基於光阻週期結構之可電控液晶光柵及其光電特性;Electrically tunable liquid crystal gratings based on periodic photoresist structures and their electrooptical properties

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題名:	基於光阻週期結構之可電控液晶光柵及其光電特性;Electrically tunable liquid crystal gratings based on periodic photoresist structures and their electrooptical properties
作者:	林志威;Lin, Chih-Wei
貢獻者:	光電科學與工程學系
關鍵詞:	向列型液晶;液晶光柵;光阻;電雙層理論;屏蔽效應;繞射;Nematic Liquid Crystals;Liquid crystals grating;Photoresist;Electrical double layer theory;Shielding effect;Diffraction
日期:	2022-08-10
上傳時間:	2022-10-04 11:12:13 (UTC+8)
出版者:	國立中央大學
摘要:	本研究將負型光阻SU-8塗佈於鍍有氧化銦錫(Indium tin oxide，簡稱為ITO)之玻璃基板表面，經黃光微影(Photolithography)製程於基板上製作週期約為30 μm的光阻/ITO光柵結構，光阻線寬約為16.4 μm，此光柵為表面浮雕光柵(Surface-relief grating)，並於結構上方塗佈PVA進行水平摩擦配向處理，搭配另一片塗佈PVA經水平摩擦配向處理之ITO玻璃基板組成可電控之光柵液晶盒。首先，我們經由實驗得知負型光阻SU-8對外加直流電場有明顯的屏蔽效應(Shielding effect)，而對外加交流電場的影響則較微弱，並嘗試以電雙層理論及RC電路模型解釋基板表面塗佈光阻薄膜對液晶盒內部電場的影響。由此推論在外加直流或交流電場作用下，液晶分子將於塗佈光阻區域經歷較弱的有效電場，於無塗佈光阻區域經歷較強的有效電場。其次，兩區域亦因表面電位(Potential)差異形成橫向電場(Transverse electric field)，造成兩區域邊界之液晶分子於靠近光阻結構一側(但非基板表面處)有略為偏離摩擦配向方向之現象，由於液晶材料具有彈性體之物理性質，故液晶分子於兩區域邊界處之排列應為連續且漸變的，此現象亦造成該區域產生相位延遲及偏振特性的改變。最後，我們沿用Zhan He教授團隊量測光柵液晶盒偏振特性之方法及理論基礎，探討摩擦配向方向平行及垂直於光柵條紋結構方向之各階繞射光繞射效率及其偏振特性。;In this thesis, we report that the electro-optical properties of surface-relief gratings, having the period of about 30 μm and the width of the SU-8 structures of about 16.4 μm, based on periodic SU-8 structures onto an induim tin oxide (ITO) substrates by photolithography process. After photolithography process, the period structures are spin-coated with polyvinylalcohol (PVA) thin flim and treated with rubbing process. Another ITO-coated substrate is also coated with PVA thin film and treated with the same rubbing process. An empty cell is fabricated by assembling the two substrates, and then filled with nematic liquid crystals (LCs) to be electrically tunable LC gratings. First, SU-8 possesses strong shielding effect for DC electric field, but weak for AC electric field according to our experimental results, and can be clearly understood by electrical double layer theory and RC circuit model. When a DC or AC electric field is applied, LCs in the region with SU-8 will be rotated by a weak effective electric field, and those in the other region will be rotated by a strong electric field. Furthermore, each region has its respective potential, which yields a transverse electric field due to the potential difference. Such transverse electric fields cause the LCs near the SU-8 structures but not on the surface of PVA thin film to be twisted from its initial alignment direction. Accorfing to the elastic continuum theory of LCs, the alignment of LCs should be continuously distributed, which changes the phase retardation and polarization state of the diffraction light. Finally, the methods of measurement and theory of electrically induced hybrid twisted nematic structure reported by He et al. is used for analyzing the diffraction efficiency and polarization state of diffraction light.
顯示於類別:	[光電科學研究所] 博碩士論文

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