GaN Integrated Micro-system for RF Applications & Piezoelectic Fused Silica Resonators for Timing References

Ansari – III-Nitride semiconductors have attracted exten- sive attention due to their superior material properties and have revolutionized the optoelectronic and electronic industries. Among them, GaN is of particular interest because of its wide band gap and strong piezoelectric properties, making it a perfect candidate for high-power, high-frequency and extreme-temperature applications. GaN-based heterostructures take advantage of a highly- conductive two-dimensional electron gas (2-DEG) sheet induced at their interface, that extends its research horizons to diverse scientific and multi-disciplinary fields.
To fully unlock the potential of GaN and add more functionalities to GaN micro-systems, it is important to integrate diverse GaN-based devices on the same platform. To this end, we have incorporated GaN micro- electro-mechanical systems (MEMS) in the baseline GaN process. This talk discusses various GaN-based MEMS, acoustic devices, AlGaN/GaN high electron mobility transistors (HEMTs), resonant HEMTs and GaN circuitry. Such GaN MMICs can be used in RF front-ends to save area, power, increase the energy efficiency, operate at higher frequencies and improve the noise performance compared to the state-of-the art transceiver modules. Finally, this talk covers some future directions for research on GaN, based on the interplay between the 2-DEG and strain in AlGaN/GaN heterostructures, as well as the "acousto-electric" effect.

Peczalski – There is a strong drive towards low size, weight, and power microelectromechanical system (MEMS) timing references to replace long-standing quartz-based timing units for applications in communication, defense, inertial sensors, and wearable electronics. To achieve this, notable improvements in resonator miniaturization, performance, and stability are required, necessitating investigation of alternate materials from the silicon devices sold commercially today. Fused silica, a purified amorphous silicon dioxide, is a viable alternative to silicon due to its excellent material and thermal properties for resonant devices and packaging.
This presentation provides a high level discussion of the design, characterization, and fabrication of fused silica MEMS resonators for use in timing references. Piezoelectric resonators with a fused silica substrate are demonstrated for the first time in reported literature, demonstrating a high quality factor with low motional impedance. A notable level of frequency instability is found in the large temperature sensitivity of fused silica, which is further investigated with a number of mitigation methods introduced, including ovenization and passive compensation. From this, a method of providing ultra-temperature stable devices are proposed using a dual-mode resonance technique.
Azadeh Ansari received her BSc in Electrical Engineering from Sharif University of Technology, Tehran, Iran in 2010. She joined the University of Michigan in Jan. 2011, where she obtained her MSc in Electrical Engineering in 2013 and is currently pursuing her PhD Azadeh's research interests include novel III-V semiconductor and acoustic devices, design and optimization of HEMTs and resonant HEMTs and GaN-based N/MEMS, integrated circuits and micro-systems for RF applications. Azadeh is the recipient of the Richard and Eleanor Towner Prize for outstanding PhD research award at the University of Michigan in 2015.

Adam Peczalski received a Bachelor's degree in elec- trical engineering from the University of Wisconsin"“ Madison in 2011, and a Master's degree in electrical engi- neering from the University of Michigan"“Ann Arbor in 2013. He is currently pursuing a PhD degree with the De- partment of Electrical Engineering and Computer Science at the University of Michigan. His research interests include resonant MEMS devices, fused silica as a micromechanical material, and MEMS process development.