Manufacturers of Gallium-Arsenide (GaAs) and other semiconductor devices use an accelerated life test to check the reliability of MESFETs. Such tests provide information about failure mechanisms, activation energies, and failure rates. With these tests, an application note from WJ Communications, Inc. (San Jose, CA) works to show that catastrophic failure may occur at conservative channel temperatures in excess of 220°C.
The four-page application note, which is titled “GaAs Reliability at High Operating Temperatures,” begins by reviewing some of the existing literature on this subject. According to data on GaAs MESFET reliability, the main failure mechanisms involve gate metallization, Schottky contact, and source/drain ohmic contacts. The dominant failure mode is channel related.
With high-temperature life tests, most physical/chemical processes can be accelerated with temperature at a rate that is correlated to a constant: the activation energy. Normal thermal-analysis techniques are listed. In addition, equations are provided for MESFET failure mechanisms. The paper shows that MESFET reliability and channel temperature are strongly linked. Under normal RF and DC conditions, the channel temperature can be in excess of 250°C without causing instantaneous catastrophic failure.
Although the company has performed much RF testing, the application note includes only two tests and their results: MMIC reliability under RF drive and FET life test. The tests do not uncover any failure mechanisms due to an excessive channel temperature of 203°C. In addition, the devices are shown to suffer an ambient temperature of 220°C without channel breakdown.
WJ Communications, Inc., 401 River Oaks Parkway, San Jose, CA 95134-1916; (408) 577-6200, FAX: (408) 577-6621, Internet: www.wj.com