Electronic Design
Big Innovations Propel Small Displays In Mobile Applications

Big Innovations Propel Small Displays In Mobile Applications

Mobile displays have been a part of communication technology and rapidly gaining in popularity ever since it was fashionable to tie a note to a rock and hurl it through someone’s window or send a written message attached to a flaming arrow. Today’s technologies are more effective, easier to use, and allegedly safer.

Screens of every type and size are everywhere, and most of us carry at least one display as part of a cell phone, media player, portable computer, or all three. Even if you don’t own any of these items, somebody who is absorbed with one will walk into you sooner or later.

All kidding aside, this is a good state of affairs as the demand for these products is increasing. And with any increase in demand there’s usually an upswing in innovation, leading to unique, highly functional, and occasionally absurd devices (see “A Quick Blast From The Past).

Today’s LCDs And Touchscreens
With users and manufacturers alike, the most popular display technology is the LCD and LCD-based touchscreen. From cell phones like the Droid and iPhone to portable and tablet PCs, through all the endless variations of ATMs and point-of-sale terminals, LCDs and touchscreens are almost everywhere. And where they aren’t, rest assured that someone is working hard on filling that void.

Corroborating this popularity claim, analysts at DisplaySearch foresee touchscreen-module revenue (Fig. 1) hitting $14 billion by 2016, up from the $4.3 billion reported for 2009. This represents a compound annual growth rate of about 18%. The analysts point to mobile phones as the top application for touchscreens, with mini-note PC/slate PCs emerging as the next area for growth.

“Over the next several years, touchscreens will undergo strong growth in large-size applications such as all-in-one PCs, mini-note/slate PCs, education/training, and kiosks for point of information and self-check in,” said Jennifer Colegrove, director of display technologies at DisplaySearch.

LCD And Touchscreen Technologies
There are quite a few approaches to creating a touchscreen, and each has its benefits and drawbacks. Since one size does not fit all, choosing which technology to use depends two things: the application and the budget. Currently, the three most commonly used technologies are resistive, capacitive, and surface acoustic wave (SAW).

Resistive touchscreens, which are the simplest and least expensive, use two conductive layers separated by a gap. Pressing down on the panel causes the two conductive layers to touch, which causes a change in current flow to a processor or controller that interprets the change as a touch (input).

Resistive touchscreens offer cost-effective, consistent, and durable performance in environments threatened by contaminants and liquids. Disadvantages include a 75% optical transparency.

Capacitive touchscreen panels coat a glass panel or other insulator with a transparent conductor. When touched by a finger, the electrostatic field caused by the touch creates a measurable change in capacitance at the touch point.

The controller or processor detects the location and change of capacitance and translates them into a particular type of input. Though a bit more physically delicate than resistive technology, capacitive technology transmits approximately 90% of the screen light.

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Surface acoustic wave (SAW) technology passes ultrasonic waves over the touchscreen panel. Upon touching the panel, the finger or touch device absorbs a portion of the ultrasonic wave. The now changed ultrasonic waves register touch positions and transmits them to the controller.

Compared to resistive and capacitive designs, SAW technology promises better image clarity, resolution, and higher light transmission. The panel is all glass with no layers to wear out. On the downside, SAW screens are not totally sealable against the elements. Viable apps include ATMs, information kiosks, and other indoor environments.

On the market
There are no shortages of LCD and touchscreen displays on the market for both designers and end users to choose from. For example, the Interactive Digital Signage (IDS) touch systems from Elo TouchSystems combine precision acoustic pulse recognition touchscreen technology with commercial-grade, large format LCD panels (Fig. 2). According to the company, they’re the only displays to employ zero-bezel, edge-to-edge glass touchscreen technology in a larger format.

Ruggedized for commercial rigors, the 32- to 46-in. panels also feature the company’s acoustic pulse recognition (APR) touch technology, which promises consistent, touch functionality. Optional computer modules supporting either an Intel Celeron Dual Core or Core 2 Duo processor optimize media bandwidth and interactivity.

Building on its commitment to active-matrix organic light-emitting diode (AMOLED) display technology, Samsung Mobile Display (Fig. 3) is improving white efficiency from current 20-cd/A levels to 40 cd/A. This should double AMOLED lifetimes from 50,000 hours to 100,000 hours with power-consumption levels dropping from 62 W to less than 30 W in the near future.

Samsung also plans to apply advanced color pattern methods in the AMOLED manufacturing process as well as a thin-film method as an alternative to current glass base encapsulation. Products should emerge in the first quarter of 2011.

Riding the 3D renaissance, Toshiba Mobile Display has developed an optically compensated bend (OCB) LCD panel for 3D glasses (Fig. 4). According to the company, OCB technology uses an active shutter and achieves a high-speed response and a wide viewing angle while maintaining high contrast.

Glasses that fit with the OCB panels feature fast shutter opening and closing times, significantly reducing 3D crosstalk. Also, the wider viewing angles provide more vivid 3D images across a wide field of view.

Specifications for OCB-based displays include shutter response speeds of 0.1 ms (open) and 1.8 ms (close), contrast ratios of 5,000:1 perpendicular to the display and 1000:1 at a 30º viewing angle, a 3D crosstalk ratio of 0.1% or less at a 30º viewing angle, and a transmittance of 33%.

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In what may raise more than a few eyebrows in the industry, Texas-based Uni-Pixel Displays Inc. claims that its unique display architecture, technology, and approach is superior to everything else in the market today. The company believes its UniPixel technology will outperform OLED, plasma, and LCD technology in every measurable dimension.

The approach, time multiplexed optical shutter (TMOS), promises a brighter, more intense image with higher contrast and more color while enabling greater readability in direct sunlight. In terms of efficiency, Uni-Pixel displays consume significantly less power than comparable technologies, the company says. They will support both very small and very large applications, including the full range of sizes covered by LCD, OLED, or plasma components.

UniPixel says that its Active Layer films make the TMOS approach simpler and less expensive while improving its performance. According to the company, a single layer of this film can replace an LCD panel’s liquid crystals, color filters, polarizers, cell structures, and brightness enhancement films. A compact edge light replaces the large backlight. Target applications for these displays range from cell/smart phones through large displays for television and signage designs.

Flexible Displays
Promising extreme portability and efficiency, flexible displays are about midway in their commercial development stage. Numerous advances have been emerging, most notably from Arizona State University’s Flexible Display Center (FDC) and companies like E Ink, Sony, Ntera, and Seiko Epson.

Unlike LCDs, flexible displays are supple, bendable, and formable components that fit easily within numerous compact and large designs. They are thin and lightweight, accommodating virtually all portable applications. Essentially, the day is not that far off when users will be able to roll up their portable computer, display and all, and simply pack it into a briefcase.

Ntera’s NanoChromics Ink Systems enable cost-effective manufacturing of printed electronic displays on a variety of flexible substrates. They employ standard printing techniques and equipment, i.e., sheet or web-fed screen printing, flexographic printing, and inkjet printing.

Displays can measure less than 30 µm thick. The process also can produce low-power displays (power consumed only during image refresh), compatibility with 1.5-V power systems, multiple colors, a single substrate architecture, and compatibility with current smart-card hot lamination processes.

Consisting of a multi-layer printed structure on a single substrate, the low-power NanoChromic displays (NCDs) rely on layer-by-layer printing, which enables flexible designs from simple iconic displays to segmented and matrix displays (Fig. 5). Ultra-thin and sunlight-readable, NCDs suit numerous products including smart cards, smart packaging, smart objects, plastic cards, packaging, labels, RFID systems, greeting cards, toys, and games.

Known for several breakthroughs in the flexible-display arena, the FDC unveiled what it calls the first touchscreen active-matrix display on a flexible, glass-free substrate enabling real-time user input.

A team effort between the FDC and partners E Ink and DuPont Teijin, the display combines the FDC’s low-temperature thin film transistor technology, DuPont Teijin Films’ Teonex polyethylene napthalate films, and E Ink’s Vizplex ink laminate to form active-matrix, electrophoretic displays, a.k.a., electronic-paper displays (Fig. 6).

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A low-power display controller, co-developed by E Ink and Epson, is responsible for touchscreen functionality. Additionally, the display supports real-time user input via stylus using Wacom’s inductive touchscreen technology. The screen consumes power only when a user activates the electronic paper.

The end goal of these efforts, according to Michael McCreary, vice president of research and advanced development at E Ink, is “to stimulate a number of applications that will allow users to input, store, or transmit real-time data from remote locations using ultra-low-power displays that are rugged, sunlight readable, lightweight, and thin.”

In May, Sony unleashed an 80-μm thick, 4.1-in. wide, 121-ppi organic-thin-film-transistor (OTFT) (Fig. 7) display capable of wrapping around a cylinder. The full-color organic light-emitting diode (OLED) display employs Sony’s original organic semiconductor material, a peri-xanthenoxanthene derivative with eight times the modulation of conventional OTFTs.

The 432-by-240 RGB display represents the first demonstration of an OLED display with an integrated gate-driver circuit with OTFTs, Sony says. Its rollup capability is made possible by the elimination of rigid driver ICs from the display.

To further enhance the display’s flexibility, Sony developed organic insulators for all the insulators in the OTFT and OLED integration circuit. Other features include 16,777,216 colors, a peak luminance greater than 100 cd/m2, a contrast ratio greater than 1000:1, and a minimum bending radius of 4 mm.

The Unique And The Oblique
As with any popular technology, there are always unique and innovative offshoots from the norm as well as the honorable mentions. The display market has its share of both.

Earlier this year, interactive-technology developer Displax introduced what it calls the first interactive technology that will transform any non-conductive flat or curved surface into a multi-touch screen (Fig. 8). Based in Braga, a.k.a., the Portuguese Silicon Valley, the company combines a patent-pending controller and software with a transparent polymer film that’s thinner than paper.

Applying the film to a glass, plastic, or wood surface, flat or curved, makes the surface interactive. Notably, the technology can also integrate with standard LCD screens, extending the capabilities of the interactive format. The film operates with flat surfaces measuring up to 3 m across the diagonal. It allows users to interact with an enabled surface not just by touching it, but by blowing on it. Currently, the capacitive technology detects up to 16 fingers on a 50-in. screen.

The controller processes multiple input signals from a grid of nanowires embedded in a polymer film attached to the touch surface. Each time a finger touches the screen or a user blows on the surface, an electrical disturbance travels to the controller for analysis and translation. The Displax multitouch technology began shipping in July.

In the mainstream market, we rarely hear of or get a chance to see those items that never made it out of the lab or ended up in the square file. Here’s one that gets a “nice try.”

The 2008 brainchild of two imaginative designers, Kyung-Ryul Lim and Miyeon Kim, the “8” mobile phone integrates two LCDs onto a figure-eight-shaped frame (Fig. 9). Each display can perform a different function ranging from a keyboard for texting and other input tasks to turning the entire unit into a digital photo frame. Hopefully, one can actually make and receive calls on the “8.”

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