Liquid crystal displays construction

Basic liquid crystal display construction. [Hamlin, fne ... 

The sharper thresholds required for the addressing of larger displays can be brought about by constructing liquid crystal cells with sharper transitions (see Fig. lc) (Boyd et al., 1982 Wilson et al., 1983), intrinsic threshold control, or by the addition of nonlinear electronic elements, extrinsic threshold control. Liquid crystal displays with gradual turn on such as DSM or GH LCDs always require extrinsic threshold control for matrix addressing. 

The twisted nematic liquid crystal display (TN-LCD) was reported by Schadt and Helfrich of F. Hoffman-La Roche in Basle, Switzerland in 1970. This was part of a tripartite collaboration between F. Hoffman-La Roche in Basle, Brown Boveri of Baden and Ebauche in Neuchatel, all in Switzerland. The intention was to design and develop flat panel displays, e.g. for digital watches. The first LCD factory was constructed in Lenzburg, Switzerland in the mid-1970s by Videlec, a subsidiary of Brown Boveri. Since then the TN-LCD has... 

Polymerization of reactive monomeric liquid crystals is one method for stabilizing the liquid-crystalline thin films. Another approach is to form chemical gels of liquid crystal molecules with low molecular weight by construction of a polymer network. This method has been investigated for the stabilization of ferroelectric liquid crystal displays. Guymon et al. reported that a polymer network produced by photochemical cross-linking accumu-... 

Important considerations for construction of a liquid crystal display include the following [111] ... 

Figure 9. Relationship between transparency (% transmittance in air at 600 nm) and applied voltage of polymer chspers liquid crystal display devices constructed using two ITO glass electrodes and two polypyrrole film (on plastic) electrodes as the conducting transparent substrates.

TAB has been developed as the special wiring material for IC chips and liquid crystal displays (LCDs). Although it was developed separately from standard flexible circuits, they have similar constructions and they use similar materials, and can be categorized as one kind of flexible circuits. 

Further work on the electro-optical properties of liquid crystals led to the above-mentioned invention of a novel liquid crystal display. This display also consists of a thin layer of a nematic liquid crystal which is situated between two electrodes. However, the molecules are now anchored at the two opposite electrodes in such way that their preferred direction is twisted within the layer. This distortion of the nematic phase can be changed by the applied voltage leading to a change of the optical properties. Almost all liquid crystal displays used today in watches and other devices are based on this simple and rather robust construction principle. 

With a few exceptions, which are noted in later sections of this chapter, the construction of the different types of liquid crystal display cell is generally similar [3]. The liquid crystal material is contained between two sheets of glass, held parallel and spaced apart by a distance of a few micrometres. The glass is coated on the inner surfaces with a succession of thin optically transparent layers that serve specific purposes in the operation of the device. Those most com-... 

The double threshold addressed matrix liquid crystal display panel uses a two-terminal device that accomplished both set and reset functions for each pixel with appropriate signal pulses from the gate electrode drivers. To realize this panel, an amorphous silicon (a-Si) PIN thin film diode (TFD) matrix construction is used. The circuit diagram of a matrix panel addressed by these diodes is shown in Fig. 1 [4], Each pixel is composed of a pair of diodes and one liquid crystal cell connected in series between a gate electrode bus and a data electrode bus. The diode pair is referred to as a diode ring, because the connection is a ring. 

Figure . Construction of thin film transistor switch matrix addressed liquid crystal display panel.

Figure 8. Construction of CdSe thin film transistor for addressing a matrix liquid crystal display panel.

Figure 8 shows the construction of an original TFT for the matrix liquid crystal display panel in which a cadmium-selenium (CdSe) TFT is used as the switch. Figure 8 (a) is a top view of the switch structure and its accompanying liquid crystal pixel electrode. Figure 8(b) shows a cross-sectional view of the switch and pixel electrode. The CdSe semiconductor layer is used as a channel between the drain and source of the TFT. 

Figure 15. Construction of a solid phase recrystallized p-Si thin film transistor and pixel for matrix liquid crystal display panel.

For the proper operation of liquid-crystal display devices, appropriate cell construction and surface treatment methods are necessary. In this chapter, first, some of the general packaging techniques that are being used today are outlined. Second, the common conductive coatings are listed and standard preparation methods given. Third, the diverse surface treatment methods are summarized and, finally, some relationships between cell construction and device operation are discussed. 

Liquid-crystal displays have also been constructed on a matrix of single-crystal silicon MOS FET s. Pictorial-gray-scale images have been created on a 1 inch display although line defects were present. Though large arrays of TFT s should be much more economical than silicon MOS FET s, TFT s have suffered in the past from stability and reliability problems. More experimentation is necessary to prove their capabilities as the threshold devices in a liquid-crystal panel. 

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