TN display under a microscope, with the transistors visible at the bottom Amorphous silicon-based TFTs are by far the most common, due to their lower production cost, whereas polycrystalline silicon TFTs are more costly and much more difficult to produce. Examples include small high-resolution displays such as those found in projectors or viewfinders. Polycrystalline silicon is sometimes used in displays requiring higher TFT performance. Transistors take up only a small fraction of the area of each pixel and the rest of the silicon film is etched away to allow light to easily pass through it. The silicon layer for TFT-LCDs is typically deposited using the PECVD process. However, rather than fabricating the transistors from silicon, that is formed into a crystalline silicon wafer, they are made from a thin film of amorphous silicon that is deposited on a glass panel. The circuit layout process of a TFT-LCD is very similar to that of semiconductor products. Each pixel is a small capacitor with a layer of insulating liquid crystal sandwiched between transparent conductive ITO layers. The one-way current passing characteristic of the transistor prevents the charge that is being applied to each pixel from being drained between refreshes to a display's image. The column and row wires attach to transistor switches, one for each pixel. To avoid this issue, the pixels are addressed in rows and columns, reducing the connection count from millions down to thousands. This would be impractical for a large display, because it would have a large number of (color) picture elements ( pixels), and thus it would require millions of connections, both top and bottom for each one of the three colors (red, green and blue) of every pixel. The liquid crystal displays used in calculators and other devices with similarly simple displays have direct-driven image elements, and therefore a voltage can be easily applied across just one segment of these types of displays without interfering with the other segments. As of 2013, all modern high-resolution and high-quality electronic visual display devices use TFT-based active matrix displays. Brody and Fang-Chen Luo demonstrated the first flat active-matrix liquid-crystal display (AM LCD) using CdSe TFTs in 1974, and then Brody coined the term "active matrix" in 1975. Dixon at Westinghouse Research Laboratories developed a CdSe ( cadmium selenide) TFT, which they used to demonstrate the first CdSe thin-film-transistor liquid-crystal display (TFT LCD). Tults demonstrated a 2-by-18 matrix display driven by a hybrid circuit using the dynamic scattering mode of LCDs. The idea of a TFT-based liquid-crystal display (LCD) was conceived by Bernard Lechner of RCA Laboratories in 1968. It was made with thin films of cadmium selenide and cadmium sulfide. Weimer, also of RCA implemented Wallmark's ideas and developed the thin-film transistor (TFT) in 1962, a type of MOSFET distinct from the standard bulk MOSFET. In February 1957, John Wallmark of RCA filed a patent for a thin film MOSFET. Further information: History of display technology and Thin-film transistor
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