Virtual-prototyping of thin-film PZT based flexible piezoelectric micromachined ultrasonic transducer (PMUT) array for high-frequency applications using finite element method

Piezoelectric micromachined ultrasonic transducers (PMUT), using PbZr Ti O (PZT) thin-films for miniaturized high-frequency ultrasound systems, were investigated. Recently, a process to remove the PMUT from an underlying Silicon (Si) substrate was developed to enable the formation of curved arrays. This research aimed to identify robust designs for high-frequency, flexible, low electric power consumption, PMUT arrays using PZFlex, a finite element method software. A 45 MHz, flexible, PMUT array, operating at 3 Volt peak-to-peak (V ) driving voltage, was designed. A unit-cell, consisting of four 3-1 bending mode diaphragms, was devised. The quad diaphragm unit-cell was structured with a 40 μm × 40 μm × 0.75 μm PZT layer on top of a 40 μm × 40 μm × 1 μm Ti elastic layer, under which were four (2 × 2) 10 μm × 1 μm cylindrical cavities, with 11 μm interspacing. Four pairs of 10 μm diameter circular top and bottom Pt electrodes were placed concentrically with the cavities, sandwiching the PZT layer. The top and bottom Pt electrodes had thicknesses of 50 nm and 100 nm, respectively. A 2 μm thick polyimide (PI) substrate was placed beneath the Ti layer, surrounding the 1 μm deep cavities. The pulse-echo and spectral response analysis of the quad diaphragm unit-cell revealed its bandwidth to be 9 %. A 2D array was constructed with 16×16 unit-cells, consisting of 1024 (32×32) diaphragms and characterized in terms of pulse-echo and spectral responses, surface displacement profile, beam profiles, and cross-talk. Details of the modeling steps and characterization results will be discussed.