Progress in high‐luminance LED technology for solid‐state lighting
Increasing the luminance of white LEDs to the 200 Mnit level and beyond, opens a completely new design space for a wide range of lighting applications, by allowing significant reductions in optics and luminaire size as well as costs. Moreover, new applications, such as dynamic beam steering, are enabled by the ability to create arrays of densely packed, individually addressable high‐luminance emitters. The development of such high‐luminance LEDs requires improvements in all LED technology elements. In this paper, we discuss recent advances in epitaxy, die, phosphor, and package technology that are critical to achieving these benefits.
Physics, Materials Science
We will describe trends in the LED market and the consequences on the technical roadmap of LEDproducts. This will prescribe the focal points and direction of the upcoming manufacturing technologies. Two main trends are reinforcing at the moment. The first is an ongoing miniaturisation; the second one is the increasing number of power applications coming up due to higher chip efficiencies. INTRODUCTION An ongoing first trend is the miniaturisation of LED chips down to 150μm in square and 100μm in chip thickness, fitting for mass production. Complete micro devices are only 1000x500μm in square. The driver for this development is the limited space in applications as mobile communication and the lowest capital cost possible for the manufacturing processes. Also the LED material itself is still expensive mainly due to substrate costs and epitaxy (Fig.1). The second direction of the trend is increasing the light flux for: power LED light sources, projection systems and exterior car LED solutions, including the head lamp where we really can gain new markets for our products. But it is even more important, that the today power LED light sources are the first step for a wide scope of general illumination with LED in the future , , , (Fig 1). These beforehand mentioned trends to miniaturisation and high flux are determining the marketing and technological roadmap and accordingly the resulting manufacturing technology. A particular requirement for both, power and miniature applications is the improvement of the efficiency of the chips and the complete application (Fig 2). In the following paragraphs we will discuss the influence of this two trends miniaturisation and power applications on the technology roadmaps of: substrates/epitaxy, chip processes and the end of line/application technologies. Fig.1: Development of LED technology from a standard LED in direction of micro and power application SUBSTRATES, EPITAXY OF CHIPS Consequences for the manufacturing technology to improve the internal efficiency are therefore: a continuous development of the epitaxy MOCVD equipment and the process itself, to be as cost effective as possible. Furthermore it is important to go on with local defect reduction even on high efficient LED structures due to continuous improvement of the substrates and the epitaxy process , . Fig. 2: Efficacy evolution of InGaAlP and InGaN LED-chips in the last decade, a) InGaN blue, b) InGaN green Most effective for high efficacy blue diodes (Fig 2), especially for blue lasers, is the use of homo substrates, i.e. GaN bulk material. This brittle, 1 inch diameter crystals, are a challenge for manufacturing technology . Standard substrates (SiC, Sapphire, and GaAs) should be compatible with the 4” technique in order to minimize fabrication costs in the next years. Therefore the focus of interest for the manufacturing technology is to reduce wafer breakage and preliminary defects as scratches, and intrinsic grown particles. Naturally these facts are more pressing for large power chips . The precision of mechanical processes as wafer grinding, dicing, advanced handling as well as other mechanic preparation methods will be much more important in the future for all the products. At first they influence directly the height of our miniature products and the chip yield due to less cracks and chipping. Secondly, because the thinnest substrates possible take us to less power consumption, it will reduce the heat resistance to a minimum, as well as the electrical resistance, in the case when a conducting substrate is used. CHIP TECHNOLOGY OSRAM thin film LED technology (Fig 3), is a significant step forward to achieve the goal of high external efficiency and scalability from micro chips up to huge, high current power chips (Fig 4), , . An other possible approach is the inverted truncated pyramid , where the absorbing GaAs substrate is replaced with a GaP window by direct wafer bonding techniques after the epitaxial growth. Further obvious realisation of modern LED is a classical flip chip concept. This can be carried out successfully especially for transparent substrates as sapphire. Fig. 3: Schematic view of a Thin Film LED A successful implementation of the thin film technology is based on the establishment of a number of new processes in a production environment. Crucial is the creation of buried micro reflectors or at least a surface roughening in the LED structure. These micro reflectors were dryor wet etched and break the internal wave guide effect in the diode structure for emission angles larger than the critical angle of total reflection (Fig. 3). With buried micro reflectors the light can be emitted by a few reflections without evident reabsorption in the active layer . A main advantage of this concept, compared to the classical flip chip or the inverted truncated pyramid is: the mainly forwarded light which leads to a lambertian emitter and a simple scalability from a small die up to big chips for high current applications. Even blue InGaN chips  and longer wavelength InGaAlP  and AlGaAs chips can be fabricated nearly in the same way and manner. For the production technology the thin film concept needs a very precise control of etch solutions, as well as control of etch depths. In general we need material sensitive etch stops throughout all the many different chip layers. The structures itself are relatively large, in the range of some tenth of microns (Fig. 4). So the photo technique in the future manufacturing will be conventional mask aligning. The resolution is sufficient for all the possible cases. May be, for photonic crystals, where we need sub a) b) micron structures, stepper technique must be used. The overlay precision from layer to layer is the critical parameter in the photo technique, simply to get the smallest chip possible. There are several reasons for this: 3-8 photo layers are necessary for a modern chip (Fig. 4), structured frontand backside contacts are used. With high overlay precision it is possible to have smaller tolerances from layer to layer, so it is possible to save the expensive LED material, this is especially true for the smallest chips. A second important production technology class are the different bonding technologies. At first the direct wafer bonding, in combination with a DBR (Distributed Bragg Reflector) needed e.g. for truncated inverted pyramids , is a possibility to make a high efficient LED. This van der Waals force supported technique is based on: atomically flat surfaces, extremely clean and particle free environments, to work with high yield. Especially for large chips, high effort is needed in production to get good yields . For the flip chip variants and also conventional high current chips soldering bumps or eutectic solder layers have to be implemented with all the difficulties well known from galvanic steps or other thick film metal deposition techniques as particle generation or chemical residuals. Figure 4: Top view on a 1mm thin film chip and a 300μm chip directly near by each other on the same wafer (buried micro reflector). This demonstrates the scalability of our Thin Film technology. For thin film technology wafer scale soldering technologies are a core competence. Wafer scale soldering enables the benefit of removing the absorbing substrate as well as direct and undisturbed front emission (Fig. 3) . For the Thin Film LED production technique, at the front side of the wafer, on top of the buried micro reflectors a contact is deposited. On top of this contact the eutectic bond is formed together with a carrier wafer. The backside substrate can be removed now, so we get the upside down eutectic bonded thin film diode. This technique needs deep knowledge of metallurgy and barrier physics. On the other hand we get a very reliable, low resistance, scalable bond , . This technique is useful especially for high flux LED (Fig. 5). Figure 5: The influence of new technologies as surface texturing and Thin Film technology (615nm) with buried micro reflectors on the luminous Flux of a LED. END OF LINE, APPLICATION The challenge in the end of line technology, especially the testing will be to identify the scrap on the lowest added value possible. The best solution is to drop the scrap direct after epitaxy, or in the early process steps of the front end. The testing area will be supported by advanced machine and process control, combined with classical electrical data management as seen in the silicon world. Additionally the testing field will be focused to ongoing cost reduction. Better yields and more process stability in the front end generate space for omitting classical testing steps. The die bonding will handle smaller chips, now we have 150μm chip size in square in production. The chips for micro devices in future will be not much bigger as the usual bond pads of a today standard chip. To handle such small dies without slowing down the cycle time of die bonders and additionally without losing reliability and precision is a big challenge. Chip soldering technologies will dominate more and more the field of power chips, due to better thermal coupling to the substrate. For power applications a high internal and external efficiency will help to minimize the heat creation and optimize the heat dissipation of the system. This is well known from high power IR lasers. Complicated material mixes will be needed as ceramic and metal core boards. Interaction of the entire LED application with LED package and chip itself is becoming more and more important for advanced applications. 0 1 2 3 4 5 6 7 8 9 10
Application of LED technology into public road lighting in Malaysia for replacing the high pressure sodium vapour lighting
The `Light Emitting Diode' (LED) is not a new technology, however, it is used widely in many related products and being adopted in our daily life. However, for the street lighting system, LED technology is not fully accepted at the moment to replace the `High Pressure Vapour Sodium' (HPSV) street light which has been used throughout the country. Due to sudden increment in operating costs and energy supply tariff, this technology starts to gain its consideration because of its ability in saving the energy. The street lighting system involves relative complex specification especially in terms of safety, therefore, the LED street light is still at its initial level. In Malaysia, the first pilot project in implementing the LED street lighting system was installed at federal road with 6-lane dual carriageway by the local authority. The pilot project focuses on the structure of the road and the on site lighting measurements. The aim of this paper is to study on the ability to identify whether the LED street lights can meet the specification requirements mentioned in MS-825. As a result, the comparison is made between HPSV and LED street lights are capable to satisfy the specification requirements. In addition, from the `Return on Investment' (ROI) shows that the paybacks can be achieved within 5 years which under warranty period by the manufacturer or supplier. This proves that the proposed of replacing HPSV with LED street light is reasonable.
Part A: The Development of mI SMART, a Nurse-Led Technology Intervention for Multiple Chronic Conditions
Background: The treatment of Multiple Chronic Conditions (MCC) is complex for both patients and providers. Used as integrated tools, technology may decrease complexity, remove the barrier of distance to obtain care, and improve outcomes of care. A new platform that integrates multiple technologies for primary health care called mI SMART (Mobile Improvement of Self-Management Ability through Rural Technology) has been developed. The purpose of this paper is to present to development of mI SMART, a nurse-led technology intervention for treating for MCC in primary care. Methods: The creation of mI SMART was guided by the model for developing complex nursing interventions. The model suggests a process for building and informing interventions with the intention of effectiveness, sustainability, and scalability. Each step in the model builds from and informs the previous step. Results: The process resulted in the integrated technologies of mI SMART. The system combines a HIPAA compliant, web-based, structure of mHealth sensors and mobile devices to treat and monitor multiple chronic conditions within an existing free primary care clinic. The mI SMART system allows patients to track diagnoses, medications, lab results, receive reminders for self-management, perform self-monitoring, obtain feedback in real time, engage in education, and attend visits through video conferencing. The system displays a record database to patients and providers that will be integrated into existing Electronic Health Records. Conclusion: By using the model for developing complex nursing interventions, a multifaceted solution to clinical problems was identified. Through modeling and seeking expert review, we have established a sustainable and scalable integrated nurse-led intervention that may increase access and improve outcomes for patients living in rural and underserved areas. The first trial of mI SMART has been completed and evaluated for feasibility, acceptability, and effectiveness in persons in rural areas living with multiple chronic conditions.
On application of heat-conductive plastics in LED technology
A comparative analysis of the characteristics of heat-conducting plastic was performed. The results of the thermal measurements of two of the same type 3W LED modules installed on heat sink with the same area of heat-dissipating surface made of aluminum and heat-conducting polymer have been presented. It has been shown that the overheating of LED module mounted on the heat-conducting polymer heat sink is 2...3 С higher than that on the aluminum heat sink (thermal conductivity is 20 times higher). The ranges of applicability of the heat-conducting plastics in LED technology have been determined.
Physics, Engineering, Materials Science
LED technology and the shaping of culture
Undertakes an overview of the technologies involved at the hardware and protocol levels in the operation of the large screen in Federation Square in Melbourne, Australia. In the first instance, it looks at LED technology. It backs that up with the protocols – in this instance the compression-decompression algorithms or codecs – used as the basis for more familiar applications software like PAL or NTSC video. This first analytical section suggests that there is a history and because of that a series of constraints to the design of the technologies deployed in urban screens. The second interpretative section uses some of the ideas circulating among contemporary media and communications researchers to inquire whether the fit between hardware and codecs expresses a particular kind of social organisation, and whether, if that is the case, innovation in design and content is inevitably constrained by those historically inherited features, or whether understanding them may be an avenue to innovation
Computer Science, Engineering
PRACTICAL IMPLEMENTATION OF THE PROGRAMMABLE PLANT IRRADIATION SYSTEM, WITH MULTIPLE RESEARCH STATIONS, BASED ON SSL LED TECHNOLOGY
This article presents the practical implementation of the six research stations system for plant supplemental lighting, based on the latest SSL LED technology. The system has been designed and made for the purposes of the research project no 2011/01/B/NZ9/00058, funded by the National Science Centre (2011-2014) and conducted at the Department of Horticulture, Agricultural University of Krakow. The presented system consists of 24 LED lamps illuminating six research units. Each of the units, whose technical parameters can be independently controlled and programmed, is equipped with four LED lamps of the same spectral characteristics. The article presents the structure of the system, the possibility of its programming, spectral lamps characteristics and a sample map of illuminance distribution. Preliminary evaluation of the usefulness of the presented SSL LED system for improvement of the lamb's lettuce yielding and its physiological or pro-healthy properties was also discussed.
Assessment of LED Technology in Ornamental Post-Top Luminaires (Host Site: Sacramento, CA)
The DOE Municipal Solid-State Street Lighting Consortium has evaluated four different LED replacements for existing ornamental post-top street lights in Sacramento, California. The project team was composed of the City and its consultant, PNNL (representing the Consortium), and the Sacramento Municipal Utility District. Product selection was finalized in March 2011, yielding one complete luminaire replacement and three lamp-ballast retrofit kits. Computer simulations, field measurements, and laboratory testing were performed to compare the performance and cost-effectiveness of the LED products relative to the existing luminaire with 100 W high-pressure sodium lamp. After it was confirmed the LED products were not equivalent to HPS in terms of initial photopic illumination, the following parameters were scaled proportionally to enable equitable (albeit hypothetical) comparisons: light output, input wattage, and pricing. Four replacement scenarios were considered for each LED product, incorporating new IES guidance for mesopic multipliers and lumen maintenance extrapolation, but life cycle analysis indicated cost effectiveness was also unacceptable. Although LED efficacy and pricing continue to improve, this project serves as a timely and objective notice that LED technology may not be quite ready yet for such applications.
Ciraldo of Rubicon Technology discusses how sapphire substrate producers need to continually improve quality to keep up with advances in LED technology . Marked advancement in sapphire crystal quality from improved process control
adopted by industry for many applications due to its broad range of favorable properties. For example, as one of nature’s hardest materials, sapphire has been frequently utilized for optical applications in environments where abrasion and subsequent wear have proven problematic for softer materials, e.g. glass. However, by far the largest adoption of sapphire has been for the LED market, particularly for the application of gallium nitride (GaN)based devices. While sapphire generally presents the best lattice match to GaN of any widely available and optically transparent substrate material, achieving a very high-quality GaN film at the GaN/sapphire interface still presents challenges. This is due in part to the lattice mismatch between the two materials, but is exacerbated by defects in the sapphire crystal that directly impact the quality of the epitaxial layers in LED devices. Defects such as surface bubbles, dislocations, and impurities are widely known within the industry to be problematic in LED applications where, for example dislocations in the substrate can be replicated in the epitaxial overgrowth. Moreover, in many LED applications sapphire is part of the structure of the final LED device, with the consequence that the optical properties of the sapphire affect the LED efficiency. Although the quality of available sapphire material has improved over time, it has struggled to keep up with the advances in LED technology. As LED producers continue to push the limits of power and efficiency in their devices, substrate quality becomes an increasingly important consideration. As a result, substrate producers need to continue to innovate and find new ways to enhance their material. Rubicon Technology takes a holistic approach to improving the quality of its sapphire (Raja Parvez, ‘Vertical integration streamlines sapphire production’, Compound Semiconductor March 2013, p50–55). For example, rather than relying on outside vendors for high-quality sapphire precursors, Rubicon has brought much of the refinement in-house, providing tighter control of purity levels. Vertical integration extends through proprietary furnace technology and crystal growth methodology to patented tools for precise crystal orientation, a high-precision polishing platform, and large-diameter custom patterning capability. By controlling every aspect of the process, Rubicon maintains greater consistency and uniformity and has earned a reputation for overall sapphire material quality. The use of x-ray diffraction (XRD) rocking curves is often employed to evaluate the quality of single-crystal materials. This technique is highly sensitive to strain, particularly in the case of single-crystal material, which is represented by a broadening in the rocking curve peak. Common causes of strain within the crystal include dislocations, vacancies, and bubbles (i.e. macro-scale vacancies within the bulk crystal). Thus, by evaluating the full width half maximum (FWHM) value of a rocking curve, one can obtain detailed information about the quality of a crystal. With the help of Dr Albert Macrander and Dr Naresh Kujala, rocking curve data was obtained at The Advanced Photon Source at Argonne National Laboratories for multiple sapphire samples. Included in the study were standard Rubicon sapphire, as well as commercially available sapphire material from other vendors. The results of this study can be found in Figure 1. As can be seen, material from Rubicon shows a greater overall intensity with a significantly narrower peak, both of which are indicators of superior crystal quality. Moreover, the peaks from Rubicon’s material show a higher symmetry, indicative Although the quality of available sapphire material has improved over time, it has struggled to keep up with the advances in LED technology. Substrate producers need to continue to innovate and find new ways to enhance their material Technology focus: Sapphire
Cutting-edge nano-LED technology
In this Perspective, we will introduce possible future developments on group III-nitride nano-LEDs, which are based on current achievements in this rapidly arising research-technological field. First, the challenges facing their fabrication and their characteristics will be reported. These developments will be set in a broader context with primary applications in lighting, display technology, biology, and sensing. In the following, we will center on advanced applications in microscopy, lithography, communication, and optical computing. We will discuss unconventional device applications and prospects for emerging photon source-based technologies. Beyond conventional and current achievements in optoelectronics, we will present hybrid nano-LED architectures. Novel device concepts potentially could play an essential role in future photon source developments and serve as a key component for optical computing. Therefore, forefront fully photon operated logic circuits, photon-based computational processors, and photon driving memories will be discussed. All these developments will play a significant role in a future highly secure, low energy consuming green IT. Besides today's environmentally friendly terrestrial industrial and information technologies, an enormous potential of nano-LED technology for a large range of applications especially in the next stage of space research is envisaged.