大氣電漿束之電漿特性與應用之研究

Study of the Characteristics and Applications of Atmospheric Pressure Plasma Jets

簡士傑

指導教授 ： 寇崇善

國立清華大學/理學院/物理學系/博士(2013年)

摘要

本研究利用大氣電漿系統研究操作頻率對電漿特性的影響、氣流對薄膜沉積和電漿分佈的影響、沉積有機矽薄膜以及藉由調整薄膜特性達到控制液晶分子預傾角的目的。
　　本研究在增加操作頻率下，觀察到以下幾種電漿特性變化：(1)電漿的崩潰電壓從256 V降低至204 V、(2)維持α模式放電的最高電漿密度從0.798×〖10〗^12 〖cm〗^(-3)上升至2.218×〖10〗^12 〖cm〗^(-3)以及電流從0.125 A提高至0.224 A、(3)放電模式轉換前的鞘層厚度從0.348 mm減少為0.257 mm、(4)電漿功率為25 W時電子激發溫度從0.535 ev降為0.316 ev。
　　本實驗在研究過程中，發現當進氣量為5 slm時，氣流分佈不均勻，進而導致薄膜厚度的不均勻分佈。藉由改變風刀結構來改善氣流分佈的均勻性，可使薄膜厚度均勻分佈在基材上，由於薄膜沉積的均勻性和電漿密度分佈有關，因此可判斷氣流分佈對電漿密度分佈有重大的影響。
　　本實驗使用大氣電漿源與有機矽化合物HMDSO沉積有機矽膜，藉由控制製程參數可調整薄膜結構與物理特性，實驗中發現HMDSO薄膜的主要結構為Si–CH3和Si–O–Si，提高分子平均能量可使薄膜結構偏向Si–O–Si；反之則偏向Si–CH3。Si–CH3為非極性分子，其結構較脆弱且較容易被破壞；Si–O–Si為極性分子，其結構較為堅固不易被破壞。當Si–O–Si的含量比例較高時，薄膜具有較高的表面能，可達68 mJ/m2，親水性質較明顯，表面硬度比較高，可達到5H；若是Si–CH3的含量比例較高，薄膜具有較低的表面能，可低至25 mJ/m2，疏水性質較明顯。
　　本實驗藉由控制薄膜的表面能，達到控制液晶分子預傾角的目的。實驗結果顯示預傾角角度會隨著薄膜的表面能改變，當表面能低於34 mJ/m2時，預傾角角度趨近於90o，當表面能高於60 mJ/m2時，預傾角角度趨近於0o，由此可知，欲控制預傾角，表面能的範圍必須控制在34~60 mJ/m2。

關鍵字

大氣電漿 ； 預傾角 ； 操作頻率 ； 氣流

並列摘要

In study, we used atmospheric pressure plasma source (APPS) to study the effect of driving frequency on the characteristic of plasma, the effect of gas flow on the deposition process and plasma density distribution, deposition of organic silicon film, and controlling the pretilt angle of liquid crystals (LCs).
The study was to investigate the driving frequency effects on the characteristics of atmospheric plasma jets system. The discharge gas is the helium. We change the power source frequency range from 10 MHz to 20 MHz. As the driving frequency is increased, we can observe the several phenomena. (1) gas breakdown voltage from 256 V down to 204 V, (2) plasma density from 0.798×〖10〗^12 〖cm〗^(-3) rose to 2.218×〖10〗^12 〖cm〗^(-3) and increase the current from 0.125 A to 0.224 A when the plasma state at highest α mode discharge, (3) sheath thickness decreased from 0.348 mm to 0.257 mm before discharge mode transition, (4) the electron excitation temperature dropped from 0.535 ev 0.316 ev when the plasma power of 25 W. Collectively, these results suggest that the high driving frequency help to improve the quality of plasma, enhance discharge efficiency, and make the atmospheric plasma jets systems have a wider application space.
From the results, the gas flow distribution became non-uniform at helium flow rate of 5 slm. By modifying the structure of nozzle, the gas flow distribution became more uniform so that film deposition became uniform. Because the uniformity of film deposition is related to the plasma density distribution, the gas flow distribution effected the plasma density distribution.
In study, the APPS was used to deposited the organic silicon film, HMDSO as the material. The process could control the structure and properties of the film. Results showed main bonds (Si–CH¬3 and Si–O–Si) can be controlled by molecular average energy (W/FM). The ratio of Si–O–Si increased when W/FM became large. The ratio of Si–CH¬3 was increasing with decreasing the W/FM. Si–O–Si are polar bonds, and Si–CH¬3 are non-polar bonds. Thus, if the ratio of Si–O–Si was higher than Si–CH¬3, the film became hydrophilic (surface energy could be 68 mJ/m2) and surface hardness became hard. If the ratio of Si–CH¬3 was higher than Si–CH¬3, the film became hydrophobic (surface energy could be 25 mJ/m2) and surface hardness became soft.
The pretilt angle of LCs could be controlled by adjusting the surface energy of the film. When the surface energy was smaller than 34 mJ/m2, the pretilt angle approached 90o. When the surface energy was larger than 60 mJ/m2, the pretilt angle approached 0o. Therefore, the pretilt angle could be controlled by the range of surface energy from 34 to 60 mJ/m2.

並列關鍵字

atmospheric pressure plasma ； driving frequency ； preitlt angle ； gas flow

參考文獻

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