Nonlinear behavior of thin film SrTiO3 capacitors at microwave frequencies

The voltage-dependent dielectric constant (e) of SrTiO3 (STO) thin films is the basis for developing cryogenic capacitors for tunable microwave applications. In this study, the effect of microwave signal level on nonlinear response at 1.7–1.9 GHz was examined by measuring the level of the third order intermodulation distortion (IMD) signal relative to the input signal level. Small signal dielectric properties such as capacitance, tuning, and loss (tan δ) were also measured at 1 MHz, 3 GHz, and 10 GHz, at temperatures from 4.2 to 300 K. Planar capacitors were comprised of highly (100)-oriented, 1 μm thick STO films deposited via magnetron sputtering onto CeO2-buffered (11_02)-oriented sapphire substrates, with 10 μm gaps between the electrodes. Deviations from the anticipated cubic dependence of the third order IMD product on incident power, for incident power ranges from −10 to 22 dBm, were attributed to conductivity nonlinearity. At incident power levels of 22 dBm and with no dc bias applied to the capac...