A STUDY ON RELIABILITY AND FAILURE-MECHANISM OF T-SHAPED GATE HEMTS

This paper describes the reliability on recess type T-shaped gate HEMT s and their major failure mechanism investigated by accelerated life t ests and following failure analysis. In this study, high temperature s torage tests with a DC bias condition have been conducted on three dif ferent recess depths of 100, 125, and 150 nm. The results have clarifi ed that the shallow recess devices of under 125 nm depth have no degra dation in minimum noise figure F-min or gain G(a) characteristics, ind icating that standard HEMT devices, whose recess depth is chosen to be far under 125 nm, possess a sufficient reliability level. However, th e devices with deep recess of 150 nm have shown degradation in both F- min and G(a). Precise failure analyses including SEM observation and v on Mises stress simulation have firstly revealed that the main failure mode in deeply recessed T-shaped gate HEMTs is increase in gate elect rode's parasitic resistance R(g), which is caused by separation of ''h ead'' and ''stem'' parts of the T-shaped gate electrode due to thermo- mechanical stress concentration.