Recent Progress on GaN HEMTs
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1108-A03-01
Recent Progress on GaN HEMTs Shigeru Nakajima, Yasunori Tateno and Seigo Sano Eudyna Devices Inc., 1, Kanai-cho, Sakae-ku,Yokohama, 244-0845, Japan.. ABSTRACT This paper is overviewed recent progress on GaN HEMTs. High power, high efficiency, and high frequency performance are reported. In addition, the results about long-term reliabilities and good manufacturability demonstrate that GaN HEMTs are ready for mass production . INTRODUCTION Owing to high critical breakdown field (3 MV/cm), high electron velocity (2.7E7cm/sec), and high two Dimensional Electron Gas densities(>1E13/cm2) at the AlGaN/GaN interface, GaN HEMTs have been attracted attention for high power and high frequency applications. As a GaN was new material for electron devices as well as optical devices, there have been many challenges of GaN HEMTs for commercial applications. The initial stage for development was focused on the crystal growth. Because of the lack of the homo substrate for AlGaN/GaN hetero-structure, many efforts have been paid to obtain the good epitaxial quality on hetero substrate, such as Sapphire, SiC, and Si [1-3]. The second stage was focused to suppress the instability phenomena, called current collapse [4]. Surface treatments or passivation films were studied to solve this problem [5, 6]. The third stage was focused on the improvement of the breakdown voltage and reliability. The field plate technologies have been introduced [7, 8]. In this paper, we report on present status of GaN HEMTs and future prospect. EXPERIMENT GaN HEMTs basically consist of AlGaN/GaN hetero-structure grown by OMVPE. The device has the gate length of 0.9 um without backside via holes for L-S band applications. Table 1 shows the typical performance. Table 1 Typical Performance of GaN HEMT Owing to the high breakdown performance, the devices can operate at 50 V, Ifmax Gm BVdg fT which leads to high power density and low 600mA/mm 200 mS/mm 350 V 14 GHz transmission loss in the systems. Fig. 1 shows the power performance of 36 mm device with efficiency and distortion matching. The device shows saturation power of 100W with drain efficiency of 65 % and linear gain of 16 dB at 2.1 GHz. When the device tunes power matching, the saturation power shows 140 W. When the gate length is shorten to 0.6 um, the linear gain improves by 2dB keeping with the same breakdown voltage and efficiency.
Fig.1. Power performance of 36mm device Vds=50V, f=2.1GHz DISCUSSION Present status of device performance Figure 2 shows the trends of output power of GaN HEMTs. An over 1 kW output power could be obtained on SiC substrates [9]. A 1 kW device consists of 4 X 36 mm chips operated at 65 V. The corresponding power density is 7 W/mm, which leads to high gain of 14.5 dB and high efficiency of 57% at 2.9 GHz. These results show that GaN HEMTs have potential to replace the TWTA (Traveling Wave Tube Amplifier) applications in the future. 1000
L-S Band POUT (W)
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Fig. 2. Trends of output power of GaN HEMT PAs.
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