Nov 6, 2017: UK’s only LED manufacturer Plessey is commercially making LEDs on silicon substrates, the first LED maker to do so in the world.
The company has three semiconductor manufacturing cleanrooms on its site. The cleanrooms has two MOCVD reactors for making 6-inch GaN-on-silicon LED wafers. Its fabs are capable of making CMOS ICs, bipolar ICs and discrete semiconductors.
The company is prepared to build a mass-production LED GaN-on-Si process from proof‑of‑concept wafers. Its GaN-on-silicon intellectual property came from University of Cambridge spin-out CamGaN, when it bought it in 2011.
GaN-on-silicon is a cheaper way to make LEDs than traditional GaN‑on‑sapphire, because silicon is the lowest-cost substrate material. Plessey insists that this cost advantage will get translated into a lower product cost.
The company’s process is automated because it uses standard silicon semiconductor manufacturing technology, while its competitors have manual process. It is on par with Cree’s four die MKR LED in efficacy.
The believes that its competitors are Cree, Osram and Lumileds. Chinese LED manufacturers have not yet achieved sufficient quality to compete with Plessey.
The Plessey 7070 has four junctions tiled in a square on a single piece of silicon, connected in series using chip‑style metallisation layers.
The separate die technique is at a disadvantage because it needs comparatively large gaps between die, leaving a ‘black cross’ in the emission surface, which translates to a central dim patch in any narrow beam created from the LED. This effect is not noticeable with the black cross of Plessey’s device which is smaller than a hair’s breadth. Protection diodes and driver circuits could also be integrated into LEDs monolithically, if the need arises.
GaN-on-Silicon TECHNOLOGY ADVANTAGES
Better thermal performance that provides three degrees of leverage:
- Lower LED operating temperature
- Higher reliability
- Simpler heat sink
- Lower system cost
- Higher drive current
- Cost down through more lumens per die area