SUBJECT: M.S. Thesis Presentation
   
BY: Yishak Habtemichael
   
TIME: Thursday, July 26, 2012, 10:00 a.m.
   
PLACE: Love Building, 109
   
TITLE: Packaging Designs for Ultraviolet Light Emitting Diodes
   
COMMITTEE: Dr. Samuel Graham, Chair (ME)
Dr. Satish Kumar (ME)
Dr. Peter Hesketh (ME)
 

SUMMARY

Deep ultraviolet (DUV) light emitting diodes (LEDs) emitting in the UV-C range of 200 - 290 nm have had growing appeal in the scientific community because of their attractive functions in areas such as disinfection, water & air purification, covert communications, and solid state lighting. The high aluminum content required for operation at shorter wavelengths also causes the reduction of radiative recombination efficiency due to piezoelectric fields in the quantum wells (QWs). Reduction in radiative recombination is directly proportional to increases in non-radiative recombination that occurs in the form of self heating in the devices. Consequently the effect of self-heating is demonstrated by the low performance (~1% EQE) of these devices. The motivation for my research thus concentrates on improving the heat dissipation of DUV-LEDs through packaging solutions. Conventional LED packaging technologies although mature are not applicable in this case because UV radiation can be limited due to the absorption rate of different materials. Methodical material selection and packaging schemes are necessary to ensure semi-transparent to fully transparent layers in these packages while still being able to keep the junction-to-ambient thermal resistances low and reject the excess heat effectively. State of the art packages for visible light LEDs are around 8 C/W while values 3-5 times this are found in DUV-LEDs. In this work, we explore the factors at the chip level package that impact the thermal resistance of the package. This is performed through 3D FEA analysis of substrates, flip chip bond pads and materials, as well as geometrical factors. The model is used to elucidate parameters which should be used to reduce the packaging thermal resistance and comparisons to experiments are made.