The development of wideband gap semiconductor devices using GaN has enabled technological progress in the areas of advanced optical devices leading to the Solid State Lighting revolution. With up to 20% of the global electrical energy consumption being utilized in lighting applications, the use of GaN is projected to dramatically reduce this figure through higher efficiency, saving $40 billion per year (U.S. Dollars) by 2025. While devices made with GaN have the ability to operate stably at elevated temperatures, the efficiency of solid state lighting sources are very sensitive to junction temperature. Challenges to the development of high-power, high-efficiency solid state lighting sources must be addressed with lowpower consumption thermal management solutions in order to become a viable lighting option in the future. In this talk, we will address the fundamentals of thermal transport and heat dissipation in GaN solid-state lighting devices. Thermal conductivity measurements of device layers, substrate materials, and their interface resistance will be discussed. Both experimental and phonon transport models will be used to determine chip level heat dissipation performance. The use of optical thermometry methods such as Raman spectroscopy and micro-Infrared spectroscopy made on multi-quantum well LEDS will also be presented. Extensions of Raman spectroscopy to measure temperature and stress simultaneously will be discussed. Finally, packaging materials and thermal management issues for highpower LEDS will be discussed. This will include the integration of 1-D nano-materials to enhance heat dissipation. Numerical simulations of packaging architecture combining new thermal management materials and concepts will be presented.
Standardization of LED measurements; recommendations of the CIE
- Dr. Kathleen Murray : National CIE Committee,USA
First the difficulties of LED measurement will be described; efforts within the CIE Division 2 will be mentioned in order to resolve the discrepancies in the measurement results between different laboratories. CIE Report #127 will be discussed in detail, especially recommendations on luminous intensity measurements. More work was needed for recommendations on flux and spectral measurements. This was accomplished within the TC2-45 Technical Committee whose report is now in the final stages, ready for publication. Finally it will be shown what direction standardization has to go in order to upkeep with the rapid development of the LED Industry.
Challenge packaging issues for flip-chip and thin-GaN LED
- C. Y. Liu : Dept. of Chemical Engineering and Materials Engineering, Institute of Materials Science and Engineering, National Central University, Jhongli, Taiwan, R. O. C.
Currently, using GaN based LED (Light Emitting Diode) as a lighting source has attracted serious attention. Thin GaN and flip-chip LED are two most promising LED structures to exceed the efficiency of white incandescent and halogen light bulk. In this talk, three packaging related issues for flip-chip and thin-GaN LED structures are addressed: (1) Soldering assembly process for Au stud bumped flip-chip LED. (2) Thermal stable Ohmic/reflection contact layer to P-GaN. (3) Wafer bonding for the fabrication of thin-GaN LED structure.
Thermal packaging of High Power LEDs
- Shin Moo - Hwan : Semiconductor Thermal Design Laboratory, Professor of the MyongJi University, Department of Materials Science and Engineering
Effective thermal management in high power LEDs is still one of the critical issues for the realization of the devices for general illumination and other applications that require high power operation. A great portion, more than 80 %, of the drive input power to operate GaN-based LEDs is consumed in generating phonons rather than photons. It is important to develop unit LED package with low thermal resistance. However, it is imperative that the systems, where the LED packages are mounted, are designed in thermally optimized manners, otherwise the inner LED chips would be burnt under the thermally closed systems.
In this paper, it will be reported on thermal packaging schemes from the package level to system level. In particular, thermal interfaces inside LED packages will be thermally analyzed using thermal transient method. The thermal effects of the epoxy mold, which used to be considered as only an optical designing parameter, will be investigated. LED packages connected to several modes of heat pipes will be thermally characterized for the real application and extracted design rules will be suggested. Thermal characterization for the array systems will be proposed as well.
Novel application of high-power LED panel in the fields of fishery, medicine, and optical communication
- Kensho Okammoto, Ph.D : Professor of the Kagawa University, School of Engineering, Department of Reliability-based Information Systems Engineering.
The author has developed various application of LED with full originality and uniqueness in the fields of engineering, horticulture, agriculture, medicine, fishery and light art. The examples are as follows; versatile visible light communication apparatus, space optical communication system and liquid-level sensor in which an LED acts two roles of light source and optical sensor, reversible solar cell -LED CELL- composed of thousands of red light emitting diodes, LED plant growing equipment with LED growth-sensor, light beam therapy apparatus for neonate jaundice, control of cancer cell proliferation by LED irradiation, blue LED fishing-lamp for squid-fishing boat, and miscellaneous LED art goods. In this lecture, application of high-power LED panel light sources to squid fishing-light, in vitro cancer cell inhibition and space optical communication will be introduced.
High brightness LED with vertical structure supported by electroplated metal
- Dr. Jong Jea Jung : LG Innotek Co., Ltd., Korea
In recent days, vertical type LEDs have been in the spotlight to overcome the problems of conventional type ones. Vertical LED has the advantages of high brightness, low operation voltage, more stable ESD property, and efficient thermal dissipation, which were limited to achieve in conventional one. When vertical LED stands free, it is mechanically weak for subsequent chip processing. Due to this problem, it requires the supporting material, which is usually fabricated in the method of wafer-bonding. The complication exists when the secondary substrate is added to the opposite surface of sapphire wafer by bonding processes and is removed after laser lift-off (LLO) of sapphire wafer.
Metal supporter produced by electrochemical deposition can be a solution for present vertical LED technology. We occupy the front end of metal supported vertical LED technology based on the patents that we own. Its noticeable technology includes device isolation by ICP-RIE, trench filling, easily removable post formation, and electroplating of metal supporter. ICP-RIE forms the wafer scheme of pre-isolated LED devices. Vacant volume of wafer resulted by ICP-RIE is filled with various materials. Posts made of easily removable materials are established for readily separation of each chip when expanding force is applied. The metal supporter, whose material can be Cu, Au, Ni, and other metals and alloys, is deposited by electroplating. It reduces the process steps of secondary substrate formation and very effectively dissipates heat created when LED is operating as well as replaces the role of sapphire substrate.
We are about to employ the above original technologies for mass production of single-wire bonded chips over 50,000 of vertical structure.
High bright LED Packaging Technology and Encapsulation Resin.
- Mr. Atsushi Okuno : Sanyu Rec Co., Ltd., Japan
Recently, the LED market has been growing very rapidly. Applications such as LED back light, car lighting, display will increase very rapidly from this year. The next step will be general lighting market. This is great market. Korea, Japan, Taiwan, China and USA are starting as national project. The target is 2010. LED chip, packaging, lighting companies are starting very rapidly developing.
We are developing high power LED encapsulation resins and packaging systems for mass production. At the first time, we developed encapsulation resin for high power white LED. These resins have good high reliability. These resin are very good effect lighting applications.
On the other hand, we developed good mass production systems for the lighting market. We developed VPES (Vacuum Printing Encapsulation Systems). This method is very suitable to make LED lense for lighting application.
We successfully developed LED resin of high power LED and packaging systems for big market of LED lighting.
Development of high power LED and importance of standardization for wider application
- Kohtaro Kohmoto : Technologue Co., Ltd.
LEDs, new generation light sources are expected to tend for general illumination more and more. One important issue for wider application on general illumination field, is luminous efficacy and absolute quantitative value of light output from one unit source (one chip).
On early stage of white LEDs (just after first commercially development), light output of one chip was only 0.5 1.5 lm Ø chip however, it was gradually increasing and recently so-called "High Power LED (or High Brightness LED - HB LED)" of 120 lm Ø chip was developed and led into actual market. As high power LEDs are principally expected to use for general illumination, proper standardization will be indispensable for wider and newly developing application. Several examples designating importance of standardization are described hereinafter. Among them, two important and principal issues, such as terminology and optical measurement are discussed in detail.
Some distributors of LEDs are often use term: "high brightness LED" or "HB LED" for more light output power LED than ordinary LEDs. This seems to have a problem of harmonization on terminology (definition). Technical terms of this field have been standardized with cooperative works in several international or national organizations, such as CIE (Commission Internationale de'Eclairge) and IESNA (Illuminating Engineering Society of North America).
According to terminology standardized by these organizations, "brightness" does not mean concrete quantitative value of light and means only perceived degree of illuminated area. In case of designating quantitative value of surface density of light on an certain area, technical term : "luminance" shall be used, not "brightness".
In case of using LEDs for general illumination, an absolute value of light output from an applicable light sources however, the most important quantitative value would be luminous efficacy (energy conversion rate). In order to evaluate true luminous efficacy, proper and precise measurement of light output, essentially total luminous flux from LEDs. Total luminous flux measurement of conventional light sources for general illumination, has been developed and standardized for long period however, as LED light sources have specific features on source structure and energy converting mechanism comparing with the conventional vacuum system light sources, conventional photometric system can not always applied. Newly investigative issues will be also introduced hereinafter.
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