- 學位論文
邊緣場效驅動液晶顯示器之電極結構及電極厚度對閃爍問題之模擬研究
Effects of Electrode Structure and Electrode Thickness on Flicker in Fringe Field Switching Liquid Crystal Display
摘要
在現今的液晶顯示器中，不論是TN、VA、IPS為最常見的液晶面板技術，以上技術各有優缺點，本文為IPS(In-Plane Switching)水平驅動顯示的延伸為FFS(Fringe-Field Switching)邊緣場效顯示器，其技術更增加原有IPS視角及出光效率的改善，而近期較新穎的研究為在低頻驅動下除了減少能源的消耗但有閃爍問題的發生，所以本篇論文利用邊緣場效作為主要架構去討論閃爍。 討論邊緣場效驅動和水平驅動技術時多使用在小尺寸行動裝置如手機筆電等，因為使用方式與其他顯示器不同須要更廣的視角，其觸摸無水紋硬屏也是選擇FFS和IPS此驅動技術的特點，能源消耗一直是人們所關注的議題，除了做容量較大的電池和更改電池的材料，液晶的驅動也是耗電中的一環，所以驅動頻率對電量的消耗也相當重要，在日常生活中除了看影片以外其餘較為靜態的瀏覽，如果在此時更改驅動頻率調整到低頻，可以節省用電量並有更長的使用時間。 本文主要討論在低頻下邊緣場效驅動，利用不同電極寬度及電極間距找到個別寬度適合的最小閃爍間距，所以利用最大傾角和最小旋轉角及電場，分析不同的結構下液晶彎曲形變和展開形變的不同，結果發現在電極寬度最小時電極間距的不同傾角和旋轉角影響幅度是最大的，利用彎曲形變和展開形變可以找到最小閃爍間距。第二點為模擬不同的電極厚度，為了保持同樣的液晶盒(Cell Gap)深度所以我們採取平坦化的結構，在電極中間加入同樣厚度的絕緣層，而結果發現電極厚度的影響僅在於電極上方的區域的液晶，而兩個電極中間上方的液晶幾乎不受電極厚度影響，所以選擇將電極厚度限制在0.15 μm會有較低的閃爍。
並列摘要
In today’s liquid crystal display, TN (Twist Nematic),VA (Vertical Alignment) and IPS(In-Plane Switching) are the most common LCD panel technologies, and all of the above technologies have their pros and cons. This thesis is based on FFS (Fringe-Field Switching) technology, which can improve the light efficiency of original IPS technology. In recent years, active research has been carried out on reducing energy consumption, which however can lead to flicker problem when we use low frequency driving. FFS technology has been used widely in small-size mobile devices such as mobile phone or notebooks. This mode is different from other display such as TV. This is because, for these small mobile touch-screen devices, there will be no touch interference pattern when we use driving technologies that are based on horizontal switching such as IPS and FFS. Unlike dynamic display such as watching movies and animations that require high frequency driving, static image requires only low frequency driving, which can help save power and extend the longevity of device. In this thesis, we investigate the flicker problem in FFS technology driven at low frequency. In the first part of this study, we use different electrode widths and electrode gap to obtain the minimum flickering. By observing the liquid crystal maximum tilt angle, minimum azimuth angle and also the electric field distribution, we can analyze liquid crystal distribution caused by flexoelectric effect. From the results we found that that when the electrode width is smaller, liquid crystal’s maximum tilt angle and minimum azimuth angle can be affected by the electrode gap more seriously. By using the corresponding splay and bend maximum tilt angles, we can obtain the electrode gap values for the minimum flicker to occur for different electrode widths. In the second part of this study, we simulate different electrode thickness. In order to maintain the same cell gap throughout the whole structure, we adopt a planarized structure, which is achieved by adding an insulator layer between the electrodes. From the results, we found that the changing of electrode thickness mainly affects the distribution of liquid crystal molecules above the electrode, the liquid crystal molecules above the middle of the two electrodes are hardly affected by the changing of electrode thickness. Finally, the result shows flicker is least when the electrode thickness is limited to at most 0.15 um.