1986 Volume 35 Issue 394 Pages 804-809
Josephson-Junction device is expected to be applied as a highly efficient computer switching device. Such a device is usually subjected to thermal cycles from room temperature in manufacturing and repairing stages to absolute 0K in actual use.
Due to these thermal cycles hillock can be initiated on the base electrode, and micro bridge may be formed between the upper and lower electrodes.
In this study, many typical hillock formations in Pb-In alloy films were observed by a scanning electron microscope. An equation for the hillock growth rate, dSh/dN, was derived experimentally as a function of film thickness, h, and temperature change amplitude, ΔT, as follows.
where Sh is the hillock area, and N is thermal cycles.
When the value of h was larger than 0.6μm, hillock was initiated at the first thermal cycle independent of ΔT. When the value of h was less than 0.6μm, the critical thermal cycles of hillock initiation increased with decreasing film thickness, h, and temperature change amplitude, ΔT. There may be the threshold region of hillock initiation under certain critical values of film thickness and temperature change amplitude.
On the other hand, hillock was not initiated easily for Au-(Pb-In) alloy film.