Fabrication of vacuum-sealed capacitive micromachined ultrasonic transducer arrays using glass reflow process

This paper presents a process for the fabrication of vacuum-sealed capacitive micromachined ultrasonic transducer (CMUT) arrays using glass reflow and anodic bonding techniques. Silicon through-wafer interconnects have been investigated by the glass reflow process. Then, the patterned silicon-glass reflow wafer is anodically bonded to an SOI (silicon-on-insulator) wafer for the fabrication of CMUT devices. The CMUT 5*5 array has been successfully fabricated. The resonant frequency of the CMUT array with a one-cell radius of 100 μm and sensing gap of 3.2 μm (distance between top and bottom electrodes) is observed at 2.84 MHz. The Q factor is approximately 1300 at pressure of 0.01 Pa.