Strontium doped hafnium oxide thin films: Wide process window for ferroelectric memories

Ferroelectricity in hafnium oxide has been reported for the incorporation of Al, Si, Y and Gd or in a solid solution with the chemically similar ZrO 2 . Here, we report strontium as the first bivalent and — so far — largest dopant in terms of atomic radius also inducing ferroelectric behavior. Besides the solid solution of HfO 2 /ZrO 2 for Sr:HfO 2 , ferroelectricity is observed in the widest concentration range of all dopants used up to now. First results of ab initio simulations also suggest such a comparatively wide window for ferroelectricity. With a coercive field of about 2 MV/cm another figure exceeds the characteristics reported before. A maximum remanent polarization of 23 μC/cm ² also ranks among the highest values reported until now. The fabricated TiN-Sr:HfO 2 -TiN capacitors exhibit switching times in the nanosecond range and still retain 80 % of their initial remanent polarization after 10 ⁶ endurance cycles. The 10 nm ferroelectric thin films prepared by atomic layer deposition are capable of integration into 3D capacitors or FinFETs.