Low-temperature, high-current lifetests on InP-based HBT´s

Accelerated lifetests have been conducted on AlInAs-GaInAs HBT devices on InP wafers. Current densities were relatively high, while junction temperatures were low enough (125 and 160°C) to provide a check for low activation energy failures. 40 devices were tested, and about 14,000 hours have been accumulated so far. Changes similar to those found in conventional higher-temperature lifetests were observed, at times which are consistent with the activation energies of 1.1 to 1.5 eV determined in those tests. Otherwise, no significant changes were observed. Based on this, and some reasonable assumptions about acceleration factors, any failure mechanism with E_a down to 0.35 eV would not be expected to occur during use at 80°C until a mean time of at least 2×10⁵ hrs, which is more than a typical 15-year product life. Also, the rate for “freak” or “random” failures is found to be 344 FITs, with 95% confidence, again with reasonable assumptions about acceleration factors