CHEAH Kok Wai (謝國偉 ) Department of Physics Hong Kong Baptist University 1. Displays of the Future 2. Basic Principles of Flat Panel Display 3. Liquid Crystal Display 4. Organic LED Display 5. Science & Science Fiction Flat Panel Display (FPD) refers to display units that do not have a bulky project unit at the back of the display unit. Bulky display unit is the old television (TV) that was being used from the 1950s to turn of 21st century. FPD is thin and light in comparison to the old TV. This new form factor means can be large (more than 100 inch now). It is now used not only for TV, but used in information display, PC monitor and most critical in mobile communicators/platforms e.g. notebook, mobile phone and tablet. 1950 Television 1990 Television Thin FPD Dynamic display from 1950s to end of 20th century is represented by television, and there is only one television technology - cathode ray tube. In cathode ray tube, electron beam is generated which sweeps a phosphor screen rapidly (faster than your eyes refreshing rate) to give an image. However, the electron beam requires a large travelling distance, so as the size of the screen increases, the TV gets bigger and heavier. Displaying information is an important way to let other people to know what you are doing An example is advertising what you are selling in your shop; what types of goods, their prices etc. However, at the moment most displays for this purpose are static. Dynamic display and interactive display allows a person greater access on selective information. Dynamic display is also more attractive. With transparent display and flexible display or both, the future display form factors can be in many forms. There are several Software and Hardware companies put forward their ideas of future communication. We will show two examples: Microsoft shows how information can be shared and notice the smart table, electronic newspaper (Harry Potter style) and NFC file transfer. Corning (they make glasses e.g. gorilla glass) shows display mirror, augmented reality, lighting control and giant outdoor transparent display. In Microsoft’s view on communication, mobile and desktop systems share files with seamless data transfer. Large transparent displays are everywhere and linked to cloud system making some tasks very smooth and fast e.g. instant translation and animation. Smart working desk/table, with Near Field Contact (NFC) for easy file sharing and transfer. Near Field Contact (NFC) is already being used. Will it emerge as something similar that Microsoft envision? Newspaper that looks similar to that of today is in fact electronic newspaper (where is the battery?) Corning being glass manufacturer focuses on how new types of glass can fit into the future communication. Architectural display glass can be installed everywhere (bedroom, sitting, kitchen, offices…) Theme transfer and not just data transfer and is not just NFC. Most impressive is remote medical consultation coupled with 3-D imaging system. Augmented reality display is major theme. Mood lighting is also featured albeit just slightly. Using shape memory alloy material, a phone can change its shape as and when desired. So the display can curve, or fold as you wish it. Then you can have a large screen that can be folded into your pocket when not in use. Cathode Ray Tube (CRT) started life as glass tube with low pressure gas. This glass tube was used for studying the properties of gas molecules/atoms. That was in 1890s; 19th century! It was soon discovered that it was electron beam that was being emitted from cathode. In fact it is possible to scan out waveforms and graphics by controlling the electron beams. J. J. Thompson who used CRT to discover electrons in1897. He got the Nobel Prize in 1906. Oscilloscope Television Since CRT based TV has great difficulty in making TV beyond 30 inches, so alternate technologies were being looked into. By 1960s, liquid crystal (LC) was beginning to be used in commercial display products. This started the flat panel display technology when typical display is less than 100mm thick. This new class of material was first noticed in in mid-19th century One of the earliest synthetic chemist to make more 2700 LC. Prof. Daniel Vorlander and he kept working in the field of LC for 30 years since 1905. • The Twisted Nematic (TN) was patented by Fergason (USA) and Helfrich and Schadt (Europe). • TN was used in calculators and watches by RCA and Ilixco. • Then Japanese companies acquired the technology through licensing agreement. • Now TN is still being used by many Asia companies. The LC molecules of TN turn by 90o when a voltage is applied. For STN, the LC molecules turn by 270o. This gives a sharper transition, giving better contrast. TN STN Backlight Unit (BLU) To have images, light is needed to pass through the LC layer - backlight. In fact LC is acting as shutters – it was referred to as light valves. Two ways to generate backlight: reflector to reflect light and an active backlight unit (BLU). Most monochrome LCD displays used reflective backlight. Most colour LCD displays use active backlight unit. Most commonly used BLU is CCFL (Compact Cathode Florescent Light). Its working principle is low pressure gas discharge just like florescent lamp. The next commonly used BLU is LED. This type of BLU uses LED matrix or light guide. LCD consists primarily of two glass plates with some liquid crystal material between them. There is no bulky picture tube. LCDs use much less power than their cathode-ray tube (CRT) counterparts. Many LCDs are reflective, meaning that they use only ambient light to illuminate the display. Even displays that do require an external light source (i.e. computer displays) consume much less power than CRT devices. Liquid crystal displays do have drawbacks; viewing angle, contrast ratio, and response time. To display dynamic graphic or text information, in colour or monochrome, the display needs to have a sophisticated electronics to deliver the signals to the pixels. Display electronics require to decode, multiplex, and drive the display pixels. Hence, they are also known as display address electronics, driving electronics, and matrix electronics. Broadly speaking there are two methods to address the display pixels. Addressing is the process by which pixels are turned on and off in order to create an image. There are two main types of addressing, direct and multiplexing. Direct addressing is convenient for displays where there are only a few elements that have to be activated. In multiplex addressing, a larger number of pixels are involved. When the elements are in a regular order, they can be addressed by their row and column instead of each element being driven separately. The passive matrix display is addressed by a set of multiplexed transparent electrodes, perpendicular to one another, above and below the liquid crystal layer in a row and column formation. Cathodes Display layers Substrate Anodes Active matrix displays are currently available in high end laptop computers. In this type of display, the addressing takes place completely behind the liquid crystal film. The front surface of the display is coated with a continuous electrode while the rear surface electrode is patterned into individual pixels. A thin film transistor (TFT) acts as a switch for each pixel. Glass (polarizer) Colour filter Liquid crystal Pixel(color cells): TFT electrode Glass (polarizer) Light Samsung 82 inch LCD-TV 2006 Sharp 108 inch LCD-TV 2007 85 inch 4K TV by Samsung 55-65 inch 4K TV by LG Plastic (polymers) do not conduct electricity normally. In 1970s, Hedeki Shirakawa, Jack G MacDiarmid and Alan Heeger (Chemistry Nobel, 2000) discovered conducting polymer. the polymers conduct is because electrons from this type of polymers are allowed to move freely (delocalised) along the main bonds (backbone) of the polymer. This type of polymer is called π-conjugated polymer. OLED History Dr. Fred CH Chen HKBU/NJTU Rochester University OLED LCD View Angle >1600 Limited Contrast Response Time high µs Low ms Light Emission Active Passive ( Backlighting) Temperature Range Mfg. Processes ~ -500C to ~800C ~ -00C to ~1000C ~6 steps ~9 steps Traditional Semiconductor Diode Organic LED Polymers have bigger molecules and therefore cannot be thermally deposited. Instead, thin films are spin coated onto the substrate. Although it has advantage of fabricating device in ambient atmosphere, it has solvent problem when depositing multi-layer thin films. An alternate approach is being considered instead of spin coating. PixDro, a subsidiary of OTB-Group, has released a new desktop inkjet printer for the development of printed electronics applications. Small molecule based full colour display is mature enough for commercial production. While Korea and Japan (e.g. Samsung and Sony) concentrate on larger display unit like TV, Taiwan and others are working hard on smaller display for handheld device application. 2007 was the lowest point for OLED and this year we see some up-turn this year. Some of the reasons are listed here: Korea display companies lead in AMOLED display with usage Samsung SDI continues to boost her AMOLED panels monthly production from 1.5 million in 2007 second half to 4.5 million in 2008 third quarter. Both Mitsubishi Heavy Industries, Toshiba and Sumitomo have declared their intention to expand their OLED activities. Nokia decided that they will use OLED display in their mobile phones (N85). Sony sells the first world OLED TV; 11” XEL-1. There are several possible device configuration for full colour display in OLED. Standard RGB, RGBW, colour by blue and colour by white. In all the configurations above one of the key colour needed is deep blue. The reason is as follow: CIE Color Coordinate vs Power Consumption in Full Color OLEDs 0.55 Power (W) 0.50 0.45 0.40 Power ratio 0.35 Blue-y 0.30 0.00 0.05 0.10 Blue-y 0.15 0.20 All Angle Ultra-thin Power Efficient High Contrast Motion OLED display has began to make appreciable inroad into the commercial market. Initially OLED display is being used in handheld devices; mobile phone, tablet and now OLED TV. Now 4G is being realised, then OLED display will have an edge because of the faster time response, contrast and better colour saturation. Larger display for TV, notebook (?) and picture frame are being actively investigated. Double sided AMOLED by AUO (10.12.04) • 143 ppi • 200 nits • Independent image • 1.8 mm • Single module design • New desiccant • Perfect for mobile phone with 2” main and 1.5” subdisplay Samsung Note 3 and Gear Bluetooth watches for iPhone and Android Samsung S series SONY XEL-1, 11” TV with luminance of 600 cd/m2 and contrast 1,000,000:1. Resolution: 960x540 Lifetime: 30,000 hours. Cost: US$2,295.00 - US$2,499.99 Samsung develops 21-in a-Si TFT AM-OLED (1.4.2005) • 1000 nits brightness • 6.22 million pixels resolution • 5000:1 contrast ratio capability • 1000 x response time over LCD • Reduced production cost using LCD G4 line • Market $830 US in 2005 • 2.2 Billion in 2008 LG 84 inch OLED TV 85 inch 4K OLED TV by Samsung SONY Panasonic 65 inch OLED TV The Future OLED is very likely to become part of the commercial display products. For example, LG, Samsung, Sony, Toshiba, Matsushita, Idemitsu Kosan and Sumitomo Chemicals have joint together to develop OLED HD TV. Other types of OLED based display are likely to emerge, e.g. transparent display, conformable display. The Return of OLED has just began Alternative 3-D Display German Effort Effort by Universal Display The transparent cathode material developed can be adapted into any existing OLED device structure with minor or no modification. 0V 3.0 V 3.4 V 3.2 V The emergent of FPD has broadened the way we use display. Large size display; thin, touch screen and even transparent and gesture responsive can be part of our office and home. For mobile communicators (phones, tablets, ultra-book etc), thin, flexible, touch screen, gesture responsive allow communication everywhere. Once other emerging technologies such as NFC, cloud computing are mature. Then the dividing line between science and science fiction becomes blurr.