gvkumar05@gmail.com

FLEXIBLE SCREEN TECHNOLOGY

Presenting by

G.VIJAY KUMAR K.PAVAN KUMAR

09AM1A04A8 09AM1A0465

3-2 SEMISTER 3-2 SEMISTER

8886992600 9703035470

gvkumar05@gmail.com pa1kumar465@gmial.com

AVR&SVR COLLEGE OF ENGINEERING AND TECHNOLGY

NANDYAL

KURNOOL (DIST)

Flexible screen technology is totally depends on A flexible organic light emitting diode (FOLED) is a type of organic light emitting diode (OLED) incorporating a flexible plastic substrate on which the electroluminescent organic semiconductor is deposited. This enables the device to be bent or rolled while still operating. Currently the focus of research in industrial and academic groups, flexible OLEDs form one method of fabricating a IC The flexible displays offer benefits of being light weight, robust, bendable, and thereby offer unique advantages over conventional display technology. Before the flexible displays enter the markets, the ancillary electronics needs to be flexible as well. This article gives an introduction and an overview to flexible electronic backplanes, which are used to control and drive the flexible displays. The market interest for flexible from their properties of being light-weight, thin, bendable and enduring against mechanical impact. In comparison to the conventional rigid glass substrates, use of flexible substrates gives freedom to the backplane manufacturing technology. Current approach to realise them is based on conventional processing methods, such as photolithography, vacuum processing and etching steps. However, the fabrication method can also be based on printing, which is a large-area and low-cost technology and thereby a natural choice for the flexible display applicationA flexible, shock-resistant, and lightweight Braille sheet display has been successfully manufactured on a plastic film by integrating a plastic sheet actuator array with a high-quality organic transistor active matrix. This is the first demonstration, to the best of our knowledge, to integrate plastic MEM (micro electro mechanical systems) actuators

with organic transistor active matrices, which opens up new versatile possibilities for flexible, large-area electronic applications including tactile displays.

INTRODUCTION

The novel and truly exciting features of Universal Display’s proprietary FOLED® flexible technology have the potential to engender a wide variety of new display and lighting products. With FOLED technology still under development today, the first commercial FOLED displays are targeted for use in portable electronics and lighting tiles – leveraging their advantages in ruggedness, thinness and light weight. Based on Universal Display's FOLED technology roadmap, the next generation of FOLEDs may provide added functionality through increased conformability. This feature may open up a wide range of new product opportunities – ranging from new shaped cell phone designs to novel communication devices that are wearable, for example, on the cuff of your shirtsleeve or your backpack.

Continued progress in Universal Display's FOLED roadmap may, then, enable the realization of Universal Display’s innovative product concept, the Universal Communication Device (UCD). Envisioned as a truly portable, cell phone-like communication device, the UCD is designed to offer advanced voice and data

communication capabilities – via a roll-out, full-color, full-motion video display that’s as flexible as it is energy-efficient.

Additional product ideas based on our FOLED technology (and TOLED transparent OLED technology) include:

· Foldable, electronic, daily-refreshable newspapers

· Ultra-lightweight and thin, wall-size television monitors

· Curved, high-contrast automotive instrumentation displays

· Heads-up instrumentation for aircraft and automotive windshields

· Office windows, walls and partitions that double as computer screens

· Color-changing lighting panels and light walls for home and office

With FOLED technology development advancing well, initial flexible OLED products may be ready for the market as soon as within the next few years. With continued product innovation enabled by these new FOLED performance features, we believe that the potential may be much greater

WORKING PRINCIPLE

Schematic of a belayed OLED: 1. Cathode (−) 2.emissive layer 3.emmission of radiation 4.conductive layer 5.anode (+)

A typical OLED is composed of a layer of organic materials situated between two electrodes, the anode and cathode all deposited on a substrate. The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over all or part of the molecule. These materials have conductivity levels ranging from insulators to conductors, and therefore are considered organic semiconductors. The highest occupied and lowest unoccupied molecular orbital’s HOMO and LUMO of organic semiconductors are analogous to the valence and conduction bands of inorganic semiconductors.

Originally, the most basic polymer OLEDs consisted of a single organic layer. One example was the first light-emitting device synthesized by J. H. Burroughs et al., which involved a single layer of however multilayer OLEDs can be fabricated with two or more layers in order to improve device efficiency. As well as conductive properties, different materials may be chosen to aid charge injection at electrodes by providing a more gradual

electronic profile, or block a charge from reaching the opposite electrode and being wasted. Many modern OLEDs incorporate a simple belayed structure, consisting of a conductive layer and an emissive layer. More recent developments in OLED architecture improve quantum efficiency (up to 19%) by using a graded hetero junction. In the graded hetero junction architecture, the composition of hole and electron-transport materials varies continuously within the emissive layer with a do pant emitter. The graded hetero junction architecture combines the benefits of both conventional architectures by improving charge injection while simultaneously balancing charge transport within the emissive region.

During operation, a voltage is applied across the OLED such that the anode is positive with respect to the cathode. A current of electrons flows through the device from cathode to anode, as electrons are injected into the LUMO of the organic layer at the cathode and withdrawn from the HOMO at the anode. This latter process may also be described as the injection of electron holes into the HOMO. Electrostatic forces bring the electrons and the holes towards each other and they recombine forming an exaction, a bound state of the electron and hole. This happens closer to the emissive layer, because in organic semiconductors holes are generally more mobile than electrons. The decay of this excited state results in a relaxation of the energy levels of the electron, accompanied by emission of radiation whose frequency is in the visible region. The frequency of this radiation depends on the band gap of the material, in this case the difference in energy between the HOMO and LUMO.

As electrons and holes are fermions with half integer spin, an exaction may either be in a state or a triplet state depending on how the spins of the electron and hole have been combined. Statistically three triplet exactions will be formed for each singlet exaction. Decay from triplet states phosphorescence is spin forbidden, increasing the timescale of the transition and limiting the internal efficiency of fluorescent devices. Phosphorescent organic light-emitting diodes make use of spin–orbit interactions to facilitate intersystem crossing between singlet and triplet states, thus obtaining emission from both singlet and triplet states and improving the internal efficiency.

Indium tin oxide (ITO) is commonly used as the anode material. It is transparent to visible light and has a high work function which promotes injection of holes into the HOMO level of the organic layer. A typical conductive layer may consist of PEDOT as the HOMO level of this material generally lies between the work function of ITO and the HOMO of other commonly used polymers, reducing the energy barriers for hole injection. Metals such as barium and calcium are often used for the cathode as they have low work functions which promote injection of electrons into the LUMO of the organic layer. Such metals are reactive, so require a capping layer of aluminums to avoid degradation.

Single carrier devices are typically used to study the kinetics and charge transport mechanisms

of an organic material and can be useful when trying to study energy transfer processes. As current through the device is composed of only one type of charge carrier, either electrons or holes,

Now for those of you who are still confused about OLEDs; it is a display technology just like LCDs, LEDs that you find on television, mobile and other display panels. But, what differentiates OLED from all the other display technologies is that it is made up of organic compounds, which are biodegradable and hence are completely eco friendly and safe. OLED displays are principally categorized under two types; those that are made of small molecules and the ones made out of polymers of organic compounds.

One of the best features of OLED is that they do not require a back light as all the other display technologies , this means you will get the deepest black levels, higher brightness, and deeper contrast ratio. The absence of back light also makes OLEDs thinner and flexible and this has lots of implications in making the future displays as thin as a plastic sheet can be and that has is unfathomable at this point of time.

ADVANTAGES

. Light weight and flexible plastic substrates

OLEDs also offer the advantage of fabricating them on plastic sheet like substrates, which will enable engineers to create flexible roll-up displays that can be embedded on fabrics, clothing and newspaper like displays, creating a world of colorful displays as you probably would have seen in Sci-Fi movies.

c. Wider viewing angles and improved brightness

OLEDs provide widest viewing angles possible on displays, up to 90 degrees without any shift of image with improved brightness and correct image reproduction.

d. Better power efficiency

They are extremely energy efficient as they do not require a back-light to illuminate light.

e. Response time

They offer an amazing response time of less than 0.01 ms enabling a 100, 000 Hz refresh rate possible.

DISADVANTAGES

Current costs

OLED technology has not completely come of age and is yet to be mass produced and its manufacturing cost is equal to that of a standard LCD. This makes it expensive to produce at the current market scenario and makes it more expensive than LCDs.

b. Lifespan

A major concern that plagues OLED displays is their lifespan. As any organic substance would do, they decay with time and they decay faster than LCD and other types of display

technologies. Though this is expected to be addressed and future OLEDs will have better lifespan than LCD and LED displays, the current set of OLED displays have a shorter lifespan than LCDs.

c. Color balance issues

Another issues faced by OLED displays is uneven color balance over a period of time as the OLED material that produces blue color tends to degrade faster than other colors and this leads to differential color output with time and unnatural color saturation.

d. Efficiency of blue OLEDs

The success of OLED display technology greatly depends on the lifetime and efficiency of blue OLEDs. It is imperative to create more efficient and deeper blue OLEDs.

e. Outdoor performance

OLEDs suffer greatly in their outdoor screen performance under the bright sunlight as they are more reflective in nature than LCD and other display technologies.

f. Power consumption

The OLED consumes about 40 percent more power than an LCD would consume to display darker objects, which jumps to 80 percent for regular images, but when it comes to a white background, an OLED can consume as much as 2 - 3 times more power than that of a regular LCD.