A self-supporting piezoelectric nanomembrane micro-actuator and a preparation method thereof

Abstract

This application provides a self-supporting piezoelectric nanofilm microactuator and its fabrication method. The fabrication method includes: forming an insulating layer on the front side of a substrate; forming a bottom electrode; forming a piezoelectric thin film with a submicron thickness; thinning the back side of the substrate; forming a top electrode with a nanometer thickness on the piezoelectric thin film; sequentially patterning the piezoelectric thin film, bottom electrode, and insulating layer to define the device shape; coating a continuous polymer protective layer on the front side of the device; forming a mask on the back side of the device to define a release window; temporarily bonding the front side of the device wafer to a carrier wafer; etching the back side according to the release window, using the insulating layer as the etching termination layer to form a deep cavity on the back side and release the support under the cantilever beam; debonding and cleaning the front side; removing the sacrificial layer, releasing the device, and obtaining the self-supporting piezoelectric nanofilm microactuator. This application can achieve low-voltage compatibility between the device and on-chip electronics and achieve high-yield manufacturing of submicron piezoelectric thin film microactuators.

Description

Technical Field

[0001] This application relates to the fields of microelectromechanical systems (MEMS) and micro / nano manufacturing, specifically to a self-supporting piezoelectric nanofilm microactuator and its fabrication method. Background Technology

[0002] Thin-film piezoelectric actuators are of great value in applications such as microrobot joints, folding mechanisms, micro-grippers, and micro-crawling robots due to their fast response, high energy density, and low static power consumption. However, traditional large-stroke solutions often rely on thick-body piezoelectric materials or high-voltage drives (tens to hundreds of volts), which are not conducive to low-voltage integration with on-chip electronic systems.

[0003] To reduce the driving voltage, the thickness of the piezoelectric layer can be reduced to the submicron level. However, sol-gel piezoelectric films have a critical thickness problem for residual stress-induced cracking on Pt / Ti / Si stacks. Submicron films are more prone to cracking, delamination, or contamination during crystallization, patterning, and release processes, leading to a decrease in yield.

[0004] When releasing self-supporting ultrathin structures, common silicon removal methods include: (1) vapor phase XeF2 isotropic etching: high silicon selectivity and no liquid capillary force, but its lateral under-etching is difficult to obtain a deep cavity with controllable boundaries in thick silicon (>200 µm) substrates, and often requires additional openings or complex channel designs; (2) back side Bosch deep reactive ion etching (DRIE): strong anisotropy, suitable for high aspect ratio deep cavities, and can use SiO2 as an etching termination layer.

[0005] However, back-side DRIE release is typically accompanied by prolonged etching and wafer thinning, requiring temporary wafer bonding to provide mechanical support. During this process, the front side of the device may be contaminated by bonding media, damaged by mechanical handling, and contaminants and particle deposits caused by plasma or gas flow. Therefore, there is an urgent need for a front-side protection strategy that is compatible with wafer thinning, temporary wafer bonding, and prolonged back-side DRIE, in order to achieve high yield and scalable manufacturing of submicron piezoelectric thin-film microactuators. Summary of the Invention

[0006] In view of the deficiencies in the prior art, the purpose of this application is to provide a self-supporting piezoelectric nanofilm microactuator and its preparation method.

[0007] According to a first aspect of this application, a method for fabricating a self-supporting piezoelectric nanofilm microactuator is provided, comprising: An insulating layer is formed on the front side of the substrate; A bottom electrode is formed above the insulating layer; A piezoelectric thin film is deposited on top of the bottom electrode and then crystallized to obtain a piezoelectric thin film with a thickness on the submicron scale; Thinning treatment is performed on the back side of the substrate; A top electrode with a thickness on the nanometer scale is formed on the piezoelectric film, and the piezoelectric film, bottom electrode and insulating layer are patterned. A continuous polymer protective layer is applied to the front side of the device after the front pattern is completed. A mask is formed on the back of the device to define the release window; Temporarily bond the front side of the device wafer coated with the protective layer to the carrier wafer; The back side is etched according to the release window, with the insulating layer as the etching termination layer, forming a deep cavity on the back side and releasing the support under the cantilever beam; The device wafer is debonded from the carrier wafer and then cleaned on the front side. The protective layer, which serves as a sacrificial layer, is removed to release the device, resulting in a self-supporting piezoelectric nanofilm microactuator.

[0008] Optionally, an insulating layer is formed on the front side of the substrate, wherein the insulating layer is a SiO2 layer formed by thermal oxidation, with a thickness of 50 nm to 1 μm.

[0009] Optionally, a bottom electrode is formed above the insulating layer, wherein the Pt / Ti electrode is prepared by physical vapor deposition and has a thickness of 50~500 nm.

[0010] Optionally, the piezoelectric material is deposited and crystallized on the bottom electrode to obtain a piezoelectric thin film with a thickness of submicron, wherein the piezoelectric material forms a piezoelectric deformation layer with a thickness of 50nm~1μm.

[0011] Optionally, the thinning process on the back side of the substrate includes reducing the overall thickness of the substrate to 50~300 µm.

[0012] Optionally, forming a top electrode with a thickness on the piezoelectric film in the nanometer range includes: forming the top electrode sequentially by photolithography, metal deposition and lift-off, wherein the thickness of the top electrode is 5~100 nm.

[0013] Optionally, the patterning of the piezoelectric thin film, bottom electrode, and insulating layer includes: The piezoelectric thin film is wet-etched using a first mask to form the desired actuator profile; The bottom electrode is wet-etched using a second mask to align it with the actuator outline; A third mask is used to perform dry etching on the exposed insulating layer to complete the shape definition and achieve trace isolation.

[0014] Optionally, a continuous polymer protective layer is coated on the front side of the device after the front pattern is completed, wherein: the material of the protective layer is poly(dimethylglutarimide); and the thickness of the protective layer is 0.1~10 µm.

[0015] Optionally, the removal of the protective layer, which serves as a sacrificial layer, to release the device includes: The device is secured in an anti-solvent fixture, which is used to suppress the movement of the device in the solvent and reduce fluid shear. The sacrificial layer is removed using a solvent, wherein the solvent is delivered via a peristaltic pump; After removing the sacrificial layer, a gradual solvent replacement was performed. After drying, a self-supporting piezoelectric nanofilm microactuator was obtained.

[0016] Optionally, the drying process includes: slow drying in an isopropanol enrichment / saturation environment or supercritical drying.

[0017] According to a second aspect of this application, a self-supporting piezoelectric nanofilm microactuator is provided, which is prepared using the method described in the first aspect.

[0018] The method for fabricating self-supporting piezoelectric nanofilm microactuators provided in this application employs an ultrathin top electrode and a submicron piezoelectric thin film, which is beneficial for obtaining a large curvature under low driving voltage and achieving low-voltage compatibility with on-chip electronics. The combined process formed by the steps of front continuous protective layer, temporary substrate bonding, and back DRIE through-through can effectively isolate contamination and avoid mechanical damage during long-term DRIE, improve the integrity and process compatibility of the submicron thin film structure, and achieve high yield and scalable manufacturing of submicron piezoelectric thin film microactuators.

[0019] Other technical effects resulting from the additional features will be further illustrated in the corresponding embodiments. Attached Figure Description

[0020] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a flowchart illustrating a method for fabricating a self-supporting piezoelectric nanofilm microactuator according to an exemplary embodiment; Figure 2 This is a schematic diagram illustrating a key release process according to an exemplary embodiment; Figure 3 This is a schematic diagram illustrating a PTFE clamp and a PEEK screw according to an exemplary embodiment; Figure 4 This is a schematic diagram of the overall structure of a microactuator according to an exemplary embodiment; Figure 5 This is a schematic cross-sectional view of an Au / Ti-piezoelectric-Pt / Ti-SiO2 multilayer stack according to an exemplary embodiment; Figure 6 The following is a representative performance curve shown according to an exemplary embodiment, wherein (a) is the curvature change Δκ-voltage relationship, and (b) is the curvature modulation and applied voltage change over time. Detailed Implementation

[0021] The present application will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application, and these all fall within the protection scope of the present application. Parts not described in detail in the following embodiments can be implemented using existing technology.

[0022] In the description of the embodiments of this application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0023] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature.

[0024] In the description of the embodiments in this application, "multiple" means two or more, unless otherwise explicitly specified. In this application, unless otherwise explicitly specified and limited, the terms "installed," "connected," "linked," "fixed," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] The terms "comprising" and "having," and any variations thereof, in the embodiments of this application are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such processes, methods, products, or devices.

[0026] In the fabrication of submicron thick piezoelectric thin film microactuators, there is a problem of front-side contamination / damage caused by prolonged back-side DRIE and temporary substrate bonding, which affects the manufacturing yield of the device. To address this issue, this application provides a method for fabricating a self-supporting piezoelectric nanofilm microactuator to solve the aforementioned problems.

[0027] Reference Figure 1 and Figure 2 As shown in one embodiment of this application, a method for fabricating a self-supporting piezoelectric nanofilm microactuator is provided, the method comprising the following steps: S1. Formation of substrate insulating layer: An insulating layer is formed on the front side of the substrate; S2, Bottom electrode deposition: such as Figure 1 In (a), a bottom electrode is formed above the insulating layer; S3, Piezoelectric thin film deposition and crystallization: such as Figure 1 In (b), a piezoelectric material is deposited on top of the bottom electrode and crystallized to obtain a piezoelectric thin film with a thickness of submicron. The piezoelectric material includes lead zirconate titanate (PZT) and the like. S4. Substrate thinning: such as Figure 1 In section (c), the back side of the substrate is thinned. S5. Top electrode patterning, piezoelectric and bottom electrode patterning: such as Figure 1 In (d), (e), and (f), a top electrode with a thickness on the nanometer scale is formed on the piezoelectric film, and the piezoelectric film, bottom electrode, and exposed insulating layer are patterned. S6. Formation of the front protective layer / sacrificial layer: such as Figure 1 In the middle (h), a continuous polymer protective layer is coated on the front side of the device after the front pattern is completed; S7. Backside DRIE Window Definition: Forms a mask on the backside of the device and defines the release window; S8. Temporary carrier bonding: Temporarily bonding the front side of the device wafer coated with the protective layer to the carrier wafer; S9, Backside DRIE through etching: The backside is etched according to the release window, with the insulating layer as the etching termination layer, forming a deep cavity on the backside and releasing the support under the cantilever beam; S10, Debonding and Front Cleaning: (e.g.) Figure 1 In step (i), the device wafer is debonded from the carrier wafer and then cleaned on the front side; S11, Sacrificial layer removal and final release: The protective layer, which serves as the sacrificial layer, is removed to release the device and obtain a self-supporting piezoelectric nanofilm microactuator.

[0028] It should be noted that the cantilever beam / cantilever structure refers to the self-supporting thin film stacked beam structure after release, such as its stack from top to bottom including top electrode layer Au / Ti-PZT-Pt / Ti (bottom electrode layer)-SiO2.

[0029] The self-supporting piezoelectric thin-film microactuator for microrobots / micromanipulation systems provided in this application employs an ultra-thin top electrode and a submicron piezoelectric thin film in its wafer-level fabrication and release processes. This facilitates achieving a large curvature at low driving voltages and enabling low-voltage compatibility with on-chip electronics. The combined process, consisting of a continuous protective layer on the front side, temporary substrate bonding, and DRIE penetration on the back side, effectively isolates contamination and avoids mechanical damage during long-term DRIE. This process suppresses contamination / damage to the front structure and ensures compatibility with the protection and release of temporary substrate bonding and long-term backside DRIE, improving the integrity and process compatibility of the submicron thin film structure. This results in high yield and scalable manufacturing of the submicron piezoelectric thin-film microactuator.

[0030] In some specific embodiments of this application, S1, an insulating layer is formed on the front side of the substrate, wherein: the insulating layer is a SiO2 layer formed by thermal oxidation, with a thickness of 50 nm to 1 μm, preferably 50–300 nm.

[0031] For example, the substrate is a silicon substrate, the insulating layer also serves as the etching stop layer in step S9, and the SiO2 layer has a thickness of 100 nm.

[0032] By setting an insulating layer, electrical insulation and surface isolation are provided, and it also serves as a dielectric etch stop for deep silicon etching on the back side. In the DRIE process, the silicon / silicon dioxide interface is often used as an etch stop layer. The above thickness range can take into account both insulation reliability and process window.

[0033] In some specific embodiments of this application, S2, a bottom electrode is formed above the insulating layer, wherein: the Pt / Ti electrode is prepared by a vapor phase physical deposition method such as magnetron sputtering, and the thickness of the bottom electrode is 50~500 nm.

[0034] Specifically, a Pt / Ti bottom electrode stack is sputtered and deposited on the SiO2 layer, where Ti serves as an adhesion layer to enhance adhesion and reduce the risk of delamination caused by subsequent high-temperature crystallization.

[0035] By using a Pt / Ti bottom electrode, Ti as an adhesion layer can significantly improve the adhesion and high-temperature stability between Pt and the substrate / oxide layer, reduce the risk of electrode dewetting / delamination during the high-temperature crystallization of subsequent PZT and other piezoelectric thin films, thereby improving stack reliability and yield.

[0036] In step S3, the piezoelectric precursor is deposited by multiple sol-gel spin coatings. After each spin coating, intermediate pyrolysis is performed to remove organic matter and densify the material. Finally, high-temperature crystallization is carried out to obtain a perovskite phase piezoelectric film. Residual stress and cracks are controlled by formula and heat treatment curves to obtain a submicron thick piezoelectric film with a thickness of 50 nm to 1 μm, preferably 0.5–0.8 µm.

[0037] Specifically, the precursor sol is PZT (PbZr). 0.52 Ti 0.48 O3) sol, in which the total metal molar concentration of Zr+Ti is 0.2–0.5 mol / L (typically 0.3 mol / L), and a certain excess of Pb can be set; after filtration using a 0.2 µm PTFE filter membrane, it is used for spin coating.

[0038] Spin coating parameters: Spin coating speed 2000–4000 rpm, time 20–60 s. After each spin coating, pre-baking and intermediate pyrolysis are performed. The pre-baking temperature can be 100–200 °C (preferably 120–150 °C, time 1–5 min); the intermediate pyrolysis temperature can be 250–450 °C, time 0.25–10 min (preferably 300–400 °C, such as 350 °C × 3 min). This decomposes organic matter layer by layer and reduces the abrupt shrinkage of the monolayer, thereby reducing the risk of blistering / porosity and cracking.

[0039] After multiple spin coatings and pyrolysis processes, a final high-temperature crystallization / annealing is performed to obtain the perovskite phase, improving grain growth and orientation stability, thereby enhancing dielectric / ferroelectric / piezoelectric output. The crystallization temperature can be 550–750 °C (preferably 600–700 °C), for example, by rapid thermal annealing (RTA) at 700 °C (1–10 min, in air or oxygen atmosphere).

[0040] It should be noted that the submicron thickness of PZT films can be controlled by the number of layers and the sol concentration through multiple spin-coating / heat treatments of sol-gel, which can be achieved using existing technologies.

[0041] Step S3 includes multiple sol-gel spin coatings, intermediate pyrolysis, and final crystallization. Intermediate pyrolysis is used to remove organic matter and densify layer by layer, and final high-temperature crystallization is used to obtain the perovskite phase. By controlling the sol concentration, number of layers, and heat treatment curves, the crystallization quality can be improved while suppressing crack / stress accumulation, thereby improving the consistency and film formation yield of submicron thick films.

[0042] In some specific embodiments of this application, S4, thinning the back side of the substrate includes: reducing the overall thickness of the substrate to 50-300 µm, preferably to 100-300 µm.

[0043] For example, the back side of the silicon substrate can be back-grinded / polished or subjected to other thinning processes to reduce the silicon thickness to 250 µm, thereby reducing subsequent back-side DRIE time and thermal load. The aforementioned thinned thickness is the remaining overall thickness of the silicon substrate after back-grinding / polishing.

[0044] By thinning the back DRIE, the etching depth is significantly reduced, which directly reduces etching time and cumulative heat load, thereby reducing the risk of process drift and wafer warpage / failure.

[0045] In some specific embodiments of this application, S5, forming a top electrode with a thickness of nanometers on a piezoelectric thin film includes: forming a top electrode on a piezoelectric thin film sequentially by photolithography, metal deposition and lift-off, with an electrode thickness of 5~100 nm.

[0046] For example, the thickness of the top electrode is about 20-30 nm, such as the thickness of the top electrode Au / Ti being 25 / 2 nm.

[0047] In some specific embodiments of this application, step S5 involves patterning the piezoelectric film, the bottom electrode, and the insulating layer, including: S501. Wet etching of the piezoelectric thin film is performed using a first mask, for example, using HBF4 solution at room temperature, to form the desired actuator profile. S502. Use a second mask to perform wet etching on the bottom electrode, for example, using hot aqua regia at about 60°C, and align it with the actuator outline. S503. A third mask is used to perform dry etching on the exposed insulating layer (such as the SiO2 layer). The dry etching can be performed using CF4 / Ar RIE to complete the shape definition and achieve trace isolation.

[0048] Step S5 uses a top electrode (such as Au / Ti 25 / 2 nm) combined with a lift-off process. The thin metal electrode can minimize the added mass / stiffness of the cantilever beam while ensuring conductivity and lead-out reliability, thereby improving driving efficiency and reducing driving voltage requirements.

[0049] In the S501–S503 patterning process selection, PZT wet etching using the HBF4 system can achieve a feasible wet patterning route; the Pt bottom electrode can be patterned using hot aqua regia wet etching at around 60°C, and with thick resist / hard baking, good resolution and controllability can be obtained; since CF4 has clear etching rate data for SiO2 in the existing technology, which is convenient for process calibration, the SiO2 insulating layer can be dry etched and the wiring isolated using CF4 / Ar RIE.

[0050] To further improve device connectivity reliability, a pad enhancement step is added after patterning the piezoelectric film and bottom electrode. Specifically, such as... Figure 1 In step (g), a thicker metal is deposited in the electrode lead-out region to form a bonding pad. The deposited metal can be Au, and the thickness can be 100–500 nm. For example, Au 300 nm is deposited to form a bonding pad.

[0051] In some specific embodiments of this application, S6, a continuous polymer protective layer is coated on the front side of the device after the front pattern is completed, wherein: the material of the protective layer is poly(dimethylglutarimide) (PMGI); the thickness of the protective layer is 0.1~10 µm.

[0052] Specifically, after completing the front-side patterning, a continuous polymer protective layer is coated on the front side of the device, which can be poly(dimethylglutarimide) or an equivalent polymer. The protective layer also serves as a sacrificial layer for subsequent removal, with a thickness of, for example, 0.1–10 µm, preferably 1–5 µm.

[0053] Specifically, an equivalent polymer refers to a polymer material that can achieve the same function and processing effect, and is equivalent in at least the following aspects: (1) Film formation and coating: A continuous, dense, low-pinhole protective layer can be formed by spin coating, and the thickness can be controlled within the range of 0.5–10 µm (preferably 1–5 µm); (2) Process tolerance: It has sufficient thermal stability / mechanical integrity during subsequent temporary bonding, back side etching / cleaning, etc., and is not easy to crack, blister or contaminate the device surface; (3) Removability (sacrificial layer properties): It can be removed by conventional desizing / stripping processes without damaging the PZT / electrode / insulating layer, and with minimal residue; for example, it can be removed by NMP-based desizing agents (such as Remover PG), or, if necessary, by oxygen plasma desizing to achieve residue removal.

[0054] For example, other polymer systems that can be used as sacrificial / protective layers and can be released by solvent or plasma removal can be other PMGI / LOR series materials, PMMA, photoresist, polyimide, etc. (depending on the subsequent process window and removal method).

[0055] like Figure 2 As shown in (a), in step S7, a thick photoresist, such as AZ4620 of about 5–15 µm, is coated and patterned on the back side to form a DRIE mask and define the release window.

[0056] In step S8, the device wafer coated with the protective layer is temporarily bonded to the carrier wafer to support long-term DRIE. The bonding medium can be fluorosilicone oil, temporary adhesive, wax, or other vacuum-compatible medium. Preferably, a medium that can be gently removed in the post-processing stage without contaminating the front side of the device is used.

[0057] like Figure 2 As shown in (b), in step S9, Bosch deep reactive ion etching is used to etch silicon from the back side until it penetrates the thinned silicon layer, and the front insulating layer (such as the SiO2 layer) is used as the etching termination layer to form a deep cavity on the back side and release the silicon support under the cantilever beam.

[0058] In step S10, after DRIE, the device wafer is debonded from the carrier; low-power oxygen plasma or solvent cleaning can be used to gently clean the residual bonding medium on the front side. During this process, a continuous polymer protective layer is located on the device surface to reduce direct damage to the piezoelectric film and electrodes by plasma / solvent.

[0059] To ensure reliable removal of the protective / sacrificial layer after DRIE penetration without damaging the ultrathin film, references are made to some specific embodiments of this application. Figure 2 In steps (c) and (d), S11, the protective layer serving as a sacrificial layer is removed to release the device, including the following steps: S1101. Fix the device in an anti-solvent fixture, which is used to suppress the movement of the device in the solvent and reduce fluid shear. S1102. The sacrificial layer is removed using a solvent, wherein the solvent is delivered by a peristaltic pump; S1103. After removing the sacrificial layer, perform stepwise solvent replacement; S1104, after drying, yields a self-supporting piezoelectric nanofilm microactuator.

[0060] Specifically, such as Figure 3As shown, the solvent-resistant fixture uses PTFE clamps and PEEK fasteners. The PTFE clamps consist of PTFE plates, and the PEEK fasteners are PEEK screws. The PTFE clamp body serves as the main load-bearing / limiting structure in contact with the solvent. Utilizing the chemical inertness and solvent resistance of PTFE, it reduces the risk of material swelling / precipitation contamination under solvent immersion and provides large-area support and limitation for the wafer / device, thereby suppressing device swaying and impact in the solvent. PEEK fasteners (such as screws) provide stable mechanical clamping force and structural rigidity (PTFE is relatively soft and not suitable as threaded load-bearing components), ensuring controllable clamping force and preventing loosening. Simultaneously, PEEK has good compatibility with NMP (N-methylpyrrolidone) at room temperature, making it suitable as a fastener material. The solvent used is NMP (N-methylpyrrolidone) solution, which is delivered at a low flow rate via a peristaltic pump, preferably about 10–30 mL / min (the actual flow rate can be adjusted within the above range according to the device size and release integrity) to reduce the impact of liquid flow shear and pulsating impact on the cantilever / ultra-thin film structure and achieve gentle and controllable peeling.

[0061] Stepwise solvent replacement can be performed using NMP → IPA to reduce surface tension and minimize sudden surface forces. The specific process of stepwise solvent replacement is as follows: After the structure release / washing is completed, the sample is kept immersed in NMP. IPA is slowly added dropwise at 10–30 mL / min using a peristaltic pump while an equal volume of the mixture is removed from the upper layer, so that the volume fraction of IPA in the system gradually increases until it is completely replaced by IPA.

[0062] For example, the solvent bath can be any of the following: NMP (fresh), NMP:IPA = 3:1 (volume ratio), NMP:IPA = 1:1, NMP:IPA = 1:3, 100% IPA (which can be replaced with fresh IPA once more).

[0063] Then proceed to drying: IPA vapor / Marangoni drying can be used, which utilizes low surface tension solvents to replace and remove residual liquid, or critical point drying can be used to avoid surface tension / adhesion caused by liquid-gas phase transition.

[0064] The PZT layer in the device is a brittle functional layer, more sensitive to shear and impact, but failure typically manifests as cracking, warping, or fracture of the entire cantilever stack. A post-processing strategy combining solvent-resistant clamping, low-flow peristaltic pump removal of the sacrificial layer, and gradual solvent replacement allows for controlled removal and cleaning of the protective / sacrificial layer after DRIE penetration. This prevents the ultrathin structure from cracking or being "pinned" by residues during solvent rinsing, significantly reducing shear impact and residual pinning during liquid release. No large-area cracking / fracture / collapse was observed in the cantilever beam structure after release, contributing to improved release success rate and integrity. The ultrathin structure refers to the entire effective working structure of the cantilever beam after release (i.e., the thin-film stacked cantilever composed of the top electrode / piezoelectric layer PZT / bottom electrode / insulating layer).

[0065] In order to suppress capillary adhesion that can easily lead to collapse or breakage of ultrathin structures during wet desizing, solvent rinsing and drying, and to further improve the device manufacturing yield, in some specific embodiments of this application, the drying process in step S1104 includes: slow drying in an isopropanol (IPA) enriched / saturated environment or supercritical drying.

[0066] Specifically, slow drying in an IPA enrichment / saturation environment within a semi-covered container can reduce evaporation-induced disturbances and suppress capillary adhesion.

[0067] By slow drying in an IPA enrichment / saturation environment to reduce capillary forces and evaporation disturbances, adhesion and collapse caused by capillary forces can be effectively suppressed in the final drying stage after release, achieving high yield and low contamination release of submicron thick piezoelectric thin film microactuators, and improving release yield and consistency.

[0068] It should be noted that the parameters in the above steps of this application are mainly determined based on (i) the reliability of the back etch termination layer, (ii) the adhesion of the electrode / film and its resistance to high temperature failure, (iii) the density / low cracking of the PZT submicron thick film, (iv) the time and thermal load of the back DRIE, and (v) the controllability and yield of the patterning.

[0069] Another embodiment of this application provides a self-supporting piezoelectric nanofilm microactuator, which is prepared using the method described in any of the above embodiments. Figure 4 and Figure 5As shown, this piezoelectric microactuator has a cantilever beam single-layer composite structure, comprising a top electrode layer, a piezoelectric layer, a bottom electrode layer, and an insulating layer (passive layer) stacked sequentially from top to bottom. A cantilever beam single-layer composite structure typically refers to an asymmetric composite beam consisting of an active layer (piezoelectric layer) and a passive layer (non-piezoelectric elastic layer / base layer); the electrodes are conductive functional layers and are not usually considered the main components in the definition of "active / passive layer". In this device, the active layer is a PZT piezoelectric layer, and the passive layer is a SiO2 insulating layer, together forming a bending-driven cantilever.

[0070] Specifically, the top electrode layer uses a combination of Au / Ti or other conductive metals / adhesive layers, with a thickness of 10–100 nm. The piezoelectric layer is a piezoelectric thin film prepared by sol-gel or sputtering, with a thickness of 0.3–1.0 µm; the composition can be PbZr. x Ti (1-x) O3 (e.g., x≈0.52). The bottom electrode layer is made of Pt / Ti or other high-temperature resistant metal / adhesive layer combination, with a thickness of 50–300 nm. The insulating layer is made of SiO2 or other dielectric layer, with a thickness of 50–500 nm, for electrical isolation and as an etching stop layer for the back DRIE.

[0071] For example, the top electrode layer has an Au thickness of 20–30 nm and a Ti thickness of 2–10 nm (if the Ti layer is too thin, a film cannot be formed). The piezoelectric layer thickness is 0.1–0.8 µm. The bottom electrode layer has a Pt thickness of 80–150 nm and a Ti thickness of 10–50 nm. The insulating layer thickness is 100 nm.

[0072] The top electrode pattern is recessed relative to the edge of the piezoelectric film, with a recess size of 5–20 µm, such as 10 µm, to compensate for lateral under-etching during wet etching of the piezoelectric film and to avoid short circuits between the top and bottom electrodes.

[0073] In the cantilever beam single-layer composite structure, the beam length is 250–500 µm; the beam width is 60–100 µm (where the width of the top electrode pattern can be about 60 µm, and the beam width of PZT / bottom electrode / insulating layer can be about 80 µm, to ensure short-circuit margin after electrode inward shrinkage and wet etching lateral under-etching); the actuator shape is a rectangular cantilever beam, and multiple actuators can be arranged in a rectangular array.

[0074] The preferred features in the above embodiments can be used individually in any embodiment, or in any combination thereof, provided they do not conflict with each other. Furthermore, parts not described in detail in the embodiments can be implemented using existing technologies.

[0075] The following examples and comparative examples will be used to further illustrate this application in order to better understand the above-mentioned technical solutions. It should be understood that the following are only some examples and are not intended to limit this application.

[0076] Application Example 1: The fabrication of a self-supporting piezoelectric nanofilm microactuator includes the following steps: (1) Thermal oxidation is performed on a silicon wafer to form approximately 102 nm of SiO2; (2) Sputter deposition of Pt / Ti bottom electrode (100 nm / 20 nm); (3) Sol-gel spin-coating deposition of piezoelectric materials (PbZr) 0.52 Ti 0.48 O3), through multiple spin coatings and pyrolysis, finally crystallized to obtain a piezoelectric thin film of about 573 nm; Specifically, the precursor sol is PZT (PbZr). 0.52 Ti 0.48 O3) sol, wherein the total metal molar concentration of Zr+Ti is 0.3 mol / L, and Pb excess can be set; after filtration using a 0.2 µm PTFE filter membrane, it is used for spin coating; Substrate pretreatment: Degas / remove adsorbed water on a hot plate at 350 °C for 5 min before spin coating; Spin coating parameters: spin coating speed 3000 rpm, time 30 s; Heat treatment per layer (layer by layer): Pre-baking: 130 °C, 3 min. Intermediate pyrolysis: 350 °C, 3 min; Crystallization: RTA was performed at 700 °C for 5 min at a heating rate of 50 °C / s in an air / oxygen atmosphere.

[0077] (4) Back grinding / polishing thins the silicon to approximately 250 µm; (5) Photolithography + sputtering + lift-off to form Au / Ti top electrode (25 / 2 nm), with the electrode recessed by about 10 µm relative to the edge of the piezoelectric film; (6) HBF4 wet etching of piezoelectric thin film (room temperature, about 45 s); hot aqua regia wet etching of Pt / Ti (about 60°C, about 2 min); CF4 / Ar RIE etching of SiO2 to form the outline and isolate the wiring; (7) Sputter approximately 300 nm Au to form bonding pads.

[0078] The release process is as follows: (1) A continuous protective / sacrificial layer is formed by spin-coating PMGI on the front side; (2) Thick adhesive (approximately 10 µm of AZ4620) on the back defines the DRIE window; (3) Fluorosilicone oil is used to temporarily bond the device wafer to the carrier. (4) Bosch DRIE etches silicon from the back side until it penetrates through and uses SiO2 as a terminating layer; (5) Gently clean the residual bonding medium after debonding (e.g., low-power O2 plasma). (6) Fix the chip in a PTFE fixture and use a peristaltic pump (20 mL / min) to deliver NMP to remove PMGI; (7) Gradually replace NMP with IPA and slowly dry it in an IPA-saturated environment.

[0079] like Figure 6 As shown, on submicron (approximately 573 nm) thick PZT devices, a drive voltage below 10 V can achieve an order of magnitude of 10. 3 m -1 The curvature change demonstrates that the device maintains its actuability and structural integrity after undergoing "temporary substrate bonding + long-term backside DRIE + debonding / cleaning + sacrificial layer removal / drying", making it suitable for low-voltage microrobot actuation.

[0080] The foregoing has described some specific embodiments of this application. It should be understood that this application is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the substantive content of this application. The above-described preferred features can be used in any combination without conflict.

Claims

1. A method for fabricating a self-supporting piezoelectric nanofilm microactuator, characterized in that, include: An insulating layer is formed on the front side of the substrate; A bottom electrode is formed above the insulating layer; A piezoelectric material is deposited on top of the bottom electrode and crystallized to obtain a piezoelectric thin film with a thickness on the submicron scale; Thinning treatment is performed on the back side of the substrate; A top electrode with a thickness on the nanometer scale is formed on the piezoelectric film, and the piezoelectric film, the bottom electrode, and the insulating layer are patterned. A continuous polymer protective layer is applied to the front side of the device after the front pattern is completed. A mask is formed on the back of the device to define the release window; Temporarily bond the front side of the device wafer coated with the protective layer to the carrier wafer; The back side is etched according to the release window, with the insulating layer as the etching termination layer, forming a deep cavity on the back side and releasing the support under the cantilever beam; The device wafer is debonded from the carrier wafer and then cleaned on the front side. The protective layer, which serves as a sacrificial layer, is removed to release the device, resulting in a self-supporting piezoelectric nanofilm microactuator.

2. The method for preparing the self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, An insulating layer is formed on the front side of the substrate, wherein the insulating layer is a SiO2 layer formed by thermal oxidation, with a thickness of 50nm~1μm.

3. The method for fabricating a self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The bottom electrode is formed above the insulating layer, wherein the Pt / Ti electrode is prepared by physical vapor deposition and the thickness of the bottom electrode is 50~500 nm.

4. The method for preparing the self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The piezoelectric material is deposited on the bottom electrode and crystallized to obtain a piezoelectric thin film with a thickness of submicron, wherein the piezoelectric material forms a deformation layer and the thickness of the piezoelectric material is 50nm~1μm.

5. The method for fabricating a self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The thinning process on the back side of the substrate includes reducing the overall thickness of the substrate to 50~300 µm.

6. The method for fabricating a self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The process of forming a top electrode with a thickness on the piezoelectric film includes: forming the top electrode sequentially through photolithography, metal deposition, and lift-off, wherein the thickness of the top electrode is 5~100 nm.

7. The method for preparing a self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The patterning of the piezoelectric film, the bottom electrode, and the insulating layer includes: The piezoelectric thin film is wet-etched using a first mask to form the desired actuator profile; The bottom electrode is wet-etched using a second mask to align it with the actuator outline; A third mask is used to perform dry etching on the exposed insulating layer to complete the shape definition and achieve trace isolation.

8. The method for fabricating a self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The device front side is coated with a continuous polymer protective layer after the front pattern is completed, wherein: the material of the protective layer is poly(dimethylglutarimide); the thickness of the protective layer is 0.1~10 µm.

9. The method for preparing a self-supporting piezoelectric nanofilm microactuator according to claim 1, characterized in that, The removal of the protective layer, which serves as a sacrificial layer, to release the device includes: The device is secured in an anti-solvent fixture, which is used to suppress the movement of the device in the solvent and reduce fluid shear. The sacrificial layer is removed using a solvent, wherein the solvent is delivered via a peristaltic pump; After removing the sacrificial layer, a gradual solvent replacement was performed. After drying, a self-supporting piezoelectric nanofilm microactuator is obtained, wherein the drying process includes: slow drying in an isopropanol enriched / saturated environment or supercritical drying.

10. A self-supporting piezoelectric nanofilm microactuator, characterized in that, The self-supporting piezoelectric nanofilm microactuator was prepared using the preparation method described in any one of claims 1-9.

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