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Views: 213 Author: Andy Publish Time: 2023-05-12 Origin: Site
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
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
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
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.
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
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.
