|Abstract: ||隨著時代演進，液晶領域越趨成熟，有許多先進的研究和應用在電光控制領域中實現，本論文主要研究無須持續施加電壓的穩態顯示元件，該類元件可應用於廣告刊板等用途。此外，此液晶元件亦有可重覆抹除及寫入的特性，主要透過切換雙穩態結構技術，將可決定液晶結構穩定於焦錐態或平面態。根據實驗結果，處於特定穩態的結構若沒有刻意施加外在變因，則將可持續穩定存在至少兩週。本研究主要是利用十二氫氧基硬酯酸以穩固膽固醇液晶的穩態，將膽固醇液晶注入鍍有聚乙烯基咔唑薄膜的液晶盒內，透過控制溫度、施加電壓以及照射紫外光於液晶盒上寫入的圖案。自組成材料-十二氫氧基硬酯酸(簡稱HSA)可藉由控制溫度以決定其氫鍵斷裂與否，若是加熱至氫鍵斷裂，並施加小幅度之電壓，則可控制膽固醇液晶處在焦錐態，此時再透過快速降溫至室溫，則可透過重組之HSA結構得到處於焦錐穩態之膽固醇液晶。且即使是長螺距且小間隙之膽固醇液晶盒，若是沒有自組成材料用以穩固液晶排列，則最穩定之液晶排列為平面態，但若有自組成材料用以穩固液晶排列，則可得焦錐穩態。反之，若欲穩固於平面態膽固醇，則需緩慢降溫使HSA均勻地重組。最後利用此製程應用於製作顯示元件，透過以紫外光照射PVK後可使PVK具備導電特性，藉此可消除內建電場並提升有效電場，透過此機制透過光罩照射紫外光於液晶盒上，使某些區域照光及某些區域不照光，如此可實現利用電光熱法寫入欲顯示之圖案。;Nowadays, liquid crystal (LC) technology is getting more and more mature due to its novel developments and applications in electro-optical fields. Recently, we would like to invent some new devices which can be applied to billboards, electronic tags, etc. By using bi-stable textures of cholesteric LCs, the structures can be chosen to be stabilized in the desired state. According to the experimental results, it shows that it can be kept in the desired state for more than two weeks.|
This study presents the multi-stable and reusable LC display devices using 12-hydroxysteric acid (HSA)-doped LCs in a poly(N-vinylcarbazole) (PVK) film-coated LC cell. Through the branches of hydrogen-bond of HSA, the structures of the cholesteric LC can be stabilized. By increasing the temperature over the melting point of HSA, the hydrogen bonds break down and HSA molecules dissolve in the LC host. If we keep increasing the temperature to the clearing point of the LC host, the cholesteric LC will turn into its isotropic state. With the application of suitable external voltages onto the LC cell at the temperature between the melting points of HSA and the clearing point of LC, we can get the focal conic state of cholesteric LC. Keep applying voltage onto the LC cell and then decrease the temperature of the LC cell to room temperature. After that, keeping at the room temperature and applying a suitable voltage onto the LC cell to make sure the structures are stable enough. Through the method described above, the LC cell will be kept in the state of the focal conic. If we decrease the temperature of the LC cell slowly without applying any voltage, the LC cell will present planar textures with the conditions of long pitch length and small cell gap. Because of the homogeneous alignment films, long pitch length, and small cell gap, the LC cell will tend to stay in the planar textures without applying any voltage. As the two methods mentioned above, the LC cell can have two different stable structures.
According to the method described above, PVK films are coated onto the LC cell and expose the PVK to UV light through a photo-mask having the desired patterns simultaneously. In the meantime, an external voltage is applied to the LC cell. The regions with UV exposure present focal conic textures, and the regions without UV exposure present planar textures. We cool down the temperature slowly and apply a suitable voltage simultaneously. Thereafter, the LC cell will have the pattern we want.