CMOS-MEMS Ultrasonic sensors

  John Neumann

Gary Fedder
Kaigham (Ken) Gabriel
Drawing of piezoresistor layout on CMOS-MEMS diaphragms, showing size scale, and two arrangements of sensing resistors, "E" (edge), and "M" (middle).

Waveforms captured by device, using an ultrasonic source 16 mm away, creating diaphragm deflections of 7 nm.
Single ultrasonic transducers may be used for flaw detection, by sensing the echo of an ultrasonic burst in a structure. Arrays of sensors allow more sophisticated applications such as medical imaging. Diaphragms may be built in CMOS-MEMS which have acoustic impedances comparable to media such as water and blood, and either capacitive or piezoresistive sensing can be used. Piezoresistors, built in the CMOS polysilicon layer and used as strain gauges, provide a space-efficient, low-impedance method of generating a signal. (J.J. Neumann, D.W. Greve and I.J. Oppenheim, "Comparison of Piezoresistive and Capacitive Ultrasonic Transducers", to appear in Proceedings of SPIE Symposium on Smart Structures and Materials/NDE 2004, San Diego, California, March 14-18, 2004.)



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