ELEVATED-TEMPERATURE STABILITY OF GAAS DIGITAL INTEGRATED-CIRCUITS

The elevated temperature stability of a commercial GaAs enhancement-de pletion-mode MESFET process has been characterized; the observations m ade are relevant to device operation at elevated temperatures, to effo rts to do optoelectronic integration on GaAs integrated circuits by se lective-area epitaxial growth, and to long term circuit and device rel iability, Although the transistor electrical characteristics are stabl e for up to five h at 500 degrees C, a metallurgical reaction between the interconnect metal AlCux core and WNx claddings has been identifie d which limits circuits to five h at 470 degrees C, This later reactio n proceeds with an activation energy of 3.5 eV and results in a 15-fol d increase in interconnect metal sheet resistance, A geometry-dependen t increase in ohmic contact resistance is seen at somewhat higher temp erature which is ascribed to the penetration of aluminum-containing co mpounds to the ohmic contact edge.