One of the biggest initial barriers to the widespread adoption of energy-efficient light-emitting diodes (LEDs) has been the cost. While considerable progress has been made on that front, further cost reductions will result in even wider adoption and thus greater energy savings – which will be deepened by continued improvements in efficacy.

A project funded by the Department of Energy (DOE) has developed an approach to lowering the cost of high-power LEDs while improving their energy efficiency. Implemented by Lumileds, the project involves the use of patterned sapphire substrates (PSS). PSS technology is an effective approach to improve efficacy and reduce cost of LEDs; the volume emission from the transparent substrate leads to high package efficiency, while the simple and robust architecture of PSS-based LEDs enables low cost. PSS substrates have gained wide use in mid-power LEDs over the past years, but much less use in high-power LEDs because of a number of technological issues. With the help of DOE funding, Lumileds has developed and industrialized a technology for using PSS with high-power “flip-chip” LEDs – which are commonly used in directional lighting applications such as spotlights and streetlights – to bring the benefits of high efficacy and low cost to a broader range of applications and accelerate adoption.

The project’s objective was to establish and industrialize a low-cost PSS high-power LED fabrication process capable of producing best-in-class performance in terms of both lumens per Watt and lumens per dollar, when combined with low-cost packaging methods. Lumileds’ state-of-the-art indium gallium nitride (InGaN) high-power LED architecture involves fabricating a thin-film flip-chip device supported by a metalized ceramic submount, which entails a series of steps to enable efficient light extraction. The alternative approach that was developed by this project involves leaving the InGaN layers on their sapphire substrate to simplify the fabrication process and enable simpler packages that utilize the sapphire as mechanical support, thereby reducing the total cost.

Lumileds’ PSS approach to LED design and fabrication was optimized not only for highly efficient light extraction, but also for high-volume manufacturability. The patterning of the sapphire was developed in an integrated fashion together with the process of depositing the InGaN layers to enable the highest possible performance. Concurrently, methods were developed to take maximal advantage of the PSS LED in different types of products that meet the needs of various lighting applications. Lumileds demonstrated an efficacy of 131 lumens per Watt at a warm-white color, with good ability to show the true colors of objects. A reduction in cost of up to 30% was demonstrated, thanks in part to a reduced need for labor-intensive LED packaging operations.

The new PSS technology has been fully implemented in manufacturing at Lumileds’ manufacturing facility in San Jose, California, and incorporated into a wide range of LED lighting products that have been successfully introduced onto the market, including LUXEON Q and LUXEON FlipChip White. “DOE funding has helped to speed up our research and development in LED lighting by cushioning some of the risk,” says Jy Bhardwaj, Lumileds’ senior vice-president of R&D. “It has enabled some of our most successful products on the market today.”