Frequency Tuning Technique of Piezoelectric Ultrasonic Transducers for Ranging Applications

This paper presents a novel low-cost technique for the frequency tuning of piezoelectric micromachined ultrasonic transducers (PMUT). PMUT devices are fabricated using the PiezoMUMPs technology with resonance frequencies of the first and second modes at 1.4 MHz and 5 MHz, respectively. The influence of process variations on resonance frequency (with a standard deviation of about 200 kHz) motivates the need for a simple and low cost frequency tuning method. This paper proposes a technique based on a single post-processing deposition of Parylene-C. Chip-to-chip transmission and distance ranging results show that the resonant frequency of the first and second modes can accurately be tuned over a satisfactory range to significantly increase ultrasonic transmission performance. The application cases for the proposed method focus on single transducer devices or small arrays thereof since Parylene deposition simultaneously occurs on all elements of a chip and results in a uniform frequency tuning of all exposed elements.