Thin, light-weight, low-power liquid crystal displays have enabled personal computers to become highly mobile. In these displays, light from a fluorescent back-light is modulated in intensity by controlling the voltage across a liquid crystal cell. The transmitted light passes through red, green, or blue color filters to produce a dot of color. Adjacent red, green, and blue dots make up a full color dot or pixel. A liquid crystal display consists of a two dimensional array containing about a million color dots. In thin film transistor liquid crystal displays (TFT-LCD) a transistor is used as a switch to control the liquid crystal voltage for each color dot.
A TFT-LCD is built using many technologies. An array of amorphous silicon thin film transistors is fabricated on a large glass plate using processes derived from the semiconductor industry. An array of color filters is formed on a second plate using pigmented photosensitive polymers. The plates are separated by about 5 microns using spacer balls and liquid crystal material is introduced between the plates and the display is sealed. Finally, driver circuitry is attached using an anisotropic conducting film.
An important metric used in displays is the number of full color pixels that can be displayed per inch. This is called the dots per inch or DPI of the display. This metric indicates the resolution of the display. The greater the number of pixels per inch, the greater the detail that can be displayed in a fixed size image or letter.
Cathode ray tube based color displays achieve 90 to 100 dpi performance using shadow mask technology. Active Matrix Liquid Crystal Display (AMLCD) technology is capable of building 150 dpi displays with full color.
An experimental 157 DPI full color AMLCD has been constructed at IBM's Watson Research Center in Yorktown Heights, NY. The increased resolution of the display permits graphical information that is typically displayed using paper to be accurately rendered on an electronic display. Textual information also benefits from high resolution displays, reading speed and accuracyincrease with increasing display resolution.
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