Passive temperature detection device and method of manufacture

Abstract

The application discloses a passive temperature detection device and a preparation method thereof. The device comprises an insulating substrate, a functional layer, a flexible piezoelectric layer and a surface acoustic wave sensor. The insulating substrate comprises a fixed part and a deformation layer, the deformation layer is suspended and fixed at one end of the fixed part. The functional layer is at least partially located on the deformation layer. The flexible piezoelectric layer is arranged on the functional layer and at least partially located in the overlapping area of the deformation layer and the functional layer. The thermal expansion coefficients of the deformation layer, the functional layer and the flexible piezoelectric layer increase in sequence. The surface acoustic wave sensor is arranged on the flexible piezoelectric layer, and the surface acoustic wave sensor comprises an interdigital transducer electrode, which is at least partially located in the overlapping area of the deformation layer, the functional layer and the flexible piezoelectric layer. The application can amplify the differential deformation effect and improve the temperature detection sensitivity.

Description

Technical Field

[0001] This invention belongs to the field of microelectromechanical systems technology, specifically relating to a passive temperature detection device and its preparation method. Background Technology

[0002] High-voltage switchgear is a core component of power supply and distribution systems. Its safe and stable operation directly affects the reliability of the power grid and plays an irreplaceable role in ensuring the orderly conduct of normal economic production and social activities. Due to the compact internal structure of high-voltage switchgear and the impedance discontinuities at the connection points of various electrical components, these parts are prone to abnormal temperature rises due to contact resistance during long-term full-load operation. If this phenomenon is not monitored and addressed in a timely manner, it can further lead to insulation aging, component burning, and other faults. In severe cases, it can even induce large-scale power outages or fires, causing significant economic losses. Therefore, real-time and accurate temperature monitoring of key components within high-voltage switchgear is a crucial means of preventing temperature-related accidents and ensuring the long-term stable operation of equipment.

[0003] Currently, traditional temperature monitoring methods, such as thermocouple temperature measurement and infrared temperature measurement, have drawbacks such as requiring active power supply, weak anti-electromagnetic interference capability, and inconvenient installation and maintenance, making them difficult to adapt to the complex operating conditions of high-voltage switchgear. Passive temperature detection devices based on surface acoustic wave (SAW) technology have become a research hotspot in the field of high-voltage switchgear temperature measurement due to their advantages such as no power supply required, fast response speed, and strong anti-interference capability. However, existing SAW temperature detection devices mostly rely on the temperature-frequency characteristics of the piezoelectric material itself to achieve temperature measurement, which has problems such as insufficient sensitivity and limited temperature drift suppression effect; although some improved solutions drive the interdigital structure change through substrate deformation, the use of an integral rigid substrate and rigid piezoelectric layer makes it impossible to amplify the differentiated deformation effect and difficult to conform to the substrate deformation process, further limiting the improvement of sensor sensitivity.

[0004] For example, patent application CN110186588A discloses a temperature detection device based on a flexible surface acoustic wave (SAW) device, including a temperature signal acquisition unit, a signal conversion unit, a data processing unit, a signal transmission unit, and a signal receiving unit. The temperature signal acquisition unit is used to acquire temperature signals and employs a flexible SAW device. When the external temperature changes, the SAW transmission will be affected by the external temperature, forming SAW waves of different waveforms. The flexible SAW device includes an interdigital transducer, a reflective grating, a piezoelectric thin film, and a flexible substrate. The piezoelectric thin film is located on the flexible substrate, and the interdigital transducer and reflective grating are located on the piezoelectric thin film. A monitoring method for the temperature detection device based on a flexible SAW device is also provided. This scheme relies entirely on the inherent, globally uniform thermal expansion and temperature drift characteristics of the PDMS substrate and PVDF piezoelectric layer materials to achieve temperature measurement. Its sensitivity comes from the inherently weak temperature response of the materials. It lacks any mechanical structure to amplify temperature changes into significant local deformations, resulting in insufficient basic sensitivity. At the same time, its structure does not have effective stress isolation and strain self-compensation capabilities. Therefore, it has insufficient signal stability when facing mechanical interference, and its overall performance is inherently limited.

[0005] Patent application CN114335319A discloses a surface acoustic wave (SAW) sensor and its fabrication method, relating to the field of sensor technology. The SAW sensor and its fabrication method of this invention include a bonding layer, a metal layer, and a single-crystal piezoelectric thin film layer sequentially deposited on a silicon substrate, with interdigitated electrodes disposed on the single-crystal piezoelectric thin film layer. While this approach achieves localized amplification of thermal deformation and improves sensitivity through a cantilever beam structure, its structure of directly stacking a rigid silicon substrate with a brittle single-crystal AlN thin film introduces fundamental limitations. Specifically, due to the lack of stress buffering and interface tuning layers, the high stress generated internally by thermal mismatch has nowhere to dissipate, which not only exacerbates temperature drift but also leads to the accumulation of microscopic damage at the interface, causing significant mechanical hysteresis and poor deformation recovery, severely limiting long-term repeatability and reliability. The rigid structure is also difficult to integrate with flexible packaging, resulting in weak environmental adaptability. Furthermore, the bonding layer and the under-metal electrode layer (such as Mo) in this approach are designed to achieve the transfer and integration of the single-crystal piezoelectric thin film and serve as acoustic electrodes to improve the electromechanical coupling coefficient. These layer materials (such as brittle SiO2 and rigid, high-strength Mo) lack controllable plastic deformation capabilities and cannot effectively dissipate cyclic stress caused by the difference in thermal expansion coefficients between layers through their own deformation.

[0006] Therefore, how to develop a sensor that can amplify the differential deformation effect and improve sensitivity is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the shortcomings of the existing technology, this invention provides a passive temperature detection device and its preparation method. It can amplify the differential deformation effect and improve temperature detection sensitivity.

[0008] In a first aspect, the present invention provides a passive temperature detection device, comprising an insulating substrate, a functional layer, a flexible piezoelectric layer, and a surface acoustic wave sensor; The insulating substrate includes a fixing part and a deformation layer, the deformation layer is suspended and one end is fixed to the fixing part; the functional layer is at least partially located on the deformation layer; the flexible piezoelectric layer is located on the functional layer and is at least partially located in the overlapping area of ​​the deformation layer and the functional layer; the coefficients of thermal expansion of the deformation layer, the functional layer and the flexible piezoelectric layer increase in sequence. The surface acoustic wave sensor is disposed on a flexible piezoelectric layer. The surface acoustic wave sensor includes interdigital transducer electrodes, which are at least partially located in the overlapping region of the deformation layer, the functional layer and the flexible piezoelectric layer.

[0009] Furthermore, the fixing part includes a substrate layer, an insulating layer and a base layer stacked in sequence, with the base layer and the deformation layer being an integral structure.

[0010] Furthermore, the thickness of the substrate layer is 1~20μm, the thickness of the insulating layer is 0.5~2μm, and the thickness of the substrate layer is 100~600μm.

[0011] Furthermore, the fixing part is annular, and the deformation layer is suspended inside the annular part of the fixing part.

[0012] Furthermore, the surface acoustic wave sensor also includes a first reflective grating and a second reflective grating, with interdigitated transducer electrodes disposed between the first reflective grating and the second reflective grating.

[0013] Furthermore, the ratio of the thermal expansion coefficients α1 between the functional layer and the deformable layer, and the ratio of the thermal expansion coefficients α2 between the flexible piezoelectric layer and the functional layer, satisfy 0.4≤α2 / α1≤1.5, α2≥3.

[0014] Furthermore, the ratio of the thermal expansion coefficients α1 between the functional layer and the deformable layer, and the ratio of the thermal expansion coefficients α2 between the flexible piezoelectric layer and the functional layer, satisfy 0.45≤α2 / α1≤0.75, α2≥3.5.

[0015] Furthermore, the passive temperature detection device satisfies at least one of the following: 1) The deformation layer is made of monocrystalline silicon, the functional layer is made of aluminum, and the flexible piezoelectric layer is made of polyvinylidene fluoride; 2) The thickness of the flexible piezoelectric layer is greater than or equal to the thickness of the functional layer, and the thickness of the functional layer is greater than or equal to the thickness of the deformation layer.

[0016] Furthermore, the thickness of the functional layer gradually increases from the fixing part to the direction away from the fixing part, and the thickness range of the functional layer is 1μm~100μm.

[0017] Furthermore, the thickness ratio of the flexible piezoelectric layer to the functional layer is 1:1 to 3:1, and the thickness ratio of the functional layer to the deformation layer is 1:1 to 5:1.

[0018] Furthermore, the functional layer includes a first functional sub-layer, a second functional sub-layer, and a third functional sub-layer stacked sequentially. A portion of the first functional sub-layer covers and is disposed on the deformation layer, and another portion is disposed on the fixing part. The second functional sub-layer overlaps with the deformation layer and a portion of the first functional sub-layer. The third functional sub-layer overlaps with a portion of the second functional sub-layer, a portion of the first functional sub-layer, and a portion of the deformation layer away from the fixing part.

[0019] Furthermore, the thicknesses of the first functional sublayer, the second functional sublayer, and the third functional sublayer are 0.2μm~20μm, 0.3μm~30μm, and 0.5μm~50μm, respectively.

[0020] Furthermore, a grounding shield is provided on the insulating substrate, and the grounding shield is sleeved on the outside of the surface acoustic wave sensor.

[0021] Furthermore, the grounding shield is a rectangular frame with a side width of 100~150μm and a thickness of 180~220 nm, and each side is 60~80μm away from the flexible piezoelectric layer.

[0022] Furthermore, both the first and second reflective gratings have 15 to 25 gratings, and the interdigital transducer electrodes have 6 to 10 pairs. The distance between the interdigital transducer electrodes and the first and second reflective gratings is 30 to 80 μm.

[0023] Furthermore, the surface acoustic wave sensor uses the 915MHz or 2.45GHz ISM (Industrial, Scientific and Medical Radio Bands) frequency band.

[0024] Secondly, the present invention also provides a method for preparing the above-mentioned passive temperature detection device, comprising: S1. Polish the upper surface of the insulating substrate blank and pre-define the fixing area and the deformation layer area. Deposit a functional layer on the upper surface of the insulating substrate blank, and the functional layer is at least partially located in the deformation layer area. S2. Using the inner contour of the fixed part and the outer contour of the deformation layer as a reference, the upper surface of the insulating substrate blank is etched to obtain part of the inner contour of the fixed part and the outer contour of the deformation layer. S3. A flexible piezoelectric layer and a surface acoustic wave sensor are formed sequentially on the upper surface of the functional layer by deposition and etching. S4. Etch the lower surface of the insulating substrate blank away from the functional layer to obtain the inner surface of the fixing part and the bottom surface of the deformation layer, and fix one end of the deformation layer to the fixing part, while the other end is suspended relative to the fixing part.

[0025] Further, in step S1, a functional layer is deposited on the upper surface of the insulating substrate preform, comprising: Ar was used as the sputtering gas, Al was used as the target material, and the vacuum level was ≤5×10⁻⁶. -3 Pa deposits Al metal with a thickness of 1 μm to 100 μm to obtain the initial functional layer; Photoresist is coated on the surface of the initial functional layer, and the photoresist is exposed and developed using a photomask. The functional layer was obtained by inductively coupled plasma etching using a Cl2 / BCl3 mixed gas to remove the photoresist.

[0026] Furthermore, a flexible piezoelectric layer is formed on the upper surface of the functional layer by deposition and etching, including: A spin-coating process is used on the surface of the functional layer to spin-coat polyvinylidene fluoride with a solution mass fraction of 10% to 20% and a thickness of 1μm to 300μm at a rotation speed of 3000 to 6000 rpm to obtain an initial flexible piezoelectric layer. Photoresist is then coated on the initial flexible piezoelectric layer, and the photoresist is exposed and developed using a mask. The initial flexible piezoelectric layer is then etched and the photoresist is removed to obtain the final flexible piezoelectric layer.

[0027] Furthermore, after obtaining the functional layer, the following optimization processing steps are also included: The functional layers are flattened. The planarized functional layer is placed in a vacuum of 1×10⁻⁶. -4 ~5×10 -5 Under the environment of Pa, multiple replacements are performed using a protective gas; First-stage heat treatment: The functional layer is heated to 180℃~220℃ and held for 25~35 minutes; Second-stage heat treatment: continue heating to 350℃~400℃ and hold for 80~100min. During the holding process, hydrogen is introduced to assist reduction and the pressure is dynamically adjusted to 50~100Pa, 10~40Pa, and 40~60Pa respectively. The total time for holding for 80~100min is the time for dynamically adjusting the pressure. The functional layer is cooled to room temperature to obtain the optimized functional layer.

[0028] Furthermore, hydrogen-assisted reduction specifically includes: Hydrogen gas at a pressure of 1 to 100 Pa is introduced at a temperature of 350℃ to 400℃.

[0029] Furthermore, dynamic pressure control specifically includes: Adjust the hydrogen pressure to 50-100 Pa and maintain it for 20-40 minutes; Adjust the hydrogen pressure to 10-40 Pa and maintain it for 20-40 minutes; Adjust the hydrogen pressure to 40-60 Pa and maintain it for 30-50 minutes.

[0030] By adjusting the hydrogen pressure in stages during the annealing process, the reduction reaction rate between hydrogen and the Al layer surface can be effectively controlled, promoting uniform nucleation and preferred growth of grains. At the same time, the dynamic atmosphere generated by the pressure change can be used to more fully eliminate internal residual stress and enhance the interfacial adhesion between the Al layer and the insulating substrate and the flexible piezoelectric layer, thereby obtaining a functional layer with high density, few lattice defects and stable mechanical properties.

[0031] Furthermore, the functional layer is gradually cooled to room temperature, including: cooling from 350℃~400℃ to 180℃~220℃ at a rate of 2℃ / min and holding for 25~35 minutes; then cooling to room temperature at a rate of 5℃ / min.

[0032] By controlling the cooling rate (i.e., temperature gradient), the thermal stress generated by the difference in thermal expansion coefficients of the hierarchical structure can be released slowly and evenly, avoiding local stress concentration, interface cracking or layer peeling caused by rapid cooling. This ensures that the cantilever beam formed in the end can maintain accurate geometric reset after repeated thermal cycles, thereby greatly improving the long-term working stability and repeatability reliability of the sensor.

[0033] Furthermore, the above-mentioned passive temperature detection device, or the passive temperature detection device obtained by the above preparation method, can be used for switchgear temperature detection applications.

[0034] The passive temperature detection device and its preparation method provided by this invention have at least the following beneficial effects: (1) The layered structure of the insulating substrate and the coefficient of thermal expansion can achieve efficient transmission of thermomechanical deformation and synergistic enhancement of strain amplification. The deformation layer of the insulating substrate responds to temperature changes with a low coefficient of thermal expansion, driving the cantilever to produce foundation bending; the intermediate functional layer, as a transition layer with a moderate coefficient of thermal expansion, can buffer the thermal stress between the upper and lower layers to avoid interface failure, and can also effectively transmit the deformation of the deformation layer upwards; while the top flexible piezoelectric layer can generate strong additional tensile or compressive strain under the constraint of the lower layer through its maximum coefficient of thermal expansion, thereby significantly amplifying the overall deformation amplitude at the end of the cantilever beam. This structure can make small temperature changes be converted into significant mechanical displacements step by step, and then efficiently converted into electrical signals by the flexible piezoelectric layer, which greatly improves the thermal response sensitivity and output signal strength of the sensor while ensuring the reliability of the multilayer structure interface.

[0035] (2) By precisely matching the thermal expansion coefficients between the flexible piezoelectric layer, the functional layer and the deformation layer, the thermal bending deformation of the cantilever beam can be significantly amplified by utilizing the high expansion characteristics of the flexible piezoelectric layer while ensuring that the interface stress is controllable. This transforms minute temperature changes into large frequency shifts, achieving a balance between high sensitivity and high reliability. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the structure of a passive temperature detection device provided by the present invention; Figure 2 A cross-sectional view along line AA of a passive temperature detection device provided in a certain embodiment of the present invention; Figure 3 A cross-sectional view along the BB direction of a passive temperature detection device provided in a certain embodiment of the present invention; Figure 4 A flowchart illustrating a method for preparing a passive temperature detection device provided by the present invention; Figure 5 This is a schematic diagram illustrating the fabrication of a passive temperature detection device provided by the present invention.

[0037] Explanation of reference numerals in the attached figures: 1-Insulating substrate, 11-Substrate layer, 12-Insulating layer, 13-Base layer, 14-Deformation layer, 2-Functional layer, 3-Flexible piezoelectric layer, 4-Surface acoustic wave sensor, 41-Interdigital transducer electrode, 42-First reflective grating, 43-Second reflective grating, 44-First PAD, 45-Second PAD. Detailed Implementation

[0038] To better understand the above technical solutions, a detailed description of the solutions will be provided below in conjunction with the accompanying drawings and specific embodiments. Obviously, the described embodiments are merely some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] The terminology used in the embodiments of this invention is for the purpose of describing particular embodiments only and is not intended to limit the invention. The singular forms “a,” “the,” and “the” as used in the embodiments of this invention and the appended claims are also intended to include the plural forms, and “multiple” generally includes at least two unless the context clearly indicates otherwise.

[0040] It should also be noted that the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that an article or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such an article or device. Without further limitation, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device that includes said element.

[0041] like Figures 1 to 3 As shown, the present invention provides a passive temperature detection device, including an insulating substrate 1, a functional layer 2, a flexible piezoelectric layer 3, and a surface acoustic wave sensor 4; The insulating substrate 1 includes a fixing part and a deformation layer 14. The deformation layer 14 is suspended and one end is fixed to the fixing part. The functional layer 2 is disposed on the insulating substrate 1 and is at least partially located on the deformation layer 14. The flexible piezoelectric layer 3 is disposed on the functional layer 2 and is at least partially located in the overlapping area of ​​the deformation layer 14 and the functional layer 2. The coefficients of thermal expansion of the deformation layer 14, the functional layer 2, and the flexible piezoelectric layer 3 increase sequentially. The surface acoustic wave sensor 4 is disposed on the flexible piezoelectric layer 3. The surface acoustic wave sensor 4 includes an interdigital transducer electrode 41, which is at least partially located in the overlapping area of ​​the deformable layer 14, the functional layer 2 and the flexible piezoelectric layer 3.

[0042] Functional layer 2 is located in the middle of the upper surface of insulating substrate 1. Utilizing the difference in thermal expansion coefficients between it and the top deformation layer 14 of insulating substrate 1, combined with the cantilever beam structure, it amplifies the temperature-induced differential deformation and stably transmits the deformation to the upper surface acoustic wave sensor 4, providing a structural basis for adjusting the interdigital spacing of the interdigital transducer electrodes 41. The surface acoustic wave sensor 4, located on the upper surface of functional layer 2, achieves passive conversion and detection of temperature signals to electrical signals through piezoelectric conversion and interdigital spacing response to temperature deformation. Specifically, flexible piezoelectric layer 3 is located on the upper surface of functional layer 2. Its flexible nature conforms to the deformation of functional layer 2 and efficiently transmits stress. Simultaneously, it achieves mutual conversion between electrical signals and surface acoustic wave signals through positive and negative piezoelectric effects. Combined with the resonant frequency shift caused by changes in interdigital spacing, it completes the conversion of temperature signals to electrical signals. Interdigital transducer electrodes 41, located on the upper surface of flexible piezoelectric layer 3, are responsible for exciting and receiving surface acoustic waves and achieving signal reconstruction. Their interdigital spacing changes regularly with the deformation of functional layer 2, thereby altering the propagation characteristics of surface acoustic waves.

[0043] The fixing part may include a substrate layer 11, an insulating layer 12, and a base layer 13 stacked sequentially, with the base layer 13 and the deformation layer 14 forming an integral structure. The substrate layer 11, base layer 13, and deformation layer 14 are all made of Si, and the insulating layer 12 is made of SiO2. Because the base layer 13 and deformation layer 14 are integrally formed, this overall structure constructs a precision sensing platform with "mechanical isolation, thermal decoupling, and electroacoustic integration." The substrate layer 11 provides robust mechanical support and a packaging interface; the insulating layer 12, as a key decoupling layer, achieves stress buffering, thermal isolation, and etching stoppage for cantilever release; the top base layer 13 forms a highly sensitive cantilever beam structure and serves as a flat substrate for depositing piezoelectric layers and fabricating interdigital transducers. The synergy of these three layers allows the added piezoelectric functional layer 2 to operate efficiently in a low-stress, low-thermal-distance, and precisely mechanically controllable environment, ultimately achieving highly sensitive, highly stable, and fast-response surface acoustic wave sensing of external physical quantities (such as temperature).

[0044] The fixing part is annular, with the deformation layer 14 suspended inside the annular part. This annular structure, together with the internal deformation layer 14, achieves ultimate mechanical decoupling and thermal isolation. Specifically, the annular frame provides a stable and symmetrical anchoring boundary for the cantilever beam, effectively suppressing the direct transmission of external vibrations and installation stresses. Simultaneously, the cantilever beam body is completely suspended within the annular cavity, significantly cutting off its heat conduction path with the underlying substrate 11, thus significantly enhancing the cantilever beam structure's response sensitivity and speed to local temperature changes. This structure forms a highly sensitive sensing unit, capable of more accurately and stably converting target physical quantities into pure mechanical deformation signals in complex environments.

[0045] In practical applications, the thickness of the substrate layer 13 is 1–20 μm, the thickness of the insulating layer 12 is 0.5–2 μm, and the thickness of the substrate layer 11 is 100–600 μm. The substrate layer 13 is the core structural layer of the cantilever beam structure and the platform supporting the interdigital transducers. Its thickness directly affects the stiffness, resonant frequency, and thermomechanical sensitivity of the cantilever beam. With a thickness of 1–20 μm, the substrate layer 13 allows the cantilever beam to be flexible and undergo significant bending deformation under external temperature or stress, thereby sensitively modulating the surface acoustic wave characteristics by changing the strain state or effective spacing of the interdigital transducers above it. As the substrate for the interdigital transducers, its single-crystal characteristics ensure surface flatness, which is beneficial for the high-quality deposition and patterning of subsequent piezoelectric layers. The insulating layer 12 can realize a multifunctional decoupling and isolation layer for high-performance cantilever beam sensors. It can serve as a perfect etch stop layer, allowing precise stopping when deeply etching the substrate silicon from the back side, thus reliably releasing the cantilever beam structure defined by the silicon substrate layer 13. Secondly, as a stress buffer layer, it effectively isolates the thermal expansion mismatch stress between the substrate layer 11 and the base layer 13, significantly reducing residual stress and thermal hysteresis in the cantilever beam, ensuring the long-term stability and repeatability of the sensing signal. Finally, it can serve as a thermal isolation layer; its low thermal conductivity significantly reduces heat conduction between the cantilever beam region and the substrate layer 11, enabling the cantilever beam to respond more quickly and independently to local temperature changes at the measured point, improving the sensitivity and response speed of thermal sensing. The substrate layer 11 serves as the mechanical support and packaging interface for the entire chip. Its thickness of 100~600μm provides the necessary structural strength, facilitating chip manufacturing, transportation, and packaging. By deeply etching from the back side of this layer, a cavity can be formed, thereby releasing the upper base layer 13 and forming a freely movable cantilever beam structure. Simultaneously, the thicker substrate also acts as a heat sink to a certain extent, helping to stabilize the overall operating temperature baseline of the device. However, since the thermal impact can be effectively isolated by the intermediate insulating layer 12, it will not interfere with the sensitive detection function on the cantilever beam.

[0046] The surface acoustic wave sensor 4 also includes a first reflective grating 42 and a second reflective grating 43, with an interdigital transducer electrode 41 positioned between the first reflective grating 42 and the second reflective grating 43. A highly efficient acoustic resonant cavity can be constructed on the surface of the cantilever beam using the first reflective grating 42, the interdigital transducer electrode 41, and the second reflective grating 43. Specifically, the first reflective grating 42 and the second reflective grating 43 on both sides can reflect and confine the surface acoustic wave energy excited by the interdigital transducer electrode 41 to the central region, forming a stable standing wave resonance. This significantly improves the quality factor (Q value) and energy density of the resonator, allowing the minute deformation or strain energy of the cantilever beam caused by temperature changes to be sensitively detected as a significant frequency shift by modulating the boundary conditions of the resonant cavity (such as sound velocity and stress distribution). In addition, two pads (first PAD44 and second PAD45) are provided on the interdigital transducer electrode 41, which can be used as signal terminals and ground terminals respectively, to realize independent and low-loss electrical input / output interfaces: the signal terminal is used to connect an external reader to excite and receive radio frequency signals, while the ground terminal provides a stable potential reference for the interdigital transducer electrode 41 and helps to shield common-mode noise. Together, they ensure electroacoustic conversion efficiency and signal integrity.

[0047] The ratio of the thermal expansion coefficients α1 between functional layer 2 and deformation layer 14, and the ratio of the thermal expansion coefficients α2 between flexible piezoelectric layer 3 and functional layer 2, satisfy 0.4 ≤ α2 / α1 ≤ 1.5, α2 ≥ 3. Preferably, the ratio of the thermal expansion coefficients α1 between functional layer 2 and deformation layer 14, and the ratio of the thermal expansion coefficients α2 between flexible piezoelectric layer 3 and functional layer 2, satisfy 0.45 ≤ α2 / α1 ≤ 0.75, α2 ≥ 3.5; wherein the material of deformation layer 14 is monocrystalline silicon, the material of functional layer 2 is aluminum, and the material of flexible piezoelectric layer 3 is polyvinylidene fluoride. By precisely controlling the ratio of the thermal expansion coefficients of each layer, this cantilever beam structure can achieve dual optimization of stress buffering and deformation amplification in thermomechanical response. Among them, the expansion coefficient of functional layer 2 is an intermediate layer between deformation layer 14 and flexible piezoelectric layer 3, which can gradually mitigate the interfacial mismatch stress caused by temperature changes, significantly reduce the risk of interlayer shear, and ensure the long-term reliability of the temperature detection device under thermal cycling. Furthermore, the flexible piezoelectric layer 3 exhibits higher thermal expansion characteristics than the deformation layer 14 and the functional layer 2. Under the constraint of the functional layer 2 and the deformation layer 14, it generates strong directional thermal strain, significantly amplifying the overall thermal bending deformation of the cantilever beam and efficiently coupling it to the interdigital transducer electrodes 41 on the surface. Ultimately, minute temperature changes can be converted into significant surface acoustic wave frequency shifts, greatly improving the sensor's thermal response sensitivity and signal strength while maintaining structural integrity and durability. Simultaneously, by precisely controlling the ratio of thermal expansion coefficients between layers, the inherent contradiction between sensitivity and reliability can be resolved. Specifically, if the expansion coefficients of each layer are too close, the flexible piezoelectric layer 3 cannot generate sufficient additional strain, resulting in a weak deformation amplification effect and low sensitivity; if the difference in expansion coefficients is too large, the interlayer thermal stress will increase sharply, easily leading to interface peeling or film cracking, severely damaging the device's durability. In this embodiment, the functional layer 2, with its moderate expansion coefficient, forms an optimized stress transition and strain transfer bridge between the deformation layer 14 and the flexible piezoelectric layer 3. This fully stimulates the high expansion characteristics of the flexible piezoelectric layer 3 while ensuring structural integrity, thus achieving a balance between high sensitivity and high reliability.

[0048] The thickness of functional layer 2 gradually increases from the fixed part to the direction away from the fixed part. The gradient thickness of functional layer 2 can achieve synergistic optimization of spatial stiffness control and thermomechanical coupling. The functional layer 2, which gradually thickens from the root of the cantilever beam (the end where the deformation layer 14 connects to the base layer 13) to the end (the suspended end of the deformation layer 14 away from the base layer 13), makes the equivalent stiffness of the cantilever beam gradually decrease along the length direction. Specifically, in the root region near the deformation layer 14, the thinner functional layer 2 can maintain the flexibility of this region, so that it can fully transmit the interfacial stress caused by the thermal deformation of the deformation layer 14 and avoid fatigue or cracking caused by stress concentration. In the front to the end of the cantilever beam, the gradually thickening functional layer 2 can significantly enhance the axial thermal expansion driving force of the local section and form a stronger strain coupling with the expansion of the upper flexible piezoelectric layer 3, thereby amplifying the thermally induced bending deformation at the free end. The thickness design of this functional layer 2 improves the overall thermomechanical sensitivity of the cantilever beam and optimizes the vibration modes and stress distribution. Ultimately, this enables the interdigital transducer electrode 41 to detect more significant and stable surface acoustic wave frequency shifts, while ensuring the long-term reliability of the overall structure.

[0049] In practical applications, functional layer 2 may include a first functional sub-layer, a second functional sub-layer, and a third functional sub-layer stacked sequentially. A portion of the first functional sub-layer covers and is disposed on the deformation layer 14, while another portion is disposed on the fixing part. The second functional sub-layer overlaps with the deformation layer 14 and a portion of the first functional sub-layer. The third functional sub-layer overlaps with a portion of the second functional sub-layer, a portion of the first functional sub-layer, and a portion of the deformation layer 14 away from the fixing part. The thicknesses of the first, second, and third functional sub-layers are 0.2μm~20μm, 0.3μm~30μm, and 0.5μm~50μm, respectively. The portion where the first functional sublayer is firmly bonded to the fixed part can serve as a stress transition zone, smoothly dispersing concentrated stress from the fixed end and improving connection reliability. The portion of the second functional sublayer that does not overlap with the third functional sublayer can maintain local flexibility together with the overlapping first functional sublayer, allowing the cantilever to bend freely while effectively transmitting the thermal deformation of the substrate. The cantilever end where the first, second, and third functional sublayers overlap can significantly enhance the driving force of cross-sectional thermal expansion, synergistically amplifying the deformation of the free end with the flexible piezoelectric layer 3. This integrated structure can ensure structural integrity while forming a continuous gradient distribution of stiffness and thermomechanical coupling efficiency along the cantilever length direction, thereby synergistically improving the sensor's mechanical durability, thermal response sensitivity, and output signal stability.

[0050] The thickness of the deformation layer 14, the average thickness of the functional layer 2, and the average thickness of the flexible piezoelectric layer 3 increase progressively, with the thickness of the functional layer 2 ranging from 1 μm to 100 μm. Preferably, the thickness ratio of the functional layer 2 to the deformation layer 14 is 1:1 to 5:1, and the thickness ratio of the flexible piezoelectric layer 3 to the functional layer 2 is 1:1 to 3:1. This progressively thicker stacked design enables functional gradient integration and performance optimization of mechanical support, stress regulation, and electroacoustic conversion. The deformation layer 14 provides the necessary initial stiffness and thermal deformation driving foundation for the cantilever; the increased thickness of the functional layer 2 enhances its effectiveness as a thermal stress buffer and deformation transfer medium, mitigating interface mismatch while promoting the transfer of thermal strain to the upper layers; the thickest flexible piezoelectric layer 3 maximizes its piezoelectric active volume, significantly improving charge output and surface acoustic wave excitation efficiency per unit deformation. Within a limited space with a total thickness on the order of micrometers, the thickness is designed to vary stepwise, which synergistically controls the mechanical response, thermal coupling efficiency, and electroacoustic gain of the cantilever, thereby achieving a comprehensive improvement in sensor sensitivity, linearity, and signal-to-noise ratio while ensuring structural stability.

[0051] A grounding shield is provided on the insulating substrate 1, and the grounding shield is fitted over the outside of the surface acoustic wave sensor 4. In practical applications, the grounding shield is a rectangular frame with a side width of 100-150 μm and a thickness of 180-220 nm, and each side is 60-80 μm away from the flexible piezoelectric layer 3. The first reflective grid 42 and the second reflective grid 43 each have 15-25 grid bars, and the interdigital transducer electrodes 41 have 6-10 pairs, with the distance between the interdigital transducer electrodes 41 and the first reflective grid 42 and the second reflective grid 43 both being 30-80 μm. The temperature detection device is located inside the switch cabinet, and the surface acoustic wave sensor 4 uses the 915 MHz or 2.45 GHz ISM band. The coordinated design of the grounding shield and the surface acoustic wave sensor 4 can achieve comprehensive optimization of efficient shielding, compact resonance, and high-frequency anti-interference. Specifically, a rectangular grounding shield with a side width of 100-150μm, a thickness of 180-220nm, and a spacing of 60-80μm from the flexible piezoelectric layer 3 can effectively suppress environmental electromagnetic coupling while minimizing the parasitic capacitance effect on the surface acoustic wave sensor 4 through spacing control. The interdigital transducer electrode 41, composed of 6-10 pairs of electrodes, works in conjunction with the first reflective grid 42 and the second reflective grid 43, each with 15-25 grid strips on both sides, forming a compact resonant structure with a short cavity pitch of 30-80μm. This ensures effective feedback of acoustic wave energy while adapting to high-frequency propagation characteristics. The setting of the 915MHz or 2.45GHz ISM band takes into account both the low sensitivity to parasitic parameters and strong anti-interference capability of the high-frequency band. Ultimately, this enables the temperature detection device to have high signal integrity, sensitive resonant response, and reliable radio compatibility in complex electromagnetic environments (switch cabinet environments).

[0052] Working principle: During operation, the cantilever beam heterogeneous structure of deformation layer 14-functional layer 2-flexible piezoelectric layer 3 senses the temperature change inside the switch cabinet. Due to the significant difference in the coefficient of thermal expansion between functional layer 2 and the top deformation layer 14 of the insulating substrate 1, they undergo differential thermal expansion or contraction, causing bending deformation at the cantilever beam's suspended end. This deformation is transmitted through functional layer 2 to the upper flexible piezoelectric layer 3, causing the flexible piezoelectric layer 3 to deform synchronously and efficiently transmit stress. This, in turn, causes a change in the spacing of the interdigital transducer electrodes 41 integrated on its surface, altering the working characteristics of the resonant cavity formed by the interdigital transducer electrodes 41 and the two side reflective grids (first reflective grid 42 and second reflective grid 43). External reading and writing devices emit radiation... The frequency excitation signal, after being received by the interdigital transducer electrode 41, is converted into a surface acoustic wave (SAW) through the inverse piezoelectric effect. Under the directional reflection of the reflector grating, the SAW propagates stably between the interdigital transducer electrode 41 and the reflector grating. Temperature-induced changes in the interdigital spacing alter the propagation speed and wavelength of the SAW, causing a regular shift in its resonant frequency. This shifted SAW is then converted into a radio frequency (RF) signal via the direct piezoelectric effect and fed back to the external reading / writing device. The external device demodulates the received signal, extracts the resonant frequency shift, and utilizes the quantitative mapping relationship between temperature and resonant frequency to achieve real-time temperature measurement within the switchgear. Furthermore, temperature changes trigger a series of chain reactions, including heterogeneous structural deformation, interdigital spacing adjustment, and changes in SAW propagation characteristics. These multi-dimensional changes ultimately manifest as a regular shift in the resonant frequency. Therefore, without needing to trace intermediate process variables, temperature measurement within the switchgear can be achieved simply by establishing and relying on the quantitative mapping relationship between temperature and frequency shift.

[0053] like Figure 4 and Figure 5 As shown, the present invention also provides a method for preparing the above-mentioned passive temperature detection device, comprising: S1. Polish the upper surface of the insulating substrate blank and pre-define the fixing area and the deformation layer area. Deposit a functional layer on the upper surface of the insulating substrate blank, and the functional layer is at least partially located in the deformation layer area. S2. Using the inner contour of the fixed part and the outer contour of the deformation layer as a reference, the upper surface of the insulating substrate blank is etched to obtain part of the inner contour of the fixed part and the outer contour of the deformation layer. S3. A flexible piezoelectric layer and a surface acoustic wave sensor are formed sequentially on the upper surface of the functional layer by deposition and etching; wherein, a flexible piezoelectric layer is obtained by spin coating process on the upper surface of the functional layer; and a surface acoustic wave sensor is obtained by DC magnetron sputtering and / or electron beam evaporation deposition and etching on the flexible piezoelectric layer. S4. Etch the lower surface of the insulating substrate blank away from the functional layer to obtain the inner surface of the fixing part and the bottom surface of the deformation layer, and fix one end of the deformation layer to the fixing part, while the other end is suspended relative to the fixing part.

[0054] Further, the functional layer material is Al; in step S1, a functional layer is deposited on the surface of the insulating substrate preform, comprising: Ar was used as the sputtering gas, Al was used as the target material, and the vacuum level was ≤5×10⁻⁶. -3 Pa deposits Al metal with a thickness of 1μm to 100μm to obtain an initial functional layer; photoresist is coated on the surface of the initial functional layer, and the photoresist is exposed and developed using a mask; inductively coupled plasma etching is performed using a Cl2 / BCl3 mixed gas to remove the photoresist and obtain the final functional layer.

[0055] Through high vacuum (≤5×10) -3 Magnetron sputtering of 1-100 μm Al layers ensures high purity and density of the functional layer. Combined with photolithography patterning and Cl2 / BCl3-based inductively coupled plasma etching, high-precision, high-selectivity Al microstructure processing can be achieved. After etching, the resist is thoroughly removed, resulting in a final functional layer with steep sidewalls, precise linewidth, and a clean surface, providing an ideal stress buffer and thermal conductivity interface for subsequent multilayer heterogeneous integration.

[0056] Furthermore, a flexible piezoelectric layer is formed on the upper surface of the functional layer by deposition and etching, including: A spin-coating process is used on the surface of the functional layer to spin-coat polyvinylidene fluoride with a solution mass fraction of 10% to 20% and a thickness of 1μm to 300μm at a rotation speed of 3000 to 6000 rpm to obtain an initial flexible piezoelectric layer. Photoresist is coated on the initial flexible piezoelectric layer, and the photoresist is exposed and developed using a mask. The initial flexible piezoelectric layer is etched and the photoresist is removed to obtain a flexible piezoelectric layer under predetermined conditions.

[0057] By employing a spin-coating process at 3000~6000rpm and a solution mass fraction of 10%~20%, polyvinylidene fluoride (PVDF) films with a thickness of 1~300μm and excellent uniformity can be obtained on the surface of the functional layer. Through photolithography patterning and subsequent etching, the micron-level pattern of the flexible piezoelectric layer can be precisely constructed. While retaining the good piezoelectric properties of PVDF, the cleanliness and bonding strength of the interface between the flexible piezoelectric layer and the underlying functional layer are ensured, providing high-quality piezoelectric functional units for high-sensitivity acoustic excitation and strain detection.

[0058] Furthermore, after obtaining the functional layer, the following optimization processing steps are also included: The functional layers are flattened. The planarized functional layer is placed in a vacuum of 1×10⁻⁶.-4 ~5×10 -5 Under the environment of Pa, multiple replacements are performed using a protective gas; First-stage heat treatment: The functional layer is heated to 180℃~220℃ and held for 25~35 minutes; Second-stage heat treatment: continue heating to 350℃~400℃ and hold for 80~100min. During the holding process, hydrogen is introduced to assist reduction and the pressure is dynamically adjusted to 50~100Pa, 10~40Pa, and 40~60Pa respectively. The functional layer is cooled to room temperature to obtain the optimized functional layer.

[0059] This segmented vacuum annealing, through a high vacuum environment, multi-stage temperature control, hydrogen reduction, and dynamic pressure regulation, can more thoroughly eliminate residual stress in the functional layer, refine grains, and significantly enhance the interfacial adhesion between the functional layer and the upper and lower layers (deformation layer and flexible piezoelectric layer). This ensures that the cantilever beam can accurately recover its initial state after repeated thermal cycling and mechanical deformation, fundamentally improving the repeatability and detection stability of the sensor during long-term operation.

[0060] Furthermore, hydrogen-assisted reduction specifically includes: Hydrogen gas at a pressure of 1 to 100 Pa is introduced at a temperature of 350℃ to 400℃.

[0061] Hydrogen reacts with oxygen that may be adsorbed on the surface of newly exposed aluminum atoms to generate water vapor. It can also react with trace amounts of oxygen or water vapor in the environment to create a strongly reducing environment, preventing further oxidation of aluminum at high temperatures and providing a clean surface for the recrystallization and diffusion of aluminum atoms.

[0062] Furthermore, dynamic pressure control specifically includes: Adjust the hydrogen pressure to 50-100 Pa and maintain it for 20-40 minutes; Adjust the hydrogen pressure to 10-40 Pa and maintain it for 20-40 minutes; Adjust the hydrogen pressure to 40-60 Pa and maintain it for 30-50 minutes.

[0063] This phased adjustment of hydrogen pressure effectively controls the reduction reaction rate between hydrogen and the Al layer surface, promoting uniform nucleation and preferential growth of grains. Simultaneously, the dynamic atmosphere created by pressure changes more effectively eliminates residual internal stress and enhances the interfacial adhesion between the Al layer and the insulating substrate and flexible piezoelectric layer, resulting in a functional layer with high density, few lattice defects, and stable mechanical properties. Specifically, adjusting the hydrogen pressure to 50-100 Pa in the initial heat preservation stage enhances hydrogen mass transport, allowing it to diffuse more effectively to the grain boundaries and interfaces of the aluminum film for cleaning and reduction reactions. Adjusting the hydrogen pressure to 10-40 Pa in the middle heat preservation stage removes water vapor (H2O) generated in the early reactions and other impurity gases released from the film (such as residual O2, Ar, etc.), preventing their re-adsorption or reaction. Adjusting the hydrogen pressure to 40-60 Pa in the later heat preservation and cooling stages maintains a sufficiently reducing atmosphere while ensuring the purity of the gas within the cavity, and provides a controllable environment for thermal stress and gas desorption during the cooling process.

[0064] Furthermore, the functional layer is gradually cooled to room temperature, including: cooling from 350℃~400℃ to 180℃~220℃ at a rate of 2℃ / min and holding for 25~35 minutes; then cooling to room temperature at a rate of 5℃ / min.

[0065] By controlling the cooling rate (i.e., temperature gradient), the thermal stress generated by the difference in thermal expansion coefficients of the layered structure can be released slowly and uniformly, avoiding local stress concentration, interface cracking, or layer delamination caused by rapid cooling. This ensures that the final cantilever beam maintains accurate geometric repositioning after repeated thermal cycling, thereby significantly improving the long-term operational stability and repeatability reliability of the sensor. Specifically, the first stage involves a slow cooling rate of 2℃ / min from 350~400℃ to 180~220℃ and holding at that temperature. This allows the intrinsic stress generated by the Al layer after high-temperature deposition and the thermal mismatch stress at the interface with the insulating substrate to be fully and uniformly released. Simultaneously, it promotes the preferential growth of Al grains and grain boundary stability, preventing warping or cracking due to stress concentration. The second stage involves a faster cooling rate of 5℃ / min to room temperature. This improves process efficiency while maintaining the optimized grain structure. Furthermore, the rapid passage through the low-temperature zone suppresses potential impurity adsorption or surface oxidation, ensuring the cleanliness and interfacial activity of the Al layer surface. This provides an ideal stress matching and adhesion foundation for the subsequent high-quality deposition of the flexible piezoelectric layer.

[0066] In practical application scenarios, such as Figure 5 As shown, the preparation of the passive temperature detection device is specifically as follows: (a) An insulating substrate preform is used as the substrate to provide mechanical support and electrical insulation for subsequent devices. It includes a top silicon layer, a buried oxide layer (insulating layer), and a substrate silicon layer. The surface is polished to meet the requirements of subsequent thin film deposition. (b) An Al metal layer is deposited on the front side of the substrate by DC magnetron sputtering. The target material is a high-purity Al target, and the cavity vacuum degree is ≤5×10⁻⁶. -3 Pa, sputtering gas is Ar, deposition thickness is about 1μm~100μm; photoresist is coated on Al metal layer surface, photoresist is exposed and developed using a mask, and then inductively coupled plasma (ICP) etching is performed on metal layer using Cl2 / BCl3 mixed gas. After etching, residual photoresist is removed to complete the definition of the initial functional layer; then chemical mechanical planarization (CMP) is performed on the surface of functional layer to ensure that the surface flatness meets the requirements of subsequent film deposition. (c) Photoresist is applied to the front side of the substrate obtained in step (b). Using the outer contour of the Al functional layer as the alignment reference, a concave cavity region is defined by exposure and development, which is surrounded by the inner contour of the fixed part and the outer contour of the deformation layer. Then, ICP etching is performed using SF6 / O2 mixed gas. The etching depth is controlled to the surface of the buried oxide layer by endpoint detection. Finally, the residual photoresist is removed to form the concave cavity. (d) Polyvinylidene fluoride (PVDF) flexible piezoelectric material is deposited on the surface of the functional layer obtained in step (c) using a spin coating process. The solution mass fraction is 10%~20%, the spin coating speed is 3000~6000 rpm, and the spin coating thickness is about 1μm~300μm. Photoresist is coated on the surface of the flexible piezoelectric layer, and the photoresist is exposed and developed using a mask. Then the flexible piezoelectric layer is etched. After the etching is completed, the residual photoresist is removed to complete the preparation of the flexible piezoelectric layer. (e) A molybdenum (Mo) metal layer is deposited on the surface of the flexible piezoelectric layer obtained in step (d) by DC magnetron sputtering. The target material is a high-purity Mo target, and the cavity vacuum degree is ≤5×10⁻⁶. -3 Pa, pre-sputter for 5-8 min, the sputtering gas is high purity Ar; coat with photoresist and pattern it through exposure and development process, then etch the molybdenum metal layer to prepare the interdigital transducer electrode structure, the first reflective grating and the second reflective grating. After etching, remove the residual photoresist to complete the patterning of the surface acoustic wave device. (f) Photoresist is coated on the surface of the flexible piezoelectric layer after step (e), and patterned by photolithography to expose the pre-defined PAD corresponding area; then, a gold (Au) metal layer is deposited in this area by electron beam evaporation; the remaining photoresist and the metal layer on its surface are removed by a stripping process to obtain the first PAD and the second PAD; (g) Coat the back of the substrate obtained in step (f) with photoresist, and use a mask to expose and develop the photoresist to define a rectangular cavity region, ensuring that the region is completely overlapped with the front concave cavity in the vertical direction; then etch the substrate silicon down to the top layer Si to achieve the connection between the front and back cavities, and finally remove the residual photoresist to form the back rectangular cavity (the rectangular cavity + concave cavity form a ring structure of the insulating substrate).

[0067] The above-mentioned passive temperature detection device, or the passive temperature detection device obtained by the above preparation method, is used for switchgear temperature detection.

[0068] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention. Clearly, those skilled in the art can make various alterations and modifications to the invention without departing from its spirit and scope. Thus, if these modifications and modifications of the invention fall within the scope of the claims and their equivalents, the invention is also intended to include these modifications and modifications.

Claims

1. A passive temperature detection device, characterized in that, Includes an insulating substrate, a functional layer, a flexible piezoelectric layer, and a surface acoustic wave sensor; The insulating substrate includes a fixing part and a deformation layer, wherein the deformation layer is suspended and one end is fixed to the fixing part; The functional layer is at least partially located on the deformation layer, and the flexible piezoelectric layer is disposed on the functional layer and is at least partially located in the overlapping region of the deformation layer and the functional layer; The coefficients of thermal expansion of the deformation layer, functional layer, and flexible piezoelectric layer increase sequentially. The surface acoustic wave sensor is disposed on a flexible piezoelectric layer. The surface acoustic wave sensor includes interdigital transducer electrodes, which are at least partially located in the overlapping region of the deformation layer, the functional layer and the flexible piezoelectric layer.

2. The passive temperature detection device as described in claim 1, characterized in that, The fixing part includes a substrate layer, an insulating layer and a base layer stacked in sequence, with the base layer and the deformation layer being an integral structure; The thickness of the substrate layer is 1~20μm, the thickness of the insulating layer is 0.5~2μm, and the thickness of the substrate layer is 100~600μm.

3. The passive temperature detection device as described in claim 1, characterized in that, The fixing part is annular, and the deformation layer is suspended inside the annular part of the fixing part.

4. The passive temperature detection device as described in any one of claims 1 to 3, characterized in that, The ratio of the thermal expansion coefficients of the functional layer to the deformable layer, α1, and the ratio of the thermal expansion coefficients of the flexible piezoelectric layer to the functional layer, α2, satisfy 0.4≤α2 / α1≤1.5, α2≥3.

5. The passive temperature detection device as described in any one of claims 1 to 3, characterized in that, Meet at least one of the following: 1) The deformation layer is made of monocrystalline silicon, the functional layer is made of aluminum, and the flexible piezoelectric layer is made of polyvinylidene fluoride; 2) The thickness of the flexible piezoelectric layer is greater than or equal to the thickness of the functional layer, and the thickness of the functional layer is greater than or equal to the thickness of the deformation layer.

6. The passive temperature detection device as described in claim 5, characterized in that, The thickness ratio of the flexible piezoelectric layer to the functional layer is 1:1 to 3:1, and the thickness ratio of the functional layer to the deformation layer is 1:1 to 5:

1.

7. The passive temperature detection device as described in any one of claims 1 to 3, characterized in that, The thickness of the functional layer gradually increases from the fixing part to the direction away from the fixing part, and the thickness range of the functional layer is 1μm~100μm.

8. A method for preparing a passive temperature detection device as described in any one of claims 1 to 7, characterized in that, include: S1. Polish the upper surface of the insulating substrate blank and pre-define the fixing area and the deformation layer area. Deposit a functional layer on the upper surface of the insulating substrate blank, and the functional layer is at least partially located in the deformation layer area. S2. Using the inner contour of the fixed part and the outer contour of the deformation layer as a reference, the upper surface of the insulating substrate blank is etched to obtain part of the inner contour of the fixed part and the outer contour of the deformation layer. S3. A flexible piezoelectric layer and a surface acoustic wave sensor are formed sequentially on the upper surface of the functional layer by deposition and etching. S4. Etch the lower surface of the insulating substrate blank away from the functional layer to obtain the inner surface of the fixing part and the bottom surface of the deformation layer, and fix one end of the deformation layer to the fixing part, while the other end is suspended relative to the fixing part.

9. The preparation method according to claim 8, characterized in that, In step S1, a functional layer is deposited on the upper surface of the insulating substrate preform, including: Ar was used as the sputtering gas, Al was used as the target material, and the vacuum level was ≤5×10⁻⁶. -3 Pa deposits Al metal with a thickness of 1 μm to 100 μm to obtain the initial functional layer; Photoresist is coated on the surface of the initial functional layer, and the photoresist is exposed and developed using a photomask. The functional layer was obtained by inductively coupled plasma etching using a Cl2 / BCl3 mixed gas to remove the photoresist.

10. The method as described in claim 9, characterized in that, After obtaining the functional layer, the following optimization steps are also included: The functional layers are flattened. The planarized functional layer is placed in a vacuum of 1×10⁻⁶. -4 ~5×10 -5 Under the environment of Pa, multiple replacements are performed using a protective gas; First-stage heat treatment: The functional layer is heated to 180℃~220℃ and held for 25~35 minutes; Second-stage heat treatment: continue heating to 350℃~400℃ and hold for 80~100min. During the holding process, hydrogen is introduced to assist reduction and the pressure is dynamically adjusted to 50~100Pa, 10~40Pa, and 40~60Pa respectively. The functional layer is cooled to room temperature to obtain the optimized functional layer.

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