Ultralow operating voltage for energy conversion performance in Hf1–xZrxO2 thin films

Abstract

Emerging ferroelectric and antiferroelectric HfO₂-based thin films are attractive candidates for energy conversion and storage applications. In this work, the polar phase transformation between tetragonal and orthorhombic phases associated with ferroelectric or antiferroelectric behaviors is utilized to manipulate the electrocaloric cooling and energy storage performances in Zr-doped, woken up HfO₂ ultrathin films. A giant electrocaloric temperature change of up to 11.85 K in Hf_0.5Zr_0.5O₂ with the morphotropic phase boundary (MPB) state and a high energy storage density of 39.34 J/cm³ in the tetragonal phase-dominant Hf_0.25Zr_0.75O₂ system are obtained. More interestingly, contrary to overdoping and excessive electric fields, an appropriate Zr concentration of 0.5 and an applicable driving field of 1.91 MV/cm are desired for the electrocaloric effect, resulting in an ultralow operating voltage as low as 1.3 V in this 6.8 nm thick Hf_0.5Zr_0.5O₂ film. These findings illustrate that the structural design strategy is a visible method for achieving optimal energy-related behaviors and highlight the great possibilities for building future energy-related devices.