- Ruijuan Xu, The University of California, Berkeley
Complex oxides, which exhibit a wide range of structures and functionalities such as superconductivities, magnetic and multiferroic properties, have driven considerable research in materials science and condensed matter physics over past decades. As one important variant of oxide materials, ferroelectric materials which possess an electrically addressable polarization hold great promise for next-generation nonvolatile, low-power nanoelectronics. Leveraging the polarizations and the coupled dielectric, piezoelectric, and pyroelectric properties, ferroelectric materials have been integrated into state-of-the-art devices such as memories, logics, and sensors/actuators. Due to the inherent bi-stability of polarization, the deterministic production of multiple states with distinct polarization values, however, remains a hallmark challenge. In this talk, I will discuss how to engineer and control the polarization switching in a deterministic manner. Leveraging advanced thin film epitaxy and multi-scale characterizations, I will demonstrate the capability to control both nanoscale switching events and mesoscale switching pathways in ferroelectric thin films. In particular, I will show the potential for tunable, multi-state polarization via control of switching kinetics in ferroelectrics. Here we observe a type of multi-state switching behavior in ferroelectrics wherein the intermediate polarization state can be deterministically written into a number of states in any order by varying the driving voltage. These states are found to be nonvolatile, stable, and deterministically accessible, providing the functionality needed for the realization of solid-state adjustable synaptic weights for adaptive neuromorphic electronics.