Assessment of GaN high-electron-mobility transistor reliability for RF amplifier applications

As an electronic material, GaN possesses several material advantages over conventional III-V semiconductors that lead to an order of magnitude improvement in transistor RF output power density. The maturity of GaN amplifier technology is currently a topic of significant interest in the DoD community as several system insertion opportunities are emerging. Serving as an objective validator of GaN amplifier technology delivered to the government, NRL plays a key role in assessing RF performance and reliability to provide feedback to both government entities and contractors. To complete this task, we use a suite of dc, RF, and pulsed I-V electrical testing to identify and monitor electrical degradation of monolithic microwave integrated circuits (MMICs) as a function of time. In our most basic testing, MMICs are biased under normal operating conditions (with peak channel temperatures between 150°C and 225 °C) and monitored for 1000–3000 hours. Nearly all GaN technology delivered by contractors today will experience no electrical degradation during this RF operational life-test, but the question still remains: Are these amplifiers reliable for the lifetime of a system? To address this question, we routinely use elevated temperature (channel temperatures between 300°C and 375°C) RF life-testing to accelerate failure mechanisms and determine lifetime at typical operating temperatures via Arrhenius extrapolation. Post-stressed, parametrically failed devices are subjected to failure analysis using a variety of materials characterization techniques, such as focused-ion-beam cross-sectioning, transmission electron microscopy, energy dispersive spectroscopy for elemental analysis, etc., in order to correlate changes in electrical behavior to physical degradation mechanisms. In this talk, an overview of our testing methodology will be presented, along with discussion about degradation mechanisms that are observed in GaN transistors.