Research

We optimize the properties of emerging active materials and develop nanofabrication techniques for forming devices. 

RF Acoustics: Emerging radio frequency (RF) applications require small resonators operating beyond 3 GHz to enable filters with wider bandwidths (driven by resonator electromechanical coupling, kt^2), low loss (driven by high acoustic quality factor, Q) and high power handling. Existing approaches to acoustic RF resonators with the desired properties for wide bandwidth do not easily scale to higher frequencies. Therefore, our group utilizes a new piezoelectric material, Aluminum Scandium Nitride (AlScN), for the implementation of bulk acoustic wave resonators (BAW), surface acoustic wave resonators (SAW), and Lamb wave resonators (LWR). Previous studies have shown that by alloying Aluminum Nitride (AlN) with Sc atoms, the piezoelectric coefficients of AlScN can reach a value five times larger than that of AlN.  We also investigate novel material structures, such as periodically poled piezoelectric films (P3F), that enable scaling of acoustic devices to much higher frequencies. Our research facilitates the development of high frequency radio frequency filters and signal processors with wide bandwidth and low insertion loss. 

Ferroelectric based non-volatile memory has demonstrated advantageous features including low write energy, fast switching speed, and long endurance. However, for ferroelectric random access memory (FeRAM), the bit density is limited primarily by the remanent polarization (Pr) because the sense charge is the product of the Pr times the ferroelectric (FE) capacitor area. The bit density of a ferroelectric field-effect transistor (FeFET) is generally determined by the coercive field (Ec), with higher coercive field leading to thinner FE layers that can be patterned into smaller features while maintaining a wide memory window. Our group researches a newly found ferroelectric material, AlScN for the next generation of ferroelectric memory. We synthesize high quality sub-20 nm AlScN thin films, and thus enable ferroelectric memory with a low write voltage, a large remanent polarization, and a significant breakdown field to coercive field ratio. Moreover, the AlScN dielectric is able to be deposited on to a variety of substrates at temperatures below 350 °C, making the fabrication process compatible with back end of the line CMOS integration. We also explore the use of AlScN for memory in extreme environments. 

Contacts: Yinuo Zhang, Dr. Dhiren K. Pradhan, Dr.  Hyunmin Cho

Collaborators: Professor Deep Jariwala and Professor Eric Stach.

The human body produces magnetic fields anywhere an electric current is present, including the heart, brain, nerves, and muscles. Multiferroic materials provide a unique way to sense these tiny magnetic fields, providing high sensitivity, lower power, and small size. In these heterostructures, a magnetostrictive material strains in response to magnetic field, which is coupled to the piezoelectric material, producing output charge in response to the magnetically induced strain. In our group, AlScN is employed in resonant multiferroics structures along with a variety of magnetostrictive materials. Our studies have greatly enhanced the quality factor and the electromechanical coupling of resonant multiferroic structures.  Additionally, similar multiferroic devices can be used for implantable or wearable wireless power transfer, where an external magnetic field can provide the power necessary for the sensors and circuits to operate in biomedical IoT applications. In addition, we explore novel, low power circuit interfaces for the multiferroic devices.

Contacts: Sydney Sofronici, Jonathan Tan, Serene Feng 

Collaborators: Professor Mark Allen and US Navy Research Laboratories.