Enhancing ferroelectricity in dopant-free hafnium oxide

In this study, we control the oxidant dose to promote ferroelectricity in dopant-free ALD hafnium oxide films. By lowering the oxidant dose during growth, we show that we can achieve near total suppression of the monoclinic phase in sub-10 nm hafnium oxide films with no major impurity doping. Using metal-insulator-metal structures, we demonstrate that lowering the oxidant dose can give rise to a six-fold improvement in remanent polarization. Using this technique, we observe a remanent polarization of 13.5 μC/cm2 in a 6.9 nm-thick hafnium oxide film and show that some ferroelectricity can persist in pure hafnium oxide films as thick as 13.9 nm. Using a trap-assisted tunneling model, we show the relationship between the oxidant dose and oxygen vacancy concentration in the films, suggesting a possible mechanism for the suppression of the monoclinic phase.