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 ZrO2. 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. 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.

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