OLED

Today i was chatting with my friend about the various options available in market for mobile phones.The conversation curved its way to the latest T.V (led t.v) and finally halted upon AMOLED screen of GALAXY S2.It halted as we both had no stuff to discuss on it.Hope reading this article somewhat makes you understand OLED (AMOLED)

                                                                        OLED

INTRODUCTION

OLED’s are simple solid-state devices (more of an LED) comprised of very thin films of organic compounds in the electro-luminescent layer. These organic compounds have a special property of creating light when electricity is applied to it. The organic compounds are designed to be in between two electrodes. Out of these one of the electrodes should be transparent. The result is a very bright and crispy display with power consumption lesser than the usual LCD and LED

HISTORY

The discovery of the electroluminescence property in organic materials in 1950s is considered to be the stepping stone of OLED.The first proper OLED was manufactured in 1980 by Dr. Ching W Tang and Steven Van Slyke. The OLED had a double layer structure. When the holes and electrons were transported separately and when combined together produced a light in the organic layer centre. This light was produced at a very low operating voltage with high efficiency. Now more research is being done with the application of OLED on polymer so as to obtain a higher efficiency OLED.

COMPONENTS

The components in an OLED differ according to the number of layers of the organic material. There is a basic single layer OLED, two layer and also three layer OLED’s. As the number of layers increase the efficiency of the device also increases. The increase in layers also helps in injecting charges at the electrodes and thus helps in blocking a charge from being dumped after reaching the opposite electrode.

An OLED consists of the following parts:

• Substrate (clear plastic, glass, foil) - The substrate supports the OLED.
• Anode (transparent) - The anode removes electrons (adds electron "holes") when a current flows through the device.
• Organic layers - These layers are made of organic molecules or polymers.
  • Conducting layer - This layer is made of organic plastic molecules that transport "holes" from the anode. One conducting polymer used in OLEDs is polyaniline.
  • Emissive layer - This layer is made of organic plastic molecules (different ones from the conducting layer) that transport electrons from the cathode; this is where light is made. One polymer used in the emissive layer is polyfluorene.
• Cathode (may or may not be transparent depending on the type of OLED) - The cathode injects electrons when a current flows through the device.

WORKING

OLEDs emit light in a similar manner to LEDs, through a process called electrophosphorescence.

The process is as follows:

1. The battery or power supply of the device containing the OLED applies a voltage across the OLED.
2. An electrical current flows from the cathode to the anode through the organic layers (an electrical current is a flow of electrons).
   • The cathode gives electrons to the emissive layer of organic molecules.
   • The anode removes electrons from the conductive layer of organic molecules. (This is the equivalent to giving electron holes to the conductive layer.)
3. At the boundary between the emissive and the conductive layers, electrons find electron holes.
   • When an electron finds an electron hole, the electron fills the hole (it falls into an energy level of the atom that's missing an electron).
   • When this happens, the electron gives up energy in the form of a photon of light 
4. The OLED emits light.
5. The color of the light depends on the type of organic molecule in the emissive layer. Manufacturers place several types of organic films on the same OLED to make color displays.
6. The intensity or brightness of the light depends on the amount of electrical current applied: the more current, the brighter the light.

Different types of OLED’s

According to the type of manufacture and the nature of their use, OLED’s are mainly classified into 8 types. They are

1. Active Matrix OLED (AMOLED)

This type of OLED is suitable for high resolution and large size display. Though the manufacturing process is the same, the anode layers have a Thin-film transistor (TFT) plane in parallel to it so as to form a matrix. This helps in switching each pixel to it’s on or off state as desired, thus forming an image. This is the least power consuming type among others and also has quicker refresh rates which makes them suitable for video as well.

2. Passive Matrix OLED (PMOLED)

The design of this type of OLED makes them more suitable for small screen devices like cell phones, MP3 players and so on. Though this type is less power consuming than an LCD and LED (even if connected to other external circuitry’s), it is the most power consuming comparative to other OLED’s. This type is very easy to make as strips of anode and cathode are kept perpendicular to each other. When they are both intersected light is produced. As there are strips of anode and cathode, current is applied to the selected strips and is applied to them. This helps in determining the on or off pixels.

3. Inverted OLED

This type uses a bottom cathode, which is connected to the drain end of an n-channel TFT backplane. This method is usually used for producing low cost OLED with little applications.

4. Foldable OLED

This type is mainly used in devices which have more chance of breaking. As this material is strong it reduces breakage and therefore is used in cell phones, computer chips, GPS devices and PDA’s. They are also flexible, durable and lightweight. As its name explains, these OLED’s are foldable and can also be connected to clothes. They use different types of substrates like flexible metallic foils, plastics and so on.

5. Top Emitting OLED

This type of OLED is integrated with a transistor backplane that is not transparent. Such devices are suitable for matrix applications like smart cards. The substrate used for this device is of the opaque/reflective type. As a transparent substrate is used the electrode used is either semi-transparent or fully transparent. Otherwise the light will not pass through the transparent substrate.

6. Transparent OLED

This device has a good contrast even in bright sunlight so it is applicable in head-up displays, mobile phones, smart windows and so on. In this device, the entire anode, cathode and the substrate are transparent. When they are in the off position, they become almost completely transparent as their substrate. This type of OLED can be included in both the active and passive matrix categories. As they have transparent parameters on both the sides, they can create displays that are top as well as bottom emitting.

7. White OLED

This device creates the brightest light of all. They are manufactured in large sheets. Thus they can easily replace fluorescent lamps. They are also cost-effective and also consumes less power.

8. Stacked OLED

This device uses the composite colours as sub pixels and also on top of each other. This causes the reduction in pixel gap and also an increase in colour depth. Thus they are being introduced as television displays.

Advantages of OLED’s

• The manufacture of OLEDD is highly economical and is more efficient than LCD and flat panel screens.
• It will be a great surprise to see displays on our clothing and fabrics. This technology will help in carrying huge displays in our hands.
• There is much difference in watching a high-definition TV to a OLED display. As the contrast ratio of OLED is very high (even in dark conditions), it can be watched from an angle of about 90 degrees without any difficulty.
• No backlight is produced by this device and the power consumption is also very less.
• OLED has a refresh rate of 100,000 Hz which is almost 9900 HZ greater than an LCD display.
• The response time is less than 0.01 ms. LCD needs a response time of 1 ms.

Disadvantages of OLED

• The power consumption of this device depends upon the colour that is displayed on the screen. Less than 50% power is only consumed when a black image is displayed, compared to an LCD. But the percentage increases to almost three times when a bright image such as a white colour is displayed. Thus, this device is disadvantageous for mobile applications.
• The OLED technology is only rising and due to this, the commercial availability of OLED products are very less. Though they can be easily made the fabrication process is considered expensive and thus the initial amount is expensive.
• As there is no reflective light technology used in such a device it has a very poor reading effect in bright light surroundings. Even if this is to be overcome additional power should be used.
• With time, the brightness of the OLED pixels will fade.
• The images displayed in this device are created by an artificial light source. So, the whole electricity has to be used to perform such an operation. LCD’s, on the other hand use some percentage of light from sunlight and also e-ink.
• The device is not at all water resistant.
• The lifetime of this device is much lesser when compared with an LCD or LED.

Applications of OLED

OLED’s are used as mobile phone screens, MP3 players, digital cameras, car radios, PDA’s and so on.

Hope you found it interesting!!

Again have prepared a presentation have a look at it.  Presentation

References

http://www.circuitstoday.com/workng-of-organic-led-oled

http://en.wikipedia.org/wiki/Organic_light-emitting_diode

http://www.oled-a.org

Working of Touch Screens

Hello!!!
Its been almost a year that am using Nokia X6 a touch-screen phone.Lately entering into Third Year of Electronics Engineering i really marveled at the technology in my touch!! I then boarded my surfing-board and started a quest to find the truth!! It really marveled me hope it does same to you too..

                                                         TOUCH-SCREENS 


A touch screen contains a visual display area which can be sensitive to the touch of our finger or other passive components. A touch screen is only called so if the contact made with it is physical in nature. The common physical contacts made for a touch screen technology is the use of fingers or a pen. If the contact is made with an active component such as a light pen, they cannot be called a touch screen.

Emergence of Touch Screen Technology

The first touch screen enabled brand was the HP-150 computer released in the year 1983. Though it did not have the same features as the new ones, it had a 9-inch CRT screen which was surrounded by transmitters and receivers. These transmitters and receivers were used to detect the precise position of the non-transparent objects on the screen. Though the technology was invented during the end of 1960’s they were only used in computer assisted learning terminals during the year 1972.

During that time, the technology was only developed to sense the availability of one point of contact at a time. This technology has further been moved to ones having multi-touch screen pads. In the beginning, the touch screen technology was not made in chips or mother-boards. They were made as separate components by after-market system integrators.

Touch Screen – Construction and Working

In the construction of a touch screen there are some parameters that have to be fulfilled. They are

• The recognition of the touch on the display [including multi-touch].
• Mechanism to find out the location of the display and to carry on the appropriate command.

touch screen interfacing

The most commonly used technologies are the resistive and capacitive sensing technologies [Both are explained below in detail]. For both these methods a touch screen should have four layers.

• A conducting metal coating with a poly-ester coating on the top. The metal coating should be transparent in nature.
• A spacing layer which is mostly an air-gap.
• A glass layer beneath the spacing with a conducting transparent coating on its top.
• An adhesive layer beneath the glass layer. This layer is mostly used for mounting purposes.

When a person presses his finger on the top of the screen, there will be a change in the electrical current in the display module. This change is measured in either ways explained below and the exact location of touch and the amount of force applied is calculated. Later, the command to be carried out is passed on to the operating system and the command is carried out.

Types of Touch Screen Technology

1. Resistive Touch Screen Technology

This type of a touch screen uses two layers that are coated with a resistive and a conductive material. These two layers are separated from each other with the help of an air gap or spacers.   On top of the whole mechanism will be a layer to provide resistance to scratches. The monitor of the display is made operational in nature. Thus, when our finger touches the screen, a contact is made between the two layers and current flows through them. As the layers make contact at the same point, the correct location of the point is noted. The location is calculated by the computer in course of the change in the electric field occurred by our touch. Thus when the position is known, it is passed on to a driver in the device which codes it and sends it to the OS of the device.

This technology can be used with the contact of any object like finger, pen, and stylus and so on. Thus it is also considered as a passive technology.

Advantages

• They are very accurate and can be used for high resolutions up to 4096X4096 dpi.
• Very cost effective in comparison with other technologies.
• It can also be used in multiple touch screen pads.
• It can transmit almost 75% of the light from the monitor.

Disadvantages

As the device is also used as a passive technology there will be problems regarding hand written notes taken on a stylus. As the person cannot use a whole hand down on the screen while he is writing there has to be a trade-off between the property of using a finger as a stylus and the pressing of a whole hand on the screen.

Capacitive Sensing Technology

This is one of the most widely used techniques for touch screens. This technology is based on the capacitor coupling effects. It has been used in devices like MP3 players, computer monitors, mobile phone displays and so on. As this technology has advantages like detecting the correct position at a very small time, less cost in production, and also a very unique human—device interface, it is widely used. It also has properties like multiple touch sensing and also gesture based touch screens. The latest and most famous gadget to be released with this technology is the Apple i-Pod click wheel. This mechanism is more advantageous than the resistive sensing because it can transmit to a maximum of 90% of the light from the monitor. Thus a much better vision can be obtained from these screens.

Here also, a glass panel is arranged on top of which a layer that is able to store electrical charge is kept. When the monitor is touched by the user, the charge begins to move from the layer to our body. This decrease in the charge on the conductive layer is measured with the help of electronic circuits which are placed inside the monitor. As the electronic circuits are placed on each corner of the monitor the difference in charge attained at each corner is calculated by the computer and the exact position of the touch is obtained. This information is then passed on to the touch-screen driver software.

Surface Acoustic Wave Technology

In this technology the use of ultrasonic waves are adapted. A glass plate is taken and two transducers are placed on the x and y axes of it. One transducer is used for sending the signal and the other is used for the reception. The glass plates will also have reflectors setup on them. These reflectors are used to reflect the electrical signal from one transducer to another. Thus when we touch the touch screen, there will be a difference in the wave and this difference will be understood by the receiving transducer. Thus, the exact position of the touch is calculated. This is the most efficient technology when compared to capacitive and resistive sensing as 100% of the light is transmitted from the monitor. Thus the screen clarity will be the highest.

This advantage makes way for this technique to be used in high end graphics devices. The disadvantages are that even a slight scratch on the surface can cause the damage of the screens. Dust and other contaminations can cause the change of its functions.

Strain Gauge

With this technology, strain gauges are mounted on the four corners of the screen. As soon as the screen is touched, a deflection occurs which is picked up by the strain gauge. This device can also be used for the measurement of the Z-axis and also the amount of force exerted while touching the screen.  The main application of such screens is in devices like ticket machines.

Optical Imaging Technique

This is the most modern technique used in touch screens. It consists of a number of image sensors that are kept on the four corners of the screen. A field of infrared lights are set inside the monitor. When a person touches the screen, a shadow will build up which will be received by the sensors. This is more than enough for the sensors to calculate the exact location of the touch and also the size of the object that touched the screen.

These days we all long for a touch screen phone....Hope now you can differentiate and bargain for a better touch-screen!!

Prepared a presentation to cover up in a zyst...
presentation touchscreen

Link no 3 gives a lot of details..

References

1.http://en.wikipedia.org/wiki/Touchscreen

2.http://en.wikipedia.org/wiki/Capacitive_sensing

3.http://www.digikey.com/Web%20Export/Supplier%20Content/Bergquist_211/PDF/Bergquist_TS_DataSheets.pdf?redirected=1

Green Lasers

Hello!!!
Jus surfing thru the net i today found a phrase GREEN LASER..First i associated it with somethin like environment friendly laser...but reading on found it interesting so sharin it with you...


                Green Lasers Overcome Last Barrier to Brilliant displays



Solidstate lasers can produce light in red and blue parts of the visible spectrum, generating laser light in all colours except green. But recent research work suggests that this ‘green gap’ could be plugged. New techniques for growing laser diodes could soon make brilliant fullspectrum displays a reality.Plugging the green gap in the redgreen-blue triad needed for full-colour laser projection and display would help speed the introduction of laser projectors for televisions and movietheatres, which will display much richer colours than other systems, and tiny handheld projectors as in cellphones.High-power green diodes might be employed in such applications as DNA sequencing, industrial process control and underwater communications.

The familiar green laser pointers used by lecturers employ a complicated two-step process to generate light. Semiconductor lasers inside these devices emit infrared radiation having a wavelength of around 1060 nanometres.This radiation then pumps a crystal that oscillates at half this wavelength—530 nanometres, which corresponds to green part of the spectrum. The process is costly, inefficient and imprecise; the second crystal can heat up, altering the wavelength of the resultant green light. Lasers that generate green light directly would avoid this problem.


Multiquantum-well fundamentals

Fig 1

Fig.1 shows the scheme of a homojunction laser where a single p-n junction is formed from only a singlecrystal semiconductor material. There is a highly reflective surface at one end and a partially reflective surface at the other end. The p-n junction is forward-biased by an external voltage source. As electrons move through the junction, recombination occurs just as in an ordinary LED light emitter. To achieve laser action, it is necessary to contain photons within the laser medium and maintain the conditions for coherence. The optical cavity,as shown in Fig.1,is known as Fabry-Perot cavity and provides positive feedback of the photons by reflection at the mirrors at either end of the cavity emitting coherent light. However, the radiative properties of a laser may be improved greatly by using heterojunctions instead of homojunctions. A heterojunction is an interface between two adjoining singlecrystal semiconductors with different bandgap energies.

Recently, double-heterojunction lasers have been fabricated with an active layer as thin as 2 nm instead of

MQW

0.1 to 0.3 µm of conventional doubleheterojunction structure. These devices are known as quantum-well lasers.In  multiquantum well (MQW) lasers, a number of such quantum wells are provided. In MQWs corresponding to multiple active layers,layers separating the active regions are called barriers. Carrier motion normal to the active layer in these devices is restricted, resulting in quantisation of the kinetic energy into discrete energy levels for the carriers moving in that direction. Due to this reason, the thin active layer causes drastic changes in electronic and optical properties in comparison with a conventional double-heterojunction laser.MQW devices score over conventional double-heterojunction lasers due to their lower threshold currents, narrower line-widths, higher modulation speeds, lower frequency chirps and lesser temperature dependence.

Green gap problem 
Scientists have long been able to build semiconductor lasers that produce light in red parts of the spectrum. In
the last decade, they conquered the blue and violet sections as well. As they try to push these lasers in the green part of the spectrum, the amount of power produced drops drastically .In the new approach, an exceedingly smooth, nanometres-thin layer of indium gallium nitride (InGaN) is sandwiched between two layers of GaN, forming the so-called heterostructure or quantum well (MQW fig). By applying a suitable voltage, an electric field is set up perpendicular to these layers.The electric field drives electrons and holes—positively charged particles that are devoid of electrons—together within the InGaN layers. Inside the
narrow central active layers ,the electrons and holes recombine, annihilating one another and generating
photons with an energy precisely determined by the properties of the active semiconductor material (Fig.MQW).By increasing the indium concentration in the alloy,one can lower this energy,thereby increasing the wavelength of the light and changing its colour from violet to blue to green.But, there is a flaw—the more the indium in these active layers, the more the likelihood of it pooling into small ‘islands’ during manufacture. The islands can alter the wavelength of light—an unacceptable flaw in laser

On either side of the InGaN active layer is a GaN barrier layer. GaN layer acting as an optical waveguide above the substrate is doped with silicon impurities to produce an excess of electrons. On the other end, GaN is doped with magnesium to give it an excess of ‘holes’ or positive charges. It also acts as an optical waveguide.The total optical thickness of the cavity is about 23.5λ, where ‘λ’ is the designed wavelength.

Fig 4 Crystal plane of substrate

In LEDs, the photons leave the well almost immediately, perhaps rebounding once or twice before exiting the device or being absorbed in other layers. But in laser diodes, which produce coherent light, the photons stay largely confined within the trench.Two highly reflective mirrors—generally polished crystal surfaces at either end of it—recycle the photons back and forth inside, further stimulating electron-hole recombination. The laser light generated by this ‘stimulated emission’ process is a tight pencil beam of exceedingly pure colour.
Initially, the scientists tried to produce green lasers by depositing layers of semiconducting materials parallely with sapphire substrate’s ‘c’-plane, which is perpendicular to the crystal’s axis of hexagonal symmetry     (Fig. 4). Unfortunately, electrostatic forces and internal stresses between successive layers of positively charged gallium or indium ions and negatively charged nitrogen ions create strong electric fields perpendicular to the ‘c’-plane. These fields, which can reach up to 100 volts per micron, counteract the applied external voltage. They pull electrons away from holes, making it harder for them to recombine and produce
light. As a result, the electrons pile up at one side of the central active layer and holes at the other end, both reluctant to cross over and recombine. The problem worsens as the wavelength shifts towards green from the violet-blue spectrum. This effect is known as quantum-confined Stark effect. And as the current through the
diode increases, the greater number of charge carriers partially blocks the internal electric fields that keep electrons and holes apart. With these fields partially screened out, electrons and holes then recombine at higher energies, shifting the light towards the blue end of the spectrum.These problems are the main reason why green laser diodes and  high-efficiency green LEDs could not be made.
Solution to green gap problem
To f ind a solution to this problem, scientists replaced the sapphire substrate with a thin wafer of pure, crystalline GaN that was sliced along a larger crystal’s ‘m’-plane as shown in Fig. 4 and then polished. Diodes fabricated on these non-polar substrates do not encounter the problems of
conventional polar ‘c’-plane devices, because the troublesome fields caused by polarisation and internal stresses are much lower. Diodes grown on GaN also produce light more efficiently than one grown on sapphire because they suffer from far fewer crystalline defects, submicroscopic irregularities and mismatches at the interfaces between successive layers. Such defects act as centres where electrons and holes
recombine to produce unwanted heat instead of light. They can easily propagate upward through the successive diode layers during the growth process and reach the active layers. Diodes grown on non-polar GaN substrate can therefore produce much more light and less heat to dispose of.


Applications 
Future models that rely on green lasers for handheld projectors allow for much brighter and efficient displays, and also shrink the projectors enough to allow them to fit inside the cell phone. Inside the laser projector, red, blue and green lasers focus onto a single mirror about the size of a pinhead. As light bounces off the
reflector, the mirror assembly rapidly scans back and forth to project pixels one by one onto a screen or wall. No use of lens means the projector never needs to be focused. The projector has DVD-equivalent resolution of 848×480 pixels



Hope you find it interesting too!!!


References..
http://en.wikipedia.org/wiki/Laser_pointer#Green
http://en.wikipedia.org/wiki/Laser_pointer#Green

Cloun Coumputing

                                      AN INTRODUCTION TO CLOUD COMPUTING


The most happenin topic these days is CLOUD COMPUTING.Google’s chief executive Eric
Schmidt publicly uttered the term‘cloud computing’in
2006. Since then the term has taken technology by a storm.Cloud computing is all the rage now.“It’s become thephrase du jour,” says Gartner’s senior analyst Ben Pring,echoing many others.

To different people there seems to be a different definition of cloud computing. An appropriate definition ,how ever, i s“ Internet-based computing where shared resources,software and information are provided to computers and other devices on demand, like the electricity grid.”

example

Cloud  computing is a harmonised  technology with scalable business policies.It is a versatile and flexible application of the Internet that promises to offer services like that of cloud or sky: anytime, anywhere, by using the Internet and central remote servers to maintain data and applications.Consumers and businesses can use applications without installing any server or software.
Consider examples of hotmail.com, yahoo.com or gmail.com where no installation of server or software is
required. all you need to access them is an Internet connection.:)  The alongside figure shows a good example of cloud computing.


               Benefits of cloud computing

One of the strongest appeals of cloud computing is its ability to contract with an Internet provider for accessing the huge amount of unused or underused computational resources to deliver an amazing ‘bang for the buck’ computing platform with very little capital expenditure but a high-bandwidth link or having to manage information and
communication technology (ICT) infrastructure



A Web definition best suited to the objective of cloud computing is that “It refers to a computing system
in which tasks are assigned through a combination of connections, service and software over a network. This collection of connections is known as ‘the cloud.’ Computing at this level allows users to sort through a vast amount of data. For example, Google is currently the forerunner of cloud computing due to its need to produce accurate and instant results for millions of search queries it receives every day."


Components of cloud

Cloud computing is broken down into three segments:  applications, platforms and infrastructure. Each

EXAMPLE OF COMPONENTS

segment serves a different purpose and offers different products for businesses and individuals around the world. Software as a Service (SaaS) optimises cost and resources, Platform as a Service (PaaS) creates, deploys and secures applications and services, and Infrastructure as a Service (IaaS) selects and commissions a computing infrastructure as a fully outsourced service.Refer the the example shown in image



Way forward
Whether cloud computing is a hype or hope, that’s yet to be ascertained. The challenge is to provide services quickly and cost-effectively.  also in the race are technologies like cluster and grid computing. The three technologies, however, are not fairly distinguishable and which one will emerge as
the winner is not clear. Cloud computing is not immune to risks and ethical objections, but the
fact is that it promises big changes.Leonard Kleinrock, one of the chief scientists at Advanced Research Projects Agency Network (ARPANET) that paved the way for today’s Internet, said in 1969, “as of now, computer networks are still in their infancy, but as they grow up and become sophisticated, we will probably see the spread of ‘computer utilities’ which, like present electric and telephone utilities, will service individual homes and offices across the country.” This vision of the computing utility is taking shape with cloud computing. If the recent market research is any indication, cloud computing may become a billion dollar market by 2012. So we can say that the Internet industry is on the Cloud!



Referencs

http://www.electronicsforu.com/EFYLinux/efyhome/cover/April2011/Cloud-Computing_Apr%2711.pdf
http://en.wikipedia.org/wiki/Cloud_computing
http://www.wikinvest.com/concept/Cloud_Computing