Dielectric, energy storage, and loss study of antiferroelectric-like Al-doped HfO2 thin films

Antiferroelectric thin films have properties ideal for energy storage due to their lower losses compared to their ferroelectric counterparts as well as their robust endurance properties. We fabricated Al-doped HfO2 antiferroelectric thin films via atomic layer deposition at variable thicknesses (20 nm or 50 nm) with varying dopant concentrations (4 at. % or 8 at. %). 50 nm thick 8 at. % Al-doped HfO2 showed a maximum energy storage density of 63 J/cm3 while maintaining an efficiency of 85%. A study comparing these thin films revealed thicker films allowed for higher operating electric fields and thus higher energy storage densities at operating voltage. The loss tangents of the thin films at operating voltage were under 2% over the range of −4 to 4 MV/cm and at frequencies ranging from 500 Hz to 100 kHz. Reliability studies showed the thin films endure up to 106–107 cycles and the breakdown field of the films yielded Weibull moduli greater than 6 for all our thin films. The Weibull modulus provides a measurement of the consistency of the breakdown strength from sample to sample, with higher moduli indicating a more invariable result. These electrical characteristics along with the thin film's cycling endurance and reliability make antiferroelectric-like Al-doped thin films a promising material for energy storage applications.