ESE PhD candidate Xu Zhao defended his thesis on Co-Design of Resonators, Piezoelectric Materials, and Acoustic Modes for Timing, Communications, and Power Applications on Tuesday, July 14th. Advised by Professor Troy Olsson, Zhao’s research focuses on piezoelectric microelectromechanical systems, particularly acoustic resonators for radio-frequency communication, frequency control, and power conversion.
“I developed resonator technologies that combine high electromechanical coupling, high quality factor, improved temperature stability, and reduced device size,” Zhao explains. “This work helps advance compact and energy-efficient electronic systems by addressing limitations in conventional acoustic devices and exploring resonators as potential alternatives to bulky magnetic components in power converters.”
Throughout his research, Zhao experienced challenges with the measured performance of microfabricated resonators. According to Zhao, they “can be strongly affected by small variations in material properties, device dimensions, support structures, parasitic electrical effects, and fabrication conditions.”
In addition, improving one performance metric can sometimes reduce another,” Zhao continues, citing for example, “how increasing electromechanical coupling may introduce additional energy loss or spurious modes.”
During the course of his research, Zhao addressed the above challenges through “repeated cycles of simulation, fabrication, measurement, and redesign. Finite-element simulations helped me understand the mechanical mode shapes and energy-loss mechanisms,” Zhao explained, adding, “equivalent-circuit modeling helped connect the measured electrical response to the physical behavior of the devices.”
Zhao credits close collaborations with his advisors, lab members, fabrication staff, and research collaborators with mitigating research challenges. “They were essential in identifying problems and developing practical solutions,” Zhao emphasized.
Speaking of gratitude, Zhao extends significant recognition to his faculty advisor, Professor Troy Olsson, “for his guidance, encouragement, and support throughout my doctoral research.” Further, Zhao extends his appreciation to dissertation committee members Professor Mark Allen and Professor Firooz Aflatouni “for providing valuable feedback and technical insight.”
Finally, Zhao expresses deep gratitude to his family and friends for “their patience, encouragement, and support throughout my Ph.D. journey.”
Several noteworthy experiences marked Zhao’s time at Penn. Friendships, collaborations, as well as technical discussions with colleagues, all contributed. So did “seeing a newly fabricated device produce a clear resonance response for the first time after months of design, simulation, and cleanroom work,” Zhao said. “That moment made the long experimental process feel especially rewarding.”
Zhao’s thesis defense represented yet another pivotal milestone. “It gave me the opportunity to bring together several years of research, explain the broader significance of the work, and discuss it with faculty members who had supported and challenged me throughout my Ph.D.”
Regarding future plans, Zhao plans to continue working in testing and development related to microelectromechanical systems and integrated electronic systems at Google.
“I am particularly interested in translating device-level innovations into mass product fabrication technologies for real application. In the long term, my goal is to develop engineering thoughts, utilizing technology to benefit peoples’ daily lives.”
When Zhao isn’t working, he enjoys traveling, playing badminton, photography, cooking,and playing video games with friends. “These activities help me relax, maintain balance, and return to my research with a fresh perspective.”
Learn more about Zhao’s work here