Effect of crystallinity on microwave tunability of pulsed laser deposited Ba0.5Sr0.5TiO3 thin films

Abstract

Barium Strontium Titanate (Ba0.5Sr0.5TiO3) thin films on (100) oriented MgO substrates were deposited by Pulsed Laser Deposition (PLD) technique. The deposition temperature of 750°C is kept constant and the oxygen working pressure is varied from ~1×10−1mbar to 1×10−4mbar. The X-ray diffraction pattern shows that higher oxygen working pressure deposited films are partially crystalline. The lower oxygen working pressure (1×10−4mbar) deposited films showed improved crystallinity. The crystallinity is further increased with a particular orientation as the laser fluence increased from 1.4J/cm2 to 2J/cm2.The microwave dielectric properties of these films were measured using Inter Digitated Capacitor (IDC) test structure. It is found that the maximum tunability (in IDC configuration) of 16.5% at 1GHz is obtained for oxygen working pressure and high fluence (1×10−4mbar and 2J/cm2) deposited films, whereas the other films tunabilities are in the range of 1–2% only. These studies also help us to explore the correlation between structure and microwave dielectric properties. Hence, in the present study the 1×10−4mbar and 2J/cm2 deposition conditions are found to be more helpful in unleashing conditions that lead to better tunability in Ba0.5Sr0.5TiO3 films.