2-D CMUT wafer bonded imaging arrays with a row-column addressing scheme

This paper presents fabrication and characterization results of two-dimensional capacitive micromachined ultrasonic transducer arrays which use a row-column addressing scheme. The devices are fabricated using a wafer bonding process where both the insulation layer and the membrane are user deposited silicon nitride. Two types of arrays with different resonant frequencies are presented. One is a 32×32 element array which has a resonant frequency of 15 MHz. In immersion, when transmitting and receiving with columns a centre frequency of 5.45 MHz is measured with a relative -6 dB bandwidth of 119%. Using rows, a centre frequency of 5.75 MHz is measured with a -6 dB bandwidth of 135%. The other device is a 32×32 element array with a resonant frequency of 28 MHz and in immersion has a centre frequency of ~12 MHz. Membrane resonant frequency uniformity across the 15 MHz device has a measured standard deviation of 0.3%.