RF Arrhenius life testing of X-band high voltage GaAs PHEMTs

We have conducted an accelerated temperature, RF Arrhenius life test study of high voltage (HV) GaAs PHEMTs fabricated with the TriQuint HV3 production process. The transistors were embedded in a single-stage MMIC with 50 ohm input and output impedances. The HV-GaAs MMIC is an X-band power amplifier with a gate width of 4.8 mm consisting of 32 gate fingers of 150 mum each. The devices were tested at channel temperatures of 275, 300, and 320degC. To maintain constant channel temperature over the course of the life test, the fixture temperature was changed to account for decreasing power dissipation during the life test. The MMICs were tested at a frequency of 10 GHz and a drain-source voltage of 14 V. The input power level was 28 dBm which corresponds to 2 dB gain compression. The MMICs were characterized with dc and RF measurements before and after life testing to assess electrical and performance changes as the result of the life tests. The transfer characteristics before and after stress are shown. The observed decrease in I_DSS was accompanied by a change in V_TH of +0.13 V. This test is still ongoing, and a few devices remain on test at 275degC. The median time to failure (MTTF) at channel temperatures of 300 and 320degC are 940 and 400 hours, respectively. The MTTF at 275degC is 2700 hours, based on the present amount of degradation. The degradation of power output and drain current were nearly linear with time. The Arrhenius relationship for this data yielded an activation energy of 1.2 eV and an extrapolated MTTF of 5times10⁶ hours at a channel temperature of 150degC. Failure analysis will be presented.