Transflective display

Several mechanisms of photoalignment reactions have been reported in the literature and hence a variety of photoalignment materials are available for director patterning. For the manufacturing of a patterned retarder applied in a transflective display (Sect. 9.4.2), we have tested two commercially avail-... 

A director patterned retarder can be used in a transflective LCD to boost the optical performance and to lower the power consumption. A transflective display is the combination between a reflective and a transmissive display. 

Response time is another important issue for guest-host displays. A typical response time of a guest-host display is around 50 ms because of the bulky dye molecules. Due to the polymer network, the response time of the dye-doped negative LC gel is fast. The rise time is 1.0 ms and decay time is 4.5 ms when the applied voltage is switched between 0 and 20 Vrm . This dye-doped LC gel can also be configured to a polarizer-free transflective display using the dual cell gap approach. 

J. Ouderkirk, S. Cobb Jr., B. D. Cull, M. F. Weber, D. L. Wortman, Transflective displays with reflective... 

It is more useful to pattern the polarizer in pixelated form. For example, it may be possible to make transflective displays with subpixels having different polarizer orientations, with one subpixel being in the transmissive mode and the other one being in the reflective mode. We shall discuss such a possibility in Section 5.3. 

Figure 5.20 The configuration of the transflective display without subpixel separation, using an antiferroelectric LC cell (AFLC) [27]. Reproduced from [27], (2001) The Society of Information Display...

From a manufacturing point of view, single cell gap designs are desirable. But in this case, the optical path for the reflective mode is twice that of the transmissive mode. Thus it is very difficult to design such transflective displays to satisfy the optical efficiency requirement. Also, it is rather difficult to match the TVC and RVC. A possible single cell gap design is shown in Figure 5.22. 

Thus for a transflective display, one is always faced with compromises, either in complexity of the design in terms of cell gap and subpixel structures, or in complexity of the driving electronics. The situation becomes easier if in-cell patterned retarders or polarizers can be made. An example of an in-cell retardation film display is shown in Figure 5.23. It can be seen that the effect of different cell... 

In fact, for the reflective subpixel of a transflective display, a single polarizer is always used. The optics of a single polarizer LCD have been analyzed by many authors [32, 33]. The most common mode is the mixed TN-twist birefringent (MTB) mode. The RVC and the TVC can be matched simply by adding a quarter-wave film, as shown in [32, 33]. Thus, if an internal retardation film can be used, such MTB modes can be used with good optical quality. 

In addition, if it is possible to have patterned alignment layers, different LC modes for the subpixels can be made and optimal performance transflective displays can then be achieved. These novel designs all require patterning of either the polarizer or the retardation film, or the alignment layers. They can all be accomplished with photoalignment [34]. One such novel design that maintains a uniform cell gap is shown in Figure 5.24. 

Figure 5.24 The transflective display with a uniform cell gap and two different LC electro-optical modes for reflective (OCB) and transmissive (TN) parts [34], Reproduced from P. Xu, H. Y. Mak, V. G. Chigrinov, and H.-S. Kwok, Transflective LCD with single cell gap containing two modes in one pixel. ECLC 2007, Lisbon, Portugal, Abstracts, PC20 (2007)...

Figure 9.21 shows a simplified cross section of a transflective LCD. It consists of two ITO covered glass plates, with the LC molecules in between, that act as the optical valve. In order to distinguish between the on- and off-state, two polarisers are required. A full colour display is created by addition of a colour filter. The reflective mode is enabled by a mirror on top of the bottom... 

This effect has been successfully implemented in seven-segment and similar fixed format displays and in simple dot-matrix displays. Such displays may be employed in a reflective mode, backlit, or in a transflective combination of both these modes. Although not outstandingly attractive in appearance, the TN LCD has proved to be versatile, relatively cheap to manufacture and drive, and reliable. Its most obvious limitations are speed (the turnoff time can be tens or hundreds of milliseconds), and the difficulty that it experiences in showing complex information. 

For outdoor applications, the displayed images of a transmissive LCD could be washed out by sunlight A reflective LCD would be a better choice. However, such a reflective display is unreadable in dark ambient conditions. Transflective LCDs integrate the features... 

In an attempt to overcome the above drawbacks and take advantage of both reflective and transmissive LCDs, transflective LCDs have been developed to use the ambient light when available and the backlight only when necessary [5]. A transflective LCD can display images in both transmissive mode (T-mode) and reflective mode (R-mode) simultaneously or independently. Since LC material itself does not emit hght, the transflective LCD must rely on... 

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. 

Polymer-dispersed LC (PDLC) [30], polymer-stabilized cholesteric texture (PSCT) [31], and LC gels [32] all exhibit optical scattering characteristics and have wide applications in displays and optical devices. The LC gel-based reflective LCD can also be extended to transflective... 

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