新型光學補償液晶光電特性分析與研究

Electro-optical Study on Optically Compensating Liquid Crystal Devices

林家強(Jia-Chiang Lin)

指導教授 ： 趙治宇

國立臺灣大學/理學院/物理研究所/碩士(2004年)

https://doi.org/10.6342/NTU.2004.00535

摘要

在本論文裡，我們利用將向列型液晶分子配向使之形成彎曲排列成來達成光學補償的效果。此彎曲排列之液晶晶胞具有快速反應時間及光學補償的效果，一般預期此光學補償效果使彎曲排列液晶晶胞具有廣視角之特性。
實驗上我們配製液晶晶胞時發現液晶分子並不像我們所預期的是處於彎曲排列。在未給予任何外力的情況下，液晶分子是處於擴展排列的狀態；而在給予外力之時，液晶分子則會在擴展與彎曲排列之間轉換。我們分別計算並比較液晶分子在擴展與彎曲排列狀態下之自由能，進而得到達成彎曲排列的條件。我們使用以下兩種方法來達成液晶分子之彎曲排列: 一種方法是配製大預傾角來降低彎曲形變之自由能，另一種則是在電驅動液晶晶胞時施加一固定偏電壓在晶胞上，而使擴展排列之液晶轉換為彎曲排列。
我們使用摩擦配向機來摩擦垂直配向膜，並藉由改變摩擦強度來配製大預傾角而成左獄s造出在60度到80度之間的預傾角。我們在計算自由能的時候便建立了預傾角的大小與彎曲排列配向之關係。我們利用此63度之預傾角來達成彎曲排列配向，並且量測分析此63度之預傾角之彎曲排列配向液晶晶胞之光電特性。
此外，我們使用日本Chisso Corporation所提供之液晶材料及小預傾角配向劑來製造偏壓型變曲排列液晶晶胞。此液晶晶胞在光電特性上比上述之大預角之彎曲排列晶胞有明顯的改進。此乃因偏壓驅動之晶胞其液晶分子排列具有比較大曲率之彎曲排列。此大曲率的彎曲排列亦具有較佳之光學補償效果，並且形成較大的相位差；也因此，使我們可以減小液晶晶胞之液晶分子層厚度。由於較小的液晶分子層厚度，此液晶晶胞具有更快的電驅動反應以及更大的視角。
即使此晶胞具有非常快的電驅動反應，但其視角只有大約60度，而此視角在顯示器應用上而言是不夠的。因此，我們利用加上補償膜的方法來改善視角上的問題。然而在實際上，補償膜是不容易製造。在此論文的最後，我們利用光學計算模擬的方式來討論如何使用補償膜以改善視角，並成左澈塈Q一補償之條件使得視角能夠大於160度。此一廣視角以及彎曲排列液晶晶胞本身所具有之快速電驅動反應特性，對於需要高速反應的液晶電視來說，是非常具應用價值及潛力的。

關鍵字

液晶 ； 補償

並列摘要

An optically compensating liquid crystal (LC) device for display is achieved by the bend structure of LC molecular configuration. The character of this bend mode is the very fast electric response and the self optical compensation, which is expected to have a large viewing angle.
In fabricating the cell of this LC display device, it is found the LC cell has a property of splay to bend transition and usually the cell is initially in the state of splay configuration. By simulating the free energy of the bend and splay states, we successfully established the condition of the bend alignment. One of the methods is using the alignment of large pretilt angle, and the other is by applying a bias voltage.
Large pretilt angle of about 60 to 80 degrees is successfully constructed by rubbing the vertical alignment polyimide film with different rubbing strength. The relationship between the pretilt angle and the transition between splay and bend states of the bend-alignment liquid-crystal cell has been established. We apply the pretilt angle of 63° to fabricate the bend alignment cell and also obtain the electro-optical performance of this cells.
The bend cell is successfully fabricated by applying a bias voltage and the alignment polyimide and LC material of the cell are provided by Chisso corporation. The electro-optical performance of this bias voltage applied cell has a significant improvement due to the larger curvature of the bend configuration which leads to better compensation. Moreover, the large curvature also enlarges the phase retardation and thus the cell gap is reduced. Hence, the response time is faster than that of the large pretilt bend cell.
Although the viewing angle is improved up to about 60° by bias voltage bend alignment, it is not good enough for display application even that the electric response is so fast. The method of adding a compensating film is a good solution of the small viewing angle. However, the difficulty to fabricate the compensating film which needs to be concerned with the materials and aligning methods. At the end of this thesis, we simulate the viewing angle of the bend aligned cell with compensating films, and the results show a very large viewing angle of larger than 160°, which makes the bend alignment LC device become more potential for LCD TV application.

並列關鍵字

Liquid Crystal ； compensating

參考文獻

References of Chapter 1

[2] D. Demus, Types and Classification of Liquid Crystals, Liquid Crystals Applications and Uses, Vol. 1, World Scientific (1992), see chapter 1.

[4] P. Yeh and C. Gu, Optics of Liquid Crystal Display, Wiley (1999).

References of Chapter 2

[1] P. Yeh and C. Gu, Optics of Liquid Crystal Display, Wiley (1999).