Highly uniform InAlAs-InGaAs HEMT technology for high-speed optical communication system ICs

The authors have developed a highly uniform, InP-based high-electron-mobility transistor (HEMT) technology for high-speed optical communication system integrated circuits (ICs). Special attention was paid to obtaining a high yield and uniformity without degrading the high-frequency characteristics of these HEMTs. An InP etch-stopper layer was employed to control the gate recess etching. The authors successfully fabricated InAlAs-InGaAs HEMTs with a cutoff frequency of 175 GHz after interconnection, which is sufficiently high for application in 40-Gb/s optical communication ICs. The standard deviation of the threshold voltage was only 13 mV across a 3-in wafer. They also developed a fabrication process for a Y-shaped gate to maintain high uniformity, enabling us to integrate more than a thousand transistors with a 0.1-μm-class gate length. With this technology, ICs with over 1000 transistors were successfully fabricated and operated at over 40 Gb/s. Furthermore, the authors fabricated a 2:1 multiplexer that had more than 200 transistors and reached an operating speed of 90 Gb/s. They have thus concluded that their InAlAs-InGaAs HEMT technology can be applied to fabricate high-speed ICs for optical communication systems.