增強型鰭狀氮化鋁鎵/氮化鎵金氧半高電子遷移率電晶體之研製

Abstract

本研究中，吾人成功製作出一種增強型鰭狀氮化鋁鎵/氮化鎵金氧半高電子遷移率電晶體，透過結合鰭狀結構與閘極掘入技術，並以光致電化學氧化法（PEC oxidation）與電漿輔助型原子層沉積技術（PE-ALD）生成之雙層氧化層作為閘極絕緣層與表面鈍化層，實驗數據顯示電晶體之臨界電壓（Vth）隨不同閘極掘入深度與不同閘極面積而呈現線性變化，斜率分別為0.36 V/nm與 -0.32 V/μm2。對於閘極長度與寬度為250nm×360nm的元件特性，其臨界電壓Vth = 1.2V，電流開關比（Current on/off ratio）高達10^8，所量得的電流增益截止頻率fT為9GHz，而最大操作頻率fMAX為36GHz。所觀察到的現象可歸因於兩個相互結合的效應：(a) 閘極掘入元件上有一介面負電荷密度為3.2 μC/cm2可以部份抵銷極化電荷的效應；(b) 側壁鈍化提供高電子遷移率的通道。

In this thesis, we present an enhancement-mode AlGaN/GaN fin-shaped metal-oxide-semiconductor high-electron mobility transistors (MOS-HEMT), fabricated by combining gate recess process and fin-shape structure, featuring double-layer oxides composed of photo-enhanced-chemical (PEC) oxidation and plasma-enhanced atomic layer deposition (PE-ALD) oxide, which was shown to support threshold voltage (Vth) with a linear slope of 0.36 V/nm and -0.32 V/μm2, respectively, scaled with recess depth and device area. The proposed device exhibited Vth = 1.2V, current on/off ratio of 10^8, and cutoff frequency of unity current gain/power gain (fT/fmax) = 9/36GHz at gate length/width = 250/360nm. These observations can be ascribed to the combination effects of (a) interfacial negative space charge of 3.2 μC/cm2 in the gate-recessed device to partially compensate the polarization charges, and (b) side-wall passivation to preserve the high mobility channel.