Today the term Liquid Crystal Display, abbreviated as LCD has become common among us. TVs, computer screens, projectors, video players, gaming devices, clocks, watches, calculators, telephones etc..with LCD displays has conquered the consumer markets. They have replaced cathode ray tube (CRT) displays in most applications. They are available in a wider range of screen sizes than CRT and plasma displays.
Liquid crystal material was first discovered in Austria in 1888, about 10 years before the invention of the cathode ray tube. The first commercial liquid crystal display appeared in 1970’s. Today we have LCD flat-panel displays with diagonals of 70 inches or more.
Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes made of Indium Tin Oxide (ITO), and two polarizing filters with perpendicular axis of transmission. The surfaces of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic device the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This reduces the rotation of the polarization of the incident light, and the device appears grey. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray. Displays for a small number of individual digits and/or fixed symbols (as in digital watches, pocket calculators etc.) can be implemented with independent electrodes for each segment.
LCD AND 3D
Active glass technology
The active glass block the image for one eye and then the other in rapid sequence, so when the panel flashes left and right images, the viewer,s brain will combine them into a 3D scene. This has been a standard approach for 3D TVs. The demerit of this is that the active glasses are expensive and inconvenient.
LG’s FPR technology
This years disruptive technology is a Film Patterned Retarder (FPR) developed by LG display. FPR uses alternating horizontal stripes of polarising film, with each stripe as tall as one row of pixels. This creates two interlaced images with opposite polarisation, which can be viewed with the same inexpensive passive glasses used in cinemas.
Samsung and RealD recently demonstrated a new approach that seems to offer the best of the active and passive designs. a second LCD panel is incorporated in the display with the sole function of reversing the polarisation of the entire screen, to multiplex the left and right images. As result viewers can use inexpensive passive glasses yet still receive the full resolution to each eye.
Other large format display technologies such as organic LED’s will face increasingly tough competition as LCD makers continue to increase performance while wringing out cost