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Liquid Crystal Displays
Published in John G. Webster, Halit Eren, Measurement, Instrumentation, and Sensors Handbook, 2017
Some organic dyes show anisotropy of light absorption, i.e., they absorb more light in a specific wavelength band when the E vector of the light is parallel to the optic axis of the dye molecules, than they do when it is perpendicular. LCDs based on this principle are called GH displays. In these displays, a small amount of a dichroic dye (guest) is mixed in the LC material (host). These dye molecules get aligned to the LC molecules; hence, their orientation can be changed (by changing the orientation of the LC molecules) by application of an electric field. When an LC material with a positive ∆ε is used, in the off-state, the E vector of the polarized light coincides with the light absorption axis of the dichroic dye; hence, light is absorbed and transmitted light is colored. When a voltage is applied for the on-state, the E vector of the polarized light is orthogonal to the absorption axis of the dye; hence, no absorption takes place, and transmitted light is not colored (white). GH LCD requires only one polarizer. Further, because the optical effect is based on absorption, the display provides a better viewing angle than a TN mode LCD.
Liquid crystal displays
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Operating with TFT removes steepness of the electro-optic transition as a critical design issue. This enables LCD modes to be chosen that meet the more stringent optical requirements for large area monitor and televisual displays. The crucial weakness of TN LCDs was the viewing angle, even with optical compensation. Viewing angle is particularly important for large area displays, where images must appear uniform from the center of viewing to the corners. The viewing angle target is harsher still if the image is to satisfy multiple viewers. The television market also requires fast response times not just for black to white transitions but also between adjacent gray levels. Extremely high contrast ratios are needed to compete with emissive technologies such as CRT, PDP, and, most recently (OLED).
Module Assembly and Optoelectronic Packaging
Published in Yufeng Jin, Zhiping Wang, Jing Chen, Introduction to Microsystem Packaging Technology, 2017
Yufeng Jin, Zhiping Wang, Jing Chen
According to the time of technology development, LCD has been through three stages. From the 1970s to the early 1980s, twisted nematic LCD (TN-LCD) was popular, which had a simple structure and fabrication process. But it had very poor display capacity and was mainly used in watches, calculators, digital displays, and similar simple electrical products. Advanced TN-LCD was used in meters, cameras, telephones, mobile meters, sound boxes, and so on. In the mid 1980s, super twisted nematic (STN-LCD) LCD was developed. With its high performance, large display capacity, and low cost, it was extensively used in automated office products and communication consuming products, such as cell phones, PDAs, GPSs, laptops, pagers, digital dictionaries, electronic diaries, learning machines, and so on. In the 1990s a new thin-film transistor LCD (TFT-LCD) was developed. Through sputtering or the chemical deposition process, various films are fabricated on glass or plastic substrate to make a large-scale integrated circuit in TFT. The cost decreased sharply using non–single crystal substrate, and conventional large-scale integrated circuits have been developed as pioneers of large area, multiple functions, and low cost. It is more difficult to fabricate controllers to switch on/off pixels (LCD or LED) on glass or plastic substrate with a large area in TFT than to fabricate large-scale IC on silicon. Requirements for the fabrication environment (class 100 level), for material purity, and for manufacturing instruments and techniques are superior to those for large-scale ICs, since they are the most advanced technologies of modern mass production. In applications, the bottleneck of TFT-LCD is to overcome the disadvantage of long response times for STN-LCD, and it also presents high-quality color displays and flexible display sizes. It is widely used in digital cameras, camcorders, televisions PCs, and especially in laptop computers.
Fabrication of vertically aligned liquid crystal cell without using a conventional alignment layer
Published in Liquid Crystals, 2018
Masanobu Mizusaki, Yohei Nakanishi, Satoshi Enomoto
Liquid crystal displays (LCDs) are the most popular type of flat-panel displays and are used in television sets, notebook computers, smartphones, tablets, car navigations, digital signage and so forth because they have features such as high resolution, low power consumption and thinness. So far, the LCDs have usually used a twisted nematic (TN) mode [1,2], but the TN mode has disadvantages of narrow viewing angle and low contrast ratio. Therefore, other modes with wide viewing angle and high contrast ratio such as in-plane switching mode [3], fringe-field switching mode [4], multidomain vertical alignment (MVA) mode [5] and patterned vertical alignment (PVA) mode [6] have been developed. Among these modes, vertical alignment (VA) modes such as the MVA and PVA modes have a significantly high contrast ratio because liquid crystal (LC) molecules are vertically aligned, which induce little retardation. To achieve VA, VA layers, which are mainly made from polyimides having side chains, are usually prepared on a pair of substrate [7,8]. The preparation of the VA layers usually requires large amount of solvent, high–temperature operation for post-baking and cleaning process [9].