Epitaxial SrTiO3 (STO) thin films were grown successfully by rf reactive magnetron sputtering on (111)Pt/(100)MgO substrates. At present, the dielectric constant of the STO film (110 nm thick) has reached 370ε0 at room temperature. Despite the general difficulty of obtaining a high dielectric constant for the ultrathin STO films, a fairly thin STO film of 39 nm showed a large value of 240ε0. The existence of an STO degraded layer at the interface was suggested by the Fourier transform infrared spectrum observed for the ultrathin STO film of 3.5 nm. The interfacial layer with poor quality diminishes the mean dielectric constant of the STO thin films. This interfacial layer effect offers an explanation for the difficulty in obtaining a high dielectric constant of the ultrathin STO films. Moreover, the band diagram of a Cr/STO/Pt metal-insulator-other metal structure is discussed. Compared to the experimental results, a space-charge-free band diagram was concluded to be appropriate and was consistent with the observed Schottky-like leakage current and the inverse proportionality of the capacitance and the STO thickness.
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