Method for manufacturing a mems transducer based on electrochemical corrosion and mems transducer

Abstract

This application discloses a method for fabricating a MEMS transducer based on electrochemical etching and the MEMS transducer itself. The method includes sequentially epitaxially forming a buffer layer, a sacrificial layer, and a functional layer on a substrate to form an epitaxial wafer structure; etching the functional layer to form an exposed region of the sacrificial layer within the functional layer; immersing the exposed region of the epitaxial wafer structure in an electrolyte and electrochemically etching the sacrificial layer starting from the exposed region to form a cavity between the functional layer and the buffer layer; and depositing metal on the surface of the functional layer to form an electrode, thereby obtaining the MEMS transducer. The embodiments of this application feature a simple, fast, and efficient process, avoiding the manufacturing costs associated with complex procedures. Furthermore, the selectivity and controllability of electrochemical etching enable non-destructive fabrication of the device structure. This application can be widely applied in the field of microelectromechanical systems (MEMS) transducer technology.

Description

Technical Field

[0001] This application relates to the field of microelectromechanical systems (MEMS) transducer technology, and in particular to a MEMS transducer fabrication method based on electrochemical corrosion and a MEMS transducer. Background Technology

[0002] MEMS transducers comprise sensors and actuators, such as pressure sensors, accelerometers, and acoustic sensors. Their performance is highly dependent on the properties of the functional materials. Traditional silicon-based MEMS transducers have limitations in harsh environments such as high temperature, high frequency, and high power. Third-generation semiconductor materials, represented by gallium nitride (GaN), have become ideal candidate materials for high-performance MEMS transducers due to their excellent piezoelectric properties, wide bandgap, high electron saturation drift velocity, and good chemical stability.

[0003] However, fabricating GaN-based MEMS transducers faces significant technological challenges, with the core difficulty lying in how to efficiently and cost-effectively fabricate high-performance movable microstructures (such as cantilever beams and diaphragms). Traditional mainstream silicon-based MEMS processes typically employ "cavity etching" to release movable structures, which involves deep reactive ion etching (DRIE) from the back of the wafer to hollow out the substrate and create cavities. This approach is lengthy, requires complex protection on the front side, is technically challenging and costly, and is unsuitable for non-silicon material systems like GaN. Another common approach is to use a "sacrificial layer" technique, where a selectively etchable material (such as silicon dioxide or polysilicon) is pre-deposited before growing the functional structure, and the structure is released by etching this layer. However, the lateral penetration of the etchant is often difficult to control precisely, easily leading to dimensional deviations or incomplete release, limiting the application of this technique in fabricating high-performance, high-reliability GaN MEMS devices.

[0004] For group III nitride materials such as GaN, finding a simple manufacturing process that can ensure accurate structural dimensions and low cost is extremely challenging. Summary of the Invention

[0005] The main objective of this application is to propose a method for fabricating MEMS transducers based on electrochemical corrosion and a MEMS transducer, which aims to simplify the process route and flow, reduce manufacturing costs, and improve the performance of MEMS transducers.

[0006] To achieve the above objectives, embodiments of this application propose a method for fabricating MEMS transducers based on electrochemical corrosion, the method comprising: A buffer layer, a sacrificial layer, and a functional layer are sequentially epitaxially grown on a substrate to form an epitaxial wafer structure. The functional layer is etched to form an exposed area of ​​the sacrificial layer within the functional layer; The exposed area of ​​the epitaxial wafer structure is placed in an electrolyte, and the sacrificial layer is electrochemically etched starting from the exposed area to form a cavity between the functional layer and the buffer layer. Metal is deposited on the surface of the functional layer to form electrodes, thus obtaining a MEMS transducer.

[0007] In some embodiments, the epitaxial wafer structure formed by sequentially epitaxially growing a sacrificial layer, a buffer layer, and a functional layer on the substrate includes: A nucleation layer, a current spreading layer, and a barrier layer are epitaxially grown sequentially on the upper surface of the substrate to form a buffer layer on the upper surface of the substrate. A sacrificial layer is epitaxially grown on the side of the buffer layer away from the substrate; A functional layer is epitaxially grown on the side of the sacrificial layer away from the buffer layer.

[0008] In some embodiments, etching the functional layer to form an exposed region of the sacrificial layer in the functional layer includes: Using the side of the functional layer furthest from the sacrificial layer as the etching start point and the sacrificial layer as the etching end point, a dry etching process is used to etch the functional layer to form an exposed area of ​​the sacrificial layer in the functional layer.

[0009] In some embodiments, immersing the exposed region of the epitaxial wafer structure in an electrolyte and electrochemically etching the sacrificial layer starting from the exposed region to form a cavity between the functional layer and the buffer layer includes: The contact electrode is generated, and the exposed area is completely immersed in the electrolyte; The contact electrode is used as the anode to form an electrical circuit with the electrolyte and the power source; Obtain cavity removal parameters, including voltage parameters and time parameters; Based on the voltage and time parameters, the electrolyte is controlled to electrochemically corrode the sacrificial layer starting from the exposed area to form a cavity between the functional layer and the buffer layer.

[0010] In some embodiments, the contact electrode is used as the anode to form an electrical circuit with the electrolyte and the power source, including: A hole is made on the surface of the functional layer to the sacrificial layer, and metal is injected to form the contact electrode; The contact electrode does not come into contact with the electrolyte.

[0011] In some embodiments, the silicon doping concentration of the sacrificial layer is higher than that of the buffer layer and the functional layer.

[0012] To achieve the above objectives, embodiments of this application also propose a MEMS transducer based on electrochemical corrosion, which is fabricated by any of the MEMS transducer fabrication methods based on electrochemical corrosion in the embodiments of this application.

[0013] In some embodiments, the sacrificial layer is obtained by N-type doping of silicon, with the N-type doping concentration ranging from 1.0 × 10⁻⁶. 19 ~2.0×10 19 cm -3 .

[0014] In some embodiments, the height of the cavity is the same as the thickness of the sacrificial layer.

[0015] In some embodiments, the material of the functional layer is gallium nitride or gallium nitride-based composite material.

[0016] The embodiments of this application include at least the following beneficial effects: by etching various complex shapes on the functional layer and utilizing the selectivity and controllability of electrochemical etching to form cavities in situ and release movable microstructures, the complex back cavity etching process is avoided. This results in a shorter and simpler process route, effectively reducing manufacturing costs, and achieving precise control over the etching range and structure release size. The method of this application is simple, fast, and efficient, avoiding the manufacturing costs caused by complex processes, while utilizing the selectivity and controllability of electrochemical etching to achieve non-destructive fabrication of device structures. Attached Figure Description

[0017] Figure 1 This is a flowchart of the MEMS transducer fabrication method based on electrochemical corrosion provided in the embodiments of this application; Figure 2 This is a schematic diagram of an epitaxial structure of a GaN-based MEMS transducer provided in an embodiment of this application; Figure 3 This is a schematic diagram of the patterned etching pattern of a single-lobed cantilever arm epitaxial wafer provided in the embodiments of this application; Figure 4 This is a schematic diagram of the patterned etching pattern of the multi-lobed cantilever arm of the epitaxial wafer provided in the embodiments of this application; Figure 5 This is a schematic diagram of the annular patterned etching pattern of the epitaxial wafer provided in the embodiments of this application; Figure 6 This is a schematic diagram of the epitaxial film patterned etching pattern provided in the embodiments of this application; Figure 7 This is a schematic diagram of the electrochemical etching apparatus provided in the embodiments of this application; Figure 8 These are a three-dimensional view and a cross-sectional schematic diagram of the cavity formed by patterned etching followed by electrochemical etching of a single-lobed cantilever arm, as provided in the embodiments of this application. Figure 9 These are a three-dimensional view and a cross-sectional schematic diagram of the cavity formed by patterned etching followed by electrochemical etching of the multi-lobed cantilever arm provided in the embodiments of this application; Figure 10 This is a three-dimensional schematic diagram of a MEMS pressure sensor device provided in an embodiment of this application; Figure 11 This is a three-dimensional schematic diagram of a MEMS ultrasonic transducer provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of this application and are not intended to limit it. In the following description, when referring to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with those of this application; they are merely examples of methods consistent with some aspects of the embodiments of this application as detailed in the appended claims.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing embodiments of this application only and is not intended to limit this application.

[0020] The MEMS transducer fabrication method and MEMS transducer based on electrochemical corrosion provided in this application avoid the complex back cavity etching process, which can achieve a shorter and simpler process route and effectively reduce manufacturing costs.

[0021] Please see Figure 1 , Figure 1 This is an optional flowchart of a MEMS transducer fabrication method based on electrochemical corrosion. Figure 1 The method may include, but is not limited to, steps 101 to 104.

[0022] Step 101: Epitaxially grow a buffer layer, a sacrificial layer and a functional layer sequentially on the substrate to form an epitaxial wafer structure; Step 102: Etch the functional layer to form an exposed area of ​​the sacrificial layer in the functional layer; Step 103: Place the exposed area of ​​the epitaxial wafer structure into the electrolyte and electrochemically etch the sacrificial layer starting from the exposed area to form a cavity between the functional layer and the buffer layer; Step 104: Deposit metal on the surface of the functional layer to form an electrode, thereby obtaining a MEMS transducer.

[0023] Steps 101 to 104, as illustrated in the embodiments of this application, involve etching various complex shapes on the functional layer and utilizing the selectivity and controllability of electrochemical etching to form cavities in situ and release movable microstructures. This avoids the complex back cavity etching process, resulting in a shorter and simpler process route, effectively reducing manufacturing costs, and enabling precise control over the etching range and structure release dimensions. The method of this application is simple, fast, and efficient, avoiding the manufacturing costs associated with complex processes, while utilizing the selectivity and controllability of electrochemical etching to achieve non-destructive fabrication of device structures.

[0024] In step 101 of some embodiments, the growth substrate may be any one of the substrates suitable for GaN epitaxial growth, including but not limited to sapphire material, N-type doped silicon material, gallium nitride material, etc.; the buffer layer includes a nucleation layer, a current spreading layer, and a barrier layer, wherein the nucleation layer may be any one of GaN nucleation layer or AlN nucleation layer, the current spreading layer may be an N-type doped GaN layer, and the barrier layer may be an undoped GaN layer; the silicon doping concentration of the sacrificial layer is different from that of the buffer layer and the functional layer, so that the conductivity of the sacrificial layer is different from that of the buffer layer and the functional layer; the material of the functional layer may be pure GaN, or a GaN-doped composite material, or the functional layer may include an AlGaN barrier layer and an undoped GaN transition layer.

[0025] A buffer layer, a sacrificial layer, and a functional layer are grown on a growth substrate using an epitaxial growth method. The epitaxial growth method can be any one of metal-organic chemical vapor deposition (MOCVD), molecular beam epitaxy (MBE), and hydride vapor phase epitaxy (HVPE).

[0026] In step 102 of some embodiments, the etching method can be any one of reactive ion etching, inductively coupled plasma (ICP) etching, electron cyclotron resonance (ECR) etching, ion beam etching (IBE), and atomic layer etching (ALE).

[0027] In step 103 of some embodiments, the epitaxial wafer is immersed in the electrolyte. At the interface between the two, a depletion layer, similar to that of a Schottky diode, is formed with almost no free carriers. Applying a positive voltage (anodic bias) to the semiconductor attracts negative ions from the electrolyte and simultaneously pulls holes from inside the semiconductor to the surface. The higher the voltage, the greater the hole concentration at the surface, and the faster the etching rate. The principle of electrochemical etching is to selectively dissolve semiconductor materials by applying an external bias, utilizing the Schottky junction or depletion layer formed at the semiconductor-electrolyte interface.

[0028] In step 104 of some embodiments, the electrode deposition method can be any one of electron beam evaporation, thermal resistance evaporation, magnetron sputtering, chemical vapor deposition, and electrochemical deposition.

[0029] In some embodiments, step 101 may include, but is not limited to, the following steps: Step 201 involves epitaxially growing a nucleation layer, a current spreading layer, and a barrier layer sequentially on the upper surface of the substrate to form a buffer layer on the upper surface of the substrate. Step 202: Epitaxially grow a sacrificial layer on the side of the buffer layer away from the substrate; Step 203: Epitaxially grow a functional layer on the side of the sacrificial layer away from the buffer layer.

[0030] This application embodiment improves the quality and electrical properties of the epitaxial crystal through a buffer layer, and introduces a sacrificial layer that needs to be electrochemically etched subsequently to form a cavity beneath the functional layer. A functional layer is grown on the sacrificial layer to maintain high-quality epitaxy. Through the above growth method and sequence, a cavity is ultimately formed between the functional layer and the buffer layer, achieving the sensor's core performance characteristics such as high sensitivity and high-frequency response.

[0031] In some embodiments, step 102 may include, but is not limited to, the following steps: Step 301: Starting from the side of the functional layer furthest from the sacrificial layer and ending at the sacrificial layer, the functional layer is etched using a dry etching process to form an exposed area of ​​the sacrificial layer in the functional layer.

[0032] This application embodiment provides a sacrificial layer exposure area in the functional layer and limits the etching endpoint to be located within the sacrificial layer, thereby enabling precise control of the etching depth to expose the sacrificial layer. This allows the subsequent electrolyte to directly electrochemically etch the sacrificial layer through the exposed sacrificial layer, avoiding the complex wafer-level back cavity etching in traditional processes and significantly simplifying the manufacturing process.

[0033] In this embodiment of the application, step 103 may include, but is not limited to, the following steps: Step 401: Generate the contact electrode and completely immerse the exposed area in the electrolyte; Step 402: The contact electrode is used as the anode to form an electrical circuit with the electrolyte and the power source; Step 403: Obtain cavity removal parameters, which include voltage parameters and time parameters; Step 404: Based on voltage and time parameters, control the electrolyte to electrochemically corrode the sacrificial layer starting from the exposed area to form a cavity between the functional layer and the buffer layer.

[0034] This application embodiment achieves precise control of the voltage and application time to perform in-situ electrochemical etching of the sacrificial layer from the functional layer patterning location. This enables the formation of cavities below the functional regions located around the etching openings, achieving precise control of the electrochemical etching process and allowing the cavity structure size to be adjusted as needed.

[0035] In this embodiment of the application, step 402 may include, but is not limited to, the following steps: Step 501: Open a hole on the surface of the functional layer to the sacrificial layer, and implant metal to form a contact electrode; The contact electrode does not come into contact with the electrolyte.

[0036] The embodiments of this application improve the purity and stability of the electrochemical corrosion process by preventing metal ions from entering the electrolyte, thus avoiding contamination of the electrochemical corrosion reaction or triggering unnecessary electrochemical reactions.

[0037] In this embodiment, the silicon doping concentration of the sacrificial layer is higher than that of the buffer layer and the functional layer.

[0038] This application embodiment grows a sacrificial layer with a high silicon doping concentration between the buffer layer and the functional layer. Through the difference in conductivity, it ensures that the sacrificial layer of a specific material is selectively etched and removed during the electrochemical corrosion process, while the buffer layer and functional layer materials remain undamaged.

[0039] This application also provides a MEMS transducer based on electrochemical corrosion, which is fabricated by any of the MEMS transducer fabrication methods based on electrochemical corrosion in this application.

[0040] This application provides a MEMS transducer based on electrochemical etching. It is fabricated by etching various complex shapes on the functional layer and utilizing the selectivity and controllability of electrochemical etching to form cavities in situ and release movable microstructures. This avoids the defects caused by complex back cavity etching processes. The method, with a shorter and simpler process route, effectively reduces manufacturing costs and achieves precise control over the etching range and structure release size. The MEMS transducer fabrication method of this application is simple, fast, and efficient, avoiding the manufacturing costs associated with complex processes. Simultaneously, it utilizes the selectivity and controllability of electrochemical etching to achieve non-destructive fabrication of the device structure.

[0041] In this embodiment, the sacrificial layer is obtained by N-type doping of silicon, with an N-type doping concentration range of 1.0 × 10⁻⁶. 19 ~2.0×10 19 cm -3 .

[0042] The embodiments of this application achieve selective corrosion removal of the sacrificial layer of specific materials during the electrochemical corrosion process by using specific sacrificial layer element doping and corresponding concentrations.

[0043] In this embodiment, the height of the cavity is consistent with the thickness of the sacrificial layer.

[0044] In this embodiment, a cavity with a height consistent with the thickness of the sacrificial layer is used to completely remove the sacrificial layer below the patterned functional layer during the electrochemical corrosion process, thereby releasing the movable structure.

[0045] In the embodiments of this application, the material of the functional layer is gallium nitride or gallium nitride-based composite material.

[0046] The embodiments of this application can achieve active design and optimization of core performance of sensors such as sensitivity and frequency response by doping different elements in the functional layer, so as to meet the performance requirements of specific MEMS transducers.

[0047] The solutions of this application embodiment will be described in detail and explained below with reference to specific application examples: Step 1: Clean the growth substrate.

[0048] Specifically, a sapphire substrate can be used as the growth substrate.

[0049] Step 2: Use epitaxial growth methods to grow a buffer layer, a sacrificial layer, and a functional layer on the growth substrate.

[0050] Specifically, a sapphire substrate that has undergone standard cleaning processes is placed in the reaction chamber of a metal-organic chemical vapor deposition system, and a buffer layer, a sacrificial layer, and a functional layer are sequentially grown on the substrate using MOCVD.

[0051] Please refer to Figure 2 , Figure 2 This is a schematic diagram of an epitaxial structure of a GaN-based MEMS transducer provided in an embodiment of this application. From bottom to top, it consists of a growth substrate 1, a buffer layer 2, a sacrificial layer 3, and a functional layer 4. The buffer layer 2 includes a nucleation layer 5, a current spreading layer 6, and a barrier layer 7. In one embodiment of this application, the nucleation layer 5 is either a GaN nucleation layer or an AlN nucleation layer, the current spreading layer 6 is an N-type doped GaN layer, and the barrier layer 7 is an undoped GaN layer.

[0052] In one example, growing a buffer layer 2 on a growth substrate 1 using an epitaxial growth method specifically includes the following steps: 1) A nucleation layer 5 is grown on the growth substrate 1. The thickness of the nucleation layer 5 can be 200-500 nm.

[0053] 2) A current spreading layer 6 is grown on the side of the nucleation layer 5 away from the growth substrate. The thickness of the current spreading layer 6 can be 500 nm, and the doping concentration of the N-type doped GaN layer used can be 3 × 10⁻⁶. 18 cm -3 ~7×10 18 cm -3 The doped atom is Si.

[0054] 3) A barrier layer 7 is grown on the side of the current spreading layer 6 away from the nucleation layer. The thickness of the barrier layer 7 can be 0.24 μm to 0.5 μm.

[0055] Through the above-mentioned GaN nucleation layer or AlN nucleation layer with a thickness of 200-500 nm, a 500 nm thick layer with a doping concentration of 3×10⁻⁶ is formed. 13 ~5×10 13 cm -3 The lightly doped layer and the undoped layer with a thickness of 500 nm together form GaN buffer layer 2, and the thickness of GaN buffer layer 2 is in the range of 1200 to 1500 nm.

[0056] In one example, a sacrificial layer 3 is grown on the side of the buffer layer 2 away from the growth substrate 1. The thickness of the heavily doped GaN sacrificial layer 3 can be 300–2000 nm. The heavily doped GaN sacrificial layer 3 is N-type doped using Si, and the N-type doping concentration can be 1.0 × 10⁻⁶. 19 ~2.0×10 19 cm -3 .

[0057] In one example, a functional layer 4 is grown on the side of the sacrificial layer 3 away from the buffer layer. The functional layer 4 can be undoped GaN, and the thickness of the undoped GaN functional layer can be 500 nm-1 μm. The functional layer 4 can also be one or more GaN-based materials with different doping concentrations and doping types.

[0058] In another example, functional layer 4 may include an AlGaN barrier layer and an undoped GaN transition layer. The AlGaN barrier layer may have a thickness of 20–25 nm and an Al molar fraction of 20%–30%; the GaN transition layer may have a thickness of 600–900 nm.

[0059] Specifically, in other embodiments of this application, the growth substrate 1 and the buffer layer 2 constitute a support layer 8, which provides mechanical support. The growth substrate 1 is a single-crystal substrate with lattice matching or mismatch within a predetermined range to the epitaxial layer. The buffer layer 2 is located on the growth substrate and is used to reduce the dislocation density and growth stress in the epitaxial layer. The sacrificial layer 3 is located on the support layer 8, and the doping concentration of the sacrificial layer 3 is higher than that of the buffer layer 2 below it and the functional structure layer 4 above it, causing a difference in conductivity to facilitate the implementation of subsequent electrochemical etching processes based on the conductivity difference. The functional layer 4 is grown on the sacrificial layer 3 and is a micromechanical structure released by electrochemical etching. The material of the functional layer 4 can be gallium nitride (GaN) or GaN-based composite materials, and its shape can be designed according to the device performance requirements.

[0060] Step 3, for Figure 2The grown epitaxial wafer is patterned and etched to define the pattern of the micromechanical structure and expose the sacrificial layer 3.

[0061] Specifically, in one embodiment of this application, the AlGaN / GaN composite functional layer 4 is etched using photoresist or silicon oxide as a mask and an inductively coupled plasma (ICP) dry etching process. The endpoint of the etching must be located within the sacrificial layer 3 to ensure that the functional layer 4 is completely patterned and the sacrificial layer 3 is exposed, so as to ensure that the electrolyte can uniformly contact the sacrificial layer 3.

[0062] Specifically, in another embodiment of this application, the GaN functional layer 4 is etched using photoresist or silicon oxide as a mask and an inductively coupled plasma (ICP) dry etching process. The endpoint of the etching must be located within the sacrificial layer 3 to ensure that the functional layer 4 is completely patterned and the sacrificial layer 3 is exposed, so as to ensure that the electrolyte can uniformly contact the sacrificial layer 3.

[0063] Optionally, the etching pattern in the embodiments of this application can refer to Figure 3 , Figure 4 , Figure 5 and Figure 6 , Figure 3 , Figure 4 , Figure 5 and Figure 6 These are etching patterns used in the embodiments of this application. The actual fabrication process includes, but is not limited to, the preferred etching patterns used in the embodiments of this application. Functional layer 4, after electrochemical etching according to the preferred etching pattern of this embodiment, can obtain shapes such as multi-lobed cantilever arms, rings, and films. Figure 3 It is a U-shaped pattern that can be selected for patterning the single-lobed cantilever arm of an epitaxial wafer. Figure 4 a is a cross-shaped pattern that can be selected for pattern etching of the multi-lobed cantilever arm of the epitaxial wafer. Figure 4 b is a cross-shaped pattern that can be selected for the patterning etching of the multi-lobed cantilever arm of the epitaxial wafer. Figure 4 c is an I-shaped pattern that can be selected for pattern etching of the multi-lobed cantilever arm of the epitaxial wafer. Figure 5 It is a circular pattern that can be selected for the ring-shaped patterning etching of epitaxial wafers. Figure 6 It is a strip pattern that can be selected for epitaxial film patterning etching.

[0064] Step 4: Perform electrochemical etching on the epitaxial wafer after ICP etching to form a cavity.

[0065] Specifically, in one embodiment of this application, please refer to Figure 7 , Figure 7This is a schematic diagram of the electrochemical etching apparatus in an embodiment of this application. The epitaxial wafer is placed in an electrochemical etching apparatus containing 0.3 mol / L oxalic acid or nitric acid and a voltage of 16-20V for electrochemical etching. The upper region of the epitaxial wafer near the AlGaN side is scraped down to the sacrificial layer 3 using a diamond glass cutter, coated with silver paste as a contact electrode, and placed at the anode. The remaining two-thirds of the region below the silver paste is immersed in the electrolyte, ensuring the electrolyte does not contact the silver paste. Since the electrolyte fully contacts the sacrificial layer 3 exposed at the ICP-etched pattern, etching begins at the ICP etching point. By precisely controlling the etching voltage and time, the etching reaction proceeds laterally inwards from the etched area until all sacrificial layer 3 material directly below the patterned functional layer 4 is completely removed. After etching is terminated, the micromechanical structure formed by the AlGaN / GaN composite functional layer 4 is released, forming a cavity 9 below it. (Refer to...) Figure 8 , Figure 8 The images show a three-dimensional view and a cross-sectional schematic diagram of the cavity formed by patterning a single-lobed cantilever arm followed by electrochemical etching, according to an embodiment of this application.

[0066] Specifically, in another embodiment of this application, please refer to Figure 7 , Figure 7 This is a schematic diagram of the electrochemical etching apparatus in an embodiment of this application. The epitaxial wafer is placed in an electrochemical etching apparatus containing 0.3 mol / L oxalic acid or nitric acid and a voltage of 16-20V for electrochemical etching. The upper region of the epitaxial wafer near the GaN side is scraped down to the sacrificial layer 3 using a diamond glass cutter, coated with silver paste as a contact electrode, and placed at the anode. Approximately two-thirds of the remaining region below the silver paste is immersed in the electrolyte, ensuring the electrolyte does not contact the silver paste. Because the electrolyte fully contacts the sacrificial layer 3 exposed at the ICP-etched pattern, etching begins at the ICP etching location. By precisely controlling the etching voltage and time, the etching reaction proceeds laterally inwards from the etched area until all sacrificial layer 3 material directly below the patterned functional layer 4 is completely removed. After etching is complete, the micromechanical structure formed by the GaN functional layer 4 is released, forming a cavity 9 below it. (Refer to...) Figure 9 , Figure 9 The images show a three-dimensional view and a cross-sectional schematic diagram of the cavity formed by patterning and then electrochemically etching a multi-lobed cantilever arm, as described in this embodiment of the application.

[0067] Specifically, in other embodiments of this application, the cavity 9 is located below the functional layer 4 and above the support layer 8. It is formed by removing the original sacrificial layer 3 through electrochemical etching, so that the patterned functional layer 4 becomes a suspended and movable structure. It can reduce residual stress, maintain stable mechanical and electrical properties (such as capacitor gaps), and improve the sensitivity and consistency of the device according to different patterned structures.

[0068] Step 5: Prepare electrodes for the structure after cavity 9 is formed.

[0069] Specifically, refer to Figure 10 , Figure 10 This is a three-dimensional schematic diagram of a MEMS pressure sensor device provided in an embodiment of this application. In one embodiment of this application, a metal is deposited on the sample surface after photolithography, and the resist is removed using acetone to form a patterned electrode. The source electrode 10 and drain electrode 11, deposited using electron beam evaporation (EBL), both comprise Ti / Al / Ni / Au with corresponding thicknesses of 20nm / 130nm / 40nm / 50nm, that is, both the source electrode 10 and drain electrode 11 comprise a 20nm Ti layer, a 130nm Al layer, a 40nm Ni layer, and a 50nm Au layer sequentially disposed from top to bottom. After depositing the source and drain electrode layers, they are annealed at 850°C in an N2 environment for 30s. Further, a patterned Ni / Au (30nm / 10nm) is deposited on the sample surface using a lift-off process as a gate 12 to obtain a MEMS pressure sensor.

[0070] This embodiment of the application directly utilizes an AlGaN / GaN heterojunction, a group III nitride composite functional layer, which possesses a high piezoresistive coefficient and achieves high sensitivity. The electrochemical etching process described in this application is suitable for heavily doped GaN sacrificial layers in AlGaN / GaN epitaxial structures, enabling cavity fabrication without back cavity etching. This significantly simplifies the manufacturing process of such high-performance sensors and provides a clear and efficient technical path for fabricating next-generation high-performance, harsh-environment-resistant group III nitride MEMS pressure sensors.

[0071] Specifically, refer to Figure 11 , Figure 11 This is a three-dimensional schematic diagram of a MEMS ultrasonic transducer provided in an embodiment of this application. In another embodiment of this application, a multi-lobed top electrode 13 is formed by depositing and patterning metal on the surface of the GaN functional layer 4, with the electrode pattern covering the cantilever beam region. Each lobe top electrode 13 can be interconnected as needed; in this embodiment, each lobe top electrode 13 is interconnected. Further, a window is etched in the peripheral region of the device to expose the sacrificial layer 3, and then patterned metal is deposited within the window to form a bottom electrode 14 that contacts the sacrificial layer 3 and is electrically in contact with the lower surface of the functional layer 4.

[0072] Optionally, the top electrode 13 and the bottom electrode 14 may be made of any one or any combination of molybdenum (Mo), titanium (Ti), aluminum (A), or platinum (Pt), and may alternately include any other suitable electrode material.

[0073] This embodiment of the present application provides a piezoelectric GaN MEMS ultrasonic transducer.

[0074] According to some embodiments of this application, the overall method for fabricating MEMS transducers based on electrochemical corrosion is as follows: On the growth substrate, a buffer layer, a sacrificial layer, and a GaN-based functional layer are epitaxially grown sequentially. The GaN-based functional layer can be grown by elemental doping (such as Si, Fe, Mg, C, etc.) or by growing composite materials or heterojunctions such as AlGaN, InGaN, and ScAlN to meet the performance requirements of specific MEMS transducers.

[0075] Anisotropic etching (such as ICP or RIE) is performed using photoresist, silicon oxide, or silicon nitride as masks. The etching penetrates the GaN-based functional layer, creating different patterns depending on the desired functional layer shape. For example, for cantilever beam-shaped functional layers, the functional layer can be etched into single or multiple lobes, with etching occurring in the central region of the device. All etching stops within the sacrificial layer, thus patterning the functional layer into a separated radial cantilever beam structure and exposing the underlying sacrificial layer. For ring-shaped functional layers, a small circle can be etched in the center of the functional layer, exposing the sacrificial layer within it. The duration of the electrochemical etching determines the width of the ring. For bridge-shaped functional layers, two closely spaced, equal-length rectangular strips can be etched onto the functional layer, exposing the sacrificial layer within each rectangle. The distance between the rectangles represents the width of the bridge.

[0076] The sample is placed in an electrolyte, with the exposed sacrificial layer as the anode, and an appropriate voltage is applied for electrochemical etching. By precisely controlling the voltage application time, the sacrificial layer in the patterned area is selectively and completely etched laterally, thereby releasing the patterned structure from the underlying support layer and forming a cavity in situ, while the unpatterned peripheral area remains connected to the support layer through the sacrificial layer.

[0077] When all electrodes are on the upper surface of the functional layer, patterned electrodes are fabricated by wiring according to the specific transducer requirements and the shape of the functional layer. When an electrode is required on the lower surface of the functional layer, a window needs to be etched in the peripheral area of ​​the device to expose the sacrificial layer inside the window. Then, patterned metal is deposited in the window to form a bottom electrode that contacts the sacrificial layer and thus makes electrical contact with the lower surface of the functional layer.

[0078] The preferred embodiments of the present application have been described above with reference to the accompanying drawings, but this does not limit the scope of the claims of the present application. Any modifications, equivalent substitutions, and improvements made by those skilled in the art without departing from the scope and substance of the embodiments of the present application shall be within the scope of the claims of the present application.

Claims

1. A method of fabricating a MEMS transducer based on electrochemical corrosion, characterized in that, The method includes the following steps: A buffer layer, a sacrificial layer, and a functional layer are sequentially epitaxially grown on a substrate to form an epitaxial wafer structure. The functional layer is etched to form an exposed area of ​​the sacrificial layer within the functional layer; The exposed area of ​​the epitaxial wafer structure is placed in an electrolyte, and the sacrificial layer is electrochemically etched starting from the exposed area to form a cavity between the functional layer and the buffer layer. Metal is deposited on the surface of the functional layer to form electrodes, thus obtaining a MEMS transducer.

2. The method of claim 1, wherein the MEMS transducer is fabricated using electrochemical etching. The method of sequentially epitaxially growing a sacrificial layer, a buffer layer, and a functional layer on a substrate to form an epitaxial wafer structure includes: A nucleation layer, a current spreading layer, and a barrier layer are epitaxially grown sequentially on the upper surface of the substrate to form a buffer layer on the upper surface of the substrate. A sacrificial layer is epitaxially grown on the side of the buffer layer away from the substrate; A functional layer is epitaxially grown on the side of the sacrificial layer away from the buffer layer.

3. The method of claim 1, wherein the MEMS transducer is fabricated by electrochemical etching. The etching of the functional layer to form the exposed area of ​​the sacrificial layer in the functional layer includes: Using the side of the functional layer furthest from the sacrificial layer as the etching start point and the sacrificial layer as the etching end point, a dry etching process is used to etch the functional layer to form an exposed area of ​​the sacrificial layer in the functional layer.

4. The method for fabricating a MEMS transducer based on electrochemical corrosion according to claim 1, characterized in that, The step of immersing the exposed area of ​​the epitaxial wafer structure in an electrolyte and electrochemically etching the sacrificial layer starting from the exposed area to form a cavity between the functional layer and the buffer layer includes: The contact electrode is generated, and the exposed area is completely immersed in the electrolyte; The contact electrode is used as the anode to form an electrical circuit with the electrolyte and the power source; Obtain cavity removal parameters, including voltage parameters and time parameters; Based on the voltage and time parameters, the electrolyte is controlled to electrochemically corrode the sacrificial layer starting from the exposed area to form a cavity between the functional layer and the buffer layer.

5. The method of claim 4, wherein the MEMS transducer is fabricated by electrochemical etching. The step of using the contact electrode as the anode to form an electrical circuit with the electrolyte and the power source includes: ​ A hole is made on the surface of the functional layer to the sacrificial layer, and metal is injected to form the contact electrode; The contact electrode does not come into contact with the electrolyte.

6. The method of claim 1, wherein the MEMS transducer is fabricated using electrochemical etching. The silicon doping concentration of the sacrificial layer is higher than that of the buffer layer and the functional layer.

7. An electrochemical corrosion based MEMS transducer, characterized in that, It is manufactured by the MEMS transducer fabrication method based on electrochemical corrosion as described in any one of claims 1 to 6.

8. The electrochemical corrosion-based MEMS transducer of claim 7, wherein, The concentration interval of the N-type doping of the sacrificial layer is 1.0x10 19 ~2.0x10 19 cm -3 .

9. The electrochemical corrosion-based MEMS transducer of claim 7, wherein, The height of the cavity is the same as the thickness of the sacrificial layer.

10. The electrochemical corrosion-based MEMS transducer of claim 7, wherein, The material of the functional layer is gallium nitride or gallium nitride-based composite material.

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