25 September 2020
Picosun’s ALD boosts UVC LED reliability and lifetime
Picosun Group of Espoo, Finland says that its atomic layer deposition (ALD) thin-film coating equipment has been used to deposit passivation and barrier films in UVC (ultraviolet-C) LEDs that have achieved excellent reliability and lifetime improvements at customer and collaboration partner Taiwan’s National Chiao Tung University (NCTU).
Specifically, an UVC LED with 50nm ALD Al2O3 passivation and normal LED packaging (no hermetic seal) maintained 80% of its original efficiency even after 500 hours environmental test at 85% humidity and 85oC temperature.
ALD passivation layers could potentially replace the expensive hermetically sealed package of the LEDs and thus lower the costs of the final device.
To reach maximum light output and long operating lifetime, LED chips require surface passivation to eliminate parasitic currents caused by traps and defects. Also, barrier coating is typically needed, as LED materials are sensitive to moisture. ALD is a suitable technique for manufacturing both the passivation and barrier films and, when LED size diminishes to micron dimensions, the only coating method capable of producing sufficiently high-quality films on the required minuscule scale. Ultra-thin, pinhole-free ALD films do not suppress the LED light intensity and they provide reliable protection against ambient conditions, whereas their superior conformality ensures no thickness variations between the facets of the LED chip. Thickness variations (a typical side effect of other coating methods) can potentially lead to uneven distribution of film stress or thermal expansion behavior and risk physical damage of the chip.
“We have used Picosun’s ALD technology already for years with great success,” comments NCTU professor Hao-Chung Kuo. “Our Picosun ALD equipment yields superior quality films, which has helped us to achieve several breakthroughs in our LED research,” he adds. “Picosun has a local presence in Taiwan and we appreciate the prompt response of their customer support if we ever have any issues. At the phase when R&D results are to be ramped up to industrial-level production, the scalability of Picosun’s ALD technology is a huge benefit.”
Short-wavelength UVC radiation destroys bacteria and viruses, so UVC LED technology is particularly topical now during the ongoing COVID-19 pandemic. Small, lightweight LEDs enable versatile design of portable, compact disinfecting equipment, they consume less power than other UVC sources, they are durable, and they pose no risk of hazardous material leaks such as mercury lamps, for example.