Fabrication of Capacitive Micromachined Ultrasonic Transducer Arrays With Isolation Trenches Using Anodic Wafer Bonding

This paper presents a novel process for the fabrication of capacitive micromachined ultrasonic transducer (CMUT) arrays with isolation trenches using anodic bonding technique. The developed fabrication process is easy, stiction-free, repeatable, reliable, requires low-temperature (<;400°C), and gives high yield. It is a four-mask process. The process is best suited for air-coupled CMUT devices, and can also be used for vacuum-sealed devices. The CMUT device is designed and fabricated successfully using the developed process, which requires silicon-on-insulator (SOI) wafer for membrane and cavity formation, and Pyrex glass wafer for cavity and bottom electrode formation. The process is used for single-cell as well as for development of 1 × 5, 5 × 5, and 10 × 10 CMUT arrays. CMUT cells were designed using MEMSCAD tool CoventorWare. The fabricated devices have been characterized using nanovibration analyzer, and the resonance frequency is found to be ~1.5 MHz.