Hybrid high-temperature-superconductor (HTS)/semiconductor planar oscillator circuits that operate at a frequency of 8.4 GHz have been developed. In the original intended application, one of these circuits would serve as a local oscillator in a cryogenic heterodyne receiver in a spaceborne experiment on high-temperature superconductivity. The same attributes that make these circuits attractive for use aboard spacecraft could also make them attractive for use on Earth — especially in applications in which high frequency stability, low phase noise, and ability to withstand vibrations are required.
Like other planar microwave oscillators based on HTS resonators, these oscillators can be made to exhibit frequency stability almost as high as, and phase noise almost as low as, those of quartz-crystal- and dielectric-resonator-stabilized oscillators. An oscillator of the present type includes integrated circuitry that is less complex and more reliable, relative to the circuitry of quartz-crystal- and dielectric-resonator-stabilized oscillators. The resonance quality factor (popularly denoted as Q and defined as the energy stored in electromagnetic field ÷ energy dissipated in one cycle of oscillation) of an HTS resonator of the present type at a temperature of 77 K in the absence of an electrical load is typically about 104 — almost equal to the Q of an unloaded dielectric-resonator-stabilized oscillator; in contrast, the Q of an unloaded typical normal-metal resonator is <103.
The figure illustrates the layout of one of the hybrid HTS/semiconductor oscillators. All of the circuit elements are formed on the surface of a LaAlO3substrate. The active circuit element is a GaAs metal/ semiconductor field-effect transistor (MESFET). The passive HTS circuit elements include the resonator, reactive feedback lines, transmission lines, and dc bias lines; these elements are formed by etching of a deposited HTS film of YBa2Cu3O7-δ. The MESFET is electrically connected to the HTS circuit elements by Au wires with a diameter of 0.7 mil (0.18 mm) that are thermosonically bonded in place. Layered Ag/Au contact pads are deposited at the outer ends of the bias lines. Ceramic-chip capacitors and thin-film resistors are thermosonically bonded in place to provide filtering for the bias lines.
At the time of reporting the information for this article, 20 of the oscillators had been fabricated and subjected to a number of tests, including vibration tests and assessments of the effects of variations in the fabrication process. Of the 20 oscillators, 10 were assembled into working units and their performances were measured. At a temperature of 77 K, levels of output power into a 50-Ω load ranged up to 10 dBm. During incorporation into a full cryogenic receiver, output power levels ranged from 0.0 to 3.0 dBm, with less than 50 mW of dissipation.
This work was done by F. A. Miranda, R. R. Romanofsky, and K. B. Bhasin of Lewis Research Center and C. M. Chorey of NYMA, Inc. For further information, access the Technical Support Package (TSP) free on-line at www.techbriefs.com under the Electronic Components and Circuits category, or circle no. 108 on the TSP Order card in this issue to receive a copy by mail ($5 charge).
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