Upset Events in Josephson Digital Devices under Alpha Particle Irradiation

Preliminary results on the effects of 5 MeV alpha particle irradiation on the electrical characteristics of large area (approximately 60 μm2) Josephson Nb-amorphous Si-Nb tunnel devices indicate that these particles are effective in producing upset events when the device is operated in a switching mode. For bias currents very close to the critical current, IC, upset rates are near 0.1 per alpha. At a reduced bias current of 0.65 IC the upset rate is decreased but is still finite (0.002 per alpha). In addition, an hysteretic effect was observed for the critical current of the device under alpha irradiation. A simple heating model does not appear adequate to explain the observed upset rate as a function of bias current and the hysteretic effect.