以高分子分散型液晶製作並利用邊緣電場調控之微型固體光圈

Abstract

本研究提出一個創新的概念來製作可連續性調變之微型固態光圈，利用邊緣電場效應原理結合高分子分散型液晶(Polymer-dispersed liquid crystal, PDLC)的特性，藉由施加不同電壓來調變光圈孔徑的大小。 在元件結構上，我們使用微影蝕刻製程在氧化銦錫(Indium Tin Oxide, ITO)玻璃基板上製作出長條形的透明電極，將兩者正交排列堆疊，利用聚二甲基矽氧烷(Polydimethylsiloxane, PDMS)模具製作間隙物(Spacer)，並於其中滴入PDLC混合液並曝光固化。在光圈元件的設計中，光圈調變的機制是利用有限平行板所產生的邊緣電場效應，隨著外加電壓上升，方形區域內的液晶分子會先偏轉，外加電壓持續上升，邊緣電場影響的範圍逐漸增加，影響方形光圈周圍的液晶分子轉動，光圈的孔徑亦隨之增加。而在元件的材料方面，我們選擇PDLC來作為調變層，使用PDLC薄膜的優點在於其反應時間短、不依賴光的偏振性，故元件不需外加偏振片。PDLC的製備使用了液晶E7與高分子聚合物NOA65以重量百分比6 : 4的比例混合，而為了降低驅動電壓，在PDLC中摻雜重量百分比10%的乙醇。在量測結果方面，本論文中使用白熾燈與透鏡組搭配CMOS感光元件進行光圈影像的擷取，並將影像進行灰階轉換後，分析光圈孔徑大小與施加電壓之間的關係。最後，藉由上述實驗結果，我們驗證了邊緣電場效應結合PDLC應用於可調變微型方形光圈之可行性。

In this thesis, we demonstrate a novel concept of tuning a solid polymer dispersed liquid crystal (PDLC)-based optical aperture using the fringing electric field. The variable aperture size can be tuned by applied different voltage. The modulation mechanism is the fringing field created by finite parallel-plate capacitors. As the applied voltage increases, the alignment direction of LC molecules in square region will rotate along the electric field. As the applied voltage increases continuously, the affected area of fringing field expands. As a result, the LC molecules nearby the square region rotate along the electric field gradually and the aperture size becomes larger as well. The device consists of a top and a bottom glass substrate with patterned ITO, and the PDLC sandwiched between them. PDLC is suitable for being tunable layer because it has short response time and is polarization-independent. Uncured PDLC mixture is formed with a weight ratio of E7 liquid crystal to NOA65 prepolymer of 6 : 4. In order to lower driving voltage, we mix PDLC with ethanol (weight percentage of ethanol = 10%). Next, we assemble the two ITO glass substrates; the uncured mixture is sandwiched between them and then cured to form the PDLC. Voltage can now be applied across the top and bottom electrodes to control the transparency in the region where the top and bottom electrodes overlap. Last but not least, we use incandescent white light source, lens assembly and CMOS image sensor to capture the aperture image information, and then transform image to gray scale. After that, we analyze the relationship between the applied voltage and aperture size. In summary, we prove its feasibility for PDLC variable micro square aperture by using the fringing electric field.