A surface micromachined electrostatic ultrasonic air transducer

We describe a technique to fabricate an electrostatic transducer using silicon surface micromachining. Using these techniques to fabricate arrays of transducers with small electrode spacing, we make efficient and broadband ultrasonic air transducers. These transducers are made using standard silicon processing techniques allowing them to be integrated, in the future, with control electronics for the fabrication of electronically scanned systems with large transducer arrays. The air transducer described in this paper operates at 1.9 MHz with an insertion loss of 26 dB (slightly worse than a reference piezoelectric transducer) and a 20% bandwidth (-4 times better than the piezoelectric transducer). The impulse response of the transducer has a short ringdown time due to the fact that the transducer has a single resonance. We present here the theory of operation, the fabrication technique used, and the characterization of the device