Three-dimensional thermal analysis of a flip-chip mounted AlGaN/GaN HFET using confocal micro-Raman spectroscopy

The authors demonstrate the potential of confocal micro-Raman spectroscopy to enable three-dimensional (3-D) thermal analysis of solid state devices. This is illustrated on a flip-chip mounted AlGaN/GaN heterostructure field-effect transistor. To better understand its heat dissipation and for device optimization, it is desirable to know temperature distribution not only in the active device area, but also in the bulk substrate. This cannot be achieved using traditional thermal imaging techniques. 3-D thermal imaging was demonstrated by probing the temperature dependent Raman shift of phonons at different depths within the bulk substrate using confocal micro-Raman spectroscopy. The heatsinking through the metal bumps connecting the active device area to the flip-chip carrier is illustrated. Experimental temperature results are in reasonably good agreement with 3-D finite difference simulations.