氮化鋁銦/氮化鎵高電子遷移率電晶體之射頻功率元件製作與分析

Fabrication and Analysis of Radio Frequency AlInN/GaN HEMTs

曾威程(Wei-Cheng Tzeng)

指導教授 ： 吳肇欣

國立臺灣大學/電機資訊學院/電子工程學研究所/碩士(2020年)

https://doi.org/10.6342/NTU202004271

摘要

近年來，氮化鋁鎵/氮化鎵高載子遷移率電晶體以其材料天生優於傳統矽的高載子遷移率、高載子濃度、寬能隙與耐溫耐壓的特性，在射頻元件及功率元件的應用中佔有一席地位，然而一般採用的氮化鋁鎵/氮化鎵電晶體在閘極線寬微縮的過程中，容易因氮化鋁鎵障壁層的厚度過厚而有短通道效應產生，若嘗試縮小障壁層厚度，又可能導致閘極漏電或載子濃度降低等問題，為了解決上述的缺點，我們選用氮化鋁銦做為障壁層，其優於氮化鋁鎵的極化特性及與氮化鎵晶格匹配的優勢，以及同樣具有寬能隙與耐溫耐壓的特性，使其在高頻的應用中有望取代氮化鋁鎵/氮化鎵結構，成為下一世代高載子遷移率電晶體的主流材料。
本論文共可分做四個部分，在第一部份中我們介紹了三五族材料及寬能隙半導體的發展背景與元件的操作原理; 第二部分我們自行設計碳化矽基板上成長氮化鋁銦/氮化鎵的磊晶結構，看中其較傳統氮化鋁鎵/氮化鎵結構之極化效應更強、二維電子氣通道濃度更高的材料特性，並做了磊晶結構設計的探討，緊接著透過快速製程基板直流分析由矽基板與碳化矽基板兩者中，選用了具較佳轉導值與漏流抑制的碳化矽基板作為正式元件使用。第三部分介紹了射頻高載子遷移率電晶體的製程流程，並做了接觸電阻與直流特性的分析。第四部分針對最佳元件進行高頻散射參數量測及負載拉曳量測，同時對元件特性進行探討與修正。
最後我們成功製作出雙指閘極結構的元件，並微縮閘極線寬至約300 nm。在直流特性的部份，元件於VD = 6 V的偏壓點可獲得的最高轉導值約為222.6 mS/mm，最大飽和電流約為896.3 mA/mm; 高頻特性的部份則透過散射參數的量測、小訊號模型及軟體輔助擬合，成功萃取出元件各外部及內部的阻抗值，並由計算成功獲得最佳元件於閘極偏壓-3 V、汲極偏壓6 V下的ft及fmax分別為35.173 GHz及76.178 GHz，最後我們進行了負載拉曳量測，並在6 GHz的操作頻率及VD = 10 V; VG = -4 V的偏壓下，獲得最大增益8.34 dB，而PAE的最大值12.18%則由Pin = 0 dB時於VD = 3 V; VG = -4 V下取得。

關鍵字

氮化鋁銦/氮化鎵異質接面結構 ； 高載子遷移率電晶體 ； 射頻元件 ； 小訊號模型 ； 負載拖曳量測

並列摘要

In recent years, the AlGaN/GaN high electron mobility transistors (HEMTs) have attracted much attention for radio frequency (RF) and high-power applications due to the higher electron mobility, higher carrier concentration, wider band gap and higher operation voltage and temperature than conventional Si-based devices. However, AlGaN/GaN HEMTs encounter the challenge of short channel effects caused by the large thickness of the AlGaN barrier layer while scaling down the gate length, and an increase of leakage current and reduction of carrier concentration may occur when trying to shrink the barrier thickness. In this thesis, AlInN was chosen as the barrier layer material to replace AlGaN due to the stronger polarization and better lattice match with GaN. At the same time, it retains the wide band gap and high operation voltage and temperature properties, which make it possible to replace AlGaN/GaN devices in next-generation RF applications.
The thesis can be divided into four parts. In the first part, we introduce the development background of III-V materials and wide band gap semiconductors, as well as their physical and electronic characteristics. In the second part, we survey other reported devices using AlInN as a barrier layer in order to design our own epitaxial structure. Then, we use a quick-and-dirty (QAD) process to select the better epitaxial structure between Si and SiC substrates. After we went through the DC analysis of both QAD devices, the SiC substrate was selected to fabricate the main device due to its better transconductance characteristics and off-current compared to Si. In the third part, we introduce the fabrication process flow of the device and analyze the contact resistance and DC characteristics. In the fourth part, high-frequency scattering parameter (S-parameter) and power added efficiency (PAE) measurements are carried out, and the device characteristics are discussed.
Finally, we successfully fabricated a device with two-finger gate structure with a gate length of about 300 nm. The highest transconductance (gm) value that can be obtained at a drain voltage VD = 6 V is about 222.6 mS/mm, and the maximum saturation current is about 896.3 mA/mm. We also discuss the small signal model and software-assisted fitting for the high frequency measurement, and the external and internal impedance values of the device were obtained. For the best device, at bias voltages of VG = -3 V and VD = 6 V, the current gain cutoff frequency ft and maximum oscillation frequency fmax are 35.173 and 76.178 GHz, respectively. Finally, we performed a load-pull measurement and measured the power characteristics of the device including PAE. Under an operating frequency of 6 GHz and bias voltages of VD = 10 V and VG = -4 V, we obtain a maximum gain of 8.34 dB. The maximum PAE of 12.18% is obtained when input power Pin = 0 dB and bias voltages VD = 3 V and VG = -4 V.

並列關鍵字

AlInN/GaN heterojunction structure ； high electron mobility transistors ； radio frequency devices ； small signal model ； load-pull measurement ； RF characteristic

參考文獻

[1] Scott E. Thompson, Srivatsan Parthasarathy, Moore's law: the future of Si microelectronics, Materials Today, Volume 9, Issue 6, 2006, Pages 20-25,ISSN 1369-7021,

[2] Mimura, Takashi. (2002). The early history of the high electron mobility transistor (HEMT). Microwave Theory and Techniques, IEEE Transactions on. 50. 780 - 782. 10.1109/22.989961.

[3] U. K. Mishra, P. Parikh and Yi-Feng Wu, "AlGaN/GaN HEMTs-an overview of device operation and applications," in Proceedings of the IEEE, vol. 90, no. 6, pp. 1022-1031, June 2002, doi: 10.1109/JPROC.2002.1021567.

[4] G. E. Stillman, V. M. Robbins and N. Tabatabaie, "III-V compound semiconductor devices: Optical detectors," in IEEE Transactions on Electron Devices, vol. 31, no. 11, pp. 1643-1655, Nov. 1984, doi: 10.1109/T-ED.1984.21765.

[5] Zetian Mi and Yi-Lu Chang "III-V compound semiconductor nanostructures on silicon: epitaxial growth, properties, and applications in light emitting diodes and lasers," Journal of Nanophotonics 3(1), 031602 (1 January 2009).