The benefits of LED over traditional lighting technology are clear – but now the first generation of LEDs is set to be overtaken by a brand new breed.
LEDs are one of the great technology success stories of the past 50 years. The huge advantages of these tiny light-emitting chips have seen them supersede traditional technologies in our homes, shops, streets, schools, transport hubs and factories – not to mention the backlit screens of our TVs, computers and mobile devices. There’s hardly an area of lighting now where LED isn’t beating the traditional technology or rapidly catching up.
But the way most LEDs are manufactured remains expensive and poorly optimised, holding back the technology’s full potential.
To unleash the technology’s full potential, the next generation of LED has arrived. Plessey has a new way of manufacturing LED chips and unlocked even greater efficiency and power.
LEDs are composed of a piece of semiconductor material (the die) placed on a base (the substrate). Traditional LEDs are made of gallium nitride (GaN) on sapphire. However, sapphire is not the only substance that can be used as an LED substrate – nor is it the cheapest. New technology has made it possible to use a much more cost-effective alternative, with some compelling advantages of its own: silicon (Si).
Plessey realised the potential of GaN-on-Si LEDs early on, and will have invested nearly £100 million in developing the technology and turning it into commercially available products.
Using a silicon wafer as a base for GaN LEDs isn’t easy. The different crystalline structures and electronic properties of GaN and silicon mean GaN-on-Si LEDs are prone to thermal strain which can impact performance. Overcoming this challenge has been the key to making Plessey’s GaN-on-Si LEDs a success. Plessey has developed a revolutionary process using a buffer layer between the GaN and the silicon, enabling a gradual transition from one material to the other.
The buffer layer has other advantages too: it enables the manufacture of larger LEDs with multiple junctions. This allows the process to be used in large die sizes that range from 3V to 24V, and to compete with multi-chip modules on performance and price.
Plessey’s proprietary LED manufacturing technology, called MaGIC (Manufactured on GaN-on-Si IC), is what makes it possible to use silicon as a substrate. Not only does this mean LEDs can be produced more cost effectively, it also improves the performance of the LEDs as measured in internal quantum efficiency (IQE).
Those familiar with the properties of silicon will know that it has one obvious potential downside as a base for LEDs: it absorbs light. Plessey’s MaGIC process solves this by adding a mirror layer in between the GaN and the silicon to reflect light back out. First the die is grown on the silicon substrate, then a mirror layer is added on top, followed by another layer of silicon. Then the whole thing is flipped over and the original silicon substrate removed, leaving a GaN die on a silicon base, separated by a mirror layer. Although this process is more complicated than standard LED production, it’s relatively straightforward compared to the complexity of making other semiconductor components, such as microchips.
GaN-on-Si LEDs are more cost-effective to produce than their traditional counterparts – but that’s just the first of many benefits. They’re more reliable than traditional LEDs because of their excellent thermal performance, which keeps their operating temperature down and helps to deliver a longer lifetime performance. This also means heatsinks don’t have to be so big and bulky, which reduces the size and cost of luminaires. They can also accept a higher drive current, meaning they can emit more light.
In 2012 Plessey – the only major LED manufacturer in the UK – became the first in the world to produce commercial LEDs on large diameter silicon substrates. The cost-effectiveness of our unique approach means that as a UK manufacturer we can compete with traditional LED manufacturers in China and the Far East.
GaN-on-Si LEDs are particularly useful in large formats, where traditional LEDs struggle. In the past, LED manufacturers have got round this problem by using multiple dies to create larger modules – compromising efficiency and leaving a tell-tale “cross-hair” shadow in the middle of the beam.
But thanks to GaN-on-Si, Plessey’s LUCIAN™ high power PLW7070 LEDs provide 30% more light output than the competition, with better thermal performance and no visible cross-hair – at half the cost. The PLW7070 is a single-die GaN-on-Si chip which outperforms multiple-die products when using any standard secondary optics, improving the performance of lighting fixtures.
When combined with beam-forming technology, Gan-on-Si technology completely transforms our vision of what LEDs can do. The small footprint and directional light emission of GaN-on-Si LEDs enabled Plessey to create its revolutionary miniature optics, which feature beam-forming technology at the individual chip level. The first product to harness this technology is the new Orion™ light module, launched last year.
For designers of directional luminaires, Orion™ represents a major step forward: a slimmer, more powerful, more precise replacement for chip-on-board LEDs, which can reduce the cost of a typical luminaire by half.
By integrating GaN-on-Si LEDs and optics into a tiny module, Orion delivers over 3,000 lumens from a unit just 5.6mm thick – with no secondary optics needed. Orion’s excellent thermal performance means heatsinks can be slimmer too. In fact, by incorporating Orion™, a 200 mm-deep industrial luminaire can be replaced by one just 36 mm deep. Finally, designers can do away with the bulky secondary optics and heatsinks that have long characterised LED spotlights, downlights and high bays.
Plessey’s fast-growing range of GaN-on-Si products are gaining considerable traction in the market, as lighting product designers see the numerous advantages in performance, flexibility, reliability, efficiency and cost. Just as LEDs have superseded older lighting technologies such as incandescent, fluorescent and sodium, we believe it’s only a matter of time until GaN-on-Si LEDs go from being a challenger technology to being a standard type of LED.