Ferroelectricity of pure HfOx in metal-ferroelectric-insulator-semiconductor stacks and its memory application

Abstract

Ferroelectricity in hafnium oxide (HfOx) and its various applications have been rigorously investigated in recent years. In particular, most studies have focused on a non-centrosymmetric ferroelectric phase that is developed via the injection of external ions into HfOx. However, the drawbacks of doped HfOx, such as serious dopant variation and thermal instability, have hindered its commercialization in low-power logic and memory applications. In this study, we demonstrated the ferroelectricity of pure HfOx without additional ion doping in metal-ferroelectric-insulator-semiconductor (MFIS) stacks. We experimentally confirmed that variation-resistant and thermally stable ferroelectric pure HfOx could be achieved with remarkable polarization by controlling the oxygen vacancies inside pure HfOx and the thermal quenching process for orthorhombic phase transition. Furthermore, to verify the feasibility of the ferroelectric pure HfOx in memory devices, the modulation of tunneling resistance was measured using MFIS ferroelectric tunnel junction (FTJ) devices, revealing that the tunneling current was adjustable over a 2-order current range via the polarization of the pure HfOx, implying that multiple current states could be obtained for multilevel memory operations.