Thermal study of semiconductor-superconductor hybrids

The authors have conducted an experiment to evaluate the thermal problems that would result if a GaAs amplifier chip were flip mounted via solder-ball connections to an otherwise superconducting receiver on a larger Si chip. The GaAs chip is modeled by a chip carrying a thin-film resistor, which is used to dissipate the same amount of heat as the GaAs IF (intermediate frequency) amplifier. The energy gaps exhibited by Nb tunnel junctions are used to monitor the temperature in a number of places surrounding the heat source. The results indicate that thermal effects do not preclude the use of semiconductor-superconductor hybrid receivers. The data indicate that for applications involving power dissipation less than 150 mW (gain of up to 45 dB) on a chip of area of approximately 0.1 cm², neither switching of lines nor thermal fluctuations of devices is likely to be a problem when the devices are at least 1 mm from the edge of the chip and away from the path of the helium bubbles. The limit on power dissipation is likely to be temperature fluctuations rather than excessive temperature