Enhanced Microwave Commutation Quality Factor of Tunable Capacitors Based on SrTiO3 Thin Films

Thin films of strontium titanate were grown on a polycrystalline aluminum oxide substrate using magnetron sputtering. These films exhibit high structural quality and nonlinear properties, which make them promising for microwave applications. Planar capacitors based on SrTiO₃ films demonstrated a tunability of 1.65 with a microwave Q-factor of at least 110 in the entire range of control voltages without deterioration of losses, and a slow capacitance relaxation level no more than 4%, which is significantly better than currently published data for planar ferroelectric elements. This is the first successful attempt to create a planar SrTiO₃ capacitor on an alumina, which demonstrates a commutation quality factor CQF of 3300 at microwaves.