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EpiPix Eliminates Dry Etching to Produce Record Performing Green Micro LEDs
March 22, 2020
UK-based University of Sheffield spun-out EpiPix, to develop and commercialize micro-LED technology for display panels in augmented and virtual reality devices, smart watches, mobile handsets and more. The company has already demonstrated prototype micro-LED arrays on single wafers with micro-LED pixel sizes from 30 microns down to five microns and less. “We are already engaged in discussions with major end-user customers for AR/VR applications, manufacturers of smart watches and smart phones and also LiFi companies,” he says.
Typical III-nitride microLEDs are manufactured using standard photolithography processes followed by dry-etching on an III-nitride LED wafer. However, dry-etching induces surface damage to the micro-LED, particularly at lower micro-LED diameters, degrading optical performance, including internal and external quantum efficiencies. As a result, industry players, far and wide, have struggled to fabricate high-brightness, sub-five micron micro-LEDs. Wang and colleagues for the past five years have been developing a direct epitaxial method for fabricating ultra-small and ultra-bright InGaN micro-LEDs that eliminates the need for dry-etching. A n-GaN layer is grown onto a silicon or sapphire substrate to create an as-grown n-GaN template. A SiO2 film is then grown onto the n-GaN layer, with an array of holes of the required micro-LED shape and diameter. LED structures can then be grown onto this pre-patterned SiO2 microhole arrayed template to form the micro-LED arrays. Crucially, the method uses standard MOCVD processes, and the arrays are designed to be compatible with any existing microdisplay fabrication techniques including pick-and-place and mass transfer technologies. “Wang's process does not involve dry-etching, damage and optical degradation, and so we've been getting some very good external quantum efficiencies with our micro-LED arrays,” says Camilleri. “This is why this process is attracting so much interest.”
Earlier this year, Wang and colleagues unveiled high luminance green microLED array bare chips, with a diameter of 3.6 micron, inter-pitch of 2 micron and an external quantum efficiency of 6%. This result has been quickly published in ACS Photonics. According to Camilleri, the researchers have fabricated blue micro-LEDs and are also developing red versions. EpiPix is also working with packaged chips. “This figure of 6% for a very small green microLED is a world record,” he says. “We are not using any reflective layers and no additional processing is taking place... This is pure light coming out of the microLED array.” Fabrication has taken place on two-inch wafers, and EpiPix will scale this to four-inch or six-inch substrates. The next 18 months to two years will also be spent on product development, beta prototyping, testing and providing samples to customers. And with process and device validation in hand, the micro-LED wafers will be ready for high volume manufacture.
“These devices can also be used for high-speed data transmission in LiFi applications, but I expect the first applications to be AR and VR as well as smart watches and mobiles,” says Camilleri. “In around two years, I want to be selling our microLED arrays to at least half a dozen global corporates in these applications.”
March 22, 2020
UK-based University of Sheffield spun-out EpiPix, to develop and commercialize micro-LED technology for display panels in augmented and virtual reality devices, smart watches, mobile handsets and more. The company has already demonstrated prototype micro-LED arrays on single wafers with micro-LED pixel sizes from 30 microns down to five microns and less. “We are already engaged in discussions with major end-user customers for AR/VR applications, manufacturers of smart watches and smart phones and also LiFi companies,” he says.
Typical III-nitride microLEDs are manufactured using standard photolithography processes followed by dry-etching on an III-nitride LED wafer. However, dry-etching induces surface damage to the micro-LED, particularly at lower micro-LED diameters, degrading optical performance, including internal and external quantum efficiencies. As a result, industry players, far and wide, have struggled to fabricate high-brightness, sub-five micron micro-LEDs. Wang and colleagues for the past five years have been developing a direct epitaxial method for fabricating ultra-small and ultra-bright InGaN micro-LEDs that eliminates the need for dry-etching. A n-GaN layer is grown onto a silicon or sapphire substrate to create an as-grown n-GaN template. A SiO2 film is then grown onto the n-GaN layer, with an array of holes of the required micro-LED shape and diameter. LED structures can then be grown onto this pre-patterned SiO2 microhole arrayed template to form the micro-LED arrays. Crucially, the method uses standard MOCVD processes, and the arrays are designed to be compatible with any existing microdisplay fabrication techniques including pick-and-place and mass transfer technologies. “Wang's process does not involve dry-etching, damage and optical degradation, and so we've been getting some very good external quantum efficiencies with our micro-LED arrays,” says Camilleri. “This is why this process is attracting so much interest.”
Earlier this year, Wang and colleagues unveiled high luminance green microLED array bare chips, with a diameter of 3.6 micron, inter-pitch of 2 micron and an external quantum efficiency of 6%. This result has been quickly published in ACS Photonics. According to Camilleri, the researchers have fabricated blue micro-LEDs and are also developing red versions. EpiPix is also working with packaged chips. “This figure of 6% for a very small green microLED is a world record,” he says. “We are not using any reflective layers and no additional processing is taking place... This is pure light coming out of the microLED array.” Fabrication has taken place on two-inch wafers, and EpiPix will scale this to four-inch or six-inch substrates. The next 18 months to two years will also be spent on product development, beta prototyping, testing and providing samples to customers. And with process and device validation in hand, the micro-LED wafers will be ready for high volume manufacture.
“These devices can also be used for high-speed data transmission in LiFi applications, but I expect the first applications to be AR and VR as well as smart watches and mobiles,” says Camilleri. “In around two years, I want to be selling our microLED arrays to at least half a dozen global corporates in these applications.”
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