Microwave phase shifter employing SrTiO3 ferroelectric varactors

Nonlinear microwave properties of thin SrTiO3 ferroelectric films at ambient temperatures were investigated. A tunability factor of 1.7 and loss tangent of about 0.01-0.015 were measured at frequencies of 2-10 GHz for SrTiO3 thin film planar varactors at room temperature. The performance of an X-band microstrip phase shifter employing the SrTiO3 planar varactors at room temperature is reported. Continuous phase shift in the range of (0-55) deg under bias voltage of 0-400 V at operating frequency band (8.6-9.0) GHz was observed. A figure of merit for the phase shifter is 110 deg/dB and the phase error is smaller than 5 deg. To our knowledge, it is the first demonstration of the microwave application of SrTiO3 varactors operating as nonlinear elements at room temperature and a record result for figure of merit for ferroelectric phase shifters.