High-temperature-resistant piezoelectric micro-electro-mechanical transducer

Abstract

The invention discloses a high-temperature-resistant piezoelectric micro-electro-mechanical transducer, which comprises a shell made of silicon carbide ceramic; the PMUT area array is positioned in the shell; the support is made of an aluminum oxide ceramic material and is arranged between the shell and the PMUT area array; the sound matching layer is coated on the PMUT area array and is made of an aluminum oxide-PDMS (Polydimethylsiloxane) composite material; and the NBPSC fireproof coating layer is coated on the sound matching layer. The transducer can resist high temperature of 1500 DEG C or above, and the problem that the performance of an existing PMUT is limited in a high-temperature environment is solved.

Description

Technical Field

[0001] This invention relates to a high-temperature resistant piezoelectric microelectromechanical transducer. Background Technology

[0002] Piezoelectric micromechanical ultrasonic transducers (PMUTs) have shown significant application value in fields such as industrial inspection and life detectors; however, the problem of their performance limitations in high-temperature environments has not yet been effectively solved.

[0003] Current PMUT devices mostly use epoxy resin or polyimide for encapsulation, and their glass transition temperature is usually below 300°C. In high-temperature scenarios such as fires, these materials will undergo thermal degradation, leading to a decrease in mechanical strength and a deterioration in dielectric properties, ultimately causing sensor failure.

[0004] Although some studies have attempted to use alumina ceramics as a packaging substrate, its brittle nature results in poor impact resistance, and it is prone to microcracks after thermal cycling (such as more than 500 cycles under a temperature difference of 800°C), which in turn affects the reliability of the equipment.

[0005] Conventional acoustic matching layers often use silicone rubber, whose elastic modulus increases significantly at temperatures above 200°C, leading to acoustic impedance mismatch and severely weakening the penetration ability of ultrasonic signals. While existing transparent fire-retardant coatings can achieve light transmittance exceeding 85%, their fire resistance limit is only 15-30 minutes, and their upper temperature resistance limit is below 400°C, making it difficult to meet the actual needs of long-term continuous detection at fire scenes.

[0006] The difference in the coefficient of thermal expansion between the PMUT chip and commonly used support materials (such as stainless steel) can lead to the continuous accumulation of interfacial stress during thermal cycling, which can cause chip debonding or plastic deformation of the support structure. Although existing technologies attempt to alleviate thermal stress through gradient materials, their interlayer bonding strength is relatively low, and interlayer delamination is prone to occur at high temperatures.

[0007] According to a 2023 market research report by Global Market Insights, the market size for high-temperature industrial detection and fire rescue equipment is projected to reach $1.25 billion by 2028. However, existing products generally have an average continuous operating time of less than 30 minutes in 800°C environments, failing to meet the minimum fire resistance requirement of 1 hour for life detection equipment as specified in ISO 7240-29:2017. Therefore, the development of PMUT (Piezoelectric Micromechanical Ultrasonic) detectors, which combine high temperature resistance, low acoustic loss characteristics, and structural stability, has significant application value. Summary of the Invention

[0008] This invention proposes a high-temperature resistant piezoelectric microelectromechanical transducer and its preparation method, which solves the problem of limited performance of existing PMUTs in high-temperature environments.

[0009] According to one aspect of the embodiments, a high-temperature resistant piezoelectric microelectromechanical transducer is provided, comprising: a housing made of silicon carbide ceramic; a PMUT array located within the housing; a support made of alumina ceramic material disposed between the housing and the PMUT array; an acoustic matching layer coated on the PMUT array, made of alumina-PDMS composite material; and an NBPSC fire-retardant coating coated on the acoustic matching layer.

[0010] In some examples, the method for preparing the acoustic matching layer includes: first, mixing alumina nanoparticles with anhydrous ethanol in a mixer, then placing the mixture in an ultrasonic cleaner for water bath ultrasonic treatment to prepare a dispersion; adding PDMS prepolymer and silane coupling agent to the obtained dispersion, then stirring with a mixer; secondly, placing the stirred mixture in an ultrasonic cleaner with anhydrous ethanol medium for vibration, and finally placing it in a vacuum chamber for degassing treatment; uniformly pouring the degassed alumina-PDMS composite material onto the PMUT array surface and performing curing treatment.

[0011] In some examples, the mass ratio of the alumina nanoparticles to the PDMS prepolymer is 1:95 to 105.

[0012] In some examples, the alumina-PDMS composite coating thickness is 5-50 micrometers.

[0013] In some examples, a thermosetting process is used to cross-link and cure the PDMS prepolymer to form the acoustic matching layer.

[0014] In some examples, the preparation method of the NBPSC fire-retardant coating includes: Step 1: Mixing nano-boehmite powder with ethanol to obtain a boehmite solution, and dispersing it in an ultrasonic oscillator; immersing the PMUT array with the completed acoustic matching layer encapsulation into the boehmite solution, and soaking treatment to make the boehmite particles uniformly deposited on the surface of the PMUT array to form a micro-nanoparticle film layer; after removal, drying it in an oven or hot air gun; Step 2: Dissolving zinc phosphate in deionized water, adding phosphoric acid to prepare a zinc phosphate solution; immersing the PMUT array treated in Step 1 into the zinc phosphate solution to form a phosphate passivation film; after removal, washing and drying.

[0015] In some examples, the concentration ratio of phosphoric acid to zinc phosphate is 1:4 to 6.

[0016] In some examples, the PMUT array is immersed in a zinc phosphate solution and chemically treated at 20-25°C for 10-30 minutes. Attached Figure Description

[0017] Figure 1 This is a PMUT array element in one embodiment of the present invention.

[0018] Figure 2 This is a front view of a PMUT area array in one embodiment of the present invention.

[0019] Figure 3 This is an example of a nano-alumina-PDMS composite acoustic matching layer and an NBPSC high-temperature resistant coating in one embodiment of the present invention.

[0020] Figure 4 This is a flowchart illustrating the preparation process of the acoustic matching layer of the nano-alumina-PDMS composite material in one embodiment of the present invention.

[0021] Figure 5 This is a flowchart illustrating the preparation process of the NBPSC high-temperature resistant coating in one embodiment of the present invention.

[0022] Figure 6 This is a schematic diagram of the outer shell structure in one embodiment of the present invention.

[0023] Figure 7 This is a schematic diagram of the top support structure in one embodiment of the present invention.

[0024] Figure 8 This is a schematic diagram of the edge support structure in one embodiment of the present invention.

[0025] Figure 9 This is the overall structure in one embodiment of the present invention. Detailed Implementation

[0026] The high-temperature resistant piezoelectric microelectromechanical transducer of the present invention can operate stably in high-temperature environments exceeding 1500°C. It includes a honeycomb-arranged PMUT array, an acoustic matching layer, an NBPSC fire-retardant coating, and an external encapsulation structure.

[0027] Figure 1 , 2 The PMUT array elements and their constituent area arrays are shown. The substrate of the PMUT array elements is made of single-crystal silicon, and the geometric centers of the regular hexagonal cavity, bottom electrode, and top electrode on the substrate coincide in the direction perpendicular to the transducer unit, thereby ensuring that the transducer unit has sufficient structural strength and excellent performance under specific operating conditions. The piezoelectric material layer is selected from aluminum nitride (AlN), scandium-doped aluminum nitride (Sc-AlN), lead zirconate titanate (PZT), or zinc oxide (ZnO).

[0028] The PMUT array elements are electrically connected in parallel, and the internal electrode feature size is 40%-80% of the feature size of the substrate silicon wafer cavity.

[0029] PMUT arrays can improve detection accuracy and efficiency, adapting to detection needs in various environments. For example, this array can sense the physiological characteristics of living organisms, such as weak biological signals like breathing and heartbeat, and convert them into detectable signals.

[0030] Figure 3 The acoustic matching layer of the transducer and the high-temperature resistant NBPSC coating were demonstrated. The fabrication process of the acoustic matching layer is as follows: Figure 4 .

[0031] 1. Preparation of dispersion.

[0032] In a high-speed mixer, alumina nanoparticles (20 nm in diameter) were mixed with anhydrous ethanol and then placed in an ultrasonic cleaner for water bath ultrasonic treatment for 5 minutes.

[0033] 2. Mixing and defoaming of composite materials.

[0034] Add PDMS prepolymer (polydimethylsiloxane) and silane coupling agent to the dispersion obtained in step 1, and stir for 2 minutes using a high-speed mixer to ensure that the alumina nanoparticles and PDMS prepolymer are uniformly dispersed without agglomeration. Control the mass ratio of alumina nanoparticles to PDMS prepolymer to be 1:95-105 (1:100 is recommended). Place the thoroughly stirred mixture in an ultrasonic cleaner with anhydrous ethanol medium and vibrate for 30 seconds, then place it in a vacuum chamber for degassing.

[0035] 3. Coating and curing.

[0036] The defoamed alumina-PDMS composite material obtained in step 2 was uniformly poured onto the surface of the PMUT array, with the coating thickness controlled within the range of 5-50 micrometers, and then immediately cured. The curing process adopted a thermosetting process, in which the PDMS prepolymer was cross-linked and cured at a certain temperature to form a composite acoustic matching layer with a stable structure and elasticity.

[0037] Figure 5 A method for coating a high-temperature resistant coating onto the acoustic matching layer is demonstrated.

[0038] 1. Pretreatment of nanoboehmite.

[0039] 1.1. Mix nano-Boehmite powder with ethanol and disperse it using an ultrasonic oscillator to ensure that the boehmite powder is evenly distributed in the solvent without agglomeration.

[0040] 1.2 Immerse the transducer substrate with the completed acoustic matching layer encapsulation into the boehmite solution prepared in step 1.1 and soak for 30 minutes to allow the boehmite particles to be uniformly deposited on the substrate surface and form a micro-nano particle film layer.

[0041] 1.3 Remove the treated substrate and use an oven or hot air gun to dry the surface and remove residual solvent.

[0042] 2. Zinc phosphate / phosphoric acid catalytic reaction and curing.

[0043] 2.1 Dissolve zinc phosphate in deionized water, add phosphoric acid to prepare zinc phosphate solution, and control the concentration ratio of phosphoric acid to zinc phosphate to be 1:4 to 6 (1:5 recommended).

[0044] 2.2. The substrate treated in step 1 (nano boehmite pretreatment) is immersed in the zinc phosphate solution prepared in step 2.1 and chemically reacted at room temperature (20-25℃) for 10-30 minutes to form a stable phosphate passivation film on the substrate surface.

[0045] 2.3 Remove the substrate from the zinc phosphate solution and wash to remove any residual solution from the surface.

[0046] 2.4 Place the cleaned substrate in a drying oven for curing treatment. Set the curing temperature to 90℃ and the curing time to 120 minutes.

[0047] Figure 6 Figure 7 and Figure 8 The outer casing, top support, and edge support of the transducer's external encapsulation structure are shown separately.

[0048] The outer shell needs to provide excellent high-temperature resistance and thermal shock resistance. Silicon carbide ceramic is used, which has excellent thermal shock resistance and high-temperature resistance (withstanding temperatures above 1500°C). High-quality silicon carbide powder is selected, and an appropriate amount of binder is added to ensure the thermal stability of the material after molding. The silicon carbide powder is pressed into the required shape of the shell, such as a handle, using injection molding, pressing, or isostatic pressing processes. High-temperature sintering ensures the density, strength, and thermal stability of the silicon carbide ceramic. The sintered shell undergoes precision machining to achieve the final dimensional requirements. High dimensional accuracy and surface finish must be maintained during machining.

[0049] The top support can be arranged between the bottom and top surfaces of the PMUT array (coated with an acoustic matching layer and an NBPSC fire-retardant coating) and the outer shell, while the edge support is arranged between the side surfaces of the PMUT array and the outer shell.

[0050] The supports are made of alumina ceramic material (Al2O3), which possesses high high-temperature resistance, mechanical strength, and good thermal stability. Alumina ceramic raw materials with a purity of over 99% are pressed into shape using injection molding or isostatic pressing processes to form the initial shapes of the top and edge supports. The formed ceramic parts then undergo sintering in a high-temperature furnace. The sintering temperature is typically above 1500℃ to ensure the density and mechanical properties of the alumina ceramic meet design requirements. After sintering, the ceramic parts require precision surface polishing and cutting to ensure dimensional accuracy and surface quality. During the processing, a special coating treatment can be applied to the surface to improve wear resistance and thermal stability.

[0051] Figure 9 This is an integrated structure assembling the PMUT array, top support, edge support, and external encapsulation. The components are secured with high-temperature resistant adhesives or sealants to ensure no physical displacement under high-temperature conditions. After assembly, the transducer undergoes a series of functional tests to ensure stable operation in high-temperature environments. These tests include, but are not limited to: high-temperature resistance, acoustic detection accuracy, thermal shock resistance, and stability.

[0052] Through these processes, the NBPSC high-temperature PMUT array life detector of this invention can work efficiently and stably in high-temperature environments, meeting the life detection needs of specific application scenarios (such as fire rescue, extreme environment detection, etc.).

[0053] The application of the high-temperature resistant piezoelectric microelectromechanical transducer (PMUT) of this invention in life detection: The PMUT array emits ultrasonic signals, which interact with the biological tissue of the object being detected when penetrating it. When a living organism (such as a human) is present, it generates weak reflected waves due to physiological activities such as breathing and heartbeat. These reflected waves are received by the PMUT array and analyzed by signal processing algorithms, ultimately outputting vital sign data. The combination of coating and special materials used in this transducer enables effective transmission of ultrasonic signals and reduces environmental noise interference, thereby improving detection accuracy. The detector can provide real-time feedback on life detection results, helping rescuers quickly locate trapped or injured individuals.

Claims

1. A high-temperature resistant piezoelectric microelectromechanical transducer, characterized in that, include: The outer shell is made of silicon carbide ceramic; the PMUT array is located inside the outer shell. The support, made of alumina ceramic material, is disposed between the outer shell and the PMUT array; An acoustic matching layer, coated on the PMUT array, is made of alumina-PDMS composite material; and an NBPSC fire-retardant coating is coated on the acoustic matching layer.

2. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 1, characterized in that, The method for preparing the acoustic matching layer includes: First, alumina nanoparticles are mixed with anhydrous ethanol in a mixer, and then the mixture is placed in an ultrasonic cleaner for water bath ultrasonic treatment to prepare a dispersion. PDMS prepolymer and silane coupling agent were added to the obtained dispersion, and then the mixture was stirred with a stirrer. Next, the stirred mixture was placed in an ultrasonic cleaner with anhydrous ethanol medium and vibrated. Finally, it was placed in a vacuum chamber for degassing. The defoamed alumina-PDMS composite material was uniformly poured onto the surface of the PMUT array and then cured.

3. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 2, characterized in that, The mass ratio of alumina nanoparticles to PDMS prepolymer is 1:95-105.

4. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 2, characterized in that, The thickness of the alumina-PDMS composite coating is 5-50 micrometers.

5. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 2, characterized in that, The PDMS prepolymer is cross-linked and cured using a thermosetting process to form the acoustic matching layer.

6. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 1, characterized in that, The method for preparing the NBPSC fire-retardant coating includes: Step 1: Mix nano-boehmite powder with ethanol to obtain a boehmite solution, and place it in an ultrasonic oscillator for dispersion treatment; immerse the PMUT array with completed acoustic matching layer encapsulation into the boehmite solution, and soak it to make the boehmite particles uniformly deposited on the surface of the PMUT array to form a micro-nanoparticle film layer; after taking it out, dry it with an oven or hot air gun. Step 2: Dissolve zinc phosphate in deionized water and add phosphoric acid to prepare a zinc phosphate solution; immerse the PMUT array treated in Step 1 into the zinc phosphate solution to form a phosphate passivation film; remove, wash, and dry.

7. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 6, characterized in that, The concentration ratio of phosphoric acid to zinc phosphate is 1:4 to 6.

8. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 1, characterized in that, The PMUT array was immersed in a zinc phosphate solution and subjected to a chemical reaction treatment at 20-25°C for 10-30 minutes.

9. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 1, characterized in that, In the array elements of the PMUT array, the recessed cavity, bottom electrode, and top electrode on the substrate are arranged in a direction perpendicular to the transducer unit, and the geometric centers of the three coincide with each other.

10. The high-temperature resistant piezoelectric microelectromechanical transducer according to claim 9, characterized in that, The piezoelectric material layer in the array element is made of aluminum nitride, scandium-doped aluminum nitride, lead zirconate titanate, or zinc oxide.

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