Technology Profile and Recent Applications
Features at a Glance:Flat panel displays use a variety of technologies. The sleek, thin screen most people associate with flat displays is the liquid crystal display or LCD. Active-matrix LCD displays alone accounted for over two-thirds of flat panel display sales in 1997 with the remainder comprised of passive-matrix LCDs, plasma displays and other technologies. How do these technologies shrink the existing bulky cathode ray tube monitor into these screens used in laptop computers, projectors, and countless other devices? A recent article in the New York Times described the LCD technology, a portion of the article appears below:Smaller Physical Size
“LCD displays apply electrical charges to liquid crystals, rod-shaped molecules that have both liquid and solid properties. The structure of the liquid crystals changes in response to electrical charge, changing the way light passes through them. In most LCD devices, the layer of liquid crystals, about 5 microns thick (a human hair is about 100 microns wide), is between two layers of plastic or glass, both of which are covered with a layer of transparent electrodes, and two alignment layers; each alignment layer orients the liquid crystal molecules in a fixed direction. Light passes through a polarizing filter, then the LCD cell, then another polarizing filter. If the second polarizing filter will allow to pass only light with waves perpendicular to the waves that went through the first filter, then only light that has changed its orientation while passing through the liquid crystals will get through and be seen.”
LCD displays can be broken down into two categories, active-matrix and passive-matrix. Active matrix or AM-LCD are used in laptop computers, projectors, touchscreens and other flat panel displays. Passive-matrix displays are used in cellular phones, calculators, pagers and other electronic devices that account for a smaller relative portion of the market. In fact out of the $12 billion in flat panel displays sold in 1997 68% were computer displays, and this number is expected to rise to 72% by 2003 . The main difference between the active and passive LCD is that the active-matrix has at least one transistor for each element that makes up the display, commonly referred to as a “pixel.”
Plasma display panels (PDP) are being touted as the new TV or large projection devices. These screens are made up of thousands of small pockets of gas plasma which are charged with an electrical signal. Once electrified the gas gives off ultraviolet rays, which then light up red, green, or blue phosphors printed on the inside surface of the glass screen. These screens are brighter than most TVs and are visible from almost angle unlike some laptop screens.
Several other technologies are being developed rapidly in an attempt to overcome the high cost associated with manufacturing LCD and plasma displays. One popular technology is called field-emission displays (FEDs). This technology enables companies to utilize core semiconducter manufacturing processes to reduce the production costs below that of AM-LCDs . A portion of this technology development has come from the Defense Advanced Research Projects Agency (DARPA) which funded a program to develop a 12 inch color FED display for use in the Abrams M-1 tank command station.