藉由大氣電漿沉積主動層之氧化鋅薄膜電晶體之研究

Abstract

本論文利用大氣電漿沉積氧化鋅作為元件的主動層，並且成功發展出高效能的薄膜電晶體。在X光繞射儀(XRD)分析中可以發現由大氣電漿沉積之氧化鋅具有優選的(002)晶向。氧化鋅薄膜對可見光的穿透率超過80%，並且具有3.25eV的能隙。這些特性使得大氣電漿沉積氧化鋅具有應用於透明電路的潛力，以及能減少光漏電對於元件的影響。我們首先利用矽晶片作為元件的基板並且逐一量測與比較各種實驗參數對元件的影響，在主動層厚度、基板加熱溫度、以及製程氣體等實驗參數中取得最佳化，並且發展出具有開關電流比2.3×107 、電遷移率3.21cm2 /Vs、臨界電壓27.3V、次臨界擺幅 3.83 V/decade的高性能薄膜電晶體。我們在論文中使用X光繞射儀 (XRD)、掃描式電子顯微鏡(SEM)、光激螢光光譜(PL)來分析及討論不同製程參數的氧化鋅薄膜中的結晶品質、缺陷種類及密度、表面形貌等等，以及利用元件的I-V轉換曲線來進行元件特性的探討。最後我們將最佳製程參數的電晶體製作在玻璃基板上，以證明本論文所採用之方法與理論是可以應用在量產的AMOLED及AMLCD電路設計中，並且使用不同的閘極絕緣層材料使臨界電壓從27.3V降低至11.8V。

In this thesis, we have successfully developed a high performance thin film transistor (TFT) with zinc oxide active layer deposited by atmosphere pressure plasma (APP) jet. Zinc oxide films show strongly preferred (002) orientation in XRD analysis. Zinc oxide films have over 80％ transmittance of visible light and band gap energy 3.25eV. Therefore zinc oxide films deposited by APP jet are suitable for transparent devices. Wide band gap can release the issue of photo-excited leakage current. At first, we fabricated TFTs on silicon substrate. Experimental parameters of APP jet which we tested and compared including thickness of active layer, hot plate temperature, carrier gas, and main gas. We have developed high performance devices with an on/off ratio of 2.3×107 ,a saturation mobility of 3.21cm2 /Vs, a threshold voltage of 27.3V, a gate voltage swing of 3.83 V/decade. In this thesis, several material analysis techniques, such as XRD, SEM, and PL were utilized to discussing the crystallization, grain size, and surface morphology of ZnO films. Electrical characteristics and conduction mechanisms of ZnO TFTs were also investigated by I-V characteristic analysis. We have fabricated TFTs successfully with ideal experimental parameters on glass substrate. It can prove that our experiments are feasible for real and mass manufacturing in AMOLED or AMLCD. The threshold voltage becomes lower from 27.3V to 11.8V because the hydrogen in gate insulator SiN：H would diffuse to active layer as donors.