Microstructure and dielectric response of SrTiO3/NdGaO3 interdigitated capacitors

Epitaxial strontium titanate (SrTiO3 or STO) thin films were prepared by an off-axis pulsed laser deposition technique on neodymium gallate (NdGaO3 or NGO) substrates held at temperature of 820 °C. This technique allows different film growth rates in a deposition. Coplanar capacitors were fabricated and dielectric responses were measured at 1 MHz and at 2 GHz, and from 300 K to 4 K. The electric field tunability of the dielectric constant and loss tangent were taken with a range of electric field. The structure and morphology of the films were analyzed using high-resolution X-ray diffractometry and atomic force microscopy, respectively. The results showed that the films are crystalline with (1 0 0) orientation and the grains are columnar. Increased in-plane grain size and reduced surface to volume ratio were found to play a major role in improved performance of the film coplanar capacitors. The film with the growth rate of approximate 40 Å/min showed the highest change in the dielectric constant with an electric field of 4 V/μm. The film also showed the largest in-plane grain size of about 3000 Å.