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2014-11-20
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Editorial: Guest Commentary: Sapphire Substrate Advances Lead To Brighter LEDs at Lower Costs
 
... The adoption of solid-state lighting is fueling market growth for high-brightness LEDs. It's a competitive market, and each manufacturer is looking for the keys to greater light output at a lower cost. In recent years, the most significant advance in cost per lumen has been the adoption of patterned...
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Commentary...
Guest Commentary: Sapphire Substrate Advances Lead To Brighter LEDs at Lower Costs

 
... The adoption of solid-state lighting is fueling market growth for high-brightness LEDs. It's a competitive market, and each manufacturer is looking for the keys to greater light output at a lower cost. In recent years, the most significant advance in cost per lumen has been the adoption of patterned...

View the full story at the bottom of the current news page, or if this is a back issue, go here...

Plessey Achieves 120 lm/W with GaN-on-Si LEDs in Lab and its GaN-on-Si LEDs to Power 8point3's Linear Lighting Products
LIGHTimes News Staff

November 20, 2014...Plessey Semiconductor of Plymouth, UK reports that the company has agreed to supply its gallium nitride on silicon MaGIC (Manufactured on GaN-on-Si I/C) high-brightness LEDs to UK-based LED luminaire producer 8point3 Ltd. 8point3 plans to use the Plessey LEDs in its new Sabre Architectural range of LED linear lighting products, which will be officially labeled ‘Made in Britain'. Plessey asserts that that recent performance improvements in its MaGIC LEDs have made them competitive with any LED technology.

In related news, Plessey announced that its GaN-on-Si MaGIC high-brightness LED technology has achieved light output of 120 lumens per watt with over 50% light output efficiency.

8point3's Sabre Architectural luminaires employ remote phosphor with a unique light emission design that provides what the company claims to be high system efficiencies and economic life. The Sabre Architectural luminaires come in a wide range of color temperatures, and are said to deliver a uniform and diffuse luminance and appearance without reflections or pixilation. The Sabre Architectural luminaires offer lighting for high lumen areas.

“A technology agreement has also been reached, whereby Plessey will design bespoke LED solutions in the UK to complement 8point3’s ongoing lighting projects,” said Mark Pinnock, Plessey’s regional sales manager for Northern Europe and account manager for 8point3.

Plessey’s range of products for lighting applications is being showcased at LuxLive (the UK’s biggest lighting show) at ExCel London (19-20 November).

Plessey hopes to achieve even greater lm/Watt efficiency soon. Plessey chief technology officer Keith Strickland commented, “Whilst 120 lumens per watt for an LED may be considered ‘acceptable’ to industry, we must remember that we have doubled our LED light output in the past six months.”

“I see no reason why we cannot reach state-of-the-art in LED die output performance within the next six months. This current process technology will become the base for our Application Specific LEDs, the ASLED that bridges the gap between the LED component suppliers and the solid-state lighting fixture designers and OEMs,” Strickland continued.

“The combination of expertise and a sustained period of light output performance improvement in the core LED material is due to our holistic approach to LED development - our in-house experts in epitaxy growth, process development and die design all working together,” said operations director Mike Snaith. “This way of working will continue and strengthen as we drive towards the next generation of higher-efficiency, silicon-based integrated LED solutions and away from discrete, plastic-packaged LED components.”

Researchers Create Heat Sensitive Color Converter to Produce Warmer Light
LIGHTimes News Staff

November 20, 2014...Researchers from the Netherlands have found a novel method to efficiently emit warm white light from LEDs.“We demonstrated a seemingly simple – but in fact sophisticated – way to create LED lights that change in a natural way to a cozy, warm white color when dimmed,” said Hugo Cornelissen, a principal scientist in the Optics Research Department at Philips Research Eindhoven, a Royal Philips corporate research entity in the Netherlands. Cornelissen and his team from Eindhoven University of Technology, Netherlands detail their new LEDs in an article published in the Optical Society’s (OSA) open-access journal Optics Express.

Incandescent lamps naturally emit warmer colors when dimmed. Cornelissen pointed out that our general preference for redder colors in low-light situations might have developed far back in time, when humans “experienced the daily rhythm of sunrise, bright daylight at noon, and sunset, each with their corresponding color temperatures.”

Unlike incandescent lamps, LEDs don’t normally change color at different light intensities. Other groups have used multiple color LEDs and complex dimmer control circuitry to make lights turn redder as the power is reduced. The added complexity requires multiple components that can increase the cost and the risk of failure, and mixing light emission from multiple LEDs without creating light artifacts such as color shadows is tricky.

The scientists noticed that when they embedded LEDs in coated textiles or transparent materials, the color of the emitted light would sometimes change.

“After finding the root cause of these effects and quantitatively understanding the observed color shift, we thought of a way to turn the undesired color changes into a beneficial feature,” Cornelissen said.

They began with white LEDs made from a blue LED and a phosphor. Essentially, the phosphor absorbs and then re-emits the blue light as white.

Cornelissen and his team knew that if more blue light is absorbed and re-emitted then the color of the white light could be shifted toward the warmer end of the spectrum if more of the blue light is absorbed and re-emitted by the phosphor. The paper describes how they developed a novel, temperature-dependent way of creating a color shift towards the warmer white.

The group produced a coating that combined liquid crystal and polymeric material that scatters light when relatively cool but becomes transparent if it is heated above 48 degrees Celsius (approximately 118 degrees Fahrenheit). At the high temperature, the liquid crystal molecules rearrange and make the composite transparent.

After the team covered the LEDs with the material and increased the power enough to make the coating transparent, the LEDs emitted a cold white light. However, when they reduced the power, the coating restructured itself into a scattering material that bounced back more of the blue light into the phosphor, creating a warmer light. The group later fine-tuned the LED design and used multiple phosphors to create lights that comply with industry lighting standards across a range of currents and colors.

“We might see products on the market in two years, but first we’ll have to prove reliability over time,” Cornelissen said. “That is one of the important things to do next.”

Cal Poly Partners with Daktronics to Update Arena
LIGHTimes News Staff

November 20, 2014...California Polytechnic State University (Cal Poly) has partnered with Daktronics of Brookings, South Dakota, to install LED displays and tables at Robert A. Mott Athletics Center this fall in San Luis Obispo, California.

"These new video displays and LED tables add excitement and provide our fans a game-day experience we have never had at Cal Poly. And our association with Daktronics over the years has been very positive," said Cal Poly Director of Athletics Don Oberhelman.

A main video display, which features surface mounted RGB LEDs at 10mm spacing, was mounted at each end of the arena. Each display measures about 11 feet high and 22 feet wide. The 3-in-1 SMDLED package reportedly allows tighter pixel spacing and wide-angle viewing.

These displays are capable of showing live video and instant replays, but can also be divided into multiple sections to highlight timely statistics and scoring information, sponsor messages, and other graphics and animations.

Eight LED scorer's tables measuring 2 feet high by 9 feet wide with 10mm line spacing placed along the sidelines offer additional opportunities to show game information statistics and sponsor ads.

Eric Cain, Daktronics sales representative said,"This integrated system will deliver an outstanding game-day experience to every seat in Mott Athletics Center. We are excited for the major impact this video system has on Mustangs fans, sponsors and student athletes."

In addition to the equipment installation, Cal Poly received a bank of hours for content creation from Daktronics in-house creative team, Daktronics Creative Services, which will produce and deliver content at the request of the university.

Carnegie Mellon Researchers Create New Form of Silicon with Potential for Solar and LEDs
LIGHTimes News Staff

November 20, 2014...While direct band gap materials can effectively absorb and emit light, indirect band gap materials, like diamond-structured silicon, cannot. A team of researchers at Carnegie Mellon university headed by Timothy Strobel, have created a new form of silicon with a quasi-direct band gap that falls within the desired range for solar absorption. The silicon they created is an allotrope, a different physical form of the same element. The silicon consists of a zeolite-type structure that is comprised of channels with five-, six- and eight-membered silicon rings.

The researchers created the new silicon with a novel high-pressure precursor process. First, the team produced a compound of silicon and sodium, Na4Si24 under high-pressure. Then, the compound was brought back down to ambient pressure. Next, it was heated under a vacuum to completely remove the sodium. According to the researchers, the resulting pure silicon allotrope, Si24, can absorb, and potentially emit, light far more effectively than conventional diamond-structured silicon. Si24 is stable at ambient pressure to at least 842 degrees Fahrenheit (450 degrees Celsius).

“High-pressure precursor synthesis represents an entirely new frontier in novel energy materials,”stated Strobel. “Using the unique tool of high pressure, we can access novel structures with real potential to solve standing materials challenges. Here we demonstrate previously unknown properties for silicon, but our methodology is readily extendible to entirely different classes of materials. These new structures remain stable at atmospheric pressure, so larger-volume scaling strategies may be entirely possible.”

“This is an excellent example of experimental and theoretical collaboration,” said Kim. “Advanced electronic structure theory and experiment have converged to deliver a real material with exciting prospects. We believe that high-pressure research can be used to address current energy challenges, and we are now extending this work to different materials with equally exciting properties.”

The research work was supported by DARPA and Energy Frontier Research in Extreme Environments (EFree), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science. Portions of the work were performed at HPCAT, Advanced Photon Source, Argonne National Laboratory. HPCAT operations are supported by DOE-NNSA and DOE-BES, with partial funding by the NSF.

Litecool LineX LED module Provides 3000-lm Linear Lighting
SSL Design News Staff

November 18, 2014...Litecool Inc. of Sheffield, UK, reported that its LineX modules offer 3000 lumens at 135 lm/Watt. The company says that the LineX modules' performance enables more high powered lighting applications with maximum reliability.

According to Litecool, the LineX module is ideal for a wide range linear lighting applications in retail, architecture, and industry. Litecool uses the company's proprietary thermal packaging around Intematix remote phosphor technology. LineX modules that are 4000K, have an Ra 90 and operate at 135 lumens per watt. The remote phosphor technology from Intematix produces a uniform lighting effect with no hot spots or color variance.

“LineX modules enable luminaire manufactures to produce a new generation of lighting fixtures for high lumen output applications,” said James Reeves, Litecool CEO, “Not only are they exceptionally bright, but they are also very uniform in appearance and combined with our thermal engineering can create miniature form factors helping luminaire manufactures reduce bill of material costs across the entire system.”

Litecool’s Linex modules now come in 5000, 4000, 3500, 3000, and 2500K corrected color temperatures (CCTs) and in standard lengths of 1000, 600, and 300mm.

Fujitsu Laboratories Develops LED Lighting Technology that Transmits Data
LIGHTimes News Staff

November 18, 2014...Fujitsu Laboratories Ltd. based in Kawasaki, Japan, announced that it has development a technology that can embed ID data in light from LEDs or other light sources onto objects. The technology allows a smartphone camera with an app to recover this ID data. Unlike RF related technologies that can go through object in a wide area, data can be conveyed to an individual object. Also unlike RF ID technology, it is limited to line-of-site.

The lighting transmits the data. What is unique about the Fujitsu Laboratory system is that in addition to transmitting the data in on and off oscillations, the data can be transmitted in very small color modulations with the RGB LEDs. Another unique thing about the Fujitsu system is that it does its best to compensate for light being reflected off an object or absorbed to ensure more accurate data transmission.

The system does not apparently use LiFi, but it employs a proprietary method of light-based data transmission that creates tiny color changes that are essentially imperceptible to people, but can be captured with a cell phone camera.

The technology can make RGB-based LED lights act like a location beacon that transmits location data to anyone with a smart device and a camera. This can be combined with GPS or other data transmission methods such as WiFi or Bluetooth.

Currently, the technology is just one-way transmission to a camera. However, in theory at a store, a smartphone app could receive the location data from a fixture, and figure out the location in the store. Then, the app could connect with a server through WiFi. The server could be linked to a database that reveals the smartphone user's ID.

It can also link with information about what the person purchased previously, and what sales are going on for the products that are on the shelves around the person. This technology appears similar to a technology previously detailed by Philips, but it uses color modulations. This Fujitsu technology will be exhibited at Fujitsu Forum 2014, running November 19-20 in Munich, Germany.

eMagin Awarded R&D Contract to Develop OLED Microdisplay Backplane Technology
LIGHTimes News Staff

November 18, 2014...eMagin Corporation, a developer of OLED microdisplays and virtual imaging technologies previously announced in the first half of October a total of $6.8 million in new R&D contract awards. Today, eMagin announced that $800,000 of that total is a contract to develop an advanced backplane technology for use with eMagin's OLED microdisplays. Funding for the award is through the US Army RDECOM CERDEC Night Vision and Electronic Sensors Directorate (NVESD) Science and Technology (S&T) Division and Naval Air Systems Command. The $750,000 contract will be executed over the next eleven months.

"This advanced backplane will enable significant performance improvements in the OLED device including more than 30% reduction in power consumption compared to the existing backplane technology," said Andrew Sculley, eMagin CEO. "This backplane program will play an integral part of eMagin's advanced OLED development efforts, complementing our ongoing multimillion dollar R&D projects, including the Defense-wide Manufacturing Science & Technology and Enhanced Ultra-high Brightness OLED contracts."

Mitsubishi Electric to Unveil World’s Largest High Definition Video Display
LIGHTimes News Staff

November 18, 2014...Mitsubishi Electric Power Products, Inc. announced the unveiling of a Diamond Vision display at 1535 Broadway in New York City’s iconic Times Square that exceeds 4k ultra-high-definition pixel density. The display measures a massive 77.69' by 329.65' for a total surface area of 25,610-square-feet. The display boasts a pixel density of 2,368 x 10,048. Mitsubishi claims that the Diamond Vision display will be the highest resolution LED video display in the world of this size.

The installation will use the company's Electric Diamond Vision AVL-ODT10 large-scale display which provides true 10mm pixel pitch spacing. It employs a 3-in-1 surface mount LED (SMD) that features Mitsubishi Electric’s Real Black™ LED technology. The company was vague about how its Real Black LED technology works.

“With 23,793,664 individual physical pixels a video quality display of this size and density is a milestone in the industry. It exceeds 4k resolution by nearly 15 million pixels,” says Todd Stih, national sales manager, Mitsubishi Electric Power Products, Inc.

Because of the extremely high pixel density and resolution of the display, Mitsubishi Electric supplied a special control system to provide pixel-to-pixel mapping of content and images. The display can be separated into segments to show multiple pixel-for-pixel 1080 HD or 4k images simultaneously. Specifically the company says that the display canvas allows two 4k images to be shown side-by-side, with pixels remaining in the height and width for other content.

The company claims that its Real Black™ LED technology allows for deep, rich black levels and unsurpassed vertical viewing angles in an outdoor LED display product. The company says that Real Black™ LED technology will ensure that Times Square crowds can clearly see the display up close and in bright sunlight.

“The Real Black™ LED technology revolution is just beginning with fifteen other displays using Real Black™ LED technology coming on line in North America over the next few months,” says Stih.

“We have worked on a number of record-breaking projects, but working with this type of pixel density and installing it in a 24/7 live environment presented unique challenges. However, we delivered the display modules earlier than scheduled and due in part to great cooperation and team work with the project team at Vornado Realty Trust, our customer, completed the project on time,” says Mike Brosko, operations manager, Mitsubishi Electric Power Products, Inc.

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Commentary & Perspective...

Guest Commentary: Sapphire Substrate Advances Lead To Brighter LEDs at Lower Costs
Akhtar Zaman

November 11, 2014...The adoption of solid-state lighting is fueling market growth for high-brightness LEDs. It's a competitive market, and each manufacturer is looking for the keys to greater light output at a lower cost. In recent years, the most significant advance in cost per lumen has been the adoption of patterned sapphire substrates. By etching a pattern onto the polished sapphire substrate, total light extraction efficiency (LEE) can be increased by as much as 30 percent.
Sapphire is the material used as a substrate in the vast majority of LED chips. Patterns etched on the surface of the sapphire wafer can significantly increase the light output of LEDs in two ways: (1) by encouraging lateral growth of the epitaxial layers, thereby reducing epitaxial defect density and increasing the light emission of the active quantum well layers, and (2) by reducing light loss, through creation of a photon scattering effect that allows more of the light generated to escape.

a. Schematics of light extractionb. Effect of light escape cone expansion
Figure 1. PSS techniques scatter photons (a) and effectively expand the light escape cone (b), which can result in up to a 30 percent gain in light extraction efficiency.

Generally, the patterns consist of shapes - cones, domes, pyramids - created in a hexagonal pattern on the surface of the sapphire through dry plasma etching. Pattern features may be 0.65 to 2 microns in height, and the pitch (the distance between the centers of adjacent features) may be 1.5 to 3 microns. These pattern designs are developed independently by each of the LED manufacturers to meet the needs of their unique epitaxial recipes and are considered proprietary technology. Because of this, no standard library of patterns exist. The critical dimensions to increasing LEE include the shape and size of the pattern features and the aspect ratio - the ratio of height to width. Deeper patterns tend to be associated with greater LEE, but can be difficult to make if conditions are not well-controlled.

In addition to developing their PSS recipes in-house, LED manufacturers originally performed the patterning operations themselves, with most still conducting some of their patterning operations in-house. With third-party patterning becoming more available in 2010 for two-inch wafers, and later four-inch wafers, LED companies had the option of outsourcing at least a portion of their patterning activity.

Concurrently with the development of patterned wafers, LED chip manufacturers have been slowly migrating to larger substrates for greater efficiency. Larger wafers provide several benefits, including increased throughput for each reactor run, effectively increasing capacity without adding additional MOCVD reactors or additional floor space; reduced edge loss; and reduced wafer handling. In 2014 we have seen 4" wafers overtake 2" wafers as the predominant wafer size in LED manufacturing, with industry leaders at the forefront using 6" wafers. Although 6" wafers are still in the minority, they are poised to be the fastest-growing LED wafer category over the next few years.

The yield for PSS at larger diameters is affected by the flatness of the wafer, and bowing of the wafer can cause inconsistent etching and lower yields. Rubicon has been successful with its introduction of larger diameter (that is, 4-, 6-, and 8-inch) PSS, largely because of the high quality of its crystal and extensive large-diameter polishing experience. Other manufacturing challenges, such as dimensional accuracy of the pattern and uniformity of the photoresist mask, have been addressed through both the technology platform and process development.

What's next for PSS? Can we get even more luminous efficiency with this technology? Nanoscale patterning has been extensively studied for its potential impact on light extraction efficiency due to both its significantly increased pattern density and its impact on internal quantum efficiency from the improvement of epitaxial quality. Indeed, academic research indicates that nanoscale patterns could potentially boost light output another 30 percent. High resolution optical lithography for nano PSS requires a very high degree of substrate flatness which is a significant challenge for current sapphire substrate suppliers. Figure 2 shows the SEM picture of 270nm pitch nanoscale patterns created on a sapphire substrate through nano-imprinting by Rubicon Technology Inc.

As we continue to test new patterns and sizes, like nanoscale patterning, it is clear that the industry hasn't reached a wall in what is possible for light output. Further advances in PSS technology will provide improvements in light extraction efficiency, contributing to the continued market success of LED technology.

 

Figure 2. SEM picture of nanoscale patterns with 270nm pitch created on a sapphire substrate through nano-imprinting by Rubicon Technology Inc.

Akhtar Zaman is Senior Vice President, Quality and Supply Line Management at Rubicon Technology

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