Interface Properties Between SrTiO 3 Thin Films and Electrodes
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A. M. CLARK, JIANHUA HAO, WEIDONG SI, and X. X. XI Department of Physics, The Pennsylvania State University, University Park, PA 16802
ABSTRACT SrTiO 3 (STO) thin films were grown by pulsed laser deposition on single crystal STO substrates with a SrRuO 3 buffer layer, which also serves as a bottom electrode. Measurements of the low frequency dielectric properties were performed in a parallel plate capacitor configuration for a range of temperatures using different top electrode materials. The contribution to the interfacial potential from Schottky barriers was investigated. In comparison to STO single crystals, thin films have continued dielectric non-linearity above T - 70 K. This complicates conventional Schottky barrier height measurements using C-V curves because both Schottky barriers and dielectric non-linearity result in a decrease in dielectric constant under applied electric fields. However, by using I-V data, difficulties related to field dependence of the dielectric constant may be removed. Barrier height measurements for both metal and oxide electrodes were performed for T > 70 K. Calculated barrier heights from a modified Schottky equation were very low for an oxide electrode, and an order of magnitude higher for a normal metal electrode.
INTRODUCTION SrTiO 3 (STO) is a ferroelectric material which has low dielectric loss and large dielectric nonlinearity at low temperatures.[1][2][3] These properties make it an ideal material for frequency and phase agile microwave devices. The loss tangent is temperature dependent, and in single crystals ranges from a minimum of 10' to 10-3 at the loss peak. However, previous reports of the dielectric loss in STO thin films have been much higher: tan5 of the order 10- 3 and increasing to 10-2 with decreasing temperature. The existence of a "dead-layer" at the interface between thin films and metal electrodes effectively reduces the dielectric constant, by an order of magnitude at low temperature in STO thin films as compared to the bulk. Device applications for STO thin films become much more attractive if, combined with a large tunabilty, the loss tangent is reduced to levels close to that of single crystal STO.
31 Mat. Res. Soc. Symp. Proc. Vol. 596 ©2000 Materials Research Society
We present here results of low frequency (lkHz)) dielectric constant and loss tangent of STO thin films of thickness 1 pm, and I-V measurements of 0.4Asm STO films. The measurements of the dielectric properties with temperature show a strong dependence on the choice of electrode material. The effect of the interfacial potential on reducing the dielectric constant was investigated by studying the Schottky barriers for different electrode materials on 0.4 pm STO thin films using a modified Schottky equation.
EXPERIMENT The STO films were grown by pulsed laser deposition (A=248 nm, energy density 02 pressure. The STO was deposited on a 100nm SrRuO 3 (SRO) electrode layer on single crystal STO substrates, heated to 750'C during deposition and cooled to room temperature in 400Torr of 02
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