A 50x20 Row-Column Addressed PMUT Array on Silicon Substrate for Imaging

• Published in: IEEE International Ultrasonics Symposium (Online) pp. 1 - 4
• Main Authors: Joshi, Sanjog Vilas, Sadeghpour, Sina, Kraft, Michael
• Format: Conference Proceeding
• Language: English
• Published: IEEE 03.09.2023
• Subjects: Fabrication; medical imaging; piezo-MEMS; piezoelectric thin films; PMUT; PZT; Resonant frequency; Sensitivity; Silicon-on-insulator; Ultrasonic transducer arrays; Ultrasonic transducers; ultrasound transducers; Vibrometers
• ISSN: 1948-5727
• DOI: 10.1109/IUS51837.2023.10307994

This paper presents a row-column (RC) addressable 50 × 20 two-dimensional (2D) rigid piezoelectric micromachined ultrasonic transducer (PMUT) array. Previously reported RC PMUTs were fabricated on a silicon on insulator (SOI) wafer with a silicon membrane. Here, the PMUTs were fabricated on a conventional silicon wafer and a polyimide layer is used as the passive layer in the PMUT membranes on top of the active piezoelectric layer which enables high resonance frequencies. The PMUT membranes are realized by backside deep reactive ion etching (DRIE) with an oxide etch stop. About 1 µm thick Lead Zirconate Titanate (PZT) thin film deposited by a sol-gel process is the active piezoelectric layer. The fabricated PMUT showed a 3.2 MHz in-air frequency with a 30 nm/V sensitivity, as measured with Laser Doppler Vibrometer (LDV). Below 10% in-air crosstalk between the PMUT elements in one array is observed. A pressure response of 80 Pa/V at 5 mm was measured underwater using a hydrophone while exciting a single PMUT element whereas pulse response captured by PMUT as a receiver suggested a 30 mV/MPa receive sensitivity. The demonstrated results show the potential to enable imaging and sensing applications in shallow-depth regions subject to some optimization.