Digital Signage and the Emissive Materials Evolution
A series of new emissive materials – miniLEDs, microLEDs, and QLEDs – seem poised to take at least a portion of digital signage market share from surface-mount device (SMD) LEDs and LCDs.
by Gary Feather
IN 2018, Display Week proved once again that it is the world’s best program for all the latest updates on business, markets, information, and processing across virtually every display category. From projection display to transmissive LCD, and emissive display to reflective, each category was robustly represented.
The emissive display category, in particular, continues to deliver compounded growth in performance and features. Solutions include both the organic (OLED) and inorganic solutions, which are maturing rapidly for large-screen televisions and near-to-eye virtual reality, respectively. The emissive inorganic solutions are undergoing a revolution in increased luminance, higher efficacy, smaller size, and best color, meeting the most stringent requirements of a very large segment of the display market. With these improvements, cost per pixel is dropping rapidly, expanding product reach closer to commercial viability.
In parallel, the emissive display industry’s exploitation of new quantum-dot (QD) material capabilities to reach beyond initial performance goals will grow the quantum-dot LED (QLED) market even faster. Acceleration of µLED development will feed the largest-area emissive display solutions, from signage to cinema, and soon, to prosumer displays.
Ken Werner’s separate show review, “Emissive Materials Generate Excitement at the Show,” outlines the vast number of improvements in emissive devices and materials. The development focus at present is coupled most closely to emerging augmented-reality/virtual-reality (AR/VR) displays and smaller display-based solutions with microLED (µLED) and now added QD material for performance.
While current display pixel-per-inch (ppi) levels > 1,000 are being reported for these applications, the alignment and placement of emissive devices for the digital signage market will be dramatically different. Large displays’ most valued solutions are in the range of 10 to 20 ppi. Digital signage by definition is very large. Therefore, the useful viewing distances are usually measured in meters, not inches. A major transition for exploitation of new display materials and devices will incorporate solutions with much lower ppi. (This is also a matter of what ppi clients are willing to pay for, and what they are able to support from a content perspective.)
Digital signage displays will transition from existing discrete, inorganic red, green, blue (RGB) LED surface-mount devices (SMDs) with 1 pixel per package, to 4 pixels per package, to 9 pixels per package. RGB-SMD LED packages with a single pixel in a package range from 2 mm per side down to .5 mm per side. With improvements in reliability and yield, the technology is moving to direct-board matrix solutions (chip on board or COB) with emitters and placement in an array size and methodology to exploit the new smaller LEDs and leverage new QD materials. Placing hundreds and maybe thousands of RGB LEDs directly on a single board and sealing that one large display array in an epoxy can drive manufacturing to a revolutionary change of methods and equipment, and significantly lower costs.
In his article, Werner also highlights the most important challenge facing COB implementations for larger displays (those with lower ppis) using bare-die LEDs, miniLEDs, µLEDs, and QLEDs – the need for a new manufacturing approach. Pick and place of these tiny dice must move as quickly as the pick and place for RGB-SMD LEDs. The challenge of shifting to rapid die placement over large areas from very close proximity on small wafers will trigger the need for increased ingenuity to arrive at solutions.
Spacing and placing dice farther apart is critical technology that was discussed at Display Week 2018. The display manufacturing process for µLEDs in particular will require new COB techniques supporting production of a “sparse-matrix” approach at ~10–20 ppi. These new processes were highlighted as a barrier in two presented talks; however, the solutions are already in development. A pixel contains a red, green, and blue LED. Today, the inorganic LEDs are in the LED dice with 150-µm-width edges to 220-µm edges. Pick and place of these dice is usually directed to a carrier for SMD packages. The packages (in sizes of 1 mm on a side in a carrier array of 50 × 25 on a side), are then scribed, separated, tested, and taped for the packaged-pixel pick and place for SMD. A typical SMD facility placing SMD LEDs on a pitch of 2.5-mm to 0.9-mm and supporting backplane/drive devices places 3 to 4 million devices per day; supports production of 1 to 2 full-HD LED displays per day. The existing RGB-SMD display industry supports about 20 billion placements per year. The current market is well supported. Over the next two to five years, new and existing LED SMD packaging will shift from being 100 percent of business to becoming part of a mix of COB modules with hundreds to thousands of pixels in a module for display system assemblers.
Seminar presentations at Display Week 2018 reinforced the momentum in emissive displays; many of these advancements directly impact advances in digital signage for indoor displays. The indoor digital signage RGB-LED display retail market is now greater than $1.5 billion annually. Digital signage has evolved over the past five years, from RGB-SMD pixel pitches of 4 to 6 mm to solutions now in production that are down to 0.7 mm; approximately equal to the spacing of the 60-in. 2K LCD TV (~ 35 ppi). It is important to remember that the metric of pixel per inch takes on a new focus in digital signage displays, with the sweet spot in the current market at 10 to 20 ppi; not 200 to 600 ppi. For a 2.5-mm pixel-pitch HD display, the ppi is ~10. The digital signage market has a focus on HD displays larger than 120-in. diagonal (~1.3 m2 using 0.8-mm pixel pitch). Most emissive-HD LED signage displays are ~220-in. diagonal (2.5-mm pixel pitch and 10 ppi) on the average with no constraint on the maximum area of these displays (usually >50 m2). Massive LED display systems are currently installed in multiple airports and casinos, demonstrating seamless video solutions in the 150-m2 to 400-m2 range, with resolutions of 10 to 15 HD displays in a single display.
Exploring the application for new LED and µLED solutions also requires understanding the luminance requirements. At Display Week 2018, there were AR/VR and display solutions with µLEDs (monochromatic) demonstrating 10,000 nits; these are dense-packed emitters. A typical LED indoor display is ~700 nits for indoor applications at 8- to 12-bit depth. Applications in e-Entertainment and e-Sports ideally require luminance more in the area of LCDs – around 300 nits. Applications for cinema are in the range of 50 to 100 nits, per the Digital Cinema Initiatives (DCI) specification. The current DCI specification was written and limited by the capabilities of the DLP projection systems using Xenon arc lamps. With the advent of LED displays in cinema, DCI members, including the studios and the creatives, are considering expanding the requirements for DCI to create more natural “real-world” displays. Future DCI requirements will expand the color space. In addition, increasing the luminance from 50 nits to 500 nits appears possible. Finally, using specular highlights at 1,000 to 4,000 nits and leveraging perceptual quantizer (PQ), as discussed in the Monday Seminar on high-dynamic range (HDR) by Dolby Laboratories, future cinema experiences will be able to emulate reality as never before.
That being said, we must also consider the emergence of the µLED. Its replacement of the currently used LED dice (with some adaptation) may be a way to lower costs dramatically at no reduction in picture quality. Consider a few examples. In a full multiplexed drive (1/32), pixel luminance for a 75-nit display for red, green, and blue requires 12 nits, 42 nits, and 7 nits respectively. With the 2.5-mm spacing, the luminance for the D6500 balanced output of the R, G, and B dice would be 5.8, 8.5, and 1.7 millicandellas (mcd), respectively. Reducing multiplexing to 1/8 (requiring more drivers) would reduce that die luminance requirement by a factor of 4, which is within the current capability of the µLED and QLED dice being discussed today. LED drives the costs of the display, so a smaller LED will drive a net lower cost.
The package-die market-valued cost for digital signage today is ~2 cents per pixel. The value of a pixel for digital signage is currently 500x that of the pixels’ value for AR/VR. If leverage of the µLED/QLED solutions can be applied to digital signage, the advantages may lead to a significant market opportunity for the emitter supplier. Based on the developments and technical presentations at Display Week 2018, it is clearly now appropriate to investigate the significant potential of µLED and QLED for digital signage.
Finally, the challenge of color, color consistency, and balanced luminance seems well in hand for the current inorganic LEDs as well as the µLEDs in development. LEDs supporting REC.709 is a typical scenario, and supporting the DCI-P3 color space in production has been specified for the past year. These fast-switching emissive devices have a powerful, fast-growth market opportunity ahead.
Digital Signage Sessions at Display Week 2018
The emerging technology track at Display Week 2018 addressed a number of digital-signage-related developments in progress. Douglas Dykaar of DifTek Lasers presented the development of a new design for scalable active pixels for digitally driven video walls. The applications of the single-crystal silicon spheres, which are embedded in ceramic and planarized, offer the promise of high-performance (mobility) solutions in the digital-signage market.
Jon Karafin of Light Field Lab showed the scope of display implementations for the creation of holographic video. He demonstrated a clear understanding of the specifications and requirements of displays leveraged to create immersive experiences and the potential requirements for true holographic displays, as well as the appreciation of the single-viewer requirement and experience of light from each physical location of a virtual object. From that understanding, Karafin presented the challenges for creating tens or hundreds of views for a multiviewer holographic system. From a display manufacturing perspective, work toward single viewer should occur this year. Adding multiple viewers will be step two in the years to follow. Proposals for a single-viewer location-adaptive image may help build demand for these visual experiences in the future.
Jorge Perez from NanoLumens presented the first-ever paper on HDR solutions for digital signage. Perez focused on the research of specifications to create more natural images. The research provides for a proper specification of HDR for signage. The exploitation of a “dynamic drive” feature enables an LED display solution that allows for 12 bits at nominal luminance and extended dynamic range in image areas where replicating highlights is required.
Last, AGC’s Kenta Kasuya demonstrated the results of a prototype system for direct-bonding a display to a glass space so as to create an integrated solution for high luminance. Test methods and test results were presented, with examples supporting solutions working in environments with 10,000 lux.
Digital Signage in the Field and on the Show Floor
Because the show was in Los Angeles, attendees had the opportunity to view the
first DCI-certified, US-based LED (SMD-RGB) display at a theater not far from the conference center
(Fig. 1). There, visitors could see a 2.5-mm pixel-pitch theater display at a full 4K resolution (8.29 million pixels/24.88 million LEDs). The system was visually better than the DLP projection system in an adjacent theater. With 188,000 digital-projection cinema systems (many aging) deployed in the US, and over 1,000 new DLP (Xenon lamp and laser illumination) systems being purchased, the opportunity for LED displays to displace DLP is now a reality. The annual market for digital cinema display is over $250 million/year. The LED offers a clear visual advantage over the two-decade-old DLP technology for studios and creative cinematographers. This fact is evident in the new DCI specification being drafted for LED. Dramatic increases in contrast ratio, extreme requirements on the first step in black, much higher luminance for viewer experiences, and perfect “focus” are just a few of the advantages of LED over DLP.
Fig. 1: The author attended a showing of Avengers: Infinity War on one of the new Samsung 4K LED “Onyx” screens at the Pacific Theatres Winnetka in Chatsworth, California. The imagery was impressive (left). At right, a business card is compared to the pixel arrays in the theater screen. All photos by Gary Feather
The exhibition provided a few notable demonstrations related to digital signage. CLEARink Displays’ 6-in. reflective-color display (Fig. 2) showed promise for video refresh rates, especially when contrasted with E Ink solutions also on the floor. Applications for e-schoolbooks and digital signage are intriguing. The current CLEARink design is for a tablet at 100 dots per inch (dpi). Extending that to a panelized lower dpi for digital signage (reflective) could be a novel addition to the market.
E Ink demonstrated large-area tiled displays (reflective) with static update capabilities as an alternative (Fig. 2, right). Non-emissive signage has yet to impact the industry; however, these solutions show promise.
Fig. 2: CLEARink’s reflective color display (left) is designed to offer video-level refresh rates. At right, E Ink was demonstrating color panels at Display Week that could be tiled and updated to provide a large, changing display.
Displays leveraging µLED devices are limited but emerging. In the I-Zone area was a demonstration from Industrial Technology Research Institute (ITRI) of an active-matrix µLED array with a silicon complementary metal-oxide semiconductor (Si CMOS) backplane (Fig. 3). The display was 960 × 540 and performed as a single-color and RGB solution. Leveraging these developments against various needs across the display market should allow for significant applications when performance and reliability requirements are met. There was no information at this time on the cost or requirements to manufacture.
Fig. 3: In the I-Zone, ITRI was showing a µLED device with longer-range potential for the digital signage space and other markets.
The Industry Rises Again
Just when many felt that displays had reached a plateau, the industry reinvents itself. The specific performance improvements in LED alone provide the opening of new $1 billion markets over the next decade. The increases in visual performance are opening up new entertainment and experiences never before seen. The integration of modules in arrays with COB can drop costs dramatically. The new display configurations with content will create new markets. Certainly Display Week opened eyes to many new aspects in 2018; be prepared for a greater expansion in 2019. •
Gary Feather is CTO of NanoLumens. He can be reached at GFeather@nanolumens.com.