HYBRID HIGH-TEMPERATURE SUPERCONDUCTOR GAAS 10 GHZ MICROWAVE-OSCILLATOR - TEMPERATURE AND BIAS EFFECTS/

Hybrid YBa2Cu3O7-x superconductor/GaAs microwave oscillators have been designed, fabricated and characterized. The planar oscillators were b uilt on a single 10 mm x 10 mm LaAlO3 substrate. The active elements i n the hybrid oscillators were GaAs MESFETs. A ring resonator was used to select and stabilize the frequency. A superconducting ring resonato r had a loaded Q at 77 K which was 8 times larger than the loaded Q of a ring resonator fabricated out of copper. S-parameters of the GaAs F ET were measured at cryogenic temperatures and used to design the osci llator, which had a reflection mode configuration. The transmission li nes, Tf chokes and bias lines were all fabricated from YBa2Cu3O7-x sup erconducting thin films. The performance of the oscillators was measur ed as a function of temperature. The rate of change of the frequency a s a function of temperature was smaller for an oscillator patterned fr om a pulsed laser deposited film than for an oscillator patterned from a sputtered film. As a function of bias at 77 K, the best circuit had an output power of 11.5 dBm and a maximum efficiency of 11.7%. The po wer of the second harmonic was 25 dB to 35 dB below that of the fundam ental, for every circuit. At 77 K, the best phase noise of the superco nducting oscillators was -68 dBc/Hz at an offset frequency of 10 kHz a nd less than -93 dBc/Hz at an offset frequency of 100 kHz. At an offse t frequency of 10 kHz, the superconducting oscillator Rad 12 dB less p hase noise than the copper oscillator at 77 K. The superconducting osc illators at 77 K had 26 dB less phase noise than the copper oscillator operating at 300 K.