Mixed-mode twisted nematic MTN cells

T = 2n d AnIA, d is the cell gap, X = cf + TjTf, is the twist angle, and is the angle between the polarization axis and the front LC director. 

Several MTN modes with twist angle varying from 45° to 90° have been used for direct-view and projection displays, depending on the desired contrast ratio and optical efficiency. In transflective LCDs, the 75° and 90° MTN cells are frequentiy used. Therefore, we only discuss these two modes here. 

For direct-view reflective displays, the outmost surface reflection (usually it is a plastic protective film without anti-reflection coating) limits the device contrast ratio. Thus, the -100 1 contrast ratio of the 75° MTN is still adequate. However, in projection displays the contrast ratio needs to exceed 1000 1. The 90° MTN and the VA cells are the better choices. 

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