Analytical calculation and fabrication of FET-embedded capacitive micromachined ultrasonic transducer

Abstract

In this paper, we present a full analytical model that can simulate an entire CMUT-FET structure with high accuracy and fast computation. Using the proposed analytical model, electromechanical properties, electrical characteristics (Id-Vg), and pressure sensitivity of the CMUT-FET are simulated and analyzed. The optimal bias point of the CMUT-FET is found to be 1.3 V (Sub-threshold operation), at which the calculated pressure sensitivity is 2.584 × 10-6 Pa-1. This optimum bias point is almost 11 times lower than 80 % pull-in voltage for conventional highfrequency CMUTs. As a consecutive work, we also report on a fabrication process of the CMUT-FET with nickel-silicided source/drain junctions and low-temperature wafer bonding. The low-temperature wafer bonding successfully demonstrates the direct integration of CMUT on FET, which is verified via crosssectional inspection. The fabrication technique is a promising solution and can be developed further to for integration with ICs.