LOW POWER-CONSUMPTION IS KEY TO CANON-TOSHIBA ‘SED’ MONITOR

Toshiba will offer a 50” SED next year and start mass production in 2006, after 5 years of near-secret research and several postponed demonstrations by the partners, Toshiba Pres. Tadashi Okamura said this month. Specs for brightness, contrast and image-latency haven’t been divulged. Price hasn’t been determined but Mktg. Vp Scott Ramirez told us “this is going to be a premium priced product.” Toshiba’s patents detail tests that convinced the companies large SED panels “can be manufactured at low cost” with Canon’s BubbleJet ink-jet printers, which are used to deposit the screen’s emitter spots and conductive tracks.

SED is made like a giant squashed CRT, with hundreds of thousands of tiny electron guns instead of the usual 3 big ones. The traditional CRT is a large vacuum tube with 3 electron guns in the neck that fire electron beams through a vacuum at a glass screen plate coated with red, green and blue phosphor dots. The beams are moved by electrical control signals to scan lines of the picture. Power consumption is about 100 watts, and the pictures are bright and sharp. But large tubes use heavy glass to prevent implosion under atmospheric pressure -- and consume more room space than other direct-view displays.

LCDs are much thinner but use about the same power as CRTs because a bright backlight is needed. They're made like a giant microchip with several hundred thousand tiny cells on a large silicon base, each cell having its own control transistor to switch the optical state of a drop of liquid crystal chemical so it acts as a shutter to pass or block light. If any cells are faulty they spoil the picture with static spots of light. Image- latency has improved, but fast-moving images sometimes smear because the chemical takes at least 15 millisec. to change state. PDPs trap xenon or neon gas between glass plates covered by electrodes. When pulses of several hundred volts jump through the gas they ionize it and create flashes of ultraviolet light that make red, green and blue phosphor spots on the top plate glow. PDPs can be larger than LCDs but consume 200-300 w. Much of that’s converted to heat, so they often need a ventilation fan to prevent overheating.

Large SEDs differ in design and manufacture from the other displays. A thin sandwich of 2 glass sheets has a high vacuum trapped between them, with mechanical spacers to stop the sandwich from collapsing under atmospheric pressure. The lower plate is covered with a conductive mosaic of spots, each working as a miniature electron gun to create one picture point or pixel. The top plate has a transparent coating which works as an anode to attract the electrons from the guns below. The top plate is also covered with a matrix of red, green and blue phosphor spots. The sandwich, just a few cm thick, works like a large flattened CRT and yields pictures equally bright. But no power is needed to make the electron beams scan in lines, as in a conventional CRT; to ionize gas, as in a PDP; or to provide a backlight, as in LCDs. Also, there’s no need to make individual image cells, as in LCDs.

The challenge with SEDs is to form an accurate mosaic of tiny electron emitters on the lower plate. The effort to accomplish this melded Toshiba’s experience in mass-producing CRTs with Canon’s in manufacturing ink jet printers.

As described in the SED patents, each emitter is a 50 micrometer spot of palladium metal with a slit -- like a mouth a few nanometers wide -- formed in the top. Applying a low voltage of about 5 v makes electrons move across the vacuum gap. A positive voltage on the plate above drags the electrons up in a fine beam, so they hit the phosphors and generate light. The palladium spots are electrically connected by a mesh of metal tracks so each emitter can be individually addressed and made to fire electrons up at the top plate.

An ink-jet printer deposits the SED’s conductive tracks and emitter spots. The palladium is carried by vinylpyrrolidone- acrylic acid, which is baked off after printing. The micro-slit mouths are made by “electro-forming": A high current is briefly fed through the spots, in a vacuum containing hydrocarbons, so the palladium cracks and the lips of the crack are coated with graphite. Patents filed recently by Toshiba claim the emitters work better if boron or tin is deposited on the lips as well.

Canon’s research lab said it sees SED as the “de facto standard for large screens in the 21st century” because SED energy consumption is half that of a CRT, and 1/3 that for PDPs. The issue of power consumption related to DTV -- in broadcast transmission as well as ever-larger home displays -- has a particularly high profile in the U.K. The Intertek Research & Testing Center, formerly the test lab of the consumer watchdog- group Consumers’ Assn., has warned about the power used by PDPs and is advising the U.K. govt. on ways to reduce domestic energy consumption.

“SED sounds like fantastic news,” said Intertek Senior Scientist Bob Harrison. He raised questions about the unknown specs for brightness, contrast and latency, but expressed optimism: “If SED passes these tests it could bring forward the plans for energy savings by 2 or 3 years.”