Liquid crystal display technology;` % X/S;G0 X4 T
A. What is a liquid crystal display (LCD) 6] U0 A1 + t % X
1. The material of the fourth state - LCD \ 4 5 C '[* g3 P & e
Ordinary matter has three states: solid, liquid and gas 9 s $r (K "D 'l1 g +]
Some organic matter in the fourth state between solid and liquid - liquid crystal state
Liquid crystal material appearance of this intermediate state is liquidity turbid liquid, with optical anisotropy crystal birefringence properties of all.
Liquid crystal material has both liquid liquidity and continuity, and retain the orderly arrangement of the crystal, physically present anisotropy.+ w + q, s!K $] 'S
2. The classification of liquid crystal. (e) z M: A + T
From the perspective of the physical condition of component and a liquid crystal phase, the LCD can be divided into two major categories of thermotropic liquid crystal and lyotropic liquid crystal.Put some heat dissolved organic matter, due to destruction of heating and the crystal lattice LCD called thermotropic liquid crystal, is such as to the liquid crystal phase due to temperature change.Put some organic matter in a certain solvent, due to destruction of solvent and the crystal lattice LCD is called the lyotropic liquid crystal, it is the result of the solution concentration change in the liquid crystal phase, the most common such as soap and water.Is used to display LCD materials are basically thermotropic liquid crystal, while in the biological system exist lots of lyotropic liquid crystal.Nearly ten thousand kinds of the liquid crystal material.Form the liquid crystal molecules, generally a slender rod or flat, and in each special liquid crystal phase formation.
When heated, thermotropic liquid crystal as a liquid crystal material in a certain temperature range present anisotropic liquid.Used to display is working at room temperature fluctuation of thermotropic liquid crystal.Most of the length of the liquid crystal molecules for dozens of ella, and width for a few.2 _;?7 L) s) y - G3 L
Liquid crystal molecules are orderly arrangement, according to the different arrangement, thermotropic liquid crystal can be divided into nematic phase, crystal phase and near cholesteric phase three kinds of liquid crystal phase.5} % | (w. s. B7 o
    1) nearly crystalline phase liquid (Smectic liquid crystals, S)
Smectic from Greek, it is a soap shape, because this type of LCD in the concentration of soap solution, all show characteristic of polarized microscopic image, thus named soap phase.Molecular layered, have the same direction, more close to the crystal, so the translated into nearly crystalline phases.Nearly crystalline phase liquid composed of bar or strip molecules, molecular arranged in layer, layer within the molecular long axis parallel to each other, their direction is perpendicular to the plane, or tilting arrangement and level.Because of molecular order, its rules on the whole close to the crystal, with 2 d order.Centroid position within the layer disorder, free translation, and thus have liquidity, but layer between molecules in the solution of viscous coefficient (big and small molecular forces between layers, will not be able to move between the lower level, each layer thickness of about 2 ~ 3 a.Because of its high order, nearly phase often appear inside examples of relatively low temperature.Nearly crystalline liquid viscosity, molecular rotation not easily, the response speed is slow, devices are generally not appropriate for display.3 b $v5 t5 J4 U6 U
2) phase Nematic liquid crystal (Nematic liquid crystals, N)
And also by the Greek Nematic, liquid crystal thin layer in the polarizing microscope, presents the filamentous structure, called silk.His son position, but the direction is roughly consistent, so the translation of nematic phase.Nematic phase liquid by length, diameter larger than a rod-shaped molecules, molecular mass center without long-range patterns are similar to ordinary the fluidity of liquid molecules cannot be arranged in layers, can slide up and down, left and right sides, front and back, just keep in the molecular long axis direction parallel or nearly parallel to each other.U $] c.?+ V + R7 h3 w
From a macro point of view, nematic liquid crystal because of its centre of gravity is chaotic, liquid crystal molecules, and can be within the scope of the 3 d mobile, can like liquid flow, all the molecular long axis pointing in the direction of a roughly, the nematic liquid crystal optical properties of uniaxial crystal (refractive index and dielectric constant, orderly arrangement along and perpendicular to the direction and different), and on the electrical has obvious dielectric anisotropy, such, can take advantage of the applied electric field with anisotropic nematic phase liquid crystal molecules, change the original molecular orderly state, and transform the optical performance of the LCD, LCD for external light modulation, achieve the goal of display.Nematic phase liquid has become the modern display device should be one of the most widely used liquid crystal materials.
  3) cholesteric phase liquid (CH)
By this found in the earliest from cholesteryl liquid crystal material, is cholesteryl after fat or halogen replace, liquid crystal phase, called cholesteric phase.This is a kind of molecules into flat, arranged in lamellar liquid crystal materials, intraformational molecules parallel to each other, the molecular long axis parallel to the plane, a slight change of the molecular long axis direction of different layer, layer along the normal direction are arranged in a spiral structure.When different molecules and shaft are arranged along the direction of the screw after the change of 360 °, returned to the initial orientation, the cyclical interlayer distance is called cholesteric phase liquid crystal screw torque (p).
Nematic phase liquid crystal and cholesteric phase liquid crystal can convert each other, join in nematic phase liquid crystal optical materials, can form cholesteric phase, to join in the cholesteric phase liquid despun nematic phase materials, light into a nematic phase to cholesteric phase.In cholesteric phase liquid crystal display technology is very useful, TN, the STN, phase change (Pc)
) displays are in nematic phase adding different proportions of cholesteric liquid crystal phase liquid crystal.
3. The lyotropic liquid crystal
Lyotropic liquid crystal is a kind of solute dissolved in a solvent to form a liquid crystal material.Solute LCD widely "m2 m# {* e) | + y: A % _ - h % V
Found in nature, organisms, is closely related to life, but there is no application in the display.6 & w5 k} : D9 a '@ 7 r;S/B
 2. Physical properties of liquid crystal
1. The order parameter
Nematic liquid crystal is a cylindrical symmetry, existing in the system of a single axis, usually call this axis spindle, nematic phase preferred tendency of the axis of the liquid crystal molecules parallel to the main shaft, but not completely parallel to the main shaft, measure its parallel degree with order parameter S said.& n5 l3] 4 I2 m7 r
S = (3 cos2 theta - 1) / 2, 1) (2 -
Order parameter related to the liquid crystal materials, temperature.Temperature rise, order parameter, K6 % q % ^ 1 B1 f7 t/V * R!V
S = K (Tc)/Tc (2 - (2)
Tc: nematic liquid crystal clear window (℃);W5 v. M1 y1 ` * I
T: the temperature of the nematic liquid crystal (℃)!A;H - _2 [6 M0 l0 S2 Q
K: proportionality constant
The LCD S = 0.3 ~ 0.8 / q) z# f!` "z" S5 V * z;S7 U) l
  2. The anisotropy of liquid crystal
1) dielectric anisotropy delta epsilon 5?- J0 t# C/S + w
Epsilon ∥ ∥ / C0 = C;Epsilon ┴ ┴ / C0 = C;% {% R (Z) j2 c
Delta epsilon = epsilon ∥ - epsilon ┴ = (C ∥ - C ┴)/C0 (2-3) '~ / I $l % x1 w. a. & o3 C
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C ∥ : when the applied electric field parallels with magnetic field measured liquid crystal capacitor!J (I6 K: ` : N
C ┴ : vertical when the applied electric field and the additional magnetic field measured liquid crystal capacitance
C0: no LCD when measured capacitance between the plate
2) resistivity rho
LCD resistivity said the purity of liquid crystal, the bigger the better, usually for 108 ~ 1012
3) optical refractive index of anisotropic delta n0 o * T6 k - I!A "e8 V & S8 m
Delta n = n ∥ -n ┴ (2-4)
N ∥ : parallel to the refractive index of the molecular long axis 7 b, {- i8 c (H
N ┴ : perpendicular to the refractive index of the molecular long axis: W "c (E3 p * (I?
Delta n general at around 0.1 ~ 0.3
4) the elastic constants K "g# O7 C9 T1 i. _7 j (Y & ` & z6?
General 10-11 ~ 10-12 K = n) {/ D "about the \" M - K
K is divided into K11, K22, K33
K33 > K11 > K22,
5) viscous coefficient of eta + 7 C1 | K;F2 z# @ 3 k "M & J * L3 B
Eta is commonly 2 ~ 10-10-3 pa. S
   3. Liquid crystal optical properties 0 q) R;I *?
1. The birefringence of liquid crystal and optical properties of * ^ - Q K# k!I _ '
LCD is one of the main characteristics of the present optical uniaxial crystal performance.After given a wave normal direction, can have two kinds of different refractive index, mutually perpendicular direction of vibration waves, namely o and e light, they are both linear polarized.Q * x "H1 U) I
In nematic phase liquid crystal and crystal phase liquid crystal
N0 = n = n ∥ ┴ can be
Delta n = ne - n0 = n ∥ -n ┴ > 0 Q6 S1 L (3, 1) * * d * S1 y7 b8 z $| B2
In the cholesteric phase liquid crystal
N0 = ((n n ┴ ∥ 2 + 2) / 2) = 1/2 can n ┴
Now there is still a n ∥ > n ┴ ne2 - n02 = 2 - n (n ┴ ∥ 2) / 2) < 0
Delta n = ne - n0 < 0 (3, 2) 6 @ 4 G3 W6 k3 {/ R!} 6 S, w
Because uniaxial optical anisotropy, liquid crystal optical properties especially useful with the following: - p8 g. I "o (o"}) u '~ 2 W
1) can make the direction of the incident light to the liquid crystal deflection along the long axis;, ~ 0 E8 Y0 g: l. f [- S2 s, j
2) can change the state of polarization of the incident light (line, circle, ellipse) or polarization direction;L4 0 k % h % b 'G7 b & L, d3 z
3) can make the incident polarized light corresponding to a left-handed or right-handed light reflection or transmission.
A variety of liquid crystal display is basically in accordance with the above three optical properties and the design and manufacture.5 h: _9 b# u - M3 S * Y2 t: I) R
   Four. Liquid crystal display device, O "e +] * ^ 0 q - s O6 X
1. The liquid crystal display device structure/E 'x 5 P;G "F3 r/K |)
2. The liquid crystal molecules along the surface arrangement;S w1 \ F3 w4 y * O * m/s)
No matter what kind of liquid crystal display device is based on the following principle: 6 ^ 1 B9 X1 d - m6 K# \
In the electric field, thermal field under the action of external force, such as liquid crystal molecules from certain initial state into other molecules arrangement, as the change of molecular arrangement, change the optical properties of liquid crystal device, so as to transform for the visual change.So, even, stable liquid crystal molecules are arranged is the basis work of liquid crystal display device.# A4 v9 "w y s (f! O
1) the kinds of molecular arrangement
2) the arrangement of the liquid crystal molecules method 9 H0 k * z7 V6 ~, x3 v - j o
(1) the oblique steam oxidation silicon w9 K: V (s8 y5 N + U v4
(2) vertical orientation method % z $w - w3 N G * * a 'a