Dielectric properties of srtio3 thin films with ca and zr partial substitutions for active microwave applications

Abstract

The structure and dielectric properties of SrTiO3 thin films with either 5% Ca or Zr substitutions have been investigated. Thin films of these materials were deposited onto (100) LaAlO3 substrates by pulsed laser deposition (PLD) at temperatures of 750°C in 350 m Torr of oxygen. As-deposited films, characterized by x-ray diffraction, were single phase and well oriented with ω - scan widths of < 0.2° 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 temperature and electric field (80 kV/cm) using Ag interdigital capacitors deposited on top of the SrTiO3 films. For unsubstituted SrTiO3, a peak in the capacitance vs. temperature curve was observed at ∼60K. The temperature dependence of the dissipation factor was similar and also exhibited a maximum at 60K with a value of 0.025. A 50% change in the capacitance can be achieved for the SrTiO3 film at ∼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 ∼0.05. In addition, the capacitance decreases more rapidly with lower electric fields for partial Ca substitution compared to pure SrTiO3. Substitution of 5% Zr for Ti leads to a dramatic reduction in the capacitance and correspondingly, the field dependence of the capacitance. However, the Zr substituted films have extremely low losses, ∼0.004. The ability to control both the magnitude of the dielectric constant and the losses will make these materials useful for frequency-tunable active microwave applications.