torn, or deformed, the polyester (PET) support film of the first dry film is removed smoothly by controlling the roller speed, pressure, and temperature of the laminating machine.

[0054] In one embodiment, during the removal of the polyethylene (PE) protective film, the roller speed of the laminating machine is controlled at 0.3~1.0 m / min, the pressure at 0.5~1.5 bar, and the temperature at 20~25°C to remove the PET support film, so as to achieve a tight bonding of the two layers of photosensitive dry film without damaging the first layer of photosensitive dry film.

[0055] In one embodiment, the soft baking conditions include a soft baking temperature of 90-115°C and a soft baking time of 2-5 minutes, which prevents air bubbles or resin extrusion during the lamination of the second layer of photosensitive dry film.

[0056] Step 3: Take a second layer of photosensitive dry film of a certain thickness, remove its PE protective film, attach the resin adhesive layer downwards to the surface of the first layer of dry film, remove the polyester (PET) support film of the second layer of dry film, and then perform pre-baking. A cavity structure is obtained on the second layer of dry film through photolithography.

[0057] In one embodiment, during the process of attaching the resin adhesive layer face down to the surface of the single-crystal piezoelectric wafer, the roller speed of the coating machine is controlled to be 0.3~1.0 m / min, the pressure to be 0.5~1.5 bar, and the temperature to be 40~100°C, in order to ensure good adhesion and uniformity between the photosensitive dry film and the wafer substrate.

[0058] In one embodiment, to prevent the resin adhesive layer of the second photosensitive dry film from becoming rough, torn, or deformed, the polyester (PET) support film of the second dry film is removed smoothly by controlling the roller speed, pressure, and temperature of the laminating machine.

[0059] In one embodiment, during the removal of the polyethylene (PE) protective film, the roller speed of the laminating machine is controlled at 0.3~1.0 m / min, the pressure at 0.5~1.5 bar, and the temperature at 20~25°C to remove the PET support film, so as to achieve a tight bonding of the two layers of photosensitive dry film without damaging the first layer of photosensitive dry film.

[0060] In one embodiment, the pre-baking conditions include a pre-baking temperature of 90-115°C and a pre-baking time of 2-5 min, which is intended to enhance adhesion and stabilize the adhesive layer.

[0061] In one embodiment, the photolithography process includes: exposing the photomask to ultraviolet light with a wavelength of 350-400 nm and an energy of 150-300 mJ / cm² for 4-10 s to transfer the rectangular pattern on the photomask onto the second photosensitive dry film.

[0062] In one embodiment, after the exposure process of the photolithography process, a post-baking hardening is performed, followed by immersion in a developing solution for development and rinsing to obtain a cavity structure. Exemplarily, the developing solution can be propylene glycol methyl ether acetate (PGMEA) developing solution, the development time is 2-4 minutes, and the rinsing process can involve IPA rinsing for 5-10 seconds or repeated rinsing.

[0063] In one embodiment, the conditions for post-baking the film include: a post-baking temperature of 100-140°C and a post-baking time of 1-3 min.

[0064] Step 4: Take a third layer of photosensitive dry film of a certain thickness, remove the PE protective film, and attach it to the surface of the second layer of photosensitive dry film with the resin adhesive layer facing down. In one embodiment, during the process of attaching the resin adhesive layer to the surface of the second photosensitive dry film with the resin adhesive layer facing down, the parameters of the laminating machine are controlled to be the same as in step 3.

[0065] In one embodiment, the parameters of the laminating machine are controlled in the same way as in step 3 during the removal of its polyethylene (PE) protective film.

[0066] In one embodiment, in order to achieve tight bonding between the piezoelectric layer, structural layer, support layer and glass substrate, and to prevent the resin adhesive layer of the third photosensitive dry film from fraying, tearing or deforming, the polyester (PET) support film of the third dry film is removed smoothly by controlling the roller speed, pressure and temperature of the laminating machine.

[0067] Step 5: Place the resin adhesive layer of the third dry film face down, align it, and attach it upside down to the substrate surface.

[0068] In one embodiment, hard baking is performed to enhance the interfacial adhesion and bonding stability between the third dry film and the glass substrate.

[0069] In one embodiment, during the process of attaching the resin adhesive layer to the surface of the second photosensitive dry film with the resin adhesive layer facing down, the parameters of the laminating machine are controlled to be the same as in step 3.

[0070] In one embodiment, the parameters of the laminating machine are controlled in the same way as in step 3 during the removal of its polyethylene (PE) protective film.

[0071] In one embodiment, the hard-baking conditions include: a hard-baking temperature of 100~140°C and a hard-baking time of 1~3 minutes.

[0072] Step 6: Using a thinning solution containing thinning particles of a specific size, the surface of the single-crystal piezoelectric wafer is thinned in multiple steps to gradually reduce its thickness. After thinning, the single-crystal piezoelectric wafer is polished with a polishing solution to remove the surface damage layer, finally obtaining a single-crystal piezoelectric thin film with high flatness, low surface damage, and the target thickness.

[0073] In one embodiment, the particle size of the thinning particles is 1~20 μm.

[0074] In one embodiment, the thinning particles can be selected as needed; for example, the thinning particles are alumina (Al2O3).

[0075] In one embodiment, the polishing fluid can be selected as needed; for example, the polishing fluid is a silica (SiO2) colloidal polishing fluid or deionized water.

[0076] In one embodiment, polishing a single-crystal piezoelectric wafer with a polishing slurry includes: performing a first fine polishing for 30-60 minutes using a silicon dioxide (SiO2) colloidal polishing slurry to remove the surface damage layer, followed by a second fine polishing for 30-60 minutes using deionized water to improve surface flatness and smoothness, ultimately obtaining a lithium niobate film with high flatness, low surface damage, and target thickness.

[0077] Step 7: Deposit a metal layer on the surface of the single-crystal piezoelectric thin film, and perform photolithography and lift-off processes on the metal layer to obtain patterned metal electrodes.

[0078] In one embodiment, the metal layer can be deposited using ion beam deposition (IBD) or magnetron sputtering deposition processes.

[0079] In one embodiment, the process of depositing the metal layer includes: sequentially depositing a 0.01~0.02 μm chromium adhesion layer and a 0.05~0.1 μm gold conductive layer on the surface of a single-crystal piezoelectric thin film using an IBD process.

[0080] In one embodiment, the process of obtaining a patterned metal electrode by performing photolithography and lift-off processes on the metal layer includes: spin-coating a 1-2 μm photoresist, transferring the electrode pattern onto the photoresist through exposure and development, and then removing excess metal using a lift-off process to form a patterned metal electrode.

[0081] Example 1 Step 1: Prepare a lithium niobate wafer with a Y-36° cut and a thickness of 380μm. First, rinse it with flowing DI water for 2 minutes to remove surface particles. Then, use propanol and IPA for 8 minutes of ultrasonic cleaning to remove organic contaminants. Finally, purge the lithium niobate wafer with high-purity nitrogen at 80°C to obtain a clean and dry lithium niobate wafer.

[0082] Step 2: Transfer the clean and dry lithium niobate wafer to a coating machine (model: M80), take the first layer of photosensitive dry film with a thickness of 10μm, remove the PE protective film, and attach the resin adhesive layer to the surface of the lithium niobate wafer with the adhesive layer facing down. Ensure good adhesion and uniformity between the photosensitive dry film and the wafer substrate by controlling the roller speed of the coating machine to 0.8 m / min, the pressure to 1 bar, and the temperature to 60°C. Step 3: To achieve tight bonding of the two-layer photosensitive dry film, without damaging the first layer, the PET support film is first removed at a roller speed of 0.5 m / min, a pressure of 0.8 bar, and a temperature of 20°C. The first layer is then soft-baked at 90°C for 3 minutes to prevent air bubbles or resin extrusion during the bonding of the second layer. Subsequently, a 20 μm thick second layer (with the resin adhesive layer facing down after removing the PE protective film) is attached to the surface of the first layer, and its PET support film is removed using the same parameters. Next, a pre-baking process is performed at 90°C for 2 minutes to enhance adhesion and stabilize the adhesive layer. Exposure to 365 nm wavelength, 150 mJ / cm² ultraviolet light for 6 seconds transfers the rectangular pattern from the photomask to the second layer. After exposure, a process is performed at 100°C for 2 seconds. After baking the film for 2 minutes, it is finally immersed in propylene glycol methyl ether acetate (PGMEA) developer for 2 minutes, then rinsed with IPA for 10 seconds. After repeated rinsing, a rectangular cavity structure is obtained on the second photosensitive dry film.

[0083] Step 4: After removing the PE protective film from the 10μm thick third photosensitive dry film, attach it to the surface of the second photosensitive dry film with the resin adhesive layer facing down. Step 5: To achieve tight bonding between the piezoelectric layer, structural layer, support layer, and glass substrate, the PET support film of the third photosensitive dry film is removed under the same conditions as the process parameters for removing the PET support film of the first photosensitive dry film. Then, the resin adhesive layer of the third photosensitive dry film is placed face down, aligned, and inverted onto the surface of the glass substrate. To enhance the interfacial adhesion and bonding stability between the third photosensitive dry film and the glass substrate, a hard bake is performed at 100°C for 1 minute.

[0084] Step 6: Fix the device with the piezoelectric layer, structural layer, support layer and glass substrate bonded together on a chemical mechanical polishing (CMP) machine (model: IVG-3035); perform multi-step thinning using an alumina (Al2O3) thinning solution with a particle size of 2 μm, then perform a first fine polishing for 30 min using a silica (SiO2) colloidal polishing solution to remove the surface damage layer, followed by a second fine polishing for 30 min using DI water to further improve the surface flatness and smoothness, finally obtaining a lithium niobate film with high flatness, low surface damage and target thickness; Step 7: First, a 0.01 μm chromium adhesion layer and a 0.1 μm gold conductive layer are sequentially deposited on the surface of the lithium niobate film using the IBD process; then, a 1 μm photoresist is spin-coated, and the electrode pattern is transferred onto the photoresist through exposure and development; finally, excess metal is removed using the lift-off process to form a patterned metal electrode.

[0085] Comparative Example 1 The fabrication process of an open-back cavity piezoelectric hydrophone includes the following steps: Step 1: Prepare a lithium niobate wafer with a Y-36° cut and a thickness of 380 μm, and an SOI wafer with a top silicon layer thickness of 10 μm, a silicon dioxide layer thickness of 2 μm, a silicon substrate thickness of 300 μm, and double-sided polishing. Perform the same cleaning process as in Step 1 of Example 1 on both wafers to remove organic matter, particulate matter, and metal contaminants from the wafer surface. Step 2: A 0.1 μm thick platinum layer is deposited on the surface of the lithium niobate wafer using the IBD process as the bottom electrode.

[0086] Step 3: Flip and bond the lithium niobate wafer containing the platinum-bottom electrode onto the SOI wafer.

[0087] Step 4: Using the same lithium niobate thinning process as in Step 6 of Example 1, the lithium niobate wafer is thinned to a lithium niobate film with a thickness of 8 μm.

[0088] Step 5: Using the same metal electrode formation process as step 7 in Example 1, a patterned metal electrode is formed on the surface of the lithium niobate film as the top electrode.

[0089] Step 6: Using deep reactive ion etching (DRIE) technology, cavities of the target thickness and width are etched on the silicon substrate of the SOI wafer until the silicon dioxide layer stops etching.

[0090] Comparative Example 2 The manufacturing process of a closed-back cavity piezoelectric hydrophone includes the following steps: The difference from Comparative Example 1 is that the prepared SOI wafer contains a closed cavity structure and the etching process in step 5 of Comparative Example 1 is reduced. The thinning of the lithium niobate wafer and the formation of the metal electrodes are the same as in Comparative Example 1.

[0091] Compared to Comparative Examples 1 and 2, Example 1 has significant advantages in both materials and processes. In terms of material cost, Example 1 uses a photosensitive dry film as both the structural and support layers, with a material price approximately one-tenth that of an SOI wafer, significantly reducing device manufacturing costs. Regarding process difficulty and cost, Example 1 forms cavities on the photosensitive dry film using photolithography, a simple and highly controllable process that eliminates the need for complex deep silicon etching, significantly reducing processing difficulty and equipment requirements. In contrast, the comparative examples require etching cavities onto the silicon substrate of the SOI wafer, resulting in a complex and costly process. In terms of bonding, the photosensitive dry film exhibits excellent adhesion, enabling low-temperature, high-reliability bonding with lithium niobate wafers, and is easy to operate. Direct bonding between lithium niobate and single-crystal silicon, however, faces challenges such as poor interface matching and inconsistent thermal expansion coefficients, making bonding difficult. Furthermore, from a structural performance perspective, the thickness of the top silicon layer of SOI wafers is usually difficult to reach more than 20 μm, which limits the thickness of the structural layer and results in weak voltage resistance of the hydrophones fabricated. However, the use of photosensitive dry film can flexibly control the thickness, making it easy to realize thick film structures and significantly improving the mechanical stability and voltage resistance of the device.

[0092] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A piezoelectric hydrophone suitable for deep-sea high-pressure environments, characterized in that, It includes an electrode layer, a piezoelectric layer, a structural layer, a support layer, a bonding layer, and a substrate, which are stacked in sequence. A cavity is provided through the support layer along the stacking direction; The piezoelectric layer is a single-crystal piezoelectric material thin film; The structural layer, the support layer, and the bonding layer are all made of photosensitive dry film. The electrode layer is a patterned coplanar metal electrode.

2. The piezoelectric hydrophone suitable for deep-sea high-pressure environments according to claim 1, characterized in that, The photosensitive dry film is a positive dry film.

3. The piezoelectric hydrophone suitable for deep-sea high-pressure environments according to claim 1, characterized in that, The thickness of the electrode layer is 0.01~2 μm.

4. The piezoelectric hydrophone suitable for deep-sea high-pressure environments according to claim 1, characterized in that, The thickness of the piezoelectric layer is 1~20 μm.

5. The piezoelectric hydrophone suitable for deep-sea high-pressure environments according to claim 1, characterized in that, The thickness of the structural layer is 5~50 μm.

6. The piezoelectric hydrophone suitable for deep-sea high-pressure environments according to claim 1, characterized in that, The thickness of the support layer is 5~50 μm.

7. The piezoelectric hydrophone suitable for deep-sea high-pressure environments according to claim 1, characterized in that, The thickness of the bonding layer is 5~50 μm.

8. The method for manufacturing a piezoelectric hydrophone suitable for deep-sea high-pressure environments as described in any one of claims 1 to 7, characterized in that, include: A clean single-crystal piezoelectric wafer is provided, and a first photosensitive dry film, a second photosensitive dry film, and a third photosensitive dry film are sequentially attached to one side of the single-crystal piezoelectric wafer as a structural layer, a support layer, and a bonding layer, respectively. After attaching the second photosensitive dry film, the second photosensitive dry film is further etched to form a through cavity. The side of the third photosensitive dry film facing away from the single crystal piezoelectric wafer is attached to the surface of the substrate; The side of the single-crystal piezoelectric wafer facing away from the substrate is thinned to form a single-crystal piezoelectric material thin film as a piezoelectric layer; A patterned coplanar metal electrode is deposited as an electrode layer on the side of the single-crystal piezoelectric material film facing away from the substrate.

9. The preparation method according to claim 8, characterized in that, Before attaching the second photosensitive dry film, the first photosensitive dry film is also softened and baked. And / or, before attaching the third photosensitive dry film, the process further includes hard baking the second photosensitive dry film through which the cavity is opened; And / or, before attaching the side of the third photosensitive dry film away from the single-crystal piezoelectric wafer to the substrate surface, the third photosensitive dry film is further subjected to hard baking.

10. The preparation method according to claim 8, characterized in that, The thinning of the side of the single-crystal piezoelectric wafer facing away from the substrate includes: The single-crystal piezoelectric wafer is thinned in multiple steps using a thinning solution containing particles to gradually reduce its thickness. After the multi-step thinning process, a first fine polishing is performed using a polishing slurry to remove the surface damage layer; After the first fine polishing, a second fine polishing is performed using deionized water to improve surface smoothness and gloss.

Images