水溶液法成長氧化鋅薄膜及其薄膜電晶體製作

Abstract

本論文主要是研究以新穎且對環境無害的水溶液方法來成長氧化鋅薄膜。本實驗共分氧化鋅、氧化鋅摻雜鎂元素與氧化鋅添加銦元素等三部分，首先是用自行研究的水溶液配方在玻璃基板上沉積ZnO薄膜；第二部分則是在ZnO溶液中摻雜Mg元素，觀察摻雜Mg元素對ZnO薄膜的影響；第三部分則是在ZnO溶液中添加In元素，並觀察添加In元素對ZnO薄膜的影響。ZnO相關薄膜成長後，以原子力顯微鏡與掃描式電子顯微鏡觀察薄膜表面型態；X光繞射儀(XRD)分析薄膜晶體結構；X光能量散射光譜儀分析薄膜組成；四點探針方式分析薄膜電阻係數；紫外光-可見光光譜分析觀察薄膜穿透率情形。最後在將上述三種薄膜以黃光微影製程做成薄膜電晶體(TFT)元件，並分析元件特性。 在ZnO系統方面，首先將醋酸鋅Zn(CH3COO)2．2H2O溶在去離子水中，然後在此水溶液中加入適量的非離子型界面活性劑，均勻混合後即可得到透明澄清液，然後取適量旋轉塗佈在玻璃基板上，在預烤80℃與300~500℃溫度退火後，可得到透明且連續的氧化鋅薄膜，經紫外光可-見光之光譜分析後，此薄膜在光波長400~800nm的範圍其穿透率大於85%。 在Zn1-xMgxO系統方面，首先將醋酸鋅Zn(CH3COO)2．2H2O與醋酸鎂Mg(CH3COO)2．4H2O溶在去離子水中，然後在此水溶液中加入適量的非離子型界面活性劑，均勻混合後即可得到透明澄清液，然後取適量旋轉塗佈在玻璃基板上，在預烤與退火後，可得到透明且連續的氧化鋅摻雜Mg薄膜，且XRD分析所有Zn1-xMgxO(x up to 0.4)薄膜並沒有MgO出現；經紫外光可-見光之光譜分析後，Zn1-xMgxO薄膜在光波長400~800nm的範圍其穿透率大於90%。 在添加In於ZnO(ZIO)系統方面，首先將硝酸鋅Zn(NO3)2•6H2O與硝酸銦In(NO3)3•xH2O溶在去離子水中，然後以上述相同於ZnO與Zn1-xMgxO的製程，可得到透明且近乎連續的氧化鋅添加銦元素薄膜，不過XRD分析顯示在薄膜中除了ZnO外還有In2O3的相出現。薄膜在光波長400~800nm的範圍其穿透率大於85%。 ZnO、Zn0.9Mg0.1O與ZIO所製作在完成所有TFT元件後，皆有元件特性，其中ZIO TFT元件的載子遷移率最高，可達0.8 cm2/Vs，是本實驗所有TFT元件中最高的載子遷移率。

In this study, we have developed a novel and environment-friendly aqueous method to deposit ZnO-based thin films, including ZnO, Zn1-xMgxO, and Zn1-xInxO material systems. For the first part, a new chemical solution has been synthesized for deposition of ZnO thin films on glass substrate by the aqueous method; for the second part of Zn1-x MgxO, Mg-contained chemicals were added into ZnO solution for film deposition; for the third part, we added indium-contained chemicals into ZnO solution. The deposited thin films were characterized by atomic force microscopy and scanning electron microscopy for the film morphology, x-ray diffraction (XRD) for the crystallinity, x-ray energy dispersive spectroscopy for the composition measurement, four-point probe method for the resistivities, and UV- visible spectrum analysis for transparencies. In addition, TFT devices were fabricated and the TFT characteristics were determined. For ZnO film deposition, Zn(CH3COO)2．2H2O was dissolved in deion -ized (DI) water, followed by addition of some nonionic surfactant into the ZnO aqueous solution. After complete mixing of the solution under stirring, a clear and homogenous solution was obtained. The solution was then spin-coated on glass substrate, followed by pre-baking at 80 □C and annealing at a temperature from 300 to 500 □C. Finally, a continuous ZnO transparent thin film can be obtained. UV-Visible analysis shows that the transparency of the ZnO thin film in wavelength of 400~800nm is higher than 85%. For Zn1-xMgxO system, some Zn(CH3COO)2．2H2O and Mg(CH3COO)2．4H2O were dissolved in deionized (DI) water. With addition of some nonionic surfactant into the Zn1-xMgxO aqueous solution, a clear and homogenous solution was obtained. After spin-coating on glass substrate, followed by pre-baking and annealing a continuous Zn1-xMgxO transparent thin film was formed. XRD shows that all the films are of single phase without MgO for x up to 0.4. UV-Visible analysis shows that the transparency of the Zn1-xMgxO thin films in wavelength of400~800nm can be higher than 90%. For ZnInO (ZIO) system, Zn(NO3)2•6H2O and In(NO3)3•xH2O were used for dissolution in deionized water. Using the same processing as shown above for ZnO and ZnMgO, an almost continuous ZIO transparent thin film was obtained. However, XRD reveals that there is In2O3 crystalline phase in addition to ZnO in the films. TFT devices were fabricated using ZnO, Zn0.9Mg0.1O, and ZIO. The electrical characterization shows that the ZIO TFT has the highest mobility of 0.8cm2/Vs