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TN ,STN, FSTN LCD display technology introduction

The article is writing about the TN LCD, STN LCD display theory, to mono lcd display mode, it is including TN and STN mode,  STN mode including yellow-green mode, blue mode, grey mode, FSTN mode, FSTN lcd display mode as one of STN mode in white-black display mode, it is special than STN mode, we also introduce the FSTN display technology in this article. Maclight is specialized in custom lcd such as custom TN, STN, VATN, FSTN, DFSTN LCD.

Twisted nematic display (TN)

The twisted nematic TN LCD display panel is based on the precisely controlled realignment of liquid crystal molecules between different ordered molecular configurations under the action of an applied electric field. This is achieved with little power consumption and at low operating voltages.

In the TN lcd display panel OFF state, i.e., when no electrical field is applied, a twisted configuration (aka helical structure or helix) of nematic liquid crystal molecules is formed between two glass plates, G in the figure, which are separated by several spacers and coated with transparent electrodes, E1 and E2. The electrodes themselves are coated with alignment layers (not shown) that precisely twist the liquid crystal by 90° when no external field is present (left diagram). If a light source with the proper polarization (about half) shines on the front of the TN LCD, the light will pass through the first polarizer, P2 and into the liquid crystal, where it is rotated by the helical structure. The light is then properly polarized to pass through the second polarizer, P1, set at 90° to the first. The light then passes through the back of the cell and the image, I, appears transparent.

In the TN LCD display panel ON state, i.e., when a field is applied between the two electrodes, the crystal re-aligns itself with the external field (right diagram). This "breaks" the careful twist in the crystal and fails to re-orient the polarized light passing through the crystal. In this case the light is blocked by the rear polarizer, P1, and the image, I, appears opaque. The amount of opacity can be controlled by varying the voltage. At voltages near the threshold, only some of the crystals will re-align, and the display will be partially transparent. As the voltage is increased, more of the crystals will re-align until it becomes completely "switched". A voltage of about 1 V is required to make the crystal align itself with the field, and no current passes through the crystal itself. Thus the electrical power required for that action is very low.

To display information with a TN liquid crystal, the transparent electrodes are structured by photo-lithography to form a matrix or other pattern of electrodes. Only one of the electrodes has to be patterned in this way, the other can remain continuous (common electrode). For low information content numerical and alpha-numerical TN-LCDs, like digital watches or calculators, segmented electrodes are sufficient. If more complex data or graphics information have to be displayed, a matrix arrangement of electrodes is used. Obviously, the voltage controlled addressing ofmatrix displays, such as in LCD-screens for computer monitors or flat television screens, is more complex than with segmented electrodes. These matrix LCDs necessitate integration of additional non-linear electronic elements into each picture element of the display (e.g., thin-film diodes, TFDs, or thin-film transistors, TFTs) in order to allow the addressing of individual picture elements without crosstalk (unintended activation of non-addressed pixels).

TN lcd display structure


Super-twisted nematic display (STN)

The super-twisted nematic display is a type of monochrome passive-matrix liquid crystal display (LCD).[1]This new type of LCD was invented at the Brown Boveri Research Center, Baden, Switzerland, in 1983.[2] 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 LCD 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 in 1984, which was considered a breakthrough for the industry.

STN LCD display 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. 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.

custom COB STN LCD blue mode

Black-white STN mode (FSTN lcd mode)

FSTN lcd is the profession name for black-white STN mode, it is white background and black display characters. it is the nearest color to paper in monochrome lcd, even its real background is a little near to gray. FSTN LCD mode is one of STN mode, instead of the background color to yellow-green color or blue color, FSTN LCD add a optics compensator on the front of FSTN LCD, the optics compensator compensate the linear polarize light and color from STN LCD, the STN LCD color turn to white background after light through the optics compensator film. if the FSTN LCD in negative mode, its background would be in black, and display white characters.  FSTN lcd is widely used in many display application because of its background.


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