Prof. Amit Lal
SonicMEMS Laboratory, School of Electrical and Computer Engineering, Cornell University
Integrated GHz ultrasonics on planar systems such as CMOS chips are enabled by integration of fast, deep sub-micron transistors and GHz thin film piezoelectric transducers. Sonic wavelengths on the order of a few microns can generate wave packets with spatial extent that is less than the substrate thickness. The role of diffraction of wave packets, coupled with time-of flight have been used to form a useful set of devices. With integration with deeply scaled CMOS that provides GHz electronics, one can envision chip-scale microsystems that provide unprecedented manipulation of sonic energy. We have used these CMOS chips to demonstrate sensing biological ultrasonic impedance to extract fingerprints and tissue type, communicate on a chip using ultrasonic pulses, and implemented ultrasonic memory. A delay block is a circuit that shifts the input signal in time by a desired amount, and delivers a delayed output like the input signal. Delay elements can be used in wide range of applications including phase modulation in clocking systems as well as different digital systems. Furthermore, stable delay elements can be used as a timing reference in delay-locked-loops where the delay can be calibrated across different temperature and process variations. Precision and stability in a delay element block is one of the key specifications that directly impacts all the applications. We have implemented a pulse-echo transmit-receive ultrasonic delay element that is stable over time and has a novel diffraction based zero temperature coefficient of delay at two temperatures. The silicon bulk wave propagation leads to stable operation owing to low loss within silicon and large mode volume. The delay element achieves < 6ppm stability and demonstrates zero temperature coefficient at 43C and 72C. A recently implemented oscillator using the delay element in an oscillator configuration achieved < 1ppm stability.