Pulsed laser deposition of ferroelectric thin films for room temperature active microwave electronics

Single phase, (100) oriented Ba0.5Sr0.5TiO3 films have been deposited by pulsed laser deposition (PLD) onto (100) LaAlO3, SrTiO3, MgO substrates and single crystal (100) Ag films. Single phase, (100) oriented KTa0.6Nb0.4O3 films have been grown on (100) SrTiO3 and MgO. The dielectric properties of these films were measured as a function of DC bias at 1 MHz and 1 to 20 GHz. The 1 MHz measurements were made as a function of temperature between 30-350 K and the 1 to 20 GHz measurements were made at room temperature. Dielectric properties were measured using interdigitated and parallel plate capacitors. A 75% change in the capacitance was achieved using a 40 V bias across a 5 mu m interdigitated capacitor gap (80 kV/cm). Capacitors with high tuning were always accompanied by low Q's (similar to 10's). Conversely, capacitor Q's in excess of 500 were observed but these films had poor tuning. Deposited films were annealed over a temperature range of 900 to 1250 C for 8 to 12 hours. Post annealing the films generally improved both the Q and percent tuning and indicates a direction for further dielectric film improvement.