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COLLEGE NAME

A Technical seminar report

on

Ferroelectric liquid crystal display (FLCD)

In partial fulfillment for the award of the degree Of

BACHELOR OF TECHNOLOGY

IN

ELECTRONICS & TELECOMMUNICATION ENGINEERING

SUBMITTED TO: SUBMITTED BY: Assistant Professor

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CERTIFICATE

This is to certify that the technical seminar Report entitled “Ferroelectric

liquid crystal display” is a bonafied work presented by ROHIT SINGH in a

partial fulfillment for the award of degree of Bachelor of technology in

ELECTRONICS & TELECOMMUNICATION ENGINEERING in COLLEGE

OF ENGINEERING ROORKEE during the year 2011-2015.

Assistant Professor

College Of Engineering Roorkee

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Content

1. Introduction on Flcd…………………………………4

2. Lcd……………………………………………………5

2.1 Advantages and disadvantages on Lcd………8

3. Introduction of Amlcd………………………………10

4. Operation On Flcd………………………………….11

5. Molecular orientation control……………………..12

5.1 Key Technologies for the Vmin Mode FLCDs..14

5.2 Device Structure & Molecular Orientation…….15

5.3 Gray Scale and Addressing…………………….17

6. Properties and uses………………………………...19

7. Challenges…………………………………………..20

8. Conclusion…………………………………………..21

9. Refrences……………………………………………22

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Ferroelectric Liquid Crystal Display

Introduction

Ferro Liquid Display, or Ferro-electric Liquid Display (FLD) or Ferro Fluid Display

(FFD), is a display technology based on the ferroelectric properties of certain liquids.

Not all such fluids are crystal but they are generically referred to as Ferro Liquid

Crystal Displays (FLCD).

The dot pitch of such displays can be as low as 10 µm giving a very dense

high resolution display on a small area. These might find applications in 3D displays

and head mounted displays (HMD) where typical LCDs have failed to provide

anything better than a 640x480 (RGB pixel) resolution on a sq.cm display area.

Displays based on these are still experimental or of less commercial value only due

to the costs. Gradual adoption in consumer electronics is expected to bring the costs

down.

A major drawback is that the angle of twist is not easily controlled by intensity of

magnetic field. To produce color scales, time multiplexing might be used exploiting

the quick switching time. The materials found so far are sensitive to vibration and

shock.

Since Clark and Lagerwall invented the basic

principle of ferroelectric liquid crystal displays

(FLCDs), much effort has been devoted to

the development of FLCDs, aiming

at practical applications.

While the conventionally existing LCDs such as

STN LCDs and TFT-LCDs utilize a nematic liquid

crystal phase, it is remarked that FLCDs utilize a

chiral smectic C liquid crystal phase with

Fig. Principle of FLCD.

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spontaneous polarization (Ps). In the chiral smectic C

phase, liquid crystal molecules have a layer

structure in which the mean direction of molecular long

axis is tilted against layers. In thin FLC cells, a bistability

appears with two bistable states as shown in Fig.1(a)(b) . Ferroelectric

liquid crystals have a spontaneous polarization (Ps) whose direction is

perpendicular to the layer. When the electric field is applied, molecules re-align in

a way that the direction of the spontaneous polarizations is the same as that of the

electric field. Combining a pair of polarizers (polarizer and analyzer), FLCDs can

realize dark and bright states.

Since nematic liquid crystal is paraelectric, the order of response time is usually

sec. On the contrary, FLC shows sec in its order of response time because of

the direct interaction between electric field and Ps. In addition, FLCDs have several

advantages, such as wide viewing angle due to the in-plane switching (IPS) and

memory effect due to the bistability. The combination of fast response time and

memory effect allows large-size direct-view simple-multiplexing LCDs with high

resolution.

LCD

LCD (liquid crystal display) (from Whatis) is the technology used for displays in

notebook and other smaller computers. Like light-emitting diode (LED) and gas-

plasma technologies, LCDs allow displays to be much thinner than cathode ray tube

(CRT) technology. LCDs consume much less power than LED and gas-display

displays because they work on the principle of blocking light rather than emitting it.

An LCD is made with either a passive matrix or an active matrix display display grid.

The active matrix LCD is also known as a thin film transistor (TFT) display. The

passive matrix LCD has a grid of conductors with pixels located at each intersection

in the grid. A current is sent across two conductors on the grid to control the light for

any pixel. An active matrix has a transistor located at each pixel intersection,

requiring less current to control the luminance of a pixel. For this reason, the current

in an active matrix display can be switched on and off more frequently, improving the

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screen refresh time (your mouse will appear to move more smoothly across the

screen, for example). Active matrix is the superior technology.

Color LCD

An LCD that can show colors must have three subpixels with red, green and blue

color filters to create each color pixel. Through the careful control and variation of the

voltage applied, the intensity of each subpixel can range over 256 shades.

Combining the subpixels produces a possible palette of 16.8 million colors (256

shades of red x 256 shades of green x 256 shades of blue), as shown below. These

color displays take an enormous number of transistors. For example, a typical laptop

computer supports resolutions up to 1,024x768. If we multiply 1,024 columns by 768

rows by 3 subpixels, we get 2,359,296 transistors etched onto the glass! If there is a

problem with any of these transistors, it creates a "bad pixel" on the display. Most

active matrix displays have a few bad pixels scattered across the screen.

LCD Features and Attributes

To evaluate the specifications of LCD monitors, here are a few more things you

need to know.

Native Resolution

Unlike CRT monitors, LCD monitors display information well at only the resolution

they are designed for, which is known as the native resolution. Digital displays

address each individual pixel using a fixed matrix of horizontal and vertical dots. If

you change the resolution settings, the LCD scales the image and the quality

suffers. Native resolutions are typically:

17 inch = 1024x768

19 inch = 1280x1024

20 inch = 1600x1200

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Viewing Angle

When you look at an LCD monitor from an angle, the image can look dimmer or

even disappear. Colors can also be misrepresented. To compensate for this

problem, LCD monitor makers have designed wider viewing angles. (Do not

confuse this with a widescreen display, which means the display is physically

wider.) Manufacturers give a measure of viewing angle in degrees (a greater

number of degrees is better). In general, look for between 120 and 170 degrees.

Because manufacturers measure viewing angles differently, the best way to

evaluate it is to test the display yourself. Check the angle from the top and bottom

as well as the sides, bearing in mind how you will typically use the display.

Brightness or Luminance

This is a measurement of the amount of light the LCD monitor produces. It is given

in nits or one candelas per square meter (cd/m2). One nit is equal to on cd/m2.

Typical brightness ratings range from 250 to 350 cd/m2 for monitors that perform

general-purpose tasks. For displaying movies, a brighter luminance rating such as

500 cd/m2 is desirable.

Contrast Ratio

The contrast ratio rates the degree of difference of an LCD monitor's ability to

produce bright whites and the dark blacks. The figure is usually expressed as a

ratio, for example, 500:1. Typically, contrast ratios range from 450:1 to 600:1, and

they can be rated as high as 1000:1. Ratios more than 600:1, however, provide

little improvement over lower ratios.

Response Rate

The response rate indicates how fast the monitor's pixels can change colors.

Faster is better because it reduces the ghosting effect when an image moves,

leaving a faint trial in such applications as videos or games.

Adjustability

Unlike CRT monitors, LCD monitors have much more flexibility for positioning the

screen the way you want it. LCD monitors can swivel, tilt up and down, and even

rotate from landscape (with the horizontal plane longer than the vertical plane) to

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portrait mode (with the vertical plane longer than the horizontal plane). In addition,

because they are lightweight and thin, most LCD monitors have built-in brackets for

wall or arm mounting. Besides the basic features, some LCD monitors have other

conveniences such as integrated speakers, built-in Universal Serial Bus (USB)

ports and anti-theft locks.

Advantages of Lcd

Thin Profile

LCDs feature very thin profiles, making them the perfect choice for small

work spaces.

Standard Screen Sizes

Unlike CRTs, there is no variance between the monitor size and the screen

size. For example, a 17-inch monitor features a 17-inch viewable image.

Bright Screens

LCDs, thanks to the florescent backlight, produce bright, rich images

Low Energy Consumption

In general, LCD monitors consume about half of the energy of standard

CRTs.

Flicker-Free Refresh Rates

Refresh rate is less of an issue with LCD monitors. LCDs are designed to

have flicker-free refresh rates at 60Hz.

High Contrast Ratios

LCD monitors tend to feature excellent contrast ratios, which insure bright,

clear images. Make sure the monitor you purchase has a contrast ratio of at

least 400:1 or more.

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Disadvantages of Lcd

Single Resolution

LCDs are generally designed to work best in a single resolution. They tend

not to have the flexibility that CRTs have to display multiple resolutions well.

Narrow Viewing Angles

LCDs tend to have a very narrow viewing angle. As you vary from looking at

a LCD straight-on the image gradually degrades. Look for at least a 160°

viewing angle.

Slow Pixel Response Time

LCDs tend to have a much slower pixel response time, which can mean

image artifacts remaining onscreen after movement. For example, when you

move your mouse quickly across the screen you might see the cursor create

shadow images of itself briefly. These disappear instantaneously. In order to

avoid this try to find a monitor that has a response time of 25 milliseconds or

faster.

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Active Matrix Crystal Display

An active-matrix liquid-crystal display (AMLCD) is a type of flat panel display, the only

viable technology for high-resolution TVs, computer monitors, notebook

computers, tablet computers and smartphones with an LCD screen, due to low

weight, very good image quality, wide color gamut and response time.

The concept of active-matrix LCDs was invented by Bernard J. Lechner at the RCA

Laboratories in 1968.The first functional AMLCD display with thin-film transistors was

made byT Peter Brody and his team at Westinghouse Electric Corporation in

1973.]However, it took years of additional research by others to launch successful

products.

Introduction on Active Matrix Crystal Display

The most common type of LCD display contains, besides the polarizing sheets and

cells of liquid crystal, a matrix of thin-film transistors to make a thin-film-transistor

liquid-crystal display.These devices store the electrical state of each pixel on the

display while all the other pixels are being updated. This method provides a much

brighter, sharper display than a passive matrix of the same size. An important

specification for these displays is their viewing-angle.

Thin-film transistors are usually used for constructing an active matrix so that the two

terms are often interchanged, even though a thin-film transistor is just one

component in an active matrix and some active-matrix designs have used other

components such as diodes. Whereas a passive matrix display uses a simple

conductive grid to apply a voltage to the liquid crystals in the target area, an active-

matrix display uses a grid of transistors and capacitors with the ability to hold a

charge for a limited period of time. Because of the switching action of transistors, only

the desired pixel receives a charge, and the pixel acts as a capacitor to hold the

charge until the next refresh cycle, improving image quality over a passive matrix.

This is a special version of a sample-and-hold circuit.

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FLCD Operating Principle

An FLCD acts as a classical half-wave plate, one whose optic axis can be reoriented

by an applied field.

If the optic axis is parallel or perpendicular to incoming polarized light, the light

passes through the FLCD unchanged and is blocked by the exit polarizer(oriented at

90o to the entrance polarizer)

If the optic axis makes an angle of 45o to the incoming polarized light, the direction of

polarization changes by 90o and is able to pass through the exit polarizer

Orientation of FLF molecules is changed by applying a voltage pulse of suitable

polarity.

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• In thin FLC cells, a bistability appears with two bistable states as shown in Fig.

• Ferroelectric liquid crystals have a spontaneous polarization (Ps) whose

direction is perpendicular to the layer.

• When the electric field is applied, molecules re-align in a way that the direction

of the spontaneous polarizations is the same as that of the electric field.

• Combining a pair of polarizers (polarizer and analyzer), FLCDs can realize dark

and bright states.

Molecular orientation control

The molecular orientation control is one of the most important key

technologies for the development of practical FLCDs. The molecular orientations

of FLCDs are classified as two layer structures: a bookshelf layer and a chevron

layer. The FLC cells with parallel rubbing, in which the rubbing directions of both

substrates are the same, have been known to show four orientational states

with a chevron layer structure: C1-uniform (C1U), C1-twisted (C1T), C2- uniform

(C2U) and C2-twisted (C2T). Among them, the C1U and C2U orientations are useful

for practical applications because of their extinction positions between cross nicols.

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• So, an unconstrained system, the azimuthal

direction in which the molecules tilt away from

the layer normal will differ slightly from one

layer to the next.

• Typically, the FLCDs are built with cell gaps

less than 2 µm for stable molecular alignment.

• Alignment layer causes perpendicular stacked

alignment.

• The cell's polarisation is determined by the

magnetic field applied.

That in turn results in opaque or transparent layer

when used in combination with polarised layers as in

LCD

The alignment film with a high pre-tilt angle (over 15 degrees) induced the selective

formation of the C1U orientation and also that the C1U orientation gave a high

contrast ratio under simple-multiplexing driving waveforms for FLCDs. Using the

C1U orientation, Hanyu et al. have developed a 21-inch color FLCD (1024 x 1280

dots, contrast ratio of 40:1 and 64 colors).

Fig. Principle of FLCD.

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Recently, Mizutani et al. developed a 15" full-color FLCD (768 x 1024 dots,

36 sec/line, CR=100:1) with a bookshelf layer structure, realizing full-color images

by a combination of 4-bit spatial dither and dither methods.Futhermore, Koden et al.

have reported that the C2U orientation can show a high contrast ratio, fast line

address time and wide memory angle if it is combined with the -Vmin.

The -Vmin mode utilizes the unique response (t) - voltage (V) characteristics of the

minimum value, which is observed in FLC materials with large positive dielectric

biaxiality (negative dielectric anisotropy). The -Vmin mode utilizing the C2U

orientation is a promising technology for digital gray scale method with temporal

dither because it can realize faster line address time than the C1U orientation and

the bookshelf orientation can.

Compared with the existing LCDs, the FLCD have received an unfavorable

reputation of poor performance in moving picture with gray scale and also in

shock stability. In this study, key technologies for the -Vmin mode were

developed in order to overcome these problems. This paper describes FLC

materials that show fast response time for the -Vmin mode, the selective

formation of the C2U orientation, the device structure with high shock stability and

the digital gray scale driving method, introducing a6-inch color prototype FLCD

which was fabricated by using these keytechnologies.

1. Key Technologies for the -Vmin Mode FLCDs

1•1 Ferroelectric Liquid Crystal Materials

In the -Vmin characteristics of FLC materials, the minimum voltage ismentioned as

Vmin and the minimum response time as min. Low Vmin and fast min are

required because the Vmin value determines the drive voltage and the min value

determines the line address time. Since the Vmin is closely related to a balance of

the dielectric biaxiality and spontaneous polarization (Ps), FLC materials for the

-Vmin mode need large positive dielectric biaxiality and small or moderate

spontaneous polarization, as well as low viscosity in order to obtain fast tmin.

An INAC phase sequence and long

helical pitches in nematic and smectic

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C phases are required in order to

yield a high quality of alignment on

cooling from the isotropic phase.In

addition, FLC materials require wide

temperature range of smectic C phase

because it is related to the operating

and storage temperature ranges of

FLCDs.

Fig. 2 The characteristic of the developed FLC material FDS-2.

A typical FLC material, FDS-2 was developed for the -Vmin mode. Its

characteristics are shown in Fig. 2. This material offers fast min value (12 sec)

and reasonable Vmin value (33V) at 25˚C.

1•2 Device Structure & Molecular Orientation

Shown in Fig. 3 is the structure of the developed FLCD. On a color filter substrate

and a glass substrate with ITO electrodes, there are an insulating film and an

aligning films coated. The material of the aligning film was polyimide. The rubbing

direction of both substrates is in the same direction (parallel rubbing). An aligning

film with a medium pretilt angle (about 3˚) was utilized in order to gain 100% of

the C2U state without any zigzag defects or any C1 states. The molecular

orientation model of the C2U state is illustrated in Fig. 4.

Each pixel is divided into two areas with 1:2 ratio so as to realize spatial dither

gray scale, as described in the next section. Spacer walls were constructed within

the panel in order to show high shock stability. The cell spacing was 1.3 m.

Optimal adhesion between both substrates was obtained, yielding higher shock

stability more than 20kg/cm2.

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Fig. 3 Device structure of

the developed FLCD.

Fig. 4 The C2U orientation.

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1•3 Gray Scale and Addressing

Combining 2-bit spatial dither and 3-bit temporal dither, 64 gray levels for each

color were achieved to realize 262,000 colors. The 2-bit spatial dither ratio was

one to two (1:2) and 3-bit temporal dither ratio was one to four to sixteen (1:4:16).

The driving waveforms are shown in Fig.5. The duty ratio was 1/480 and the line

address time was 23 sec/line. The typical values of voltages were Vs=40V and

Vd=7V.

Fig. 5 Drive waveform which is applied in the 6"-prototype FLCD.

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2. 6-Inch Color FLCD (Prototype)

A color 6"-prototype FLCD with 240x320

dots was fabricated, utilizing key technologies

described in the above. The main

specifications are as follows:

Number of Pixels 240 x 320 dots

Number of Colors 262,000 colors

Contrast Ratio 60:1

Shock Stability 20kg/cm2

Memory Angle 30 degrees

More detailed specifications are summarized in

Table 1 Conclusion

The development described in this paper has

solved two fundamental problems of FLCD.

The one is gray scale and the other is shock

stability. Further development is required in

order to realize large size FLCDs with high

information content and also to solve the

pseudo edge problem,which is induced by

digital gray technique as well as PDP.

Table 1 The specifications of the developed

6"color FL

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Properties and uses

Very thin layer (less than 2 µm thick) can help produce a 90° polarisation

twist.

1) High density displays with small display areas can be produced.

2) DisplayTECH claims that a stamp sized FLCD can drive resolutions

needed for 50 inch screens.

Switching time is less than 100 µs

1) High frame rate video displays are possible.

Magnetic polarisation effect is bistable.

1) Can be used for low frame rate displays that can run on very low

power

2) This property can help build display with non-volatile memory with the

advantage that the memory can be changed easily.

Viewing angle is greater than 120°

1) This makes it suitable for commercial TV applications.

Some commercial products do seem to utilize FLCD.

High switching allows building optical switches and shutters in printer heads.

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Challenges

• The problems facing ferroelectric researchers are numerous.

• Alignment defect control (sensitive to shock and vibration)

• Cell spacing control

• Temperature range

• Response time, and Gray Scale

New fluorinated liquid crystal compounds are being developed to

help decrease the response time and improve the contrast ratio

(contrast is limited by defects).

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Conclusion

• Prospects for the future are mixed for this technology.

• While much research continues, it is unclear what market the

ferroelectric LCD will serve.

• Certainly, if the problems can be solved, then the high contrast

and wide viewing angle achieved with ferroelectric LCDs will

put them in competition with active matrix LCDs.

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References

N. A. Clark and S. T. Lagerwall, Appl. Phys. Lett., 36, 899 (1980).

Mitsuhiro Koden, Optronics, No.2, 52 (1994).

M. Koden, Ferroelectrics, 179, 121 (1996).

M. Koden, H. Katsuse, A. Tagawa, K. Tamai, N. Itoh, S. Miyoshi and

T. Wada, Jpn. J. Appl.

A. Tsuboyama, Y. Hanyu, S. Yoshihara and J. Kanbe, Proc. Japan

Display '92, 53 (1992).

M. Koden, T. Numao, N. Itoh, M. Shiomi, S. Miyoshi and T. Wada,

roc. Japan Display '92,

Y. Hanyu, K. Namamura, Y. Hotta, S. Yoshihara and J. Kanbe, SID

93 Digest, 364 (1993).

H. Mizutani, A. Tsuboyama, Y. Hanyu, S. Okada, M. Terada and K.

Katagiri,

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