Failure analysis for RF characteristics of GaAs MESFETs

The effect of thermal stress on the noise degradation of GaAs MESFETs was i nvestigated. Minimum noise figure, associated gain, scattering parameters, and capacitance-voltage profiles were measured during the tests, and the el ectro-chemical properties after thermal stress were analyzed by means of Au ger electron spectroscopy, X-ray diffractometery, cross-sectional transmiss ion electron microscopy, and capacitance-voltage measurements. The RF failu re mode consists of an increase of the minimum noise figure and a decrease of associated gain of the FETs. The extracted equivalent circuit elements f rom measured scattering parameters were used to evaluate the influence of e ach parameter on the noise degradation. The parametric estimation showed th at the noise degradation was mainly attributed to the decrease of a.c. tran sconductance. From the C-V analysis, we found that the decrease of a.c. tra nsconductance was caused by the decrease of effective carrier concentration . From the electro-chemical analysis, the decrease in effective carrier con centration was resulted from the gate-sinking by the thermally activated in terdiffusion between the gate metal and the GaAs channel layer. Therefore, the thermally activated carrier compensation by Ga vacancies in the channel is proposed to be the main failure mechanism for noise degradation of GaAs MESFETs. (C) 1999 Elsevier Science Ltd. All rights reserved.