Super twisted nematic LCDs

A plot of the twist angle at the centre of a cell against applied voltage for a series of twist angles of nematic LCDs. 

In principle, this mode of operation creates the possibility of producing high-information-content displays due to the short frame times associated with bistable displays, since they are basically a memory effect and only new information must be changed. Unfortunately, metastable twist states of intermediate twist, which degrade the optical performance of the device, form around dust particles in cells with a cell gap below a certain value (d 20 m). Therefore, since the response time is proportional to d, very long response times are observed ( 1 s) for LCDs with a cell gap above this critical value. These optically disruptive metastable twist states also form at the interface with spacers used to generate a uniform cell gap. 

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In the 1980s, the research and development of AM LCDs were very active, but it had not yet opened great application. On the other hand, STN-LCD (super twisted nematic LCDs) for PCs and Japanese word processors were realized in the 1980s [7], and also colored STN-LCDs for PCs were developed. The electro-optical response increased steeply with increasing applied voltage for those cells and enough contrast was provided even if the number of scanning lines increased, and... 

Table 4.1 summarizes which type of the LC film series is compatible for each LCD mode. Twisted oriented films can be used for color compensation of STN (super twisted nematic)-LCDs [36], in particular for color STN-LCDs in mobile devices. Because such color mobile STN-LCDs use only one polarizer, it is necessary that the combination of the compensation film and STN cell functions as a wideband A/4 plate. Multiple films are required in order to achieve this condition for usual, stretched films, but by using the twisted oriented film this can be realized by just one film [37-39]. 

Supertwisted nematic display, 15 114 Super twisted nematic liquid crystal display (STN-LCD), 9 340 Super ultra-low emissions vehicle (SULEV), 13 855... 

Super-twisted nematic liquid crystal displays (STN-LCDs) 45000000... 

The first TN-LCD were simple, directly addressed segment displays as still used, e. g., for wrist watches. When attempts were made to increase the information content of the displays by time-sequential addressing in rows and lines (multiplexing) the limits of the TN cell were soon met. At higher multiplex ratios [14] contrast loss occurred, because of ever shorter addressing times. The development of the super-twisted nematic (STN) cell in 1984 [15] pushed the practicable limit to higher multiplex ratios, but it did not lead to a general solution of the problem. 

In LCDs various LC modes of operation are applied like twisted nematic (TN) [5], super twisted nematic (STN)[6], vertically aligned nematic (VAN) [7,8], optically compensated birefringence (OCB) [9] and in plane switching (IPS) [10-12]. The LC mode used depends on the demands of a specific application, like the viewing angle, power consumption and manufacturing cost. 

T. Scheffer and J. Nehring, Twisted nematic and super-twisted nematic mode LCDs, in Liquid crystals -applications and uses, Vol. 1, ed. by B. Bahadur (World Scientific, New Jersey, 1990). 

Compared to the conventional transmissive TN LCD, the above transflective TN LCD only requires one additional transflector between the bottom polarizer and the TN LC layer. Naturally, this transflective LCD device configuration can also be extended to an STN-based transflective LCD [42]. In contrast to the so-called polarization rotation effect in TN LCD, the STN LCD uses the birefringence effect of the super-twisted nematic LC layer [43]. Therefore, a larger twist angle (180 270°), a thicker LC cell gap, and a different polarizer/analyzer configuration are required. 

More advanced LCDs take advantage of so-called super-twisted nematic displays, in which the director rotates 270° between the two polarizers. This leads to a crisper distinction between on and off states. Color LCDs simply include appropriate dyes to make red, green, and blue (RGB) pixels—simple in principle but a fairly complex technology. 

One of the most important necessary conditions in recent LCD such as thin film transistor and super twisted nematic modes is to have higher voltage holding ratio Ry > 95%) even in a high-temperature... 

Silver halide photosensitive materials for photographic purposes were the main products of FUJIFILM, and in the 1990s, future market projections did not hint any decline. Thus, silver hahde photosensitive materials were mainstream materials in our company. As a result, less than 1 % of researchers developed optical films for LCDs. Our team had developed and commercialized an optical compensation film for super twisted nematic (STN) LCDs since 1987, but we were greatly defeated by competitions that had products with better performance, but we were greatly defeated by competitors that had products with better performance. Thus, in 1992 we faced the closing down of our unit. 

Fig. 7.12 (a) Photo-aligned LCP retarder integrated onto the substrate of a photo-aligned LCD. (b) Black-white super twisted nematic (STN)-LCD with integrated color compensating a-plate... 

The super birefringent effect (SBE-LCD) reported by Scheffer and Nehring from Brown Boveri in Baden, Switzerland, uses the optical interference of two normal, elliptically polarised modes of transmitted light generated by a high-tilt, highly-twisted nematic structure viewed between two polarisers set in an unusual way, i.e. the input polarisation direction is not parallel to the nematic director at either substrate surface and the polarisers are not crossed at 90°, see Figure 3.10. 

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