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SEMINAR ON LCD _ FLAT PANEL DISPLAYS

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SEMINAR ON LCD _ FLAT PANEL DISPLAYS Powered By Docstoc
					      SEMINAR ON LCD & FLAT PANEL DISPLAYS


                                      BY
                          CLOVER DISPLAY LTD.
                        (HONG KONG S.A.R, CHINA)
                    AN LCD MANUFACTURER SINCE 1983
                       URL http://www.cloverdisplay.com
                                      &
                                   DATE :
                                 Sept 29, 2005

                                SPEAKER
                         Mr. JOHNNY C. L. CHOU




<Topics>
1. FLAT PANEL DISPLAY
2. INTRODUCTION TO LCD TECHNOLOGY.
3. HOW LCDs ARE MADE.
4. COLOR LCD
5. TODAY’S LCD
6. CUSTOM DESIGN LCD & LCM (MODULES).
7. TOUCH PANEL, Bi-STABLE LCD & ORGANIC LED.
8. QUESTION & ANSWER.

Edition #7 (2005)
1.0. FLAT PANEL DISPLAYS

Display Types                    Emits   Voltage   Current   Patterning
( commonly used Display )        Light                       Flexibility

CRT ( Cathode Ray Tube )         Yes     High DC   Low       ( scanning )

VFD ( Vacuum Florescent          Yes     High DC   Low       Medium
Displays )
LED ( Light Emitting Diode )     Yes     Low DC    Medium    Low

Plasma Displays                  Yes     High DC   Low       Low

EL ( Electro Luminescent         Yes     High DC   Low       High
Displays )
LCD ( Liquid Crystal Display )   NO      Low AC    Low       High

OLED (Organic LED)               Yes     Low DC    Low-      High
                                                   medium


                                                                            P.1.
2.0. LIQUID CRYSTAL
   2.1. Three major characteristics of Liquid Crystal
     2.1.1. The Thermal Nature
                Solid State    Liquid Crystaline          Liquid
                (Crystal)      State                      State
     Low Temp                                                             High Temp
                        Melting Point           Clearing Point

      2.1.2. The Optical Nature of a LC molecule

                                        XXX      NO light passing through
                Light
                                                 Light passing through


      2.1.3. The Electrical Nature of the LC molecules



                                          Electrodes

                 No potential field                              AC potential
                                                                                      P.2.
2.2. COMMON STRUCTURAL PHASES in the Liquid Crystal State

    Smectic Phase            Nematic Phase        Cholesteric phase




2.3. Two other components to make a Liquid Crystal Display Panel
  2.3.1. Transparent Electrodes ---- Glass with conductive ITO layer which is
                   etched to form a pattern.
  2.3.2. The Polarizer Film




       Light wave      Polarizer &                       Outgoing light
       & its axis      its light axis                    & its axis




                                                                                P.3.
2.4. A TYPICAL TN TYPE LCD CELL

                                          Polarizer
                                          (Axis 0 degree)

          Glass with electrodes



               NO power                         With AC Volts
               supply                           connected



       Glass with electrodes
                                          Polarizer
Cell Gap =                                (Axis 90 degrees)
The separation
between two glasses
                                           Positive Mode =
                                           Black digit on the grey background
                                           Negative Mode =
                                  Light    Clear digits on the dark background

                                                                        P.4.
2.5. THREE COMMON TYPES OF LCD
 2.5.1. TRANSMISSIVE TYPE
                                LCD

      Eyes                                    Light
                                              (Back Light)

                                      POLARIZER ON BOTH SIDES
 2.5.2. REFLECTIVE TYPE
                                      LCD


               Incident Light

   POLARIZER ON THE FRONT SIDE              REFLECTOR ON THE BACK SIDE


 2.5.3. TRANSFLECTIVE TYPE
                                      LCD

                 Day Light
                                                  Night Light
                                                  (Back Light)

   POLARIZER ON THE FRONT SIDE              TRANSFLECTOR ON THE BACK SIDE
                                                                         P.5.
2.6. CHARACTERISTIC CURVES
                                           Vs (Saturation Voltage)
  % LIGHT
  ABSORPTION                                                             Vth of LC
                                              90% changes
  (or TRANSMISSION)           At higher
                              Temp.
                                                                        5v
                                                                        4v

                                          10% change
                                                        VOLTS
  0 volt                                                                 -40 deg C   +80 deg C
                                     Vth (Threshold Voltage)


                                                                        LC Fluid
    % Light                                                             Viscosity
    Absorption                                                          mm2/sec

                                                                     10,000
                        At a lower
                        Temp.
                                                                       100
                                                         Time
           Ton 5ms to 100ms      Toff 20ms to 300ms                      -40 deg C   +80 deg C
       Depending on how the LCD fluid is formulated.
       The smaller the cell gap, the faster response.
                                                                                          P.6.
2.7. TN & STN (Super Twisted Nematic)

                                 The LC molecule
                                mid-plane tilt angle
                                                                  Vth          Vs


 % Light Absorption               % Light Absorption          % Light Absorption


                90 deg                             180 deg                  240 deg
                Twisted                               Twisted                   Twisted



     0                           V      0                     V         0                 Volts


     Narrow View Angle                      Wide View Angle




              TN LCD                         STN LCD
         Grey Background                     Yellow Green background color
         in the positive mode                In the positive mode                                 P.7.
2.8. HTN (Highly Twisted Nematic) & FSTN (Film STN)
                                                STN
                                                180 deg or higher deg
TN                                              Twisted
90 deg Twisted
                                                Wide View Angle BUT with
Narrow View Angle                               Darker Color Background &
                                                Blue or dark blue patterns.

                               HTN                                  FSTN
 1st Minimum TN                110 deg                              240 deg or higher deg
                               Twisted                              Twisted
 Little wider View
 Angle than TN                 Wider View Angle than TN             View angle same as 240 deg STN
 (see later pages)             but narrower than STN                BUT in Grey Background Color
                                                                    & Black patterns.


                      DSTN (Double STN Cells)                                           Polarizer

    Old way          1st Cell with patterns                             LCD Cell
    when NO          Same as usual STN
    Retardation
                     2nd Cell without pattern
    film                                                            Retardation Films on Polarizers
                     But in reverse twisting
                                                                    to correct the color phase
                                                                                                   P.8.
2.9. COMPARISON AMONG TN, HTN, STN & FSTN
  2.9.1. Positive Mode (Pattern on a Clear Background)
Either        TN            HTN            STN               STN               FSTN

Deg Twisted   90            110            180               240               240
Background Grey             Grey           Yellow Green      Grey or           Grey
Color                                      or Grey           Yellow Green

Pattern       Black         Black          Dark Blue         Blue or           Black
Color                                      or Blue           Dark Blue

Temp Range -40C to +85C     -20C to +40C   -20C to +70C      -20C to +70C      -20C to +70C
Multiplex     =< 1/8 duty   =<1/16 duty    =<1/32 duty       =<1/240 duty      =<1/240 duty
Ratio
View Angle    60 deg        80 deg         120 deg           120 deg           110 deg
View          At 6 or 12    At 6 or        May specify       May specify       All
Direction     O’clock       12 O’clock     6 or 12 O’clock   6 or 12 O’clock
              ONLY          ONLY
Voltage       2.5v min      3v min         3v min            5v typical,       5v typical,
              5v typical    5v typical     5v typical        (higher duty,     (higher duty,
                                                             higher volts)     higher volts)

                                                                                               P.9.
       2.9.2. Negative Mode (Clear Pattern on a Color Background)
                      TN             HTN          STN             STN                FSTN

 Degree Twisted       90 deg         110 deg      180 deg         240 deg            240 deg
 Background           Black          Black        (Seldom used)   Dark Blue          Black
 Color
 Pattern Color        Clear          Clear        (Seldom used)   Clear              Clear
      Other natures same as the Positive Mode.

2.10. Gooch-Tarry Curve --- The 1st Minimum TN LCD
  % Transmission
                                                        n : Birefringence (reflective indices of
  12%                                                   Light transmitted in parallel & perpendicular
                                                        To the director of LC molecules.
   8%                                                             d : the cell gap


   4%


   0%                                                                                     d n
                  0.48 (1st Min* )    1.05 (2nd Min)          1.64 (3rd Min)              (um)      P.10.
*The 1st Min process is patented by E. Merck.
2.11. THE STATIC & MULTIPLEX DESIGN OF ELECTRODES




  4 pairs of electrodes           5 electrodes                         4 electrodes in matrix
  8 connectors needed.            5 connectors needed.                 4 connectors needed.

  No time sharing for             1/4 time sharing for                 1/2 time sharing for
   the input signals –             the input signals to                 the input signals to
  The STATIC Design                each of the top electrode.           both the top and
                                  No time sharing for                   bottom electrodes----
                                   the bottom glass.                   The MULTIPLEX Design.
                                  We call the top electrodes
                                   the SEGMENT while                   We call it 1/2 duty if the
                                   the bottom electrodes                1/2 time sharing is used
                                   the COMMON.                          on the Common.
  PROBLEM:
  The higher the duty ratio, the shorter time the power signal goes into each electrode pair.
  Finally the power rms value may NOT be enough to fully drive the LC twisting properly.
                                                                                                    P.11.
2.12. THE PASSIVE AND ACTIVE LCD                                              Y1         Y2

       Signal
                                                                  X1


                              Time
                                                             X2
        Signal
                                                                   An ACTIVE Component ;
                                                                   MIM (metal insulator metal) Diode
                                                                   Or
                              Time                                 TFT (thin film transistor)
                                                                   The LCD Pixel

    The TFT method is commonly used today on the large DOT MATRIX LCD,
    we call it the ACTIVE MATRIX LCD, or AMLCD

    The LCD built together with the Active Component is not only the TFT LCD. The LCOS
    is also an LCD built on a silicon wafer with active components to control the LCD.

    In general, the duty ratio over 1/256 may not give a good contrast in the Passive design.
    But there are still some special design to work in the Passive way, such as;
    Dual Scan STN (DSTN), High Performance Addressing (HPA), …. etc

                                                                                                P.12.
 2.13. THE HISTORY OF LC & LCD
Application   Approx Year                   Major Development

               1888         Liquid Crystalline initially described by an Austrian Scientist,
                            Mr. Friedrich Reinitzer.
               1904         E. Merck sold the first Liquid Crystal substrates to the research market.
               1960         Westinghouse used the cholesteric LC as a temperature indicator.
Thermometer    1965         RCA demonstrated a dynamic scattering LCD to show numeric symbols.
                            Kent State Univ. in Ohio USA presented an LCD operated at room temp.
               1970         Rockwell (USA) and Sharp (Japan) made LCD Calculators.
Calculator                  Hull Univ. in England synthesised new biphenyls with excellent physical
                            properties for display use.

                            Higher Contrast Twisted Nematic Mode in use.
Time pieces                 OCLI (USA) coated ITO on glass as electrodes.
                            BDH (UK) sold LC to LCD manufacturers.
               1975
                            Hamlin Inc (USA) in TN LCD mass production.
Instruments                 E. Merck introduced Biphenylcyclohexanes LC for higher multiplex.
                            Motorola built LCD on 4 ½”x 4 ½” glass substrates
                            Microma (USA) further improved the mass production technique and
                            Fairchild Semiconductor Inc. moved LCD production to Hong Kong.
Data bank & PDA             Timex (USA) bought RCA LCD facility and merged with Fairchild.

                            The Japanese developed a Chemical Sealing process for cost reduction.
                                                                                             P.13.
 2.13. THE HISTORY (continued)
Application     Approx Year                    Major Development
                              The first LCD scriber made by Villa Precision Inc. (USA)

                1980          Roche, BDH, E.Merck improve LC mixtures for TN, STN
5x7 Character                 Fairchild scaled up to 14x14” substrates

Dot Matrix Graphic            Clover Display Ltd established in May 1983
Word Processor
                              MIM & TFT AMLCD invented
Full Dot Matrix &
TV Panels                     Brewer Science Inc. & OIS of Troy, USA developed colour
                1985
                              AMLCD for space shuttle use.
PDA, Laptop &
Notebook PC                   Full color TFT panel for Notebook PC
                1990

Mobile phones
                1995          Bi-stable Cholesteric LCD

 E Books
                2000           New Display to replace LCD ?---- OLED, PLED


                                                                                         P.14.
3.0. HOW LCDs ARE MADE
 3.1. THE FRONT END PROCESS

ITO Glass             ITO = Indium Tin Oxide, a transparent conductive layer coated on the
                      Sodium Lime Glass. Its resistance is from 10 Ohms to 120 Ohms/square.
                      Glass area usually in 14x16”. Thickness in 1.1, 0.7, 0.5, 0.4, 0.3mm

Clean Glass                Artwork & Mask Design
with DI water


Patterning the             Methods: Photo Masking, Resist Ink Printing,
Electrodes on ITO                    ITO Ink direct Printing, Laser Cutting.


Alignment Layer            To form a rough surface to hold the LC molecule chains


Sealing Frame &            To form the cell and the inter-connections between the top and bottom glasses
Silver Dot Printing


Top/bottom Glass             The Laminated pairs
Alignment and Seal



                                                                                                   P.15.
3.2. THE BACK END PROCESS


Laminated Pair
Cutting into cells
                                  Liquid Crystal Mixture
                                  Formulation

Liquid Crystal Filling



End Sealing & Cleaning


Testing & Inspection
                                   Polarizer Cutting

Polarizer Fixing
                                                  Metal Pin or Heat Seal Connector fixing

Cosmetic Check
                                                   LCD Module Assembly (COB, TAB, COG, COF)
                     Optional Process
Shipments

                                                                                            P.16.
4.0. THE COLOR LCD
  4.1. THE FULL COLOR LCD
                  Black and White LCD                        Full Color LCD

                                                 Slice ITO
  Segments                                  into narrow
                                           sections


   Common                                                                                RGB
                                                                                      Color
                                                                                     Filter



                                                                                   Common



 In order to give a better color mixing,
 the RGB line widths are usually less           The color LCD can be built as a Passive LCD.
 than 30 micron in width per color.             But most large size Dot Matrix Color LCDs
 Hence the same for the ITO electrodes.         are built in the Active design.




                                                                                               P.17.
4.0. THE COLOR LCD (continued)
 4.2. THE ECB (ELECTRICALLY CONTROLLED
         BIREFRINGENCE) COLOR LCD

  % Light
  Absorption                                              Various ECB Types;

                                                          1) Homogeneous Type
                                                          Red->Yellow->Green->Blue

                                                          2) Deformation of Vert Aligned
   0                                              V       Plane (DAP) Type
       Clear   Dark   YO R P B G     Dark                 Blue->Green->Yellow->Red
               Grey   Color around
                      2.4v to 3.7v                        3) Hybrid Aligned Nematic
                                                          (HAN) Type
                                                          Green->Red->Blue

                                                          4) Vertical Aligned Nematic
                                                          (VAN) Type


                                                  V
                          No pure color,
                          50% Green + 25% Red + 25% Blue at this point
                                                                                        P.18.
4.3. DOUBLE CELL COLOR LCD
  There are two kinds of double cell can generate colors;
  A) With Color Polarizer                          B) With usual Polarizers at certain angles
     (Only working in Transmissive Mode)              (Reflective Mode is also possible)




4.4. GUEST HOST LCD (Single fixed color)
    Mixing color dye in the LC fluid and build LCD in Negative Mode.
    It will show clear pattern on a color background.
    Such method was used in the early date.

4.5. LCD WITH COLOR POLARIZER, COLOR FILM OR
     COLOR REFLECTOR IN CERTAIN AREA (fixed color)
     Pre-printed color polarizer is expensive.

4.6. COLOR INK PRINTING ON THE BOTTOM GLASS SURFACE
     (fixed color)
     This is the cheapest way to make LCD with fixed colors.
     The LC image & color area may not coincide well due to the glass thickness.
                                                                                                P.19.
 5.0. TODAY’S LCD
 Duty Ratio                 Active LCD

                                                                   LCD TV & Monitors
 1/256    Passive LCD
                               Projector         Portable TV              Notebook Panels

 1/128                                     Digital Camera                            1M+ Pixels
                                           Office Equipment
  1/64                              PDA
                                                                          100K Pixels
  1/32
                            Mobile Phone        Digital Instruments
                                                                           STN
  1/16
                                                             10K Pixels        TN
  1/8                Data Bank

   1/4        Film Camera                        1K Pixels

   1/3            Calculator
                                    100 Pixels
  1/2    Time pieces
         Hand Held Games
   1/1                                                                                            Panel
Static                                                                                            Size
         10 mm2       100           1,000            10,000                     100,000 mm2
                                                                                                   P.20.
6.0. CUSTOM DESIGN LCD & LCM --- The factors to consider
   6.1. LCD PANEL DIMENSIONS
                                                     Outer Dimensions (Be economical size)
                                                     View Area (normally 2mm from the edges)
                                                     End Seal (0.5mm thick)

                                                     Active Area (Area with patterns)
                                                      Pinout or Connection Area (2 to 2.5mm)
       Glass Thickness (1.1, 0.7, 0.5, 0.4 or 0.3mm/one side)
       ( Glass Material: Sodium Lime Glass with SiO2 barrier, surface polished for STN use )

      Economical Panel Size: The outer dimension may use up most the raw glass sheet area.

                                  or                               For small order size or pilot run,
Raw Glass Sheet                                                    7x8 inches sheets are used to boost
                                                                   up the yield and save the tool cost.

                                                  7x8 inches
                                                  (178x203mm)

         14x16 inches                  (The usable area is 7mm off the edge)
         (355x406 mm)

                                                                                                   P.21.
6.2. PANEL CONFIGURATIONS
                                                       The thick lines representing
             A      B         C          D             the pinout areas.

Eyes                                               Connectors suitable:
                                                   Zebra (Silicone Rubber) – A, B,
                                                   Heat Seal or TAB – A, B, C, D,
                                                   Metal Pins – C, D,

  All the above 4 models required Ag (silver) connections inside the LCD cell.
  If such Ag connection not to be used or unable to be used, the configurations will be as follows;




                   E                               F                                G



   Models E, F & G are good for combination use of Zebra and Heat Seal connectors together.
   Most TAB connections are also applying on such models.
                                                                           40+deg          40+deg
  For TN LCD, don’t forget to         45+deg              15+deg
  specify the View Direction
                                     15+deg            45+deg

                                    12 O’clock              6 O’clock                                 P.22.
6.3. PATTERN LAYOUT            Too Long Trace   Cross Over   Narrow down trace



                         Good Bad
                         Layout Layout


   C S1 S2 S3 S4 S5 S6                     S6 S3 C S1 S2 S4 S5



                +




                                                                            P.23.
6.4. ZEBRA CONNECTORS                                                Three kinds of Rubber
                                          Side Wall Insulators       1. Sponge Rubber
                                          Conductive Layers
                                                                     2. Silicon Rubber
                                          Insulation Layers
                                                                     3. Super Soft Rubber


                                                              Metal Mounting Bezel
  Pitch: (Conductor/Insulator Layers)
      Low Cost Type --- 0.25+-0.05mm                                    LCD              Assembly
      General Type ----- 0.18+-0.04 mm
      Dot Matrix Type – 0.10+-0.03 mm                               Zebra
      Graphic Type ------0.05+-0.025 mm
                                                              PCB
  Contact Resistance:
   1000 –1500 ohms at 10%-15% compression                 Precautions in Assembly
                                                         •Pre-clean Zebra
                                                         •Three or more conductors in contact
                                     LCD
                                                         •PCB wraping <0.375mm / 50 mm
                                    Zebra                •Bezel has opening gaps with PCB
                                                         •0.3mm or 10%-15% compression
                                                         •Dummy zebra use with single side
                                                          contact LCD.
  Mis-aligned Good A safer way                           •Insulation side wall quality.
                   (wider contact on PCB)                                                       P.24.
6.5. HEAT SEAL CONNECTORS
                    Conductors (~20 um particles) printed on a Polyester (PET) Film of 20 -25um


                                        Contact Resistance      &    Pitch
                            Graphite Type --- 35 to 100 ohms/sq   0.40, 0.60, 2.80 mm
                            Silver Graphite Type ---- 0.5 ohm/sq  0.23, 0.35, 2.80 mm
                            Silver Type ------ 0.05 ohm/sq        0.23 mm


  Choose proper LCD configuration:            Hot Press
                                                                  PET film
  LCD             Conductor side

  PET side                                                    Welded
                                     PCB

    PCB                              Precautions in Assembly
                                     •The Hot Press head temperature 120-140 deg C at joint
  LCD         PET side               •32 Kg/sq cm pressure is recommended
                                     •Leveling the press for even pressure along the joint.
                                     •Properly select the sealing time to prevent uneven flow or
                                        wash away the conductor particles.
    PCB                              •100pcs/mm2 particles at contact area is suggested.
                PET side             •Peeling off strength be >200gm (Vertical)
                                        & >500gm (Horizontal)

                                                                                             P.25.
6.6. METAL PIN CONNECTORS ( for 0.7 & 1.1mm glass )
                                          Standard Pitch: 1.27mm, 1.8mm, 2.0mm, 2.54mm
                                          Pin Length:      20mm, 30mm, & 45mm max
                      LCD
                                          Clip Depth      2.0mm to 2.4mm max
                                          Contact Resistance: <0.05 ohm
                                          Precautions in Assembly:
                                         • Prolong soldering may damage the Pin contact to glass
                                            ---- A good LCD will add carbon cushion between pin
                                                 clip and glass contact area.
                 Epoxy enforcement
                                         • Care on bending the pins ---- LCD maker provides pin
                 Wider seal area is
                                                  lead forming.
                 required.
                                         • Pin length under 4.0mm is not recommended.
                                         • Wave solder is not recommended ---- Polarizer is weak
                                         • Mechanical stress on pin or temperature changes may
                                                 cause LCD background color changed.
 All the above connections may have IC on PCB by SMT, Wire Bonding (COB) or Insert & Solder.

 6.7. TAB (TCP IC BONDING)
               IC on a flexible film                               LCD
               with conductors.
               The Film is heat sealed
               onto the LCD pinout area

     TAB = Tape Automation Bonding                                                                 P.26.
     TCP = Tape Carrier Package
6.8. CHIP ON FILM (COF)
                                                                   LCD
    Same as TAB, but with more
    components on the film like
    a circuitry on PCB




6.9. CHIP ON GLASS (COG)

    The IC Chip              Same as an               LCD
    for COG is               usual LCD
    different from
    those for usual
                             Glass with
    wire bonding
                             Fine traces
    on PCB.
                             Fan-in &
                             Fan-out

    ACF* film is used to fix the
    COG chip onto the glass.                    Most panels with           IC Chip
    The ACF film is similar to                  Metal Pins
    Heat Seal but with much finer
    Pitch and conductive particles.        * ACF=Anisotropic Conductive Film         P.27.
6.10. TRICKS ON THE LCD PANEL DESIGN                             Recommended Driving Freq
                                                                 60 Hz to 120 Hz
   6.10.1. THE BIAS VOLTAGE
                                                 Theoretical Driving Waveform
  % LIGHT
  ABSORPTION                                      Applied to
                         90%                      Segment

                                                  Applied to
                                                  Common

                     10%                          Resulting
                               Volts
 0 volt       Vth                                 Waveform
                                                  to LCD
                                       Volts
                                                                     Off        On

                                                  Practical Design Waveform
                                                  (Example: Waveform to LCD at 1/3 Bias)

                                                   V
                                                2/3V           Off         On        Off
                                                1/3V
   The Bias     The driving                        0
   Voltage      Voltage
                                               -1/3V
                                               -2/3V
 Time                                             -V
                                                                                      P.28.
6.10.1. THE BIAS VOLTAGE (continued)
  The formula and design facts;
  N: Multiplex Rate. Example: N=3 for 1/3 duty
  S: Bias The ideal design S=1+ N
  Vd: The supply voltage to the panel.

  Von = ( Vd / S ) x    ( N-1+S 2 ) / N

  Voff = ( Vd / S ) x   [ N – 1 + ( S – 2 )2 ] / N

  N                           2              3         4              8            16
  S                           2              2         3              4            5
  Vd                          3 volts        3 volts   3 volts        3 volts      5 volts
  Voff                        1.06 v         1.22 v    1.00 v         0.88 v       1.22 v
  Von                         2.37 v         2.12 v    1.73 v         1.27 v       1.58 v
  Von – Voff                  1.31 v         0.90 v    0.73 v         0.39 v       0.36 v


                                                           Less than 1 volt !
                                                           Beware the drifting under temp changes




                                                                                                    P.29.
      6.10.2. CROSS OVER LAYOUT                                     Epoxy Sealing Frame
                   S1      S2      S3        S4




Ag Dot            C1                                                     Hided under Frame
Connection                    C2
                                        C1
                  2 cross over points

      6.10.3. THE POLARIZER SELECTION
             •The Glue Type or Non-glue Type polarizer.
             •The Polarizer with the UV Barrier may extend the LCD Life under strong UV exposure.
             •The Anti Glare Polarizer may improve the contrast.
             •The high durability polarizer may stand for wider temperature environment.
             •The slightly orientation of Polarizer axis may change the background color.

     6.11. THE THERMAL COMPENSATION
             It is recommended to use the thermal compensation circuit when a LCD will be operated under
             a wide temperature range.



                                                                                                      P.30.
6.12. TEMPERATURE RANGE

                                         Wide Temp Type
       Melting                            Low Temp Type                          Clearing
        point                                                                     point
                                          General purpose
                                                                                            Temp
                                                                                            Deg C
Operating
Temp.             -30      -20      0 deg                   +50      +60      +75 deg

Storage
Temp                10 deg C lower                             10 deg C higher
                            The STN temp is 10 deg narrower than TN

Problem                 Black Spots                          Background blackened
when exceeds            Slow response                        Cross Talk
rated temp.
                          All the above defects are reversible at room temp

Possible design
                                                                Specific for High Temp
               Specific for Low Temp

                                                                                             Temp
            -40 deg                     +10          +30 deg                      +100
                                                                                                    P.31.
6.13. BACK LIGHTS
 Choice of               Descriptions                                           Common
 Back Light                                                                     Color
 Side LED Type           Wedge diffuser (Light Guide) and reflector are         Yellow Green,
 ( Fig. 1 )              needed.                                                Blue, White
                         Poor illumination for large panel
 Array LED Type          Consuming more power and generating more heat.         Yellow Green,
 ( Fig. 2 )              Beware the difference in supply voltages of each       Red.
                         model. Easy assembly
 EL (Electro-            The best in even brightness and light weight. But      Green, Blue,
 Luminescent)            less brighter than LED Backlight. High voltage and     White.
                         EMC consideration.
 CCFL (Cold Cathode The strongest illumination.                                 White.
 Fluorescent Lamp)  High voltage and EMC consideration.

Important: The Transmissive and the Transflective Type LCD absorb the different light intensity.

  Light                                                Light
                          Diffuser Paper                                        -
                          Light Guide                                                       LED wiring
                             LEDs
                          Reflector domes                                       +
  Fig. 1.                 Reflector Paper                      Fig. 2.                             P. 32.
7.0. BI-STABLE LCD
  Bi-stable Cholesteric Display, or
  SSCT – Surface Stabilised Cholestric Texture Display, or
  Multi-stable Chiral Nematic Display, or
  E-Book Display
     This is a new technology in LCD making use of the Cholesteric Liquid Crystal. Mr. John West
 and Mr. D. K. Yang of Kent State University, Ohio, USA filed the patent in 1995.
     The display image is retentive in the absence of an electric field. It has a excellent readability
 and wide view angle under the daylight or strong ambient light.
     No Polarizer is required on this kind of display panels.

     The Liquid Crystal is switchable and stable in two kinds of texture.
 (a) The Twisted Planar Texture, which has the LC layers parallel to the display surface,
      reflects the incident light.
 (b) The Focal Conic Texture, whose LC is in fragmentary, scatters the incident light.




                                           Switch-able

      (a)                                                 (b)

    The above two textures are switch-able under 30V to 180V pulse of 10ms to 100ms,
 and stable in zero electric field.
    By properly adjust the pitch of the Twisted Planar Texture, it can reflect R, G, B lights.
                                                                                                          P.33.
8.0. ORGANIC LED
   The Organic Electro Luminescent Displays (OELD) , or The Organic Light Emitting Devices (OLED)

    The EL ( Electro-luminescence ) Back Light for LCD has been used for many years. It operates
at high voltage (>100V). In 1987, Tang and Van Slyke in Kodak, USA reported a low voltage (<10V)
Organic EL. It comes a new display ---- the OELD.

 8.1. THE BASIC STRUCTURE                                    Metal Cathode
                                                             Electron Transport Layer
         DC                                                  Re-combination and Emission Layer
         volt
                                                             Hole Transport Layer
                                                                   ITO Layer (Anode)
                                                                   Glass Substrate
                                               Light emits

  8.2. THE DIFFERENCE BETWEEN LCD & OLED
            LCD                                    OLED
    No Light emission                 Emits light in colours (100cd/sqm)
    Narrow view angle                 Wide view angle (>150 degrees)
    Slow response                     Fast response (<10 microsec)
               OLED has most the advantage of LCD such as;
               Easy patterning
               Low operating voltage but at high current ( 20ma/cm2)
               Low manufacturing cost
               Thin and light weight                                                               P.34.
8.0. ORGANIC LED (continued)
  8.3. THE OLED & PLED
      There are two major ways to build the OLED;
 a.    The small molecule process ---- by spluttering the organic materials onto the ITO patterns.
             Kodak uses such way.
 b.    The large molecule process, or the polymer process ---- by spin coating, dip coating or screen
             printing the organic pastes layer by layer. Cavendish Lab in Cambridge, UK and Dow
             Corning, USA developed such process and materials in ’90s.

 Some people now call the OLED made under polymer process the PLED.
 The small molecule process is also applying to making the ACTIVE OLED.
 Pioneer, Japan seems the first one in mass production for the OLED.
 It is expected the OLED will replace the LCD step by step from 2005.

 CLOVER DISPLAY GROUP has started a joint venture with the University of Hong Kong to research
 and develop the materials and process for OLED.
 The newly formed joint venture company is named COLED DISPLAY LTD., established Sept 2002.




                                                                                                        P.35.
9.0. TOUCH PANELS                             PE Film
                                              With ITO
  9.1. ANALOG TYPE                                          Ra        Rb
                                                                           Silver
     A PE film with ITO layer is sealed                                    Conductors
 onto an ITO Glass with epoxy dots as
 Spacer to maintain a gap.                    Epoxy dots
      When the external pressure of           As Spacer
 touching makes contact of two ITO            Glass with              Rd
 layers, the sensing IC circuit with give     ITO                          Pin out
 an analog reading corresponding to the                          Rc        Area
 touch position.

  9.2. DIGITAL TYPE
     The ITO on the PE Film and the           PE Film
  ITO Glass are etched out into sectors.      With ITO
  When touched, the corresponding
  sectors are shorted circuit and reflected
  to the pins concerned.
                                              Epoxy dots
                                              As Spacer
                                               Glass with
                                               ITO                         Pin out
                                                                           Area


                                                                                     P.36.
10.0. CUSTOM LCD/LCM DEVELOPMENT GUIDE.
    Enquiry from Customer


    Feasibility Study & NRE          Free quote in 2-4 working days
    Charge / Unit Price Quoted


    NRE Order Confirmation           NRE payment in advance


    LCD Panel        PCB & Circuit       External Casing              ** normally 10-20 LCD
                                                                      or 3-5 LCM samples
          1 week           1 week                 1-3 weeks           will be free. For more qty,
                                                                      please notice us in advance
  Panel Drawing      Circuit diagram      Case Drawing                when confirm the NRE order.
  for Approval       & PCB Layout
                                                  3-6 weeks
         3-4 weeks         3-10 weeks

  Mask Design        PCB Tool Design      Hand mould up sample         Final Case
  & Samples**        & Samples** for                                   Mould
  for Approval       Approval                                                       3-9 weeks

                                                 Primary Sample             Final Sample
Total development time;
LCD Panels 4-7 weeks, LCM Modules 4-10 weeks; With External Case 7-18 weeks
                                                                                                P.37.
11.0. ACKNOWLEDGEMENT & DECLAIMER
       We have tried our best to present up-to-date and correct information here. Some of them to be
  explained together with photographs and demonstration samples to form a complete part of the
  Introduction.
       We wish that the information discussed in this seminar may help the design engineers to make
  a cost effective and quality custom design in an easier and logical way.
        However, this is not an academic seminar that we have used a simply way in the presentation.
  All information here is provided in good faith without any expressed or implied warranty. The reader
  should seek for more detail advice from the industry.

      The information in above are partly referring to the following documents;
 1.    Proceedings of the Liquid Crystal Seminar HK by E. Merck, Darmstadt, Germany.
 2.    Various articles in the SID International Symposium and Information Display by the Society for
       Information Display, Inc. USA
 3.    LCD Displays, the leading edge in flat panel displays, by Sharp Technical Library, Vol. 1, of
       Sharp Corporation, Osaka, Japan.

  Prepared by;                                                        Editions:
  Johnny C. L. Chou,                                                  7th edition Sept 29, 2005
  Clover Display Ltd.                                                 6th edition Mar 13, 2003.
   Room 1006, 26 Hung To Road, 10/F, Kwun Tong, Hong Kong             5th edition Sept 19, 2001.
   Tel: 23428228, 23413238                                            4th edition Apr 16, 2000.
   Fax: 23418785, 23574237                                            3rd edition Sept 6, 1999.
   email: cdl@cloverdisplay,com                                       2nd edition Sept 1, 1998.
   URL: http://www.cloverdisplay.com (in English)                     1st edition May 19,1997.
          http://www.cloverdisplay.com.hk (in Japanese)               All copy rights reserved
          http://www.cloverchina.com (in Chinese)                     Clover Display Ltd. H.K.
                                                                                                     P.38.

				
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