1-D CMUT arrays fabricated using a novel wafer bonding process

This paper presents the fabrication and characterization of phased array imaging suitable capacitive micromachined ultrasonic transducers realized using a novel wafer bonding process where both the insulation layer and the membrane are user deposited silicon nitride. Two types of one-dimensional arrays were fabricated. A 128times1 element array has a resonant frequency of 15 MHz and in immersion has a centre frequency of 6.6 MHz with and a relative -6 dB bandwidth of 130%. The cell cavity diameter is 25 mum, the cell depth is 160 nm and the membrane thickness is 500 nm. The other device is a 64times1 element array with a resonant frequency of 37 MHz and in immersion has a centre frequency of 13.2 MHz with a relative -6 dB bandwidth of 97%. The cell cavity diameter is 15 mum, the cell depth is 160 nm and the membrane thickness is 500 nm. The 128 and 64 element arrays have element pitches of 100 mum and 32 mum respectively making them suitable phased array imaging without grating lobes.