Super-twisted nematic display

A super-twisted nematic display (STN) is a type of monochrome passive-matrix liquid crystal display (LCD). This new type of LCD was invented at the Brown Boveri Research Center, Baden, Switzerland, in 1983. For years a better scheme for multiplexing was sought. Standard twisted nematic (TN) LCDs with a 90 degrees twisted structure of the molecules have a contrast vs. voltage characteristic unsuitable for passive-matrix addressing as there is no distinct threshold voltage. STN displays, with the molecules twisted from 180 to 270 degrees, have superior characteristics. The main advantage of STN LCDs is their more pronounced electro-optical threshold allowing for passive-matrix addressing with many more lines and columns. For the first time, a prototype STN matrix display with 540x270 pixels was made by Brown Boveri (today ABB) in 1984, which was considered a breakthrough for the industry.

STN LCDs require less power and are less expensive to manufacture than TFT LCDs, another popular type of LCD that has largely superseded STN for mainstream laptops. STN displays typically suffer from lower image quality and slower response time than TFT displays. However, STN LCDs can be made purely reflective for viewing under direct sunlight. STN displays are used in some inexpensive mobile phones and informational screens of some digital products. In early 1990s, they had been used in some portable computers such as Amstrad's PPC512 and PPC640.