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oped for new markets. Recently, power electronics using GaN are attracting much attention. In these applications, enhanced-mode operation has been required with high reliability. This commercialization will start after 2010.2 Experimental procedures in Fujitsu A specific device structure to achieve high efficiency operation for wireless communication application at 2 GHz was developed in Fujitsu. This GaN HEMT consists of metal organic vapour phase epitaxy (MOVPE) grownn-GaN/n-AlGaN/ i-GaN structure, which was called surface-charge-controlled structure as shown in Fig. 2 [4]. The n-type doped GaN cap layer can suppress dispersion in I-V characteristics up to V ds of 100 V. Figure 3 shows device simulation results of un-doped AlGaN-cap case and n-GaN cap case. The n-AlGaN electron supplying layer was used for both cases. In the AlGaN-cap layer device, its built-in electric field almost reaches the breakdown electric field strength, causing low reliability. When using n-GaN cap layer, built-in electric field can be suppressed by piezoelectric charge between the n-GaN cap layer and n-AlGaN layer. Recessed ohmic technique was used to reduce the ohmic contact resistance [5]. SiN passivation layer was optimized to obtain lower trap device structures. SiC substrates were used to obtain good thermal managements.In this paper, a current status and future technologies of highpower GaN HEMTs was described. First, commercialization roadmap was shown with output power and efficiency status. Power electronics benchmark was also introduced. Reliability improvement technologies were addressed with recent issues such as drift phenomena. Then, future requirements for ex-panding GaN electronics market were shown with some recent device developments. Novel E-mode recessed GaN-HEMT has been developed using the triple cap layer structure. High-k insulated gate HEMTs using Ta 2 O 5 were also developed. Finally, we described the next generation GaN HEMTs for millimeter-wave applications. 1136 T. Kikkawa et al.: High performance and high reliability AlGaN/GaN HEMTs

AIGaN/GaN high electron mobility transistors (HEMTs) have been developed for current-collapse-free operation at high drain bias voltages. The newly designed single-chip GaN H E W amplifier for W-CDMA h e station applications achieves a record CW output power of 150 W with a high power-added efficiency (F'AE) of 54% at 2.1 GHz. The amplifier, combined with a digital pre-distortion (DPD) system, also demonstrates a state of the art efficiency of 40% with an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 4 4 e i W-CDMA signals and reaches the saturated peak power level of 174 W with a drain supply voltage of 63 V. We prove for the first time that the AIGaN/GaN HEMT amplifier can completely fulfills the W-CDMA system requirement.

A state-of-the-art highly reliable 250 W AlGaN/GaN high electron mobility transistor (HEMT) push-pull transmitter amplifier operated at a drain bias voltage of 50 V is described. The amplifier, combined with a digital predistortion (DPD) system, also achieved an adjacent channel leakage power ratio (ACLR) of less than -50 dBc for 4-carrier wideband code division multiple access (W-CDMA) signals with a drain supply voltage of 50 V. I also demonstrate its stable operation under RF stress testing for 1000 h at a drain bias voltage of 60 V. Stable gate-leakage current for high-temperature operation was verified. Device fabrications on 4 inch sapphire and 3 inch semi-insulating (S.I.) SiC substrates were also addressed. These performances clarify that an AlGaN/GaN HEMTs amplifier is suitable for 3G W-CDMA systems.