Chris: I recently learned that you were one of the inventors of the monolithic microLED process with patents dating back to the early 1990s. The approach that most of the companies currently working on microLED microdisplays are bonding an LED wafer to a silicon wafer using a process that is similar to the one Kopin patented almost 30 years ago. Can you tell us a little more about the reason why you developed the technology and what you were trying to solve at the time?
John: In the early 1990’s, we were working on monolithic LED bars on glass (at that time all the LEDs were discrete) in addition to micro LCDs. We developed the lift off and substrate removal technology to transfer a thin silicon active matrix to a glass substrate to make an LCD-based microdisplay. We thought a similar lift off process might work to transfer a thin film LED structure to a transparent substrate. One need we identified were very small-pitch monolithic LED bars for commercial printers that used an LED bar formed from discrete LEDs those days. The thin-film monolithic LED bar could be used for such printers. The second need was two-dimensional arrays that have uniform performance characteristics. If we could bond thin film LED arrays to Si driver circuits fabricated on bulk Si wafers, this would offer what has become to be known as a microLED-based microdisplay. Such a device would also minimize the crosstalk among LEDs by having high lateral resistance, thus improving performance over existing microdisplays.
Chris: How was this early work funded?
John: The project was funded by the Office of Naval Research (ONR) and DARPA.
Chris: This work led to two patents in the 1990s (U.S. patents 5,300,788 and 5,453,405). Can you tell us what these patents describe?
John: The claims of the ‘788 patent apply to the LED bars and arrays made with thin film structures having high lateral resistance between pixels. The ‘405 patent claims the methods of making thin film LED bars and arrays using a lift off technique. Another claim relates to a method of bonding LEDs to silicon wafers with a eutectic solder.
Chris: Why was development of microLEDs not pursued at that time?
John: As laser printers became better and cheaper, the LED printers became obsolete. The technology for thin film LEDs and bonding to Si was immature and possible applications for LED microdisplays was not clear. In addition, we became very busy with our successful LCD microdisplay business based on liftoff and film transfer technology.
Chris: In 2002 Kopin was granted another microLED related patent (U.S. patent number 6,403,985). What drove development of this patent and what does it describe?
John: In fact, the patent application was filed in 1994 but the patent was granted much later. We were successful in bonding LED bars and arrays to Si wafers with embedded driver circuits. At that period, we were developing thin, lightweight III-V solar cells for Boeing’s space satellite programs, and III-V concentrator cells for the Solar Energy Research Institute. So, we actually were able to grow GaAlAs red LEDs on GaAs bulk substrates, remove the bulk substrates, and bond red LED monolithic arrays on Si driver circuits fabricated in bulk Si wafers. We used eutectic metallic bonds to connect the LED arrays to Si driver circuits. We actually made about a dozen working prototypes of red LED microdisplays on Si, some of which were delivered to ONR and DARPA. Our patent claims a light emitting video display comprising multiple light emitting pixel elements, each pixel element smaller than 30 um2, which are monolithically connected to row and column driver circuits and a display control circuit. Amazingly, it is very similar to what a lot of folks are doing right now. Too bad our patent expired in June of last year. We were way ahead of the time. History often repeats itself.
Chris: MicroLEDs is a very hot topic today, but Kopin has focused on other display technologies over its 30+ year history. For example, you offer microdisplays using LCD, FLCOS and OLED technology today, but not microLED. How do you see microLEDs fitting into the portfolio going forward?
John: As you mentioned, we offer many different display types and they have their own pro’s and con’s. We used to say no display is perfect for all applications. We are investigating the microLED displays to complement our display portfolio. This would be a logical progression. The biggest advantage of the microLED display is the potential for very high brightness, which would be useful for see-through AR applications. We have recently showed our roadmap to increase the OLED display brightness to 30,000 nits. LED microdisplays can provide even higher brightness than the OLED displays. However, the LED microdisplays are still in an early stage of development. After decades, it is so interesting to observe that almost all of the current LED microdisplays are based on our approach of monolithic transfer of LED pixel arrays onto a Si backplane. If the LED microdisplays can be successfully developed and economically produced, they could be the ultimate display.
John C.C. Fan Dr. Fan is founder, chairman, CEO, and president of Kopin Corporation, a NASDAQ public company since 1992. Kopin, headquartered in Westborough, Massachusetts, is a leading provider of components and technologies for mobile and wearable devices. Kopin has over 300 patents and patents pending in this emerging growth area. Fan began his career at MIT’s Lincoln Laboratory, where he researched semiconductor materials and devices. He was leading the Electronic Materials Group at Lincoln Laboratory when he left MIT in 1985 to found Kopin Corporation. Fan grew up in Hong Kong and obtained his Bachelor of Science, Electrical Engineering with highest honors from Berkeley, California. He went to Harvard University under a Harvard fellowship and obtained his Master and Ph. D. degree in Applied Physics in 1972. Fan has authored over 200 publications, edited three books, and owns over 70 patents. Fan was also the co-founder and Chairman of several integrated circuit and advanced materials companies. Three of them were sold to large public-listed semiconductor corporations. Fan received the Society of Information Displays Special Recognition Award in 1999. Fan was the Ernst & Young New England Entrepreneur of the Year in 2000, and also the National Finalist. He was chosen one of the Top 25 Asian American Entrepreneurs by Asia Week in 1999, and one of the top 100 Asian American Entrepreneurs between 1999–2004 by Asia.net. Fan was chosen as one of the USA’s top 15 nanotechnology innovators by NASA’s Nanotech Briefs in 2005. In 2020, Fan has also been elected as a member of the USA National Academy of Engineering (NAE) for his contributions “For Innovation and Entrepreneurship in Electronic Materials and Devices for Displays.” Only a very select group of engineers are admitted to NAE membership, which is one of the highest professional honors accorded an engineer.