Ferroelectricity in hafnium oxide: CMOS compatible ferroelectric field effect transistors

We report the discovery of ferroelectricity in crystalline hafnium silicon oxide. If HfO ₂ based thin films, at a composition where the tetragonal phase is not yet stable, are crystallized in presence of a cap, the formation of an orthorhombic phase is observed. o-HfO ₂ shows a piezoelectric response, while a polarization measurements exhibit a remanent polarization above 10 μC/cm ² at a coercive field of 1 MV/cm, confirming this phase to be ferroelectric. Transistors fabricated with this material exhibit a permanent and switchable shift of the threshold voltage, allowing the realization of CMOS-compatible ferroelectric field effect transistors (FeFET) with sub 10 nm gate insulators for the first time.