A monolithically integrated LED array is being developed with applications in the projection display industry and other non-display market areas such as scanning, computational photography, and depth analysis. The team's process begins with a compound semiconductor LED wafer upon which individual LED pixels are lithographically patterned to create a display. Light is generated from each individual LED pixel only where and when needed for the display. Both an active and passive matrix version are under development, the active matrix version uses laser crystallized polycrystalline silicon, whereas the passive matrix version takes advantage of direct addressing and/or rectification in the LEDs. The final calculated light path efficiency is approximately 75%, which represents a 5-10X improvement over the efficiency in current commercial systems. The reduced parts count allows for a smaller total system size, a smaller bill of materials, and a dramatically-decreased system cost for both direct view and projection microdisplays. This approach increases the brightness, decreases the cost, and reduces the overall size of this class of displays, eliminating the obstacles for mainstream adoption of this system in display and non-display markets.
This system has the potential to develop a picoprojector with a power efficiency, brightness, cost, and form factor unavailable in incumbent systems. In addition to applications in displays, picoprojectors with this efficiency, brightness, and form factor can be used in a number of other applications including depth imaging, in-situ guidance for medical procedures, and computational photography. Commercialization of this device will impact all of these areas and enable a range of new downstream applications. This approach will also demonstrate the potential for commercial integration of compound semiconductors with silicon using laser recrystallization. This approach also has the potential to impact a range of other devices that currently use silicon backplanes integrated with compound semiconductor devices, such as focal plane imagers. These devices, which are primarily used in hyperspectral imagers today, have a range of applications in the medical, military, earth science, and metrology space and further development in this area has the potential to impact these project areas as well.
The parent program to this I-Corps effort proposed the use of advanced laser processing to create systems that have silicon transistors integrated with other semiconductor materials and devices. We achieved this by using a transistor fabrication process that takes advantage of excimer laser processing, which is able to deliver energy quickly to thin silicon films, before any heat diffusion or damage occurs. This approach allows the fabrication of high performance electronic devices with virtually no thermal impact to the substrate. In addition to developing the processes necessary to achieve this vision, we developed a high power/high efficiency light emitting diode-based display that builds transistors directly on a foundry-sourced compound semiconductor wafer. The wafer was processed to create individual LEDs that are then externally addressed or (in the ultimate implementation) driven by the recrystallized transistors. The I-Corps component of this program led to the founding of a company to commercialize some of the developed technologies. We identified several potential customers and target market areas, and together with support from some of the target customers, have begun commercializing the technology. The two students involved in the project are working for this company as a direct outcome of the technical and commercialization activities supported by the NSF. Intellectual Merit: This program advanced a device concept in which high quality compound semiconductors can be integrated with high performance silicon devices. This brings a new option to hybrid device integration, and avoids many of the complications associated with heterepitaxial growth and wafer bonding. We demonstrated a variety of devices and integration options, including the processing and handling of LED substrates, the development of an LED-based projector, and the processing of high performance silicon transistors on a variety of temperature sensitive substrates. Through the I-Corps program and the customer development process, we narrowed down the commercial possibilities for the technology and selected the most promising areas for initial commercial activity. Broader impact: The products of this program have a variety of possible applications in displays, night vision, sensing, and high performance computing. This supports many national goals including higher energy efficiency in computing and displays, the development of higher performance energy conversion sytems, and the further extension of CMOS scaling. There was also a significant educational and outreach component to this work. This program helped support several educational initiatives, including the development of a suite of laboratory exercises for a class that have been released to other educators and the public under an open source license (https://sites.google.com/site/elen4193/home) and participation in citizen-scientist/hobbyist events in the New York area including Maker Faire and Botacon.
