THESIS
2007
xiv, 81 leaves : ill. ; 30 cm
Abstract
Matrix-addressable light emitting diode (LED) micro-arrays on sapphire substrates have been reported. In the fabrication process, complicated chemical-mechanical polishing after planarization with oxides, or conformal sputtering metallization process were needed to ensure smooth metal interconnections. The resistance of each individual device was reported to depend strongly on the n-type GaN stripe length and distance of the die from the contact at the end of the column, leading to significantly larger turn-on voltages with great variation....[
Read more ]
Matrix-addressable light emitting diode (LED) micro-arrays on sapphire substrates have been reported. In the fabrication process, complicated chemical-mechanical polishing after planarization with oxides, or conformal sputtering metallization process were needed to ensure smooth metal interconnections. The resistance of each individual device was reported to depend strongly on the n-type GaN stripe length and distance of the die from the contact at the end of the column, leading to significantly larger turn-on voltages with great variation.
We have developed a simpler and more reliable fabrication process with much improved performance using a flip-chip configuration on a silicon wafer. The p-type contact aluminum bus lines were fabricated on the silicon carrier under the solder bumps, with very simple steps. The contact pads of the matrix were formed on the silicon wafer, with light emitting from the sapphire side.
A high resolution 8x8 LED dot matrix display has been designed and fabricated. An individual device size was 300x300μm2. The turn-on voltages of the devices on the display were found to be strongly dependent on the n-type metal bus line design. Various n-type metal bus line designs were fabricated on the same LED wafer for investigation. Our optimum design showed an average turn-on voltage of the matrix fabricated on the same LED wafer not much higher from individual ones fabricated with conventional process. The variation was also small, from 3.21V to 3.36V. The matrix was flipped onto the silicon wafer afterward. We demonstrated that each LED on the matrix was addressed and lit up successfully.
2mm x 2mm large LED with two different designs were also fabricated from the same fabrication process as the dot matrix display. These large LED provided higher wall-plug efficiency than the standard 0.3mm x 0.3mm LED at the injection current density range (0-225mA/mm
2).
Post a Comment