Fabrication and Analysis of High Frequency AlGaN/GaN HEMTs with T-shaped Gate

• Main Authors: Yung-Ting Ho, 何咏庭
• Other Authors: Chao-Hsin Wu
• Format: Others
• Language: zh-TW
• Published: 2019
• Online Access: http://ndltd.ncl.edu.tw/handle/fk6ap3

碩士 === 國立臺灣大學 === 光電工程學研究所 === 107 === In this thesis, we take advantages of the superior properties of Gallium Nitride, such as wide bandgap, high breakdown voltage, high electron mobility to fabricate the RF devices with AlGaN/GaN heterostructures on 4-inch HR-substrate. We replace normal gate structure with T-shaped gate fabrication process due to some advantages of T-shaped gate structure, which improves the device performance at high frequency condition. The first part is the development of T-shaped Gate structure. In order to improve the maximum oscillation frequency (fmax) and current gain cutoff frequency (fT), we use Four-Layer Resist method to fabricate the T-Shaped Gate structure. The second part we analyze the DC characteristics of device. We successfully use E-beam lithography technology to fabricate T-Shaped Gate high electron mobility transistors, and the minimum gate length of the device is about 60-80 nm. The small gate length leads high transconductance(gm) about 367 mS/mm. The devices with gate length smaller than 100 nm will suffer from serve short channel effect., we use gate recessed technology to narrow the thickness of AlGaN barrier to avoid problem, and improve the On/off ratio about 3-4 orders of the devices. Finally, we discuss the DC characteristics of device with different AlGaN barrier thickness and geometric size. The last part is the analysis of RF characteristics, we build a Small-signal model and simulate each component in the circuit to help us understand the influence of each elements. We discuss the RF characteristics at different bias conditions and geometric size. At gate bias of -3.5 V and drain bias of 6 V, the fT and fmax of the golden device are 51.2/97.7 GHz, respectively.