| 摘要: | 本論文針對不同基板氮化鎵電晶體之變溫特性進行研究，主要分成兩個部分討論:(1)不同基板氮化鎵電晶體之變溫靜態特性與熱阻討論;(2)不同基板氮化鎵電晶體之變溫動態特性。
本篇論文探討不同基板的氮化鎵電晶體，分別使用傳統矽基板與QST基板，後者優點為熱膨脹係數與氮化鎵較匹配，能成長較厚的緩衝層，且熱傳導係數較高，讓電晶體在高溫下操作更為穩定。藉由變溫量測得出兩種電晶體的變溫係數，其中包含導通電阻、最大汲極電流、最大轉導值、功率與電晶體漏電流等等，結果上呈現GaN-on-QST電晶體的溫度係數較低;利用汲極電流-電壓特性圖來萃取出兩種電晶體的熱阻，結果上以GaN-on-Si之熱阻較低;使用Silvaco TCAD模擬可以發現較高熱阻的電晶體會因為散熱能力較差有較高的接面溫度。
論文中第二部分則是探討這兩種電晶體的動態特性，首先利用軟切換與硬切換來評估電晶體動態電阻，GaN-on-QST在這兩種切換測試下皆得到較低的動態電阻，而硬切換會有熱電子的產生，導致兩種電晶體在硬切換測試下的動態電阻皆比軟切換高;利用脈衝量測讓電晶體達成連續的開關，在關閉狀態下量測電晶體的動態漏電流，GaN-on-Si動態漏電流較靜態漏電流大，因為電洞注入讓閘極下方導電帶變低，源極電子更容易傳輸，GaN-on-QST則因為靜態漏電流較大，電洞注入反而複合了高濃度電子，導致較低的動態漏電流;藉由雙脈衝動態量測來觀察電晶體切換情形，GaN-on-Si因為有較小的電容，開關切換特性較好，溫度升高後，兩種元件皆因為轉導值下降讓開啟特性退化，關閉時因為溫度上升而變小的電容則讓電晶體關閉特性變好。;In this paper, the analysis of variable temperature characteristics of GaN HEMTs with different substrates has been investigated, and divided into two parts: (1) variable temperature static characteristics and thermal resistance of GaN HEMTs with different substrates; (2) variable temperature dynamic characteristics of GaN HEMTs with different substrates.
This paper discusses GaN HEMTs with different substrates which use traditional Si substrates and QST substrates respectively. The advantage of QST substrate is that the coefficient of thermal expansion match GaN, and can grow a thicker buffer. Also, GaN-on-QST is more stable to operate at high temperature than is GaN-on-Si because of higher thermal conductivity. The temperature coefficients of two GaN HEMTs are obtained by variable temperature measurement, including on-resistance, maximum drain current, maximum transconductance, power, and leakage current. The results show that GaN-on-QST has lower temperature coefficients. The thermal resistance of two GaN HEMTs is extracted by drain current-voltage characteristics, and the thermal resistance of GaN-on-Si is lower. By Silvaco TCAD simulation, it can be found that GaN HEMTs with higher thermal resistance have higher junction temperatures due to weak heat dissipation.
The second part of the paper is to discuss the dynamic characteristics of these two GaN HEMTs. Using the soft and hard switching to evaluate dynamic on-resistance, GaN-on-QST has lower dynamic on-resistance in these two switching tests; for the consecutive switching, the pulse measurement is used to evaluate the dynamic off-current in the off-state. The GaN-on-Si dynamic off-current is higher than the static, due to the lowered conduction band in the gate region induced by hole injection from p-GaN, the electrons from the source are easily transported. Due to the high static off-current of GaN-on-QST, the injected hole is recombined with the high electron concentration resulting in lower dynamic leakage. The double pulse dynamic measurement is used to observe GaN HEMTs switching behavior, GaN-on-Si has better switching characteristics because of its lower capacitance. Both GaN HEMTs turn on characteristics degrade due to transconductance decreases, the capacitance decreases induced by higher temperature makes the GaN HEMTs turn on characteristics better. |
