October 17, 2005 – Oki Electric Industry Co. Ltd., Tokyo, Japan, has unveiled the development of a gallium nitride high electron-mobility transistor (GaN-HEMT) formed on a silicon substrate. The transistor, which was jointly developed with the Research Center for Micro-Structure Devices at the Nagoya Institute of Technology, was revealed at the 208th Meeting of the Electrochemical Society, in Los Angeles, CA, this weekend. The GaN-HEMT has achieved improved amplification performance, with its transconductance rating of 350mS/mm (reportedly a world record) and maximum oscillation frequency of 115GHz. Oki Electric plans to produce the transistors for smaller and lower power-consumption wireless communication systems.
Power transistors using GaN are traditionally developed on a silicon carbide substrate because of its relatively easy crystal growth capability, but the downside is the low quality, difficulty in moving to larger diameters, and expense of the substrate. The company claims that the AlGaN/GaN structure is grown on the silicon substrate with fewer defects and lower cost. High electron mobility was achieved by forming the gate electrode on a recessed structure, reducing gate length to 0.2µm, developing a recessed structure for the ohmic electrodes, and optimizing the device structure.