Recent advances in GaN transistors for future emerging applications

In this paper, recent advances in GaN-based transistors for power switching and millimeter wave communications are reviewed. These two applications are emerging in addition to the widely developed power amplifiers at microwave frequencies mainly for cellular base stations. Reduction of the fabrication cost is strongly required for power switching GaN transistors, which is enabled by our epitaxial growth technology on large area Si substrates. Another requisite for the application is to achieve normally-off operation and our novel device structure called Gate Injection Transistors (GIT) enables it with low enough specific on-resistance (R on · A) and high drain current. Here, we also present the world highest breakdown voltage of 10400 V in AlGaN/GaN HFETs, extracting full advantage of the high breakdown strength of GaN. The used poly AlN passivation works as a surface heat spreader with its high thermal conductivity, which effectively relieves the channel temperature resulting in lower thermal resistances. The GaN device for future millimeter wave communication consists of MIS-type gate using so-called "in-situ" deposited SiN as a gate insulator, which exhibits high f max of 203 GHz and low noise figure of 1.4 dB at 28 GHz. The presented GaN transistors are promising for the two future emerging applications demonstrating high enough potential of the material systems.