Reliability of E/D PHEMT process for control circuit applications

WA-COM has developed an E/D pHEMT process for use in control circuit applications. By adding an E-mode FET to our existing D-mode pHEMT switch process, we are able to integrate logic circuits onto the same die as the RF portion of complex control products (multi-throw switches, multi bit attenuators, etc.). While this capability is not uncommon in the GaAs community, it is new for our fab, and provided new challenges both in processing and in reliability testing. We conducted many tests that focused on the reliability characteristics of this new Emode FET; in the meanwhile, we also needed to assure no degradation of the already qualified D-mode FET. While our initial test suggested low mean-time-tofailure (MTTF) for E-mode devices, recent reliability results have been much better, exceeding our minimum MTTF requirement of 106 hours at channel temperature TCH= 125 °C. Our analysis also shows that devices from this process have high activation energy (Ea 1.6 eV).