Low temperature capacitive micromachined ultrasonic transducers (cMUTs) on glass substrate

The possibility of fabricating capacitive micromachined ultrasonic transducers (cMUTs) on glass substrates may open the way for new fields of application in which the transparency of the substrate is advantageous. In this study, we demonstrate that a low-temperature process can be carried out to achieve cMUTs on glass substrates. Limited to temperatures lower than 400 degrees C, the process is based on the use of nickel as a sacrificial layer. The cMUT electromechanical behavior is studied and the performance compared to those obtained with silicon substrates. The cMUTs fabricated on glass substrate showed performance comparable with the Si ones. A slight shift in the resonance frequency and collapse voltage was observed. It is shown that these differences arise from the residual mechanical stresses in the substrate.