Improved dielectric response in strontium titanate thin films grown by pulsed laser ablation

We have grown epitaxial strontium titanate films on lanthanum aluminate substrates at a range of oxygen pressures and substrate temperatures. The complex dielectric function was measured versus frequency (10 kHz to 1 MHz) and temperature (room temperature to 4.2 K) on coplanar capacitors patterned on the films. Preliminary data from 1.5 to 2.5 GHz is also presented. The dielectric constant epsilon(r) was as high as 4600 at 65 K, a factor of two greater than previously reported for strontium titanate thin films and a factor of 1.8 greater than the bulk value at the same temperature. Tuning the capacitor by applying a de bias of +/- 15 V across the 3 mu m coplanar gap at 4.2 K yielded a ratio of maximum to minimum dielectric constant of 2.8. At 101 K this ratio was 2.2. A bulk capacitor does not show tuning over such a large temperature range.