LCD TECHNOLOGY OVERVIEW
C O N T E N T S:
TN
STN
FSTN
DOUBLE STN
ECB COLOR (F)STN
MULTI-COLOR TN
SURFACE MOUNT TECHNOLOGY
CHIP-ON-BOARD
CHIP-ON-GLASS
TAPE AUTOMATED BONDING
BACKLIGHTING
INTERFACE
TEMPERATURE RANGES
Tianma Microelectronics (USA) Inc.
TN
TN – Twisted Nematic. A type of liquid crystal
whereas the alignment surface and therefore the LC
molecules are oriented 90° from each surface of
glass. Produces images in two modes: Positive and
Negative. Positive Mode provides white background
with black segments. Negative Mode provides black
background and white segments.
FEATURES
* Backgrounds: Black, White
* Viewing Angle: 45 degrees (typical)
* Multiplex Ratio: up to 64:1 (segments / commons)
* Most inexpensive
When two polarizing filters are arranged along
perpendicular axes, as in the first illustration, light
passes through the lead filter and follows the helix
arrangement of the liquid crystal molecules. The
light is twisted 90 degrees, thus allowing it to pass
through the lower filter. When voltage is applied,
however, the liquid crystal molecules straighten out
of their helix pattern. Light is blocked by lower filter
and the screen appears black because of there being
no twisting effect.
The multiplex rate is equal to the number of
rows that can be displayed simultaneously. For
example, a display with a multiplex rate of 16
can
display
16
rows
of
information
simultaneously.
STN
STN – Super Twisted Nematic. A high information
content LCD that uses adjustable interference of two
optical modes to achieve a large number of
multiplexed lines, higher contrast and higher level of
gray scale. It results in the birefringence mode. An
improved twisted nematic fluid (200° twist or greater)
which has better contrast and optimum viewing range
than standard twisted nematic.
The graph shows a comparison of a voltage
versus transmitted light curve of a typical TN and
a supertwist nematic (STN) display. (Generally, a
greater twist angle equates to higher
multiplexibility.) The V90 and V10 points on the
graph indicate the voltages that yield 90 percent
and 10 percent light transmission, respectively.
FEATURES
* Backgrounds: Yellow-Green, Gray, Blue
* Viewing Angle: 75 (typical), 90 (maximum) degrees
* Multiplex Ratio: up to 480:1 (segments / commons)
* Response Time: 150 msec (lower than TN)
* Suitable for Graphic applications
As the figure shows, STN displays have a
steeper curve than TN displays, which allows
higher multiplex levels for STN displays. (STNs
were developed primarily to overcome the
difficulties encountered in multiplexing TN
displays.)
The multiplex rate is equal to the number of rows
that can be displayed simultaneously. For
example, a display with a multiplex rate of 400
can
display
400
rows
of
information
simultaneously.
FSTN
FSTN – Film Compensation Super Twisted Nematic.
LCD with an extra film added to the outside of the
cell to compensate the color shift of blue on green to
black on white. The film is made of a polymer with
double refraction to remove the interference of
colors. It results in retardation compensation.
The film (the top layer in the figure) is placed in the
display, either under or over the top polarizer. Some
film compensation systems use two films, one on the
rear that serves as a collimator, and one on the front
that serves as a dispersion film to broaden the
viewing cone. Film compensation improves the
viewing angle, but does not affect switching time.
FSTN is all standard STN displays with a polymer
film applied to the glass as a compensation layer
instead of the second cell as in the case of the
DSTN. This simpler and more importantly cost
effective method provides the preferred black on
white image for this display technology.
FEATURES
* Backgrounds: Black, White
* Viewing Angle: 80 degrees (typical)
* Multiplex Ratio: up to 480:1 (segments / commons)
* Response Time: 150 msec (lower than TN)
DSTN
DSTN, developed by Sharp Corporation, was the first
commercial black and white conversion of the STN display
and refers to Double Super Twisted Nematic. DSTN displays
are actually two distinct STN filled glass cells glued together.
The first is a LCD display, the second is a glass cell without
electrodes or polarizers filled with LC material for use as a
compensator which increases contrast and gives the black on
white appearance.
There are only a few manufacturers that offer this
technology: Tianma, Optrex, Hyundai, URT, Varitronix and
CFG. Here is an overview of DSTN technology by different
criteria:
Contrast: better than STN, FSTN; offers automatic contrast
compensation with temperature.
Response Time: significantly enhanced.
Optical Cast: DSTN reduces the tendency of a screen to be
slightly red, green or blue.
Viewing Angle: combination of 6 and 12 o’clock optimal
viewing directions together
Temperature Range: -30 to +80 C operating, -40 to +90 C
storage
Polarizer Mode: Negative, so DSTN LCD’s need
backlighting
Back Light: CCFL or LED only
Resolution: up to 122 x 32 dots
Suitable Applications: Automobiles, Gasoline Pumps, etc.
Always custom designed
ECB
Features of ECB Color LCD Modules:
Low power consumption – Under most lighting conditions, no
backlight is required which saves the highest power-consuming
element of the display.
Simple drive electronics – The single pixel for all four colors
requires only one set on common and segment drivers. This also
reduces the connector pitch, the cost, and complexity of the
assembly.
No color filters – Reflective operation is possible in most
environments. Color filters add cost and require a backlight to
provide enough illumination to overcome the loss of a given
pixel.
Low cost – The reduced electronics and lack of filters make the
module significantly lower in cost comparatively with passive
color STN modules.
Response Time: about 250 msec (low)
Low Transmission: about 1.5 to 20 %
Applications: Gaming, etc. Being very sensitive to extreme
temperatures and responsively slow, ECB technology is not
suitable for the automotive industry or video applications.
Always custom designed.
Electronically Controlled Birefringence (ECB) or Vertically
Aligned Nematic (VAN) is a electro-optical effect that was first
described in 1971. Through this effect a number of distinct colors
can be displayed in a LCD.
The ECB mode color displays are realized by controlling both
the birefringence of liquid crystals and a pair of optimizing
polarizers with retardation films, which are brought from
operating voltage rate impressed to liquid crystal layer and
inclination of liquid crystal molecules. Thus, the wavelength of
light exciting a pixel is determined by the voltage applied to that
pixel.
Almost every other LCD manufacturer offers this technology
today.
TYPES OF ECB PRODUCT
STN: multiple colors on green background
FSTN: multiple colors on pale background
MULTI-COLOR TN
Advantages:
•Allows a limited number of colors
that are not subjected to change
•Less parallax and durability
problems compared to most
conventional designs available on
the market
•Resistant
to
wide
range
temperatures (-30 to +80 C
operating )
•Inexpensive (TN technology has
become conventional almost 30
years ago)
• Applications: high quality audio
and car displays, etc.
The newly developed Selective Multi-Color TN LCD
technology is offered only by Tianma, Optrex, and
Varitronix. Multi-Color TN display is based on the negative
mode. The color coatings and the black matrix (mask) are
inside the LCD cell. The black mask allows the light go
through characters and icons only, not the background. The
total number of colors ranges from one to three in addition
to the black matrix. Customers can select the color for each
segment. No bleaching of colors is observed even when
operating at 80 C, ideal for automotive and other outdoor
applications. Displays from static to 1/8 multiplex are
available.
Black mask is used to mask off non- switching areas in
alpha-numeric segment displays. The purpose is to improve
contrast and readability. This way, a stronger backlight can
be used.
IC MOUNTING TECHNOLOGIES
IC COMPARISON
Tianma Microelectronics implements a
variety of integrated circuit mounting
methods in designs of printed circuit
boards used with standard and custom
made liquid crystal modules. Tianma has
full
production
capabilities
that
incorporate design requirements for the
following IC mounting technologies:
Surface Mounting Technology (SMT)
Tape Automated Bonding (TAB)
Chip-On-Board (COB)
Chip-On-Glass (COG)
During the days of high demand of
integrated circuit components on the
LCD market, Tianma Microelectronics
manages to keep firm control of
receiving IC supplies from contractors.
Despite the shortage of micro-controllers
and drivers in the LCD industry, it is
entirely within Tianma Microelectronics’
capabilities to provide its customers with
large quantities of high quality electronic
chips supporting the present product line.
SURFACE MOUNT TECHNOLOGY (SMT)
QUAD FLAT PACKAGE
Surface Mounting Technology (SMT) using quad
flat packages on printed circuit boards was the
most popular at the early years of liquid crystal
display industry, and is still available for mass
production.
Plastic Quad Flat Package (QFP) represents itself
as a flat rectangular integrated circuit package
with its leads projecting from all four sides of the
package without radius. Used with surface
mounting method. Made of black epoxy resin. Very
moisture absorbent.
CHIP-ON-BOARD (COB)
BARE DIE
Chip-on-Board (COB) is a popular IC mounting
method that provides wire bonding as the direct
attachment of bare die to laminated printed circuit
boards. The LCD driver is formatted into an area on
the PCB. Electrical connections are made by micro
diameter gold wires. The entire area is then covered
with epoxy. All of Tianma’s standard Character LCD
modules are of the Chip-On-Board design.
Advantages:
• Very compact
• Space savings over Surface Mount Technology
assembly.
• Cost savvy comparatively with SMT, since there is
no plastic package.
CHIP-ON-GLASS (COG)
Chip-On-Glass – is one of the high-tech mounting methods that uses Gold Bump or
Flip Chip IC’s, and implemented in most compact applications. Chip-On-Glass
integrated circuits were first introduced by Epson. In flip-chip mounting, the IC chip
is not packaged but is mounted directly onto the PCB as a bare chip. Because there is
no package, the mounted footprint of the IC can be minimized, along with the
required size of the PCB. This technology reduces a mounting area and is better
suited to handling high-speed or high-frequency signals. Currently, there are 3
standard C.O.G. LCD modules available at Tianma with the regular mass production
delivery time.
Advantages:
1. Very space economical. Chip-On-Glass LCD modules can be as thin as 2 mm.
2. Cost effective over COB, especially in graphic LCD modules, because much less
IC's are required.
3. More reliable than TAB because of the weakness in the bond area of TAB.
Disadvantages:
1. COG can only be used at a certain resolution level where the lines are not too fine.
At very fine pitches COG becomes difficult to test, and TAB is the preferred
approach.
2. It may be more cost-effective to use TAB or COB, if a designer has to integrate a
keypad or indicator around the display.
3. The active area is not centered within the outline but offset, because of the area
where the circuits are.
Since the Chip-On-Glass integrated circuit has been invented by Epson, COG
technology became very popular due to the demand for more compact applications.
In the near future we will see this IC mounting method finding its applications in
many other equipment than cellular phones, PDA's, computer network servers,
satellite receivers, etc.
This year Tianma Microelectronics is going to announce 7 standard Chip-On-Glass
LCD modules available for the regular product lead time.
TAPE AUTOMATED BONDING (TAB)
TAPE CARRIER PACKAGE
Tape Automated Bonding (TAB) LCD driver or controller electronics
are encapsulated in a thin, hard bubble package, of which the drive
leads extend from the bubble package on a thin plastic substrate. The
adhesive along the edges is used to attach the TAB to the LCD glass
and/or PCB.
Tape Automated Bonding IC mounting method uses the same type of
integrated circuits as Chip-On-Glass technology - Gold Bumped Flip
Chips. After this type IC chip has been produced, we a gold bump is
placed on the IC chip and then sealed onto the polymide board. (This
procedure is called ILB or Inner Lead Bonding) and is how the TCP IC
is produced. TAB LCD modules are always custom made from Tianma.
Advantages:
• Offers compactness (IC and its interfacing circuitry can be bent
behind the LCD glass panel).
• Some times more cost-effective than Chip-On-Glass, if a designer has
to integrate a keypad or indicator around the display.
• The active area is centered (differently from COG).
• Can provide interfacing at very fine pitches.
Disadvantages:
• The bonding area is weak. Less reliable than COG.
• More expensive than COG. Even though TAB LCD modules use the
same type of IC as COG, tape automated bonding requires a package.
TYPES OF LCD BACK LIGHT
LED (Light-Emitting Diode) - Consists of surface mount LED’s, which are situated in series along
the bottom of a shallow plastic tray.
Features:
•Available Colors: Yellow-Green (standard), Red, Amber, Green, Blue, White
•Life time: long, typically 50,000 hours
•Operating temperature range: -30 to +70 degrees C
•Requires low voltage DC. No DC/AC inverter required
•Simple connection +5 VDC (Anode) and ground (Cathode)
•Two methods: matrix (array)or edge lighting
•The typical voltage for all standard LED versions of LCE modules is 4.2 VDC.
EL ( Electro Luminescent) - A thin membrane consisting of two coated electrode plates with an
aluminum reflector. When AC voltage is applied to the electrodes, the electrons collide with the
light emission core. The energy given off is light. Inverter (DC to AC) is used to power electro
luminescent lamps.
Features:
•Available Colors: White (standard), Blue, Yellow-Green
•Service Life: 4000 hours (driven with inverter, 20 C temp, and 70% humidity) and 1500 hours
(driven with a fixed power supply and frequency generator, 20 C temp, and 70% humidity)
•Operating temperature range: -20 to +50 degrees C
CCFL (Cold Cathode Fluorescent Lamp) - A miniature high voltage cold cathode (field emission)
lamp made of lead-glass with mercury inside that provides fluorescent back lighting or edge lighting .
Uses a diffusing light guide. High brightness, high efficiency and vibration-proof.
Features:
•Available Colors: White (standard)
•Life time: 15,000; 20,000 hours
•Operating temperature range: -20 to +50 degrees C
•Low power consumption and excellent lighting characteristics
•Easy intensity control
•Low heat generation and thin diameter lamps
FIBER OPTIC - Fiber optics are flattened and then sandwiched between two pieces of pliable
plastic. The top piece is used as the diffuser. The opposite ends are tied into a coupler, which is
connected to an LED or Halogen light source.
Features:
•Available Colors: White, Green, Blue, Amber and Red
•Life time: long, remote light source offers 10,000 to 100,000 hours life and easy replacement.
•Operating temperature range (optical fibers): -40 to +85 degrees C
•Low power consumption. Sources require less power than EL, CCFL, or LED Array and no inverter.
As low as 10-20mA at 2vdc
•Compact, panels are thin and sources are smaller than EL or CCFL inverters
•Heat free, adds no heat or EMI to interfere with switch operation
•Very durable. Optical Fibers are not affected by extremes in humidity (0% to 100%) and temperature
TYPES OF CONNECTORS
FFC (Flexible Flat Cable) - cable with two
smooth or corrugated, but essentially
flat, surfaces. Attached to the PCB by soldering
or plugging into a zero insertion force
connector. Very reliable.
FPC (Flexible Print Circuit) is a circuit
substrate of patterning Cu electrode with
Polyimide film as a base. Usually offers more
flexibility than Flexible Flat Cables.
Heat Seal - consists of microscopic metal
particles within the Hot Melt Adhesive covering
the entire area. Very flexible and eligible for
connecting a large number of terminals
simultaneously by single sealing operation.
Pins - allow self-aligning connection to printed
circuit boards via plug in strip sockets. Work
well in harsh environments. Two conventional
methods: DIL (Dual-In-Line) and SIL (SingleIn-Line).
Zebra Strips or “Elastomeric” - strips of
silicone rubber made up of sequentially spaced
conductive and non-conductive material. This is
the most common connection method for
complete LCD modules. Resistant to shock and
vibration.
TEMPERATURE CHARACTERISTICS
TN MODULES
OPERATING
STN MODULES
STORAGE
NORMAL
RANGE
WIDE
0 ~ +50
-20 ~ +70
-20 ~ +60
RANGE
-30 ~ +80
-20 ~ +60
RANGE
-20 ~ +70
-30 ~ +80
STN PANELS
OPERATING
STORAGE
0 ~ +50
-20 ~ +60
-10 ~ +60
-20 ~ +70
WIDE
RANGE
0 ~ +50
WIDE
TN PANELS
RANGE
STORAGE
NORMAL
RANGE
NORMAL
OPERATING
-20 ~ +70
-30 ~ +80
-30 ~ +80
-40 ~ +90
OPERATING
STORAGE
RANGE
0 ~ +50
-20 ~ +60
WIDE
-20 ~ +70
-30 ~ +80
-30 ~ +85
-40 ~ +90
NORMAL
RANGE
The above numbers are in °C.