| Summary: | 碩士 === 國立臺灣大學 === 光電工程學研究所 === 107 === Fast response time is significant for LCD because it can avoid unwanted motion blur. Based on VA-FFS (vertically-aligned fringe field switching ) mode, which features fast response time, we continue to study other factors that can affect response time. The relation of switching mechanism and response time in VA-FFS mode has been studied in this thesis. The result shows that negative LC is slower than positive LC in VA-FFS mode, due to its special molecule behavior in vertical fields and the lower density of virtual walls in the LC cell. We name this molecule behavior of negative LC as the “two-step process”, owing to the feature that negative LC will begin the rotation in some regions, and then the others. The root cause is that “hesitant LC molecules” without clear falling direction would be waiting for those with determined directions to guide them. Negative LC still has an advantage in VA-FFS mode, which is higher transmittance, although it means less disclinations that can be used as virtual wall for faster fall time.
The comparison between 2D and 3D electrodes has also been discussed. We find that 3D electrode can restrict the rotating directions of LC molecules to achieve faster rise time. In other words, there are less “hesitant LC”. This is especially obvious for negative LC. Another reason why 3D electrode using negative LC is faster is that in 2D pattern, all negative LC molecules are allowed to fully rotate, which extends the overall rise time. However, in 3D pattern, parts of the negative LC molecules could not fully rotate due to equal distribution of electric fields in all directions.
Finally, we find that positive LC in 3D electrode is most competitive for fast response time device, but it has much lower transmittance than negative LC does. Therefore, we use three methods to improve its transmittance: DFFS, DFFS with 3-level electrode design, and protrusion. Eventually, we can improve transmittance by 10-15%.
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