Better Form, Lower Power

Better Form, Lower Power

Display Week 2016 offered an inside look at the state of the art for mobile and wearable displays.

by Jyrki Kimmel

THE mobile and wearable display technologies showcased at the booths of the major display makers at Display Week 2016 exhibited clear improvements that will serve end users well over the coming few years.  While there were no radical departures from the steady path of innovation, the improvements in form factor and advances toward low-power dissipation in wearable designs were among the highlights of the show.  These improvements, described below, were also emphasized in the symposium keynotes as well as in the Market Focus Conference presentations.

Edge-to-Edge Mobile Displays Incorporate a Plethora of Sensors

Even before Display Week opened, the symposium keynotes provided some insight into what the exhibitors on the show floor had in store for attendees.  Hiroyuki Oshima from Japan Display Inc. (JDI) gave a keynote on mobile displays, highlighting JDI’s strategy of concentrating on core technologies.  One of these is its in-cell touch-based user interface.  Other core technologies, LTPS and IPS, support touch functionality in the display itself that may take on new capabilities in more generalized input devices.

As the mobile-phone market saturates, JDI sees the future growth for the display business in new applications that will be enabled by advanced sensor technologies such as edge and hover touch, fingerprint sensors, and physiological sensors that will be incorporated in display modules.  As a result of new sensing technologies, the mobile-phone display will become the main input device as well as the main output device for the phone, as these new sensor technologies can be leveraged in light-based sensing and imaging in addition to finger-based touch applications.

And with the increasing pixel density in mobile screens, stylus-based input becomes meaningful once again, allowing for higher definition in character input as well as in artistic applications.  The increased pixel density, in turn, will be enabled by higher-pixel-density LTPS processes as well as by the IPS LC mode applied as the electro-optical modulation medium in these displays.

The new touch-technology landscape was also broadly outlined by Calvin Hsieh from IHS, who gave the lead presentation in the Market Focus Conference on Touch.  In IHS’s forecast, in-cell touch for AMLCDs and on-cell touch for AMOLED displays play a large role, as shown in strong projected growth for these technologies.  For touch in general, as well as for mobile-display technologies, new applications drive the growth of the business.  Many of these rely on sensors that are being integrated into the module itself.  These sensors give the mobile display capabilities for multimodal user interaction, from fingerprint and proximity sensing to hover touch.  These interaction modalities can then be leveraged over a wide range of application areas, even for automotive use.

JDI’s strategy was demonstrated by its exhibit lineup of mobile AMLCDs.  One IPS-based product family, for instance, sported WQHD screens from 5.2 to 5.7 in., all at a luminance level of 500 nits.  This makes it possible to pick and choose a display based on product form factor.  One concept helpful in improving mobile-device integration was JDI’s 5.2-in. super-narrow-border 0.5-mm-bezel screen in FHD resolution.  This development will become a necessity for high-end design, once the resolution can be brought on par with mainstream display modules (see Fig. 1).

Fig. 1:  The inactive space at the edges of JDI’s super-narrow-border display module (right) is only 0.5 mm wide.  The difference from the conventional example (left) is noticeable.  Photo courtesy Jyrki Kimmel.

There were many examples of innovative integration in mobile displays on the show floor.  The LG Display booth, for example, was featuring an interesting concept with dual display drivers.  This product had a low-power information screen at the top of the 6-in. dual 513-dpi display, with a normal-looking smartphone display at the bottom (see Fig. 2).  This concept enables the idle screen to operate on a transmissive LCD, a feature seen only on AMOLED display screens today.

Fig. 2:  LG Display’s 6.0-in. dual-driver QHD+ mobile display had a 160-pixel extra screen strip at the top, leaving the bottom as the “normal” smartphone screen.  Photo courtesy Jyrki Kimmel.

Another interesting mobile display from LG had an 806-ppi 5.5-in. screen.  This same pixel density was achieved by JDI on its 5.46-in. 4K × 2K display.  The “ppi race” was trumped by Sharp, however, which showed extremely high-pixel-density examples from its collaboration with Semiconductor Energy Laboratory (SEL).  One Sharp IGZO-based panel was optimized for use with VR goggles, and the display was in fact shown under magnifying optics.  The 2.5-in. panel had a pixel density of 1210 ppi, with a resolution of 2560 × 1600 pixels.

In the AMOLED technology space, Samsung had an interesting showcase lineup of its development in this area (not including TVs this year), starting with small-form-factor screens from 2007 and culminating with the most recent curved-edge Samsung Galaxy S7 Edge phone.  This lineup showed the developments in AMOLED technology thus far in a very concrete and understandable way.  According to the AMOLED development timeline Samsung was displaying in its booth, 1-billion AMOLED screens had been sold by February 2016.

One surprising innovation – again from JDI – involved power savings.  A 10.2-in. panel in JDI’s booth had an RGBW matrix with local dimming.  The increased white transmission combined with the local-dimming scheme improved the power characteristics by 15–20%, which is a significant improvement for an LCD module.  The local-dimming feature was the first demonstrated on a mobile-sized tablet display, and JDI claimed it increased the perceived contrast 100-fold, over a conventional globally dimmed RGB module (see Fig. 3).

Fig. 3:  JDI’s local-dimmed 10.2-in. tablet display module had a CR of 110,000:1 or above, according to the company.  Photo courtesy Jyrki Kimmel.

Curves Ahead

Another trend in the mobile space is the proliferation of organic form factors.  Sharp comes into this area from another direction, taking the form language from its automotive curve-edged displays and transforming mobile-sized displays from rectangular-shaped objects to round- and oval-shaped objects.  These affordances to form factor, combined with curved-display integration, led by Samsung, open a way for totally new device classes, beyond the mobile phone and rectangular passive information screens in automobiles.

Despite this evident progress, judging from the presentations in the conferences and the modules shown in the exhibition booths, it seems that the predicted curved and flexible displays are still as far in the future as roadmaps depicted a few years ago.  Many companies, including new entrants such as JDI, showed very similar curved AMOLED screens, and also similar dynamically foldable or rollable demonstration prototypes.

Samsung seems to be leading the development toward mass-producible flexible-display technology, with its Galaxy Edge displays already on the market.  At Display Week, Samsung showed a 5.7-in. 518-ppi curved display in a demonstrator mockup (see Fig. 4).  Sensor and system integration as well as touch user-interface evolution will play a major role as constituent technologies in this development.

Fig. 4:  Samsung showed a 5.7-in. curved demonstration display.  Photo courtesy Jyrki Kimmel.

Until we get to see mass-produced flexible display modules, there will be many advancements in “classic” mobile-display technologies that are extremely useful, if not as exciting as foldable and rollable.  These advancements can, in turn, propagate to other application areas, making developments in mobile displays the vanguard of evolution in display technology.

Wearable Displays Sport Classic Designs

In the last couple of years, “connected watches” or “smartwatches” have become a wearable part of the mobile ecosystem, and their design has approached that of classic wristwatches.  The intuitively designed round-face interface has pulled through once again, creating a new customer demand for design-driven smartwatches that can do much more than the single-purpose timepieces of the 20th century.  Health and fitness applications, in particular, are being integrated into the smartwatch oyster shell, as well as the ability to interface with the user’s smartphone to receive alerts and messages conveyed to the watch by the mobile terminal.

Even more than in mobile displays, power dissipation in wearable devices is a critical factor in user adoption.  As is customary in watch form-factor devices, the user preference is not to have to charge the battery every day or, as has been the case in some early smartwatches, even a couple of times a day.  The demand for low-power LCDs in wearable form factor is already being served by JDI’s round 1.2-in. 218 × 218 and 0.99-in. 180 × 186 and rectangular 1.39-in. 205 × 148 reflective color displays with memory-in-pixel (MIP) function, all at 182 ppi (see Fig. 5).

There were other small-form-factor low-power displays at the show, including some in black and white with dithered gray scales from Sharp (see Fig. 6).  Kyocera also showed a round 128 × 128-pixel display.


Figs. 5 and 6:  At left, JDI’s demonstrator was a 1.2-in. round MIP display.  At right, Sharp’s round 128 x 128 pixel display featured ultra-low power.  Photo courtesy Jyrki Kimmel.

Another approach toward low power is with bistable e-paper displays, as shown in the E Ink booth.  One such product on the market, the Withings activity monitor, was featured.  It sported a reflective e-paper display in a round design (see Fig. 7).  Sony’s wrist-band form-factor activity monitors also had e-ink screens, as did the Wove wrist-band device shown at the Canatu booth (see Fig. 8).

Fig. 7:  The Withings activity monitor device uses an electronic-ink screen.  Photo courtesy Jyrki Kimmel.

Fig. 8:  The Wove wrist device prototype features an electronic-ink screen integrated with Canatu’s carbon-nanobud touch screen.  Photo courtesy Jyrki Kimmel.

The Wove/Canatu carbon-nanobud touch panel was assembled in an “on-screen” touch fashion to make a complete integral structure without any separate outside encapsulation.  The entire module thickness is only 0.162 mm.

Assuming that customer demand drives the adoption of consumer devices, once the technology to realize these is available, we can infer from the exhibits shown that there is a demand to minimize the bezel and dead space in a round watch form-factor display.  Companies are striving to provide a bezelless design similar to those that have become possible in mobile-phone displays.  This is a much more difficult feat using a round shape.  AU Optronics (AUO) showed in two symposium presentations how this can be done using a plastic-substrate display.  Instead of placing the driver chip on the face of the display, in a ledge, or using a TAB lead, AUO bends the flexible substrate itself to place the driver at the back side of the display.  In this way, a bezel of 2.2 mm can be achieved, with clever gate-driver placement and bringing the power lines into the active area from the opposite side of the display face.

The Way Forward

Based on the mobile- and wearable-display offerings at Display Week, as well as the presentations given by display manufacturers and analysts, it seems that the small-form-factor displays are leading the advances in many display technology areas.  Whereas before, the development cycle in flat-panel displays entered the mobile-display space with a few years’ delay, now mobile- and wearable-display manufacturers are leading the way in innovation, as is demonstrated by the advances in pixel density, substrate materials, narrow bezel designs, decreasing power dissipation, sensor integration, and organic form factors.  In the coming few years, these innovations enabled by new mobile- and wearable-display technologies will benefit the users of smartphones, connected watches, and other devices yet to be designed.  •

Jyrki Kimmel is a Distinguished Researcher at Nokia Technologies in Tampere, Finland.  He has been investigating new display technologies in the mobile domain for over 20 years.  He can be reached at  +358-50-4835484 or