研究目的
To design, fabricate, and characterize a piezoelectric micromachined ultrasonic transducer (pMUT) array using ceramic PZT with a new polishing process to achieve thin layers for high sensitivity and specific frequency operation.
研究成果
A ceramic PZT-based pMUT array operating at 2 MHz was successfully designed, fabricated, and characterized, demonstrating a resonance frequency of 1.67 MHz and a coupling coefficient of 5.73%. The novel polishing process enables the use of high-performance ceramic PZT in pMUTs, offering improved sensitivity and potential for applications in ultrasonic sensing and imaging. Future work could focus on further thinning, reducing defects, and expanding array sizes.
研究不足
The process may face challenges such as defects from polishing (e.g., porosity, fractural damage), wafer-level uniformity issues, and potential voids in bonding layers. The achieved thickness of 5 μm, while thin, may still have limitations for even smaller devices or higher frequencies. Integration complexities and scalability for large arrays could be areas for optimization.
1：Experimental Design and Method Selection:
The study involves designing a pMUT array with a circular membrane structure operating in the piezoelectric d31 mode, using analytical modeling (lumped element model) and finite element method (FEM) simulations for performance prediction. A novel process for thinning ceramic PZT to 5 μm via wafer bonding and chemical mechanical polishing (CMP) is developed.
2：Sample Selection and Data Sources:
Ceramic PZT wafers (PZT-5H from CTS) with an initial thickness of 660 μm are used. Silicon on insulator (SOI) wafers serve as the substrate.
3：List of Experimental Equipment and Materials:
Equipment includes sputtering systems for electrode deposition, CMP tools for polishing, DRIE for silicon etching, vapor HF for oxide removal, and an Agilent 4294A impedance analyzer for characterization. Materials include SU-8 photoresist, PermiNex1000 polymer, Au and Cr for electrodes, and chemical etchants like 4.5%HNO3/4.5%BOE/91%H2O.
4：5%HNO3/5%BOE/91%H2O.
Experimental Procedures and Operational Workflow:
4. Experimental Procedures and Operational Workflow: The fabrication process involves temporary bonding of PZT to silicon with SU-8, grinding and polishing PZT to 100 μm, sputtering bottom electrode, bonding to SOI wafer with PermiNex, further polishing to 5 μm, etching vias, forming top electrode, backside photolithography, DRIE etching, and oxide removal to form membranes.
5：Data Analysis Methods:
Impedance measurements are performed to determine resonance frequencies and coupling coefficients. Simulations using COMSOL Multiphysics and lumped element modeling are used for design validation and frequency response analysis.
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