LCD with Parasitic Current-Reduction Technique,” used as a capacitive sensor the ITO layer (on the color filter) that a standard IPS-TFT display incorporates as an anti-static measure. NEC’s enabling technology was a method of minimizing the large parasitic capacitance that exists between the ITO surface layer and the TFT backplane.
On-cell resistive moved into greater promi- nence this year, with three exhibitors showing it. Similar to on-cell capacitive, it uses the color-filter glass as the substrate in a tradi- tional film-glass analog resistive touch-screen. The film layer is placed between the color- filter glass and the LCD’s top polarizer, sepa- rated from the color-filter glass by spacer dots, exactly like in a standard resistive touch screen. The primary advantages of on-cell resistive are (a) the elimination of one sheet of glass, with resultant reduction in thickness and ambient light reflections and (b) the cost- savings achieved by integrating the touch screen at the time of LCD manufacture.
It is worth noting that some of the on-cell touch screens shown on the exhibit floor were actually labeled as “in-cell” (for example, in the Wintek booth). When questioned, the exhibitors in question all agreed that their technology was actually on-cell. Samsung has started using a new term for both in-cell and on-cell touch, namely, “embedded touch.” This is probably a very good idea because it minimizes the temptation for marketers to mislabel their touch technology for perceived marketing advantage. It is also a good idea because it recognizes that from the perspec- tive of the LCD module, both in-cell and on- cell touch technologies are beneath the polar- izer and are thus invisible. The side of the color-filter glass on which the touch technol- ogy appears is not actually that relevant.
Other Interesting Bits RPO showed the latest iteration of its wave- guide infrared touch-screen technology in the form of a 13.3-in. touch screen with a profile
Fig. 3: Dawar Technologies’ prototype analog multi-touch resistive (AMR) touch screen is an example of the type of AMR in which the intersection of each set of conductive strips is treated as a miniature four-wire analog-resistive touch screen. The connections for the 20 relatively wide vertical ITO stripes can be clearly seen across the top of the screen. The relatively large border width of this prototype screen is not typical of production screens.
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(bezel) height of only 0.5 mm and a border width of 3–5 mm. The reduction in profile height and border width since the company first announced its technology in 2007 is quite significant. RPO also showed a touch screen integrated with an E Ink electrophoretic display, side-by-side with a resistive touch screen. The difference in optical performance was immediately noticeable. The integration with E Ink was unique in that the waveguides were on top of the screen while the light- spreading glass was mounted under the screen. The resulting freedom from any over- lay produced excellent optical performance. RPO’s touch screen also appeared in two other booths – LG Display, where it appeared in a 13.3-in. notebook, and Qualcomm, where it was integrated on top of the mirasol® reflec- tive display. The clear-glass nature of RPO’s touch screen is optimum for a reflective dis- play, where ambient light must travel in both directions through the touch screen.
Elo TouchSystems showed an interesting demonstration based on its acquisition of Sensitive Object in January of this year. The demo, which used a large sheet of acrylic with two acoustic sensors clamped to the sheet in arbitrary locations, illustrated how Sensitive Object’s “ReverSys” technology uses stored waveforms of acoustic signatures to identify touches at a specific location. Another inter- esting demo by Elo TouchSystems was of a surface-acoustic-wave (SAW) monitor with zero-bezel (edge-to-edge glass) design. SAW normally has a set of reflectors around the border of the screen that prevents a bezel-less configuration; Elo has figured out how to locate the reflectors (and the piezo transduc- ers) on the back of the glass, leaving the front of the glass as an entirely flat surface. The trick is in shaping the edge of the glass so that the acoustic waves are guided from the back of the glass around to the top surface.
Optical touch technology made a strong showing at Display Week 2010 with exhibits from three companies. NextWindow demon- strated its new 2500-series large-format touch screen aimed at high-volume monitor OEMs; LG Display showed a prototype of a 21.5-in. optical touch screen; and Baanto, a Canadian startup, showed a technology demonstration of a low-cost 19-in. optical touch solution.
E Ink demonstrated a new method of inte- grating a touch screen with an electronic- paper (e-paper) display, placing a standard analog-resistive touch screen under a flexible