Processing and packaging for large format infrared LED emitter arrays for scene generation

Date
2017
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University of Delaware
Abstract
Infrared light emitting diode (IRLED) arrays are a next-generation technology for infrared scene generation, which can be used for the calibration and testing of infrared (IR) cameras. These LED arrays can function as IR scene projectors (IRSPs) that emit narrowband IR light through individually addressable pixels. LEDs have the potential for faster framerates and brighter light output than the thermal pixel arrays traditionally used. A large team of collaborators in our research group and at the University of Iowa have built a full LED IRSP system that operates at 100 Hz and displays an equivalent blackbody emission of 1350 K within the 3-5 μm band. Since our initial success in 2012, higher temperature, higher resolution and faster framerate arrays have been developed and are currently being tested by our team at the University of Delaware. Most of the development by our team has been on hybrid arrays, which consist of a gallium antimonide (GaSb) emitter flip-chip bonded to a silicon CMOS read-in integrated circuit (RIIC). Building an LED microdisplay to work with custom electronics requires materials processing to facilitate flip-chip die bonding, which presents many challenges. Along with this work, packaging the array in a cryostat needs careful planning and engineering to allow enough heat removal on the array and strong integrity of the analog electrical signals coming in. In this dissertation the processing and packaging of the IRSP systems are described in detail. ☐ Two key improvements that need to be made with our IRSP systems are dynamic range of light output and heat removal. The RIIC requires innovations in its design to both scale down in size and improve dynamic range of the LED’s emission. Part of implementing these innovations is modelling and improving the RIIC, specifically the transistors and pixel circuit used to power the LEDs. To reduce heating, an investigation into etching a lens shape to the output surface of each LED hopes to show a path to decreased reabsorption of emitted light. ☐ Lastly, infrared light is used to transmit signals for chip-to-chip communication. Normally, optical interconnects require additional optical components to generate and direct light, but by using bond wires as transmission lines, optical connections can be made between CMOS chips without additional wave guiding components. A theoretical loss analysis for a two wire optical transmission line is presented. Experiments to show IR light transmission through the two wire transmission line have been attempted without any success yet at this time.
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