Reliability of High-Temperature Operation for GaN-Based Operational Amplifiers
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1195-B08-02
Reliability of High-Temperature Operation for GaN-Based Operational Amplifiers Kazuki Nomoto, Kazuya Hasegawa, Masataka Satoh and Tohru Nakamura Research Center for Micro-Nano Technology, Hosei University, JAPAN
3-11-15 Midori-cho Koganei-shi, Tokyo, Japan ABSTRACT We demonstrated electrical characteristics of operational amplifier (OPAMP) circuits fabricated by GaN/AlGaN/GaN HEMTs operating over 100 oC. GaN/AlGaN/GaN HEMTs, with the extremely low source resistance were fabricated by multiple ion implantation, precisely controlled ion-implanted (I/I) resistors and Schottky barrier diodes were integrated on the silicon substrate. The GaN cap layer on the AlGaN was grown to decrease the gate leakage current and current collapse for AlGaN/GaN HEMTs. INTRODUCTION GaN is a wide bandgap semiconductor material, with a high breakdown electric field, high saturation drift velocity, and good thermal conductivity as compared to Si and GaAs. In addition, one of the most important features of AlGaN/GaN system is its large piezo-electric polarization in the strained AlGaN, which generates highly dense two-dimensional electron gas (2 DEG) with concentrations exceeding 1013 /cm2. Due to their high power handling capability at high frequencies, AlGaN/GaN high electron mobility transistors (HEMTs) are emerging as the promising candidates for radio frequency and microwave frequency power amplifiers used in advanced wireless communication systems. Performance of these devices has been thus far limited by self-heating. Most of the AlGaN/GaN HEMTs structures have been grown on sapphire or SiC substrates1-3. The sapphire substrates are low-cost, but feature inefficient heat dissipation due to their poor thermal conductivity. Epi-layers with excellent crystal quality and devices with the highest output power densities have been obtained on SiC substrates4-7. Recently, there have been increasing activities in AlGaN/GaN structures on silicon substrates, which offer several advantages, including large-size substrates, low cost, and good thermal conductivity. There have been increasing applications that require electronic devices, digital and analog circuits to operate at higher temperatures. These applications include engine control, DC-DC converters and analog-digital converters for automotive hybrid systems8. Wide bandgap FETs have fundamental advantages for high-temperature operation. AlGaN/GaN HEMTs and GaNbased digital ICs operating at high temperature atmosphere have been reported9, 10, but there has few reports about analog circuit operation. It is important to characterize the high-temperature behavior of GaN-based analog circuits. FABRICATION AND DESIGN The GaN (5 nm)/Al0.25Ga0.75N (25 nm)/GaN (2 µm) HEMT structure was grown on a silicon substrate by metalorganic vapor phase epitaxy (MOVPE). The sheet resistance of the 2 DEG layer was 415 Ω/sq. The GaN cap layer on the AlGaN was grown to decrease gate leakage current and current collapse for AlGaN/GaN HEMTs [4]. Figure 1 shows the cross-sectional
structure of the I/I
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