Reliability of collapse mode CMUT

Capacitive Micro-machined Ultrasonic Transducers (CMUT) enable smaller form factors, larger arrays, larger bandwidths, and integration with driver circuitry for new medical ultrasound applications. We developed a CMUT platform, which requires a relatively low number of mask steps and gives the freedom to design multi-purpose transducers due to its frequency flexibility. The focus is on low-frequency CMUT (3MHz), operated in collapse mode showing good acoustic performance. However, CMUT is known for charge trapping, which may hamper this technology's reliability and lifetime. The collapse mode variant of CMUT could suffer significantly from this effect. During operation, charge trapping in the dielectrics causes a shift in collapse voltage (drift) and can cause an electrical breakdown. This work investigates low-frequency collapse mode CMUT on drift and lifetime. The main objective is to show that collapse mode CMUT can be used for many ultrasound imaging applications.