Recent Reliability Progress of GaN HEMT Power Amplifiers
- PDF / 330,607 Bytes
- 12 Pages / 432 x 648 pts Page_size
- 43 Downloads / 229 Views
Recent Reliability Progress of GaN HEMT Power Amplifiers Toshihiro Ohki, Masahito Kanamura, Yoichi Kamada, Kozo Makiyama, Yusuke Inoue, Naoya Okamoto, Kenji Imanishi, Kazukiyo Joshin and Toshihide Kikkawa Fujitsu Laboratories Ltd. 10-1 Morinosato-Wakamiya, Atsugi, Kanagawa, 243-0197, Japan ABSTRACT In this paper, we describe highly reliable GaN high electron mobility transistors (HEMTs) for high-power and high-efficiency amplifiers. First, we present the reliability mechanisms and progress on the previously reported GaN HEMTs. Next, we introduce our specific device structure of GaN HEMTs for improving reliability. An n-GaN cap and optimized buffer layer were used to suppress the trap-related phenomena, such as a current collapse. Gate edge oxidation is effective for reducing the gate leakage current. A Ta-based barrier metal was inserted between an ohmic electrode and interconnection metal for preventing increase in contact resistance. SiN of passivation film was optimized for reducing the current collapse of short-gatelength HEMTs. INTRODUCTION Gallium nitride HEMTs have high breakdown voltages with high cutoff frequencies as compared with devices based on other materials, leading to high-power and high-efficiency amplifiers for next generation wireless communication, satellite communication, and radar systems. Currently GaN HEMTs for transmitter amplifiers of wireless base stations have been commercialized since 2005. In the last few years, the output power of GaN-HEMT power amplifiers has increased steadily up to 1 kW in the L~S-band and 250 W in the X-band [1]-[2]. In addition to device performance, reliability is the highest priority issue to be addressed for mass production. To supply GaN HEMTs in the market, their high reliability should be proven. In this paper, we describe the current status of GaN HEMT reliability and introduce Fujitsu's device technologies and reliability measurements for high-power and high-efficiency amplifiers. CURRENT STATUS OF GAN HEMT RELIABILITY Previously reported work related to GaN HEMT reliability has identified the leakage current and trap-related phenomena as the main issues to be solved. Concerning the leakage current, both gate leakage current and drain sub-threshold leakage current (Id in pinched-off conditions) must be considered. Following a device stress test, two main degradation modes have been observed so far: increase of leakage current and enhancement of trap-related phenomena [current collapse and quiescent current (Idsq) drift], leading to a reduction of the drain current. There are many previous reports about the degradation mechanisms of GaN HEMTs [3][4]. Joh et al. reported that degradation arises from the formation of defects in the AlGaN barrier as a result of a high vertical electric field right next to the gate [5]. They said that these defects
131
provide a leakage path for electrons and effectively lower the Schottky barrier height of the gate. Jimenez et al. also observed crack- and pit-shaped defects in the AlGaN/GaN crystal material under the drain
Data Loading...
