Super twisted nematic type displays was discovered in the early 1980s that increasing the twist angle of a liquid crystal cell to about 180–270° also allows a much larger number of pixel rows to be used, with a consequent increase in the complexity of images that can be displayed.
These super twisted nematic (STN) displays achieve their high twist by using a substrate plate configuration similar to that of TN displays but with an additional optically active compound, known as a chiral dopant, dissolved in the liquid crystal.
The display is activated using passive-matrix addressing, for which the pixels are arranged in rows and columns; selective application of a voltage to a particular row and column will activate the corresponding element at their intersection.
Compared to 90° twisted cells, the supertwist results in a greater relative change in optical transmission with applied voltage. By lowering “cross talk,” or the lighting of undesired pixels, the number of rows that may be triggered in passive-matrix addressing is increased.
The more recent thin-film transistor TN displays (explained below), which offer superior viewing angles, colour, and reaction speed, are replacing colour STN displays for computer monitors on the market.
Monochrome STN displays are still widely used in mobile telephones and other devices that do not require color.
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