Strain engineering of dischargeable energy density of ferroelectric thin-film capacitors

Ferroelectric oxide thin-film capacitors find applications in microelectronic systems, mobile platforms, and miniaturized power devices. They can withstand higher electric fields and display significantly larger energy densities than their bulk counterparts and exhibit higher maximum operating temperatures and better thermal stabilities than polymer-based dielectric capacitors. However, ferroelectric oxide thin films typically possess large remanent polarization and exhibit significant dielectric loss, thereby limiting their dischargeable energy densities. Here we demonstrate, using phase-field simulations, that strain can be utilized to modify the polarization response to electric field and thus optimize the energy-storage performance of ferroelectric thin-film capacitors. For example, an in-plane tensile strain can significantly narrow hysteresis loops by reducing the remanent polarization without significantly decreasing the out-of-plane saturated polarization. As a result, both the dischargeable energy density and charge-discharge efficiency can be significantly enhanced. We analysed the domain structures and energy surfaces to understand the underlying mechanisms for the enhancements. We also propose a bending strategy to further improve the dischargeable energy density, which can be achieved, e.g., by growing ferroelectric thin films on a flexible substrate (e.g., mica). This work provides a general strategy to optimize the energy-storage performance of ferroelectric thin-film capacitors for high-energy/power-density storage applications.