Enhanced polarization switching characteristics of HfO2 ultrathin films via acceptor-donor co-doping

Abstract

In the realm of ferroelectric memories, HfO2-based ferroelectrics stand out because of their exceptional CMOS compatibility and scalability. Nevertheless, their switchable polarization and switching speed are not on par with those of perovskite ferroelectrics. It is widely acknowledged that defects play a crucial role in stabilizing the metastable polar phase of HfO2. Simultaneously, defects also pin the domain walls and impede the switching process, ultimately rendering the sluggish switching of HfO2. Herein, we present an effective strategy involving acceptor-donor co-doping to effectively tackle this dilemma. Remarkably enhanced ferroelectricity and the fastest switching process ever reported among HfO2 polar devices are observed in La3+-Ta5+ co-doped HfO2 ultrathin films. Moreover, robust macro-electrical characteristics of co-doped films persist even at a thickness as low as 3 nm, expanding potential applications of HfO2 in ultrathin devices. Our systematic investigations further demonstrate that synergistic effects of uniform microstructure and smaller switching barrier introduced by co-doping ensure the enhanced ferroelectricity and shortened switching time. The co-doping strategy offers an effective avenue to control the defect state and improve the ferroelectric properties of HfO2 films.

Control of intrinsic ferroelectricity and structural phase in pure HfO2 films via crystalline orientation

“…Shi et al demonstrated that ferroelectricity of Hf 0.5 Zr 0.5 O 2 epitaxial thin films was related to different terminations of La 0.7 Sr 0.3 MnO 3 (LSMO) layer [29]. Zhou et al reported enhanced ferroelectricity in the HfO 2 ultrathin films using La 3+ -Ta 5+ co-doped strategy [30].…”

“…It was also proposed the epitaxial orientation significantly affects strain-induced phase transitions in ferroelectric BaTiO 3 films [32]. However, most studies on the ferroelectric properties of HfO 2 -based epitaxial films have focused predominantly on (111)-orientation [9,17,18,20,[28][29][30][37][38][39], leaving the correlation between crystalline orientation and ferroelectricity unexplored. Few studies have addressed on (001)-oriented HfO 2 -based epitaxial films [40,41], despite this orientation being more aligned with the direction of spontaneous polarization in ferroelectric hafnia-based films, which is crucial for understanding ferroelectric properties.…”