High Round-Trip Gain Piezoelectric-Capacitive Hybrid Micromachined Ultrasonic Transducer Based on Anodic Bonding Technology

In this work, a piezoelectric-capacitive hybrid micromachined ultrasonic transducer (HMUT) with a high round-trip gain was developed to achieve superior pulse-echo imaging performance. Initially, an equivalent circuit model (ECM) and a finite element model (FEM) were constructed to design and simulate the HMUT cell. A patterned etching technique for the piezoelectric layer was incorporated into the HMUT design. Simulation results indicated that the round-trip gain of the HMUT with patterned piezoelectric layer is 33 dB higher than that of the piezoelectric micromachined ultrasonic transducer (PMUT) and 3 dB higher than that of the capacitive micromachined ultrasonic transducer (CMUT). One of the innovative aspects of this technique is its ability to fabricate vertically stacked PMUT and CMUT. Based on anodic bonding technology, prototypes of 3 MHz PMUT, CMUT, and HMUT were fabricated on the same substrate. Finally, an electric impedance test and pulse-echo test were conducted. Experimental data confirmed that the HMUT exhibits higher round-trip gain, consistent with the simulation results. The successful fabrication of these prototypes demonstrates the feasibility of integrating multiple ultrasonic transducers on a single platform, enhancing the device's compactness and versatility. Furthermore, it opens new avenues for the development of high-quality ultrasonic imaging.