Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Physics Term paper TOPICS:- Liquid crystal display( What are liquid crystals displays, applications of LCD) Submitted to: AMANDEEP SINGH Dept. Of physics LITCA LPU phagwara Submitted By: SUDHANSHU SEKHAR Roll no: B38 Reg. No.: 11009489 Sec: K4002 Batch: B.tech –MBA (ME) Session: 2010-2015 Acknowledgement Gratitude cannot be seen or expressed. It can only be felt in heart and is beyond description. Often words are inadequate to serve as a model of expression of one’s feeling, specially the sense of indebtedness and gratitude to all those who help us in our duty. It is of immense pleasure and profound privilege to express my gratitude and indebtedness along with sincere thanks to Sir AMANDEEP SINGH lecturer of PHYSICS of Lovely Professional University for providing me the opportunity to work for a project on “LCD ”. I am beholden to my family and friends for their blessings and encouragement. Yours obediently, SUDHANSHU SEKHAR CONTENTS INTRODUCTION WHAT IS LCD History of Liquid Crystal Displays – LCD SPECIFICATIONS Types of LCD How an LCD Works Applications of Liquid Crystals LCD Market Trend LCD Technology Advantages of LCDs Disadvantages of LCDs LCD Future Trends Conclusion References INTRODUCTION A liquid crystal display (LCD) is a thin, flat electronic visual display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly. They are used in a wide range of applications including: computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have displaced cathode ray tube (CRT) displays in most applications. They are usually more compact, lightweight, portable, less expensive, more reliable, and easier on the eyes.[citation needed] They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in. LCDs are more energy efficient and offer safer disposal than CRTs. Its low electrical power consumption enables it to be used in battery-poweredelectronic equipment. It is an electronically-modulated optical device made up of any number of pixels filled with liquid crystals and arrayed in front of alight source (backlight) or reflector to produce images in colour or monochrome. Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other. With no liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. The surface of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Electrodes are made of a transparent conductor called Indium Tin Oxide(ITO).Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces. In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. Because the liquid crystal material is birefringent, light passing through one polarizing filter is rotated by the liquid crystal helix as it passes through the liquid crystal layer, allowing it to pass through the second polarized filter. Half of the incident light is absorbed by the first polarizing filter, but otherwise the entire assembly is reasonably transparent.LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are crossed.When a voltage is applied across the electrodes, a torque acts to align the liquid crystal molecules parallel to the electric field, distorting the helical structure (this is resisted by elastic forces since the molecules are constrained at the surfaces). This reduces the rotation of the polarization of the incident light, and the device appears grey. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray. LCD with top polarizer removed from device and placed on top, such that the top and bottom polarizers are parallel. The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case the bright and dark states are reversed WHAT IS LCD A liquid crystal display (LCD) is an electro optical amplitude modulator realized as a thin, flat display device made up of any number of color or monochrome pixels arrayed in front of a light source or reflector. It is often utilized in battery-powered electronic devices because it uses very small amounts of electric power. . Above picture represents us Reflective Twisted Nematic liquid crystal display. The main features of this particular liquid crystal display are as follows:1. Glass substrate with ITOelectrodes. The shapes of these electrodes will determine the shapes that will appear when the LCD is turned ON. Vertical ridges etched on the surface are smooth. With LCD (Liquid Crystal Display) technology it is possible to produce space-saving, flicker-free, low-radiation displays that are easier on the eyes than conventional television or computer monitors. In addition, liquid crystal displays have a sharper picture with greater contrast and they use less power. The function of LCD monitors is always identical. The chromophore pigments are located in a layer that is only a thousandth of a millimeter thick. All of the picture elements, the so-called pixels, are composed of the colors red, green and blue. All shades 2. 3. 4. 5. of color can be produced from these three basic colors. Each color in a pixel is dedicated to a liquid crystal cell, whose transparency can be changed by an applied voltage. If a pixel allows all of the light through, a white picture element appears. A black pixel is seen with total opacity. All other color mixtures and basic colors are possible through partial or complete transparency of the individual liquid crystal cells in a pixel. Twisted nematic liquid crystal. Glass substrate with common electrode film (ITO) with horizontal ridges to line up with the horizontal filter. Polarizing filter film with a horizontal axis to block/pass light. Reflective surface to send light back to viewer. Liquid crystals are substances that exhibit a phase of matter that has properties between those of a conventional liquid, and those of a solid crystal. 6. liquid crystal (LC) may flow like a liquid, but have the molecules in the liquid arranged and/or oriented in a crystal-like way. An example of LCD:LCD monitor Liquid Crystal display or LCD monitor is a thin and flat device for display. It is made by large number of color or monochromatic pixels which are arrayed in way of a light source or a reflector. History of Liquid Crystal Displays – LCD • • • • • Liquid crystals were first discovered in 1888 by Austrian botanist Friedrich Reinitzer. Melt cholesterol-like substance. When cooled, the liquid turned blue before finally crystallizing. RCA made the first experimental LCD in (1968). Manufacturers have been developing creative variations and improvements since on LCDs. LCD Market Trend • • • • • Market for flat screen LCDs grew rapidly during the ‘90s. Huge success of the laptop computer. It has still been slow in matching the market share of the CRT. Color LCDs hit the market in the early ‘90s. Has only now become popular enough for vendors to mass-produce. In 1888, liquid crystals were first discovered in cholesterol extracted from carrots by Austrian botanist and chemist, Friedrich Reinitzer. In 1962, RCA researcher Richard Williams generated stripe-patterns in a thin layer of liquid crystal material by the application of a voltage. This effect is based on an electro-hydrodynamic instability forming what is now called “Williams domains” inside the liquid crystal. According to the IEEE, "Between 1964 and 1968, at the RCA David Sarnoff Research Center in Princeton, New Jersey, a team of engineers and scientists led by George Heilmeier with Louis Zanoni and Lucian Barton, devised a method for electronic control of light reflected from liquid crystals and demonstrated the first liquid crystal display. Their work launched a global industry that now produces millions of LCDs." Heilmeier's liquid crystal displays used what he called DSM or dynamic scattering method, wherein an electrical charge is applied which rearranges the molecules so that they scatter light. The DSM design worked poorly and proved to be too power hungry and was replaced by an improved version, which used the twisted nematic field effect of liquid crystals invented by James Fergason in 1969. Inventor, James Fergason holds some of the fundamental patents in liquid crystal displays filed in the early 1970's, including key US patent number 3,731,986 for "Display Devices Utilizing Liquid Crystal Light Modulation" In 1972, the International Liquid Crystal Company (ILIXCO) owned by James Fergason produced the first modern LCD watch based on James Fergason's patent. In the 4Q of 2007 for the first time LCD surpassed CRT in worldwide sales. In 2008, LCD TVs are the main stream with 50% market share of the 200 million TVs forecast to ship globally in 2008 according to Display Bank SPECIFICATIONS Important factors to consider when evaluating an LCD monitor: Resolution: The horizontal and vertical size expressed in pixels (e.g., 1024x768). Unlike monochrome CRT monitors, LCD monitors have a native-supported resolution for best display effect. Dot pitch: The distance between the centers of two adjacent pixels. The smaller the dot pitch size, the less granularity is present, resulting in a sharper image. Dot pitch may be the same both vertically and horizontally, or different (less common). Viewable size: The size of an LCD panel measured on the diagonal (more specifically known as active display area). Response time: The minimum time necessary to change a pixel's color or brightness. Response time is also divided into rise and fall time. For LCD Monitors, this is measured in btb (black to black) or gtg (gray to gray). These different types of measurements make comparison difficult. Refresh rate: The number of times per second in which the monitor draws the data it is being given. A refresh rate that is too low can cause flickering and will be more noticeable on larger monitors. Many high-end LCD televisions now have a 120 Hz refresh rate (current and former NTSC countries only). This allows for less distortion when movies filmed at 24 frames per second (fps) are viewed due to the elimination of telecine (3:2 pulldown). The rate of 120 was chosen as the least common multiple of 24 fps (cinema) and 30 fps (TV). Matrix type: Active TFT or Passive. Viewing angle: (coll., more specifically known as viewing direction). Color support: How many types of colors are supported (coll., more specifically known as color gamut). Brightness: The amount of light emitted from the display (coll., more specifically known as luminance). Types of LCD Flat panel displays are now challenging CRT as the display of choice in many applications. Liquid Crystal Displays (LCDs), both passive matrix and active matrix technologies have been developed to replace the once CRT dominated displays market. Passive matrix display costs are lower, but their performance is inferior to active matrix. This application note examines the two addressing techniques used in current LCDs. 1.Passive Matrix Passive matrix displays have rows of electrodes on one half of the display glass and columns of electrodes on the other. The electrodes are usually fabricated out of Indium Tin Oxide (ITO), a semi-transparent metal oxide. When the two pieces of glass are assembled into a display, the intersection of a row and column form a pixel element (Figure 1). When a voltage is applied between the two points, the crystal realigns and changes the light transmission properties of the liquid crystal. By repeating this process, scanning through the pixels an image can be formed on the display Problems arise as the number of rows and columns increase. With higher pixel density, the electrode size must be reduced and the amount of voltage necessary to drive the display rapidly increases. The higher driving voltage creates a secondary problem; charging effects. Even though only one row and column are selected, the liquid crystal material near the row and column being charged are affected by the pulse. The net result is the pixel selected is active (dark), but the areas surrounding the addressed point are also partially active (greys). The partially active pixels reduce the display contrast and degrade image quality. This effect is known as cross talk Passive Matrix Addressing 2 Active Matrix Passive matrix displays suffer from fundamental problems leading to poor performance. Matrix addressing solves these problems. By placing an electronic switch device in each LC pixel (Figure 2), controlling the charging of the LC cell to the desired grey level. Figure SUMMARY: Active matrix LCD has been proven to be a superior technology in terms of optical performance; however this comes at a price. Therefore with continued improvement in passive matrix LCD technology and low price compared to AMLCD, passive matrix LCD will continue to be used in many applications and outsell AMLCD for the foreseeable future. How an LCD Works According to a PC world article, liquid crystals are liquid chemicals whose molecules can be aligned precisely when subjected to electrical fields, much in the way metal shavings line up in the field of a magnet. When properly aligned, the liquid crystals allow light to pass through. A simple monochrome LCD display has two sheets of polarizing material with a liquid crystal solution sandwiched between them. Electricity is applied to the solution and causes the crystals to align in patterns. Each crystal, therefore is either opaque or transparent, forming the numbers or text that we can read. Applications of Liquid Crystals Liquid crystal technology has had a major effect many areas of science and engineering, as well as device technology. Applications for this special kind of material are still being discovered and continue to provide effective solutions to many different problems. Liquid Crystal Displays The most common application of liquid crystal technology is liquid crystal displays (LCDs.) This field has grown into a multi-billion dollar industry, and many significant scientific and engineering discoveries have been made. Please refer to the LCD chapter for more detail. Liquid Crystal Thermometers As demonstrated earlier, chiral nematic (cholesteric) liquid crystals reflect light with a wavelength equal to the pitch. Because the pitch is dependent upon temperature, the color reflected also is dependent upon temperature. Liquid crystals make it possible to accurately gauge temperature just by looking at the color of the thermometer. By mixing different compounds, a device for practically any temperature range can be built. The "mood ring", a popular novelty a few years ago, took advantage of the unique ability of the chiral nematic liquid crystal. More important and practical applications have been developed in such diverse areas as medicine and electronics. Special liquid crystal devices can be attached to the skin to show a "map" of temperatures. This is useful because often physical problems, such as tumors, have a different temperature than the surrounding tissue. Liquid crystal temperature sensors can also be used to find bad connections on a circuit board by detecting the characteristic higher temperature. [Collings, 140-142] Optical Imaging An application of liquid crystals that is only now being explored is optical imaging and recording. In this technology, a liquid crystal cell is placed between two layers of photoconductor. Light is applied to the photoconductor, which increases the material's conductivity. This causes an electric field to develop in the liquid crystal corresponding to the intensity of the light. The electric pattern can be transmitted by an electrode, which enables the image to be recorded. This technology is still being developed and is one of the most promising areas of liquid crystal research. Other Liquid Crystal Applications Liquid crystals have a multitude of other uses. They are used for nondestructive mechanical testing of materials under stress. This technique is also used for the visualization of RF (radio frequency) waves in waveguides. They are used in medical applications where, for example, transient pressure transmitted by a walking foot on the ground is measured. Low molar mass (LMM) liquid crystals have applications including erasable optical disks, full color "electronic slides" for computer-aided drawing (CAD), and light modulators for color electronic imaging. LCD Technology • • • • • • • Used for displays in notebooks, small computers, pagers, phones and other instruments. Uses a combination of fluorescent-based backlight, color filters, transistors, and liquid crystal to create and illuminate images. Until recently, was only used on notebook computers and other portable devices. In 1997, manufactures began to offer full size LCD monitors as alternatives to CRT monitors In 1981, IBM introduced the Color Graphics Adapter (CGA) display, able to display 4 colors and max resolution of 320x200. In 1984, Enhanced Graphics Adapter (EGA) display, able to display 16 colors and resolution of 640x350. In 1987, Video Graphics Array (VGA) display. • Most computers today support the VGA standard. • • • • • • • In 1990, Extended Graphics Array (XGA) display, capable of resolutions 800x600 in true color ( 16.8 million colors) and 1024x768 in 65,536 colors. Released in 1977 First true “personal computer” Based on the Apple I design with some additions Plastic case Able to display color graphics Able to display 6 colors at 280x192 resolution. • • • • • • • Developed in late 1970s by Radio Shack. First product in store history to fetch more than $500. Monitor was basically an RCA TV with the tuner removed. Became a direct competitor to the Apple computer. IBM’s 5150 model introduced in 1981. The PC featured a 5-MHz Intel processor, 18K of memory and an optional color monitor. Starting price: $1,565 Advantages of LCDs • • • • Physical Size – Compact and Lightweight – Space saving – Can be mounted on a wall or panel Display Size – Available at comparable in screen size as traditional CRT – Shown on the next slide, a 12.1" LCD display (left) has only a slightly smaller viewing area than a typical 14" CRT monitor. Newer, larger LCD monitors are also appearing that have 15", 17", and even larger screen sizes that are comparable to the largest CRT monitors. (One thing to note is that LCD monitors are typically sized by their actual viewable diagonal measurement, but CRTs typically are not.) Power Consumption and Radiation Emission – Consume less energy and more durable • A typical CRT losses approximately 50% of its brightness after 10,000 hours. An LCD bulb will maintain its brightness anywhere from 25,000 to 50,000 hours. • LCD consumes fewer watts than a CRT. LCD will use an average 30 watts compared to 120 watts for the CRT. • Can reduce electric bill by 40-85%. • Uses a combination of fluorescent-based backlight, color filters, transistors, and liquid crystal to create and illuminate images. It blocks light rather emit light Power Consumption and Radiation Emission – Doest not emit Radiation • • • • – Not subject to Electromagnetic Interference Viewing – Cause less eyestrain – Does not flicker or glare Viewing – Cause less eyestrain – Does not flicker or glare Response Time – Faster response time. Critical to people who watch videos or play games on their PC’s. – The fastest LCD’s offer a response time of about 25 milliseconds as apposed to CRT’s that have a response time of about 13 milliseconds. Response Time – Faster response time. Critical to people who watch videos or play games on their PC’s. – The fastest LCD’s offer a response time of about 25 milliseconds as apposed to CRT’s that have a response time of about 13 milliseconds. Disadvantages of LCDs • • • • Resolution • Displays Native Resolutions (Resolution that it displays best) Viewing Angle • Smaller, needed to be viewed more directly from the front. • From the side the images on an LCD screen can seem to disappear, or invert colors. • Newer displays that are coming out have a wider viewing angle so this is not as much of an issue as it has been in the past. Price • Upfront cost it is more costly but long-term cost but will conserve energy in the long run. • The energy savings may not be much for an individual use, but for a corporate office where 50 displays or more are in use, the energy savings might be more of an issue. Installation • Need a plug interface to connect to the computer. • Some require a special digital plug-interface in order to work . • Problem: is that this plug is not available on most computers, so another video card or adapter must be purchased to plug these LCD monitors into the computer. LCD Future Trends • New Technologies o On-Glass Circuitry unveiled Oct. 22, 2002 The new screens use Sharp’s CGS (continuous grain silicon) Microprocessor circuitry applied directly on the glass, enabling it to function like a computer Produces ultra fine resolutions o ThinCRTs from Candescent Technologies quarter-inch thin form factor: a "thin CRT." Thousands of emitters instead of a single large cathode tube Has the best of both CRTs and LCDs Conclusion From the above detailed explanation about LCD technology I have concluded that LCD is a growing technology . LCD technology will be used in many fields like High Performance LCD Blacklighting using high intensity Red,Green and Blue light emitting Diodes. In future LCD technology will be overcomed by latest DLP technology which is invented by TEXAS INSTRUMENT. As DLP have small package size. DLP consists of one single chip than 3 in LCD Panels.DLP panels are more compact than LCD. DLP can produce higher contrast video with deeper blacklevels than we get in LCD projectors. recognize that the organic compounds in LCD panels and polarizers are susceptible to high heat and light energy stress, and will eventually break down if deployed in high stress environments—in particular 24x7 operation with higher than normal ambient temperatures. Compact portable LCD projectors are in general not recommended for 24x7 duty cycles because of this. On the other hand, DLP technology does not use organic compounds. Thus the elements which can be expected to degrade over time under high stress in an LCD projector do not exist in a DLP projector. Therefore when these two technologies are placed side-by-side in an unusually high stress environment as they were in this test, the DLP-based products should be more resistant to image shift over time. TI's test demonstrated this in no uncertain terms. REFRENCES 1] INTRODUCTIN FROM http://en.wikipedia.org/wiki/Liquid_crystal_display 2] What is LCD?? From www.wikipidia.com 3] LCD History & LCD Market Trend FROM :www.scribd,com 4] Types of LCD from: http://www.hitachi-displays-eu.com/doc/an002_passive_and_active_matrix.pdf 5] Advantages & Disadvantages of LCDs & LCD Future Trends http://www.doxtop.com/browse/aff4ef8d/lcd-monitors---history-and-futuretrends.aspx Help Site: http://www.webopedia.com/TERM/L/LCD.html www.wikipidia.com www.lcdtv.me.uk WWW.GOOGLE.COM from