64-Pixel solid state CMOS compatible ultrasonic fingerprint reader

We report on a 1D linear array of GHz ultrasonic transducers as an ultrasonic impedance imager for fingerprint sensing. This device is based on an all solid state aluminum nitride (AlN) transducer array that eliminates the need for released membranes. Compared to lower frequency (10-50 MHz) ultrasonic sensors, our device uses GHz ultrasonic pulses, generated by driving AlN pixel transducers at resonance with 1.3 GHz RF pulses at a CMOS compatible voltage of 2V. In addition to faster acquisition speed, GHz ultrasonic imaging enables much higher resolution owing to the smaller wavelength by phase driving several pixels. From noise levels of signals and point measurements, we estimate that the ultimate single point resolution possible for the sensor is 15-20 um or ~1700 dpi.