Bulk-like dielectric properties from metallo-organic solution–deposited SrTiO3 films on Pt-coated Si substrates

Abstract

SrTiO3 (STO) thin films were grown onto Pt/Ti/TiO2/SiO2/Si and bare Si substrates via metallo-organic solution deposition (MOSD). X ray diffraction, scanning electron microscopy, atomic force microscopy, spectroscopic ellipsometry (SE), and dielectric/insulating measurements were utilized to characterize the STO thin films. By optimizing the solution molarity, it is shown that it is possible to obtain low-frequency dielectric properties in STO thin films on Si substrates that approach those of bulk STO: a dielectric permittivity of 325 at 100 kHz with a tunability of ∼28% at ∼650 kV/cm, a low loss (<2%), and a leakage current density of 1.0 × 10−6 A/cm2 at 100 kV/cm. The bulk-like dielectric response of these films is attributed to the elimination of the relatively large in-plane tensile thermal stresses, which arise due to the thermal expansion mismatch between the STO film and the Si substrate. These tensile thermal stresses may be relaxed or completely eliminated through modification of the post-coalescence compressive growth stresses by precursor solution optimization. The SE data indicates that the STO thin films have a refractive index of ∼2.04 at 633 nm wavelength, which is lower than that of bulk STO. The dielectric, physical, and optical characterization results above the bandgap are consistent, but below the bandgap, the optical-frequency results demonstrate a ∼25% reduced dielectric response as compared to the bulk, which may be due to the different polarization mechanisms at work at high frequencies. These findings demonstrate that high-quality, electronic-grade, thin film STO films can be grown on Si substrates via the affordable, simple, and industry-standard MOSD technique by carefully adjusting the deposition parameters.