LCD
History:
LCD stands for Liquid Crystal Display, and falls within the category of Flat Panel Displays (FPD's). 1 They can be found all around in objects such as laptop computers, cellular phones, and calculators. LCD's came into the market as a replacement for the widely-used Cathode-Ray Tube (CRT), the recent technology used in such applications as picture tubes for televisions. CRT's have a high power consumption, on the order of 100W. LCD's can be as low as 20W, an obvious remarkable difference.
Description:
The display of an LCD is dependent on a backlight source, a polarizing material, and two layers of glass substrate which sandwich a liquid crystal layer between. The layers of glass are transparent, allowing light to pass through. The light that originates from the backlight source first passes through a polarizing film, then through the first layer of glass. The liquid crystal layer in between is in an intermediate phase between an isotropic liquid and a crystalline solid.2
Being sensitive to electrical fields, they are particularly applicable for optical display technologies. The crystals themselves are best described as molecules shaped like elongated cigars. The axis of the molecule is defined by the direction of elongation.3 When liquid crystals lack an applied voltage, they will form spiral shapes and flow at room temperatures.4
When linearly polarized light passes through at this stage, it will follow the twists of the crystals and become circularly polarized. When an applied voltage is added to the display, the crystals unwind and stand up 'in attention' in the direction of the field – a change in molecular orientation.5
It is in this way that the light passing through can be controlled. Some of the latest technology with LCD panels is related to the components used to create the display. Using the same fabrication technology employed today to make LCD's, layers of clear glass can be built-up and rotated slightly to produce a spiral-effect. When light passes through, it is circularly polarized.
Current LCD's use linear polarization as mentioned above, which cancels out and wastes half of the light from the backlight source. In this new method, residual light is reflected and recycled, therefore creating brighter, more efficient displays. With this innovation, one half of the energy is needed compared with other similar systems.6
Some downfalls of the LCD industry is it not being able to produce viable low-power alternatives in applications needing this requirement. Also, as mentioned above, LCD's are the only current display that is not light-emitting, and therefore, the additional component of a backlight effects costs. Without the component of the backlight, LCD's are not viable in the dark, which is another design constraint.
Current Applications:
LCD's are presently found in such fields as communications, medical electronics,
industrial process control, wireless data collection, office automation markets, and
display manufacturers in the areas of computers, televisions, entertainment systems,
cellular phones, watches, calculators, and 3-D displays. The driving growth in the market
is dependent on larger panel sizes and substrates, displays with larger pixel counts and
increased brightness, wider viewing angles, and improved color-saturation. 7
Potential Applications:
LCD's have obvious potential as they are found in objects all around us. At the same time, it is questionable to what extent they will be able to advance from where the technology is presently. It seems that devices that create their own light and use far less energy are the direction that things must go. Options such as these are discussed in the following section. Also, the LCD technology presently relies on inefficient means (linear polarizers) to direct the light. New technologies are being discovered to create circular polarized light, making the technology a viable one for future potential applications.
Many designers are proposing ideas of digital panels on surfaces never imagined before in areas of the home and the office. Walls and countertops could be designed to be LCD panels, much like the computer screen today, where information could be retrieved, or visual outputs of one's desire could be created. LCD's coupled with Light-Emitting Devices could open up new potential in terms of the two displays working together, and then the ability to only use one (i.e.:Light-emitting device) as a light source.
Light-Emitting Devices
The other display technologies discussed from here on are all light-emitting, or electroluminescent. The most commonly used example of this up until recently is the cathode ray tube that is found in televisions, mentioned earlier. Known as cathodluminescence, it is the light produced from the collision of electrons with the phosphor coating on the inside lining of the cathode tube.8 Another example of electroluminescence which is less common is the p-n junction, which was noted as early as 1923.9 A p-n junction emits photons, which produces light. It is this finding that has led to the discovery and advancement of LED’s and other display technologies to be discussed.
LED
History
LED’s, or Light Emitting Diodes, have been found in the areas of display and information technologies and photocouplers for the past three decades. Up until the past year or so, LED’s were only able to produce red, green and yellow colors. Due to this limitation, applications such as instrument panels and third brake lights in cars were the primary applications that they were use for. 10
Description
The light that is produced from an LED is based on semi-conductor connections. These connections convert electric current directly to light. LED's offer many advantages over conventional lighting, such as a lifespan of 100,000 hours, very high impact resistance, compact design, and dramatically reduced energy consumption. 11
Present Applications
LED's have been used in flat-panel displays even with the limited color palate they have had to offer. The current market for such displays is estimated at 1.8 billion dollars, and expected to grow 15% annually.12 Within the current year, companies such as Siemans and GE Lighting have been able to create the colors white and blue. Blue is considered the most difficult color to achieve because it is found at the far end of the visible spectrum. This development creates a large new market for light-emitting diodes in standard lighting found in the home or office. GE Lighting with Emcore intends to develop and market replacements for mini automotive lights, compact fluorescent, halogen, and traditional incandescent lighting. 13
Future Applications
A general goal that scientists are currently working on is to bend and steer light in the same manner computer chip can manipulate electronic signals. desire do this based concept could carry thousands of times more information than electrons can. turn would increase transfer speed such objects as modems telecommunication equipment.14 A means in which scientists are attempting to control the bending of light is through PHOTONIC CRYSTALS. These are composites of plastic and air that can 'build themselves' into systems based on the chemical properties that are applied to the composite. They produce similar optical properties as opals, creating a striking mix of color. Photonic crystals are proposed to be coupled with LED's in order to create more efficient lighting systems based on controlling the light output.15
Another area of research that is currently going on is related to 'lasing' and LED's. Lasing refers to the process of 'pumping' light through a solid state material (such as zinc oxide or gallium nitride). This process creates brighter light (speculated at 1000 times more intense) and does so with the same power consumption. The theory is based on the outcoming light is directional with lasing, where as the light from an LED shines in every direction. It is a technology that could replace the light-emitting diode, as it is possible that it may be able to be made cheaper. 16
LEP
History
Electroluminescence through the device of Light-Emitting Polymers is one of the more recent technologies to be discovered. C.W. Tang and coworkers developed and demonstrated efficient organic EL diodes in 1987. The advent of EL coupled with polymers began as early as 1990. The discovery of this new light-emitting potential attracted attention for large area display technologies because of the low-cost issues, low drive voltages, and the variety of colors available.17
Description
LEP's are an organic polymer material that emits light when a voltage is applied to electrodes on both sides of the material. They produce their own light, in contrast to LCD's needing their own backlit source. 18 These plastics can glow in a variety of colors by using very little power, which makes them an obvious advantage over conventional lighting. Due to the fact that they are a plastic material, they are very flexible, to the point that they can bend around corners and are able to stretch to a degree. This opens up entirely new possibilities in the areas of lighting and display; and specifically in the area of wearable computing. 19
Present/Potential Applications
Due to the effectual 'newness' of this technology, the applications are more or less 'projected' (i.e.: potential) as opposed to 'present'. It is speculated that LEP's could be found in such areas as printers, cell phones, and PalmPilots. As mentioned above, the area of wearable computing has obvious interest in a light-emitting material that if flexible. It can be assumed that any flat display which harbors its marketability on the ability to produce thinner and lighter products (i.e.: laptop computers) would be interested. The idea that it produces a glowing light also suggests the potential for Light-Emitting Polymers to be found in homes or offices in lighting devices, or even on entire walls. The desire to find the means to produce the same light intensity with less power consumption makes LEP's an obvious viable future possibility.
BIBLIOGRAPHY - LCD’s & LED’s & others...
LCD
http://www.gsd.harvard.edu/~newtech
lecture/presentation information on various display technologies in general http://www.refr-spd.com/article.html
more general information about Suspended Particle Displays http://news.laboratorynetwork.com/industry-news/19990422-588135160.html
article on Three-Five Systems work with LCD technology
http://www.threefive.com/
home page for Three-Five Systems company - largest manufacturer of LCD’s and have an
R&D lab
http://news.laboratorynetwork.com/industry-news/19990216-5791.html
article on new materials that create circular polarized light in relation to latest
technologies with LCD’s and efficiency
http://news.laboratorynetwork.com/industry-news/19990121-1985.html
article on latest market growth in relation to LCD technology
LED
http://news.laboratorynetwork.com/industry-news/19990127-2861.html
article on white light LED’s - next generation in lighting (GE Lighting) will
replace current conventional lighting - much more efficient and cost effective http://news.laboratorynetwork.com/industry-news/19981130-5245.html
article on LED’s and Siemans; provides some history/background information http://news.laboratorynetwork.com/industry-news/1999218-7926.html
article on new technology in relation to LED’s - claim will replace LED’s -
‘lasing’ light http://news.laboratorynetwork.com/industry-news/19990121-1985.html
article on latest market growth in relation to LCD technology http://news.laboratorynetwork.com/industry-news/19990118-473.html
article on photonic crystals being used with LED’s; interesting information on the
future
of light in relation to information transmission.
http://gilway.com/leds_dw.html
company web page
http://kingbright-led.com/
company web page
LEP
http://news.laboratorynetwork.com/industry-news/19990208-4438.html
article on latest discoveries with blue-light emitting polymers by Cambridge Display
Technologies; opens up many possibilities
http://news.laboratorynetwork.com/industry-news/19990422-346.html
provides general information about LEP’s and their future applications http://news.laboratorynetwork.com/industry-news/19990610-4745.html
provides general information about LEP’s and future applications
OLED
http://news.laboratorynetwork.com/industry-news/1999112-636.html
article on Organic Light Emitting Displays on background information and applications
SSD
http://news.laboratorynetwork.com/industry-news/19990205-4323.html
provides information regarding Solid State Displays in terms of advantages and
applications
ARTICLES:
‘Displaying a Wining Glow’ Technology Review;
Kenward, Michael. Jan-Feb 1999.
‘New Design Technologies’ Information Display; Apr-May 1996.
‘Suspended Particle Devices’ Saxe, Robert & Thompson, Robert. Science;
Janekhe, Samson & Chen, Linda. Jan. 15, 1999. Nature; Katsis, Dimitris. Feb.
11, 1999.
COMPANIES:
Cambridge Display Technologies (CDT) (LEP)
(+44) 1223-276351
GE Lighting & Emcore Corp. (LED)
216.266.2185 Siemans (LED)
408.777.4546 Three-Five Systems (LCD)
602.389.8835
http://www.threefive.com/ Kaiser Electronics,
Silicon Valley (LCD)
716.275.7954 716.275.0909 DisplaySearch Austin, TX (LCD)
512.459.3128 512.459.3126 Westain Display Technology, Inc. Toronto, CA (SSD)
416.246.1030 ext. 223
ENDNOTES
1 R.L. Saxe, R.I. Thompson, "Suspended Particle
Devices", Information Display; April/May 1996.
2 M. Addington, New Technologies and Materials lecture presentation.
3 M. Addington, New Technologies and Materials lecture
presentation.
4 Article at http://news.laboratorynetworks.com/industry-news/19990208-4438.html/
5 M. Addington, New Technologies and Materials lecture presentation.
6 Article at http://news.laboratorynetworks.com/industry-news/19990216-5791.html/
7Article at http://news.laboratorynetworks.com/industry-news/19990121-1985.html/
8 Gage, S,; Evans, D.; Hodapp, M.; Sorensen, H.; Optoelectronics
Applications Manual, McGraw-Hill Book Company, New York:1977. pg. 1.1.
9 Gage, S,; Evans, D.; Hodapp, M.; Sorensen, H.; Optoelectronics
Applications Manual, McGraw-Hill Book Company, New York:1977. pg. 1.1.
10 Article at http://news.laboratorynetworks.com/industry-news/19981130-5245.html/
11 Article at http://news.laboratorynetworks.com/industry-news/19990127-2861.html/
12 Article at http://news.laboratorynetworks.com/industry-news/19990127-2861.html/
13 Article at http://news.laboratorynetworks.com/industry-news/19990127-2861.html/
14 Article at http://news.laboratorynetworks.com/industry-news/19990118-1473.html/
15 Article at http://news.laboratorynetworks.com/industry-news/19990118-1473.html/
16 Article at http://news.laboratorynetworks.com/industry-news/19981218-7926.html/
17 An, H.; Xue, S.; Chen, B.; Hou, J.; Huang, J.; Liu, S.; Yu, J.;
"Blue-Emission Dye Doped Polymer-Based Electroluminescent Devices for Display".
Display Devices and Systems, SPIE Publishing, Bellingham, WA:1996.
18 Article at http://news.laboratorynetworks.com/industry-news/19990422-346.html/
19 Article at
http://news.laboratorynetworks.com/industry-news/19990610-4745.html/