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

Ferroelectricity in hafnium oxide was reported for the incorporation of Al [1], Si [2], Y [3] and Gd [4] or in a solid solution with the chemically similar ZrO₂ [5]. 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 HfO₂/ZrO₂ for Sr:HfO₂, 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/cm² also ranks among the highest values reported until now [6]. The fabricated TiN-Sr:HfO₂-TiN capacitors exhibit switching times in the nanosecond range and still retain 80 % of their initial remanent polarization after 10⁶ endurance cycles. The 10 nm ferroelectric thin films prepared by atomic layer deposition are capable of integration into 3D capacitors or FinFETs.