It’s a “Touchy-Feely” World for Mobile Devices

Touch-screen technology has gone from a curiosity at the turn of this century to almost a “check-list” feature that just about every cell phone, tablet, and many other products incorporate as part of their base functionality. To achieve that, silicon suppliers and materials suppliers have been working hard to craft the “ideal” solutions to allow multiple simultaneous finger touches (multitouch), thinner screens by reducing the number of layers needed to implement the touch-sensor grid, and even provide haptic feedback to confirm that the touch-panel “buttons” were pressed. Many of the latest developments in these areas were discussed in early August at the DisplaySearch Emerging Displays conference held in Santa Clara, Calif.

All the presentations at the event were interesting, from the basic overviews of various touch-screen technologies, to forward-looking presentations that discussed emerging and novel touch technologies and new approaches to haptic feedback. Of all the presentations, there were several that I felt provided a glimpse of the future for touch and haptics technology.

One such presentation, “The Future of Multisensing” by Douglas Young, the VP and General Manager of Neonode Inc., projected future integration directions targeting cost reduction and new features. In their vision, Young expects to see the often separate touch-screen controller integrated into the system’s application processor, thus shrinking component count and system cost. The first step in that direction was the creation of a single-chip analog/digital front end, the NN1001, which was developed in cooperation with Texas Instruments. This chip has a high scanning rate (1000 Hz) but ultra-low-power operation (just 10 microamps) so it can remain active even when the application processor is in sleep mode.

Young also expects to see proximity sensing incorporated into systems. Such a sensing scheme would permit touch-less object detection (of up to 30 cm) and the use of near-device gestures while providing a fast response with only a millisecond or so of latency. Also possible with touch-less detection are 3D and plane sensing as shown in Neonode’s concept device (see Figure 1).

Figure 1: Touchless sensing developed by Neonode Inc. allows concepts such as 3D and Plane Sensing to be implemented as this conceptual design illustrates.

Touch-less operation would also eliminate the need for a glass overlay, thus reducing display thickness and weight, as well as allow underwater operation by sealing the equipment into a waterproof case since no direct contact with the display panel is required.

To improve and lower the cost of the touch-screen panels, Dr. Michael Spaid, VP of Product Development at Cambrios discussed the use of silver nanowires as a replacement for the Indium-Tin-oxide (ITO) conductive layer currently used by almost every touchscreen panel. The silver nanowires provide high conductivity (10 to 70 ohms/square depending on the nanowire concentration), are highly transparent, and are a lower-cost alternative to ITO. Additionally, stated Spaid, since the nanowire sheet resistance is lower than that of ITOs, the nanowires can be used in larger-area displays than practical with ITO films.

The multilayer glass sandwich typically used for most mobile backlighted display panels causes a significant amount of light transmission loss and is also subject to the most abuse during the mobile device’s lifetime. To improve the display durability and to reduce the light transmission loss, Dr. Wagulh Ishak, Division Vice President, at Corning Glass, the Corning West Technology Center, detailed Cornings efforts to develop the second generation of its popular Gorilla Glass and to create an ultra-thin glass it calls Willow Glass that offers a 30 to 70% reduction in display module thickness. Both of these activities were highlighted in Dr. Ishak’s presentation “Evolutionary Glass, Revolutionary Displays: Why and How Advanced Glass Matters”. The second-generation Gorilla Glass offers options that allow a 25% increase in damage resistance or up to a 20% decrease in panel thickness, as well as a potential for cost reduction. The glass also offers improved optical and scratch performance.
The Corning Willow Glass combines the benefits of glass with the ability to bend and flex without breaking, thus providing improved durability. The glass is so thin that it can be bent into extremely curved shapes, as demonstrated by the hand holding a flexed sheet of the thin glass (Figure 2).

Figure 2: An ultra-thin but rugged and flexible glass, Willow Glass, developed by Corning, can be bent into various shapes without breaking

Such glass enables companies to build lighter, thinner devices that could also employ new form factors thanks to the flexible glass.
Forming actual buttons on a touch-screen display through the use of electrowetting technology, Dr. Micah Yairi, the Chief Technical Officer at Tactus Technologies presented details of the novel approach to a haptics touch screen in his paper “Dynamic Touchscreens and Surfaces”. Electrowetting uses an applied electric field to move liquid into and out of an expandable pocket in a tactile elastomer layer (Figure 3).

Figure 3: In the Tactus Technology microfluidic keypad, tiny pockets in a tactile layer can be filled with liquid to create buttons. The scheme uses the electrowetting properties of the liquid to draw the liquid into the pockets and send the liquid back to the local reservoirs when the buttons are no longer needed.

The expandable pockets in the tactile layer are positioned over the display regions that indicate a button. When electrowetting draws the liquid from local reservoirs into the pocket, the surface of the pocket rises by 0.25 to 2.5 mm to form a physical button, which provides tactile feedback when pressed.

Dave Bursky
Semiconductor Technology Editor
Chip Design Magazine

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