40-Gbit/s InP-based HEMT IC technology for future lightwave communication systems

Over the past ten years, high electron mobility transistors (HEMTs) consisting of an InAlAs-InGaAs modulation-doped structure on an InP substrate have grown rapidly, not only as the highest speed-potential three-terminal devices but as excellent uniform devices that can be applied to a wide variety of ICs for microwave, millimeter-wave, and lightwave communication systems. In our HEMT structure, the electron channel is formed with a 15 nm thick InGaAs layer beneath a T-shaped gate with a 0.1 μm footprint. A novel InP gate-recess-etch stopper inserted into the InAlAs barrier layer dramatically improves the uniformity of transistor performance (average threshold voltage of -0.65 V has a standard deviation of <40 mV in a 3" wafer), which is essential for large-scale integration of digital logic circuits. The average transconductance, f/sub T/, and f/sub max/ are 1050 mS/mm, 195 GHz, and 230 GHz, respectively. In the last three years, 40 Gbit/s class lightwave communication ICs have been developed using InP-based HEMTs. The fabricated IC chips (2:1 time-division multiplexer IC, baseband amplifier IC, decision IC, 1/2 frequency divider IC, 1:2 demultiplexer, and exclusive-OR) offer practical speed performance beyond 40 Gbit/s with good yield.