Nucleation and growth of ultrathin BaTiO3 films on single terminated Nb:SrTiO3 (100) substrates for ferroelectric tunnel junctions

The authors report on a new table top radio frequency (RF)-magnetron sputtering unit and process for the sputter deposition of barium titanate thin films. Like silicon substrate in conventional electronics, strontium titanate (SrTiO3) is the substrate of choice in the emerging field of oxide electronics and hence Nb doped SrTiO3 n-type semiconducting substrates were considered. The authors observe substrate etching and nonstoichiometry in the film composition at high RF-power and low processing pressure, respectively. However, films deposited at 20 mTorr and 10 W of RF power resulted in stoichiometric BaTiO3. Layer by layer (two-dimensional) growth, prerequisite for epitaxial BaTiO3 on Nb:SrTiO3 (100) substrates, were realized at 600 °C. Hysteresis loops (phase angle versus applied voltage) in piezoresponse force microscopy confirm ferroelectricity of the films. Ultrathin epitaxial BaTiO3 on Nb:SrTiO3 (100) is of great interest as a ferroelectric tunnel junction with pronounced contrast between the ON/OFF...