Bias acceleration of InP HEMTs degradation was examined and drain resistance increase dependence on gate-drain bias was clarified. It was found that both a strong electric field and a high current density, when impact ionization rate was high, enhance the R{sub}d increase. By reducing surface contamination in the fabrication process, which we speculated to be responsible for donor inactivation and drain resistance increase, we were able to improve device lifetime and thereby achieve long-lifetime HEMTs and 40-Gbit/s InP HEMT-ICs. In addition reducing operating bias resulted in the T-FFs lifetime of over 1 × 10{sup}7 hours at 100℃, indicating that this is the key to achieving high IC reliability.
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