Capacitive micromachined ultrasonic transducer arrays incorporating anodically bondable low temperature co-fired ceramic for small diameter ultrasonic endoscope

A process for the fabrication of a capacitive micromachined ultrasonic transducer (CMUT), with a resonance frequency of 2.88 MHz, using an anodically bondable custom-designed low temperature co-fired ceramic (LTCC) substrate with a 60 μm via diameter made of Au is presented. Fabrication of CMUTs with a high fill factor on the LTCC via with a pitch distance of 150 μm is good candidate for medical applications of a miniaturised ring shape CMUT endoscope. Electrical connection between the front side where the device is fabricated and the backside of the LTCC can be achieved with horizontal and vertical interconnects. Investigation of limitations with respect to the device dimensions and experimental fabrication results are discussed. CMUT arrays on LTCC provide a simplified fabrication process with advantages of LTCC architecture compared with typical glass counterparts used in the microelectromechanical systems field.