A AlGaN/GaN HEMT with WNx T-gate for high temperature application
Dr. Edward Y. Chang
Dr. M. S. Feng
|關鍵字:||氮化鎢;高電子遷移率電晶體;氮化鎵;WN;high electron mobility transistor;GaN|
GaN HEMTs have enormous potential for high-power solid-state amplifier application at microwave frequencies, due to their characteristics such as high breakdown field, high electron saturation velocity and high operating temperature. These characteristics are attributed to the wide bandgap nature of the GaN material. The study focuses on the GaN HEMTs under high temperature operation. The selections of electrode materials are very critical for HEMTs to operate at high temperature. The candidates must have thermal stability and good electrical properties under high temperature operation. No reactions between electrode materials and GaN substrate should occur. Therefore, the changes of electrical properties caused by material interactions at high temperature were focused in this study. Besides electrode material study, the GaN HEMT fabrication processes were also completed in the study. Due to the wide band-gap nature, the GaN material was chemically very stable, however, its process technology is not as mature as other Ⅲ-Ⅴ compounds. Good etching technique, damages caused by physical etching, 2DEG degradation in epitaxial layer caused by changing in electron polarization caused by physical and chemical etching, isolation technique and the passivation technique are among the most important issues in GaN process now. The fabrications process development was described in details in this thesis. Another important issue in this study is the thermal stability of the transistor DC characteristics. Transistors must have thermally stable Ohmic contacts for Source & Drain, and stable Schottky for the Gate with good ideality factor (n) and high barrier height (ψb) under high temperature operation. We have developed a WNx T-gate process by sputtering and lift-off process. A AlGaN/GaN HEMT with the WNx T-gate were processed in this research. The DC characteristics of the AlGaN/GaN HEMT processed is Imax =30~32 mA/mm, gm =46~50 mS/mm under 0 V gate bias and at 300K, and pinch-off voltage is –1.4 V.
|Appears in Collections:||Thesis|