FBAR-based slip spectrum tactile sensor, sensor array and preparation method

Abstract

The invention relates to the technical field of touch, in particular to an FBAR-based slip spectrum touch sensor, a sensor array and a preparation method. The tactile sensor comprises a thin film bulk acoustic resonator, the thin film bulk acoustic resonator comprises a substrate, a Bragg reflector, a lower electrode, a piezoelectric layer and an upper electrode, and the substrate, the Bragg reflector, the lower electrode, the piezoelectric layer and the upper electrode are sequentially stacked from bottom to top; moreover, the upper electrode is provided with a microstructure far away from the piezoelectric layer or close to the piezoelectric layer, and the microstructure is used for converting slippage into shear load. According to the designed tactile sensor structure, high-signal-noise output of the slip signal can be achieved, accurate slip detection can be achieved through the output slip spectrum, and meanwhile the friction state and material texture fingerprint output can be quantized.

Description

Technical Field

[0001] This invention relates to the field of tactile technology, specifically to a slip spectrum tactile sensor, sensor array, and fabrication method based on FBAR. Background Technology

[0002] With the continuous development of wearable devices, wearable devices now possess flexible functions such as bending, folding, and stretching. These characteristics make flexible wearable devices highly adaptable, giving them great application potential in smart scenarios such as healthcare, sports, and daily life.

[0003] Existing tactile sensors mostly rely on structures such as resistors, capacitors, or piezoelectric films, which are susceptible to electromagnetic interference, difficult to wire over long distances, and lack reliability in humid / hot / strong electromagnetic environments. Slippage is one of the most critical but also the most difficult quantities to measure stably in tactile systems. Most force / tactile solutions are good at static normal forces, but struggle to capture the tribodynamic processes of adhesion, partial slippage, and full slippage in milliseconds. Therefore, they are prone to dropping and misjudgment when grasping wet, slippery, oily, dusty, or soft and brittle objects.

[0004] In the process of developing this invention, the inventors discovered that current FBAR / BAW devices possess advantages such as high Q, high stability, high frequency output, ease of digital counting, integration with CMOS, and ease of arraying. However, existing FBARs still have the following problems when used in the tactile field: shear disturbances generated by tangential friction / slip are difficult to effectively couple into the resonator; interface friction events have high randomness and poor repeatability; and there is a lack of structures and readout systems that can be extended to arrays and output slip spectra. Summary of the Invention

[0005] One of the objectives of this invention is to provide a slip spectrum tactile sensor and pressure sensing method based on FBAR, in order to solve the shortcomings of existing thin-film bulk acoustic resonator sensor technology, such as inaccurate slip detection and the inability to form a slip spectrum array.

[0006] To solve the above-mentioned technical problems, the embodiments of the present invention are implemented as follows: In a first aspect, a FBAR-based slip spectrum tactile sensor is provided, the tactile sensor including a thin-film bulk acoustic resonator, wherein the thin-film bulk acoustic resonator includes: a substrate, a Bragg mirror, a lower electrode, a piezoelectric layer and an upper electrode, the substrate, the Bragg mirror, the lower electrode, the piezoelectric layer and the upper electrode are stacked sequentially from bottom to top; Furthermore, a microstructure is provided on the upper electrode away from or near the piezoelectric layer. The microstructure is used to convert slip into shear load, thereby causing the thin-film bulk acoustic resonator to vibrate mechanically and convert the mechanical vibration into an electrical signal. The electrical signal includes the resonant frequency, quality factor, or phase noise dynamic change signal.

[0007] The second aspect also discloses a sensor array comprising at least two FBAR-based tactile sensors as described in any one of the first aspects above, wherein the sensor array is composed of tactile sensors.

[0008] The third aspect also discloses a method for acquiring a slip spectrum using the sensor array described in the second aspect, characterized in that... Acquire dynamic electrical signals that change dynamically from the tactile sensor, including dynamic changes in resonant frequency, quality factor, or phase noise. The dynamically changing electrical signal is preprocessed, including temperature compensation and detrending processing. The detection and acquisition of the slip event window is used to determine the window sequence, wherein the slip event window is obtained by detecting indicators such as short-time energy, spectral entropy or phase noise rise to obtain the slip start time or end time; The time-frequency analysis is performed on the window sequence to obtain the slip spectrum. The time-frequency analysis is to perform STFT or wavelet packet decomposition on the slip window to obtain the slip spectrum. The peak position, bandwidth, energy distribution, spectral centroid, or 1 / f noise slope change are extracted and output based on the slip spectrum to determine the slip intensity, direction, or material texture fingerprint.

[0009] The fourth aspect also discloses a method for fabricating a sensor, used to fabricate the FBAR-based slip spectrum tactile sensor described in the first aspect above, the steps of which include: A stack of mirrors is grown on a substrate using a deposition process. The stack of mirrors is made of two materials with similar acoustic impedance and presents a layer structure with alternating high and low acoustic impedance from bottom to top. A metal layer is fabricated on the mirror stack by sputtering, and a pixel electrode pattern is etched on the metal layer by photolithography to obtain the lower electrode. A piezoelectric thin film is obtained on the upper part of the lower electrode by deposition process, and the stress and crystal orientation of the piezoelectric thin film are controlled to obtain a piezoelectric layer. A metal layer is fabricated on the piezoelectric layer by sputtering, and a pixel electrode pattern is etched on the metal layer by photolithography to obtain the upper electrode. Microstructures are fabricated on the surface of the upper electrode; A tactile sensor is obtained by filling or coating a microstructure to form a polymer layer on the microstructure.

[0010] The beneficial effects of the above-described technical solutions provided in the embodiments of the present invention include at least the following: This invention discloses a slip spectrum tactile sensor based on FBAR. A microstructure is positioned at the upper electrode corresponding to a thin-film bulk acoustic resonator (FBAR), and a polymer layer is deposited on the surface of the microstructure to form a stable friction coupling interface and a stress-shaping layer. This design allows the microstructure at the upper electrode to convert slip into mechanical vibration, efficiently coupling the shear friction / slip micro-vibrations of the contact interface into detectable mechanical vibrations by the FBAR. The microstructure couples the normal load generated by slip to a detectable mode; the FBAR converts the mechanical vibration into an electrical signal, and finally, slip detection is achieved by outputting a slip spectrum through the output electrical signal.

[0011] The tactile sensor structure designed in this invention can achieve high signal-to-noise output of slip signals. The output slip spectrum can not only achieve accurate slip detection, but also quantify the friction state and material texture fingerprint output.

[0012] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0013] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0014] Figure 1 A schematic diagram of a slip spectrum tactile sensor based on FBAR, provided for the first embodiment of the present invention; Figure 2 A schematic diagram of a slip spectrum tactile sensor based on FBAR, provided as an embodiment of the present invention; Figure 3 A schematic diagram of a slip spectrum tactile sensor based on FBAR, provided as a third embodiment of the present invention; Figure 4 This is a graph showing the variation of frequency shift (Δf) and load (N) over time during the sliding process according to an embodiment of the present invention. Figure 5 This is a time-spectrum diagram of a slip event according to an embodiment of the present invention; Figure 6 This is a time-domain curve of the in-band energy in an embodiment of the present invention; Figure 7 This is a two-dimensional graph showing the response intensity of a slip event on the sensor pixel array according to an embodiment of the present invention; Figure 8 This is a three-dimensional graph showing the response intensity of a slip event on a sensor pixel array according to an embodiment of the present invention.

[0015] The image shows: 10. Substrate; 20. Bragg mirror; 30. Lower electrode; 40. Piezoelectric layer; 50. Upper electrode; 60. Microstructure; 70. Polymer layer. Detailed Implementation

[0016] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0017] In this application, the term "exemplary" is used to mean "serving as an example, illustration, or description." Any implementation described as "exemplary" in this application is not necessarily to be construed as being more preferred or advantageous than other implementations. The following description is provided to enable any person skilled in the art to implement and use this application. Details are set forth in the following description for illustrative purposes. It should be understood that those skilled in the art will recognize that this application can be implemented without using these specific details. In other instances, well-known structures and processes are not described in detail to avoid obscuring the description of this application with unnecessary detail. Therefore, this application is not intended to be limited to the embodiments shown, but rather to be consistent with the broadest scope of the principles and features disclosed in this application.

[0018] Before describing the embodiments of the present invention in detail, the design concept of the present invention will be summarized below.

[0019] This invention provides a slip spectrum tactile sensor based on FBAR, and the specific implementation is as follows. Figure 1 As shown, the core process of this invention includes: setting a microstructure at the position of the upper electrode corresponding to the thin-film bulk acoustic resonator, and then setting a polymer layer on the surface of the microstructure to form a stable friction coupling interface and stress shaping layer. Through this design embodiment, the microstructure on the upper electrode converts slip into mechanical vibration, thereby efficiently coupling the shear friction / slip micro-vibration of the contact interface into mechanical vibration detectable by the thin-film bulk acoustic resonator. The microstructure couples the normal load generated by slip to a detectable mode; the thin-film bulk acoustic resonator then converts the mechanical vibration into an electrical signal, and finally, slip detection is achieved by outputting a slip spectrum through the output electrical signal. The tactile sensor structure designed in this invention can achieve high signal-to-noise output of slip signals. The output slip spectrum not only enables accurate slip detection but also quantifies the friction state and material texture fingerprint output. Example 1:

[0020] Firstly, please refer to the appendix. Figure 1 As shown, a slip spectrum tactile sensor based on FBAR is disclosed. The tactile sensor is based on a thin-film bulk acoustic resonator. The thin-film bulk acoustic resonator includes a substrate 10, a Bragg mirror 20, a lower electrode 30, a piezoelectric layer 40, and an upper electrode 50. The substrate 10, the Bragg mirror 20, the lower electrode 30, the piezoelectric layer 40, and the upper electrode 50 are stacked sequentially from bottom to top. Furthermore, a microstructure 60 is provided on the upper electrode 50 away from or near the piezoelectric layer 40. The microstructure 60 is used to convert slip into shear load, thereby causing the thin-film bulk acoustic resonator to vibrate mechanically and convert the mechanical vibration into an electrical signal, which includes the resonant frequency, quality factor or phase noise dynamic change signal.

[0021] Understandably, using thin-film bulk acoustic resonators (FBARs) directly in tactile sensors still presents the following problems in slip detection: existing FBARs used in the tactile field also have the following problems: shear disturbances generated by tangential friction / slippage are difficult to effectively couple into the resonator; and the interface friction events have high randomness and poor repeatability.

[0022] The film bulk acoustic resonator (FBAR) is a micro-resonant device based on a piezoelectric thin film operating in bulk wave mode. It belongs to the category of bulk acoustic wave (BAW) filters and is primarily manufactured using silicon substrates combined with microelectromechanical systems (MEMS) technology and thin-film processes. Its core structure consists of a piezoelectric layer 40 and metal electrodes on both sides. The resonant frequency is determined by the sound velocity of the piezoelectric material and the film thickness. It is widely used in radio frequency communication, sensing, and oscillation fields. It mainly utilizes the inverse piezoelectric effect of the piezoelectric layer 40 to generate mechanical vibrations (bulk acoustic waves) in an extremely thin film and convert them into electrical signals. Common materials for the piezoelectric layer 40 include aluminum nitride, zinc oxide, or lithium niobate.

[0023] The substrate 10 serves as the main support structure for the entire sensor; in this embodiment, Si, glass, or sapphire can be used as the substrate 10. The Bragg reflector 20 plays a crucial role in the thin-film bulk acoustic resonator (TBAR) for sound wave reflection and energy confinement. The Bragg reflector 20 is a key acoustic component of the TBAR, its core function being to confine sound wave energy through periodic reflection, forming a highly efficient resonant cavity, reducing losses, and improving the Q value. This characteristic enables the TBAR to maintain high stability at GHz high frequencies, making it a core component for applications such as 5G / 6G RF filters and sensors.

[0024] The microstructure 60 is a microstructure located on the upper electrode 50, possessing a specific geometric morphology at the micrometer or millimeter scale. Specifically, it is a non-flat, specific micrometer-scale structure set on the outer or inner wall of the upper electrode 50. When minute slippage occurs on the surface, these microstructures 60 generate a stick-slip frictional vibration phenomenon, manifested as periodic alternating "stickiness" and "sliding" motions between contact surfaces, commonly seen in scenarios with low relative speeds or high system elasticity. When slippage occurs on the surface, the microstructure 60 can produce at least the following effects: 1. Friction enhancement effect, specifically by increasing the effective friction coefficient of the interface and the number of micro-contacts, enabling stable and repeatable stick-slip micro-events; 2. Stress shaping and conversion effect, the microstructure 60 converts tangential shear loads into axial tension or periodic perturbations that can be sensed by the thin-film bulk acoustic resonator, and improves the dynamic coupling bandwidth. The microstructure 60 enables interpretable and repeatable measurement of the slip spectrum, i.e., high signal-to-noise output of the slip signal.

[0025] In this embodiment, a thin-film bulk acoustic wave resonator (BAS) is constructed by sequentially arranging the substrate 10, the Bragg reflector 20, the lower electrode 30, the piezoelectric layer 40, and the upper electrode 50 from bottom to top. A microstructure 60 is disposed on the upper electrode 50 of the BAS, and a polymer layer 70 is disposed on the surface of the microstructure 60, thereby forming a stable friction coupling interface and a stress shaping layer. This structure design allows the microstructure 60 on the upper electrode 50 to convert slip into mechanical vibration, thus efficiently coupling the shear friction / slip micro-vibrations of the contact interface into detectable mechanical vibrations by the BAS. The microstructure 60 couples the normal load generated by slip to a detectable mode. The BAS converts the mechanical vibration into an electrical signal, and finally, slip detection is achieved by outputting a slip spectrum through the output electrical signal. Furthermore, the slip spectrum can not only detect whether slip has occurred but also quantify the friction state and material texture fingerprint, supporting robot-assisted dexterous grasping and quantitative palpation.

[0026] In one specific embodiment, sapphire is used as the substrate 10, and... and A Bragg reflector 20 is obtained by alternating deposition of high and low acoustic impedance material layers. Mo is used as the lower electrode 30, AlN or ZnO piezoelectric thin film is used as the piezoelectric layer 40, and Mo is used as the upper electrode 50. These layers are then stacked sequentially to form a thin-film bulk acoustic resonator. A microstructure 60 is fabricated on the side of the upper electrode 50 away from the piezoelectric layer 40. The microstructure 60 is an array of annular grooves, which can be multiple concentric rings or segmented closed loops. The depth of the annular grooves is controlled to d = 0.1-2 µm, and the pitch between the annular grooves is controlled to p = 10-80 µm. When slip occurs, a normal load is applied to the microstructure 60, causing frictional vibration. This causes the thin-film bulk acoustic resonator to produce an inverse piezoelectric effect, which is detected by a pixel oscillator and output in real time Δf(t). STFT is performed on the slip window to obtain the slip spectrum S(f,t), and the slip initiation and peak shift are output, thus achieving slip detection.

[0027] In summary, in this embodiment, during the slip process, interfacial friction generates shear force Fx(t) and micro-vibration a(t). The shear load is locally amplified by the microstructure 60 on the upper electrode 50, inducing a repeatable stick-slip effect. That is, the slip is converted into frequency shift, phase noise, amplitude noise, etc. that can be modulated by FBAR through the microstructure 60, so as to realize accurate measurement of slip spectrum, and significantly enhance the modulation of tangential friction and slip on FBAR resonance characteristics, thereby improving slip signal-to-noise ratio.

[0028] Please refer to the attached document. Figure 2 and 3 As shown in the embodiment, the tactile sensor further includes a polymer layer 70, which is disposed on the outer surface of the thin-film bulk acoustic resonator. The polymer layer 70 is used to enhance lateral frictional coupling and slip signal-to-noise ratio.

[0029] Understandably, in this embodiment, by filling or covering the microstructure 60 with a polymer layer 70 made of a polymer material, a high-friction coupling layer and a shear stress shaping layer are formed on the surface of the thin-film bulk acoustic resonator. When slippage occurs, the shear force and micro-vibrations induced by interfacial friction of the polymer layer 70 are amplified and stabilized by the microstructure 60. Furthermore, the polymer layer 70 has its equivalent shear modulus and loss factor set within appropriate ranges to select the target slip spectrum frequency band and energy distribution, thereby achieving tuning of the slip spectrum frequency band.

[0030] The polymer layer 70 is a material layer with corresponding requirements for equivalent shear modulus and loss factor. The equivalent shear modulus is selected according to the target frequency band and load. In this embodiment, the equivalent shear modulus G is controlled between 0.2 MPa and 20 MPa; the loss factor tanδ is controlled between 0.01 and 0.2, and the lower the tanδ, the better it is for retaining the high-frequency slip spectrum. The materials used to make the polymer layer 70 include polyurethane (PU / TPU), modified silicone rubber, or elastomer composite materials. SiO2, carbon black, or microparticles can be added to the material to improve friction and wear resistance. The polymer layer 70 is disposed on the surface of the microstructure 60 and plays the following roles: 1. Improve frictional coupling; 2. Provide controllable viscoelasticity to adjust the spectral energy distribution; 3. Protect the microstructure 60 and improve wear resistance. In this embodiment, by filling / covering the surface of the microstructure 60 with a polymer material with adjustable elastic modulus and loss characteristics, a stable frictional coupling interface and stress shaping layer are formed on the surface of the microstructure 60, achieving an adjustable spectral energy distribution and enabling interpretable slip spectrum measurement.

[0031] In one specific embodiment, sapphire is used as the substrate 10, and... and A Bragg reflector 20 is obtained by alternating deposition of high and low acoustic impedance material layers. Mo is used as the lower electrode 30, AlN or ZnO piezoelectric thin film is used as the piezoelectric layer 40, and Mo is used as the upper electrode 50. These layers are then stacked sequentially to form a thin-film bulk acoustic resonator. A microstructure 60 is fabricated on the side of the upper electrode 50 away from the piezoelectric layer 40. The microstructure 60 is an array of annular grooves, which can be multiple concentric rings or segmented closed loops. The depth of the annular grooves is controlled to d = 0.1-2 µm, the pitch between the annular grooves is controlled to p = 10-80 µm, and the width of the annular grooves is controlled to 0.2p–0.8p. Controlling the width affects the contact area and friction enhancement. PU material is filled into the annular groove array to obtain a polymer layer 70. The Shore hardness of the polymer layer 70 is controlled to 70–95, and the thickness of the polymer layer 70 is controlled to 10–200 µm. Excessive thickness will filter out high frequencies.

[0032] The equivalent shear modulus of the polymer layer 70 is controlled between 0.2 and 50 MPa, which is used to tune the coupling bandwidth and wear resistance. A larger modulus is more beneficial for high frequencies but may reduce adhesion. The loss factor tanδ is controlled between 0.01 and 0.3. The loss factor determines the spectral energy fidelity. An excessively large loss factor will cause low pass.

[0033] In a further embodiment, the polymer layer 70 has a protective layer or anti-slip texture on the side away from the upper electrode 50.

[0034] To ensure the wear resistance and anti-slip properties of the touch sensor, a protective layer and / or anti-slip texture are provided on the surface of the polymer layer 70 in the embodiment.

[0035] In one embodiment, a protective layer is provided on the side of the polymer layer 70 away from the upper electrode 50, the protective layer comprising a thin Parylene or a thin PU layer; in another embodiment, an anti-slip texture is provided on the side of the polymer layer 70 away from the upper electrode 50, the anti-slip texture being a texture obtained through secondary surface treatment, such as a fine knurled texture; in yet another embodiment, a PU layer is provided on the side of the polymer layer 70 away from the upper electrode 50, and a knurled pattern is also provided on the surface of the PU layer.

[0036] In a further embodiment, the microstructure 60 is an anisotropic structure, used to obtain different spectral characteristics generated by sliding friction in different directions, so as to determine the sliding direction.

[0037] Understandably, in order to address the current inability of touch sensors to accurately detect the sliding direction, the embodiment is to set the microstructure 60 as an anisotropic structure.

[0038] The anisotropic structure refers to a material exhibiting different physical properties in different directions. In an embodiment, the microstructure 60 is designed as a directional microstructure, so that when it slides along different directions, the microstructure 60 will receive completely different feedback, thereby realizing the detection of direction.

[0039] In one specific embodiment, the microstructure 60 is an anisotropic microridge structure with ridges arranged in one direction. When sliding along the direction of the ridge of the microridge structure, the coefficient of friction is very low and the sliding is smooth. When sliding against the direction of the ridge, the coefficient of friction increases sharply, producing a stopping effect. Thus, sliding in different directions causes the microstructure 60 to produce different spectral characteristics in different directions. The embodiment utilizes this directional difference to achieve accurate detection of the direction of micro-motion.

[0040] Please refer to the attached document. Figure 1 , 2 As shown in Figure 3, in a further embodiment, the microstructure 60 includes one or more of periodic grooves, microridges, micropillars, spiral grooves, or serrated ridges.

[0041] Understandably, in order to solve the problem that standard thin-film bulk acoustic resonators cannot detect slip, in this embodiment, a different type of microstructure 60 is used to couple the slip to the axial direction of the thin-film bulk acoustic resonator for detection, thereby realizing slip detection.

[0042] Please refer to the appendix. Figure 3As shown, the periodic grooves are a micro-groove array arranged according to a certain pattern, specifically a micro-groove array in which the grooves are arranged at a certain interval and in the same direction.

[0043] The microridges are an array of ridges arranged in one direction, which can produce different spectral characteristics in different directions of slip, thus enabling slip direction determination.

[0044] Please refer to the attached document. Figure 1 As shown, the spiral groove is a spiral groove structure. In this embodiment, the tangential force can be decomposed into an axial component by the spiral angle of the spiral groove, thereby enhancing the axial strain response of the thin-film bulk acoustic resonator.

[0045] The serrated ridges are arranged in an array along one direction, and a serrated structure is provided on the upper part of the ridges. The serrated structure of each ridge can also be staggered. In this embodiment, the serrated structure makes the spectral peaks and energy distributions of forward / reverse sliding different, thereby improving directional resolution.

[0046] In this embodiment, different microstructures 60 can be selected according to different usage scenarios. The microstructure 60 can consist of one, two, or three microstructures, thereby improving the detection effect of slippage. When slippage occurs on the surface, the microstructure 60 can produce at least the following effects: 1. Friction enhancement effect: specifically, by increasing the effective friction coefficient of the interface and the number of micro-contacts, the slippage generates stable and repeatable stick-slip effect micro-events; 2. Stress shaping and conversion effect: the microstructure 60 converts tangential shear loads into axial tension / compression or periodic perturbations that can be sensed by the thin-film bulk acoustic resonator, and improves the dynamic coupling bandwidth. The microstructure 60 enables interpretable and repeatable measurement of the slip spectrum, that is, it enables high signal-to-noise output of the slip signal.

[0047] In a further embodiment, the piezoelectric layer 40 shown is enhanced by one of the following processes: orientation, doping, or tilting the c-axis.

[0048] Understandably, the piezoelectric layer 40 enhances its shear response through orientation, doping, and c-axis tilting processes, primarily by addressing the physical mechanisms of the piezoelectric effect (especially the shear piezoelectric coefficient d). 15 or e 15 Starting from this point, these three processes can optimize the lattice structure, electronic state, or stress-polarization coupling, thereby improving the electromechanical conversion efficiency in the shear direction.

[0049] The essence of the piezoelectric effect is the interconversion between mechanical stress and polarization, where the shear response corresponds to the shear stress. or polarization or From the shear piezoelectric coefficient, such as Characterization. For hexagonal piezoelectric materials, such as AlN and ZnO, the strength of the shear response is closely related to grain orientation, lattice distortion, and electronic structure. The core objective of enhancing the shear response is to more efficiently convert shear stress into polarization, or to more efficiently drive shear vibrations through polarization.

[0050] The orientation is achieved by controlling the polarization axis orientation of the piezoelectric layer 40 through epitaxial growth, making the grain polarization direction more aligned with the shear stress direction or shear vibration direction, thereby enhancing the shear response. The epitaxial growth can be methods such as sputtering or MOCVD. In other words, by controlling the grain polarization direction, the stress-polarization coupling is optimized, thereby improving the shear piezoelectric coefficient. The electromechanical coupling coefficient of the enhanced shear wave mode .

[0051] The doping involves introducing impurity atoms, such as Sc, Mg, or Ti, into the piezoelectric thin film. This enhances the shear piezoelectric effect by altering the lattice constant, elastic modulus, or electronic energy levels. In other words, by introducing impurity atoms, the lattice and electronic structure are modulated, enhancing the shear response and potentially improving the material's thermal stability. For example, Sc-doped AlN has a thermal expansion coefficient that better matches the substrate or mechanical strength.

[0052] The tilted c-axis process refers to the growth process that makes the c-axis of the piezoelectric thin film form a certain angle with the normal direction, such as 10°-45°, thereby enhancing the coupling between shear stress and polarization. In other words, by adjusting the geometric matching between the polarization direction and the stress direction, the electromechanical coupling of the shear wave mode is significantly enhanced. For example, the stability of the shear wave resonant frequency is improved in AlN thin films with a tilted c-axis.

[0053] In a further embodiment, the substrate 10 is made of silicon, glass, or sapphire.

[0054] In a further embodiment, the polymer layer 70 includes: an adhesive layer, which is attached to the surface of the outer periphery of the upper electrode 50 and positioned relative to the microstructure 60; and a friction outer layer, which is disposed on the surface of the outer periphery of the adhesive layer.

[0055] Understandably, the bonding layer is used to bond with the microstructure 60 of the upper electrode 50 to ensure that external forces can be accurately transmitted to the thin-film bulk acoustic resonator, thus solving the problems of interface bonding and stress transmission.

[0056] The outer friction layer comes into direct contact with the object being measured, such as a finger, fabric, or metal surface. It can directly interact with the complex external world, generating friction signals that determine what textures and forces the sensor can detect, thus addressing the issues of signal generation and durability.

[0057] In one embodiment, the polymer layer 70 can also be made into a replaceable patch. The bonding layer of the polymer layer 70 has pre-formed microstructures 60, which are aligned with the microstructure 60 region of the upper electrode 50 via positioning grooves, ensuring the accuracy of polymer layer 70 replacement. When the polymer layer 70 wears down, it can be quickly replaced, maintaining long-term consistency of the slip spectrum and facilitating engineering applications and batch maintenance.

[0058] In a further embodiment, the outer friction layer is PU / TPU or modified silicone rubber, and the shear modulus and loss factor of the outer friction layer are set within a preset range.

[0059] In this embodiment, by filling / covering the surface of the microstructure 60 with a polymeric material having adjustable elastic modulus and loss characteristics, a stable frictional coupling interface and stress shaping layer are formed on the surface of the microstructure 60, thereby achieving an adjustable spectral energy distribution and enabling interpretable slip spectrum measurement.

[0060] The shear modulus, as mentioned here, is a measure of a material's resistance to shear deformation when subjected to shear force or a force parallel to its surface. It is directly related to the material's hardness or stiffness. For viscoelastic materials, the higher the shear modulus, the harder the material; the lower the shear modulus, the softer the material. Here, the equivalent shear modulus is controlled between 0.2 MPa and 20 MPa, and selected according to the target frequency band and load.

[0061] The loss factor refers to a measure of the internal friction of a viscoelastic material, reflecting the material's ability to convert mechanical energy into heat energy during deformation. The loss factor tanδ is controlled between 0.01 and 0.2, where a lower tanδ is more conducive to preserving the high-frequency slip spectrum.

[0062] In this embodiment, by setting the preset range of these two parameters, the purpose is essentially to customize the tactile conduction characteristics of the friction outer layer, making it like the skin of a human hand: by setting the shear modulus appropriately, the friction outer layer has enough softness to conform to the object, and by setting the loss factor appropriately, the friction outer layer can sensitively sense the subtle vibrations of the texture, thereby obtaining a high-quality slip spectrum.

[0063] Example 2: Based on the same inventive concept, the second aspect discloses a sensor array comprising at least two FBAR-based slip spectrum tactile sensors as described in the first aspect, wherein the tactile sensors form the sensor array.

[0064] In this embodiment, by arranging the FBAR-based slip spectrum tactile sensors as required, a sensor array is formed. The sensor array can output an array of pixel images and output a slip spectrum time-frequency image and spatial distribution in a pixel array manner, thereby realizing slip direction, slip intensity and material texture fingerprint recognition.

[0065] Since each thin-film bulk acoustic resonator's upper electrode 50 in the FBAR-based slip spectrum tactile sensor is equipped with a corresponding microstructure 60, during detection, the slip is coupled to the inverse piezoelectric effect of the thin-film bulk acoustic resonator through the microstructure 60, i.e., an independent sensing point, which can be regarded as a tactile pixel. By arranging multiple sensors horizontally and vertically within a flexible substrate to form a sensor array, a two-dimensional tactile image composed of multiple tactile pixels is achieved. In this embodiment, the slip vector field can be jointly estimated by multiple pixels, and a tactile image, such as Fz, Fx / Fy, and the slip spectrum, can be output. The slip spectrum includes a slip spectrum energy map, a slip direction field, or a contact area map.

[0066] In a further embodiment, the sensor array also includes a reference thin-film bulk acoustic resonator for data compensation as a reference to eliminate temperature drift and load drift.

[0067] Understandably, in order to reduce cross-contamination of temperature, the embodiment can set a stress-free reference thin-film bulk acoustic resonator in the flexible substrate, and perform temperature compensation through differential processing, thereby eliminating the effects of temperature drift and load drift, and obtaining more accurate data.

[0068] In some embodiments, multiple FBAR-based slip spectrum tactile sensors are disposed within the flexible substrate, and the sensor array is arranged, for example, by distributing the sensors in a rectangular pattern on the same plane to form a rectangular sensor array. This design enables two-dimensional tactile imaging. Please refer to the appendix. Figure 7 As shown, the two-dimensional graph of the response intensity of a slip event on the sensor pixel array illustrates the spatial response distribution of the sensor pixel array during a slip event. The graph, through color coding and spatial distribution, visually presents the spatial non-uniformity of the response intensity of the slip event on the sensor pixel array: the central region (contact core) has the strongest response, while the edge regions have a weaker response. It is a key visualization tool for analyzing the spatial resolution of tactile sensors, the localization of slip contact areas, and the spatial characteristics of array signals, providing a data foundation for slip direction determination and spatial analysis of texture fingerprints.

[0069] Please refer to the attached document. Figure 8 As shown, this 3D plot of the response intensity of a slip event on the sensor pixel array visually illustrates the spatial distribution of the sensor pixel array's response intensity during a slip event. By visualizing height and space, this plot elevates the sensor pixel array's response intensity distribution from planar to three-dimensional, more intuitively presenting the spatial non-uniformity of the slip event's response. It is a key tool for analyzing the spatial resolution of haptic sensors, contact area localization, and the spatial characteristics of array signals, providing intuitive data support for slip direction determination and spatial resolution of texture fingerprints.

[0070] A concrete example: M=4-32 rows of tactile sensors are laid out at intervals in one direction on a flexible substrate 10, while N=4-32 columns of tactile sensors are arranged, thus forming an M×N array to create tactile imaging. Partitioned frequency division multiplexing and row and column addressing are used to reduce readout complexity. The slip spectrum energy heat map and orientation field output by the array are used to drive the gripper / finger controller to adjust the gripping force in real time, realizing anti-slip gripping of wet / oily objects.

[0071] In this embodiment, the stripe arrangement directions of the microstructures 60 of adjacent FBAR-based slip spectrum tactile sensors on the sensor array are not the same. For example, in two adjacent FBAR-based slip spectrum tactile sensors, the first tactile sensor has a groove as its microstructure 60, which is arranged along the first direction of the array, while the second tactile sensor has a ridge as its microstructure 60, which is arranged along the second direction of the array. The first and second directions are not the same. In this way, mutually orthogonal stripe microstructures 60 are formed on the pixel, or a cross-shaped composite texture is formed on the same pixel. By comparing the in-band energy and spectral peak differences of different textured pixels, the slip direction and front propagation speed can be obtained from the output slip spectrum.

[0072] Example 3: Based on the same inventive concept, a third aspect discloses a method for acquiring a slip spectrum using the FBAR-based slip spectrum tactile sensor described in the first aspect. Step 001: Acquire the dynamic electrical signal of the tactile sensor, which includes the dynamic changes in resonant frequency, quality factor, or phase noise.

[0073] In this process, using equipment such as network analyzers, oscilloscopes, and data acquisition cards, and combining techniques such as spectrum analysis, amplitude measurement, and phase difference measurement, the friction and vibration between the object and the sensor surface during the sliding process will cause changes in the mechanical response of the piezoelectric layer 40 of the FBAR, which will then be converted into dynamic changes in the electrical signal. The frequency / phase / amplitude time series of the FBAR are collected. In other words, the embodiment quantifies the dynamic response of the FBAR, such as changes in environmental parameters or sliding events, to provide time-domain feature data for tactile sensing, radio frequency communication, or sensor applications.

[0074] The frequency During slippage, texture impact, mass load, or stress changes can alter the sound velocity / thickness of the piezoelectric layer 40, causing the resonant frequency to drift. For example, the ratio of texture spacing to slippage velocity corresponds to the dominant frequency.

[0075] The quality factor This refers to energy loss during slippage, such as frictional heat generation and material internal friction, which reduces [the energy lost during slippage]. The value reflects the damping characteristics of slip.

[0076] The phase noise is the frequency fluctuation during slip. Random vibration will increase the phase noise, reflecting the stability of slip.

[0077] Please refer to the attached document. Figure 4 As shown, the time-domain curves of frequency shift versus load illustrate the relationship between frequency shift (Δf) and load (N) over time during the slip process, providing a visual representation of the dynamic response characteristics of the tactile sensor during slip events. The attached figure visually illustrates the coupling relationship between load and frequency in slip events. By analyzing this temporal relationship, a mapping model of "load-frequency shift-slip characteristics" can be established, providing a data foundation for the quantitative calibration of tactile sensors, such as slip intensity and direction determination.

[0078] Step 002: Preprocess the dynamic electrical signal of the thin-film bulk acoustic resonator. The preprocessing includes temperature compensation and detrending processing.

[0079] In this embodiment, the preprocessing is for the purpose of purifying the dynamic signal, that is, before extracting the slip spectrum, environmental interference must be removed to ensure the accuracy of the data.

[0080] The temperature compensation is achieved by using a reference thin-film bulk acoustic resonator or a differential processing method to eliminate the dynamic electrical signal caused by changes in ambient temperature, ensuring that the remaining signal is purely caused by mechanical contact. For example, in this embodiment, two thin-film bulk acoustic resonators are used: a reference resonator and a sensing resonator. During slippage, the reference resonator is not affected by force but only by temperature, thus serving as a reference; the sensing resonator contacts the object being measured and is thus affected by both temperature and force. By measuring the frequency difference between the two, the effect of temperature on the sensing resonator is eliminated.

[0081] The detrending process removes the influence of slowly varying normal loads / attitudes to obtain a pure signal with zero mean, containing only high-frequency vibration components. Specifically, the detrending includes: removing the influence of normal force: gripping force (normal load) is usually a slowly varying low-frequency signal that can drown out weak slip vibrations; high-pass filtering or adaptive moving average is used to remove low-frequency trends; removing attitude interference: the movement of the robotic arm can cause baseline drift, which needs to be eliminated through dynamic baseline estimation.

[0082] Step 003: Detect and acquire the slip event window to determine the window sequence, wherein the slip event window is acquired by detecting indicators such as short-time energy, spectral entropy, or phase noise rise to obtain the slip start time or end time.

[0083] In this embodiment, to avoid wasting computing resources, the system needs to know when a slip occurs in order to initiate subsequent spectrum analysis. This embodiment uses the window at which the slip event occurs as a trigger mechanism. Specifically, when a slip occurs, the detection device can obtain changes in indicators such as short-time energy, spectral entropy, or phase noise rise, which are used as the start and end times of the slip event, thus obtaining the window sequence of slip events.

[0084] The short-term energy refers to the frictional vibration energy that rises sharply when slippage occurs, and is determined to be the start of slippage if it exceeds a set threshold.

[0085] The spectral entropy measures the complexity and randomness of a signal. Specifically, when the signal is stationary or in a stable grip, it is usually smooth with a low spectral entropy; when the slip begins, the signal becomes chaotic and rich, and the spectral entropy suddenly increases.

[0086] The phase noise rise occurs in the very early stages of slip, before vibration even appears. The phase noise begins to increase due to the interaction of surface micro-roughness. This indicator can be used to achieve early slip warning.

[0087] The window sequence refers to the sequence of electrical signals of the thin-film bulk acoustic resonator captured according to the start and end times of the slip event when slip occurs. In this embodiment, the sensor converts the normal load of the slip to the piezoelectric layer 40 of the thin-film bulk acoustic resonator, thereby detecting the frequency / phase / amplitude time sequence of the electrical signal of the thin-film bulk acoustic resonator over time.

[0088] Step 004: Perform time-frequency analysis based on the window sequence to obtain the slip spectrum. The time-frequency analysis involves performing STFT or wavelet packet decomposition on the slip window to obtain the slip spectrum.

[0089] In this example, after capturing the sliding window sequence, the acquired data needs to be analyzed. Here, time-frequency analysis is used to transform the one-dimensional time signal into a two-dimensional time-frequency graph. .

[0090] Window capture: Capture valid slip signal segments based on the detected start and end times.

[0091] STFT (Short-Time Fourier Transform): Applicable to smooth sliding processes. By applying a windowed Fourier transform, the changes in frequency components over time during the sliding process can be observed.

[0092] Wavelet packet decomposition is suitable for non-stationary, transient slip signals, such as stick-slip impacts. Wavelet packets can provide high frequency resolution in both low and high frequency bands. They can accurately capture the high-frequency impact at the initial stage of slip and the low-frequency components during the viscous phase.

[0093] In this example, after time-frequency processing, a slip spectrum is output with time as the horizontal axis, frequency as the vertical axis, and energy (or amplitude) as the color value. This spectrum is similar to the fingerprint of an object. In other words, the slip spectrum obtained after time-frequency analysis is the frequency domain fingerprint of the slip event, containing dynamic information in the time dimension.

[0094] Please refer to the attached document. Figure 5 The above is a time-frequency spectrum diagram of the slip event in an embodiment of the present invention. The time-frequency spectrum is usually generated by time-frequency analysis methods such as short-time Fourier transform (STFT) or wavelet transform, and is used to show the frequency components and energy distribution of the signal at different time points. Figure 5 The temporal spectrum visualizes the frequency energy changes of slip events through color coding and spatiotemporal distribution: the low-frequency band corresponds to the static / recovery phase, while the mid-to-high frequency band (yellow highlights) corresponds to the dynamic texture excitation during slip. It is a key tool for analyzing slip spectra and extracting slip intensity, direction, or material texture fingerprints, providing an intuitive frequency domain feature basis for the quantitative calibration of tactile sensors.

[0095] Please refer to the attached document. Figure 6 The above is a time-domain curve of the in-band energy in an embodiment of the present invention; Figure 6 It can quantify the energy intensity during slippage, reflecting the severity of frictional vibration.

[0096] Step 005: Extract the output spectral peak position, bandwidth, energy distribution, spectral centroid, or 1 / f noise slope change based on the slip spectrum to determine the slip intensity, direction, or material texture fingerprint.

[0097] In this embodiment, the required physical features are extracted from the obtained slip spectrum. The extracted physical features include the position of the spectral peak, bandwidth, energy distribution, spectral centroid, or 1 / f noise slope change. The slip intensity, direction, or material texture fingerprint is determined by these extracted material features.

[0098] Among them, the spectral peak position is the spacing of the surface texture of the object during slippage. With slip velocity Together they determine the resonant frequency The position of the spectral peak corresponds to the dominant frequency during the slip process, directly reflecting the interaction between velocity and texture.

[0099] For example, in determining direction, if the sliding speed increases, such as when the finger slides faster... If the rate increases, the spectral peak position shifts to higher frequencies; if the rate decreases, it's like decelerating. A decrease in spectral peak position indicates a shift towards lower frequencies. The dynamic trend of the spectral peak position, such as rising or falling, can indicate the direction of slippage, i.e., acceleration or deceleration. For example, when a robot grasps an object, if the spectral peak position rises rapidly, it indicates accelerated slippage, meaning the object is sliding away from the robot, and the gripping force needs to be increased immediately.

[0100] The bandwidth is the frequency range of the vibration energy distribution. For example, a wide bandwidth typically implies a rough surface or severe slippage; a narrow bandwidth may imply a smooth surface or slight vibration.

[0101] The spectral centroid is the average position of energy in the frequency domain. It is used for texture recognition. Rough textures typically have high friction and strong impact, so their centroid is biased towards high frequencies; smooth textures have their centroid biased towards low frequencies. It is also used to determine slip velocity; the faster the velocity, the more high-frequency components are typically excited.

[0102] The change in the 1 / f noise slope reflects the attenuation law of low-frequency noise and is positively correlated with the friction coefficient of the material. High-friction materials, such as rubber, have high friction and more random vibrations, resulting in a steeper slope; low-friction materials, such as PTFE, have low friction and a gentler slope.

[0103] In this example, the slip intensity, direction, or material texture fingerprint is determined as follows: the slip intensity is determined by quantifying the magnitude of the slip force through the total energy or spectral peak amplitude; whether slip is determined is determined by judging whether the object is sliding through changes in the spectral peak position or spectral centroid; the slip direction is determined by the trend of the spectral peak position / spectral centroid, i.e., rising or falling, such as the object sliding away from the robot.

[0104] For example: When a robot grasps an object, it needs to determine the sliding state (whether sliding has occurred), the sliding direction, and the sliding intensity (the magnitude of the force) to adjust its grip strength strategy. Slip detection: Determines whether an object is sliding by observing changes in the position of spectral peaks or the centroid of the spectrum; Direction determination: Determine the sliding direction by the trend of the spectral peak position / spectral centroid, such as the object sliding away from the robot; Intensity quantification: The magnitude of the slip force is quantified by the total energy or peak amplitude. For example, "strong slip" requires an increase of 20% in grip strength. Material compatibility: Identify materials by bandwidth, energy distribution, and 1 / f noise slope, such as rubber requiring flexible grip and metal requiring rigid grip.

[0105] For example, when a robot grasps a rubber ball, it detects a drop in the spectral peak position, indicating deceleration and slippage; a large bandwidth, indicating rough texture; and a steep 1 / f noise slope, indicating high friction. This indicates "strong slippage and high friction material," requiring an immediate increase in gripping force and adjustment of the grasping posture.

[0106] Example 4: Based on the same inventive concept, a fourth aspect discloses a method for fabricating a sensor, used to fabricate the FBAR-based slip spectrum tactile sensor described in any one of the first aspects above, comprising the following steps: Step 100: A stack of mirrors is grown on the substrate 10 using a deposition process. The stack of mirrors is made of two materials with similar acoustic impedance and has an alternating layer structure of high and low acoustic impedance from bottom to top.

[0107] Understandably, the substrate 10 needs to be cleaned before deposition. Specifically, the substrate 10 is made of one of Si, glass or sapphire materials, and the surface of the substrate 10 is cleaned, then dehydrated and baked to complete the cleaning of the substrate 10, so as to ensure the surface cleanliness of the growing emitter mirror.

[0108] The emitter mirror is fabricated by growing it on the side of the substrate 10 using a deposition process, employing W and Or Mo and Two sets of materials are deposited alternately from the substrate 10 upwards to grow a layered structure of alternating high and low acoustic impedance materials, resulting in a reflector stack. In one embodiment, the reflector stack comprises six layers, wherein the first layer is... The second layer is The third layer is The fourth layer is The fifth floor is The sixth floor is .

[0109] Step 200: A lower metal layer is fabricated on the mirror stack by sputtering, and a pixel electrode pattern is etched on the metal layer by photolithography to obtain the lower electrode 30.

[0110] In this embodiment, after a reflector stack is grown on the substrate 10, it is placed in a sputtering apparatus to sputter a lower electrode 30 layer on the reflector stack. The material used for sputtering the lower electrode 30 includes at least one of Mo, W, Pt or Al. Then, a pixel electrode pattern is formed on the lower electrode 30 by a photolithography etching process to obtain the lower electrode 30.

[0111] In one specific embodiment, the metal layer is obtained by sputtering four materials: Mo, W, Pt, and Al. This embodiment utilizes the adhesion of Mo / W, the conductivity of Pt, and the cost advantage of Al to construct a multilayer electrode structure that meets the electrical performance requirements of the FBAR / sensor. A dense and uniform metal film is formed on the substrate 10 through PVD process to ensure interface quality and conductivity. Finally, the electrode pattern is refined through pattern transfer technology to achieve pixel-level sensing unit fabrication, thereby improving the resolution and performance of the array and obtaining the lower electrode 30.

[0112] Step 300: A piezoelectric thin film is obtained on the upper part of the lower electrode 30 by deposition process, and stress and crystal orientation control of the piezoelectric thin film are performed to obtain a piezoelectric layer 40.

[0113] In this example, piezoelectric thin films are deposited using aluminum nitride and zinc oxide, commonly used piezoelectric materials in FBARs. The deposition method is primarily based on physical vapor deposition (PVD), with magnetron sputtering being the main process choice due to its controllable process and high film quality. During the deposition of AlN or ZnO piezoelectric thin films, shear response is enhanced through orientation, doping, and c-axis tilting processes. Essentially, this optimizes the lattice structure or polarization direction, allowing shear stress to more efficiently excite polarization. Simultaneously, stress and crystal orientation control ensure the stability and performance consistency of the thin film. These processes enable FBARs to achieve high-sensitivity, high-stability sensing or radio frequency functionality.

[0114] For example: In the AlN deposition example, radio frequency magnetron sputtering was employed with a high-purity Al target (99.999%) and (or The mixed gas is the reactive gas. The substrate temperature is controlled at 200–500℃, and for sapphire substrates, it can be increased to 600℃ to promote c-axis orientation. The sputtering power is 100–300 W, and the gas pressure is 0.5–2 Pa. By adjusting parameters, such as... Flow rate and substrate temperature can control the crystallinity and orientation of the thin film.

[0115] The shear response is enhanced by a doping process, wherein the AlN doped Sc is: using an ionic radius of 0.745 Å. Replace 0.535 Å This leads to lattice expansion, i.e., an increase in the a-axis and a decrease in the c-axis, resulting in a change in the elastic modulus, making shear stress more likely to induce polarization. For example, Sc-doped AlN (Sc concentration 2%)... It can be from -0.5 Increased to -0.8 This represents a 60% improvement.

[0116] Stress control refers to the process during sputtering, where high-energy ions bombard the substrate 10, causing internal stress (such as tensile stress) in the thin film, which affects the lattice structure and shear response. Crystal orientation control refers to maintaining crystal orientation consistency, which is crucial for ensuring stable shear response. This requires in-situ monitoring and post-processing control, such as ensuring the uniformity of the c-axis orientation by adjusting the substrate tilt angle to ensure consistent c-axis tilt angle and avoid local orientation deviations.

[0117] Step 400: A metal layer is formed on the piezoelectric layer 40 by sputtering, and a pixel electrode pattern is etched on the metal layer by photolithography to obtain the upper electrode 50.

[0118] In this embodiment, the piezoelectric layer 40 is sputtered in a sputtering apparatus to form an upper electrode 50 layer. The material used for sputtering the upper electrode 50 includes at least one of Mo, W, Pt or Al. Then, a pixel electrode pattern is formed on the upper electrode 50 by a photolithography etching process to obtain the upper electrode 50.

[0119] In one specific embodiment, the metal layer is obtained by sputtering four materials: Mo, W, Pt, and Al. This embodiment utilizes the adhesion of Mo / W, the conductivity of Pt, and the cost advantage of Al to construct a multilayer electrode structure that meets the electrical performance requirements of the FBAR / sensor. A dense and uniform metal film is formed on the substrate 10 through PVD process to ensure interface quality and conductivity. Finally, the electrode pattern is refined through pattern transfer technology to achieve pixel-level sensing unit fabrication, thereby improving the resolution and performance of the array and obtaining the upper electrode 50.

[0120] Step 500: Microstructure 60 is fabricated on the surface of the upper electrode 50.

[0121] Because the microstructure 60 has the function of locally amplifying shear load and inducing a repeatable stick-slip effect, that is, converting slip into frequency shift, phase noise, amplitude noise, etc. that can be modulated by FBAR through the microstructure 60, the embodiment requires the fabrication of the microstructure 60 on the upper electrode 50. The fabrication of the microstructure 60 is carried out by photolithography or dry etching to form trenches or hole arrays; or by laser direct writing or femtosecond laser microprocessing to form annular trenches; or by nanoimprinting or template transfer to form surface textures.

[0122] For example: First, a thick layer of adhesive is applied to the surface of the upper electrode 50, and a hole or pillar array pattern is defined by photolithography. Then, an etching process is used to fabricate the microstructure 60. Specifically, high aspect ratio trenches or holes are locally etched into the metal of the upper electrode 50 and the piezoelectric layer 40 using ICP deep etching (DRIE) technology. These structures can change the local stiffness of the contact interface.

[0123] Step 600: Fill or deposit a film on the microstructure 60 to form a polymer layer 70 on the microstructure 60, thereby obtaining a tactile sensor.

[0124] To enable the polymer layer 70 to be readily available on the microstructure 60, in embodiments, it is understood that this is done to improve the sensor's frictional coupling; provide controllable viscoelasticity to regulate the spectral energy distribution; protect the microstructure 60; and enhance wear resistance. A filling or coating process is used on the microstructure 60 to form the polymer layer 70, resulting in a high-friction coupling layer and a shear stress shaping layer on the surface of the thin-film bulk acoustic resonator. When slippage occurs, the interfacial friction-induced shear forces and micro-vibrations of the capping layer are amplified and stabilized by the microstructure 60.

[0125] In one embodiment, a low-viscosity polymer precursor solution is dropwise added to the microstructure 60, and the polymer precursor solution completely fills the microstructure 60 using capillary action or vacuum assistance. By dropwise adding the polymer precursor solution onto the processed microstructure 60, a layer of polymer solution is filled or coated onto the microstructure 60. It is also possible to coat the microstructure 60 with a thin film made of polymer, thereby forming a polymer layer 70.

[0126] In one specific embodiment, a polymer filler is used to form a polymer layer 70. The specific steps involve preparing a low-viscosity polymer precursor from materials such as PU / TPU / modified silicone rubber, and then dropping the low-viscosity polymer precursor into the groove-shaped microstructure 60 region. During this process, capillary action or vacuum assistance can be used to completely fill the annular groove.

[0127] In one embodiment, the polymer layer 70 may be configured as a layered structure, including an adhesive layer that is attached to the surface of the outer periphery of the upper electrode 50 and positioned relative to the microstructure 60, with a thickness controlled to be <10 µm, and a friction outer layer disposed on the adhesive layer, with a thickness of 10-500 µm.

[0128] In one embodiment, before fabricating the polymer layer 70, the microstructure 60 region needs to undergo surface activation and adhesion enhancement to improve polymer wetting and adhesion strength. Specifically, the microstructure 60 region can be treated with plasma and silanization.

[0129] Step 700: After covering the microstructure 60 of the upper electrode 50 with the polymer layer 70, a curing process is performed.

[0130] After the polymer material is filled onto the microstructure 60, curing is required. In this embodiment, depending on the material system, thermosetting or UV curing can be selected. After curing, a protective coating of Parylene / thin PU film can be applied, and secondary surface micro-texturing can be performed to improve the wear resistance and long-term consistency of the polymer layer 70.

[0131] In practical applications: In practice, to realize the application of the slip spectrum tactile sensor based on thin-film bulk acoustic resonator in real-world scenarios, two key issues must be addressed: signal addressing (multiplexing) of large-scale arrays and quantization mapping (calibration) of physical signals.

[0132] In practical applications, array packaging and multiplexing are also required. For FBAR haptic arrays containing tens to thousands of pixels, directly leading out wires for each pixel would result in huge wiring complexity and parasitic capacitance, severely affecting high-frequency performance. An example is that the pixel array achieves row-column or frequency-division multiplexing interconnection through RDL or a packaging substrate, and then uses an integrated oscillator, PLL, or counting readout circuit.

[0133] Specifically, the RDL is a back-end process performed at the wafer level, used to rearrange the tiny, densely packed Al pads on the FBAR pixel array into larger-pitch array pads using a fan-out method. Simultaneously, to reduce the number of leads, multiplexing strategies are typically employed, including one or a combination of row-column addressing and frequency division multiplexing. The FBAR outputs a high-frequency electrical signal, i.e., a frequency- or phase-changing signal, which must be converted into a signal processable by a digital system using an integrated oscillator, PLL, or counting readout circuit.

[0134] After the signal is read, the originally chaotic electrical signal needs to be converted into tactile parameters with clear physical meaning. This involves calibrating the frequency shift, in-band energy, and spectral feature mapping under known normal / tangential loads and slip velocity conditions, forming a slip spectrum quantization model. Using the extracted feature set and true values ​​of physical quantities, a model is constructed through regression or classification algorithms. The calibration in this embodiment involves not only establishing a data table but also decoupling complex force, heat, and acoustic coupling effects, enabling the sensor to understand the physical state of the contact surface. This process can be referenced from methods for developing tactile sensors.

[0135] The implementation example utilizes RDL and row / column / frequency division multiplexing to solve the high-density interconnection problem of large-scale arrays, and uses oscillators and PLLs to achieve precise readout of high-frequency signals. Furthermore, through multi-physics calibration, a quantization mapping from frequency domain slip spectrum to tactile physical quantities such as force, velocity, and texture is established, giving the sensor the ability to understand the surface properties and motion state of the contacted object.

[0136] Based on the same inventive concept, the fifth aspect also discloses an application method of the FBAR-based slip spectrum tactile sensor, which is applied in wearable health monitoring, robot tactile sensing and human-computer interaction and other application scenarios.

[0137] In the field of robotic tactile sensing, it enables robots to achieve dexterous grasping by providing closed-loop control and anti-falling in wet / dusty / oil film environments. In the field of wearables / prosthetics, it is used for fingertip tactile skin to achieve sliding feedback and material sensing; In the field of medical palpation, slip spectrum and shear distribution are used to assist in the assessment of tissue stiffness / fibrosis. It is used in the field of industrial inspection to monitor surface roughness, coating condition, and friction degradation online; Applications in strong electromagnetic environments, such as power equipment and magnetic resonance environments, require tactile sensing that is resistant to electromagnetic interference.

[0138] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. This disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims. Thus, if these modifications and variations of the invention fall within the scope of the claims of the invention and their equivalents, the invention is also intended to include these modifications and variations.

Claims

1. A slip spectrum tactile sensor based on FBAR, characterized in that, The tactile sensor includes a thin-film bulk acoustic resonator, wherein the thin-film bulk acoustic resonator includes: a substrate, a Bragg mirror, a lower electrode, a piezoelectric layer, and an upper electrode, wherein the substrate, the Bragg mirror, the lower electrode, the piezoelectric layer, and the upper electrode are stacked sequentially from bottom to top; Furthermore, a microstructure is provided on the upper electrode away from or near the piezoelectric layer. The microstructure is used to convert slip into shear load, thereby causing the thin-film bulk acoustic resonator to vibrate mechanically, and then converting the mechanical vibration into an electrical signal.

2. The tactile sensor according to claim 1, characterized in that, The tactile sensor also includes a polymer layer disposed on the outer surface of the thin-film bulk acoustic resonator, which is used to enhance lateral frictional coupling and slip signal-to-noise ratio.

3. The tactile sensor according to claim 2, characterized in that, The polymer layer has a protective layer or anti-slip texture on the side away from the upper electrode.

4. The tactile sensor according to claim 1, characterized in that, The piezoelectric layer shown is enhanced by one of the following processes: orientation, doping, or tilting the c-axis.

5. The tactile sensor according to claim 1, characterized in that, The substrate is made of one of silicon, glass, or sapphire.

6. The sensor according to claim 1, characterized in that, The microstructure includes one or more of the following: periodic grooves, microridges, microcolumns, spiral grooves, or serrated ridges.

7. A sensor array, characterized in that, It includes at least two FBAR-based tactile sensors as described in any one of claims 1-6, and consists of a sensor array composed of tactile sensors.

8. The sensor according to claim 7, characterized in that, The sensor array also includes a reference thin-film bulk acoustic resonator for data compensation as a reference to eliminate temperature drift and load drift.

9. A method for acquiring a slip spectrum using the sensor array described in claim 7 or 8, characterized in that, Acquire dynamic electrical signals that change dynamically from the tactile sensor, including dynamic changes in resonant frequency, quality factor, or phase noise. The dynamically changing electrical signal is preprocessed, including temperature compensation and detrending processing. The detection and acquisition of the slip event window is used to determine the window sequence, wherein the slip event window is obtained by detecting indicators such as short-time energy, spectral entropy or phase noise rise to obtain the slip start time or end time; The time-frequency analysis is performed on the window sequence to obtain the slip spectrum. The time-frequency analysis is to perform STFT or wavelet packet decomposition on the slip window to obtain the slip spectrum. The peak position, bandwidth, energy distribution, spectral centroid, or 1 / f noise slope change are extracted and output based on the slip spectrum to determine the slip intensity, direction, or material texture fingerprint.

10. A method for manufacturing a sensor, characterized in that, The steps for preparing the FBAR-based slip spectrum tactile sensor according to any one of claims 1-6 include: A stack of mirrors is grown on a substrate using a deposition process. The stack of mirrors is made of two materials with similar acoustic impedance and presents a layer structure with alternating high and low acoustic impedance from bottom to top. A metal layer is fabricated on the mirror stack by sputtering, and a pixel electrode pattern is etched on the metal layer by photolithography to obtain the lower electrode. A piezoelectric thin film is obtained on the upper part of the lower electrode by deposition process, and the stress and crystal orientation of the piezoelectric thin film are controlled to obtain a piezoelectric layer. A metal layer is fabricated on the piezoelectric layer by sputtering, and a pixel electrode pattern is etched on the metal layer by photolithography to obtain the upper electrode. Microstructures are fabricated on the surface of the upper electrode; A tactile sensor is obtained by filling or coating a microstructure to form a polymer layer on the microstructure.

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