Extreme value analysis of the impact of the effective gap tolerance on the acoustic transmit and receive performance of reverse-CMUT arrays

We assess the impact of the fabrication-related variability of the thickness of the effective gap layers on the transmission (TX) and reception (RX) performance of a reverse-fabricated CMUT array by means of finite element analysis (FEA). The extreme values of the thickness of the passivation layers and of the cavity height, obtained by interferometry measurements during in-line wafer inspection, are applied to the simulated design of a reverse-fabricated CMUT array of circular cells. The analysis follows a 2-by-2 factorial approach to evaluate the variability of the TX and RX sensitivity amplitude, phase, and bandwidth caused by the fabrication tolerances, and compute the main effects and interactions of the effective gap layers.