DIELECTRIC-PROPERTIES OF SRTIO3 THIN-FILMS WITH CA AND ZR PARTIAL SUBSTITUTIONS FOR ACTIVE MICROWAVE APPLICATIONS

The structure and dielectric properties of SrTiO3 thin films with eith er 5% Ca or Zr substitutions have been investigated. Thin films of the se materials were deposited onto (100) LaAlO3 substrates by pulsed las er deposition (PLD) at temperatures of 750 degrees C in 350 mTorr of o xygen. As-deposited films, characterized by x-ray diffraction, were si ngle phase and well oriented with omega - scan widths of < 0.2 degrees for the (002) reflection. The capacitance and dissipation factor were measured at 1 MHz to 1 GHz for the deposited films as a function of t emperature and electric field (80 kV/cm) using Ag interdigital capacit ors deposited on top of the SrTiO3 films. For unsubstituted SrTiO3, a peak in the capacitance vs. temperature curve was observed at similar to 60K. The temperature dependence of the dissipation factor was simil ar and also exhibited a maximum at SOK with a value of 0.025. A 50% ch ange in the capacitance can be achieved for the SrTiO3 film at similar to 80 kV/cm. Substitution of 5% Ca on the Sr site does not change the temperature dependence of the capacitance but leads to an increase in dissipation factor at 60 K to similar to 0.05. In addition, the capac itance decreases more rapidly with lower electric fields for partial C a substitution compared to pure SrTiO3. Substitution of 5% Zr for Ti l eads to a dramatic reduction in the capacitance and correspondingly, t he field dependence of the capacitance. However, the Zr substituted fi lms have extremely low losses, similar to 0.004. The ability to contro l both the magnitude of the dielectric constant and the losses will ma ke these materials useful for frequency-tunable active microwave appli cations.