What is Twisted Nematic display technology?

What is Twisted Nematic display technology?

In order to fully understand TN LCD (Twist Nematic Liquid Crystal Display Technology), we will understand what is

nematic liquid crystal first.

More information about LCD technology can be found here:

LCD History

LCD Introduction

How does LCD work?

STN LCD

Positive and negative modes

LCD temperature range

LCD Pixel Terms and Resolution Guide

Difference between LCD, TFTIPSLED, and OLED

LCD and TP Glossary

What is an LCD display on an Arduino?

Passive LCD vs. Active LCD and PMOLED vs. AMOLED

What is Nematic Liquid Crystal?

All of us know that water (whose chemical formula is HO) has 3 states: solid (ice), liquid (water), and gas vapor. Liiquid

state is isotropic, which means that its properties are uniform in all directions—the result of Ho molecules being in

constant random motion. The solid state is crystalline,all the H20 molecules have their fixed positions, and it is anisotropic.

Optical and other properties, such as thermal and electrical conductivity, vary with direction.

The nematic liguid crystal state is a unique state not included in the above three states. It is a state between the

crystallinesolidand isotropicliquid)states. Even in the state of liquid crystals, there are several types of liquid.

Crystalstatesasbelow

NematicPhase

The nematic liquid crystal phase is characterized by molecules that maintain the general order of tending to point in the

same direction. It has one-dimensional order. See Fig.1

Smectic Phase

in the smectic phase. Molecules show two-dimensional order that is not present in the nematic. The molecules maintain the

general orientation of nematics, but also tend to align themselves in layers or planes. It is the state between nematic

(one-dimensional order) and solid states (three-dimensional order). See Fig.1.

Cholesteric Phase

The cholesteric (or chiral) nematic liquid crystal phase is typically where the molecules are directionally oriented and stacked in

ahelicalpattern witheachlaverrotatedataslightangletotheonesaboveandbelowit SeeFig1

InLCDdisplaytechnology onlynematicliquidcrystalhaspracticallyuseandcholestericliquidcrystalisdopedwith

small amount to help nematic liquid crystal molecules twist. That is the origin of the term "Twisted Nematic," or TN.

forNematicDisplayinshort

What isTN(TwistedNematic display

How the TN display works

A most simple TN LCD panel contains two polarizers,two glass substrates, and transparent electrodes (Indium).

TinOxide andathinliguidcrystalmateriallaversandwichedbetweentheelectrodes SeeFia2

Whenthevoltageisoff thenaturallightfromthelightsourcegoesthroughthetoppolarizertobecomepolarized

linear light. When it meets with nematic liquid crystal molecules, it twists with the liquid crystal twist layer. After

twisting 90°, it passes through the bottom glass and arrives at the bottom polarizer. As the polarized light is in parallel

position with the bottom polarizer, it goes through the polarizer, and we can see the light white or grey pixel.

When the voltage is on, the liquid crystal molecular will be perpendicular to the glass surface and lose its twist.

under an electric field. When the polarized light meets the nematic liquid crystal laver, it keeps the original transmissive

without twisting. It will be blocked by the bottom polarizer as the linear light and bottom polarizer are ttom polarizer are perpendicular.

position. We do see the light (a black pixel).

From the above, we understand

Why do we name TN "the twist display" as it twists 90°?

We get a positive display above, which is black characters on a white or gray background.

Glass panels have two modes. Positive mode (black characters on a white or gray background) or negative mode (white or gray background)

characters on a black background). The reason why the TN LCD can’t get paper white backround is the fact that polarization cuts

outmostofthelight only 20% to 40% lightcangothroughaTNLCD.