High-Performance Electrode-Post CMUTs: Fabrication Details and Best Practices

Capacitive micromachined ultrasound transducers (CMUTs) have been investigated for over 25 years due to their promise for mass manufacturing and electronic co-integration. Previously, CMUTs were fabricated with many small membranes comprising a single transducer element. This, however, resulted in sub-optimal electromechanical efficiency and transmit performance, such that resulting devices were not necessarily competitive with piezoelectric transducers. Moreover, many previous CMUT devices were subject to dielectric charging and operational hysteresis that limited long-term reliability. Recently we demonstrated a CMUT architecture using a single long rectangular membrane per transducer element and novel electrode post structures. This architecture not only offers long-term reliability, but also provides performance advantages over previously published CMUT and piezoelectric arrays. The purpose of this paper is to highlight these performance advantages and provide details of the fabrication process, including the best practices to avoid common pitfalls. The objective is to provide sufficient detail to inspire a new generation of microfabricated transducers which could lead to performance gains of future ultrasound systems.