- 學位論文
含氫非晶碳薄膜的氬氣電漿浸沒處理及其液晶配向的研究
Liquid Crystal Alignment on the a-C:H Films Treated with Ar Plasma Immersion
摘要
本論文研究一種新的液晶配向技術，此技術的重點是利用氬氣(Ar)電漿浸沒處理斜向放置於基板上之含氫非晶碳膜(hydrogenated amorphous carbon，簡稱a-C:H)，經此製程處理過的a-C:H膜有利於液晶配向。本研究採用平面型電感式偶合電漿系統所產生之Ar電漿，進行Ar離子轟擊處理。除了觀察不同斜向放置角度、Ar電漿處理時間與試片基座所施加之脈衝負偏壓大小對a-C:H配向膜的配向效果影響外，並提出一理論模型來探究造成液晶配向效果之原因。 為了確定經過各種不同製程條件處理過之a-C:H配向膜的液晶配向效果，本研究也將經Ar電漿浸沒處理過之a-C:H配向膜組成液晶晶胞樣品，以進行偏光顯微鏡、預傾角與水平錨定強度的量測。此外，本實驗也利用接觸角測量儀、原子力顯微鏡、Raman光譜儀、UV-Vis穿透光譜儀與X-ray光電子能譜儀等儀器，探討a-C:H配向膜經過Ar電漿浸沒處理前後之性質變化。最後則採用Langmuir probe對本研究所使用之電漿系統進行電漿特性分析，以了解形成液晶配向效果之原因。 研究結果得知，a-C:H配向膜的斜向放置角度為0o時，並無液晶配向效果。當斜向放置角度為30o時就呈現液晶配向效果，但對比低且缺陷密度高。然而，當斜向放置角度提升至60o時，可以大幅提升液晶配向之效果。此外，本研究亦發現可藉由調整電漿處理的條件加以控制液晶分子之預傾角。在200瓦的射頻功率下，利用Ar電漿浸沒處理斜向放置角度為60o的a-C:H配向膜，於基座上外加1000 伏特的脈衝負偏壓，在經過10~15分鐘之電漿處理後，預傾角會出現最大值，約2.0o。同時，預傾角大小也會隨著a-C:H配向膜所施加的脈衝負偏壓降低而增加。同樣在200瓦的射頻功率下，利用Ar電漿浸沒處理斜向放置角度為60o的a-C:H配向膜10分鐘後，研究結果顯示在無外加偏壓的情況下預傾角會出現最大值，約2.6o。 本研究認為利用Ar電漿浸沒處理斜向放置的a-C:H配向膜之配向機制為在Ar電漿浸沒處理的過程中，因電漿密度不均勻分布，造成電漿中sheath厚度不均勻，導致Ar離子斜向轟擊a-C:H表面所致。
並列摘要
Abstract The objective of the thesis is to study a new plasma immersion technique for liquid crystal (LC) alignment. The key step of this technique is to immerse in Ar plasma on sample holders with different holder-tilted angles, which is favorable to LC alignment. In this research, a planar-type inductive-coupled plasma system is used to generate Ar plasma for the plasma immersion treatment. Several plasma parameters such as different holder-tilted angles, treated time, and pulsed biased voltage have been used to modify the surface of a-C:H films to investigate the effect of LC alignment. In addition, a theoretical model is proposed to explain the phenomenon of LC alignment for the Ar plasma immersion treatment. In order to study the LC alignment properties of the treated a-C:H films, different LC cells were assembled for the measurement of polarized optical microscope, pretilt angle, and azimuthal anchoring strength. Moreover, the contact angle instrument, atomic force microscope (AFM), Raman spectroscope, UV-Vis spectroscope, and X-ray photoelectron spectroscope (XPS) were also used to characterize a-C:H films with and without Ar plasma immersion treatment. A Langmuir probe was used to measure the plasma characteristics in order to analysis the mechanism of the LC alignment. Experimental data indicate that no LC alignment appears for the a-C:H films treated at the holder-tilted angle of 0o; LC alignment which exhibits low contrast and high defect density for the a-C:H films treated at a holder-tilted angle of 30o. The quality of LC alignment is greatly improved for the a-C:H films treated at a holder-tilted angle of 60o. Furthermore, the pretilt angle of LC molecules can be adjusted to some extent by changing the experimental parameters of Ar immersion plasma treatment. In one case, a-C:H films, biased with a pulse voltage of -1000 V at the holder-tilted angle of 60o, was treated with Ar plasma immersion at a RF power of 200 W. A maximum magnitude (about 2.0o) of pretilt angle is achieved after the Ar plasma treatment for 10~15 minute. In addition, the magnitude of pretilt angle can be controlled by altering the pulsed biased voltage. The pretilt angle increases as the pulsed biased voltage decreases. A maximum magnitude (about 2.6o) of pretilt angle could be achieved after treating a-C:H films in the Ar plasma at a RF power of 200 W at zero pulsed biased voltage at the holder-tilted angle of 60o. The mechanism for LC alignment, using a-C:H films treated with Ar plasma immersion, is attributed to the non-uniform thickness of the sheath layer. The non-uniform sheath width, generated by the inhomogeneous plasma density distribution in the planar-type ICP system, results in the oblique incidence of Ar onto the a-C:H film surface.