One-dimensional capacitative micromachined ultrasonic transducer arrays for echographic probes

In this paper we report the design and the fabrication process for a 64-element capacitive micromachined ultrasonic transducer (cMUT) array, for application in medical imaging. The element size and separation between adjacent elements are chosen for operation at 7 MHz, a frequency typically used in tissue imaging. The fabrication process is based on surface micromachining techniques and is compatible with standard CMOS process, due to the materials used and the low-temperature deposition steps (PECVD silicon nitride for structural layer, evaporated chromium as sacrificial layer and sputtered aluminum for metallization). Electrical tests in air show typical resonance behaviour and no significant degradation during operation. Tests in water show wide bandwidth and pulse-echo operation