Development and Processes for High-Temperature Lithium Niobate Acoustic Devices
Description
Student’s name: Neinei Du
Home Institution: Stony Brook University
NNCI Site: The University of Texas at Austin
REU Principal Investigator: Dr. Ruochen Lu – Chandra Family Department of Electrical and Computer Engineering at The University of Texas at Austin
REU Mentor: Jack Kramer - Chandra Family Department of Electrical and Computer Engineering at The University of Texas at Austin
Abstract: Ultrasound is widely utilized for non-destructive evaluation, yet conventional piezoelectric transducers are limited by penetration depth, energy transmission, and reduced bandwidth. These issues can be addressed through piezoelectric micromachined ultrasound transducers (PMUTs). Nonetheless, functionality is also influenced by harsh thermal conditions. Ultrasonic transducers capable of withstanding extreme heat are essential for in-situ monitoring of systems such as nuclear power plants, where temperatures can exceed 800°C. The selection of piezoelectric material is critical for high-temperature applications. Lithium niobate is a suitable candidate due to its strong piezoelectric properties, high crystal quality, and a melting point exceeding 1200°C. For the development of high-temperature PMUTs, the longitudinal vibrational mode of lithium niobate must be excited. To this end, we have fabricated acoustic resonators to assess the high-temperature and electrical performance of platinum electrodes on lithium niobate. Despite challenges such as poor adhesion and photoresist reflow during platinum deposition, the resonator—comprising lithium niobate on amorphous silicon on a high-resistivity silicon stack—demonstrates potential. The fabrication process involves Argon gas etching, platinum thin film deposition, and xenon difluoride etching to suspend the lithium niobate, thereby reducing acoustic radiation loss and enhancing device performance. These devices will undergo high-temperature treatments for performance evaluation.
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