Acoustoelectric Amplification in Composite Piezoelectric-Silicon Cavities: A Circuit-Less Amplification Paradigm for RF Signal Processing and Wireless Sensing

The University Of Central Florida Board Of Trustees, Orlando FL

Investigators

Abstract

This project aims to introduce a new family of electro-acoustic devices that utilize the coupling between the electrons and phonons in a semiconducting substrate to amplify bulk acoustic waves in a micro-scale piezoelectric-on-silicon acoustic cavity/resonator. Acoustic resonators are used in a wide variety of applications including wireless transceivers and miniaturized sensors, and their significance in facilitating technological innovation is only going to grow for the foreseeable future. For many decades, surface acoustic wave (SAW) devices fabricated on piezoelectric substrates and quartz-based resonators dominated this field. During the past decade, bulk acoustic wave (BAW) devices fabricated based on sputtered thin-film Aluminum Nitride have changed the landscape by extending the application of acoustic devices to higher frequency bands at smaller footprint and lower manufacturing cost. This proposal, if successful, will have a sizable impact on further extending the application of BAW resonators in new fields as the proposed acoustoelectric amplification will offer unmatched overall system-level reduction in cost, size, and power consumption while offering improved overall performance. The principal investigator (PI) has a track record of promoting diversity, particularly through supporting female students to engage in research and working with university-wide programs that are dedicated to promoting research experience for minorities. He is also a co-PI on an NSF-supported research experience for teachers (RET) site. The resources available through this project will directly impact the PI's involvement in all such activities by providing new research/teaching opportunities. The objective of this project is to demonstrate that bulk-mode resonant cavities made of thin composite piezoelectric-silicon substrates such as lithium-niobate (LN)-on-silicon can be a breeding ground for a flurry of devices in which bulk acoustic waves are amplified through application of a DC current, eliminating the need for large actuation areas to achieve low signal loss. The models and preliminary results predict that >50 dB of signal gain is achievable in a 0.2-mm-long LN-on-silicon cavity at GHz frequency range. The magnitude of the achievable gain is limited to the coupling efficiency of the piezoelectric material and the electron mobility in the semiconductor (i.e., silicon) which could be independently optimized in the proposed composite structure. To study this novel concept and explore the performance limit, the following specific tasks are planned: 1) The underlying theory of acoustoelectric amplification in composite structures will be studied in detail, and the design guidelines for optimized gain and power efficiency will be developed. 2) Devices will be designed and fabricated for two specific applications; first, circuit-less oscillators at GHz frequency in which the acoustoelectric amplification compensates for the total acoustic cavity loss in order to achieve sustained spontaneous oscillation; and second, bulk-mode monolithic filters with near-zero insertion loss. 3) Application of circuit-less signal amplification will also be explored in passive wireless piezoelectric resonant sensors to improve their limited resolution and range. The circuit-less signal amplification, if successfully demonstrated, will advance the development of filters to achieve comparable signal-to-noise ratios with much smaller size than existing BAW/SAW filters used in wireless transceivers today. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.