NONLINEAR BEHAVIOR OF THIN-FILM SRTIO3 CAPACITORS AT MICROWAVE-FREQUENCIES

The voltage-dependent dielectric constant (epsilon) of SrTiO3 (STO) th in 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 t he level of the third order intermodulation distortion (IMD) signal re lative to the input signal level. Small signal dielectric properties s uch as capacitance, tuning, and loss (tan delta) were also measured at 1 MHz, 3 GHz, and 10 GHz, at temperatures from 4.2 to 300 K. Planar c apacitors were comprised of highly (100)-oriented, 1 mu m thick STO fi lms deposited via magnetron sputtering onto CeO2-buffered (<1(1)under bar 02>)-oriented sapphire substrates, with 10 mu m gaps between the e lectrodes. Deviations from the anticipated cubic dependence of the thi rd order IMD product on incident power, for incident power ranges from -10 to 22 dBm, were attributed to conductivity nonlinearity. At incid ent power levels of 22 dBm and with no de bias applied to the capacito r, the level of the third order IMD product was 21 dB below the fundam ental signal level. Application of a 10(7) V/m de electric held bias a cross the capacitor suppressed the third order IMD by an additional 10 dB. The nonlinear properties of thin film STO capacitors as a functio n of microwave voltage were determined by comparing the experimental a nd theoretical dependencies of the IMD products. (C) 1998 American Ins titute of Physics.