Projects

Piezoelectric acoustic wave devices are utilized broadly in consumer electronics. These devices serve important roles such as oscillators, filters, sensors, and transducers. However, until recently, these devices have always operated in a frequency range below 10 gigahertz due to challenges associated with design and fabrication. To overcome this, implementing clever configurations of thin film lithium niobate provided an opportunity to upscale the operation of frequency into the tens to even hundreds of gigahertz. Continuing work on this front aims to explore the ultimate frequency limits of acoustics as elastic theory transitions to being dominated by the quantum interactions of phonons.

Highlighted relevant publications: 

1. Jack Kramer, Sinwoo Cho, Michael E Liao, Kenny Huynh, Omar Barrera, Lezli Matto, Mark S Goorsky, Ruochen Lu, "57 GHz Acoustic Resonator with k2 of 7.3 % and Q of 56 in Thin-Film Lithium Niobate", 2022 International Electron Devices Meeting (IEDM) 

2. Jack Kramer, Bryan T Bosworth, Lezli Matto, Nicholas R Jungwirth, Omar Barrera, Florian Bergmann, Sinwoo Cho, Vakhtang Chulukhadze, Mark Goorsky, Nathan D Orloff, Ruochen Lu, "Acoustic resonators above 100 GHz" Applied Physics Letters 2025

Conventional piezoelectric acoustic systems utilize a single piezoelectric layer. This usually is used to form a cavity or to transduce acoustic waves into another medium. However, introducing additional functional layers opens the doors for creating coupled systems that can offer greater opportunities. This could include implementing multi-orientation piezoelectric layers to tune acousto-optic coupling, introducing hybrid semiconductor-piezoelectric structures to enable frequency mixing and nonlinear effects, or stacking 2D materials on piezoelectrics to provide strain tuning of optical absorption. On going work includes exploring these opportunities for optimized hybrid systems. 

Highlighted relevant publications: 

1. Jack Kramer, Ruochen Lu, "A Generalized Acoustic Framework for Multilayer Piezoelectric Platforms", IEEE Transactions on Ultrasonics, Ferroelectrics, and Frequency Control, 2025

Acoustic wave theory is used to describe the mechanical motion of macroscopic vibrations. When length scales approach that of atomic spacings, then these vibrations are now treated as quantum mechanical oscillations called phonons. In attempting to generate higher frequency acoustic waves, these two regimes converge and can no longer be treated independently. To explore this regime, systems are cooled to single kelvin temperature scales where the impact of thermally excited phonons can be minimized. On going work looks to quantize the impact of phononic interactions on high frequency acoustics, as well as gaining a better understanding of the grey area between classical and quantum regimes. 

Highlighted relevant publications: 

1. Jack Kramer, Omar Barrera, Sinwoo Cho, Vakhtang Chulukhadze, Tzu-Hsuan Hsu, Ruochen Lu , "Experimental study of periodically poled piezoelectric film lithium niobate resonator at cryogenic temperatures", 2024 IEEE/MTT-S International Microwave Symposium