Ultra-high energy storage performance of field-induced ferroelectric Al2O3-inserted Hf0.5Zr0.5O2 thin films for electrostatic supercapacitors

This study investigates the impact of Al2O3 doping on the structural and chemical characteristics and the energy storage performance of atomic layer deposited Hf0.5Zr0.5O2 (HZO) thin films. By adjusting the number of Al2O3 dopant cycles and layer insertion positions, optimized Al2O3-inserted HZO films achieve a record-high energy storage density (ESD) of -138 J cm-3 among planar-structured (Hf,Zr)O2-based thin films, with a high efficiency of -80 %. The films maintain stable energy storage performance over 109 cycles at 6.0 MV cm-1 without electrical breakdown. A single Al2O3 cycle (-0.12 nm), uniformly diffused at multiple locations within the HZO matrix, suppresses the monoclinic phase and stabilizes the tetragonal phase. This structure enhances the fieldinduced ferroelectric (FFE) switching, decreases the hysteresis loop area, and increases the breakdown field (above -8.0 MV cm-1). In contrast, thicker Al2O3 layers (-0.24-0.36 nm) form continuous, non-diffusive layers that hinder FFE tetragonal phase stabilization. These findings highlight the critical role of precise Al2O3 insertion in maximizing the energy storage capabilities of (Hf,Zr)O2 thin films. High ESD was maintained at fast discharge times below 1 mu s. The effective discharge time is proposed as an efficient metric for future evaluations.