TMOS displays literally frustrate one of fibre optics’ fundamental phenomena. But as Tim Kridel explains, that frustration is a major reason why TMOS eventually could displace LCDs.
Does the world really need another display technology? The question is almost rhetorical because despite the deepest recession in generations, display R&D continues unabated, a sign that even in the worst of times, investors believe there’s always room for one more.
The latest is Time Multiplexed Optical Shutter (TMOS), which combines several existing technologies – LCD, LED and fibre optics – to create displays that are brighter, thinner, lower power and better able to support 3D video. Although TMOS displays are at least three years away from mass-market commercialisation, they’re worth looking at now partly because the technology already has a toehold in pro verticals such as health care and broadcast.
“We’re going to focus on the niches where we can get in quickly with low volumes where [they’re] not price-sensitive and hopefully build on that to get the volumes up to where we can start to expand our application base,” says Jim Tassone, CFO of UniPixel Displays, a U.S.-based company that’s developing TMOS displays.
Bright ideasTMOS borrows a fundamental principle from fibre optics: total internal reflection (TIR), which keeps light bouncing down a glass strand until it reaches the other end, instead of leaking out along the way.
Like an LCD display, a TMOS display features two sheets of glass. But in TMOS, one sheet serves as a waveguide, using the TIR phenomenon to manipulate the light, which comes from LEDs mounted along the display’s edge. (The LEDs’ location also enables a slimmer display than one with a backlight.) Mirrors on the remaining edges keep the light from escaping. UniPixel’s prototypes currently use red, green and blue LEDs, although future versions could use additional colours to increase the gamut.
UniPixel’s TMOS technology uses Frustrated TIR (FTIR), a patented variant that gets its name from the way it upsets the TIR to direct the light out to the viewer. TMOS replaces the liquid crystal, sandwiched between the glass in LCD displays, with a polymer membrane, branded as Opcuity Active Layer.
FTIR causes the frustration effect by oscillating the Opcuity membrane in specific areas of the display, causing the light to escape from the waveguide in those spots. (For more details about how Opcuity works, see the white paper at www.unipixel.com/assets/unipixel_whitepaper_20070717.pdf.) Opcuity’s surface is covered with
Opcuity’s surface is covered with microscopic, truncated pyramids, which direct the escaping light toward the viewer. The pyramids are surrounded by an opaque material that helps create a capacitor and improves the contrast ratio. When voltage is applied, the oscillation effect pulls the pyramids down to the glass waveguide that’s carrying the light. Touching the waveguide activates the pixels, and the light escapes, thanks to the FTIR effect.
UniPixel says TMOS has no “screen door” effect.
“If you put a magnifying glass on this, you cannot see any pixels,” Tassone says.
The Opcuity membrane also eliminates the need for colour filters and polarisers, a design that also allows more light to reach the viewer, increasing brightness without using more power in the process. That low-power design helps TMOS displays leverage the industry trend toward green products.
“Instead of 5 to 8 percent of the light making it from a backlight through a liquid crystal, we can get up to 60 percent of the light from the LEDs out to the viewer using this method,” Tassone says.
650 frames per second
The red, green and blue LEDs also enable field sequential colour generation, a technique currently used by Texas Instrument’s Digital Light Processing (DLP) system.
“We don’t do spatial modulation through sub-pixels,” Tassone says. “We do time modulation by time slicing the red, blue and green of the LEDs, so we create colour the same way as TI’s DLP.”
Field sequential color generation also requires only one thin-film transistor (TFT) per pixel.
“There are no sub-pixels, so we reduce the TFT count by two-thirds [compared to LCD],” Tassone says.
That design means more pixels can be shoehorned in, enabling small displays – such as one the size of a cell phone’s – that can support 1080 HD. UniPixel’s technology also has high pixel speeds, enabling high frame rates that make it a good fit for 3D video.
“As opposed to being in the millisecond regime, like LCD, we’re in the 2 microsecond arena for pixel actuation speed,” Tassone says. “We’ve demonstrated over 650 frames per second.”
At the Consumer Electronics Show, UniPixel demoed a 15 inch TMOS display running 3D.
“An analyst who saw this claimed it was the best 3D at the show,” Tassone says.
Incremental stepsBy adapting so many existing technologies, UniPixel aims to improve TMOS’ chances of wide commercialisation, instead of languishing in history’s dustbin of great ideas that never made it. For example, UniPixel says that the Opcuity membrane can be manufactured with existing roll-to-roll technologies.
TMOS and LCD displays also both feature a glass sandwich, a design commonality that should mean LCD fabs can be modified to make TMOS displays, instead of requiring a brand-new – and thus expensive – manufacturing process that would make some vendors shy away. That cost savings reduces the vendor’s overhead and improves the chances that TMOS displays can be priced competitively yet profitably.
UniPixel sees TMOS as a way to extend the life of older LCD fabs because switching to TMOS production removes multiple steps. That strategy could be attractive to vendors because it means their newer fabs can continue to produce LCD displays, so they can target two markets instead of one.
In February 2009, UniPixel signed a joint development agreement with Samsung Electronics, although that doesn’t imply that Samsung will soon start converting some of its LCD fabs to produce TMOS displays.
“We’re two to three years minimum before you’d see the adoption of a TMOS manufacturing process,” - Jim Tassone, CFO UniPixel Displays.
“We’re two to three years minimum before you’d see the adoption of a TMOS manufacturing process,” Tassone says.
For vendors, a big part of TMOS’ appeal likely will be a lower bill of materials: up to 60 percent less than LCD, according to UniPixel. Those savings come from the way that TMOS eliminates the need for components such as colour filters, polarisers and backlights.
For end users, TMOS’ appeal could include higher brightness, a better colour gamut and lower power consumption.
“Using less power – up to 90 percent less – you can get the same light output [as an LCD display],” Tassone says. “Or by increasing the power a little bit, you can get much brighter output and still have significantly less power consumption.”
Better than OLEDs?
TMOS’ low power consumption should make it attractive to cell phone and laptop manufacturers because the technology enables bright displays that draw relatively small amounts of battery power. Another emerging display technology – Optical Light Emitting Diode (OLED) – has successfully used low power consumption to break into the market. OLED uses about 50 percent less power than LCD, compared to TMOS’ 90 percent savings.
Today’s OLEDs have relatively short life spans of about 20,000 hours before the material degrades to the point that brightness suffers noticeably. That’s not a problem for mobile phones and laptops, which usually are replaced before 20,000 hours of the screen being on, but it’s a drawback for other, future applications, such as TVs and digital signage.
UniPixel says TMOS has a life span of up to 200,000 hours. That’s roughly twice as long as an LCD. OLED life spans will increase as the technology is refined, so one wild card is how much they’ve improved by the time TMOS displays make their commercial debut.
UniPixel says that gaming companies also are showing interest in TMOS for its brightness, colour gamut and support for 3D. All of these potential consumer applications are noteworthy because if TMOS takes off there, then the high equipment volumes will drive down the technology’s cost, making it easier for pro AV vendors to adopt it – a market expansion that many other technologies have gone through as they’ve matured.
But TMOS’ ability to sell into mass-market devices hinges on how easy it is for LCD vendors to modify their manufacturing processes, not just to build TMOS displays, but to crank them out in high volumes. That’s because makers of cell phones and laptops won’t commit to a new technology unless they’re convinced that their suppliers can deliver it in volumes big enough to meet their needs. For example, even a smartphone that’s considered a total flop still sells several hundred thousand units, so a handset vendor would expect a TMOS supplier to be able to deliver at least that many.
“Fifty thousand units doesn’t get you anywhere,” Tassone says.
Ramping up that level of production will take several years. In the meantime, UniPixel is taking incremental steps by working with vendors that can build products today that use parts of TMOS technology.
One example is field sequential colour generation, which can be applied to standard LCDs to produce HD displays that are small yet provide 1080 HD. UniPixel has demoed what it calls the world’s smallest full HD (1080x1920) display – 6½ inches – and says a vendor is using the underlying technology for surgical equipment sold in Japan. LCD displays enhanced with field sequential colour generation also are in prototype viewfinders for HD broadcast cameras, where the display needs to be compact yet good enough to provide an exact representation of what the captured image looks like.
The Aftermarket comes firstThe surface of UniPixel’s Opcuity Active Layer membrane is covered with truncated pyramids, each about 6 microns tall. When touched, the skin’s oil disperses into the valleys between the pyramids, instead of forming fingerprints and smudges.
Although Opcuity is designed to be sandwiched inside a TMOS display, UniPixel developed a version that can applied as a film to the outside of a display. In January, Targus began offering it as a protective cover for touch screens such as wayfinders and other interactive public displays.
“If you want to go a step further, we can add an anti-microbial to it for the germophobes out there,” Tassone says.
“If you want to go a step further, we can add an anti-microbial to it for the germophobes out there,” - Jim Tassone
In late 2009, another vendor, CubicVue, approached UniPixel about an aftermarket filter that lets 2D displays show 3D images without requiring the user to wear glasses. CubicVue saw Opcuity as a way to produce its filters in larger volumes. That’s more revenue for UniPixel and helps nudge full-blown TMOS toward commercial reality.