Monolithic 180nm CMOS Controlled GHz Ultrasonic Impedance Sensing and Imaging

For the first time we demonstrate monolithically integrated solidly mounted piezoelectric AlN (aluminum nitride) thin film transducers integrated onto 180nm CMOS wafers to realize CMOS driven GHz ultrasonic transducers. GHz ultrasonic transducers can be used to image surface ultrasonic impedance via reflectometry of short 10-20ns ultrasonic pulses into the silicon bulk. In this paper we are able to identify different solution concentrations and image a rubber fingerprint phantom by measuring their ultrasonic impedance using a tiny chip implementation. The effect of ultrasonic pulse transmission through different Back End of Line (BEOL) metal layers with differing metallization is quantified indicating that variations on CMOS layers have a minimal effect on the overall pulse transmission. The transmitting transducer is driven by integrated CMOS circuits (VCOs, switches). The signal at the receiving transducer is sensed by Transimpedance Amplifier (TIA), voltage amplifiers and Envelope detector (ED), all the circuits are fabricated in Global Foundries (GF) CMOS 180 nm technology. The sensor is used to sense different solution concentrations of NaCl and KCl, and image fingerprint phantoms with high resolution, proving that 2D arrays can achieve a multimodal sensing chip.