Plasma Technology for Advanced Devices
Fig. 1: Comparison between CRT and SED
Surface-Conduction Electron-Emitter Displays
Surface-Conduction Electron-Emitter Displays (SED) displays operate on the same principle as cathode-ray television, emitting light by shooting electrons into a phosphor-coated screen. But where cathode-ray TVs use a single large electron gun that has to be set back from the glass screen (meaning they're usually as deep as they are wide), SED screens are illuminated with millions of emitters, enabling images to be projected across wide screens only a few centimeters deep (Fig. 1).
The SED is being developed by Canon and marketed by a joint venture between Canon and Toshiba (SED Inc.), and Canon has invested $1.8 billion in developing the technology for the screens and building the factories to produce them. It plans to roll out the first 55-inch screens for consumers in Japan later this year. Fig. 2 shows one of the prototypes. Canon claims that SED yield images of superior quality to liquid-crystal or plasma screens while consuming far less power (5 lumens/watt or better). The film layers can be printed using ink jet method which reduces the cost and is one of Canon's competencies. SEDs can be made very thin and light: A 40-inch SED panel would weigh less than 45 lbs and can be thinner than 1/4 inch. The black level and grayscale performance matches that of a CRT.
The key to the electron emitters, at the heart of the SED, is an extremely narrow slit several nanometers wide between two electric poles. Electrons are emitted from one side of the slit when approximately 10V of electricity are applied. Some of these electrons are scattered at the other side of the slit and accelerated by the voltage (approximately 10 kV) applied between the glass substrates; causing light to be emitted when they collide with the phosphor-coated glass plate (Fig. 3).
Alternatives to Surface-Conduction Electron-Emitter Displays include:
- Organic Light Emitting Diodes (OLED's): Today mostly used for small displays in MP3 players and mobile phones
- Liquid Crystal Displays (LCD's): Competing with PDP's for sub 42 inch TV's and being the display of choice for computer screens.
- Field Emission Displays with Carbon Nanotubes: In a very early development phase.
- Plasma Display Panels: Competing with LCD displays for dominance in the HDTV market
Fig. 2: Commercial SED display
Fig. 3: Functional Principle of a SED display