Twisted Nematic (TN) was one of the earliest fluid types to be implemented in LCD displays. Twisted Nematic LCD fluid uses a 90-degree twist between the top and bottom alignment layers of the LCD cell. The contrast of TN fluid displays is very high, but the limitations are that TN fluid can only support a limited multiplex rate, or limited number of rows. These displays are ideal for low information content, like simple character, segmented, or icon-based displays, commonly found in calculators, digital wristwatches, digital clocks, simple meters systems, or any other low information content display application.
Additionally, the TN fluid type is now widely used in full-color TFT displays for its high switching speed, high contrast, and wide viewing angle capabilities. The advent of the active matrix TFT backplane, which employs a transistor at each pixel location, allows a low multiplex rate at each individual pixel location to support the low mux rate requirement of the TN fluid.
Super Twisted Nematic, or STN, is ideal for dot matrix formatted displays, both character and graphic displays, with higher information content. STN is used over TN when the mux rate, or number of rows, is above 8-12. Super Twisted Nematic displays enable this higher mux by increasing the rotation of the molecules from 90 degrees (TN twist) to 260 degrees. This type of crystalline structure is used on almost all passive character and graphic displays of two lines or greater.
Film Compensated Super Twisted Nematic (FSTN) is the same STN fluid technology, but employs an additional compensation layer, retarder, which helps compensate for the STN polarizer’s inability to block or pass some of the circular polarized light that comes through the cell. FSTN is an STN cell with an improved polarizer, which improves the contrast by making a darker pixel with a lighter, more neutral-colored background. In simplest terms it gives a more paper-like, black-on-white appearance.