高頻應用之氮化鋁鎵/氮化鎵金氧半 高電子遷移率電晶體之製作與特性研究

Fabrication and Characterization of AlGaN/GaN MOS High Electron Mobility Transistors for High Frequency Applications

許旻棟(Ming-Dung, Hsu)

指導教授 ： 彭隆瀚

國立臺灣大學/電機資訊學院/光電工程學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.01114

摘要

本研究參考傳統歐姆接觸製程，設計元件的歐姆接觸，並利用傳輸線模型(Transmission line model，TLM)，濺鍍金屬鈦/鋁/鈦/金(15 nm/100 nm/60 nm/200 nm)，在850度60秒的熱退火條件下，製作出6.654*10-6Ω-cm2的歐姆接觸特徵電阻值，並改良電晶體元件結構成為啞鈴狀之高台；再應用光致電化學氧化法，即在氮化鋁鎵/氮化鎵表面生成氧化物，期望得到自我鈍化的作用。當閘極偏壓為1V時，前述方法可使其直流飽和電流密度從950mA/mm提升至氧化後的1013mA/mm，約可增加6.6％的飽和電流密度，轉導增益從181mS/mm提升至氧化後的191mS/mm，約可增加5.5％的轉導增益值。
本研究延續使用光致電化學氧化法製作電晶體元件，以閘極長度與寬度為2μm/2μm，並調變汲極與源極間距為10μm、8μm、6μm及4μm，作了直流飽和電流、轉導增益以及高頻特性的量測分析。實驗結果發現，縮短間距不但可提升直流特性，並可增加截止頻率由原先的12.6GHz提升至25.6GHz。此外本研究更顯示當歐姆接觸電極縮小時，可減少寄生電容的產生對於高頻特性的影響，使截止頻率提升至30.1GHz；最後，本研究也完成光致電化學氧化對於電流崩塌效應(Current collapse)之分析，利用直流偏壓與脈衝偏壓對元件進行應力測試(Stress test)，實驗結果顯示自我表面鈍化處理對電流崩塌效應具有抑制的效果。

關鍵字

氮化鎵 ； 高電子遷移率電晶體

並列摘要

We investigate the methods to improve the electric properties of AlGaN/GaN MOS High Electron Mobility Transistors (MOS-HEMTs). Using a transmission line model (TLM) analysis, we obtained an ohmic contact specific resistance of 6.654*10-6Ω-cm2 on the AlGaN/GaN samples patterned with a stack electrode of Ti/Al/Ti/Au (15nm/100nm/60nm/200nm) and annealed at 850℃ for 60s.We applied a new transistor structure with a dumb bell shape mesa and the photo-electro-chemical (PEC) method to form self passivation oxide layers on the surfaces of AlGaN/GaN. We note the device characteristic of saturation current increase from 950mA/mm to 1013mA/mm operated at VGS=1V and the Gm value increase from 181mS/mm to 191mS/mm for device of LG/WG=2μm/2μm.
When the PEC process was applied to the fabrication of AlGaN/GaN MOSFET, we can observe improvement in the direct current (DC) saturation current and the trans-conductance (Gm) measurement on transistors. By varying the drain-source LDS distance from 10 to 4μm while keep a fixed gate length LG=2μm, one not only can improve the DC properties but also increase the unit current gain cut off frequency (fT) from 12.6GHz to 25.6GHz. Furthermore, by reducing the device area to LDS=2μm to decrease the parasitic capacitance, the device cut-off frequency can be increase to 30.1GHz. Finally, from the DC and pulse current stressing experiment we denote that the AlGaN/GaN MOSFET encountered the PEC processing to provide surface passivation can exhibit improved performance against the current collapse effect.

並列關鍵字

GaN ； HEMT

參考文獻

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