  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.
