Thermal raman and IR measurement of heterogeneous integration stacks

Thermal management and planning is important for heterogeneous integration due to the introduction of a complex thermal path. Thermal measurement of operating devices provides necessary data points for future design as well as validation of models. In this paper, two methods for measuring thermal performance of DAHI (Diverse Accessible Heterogeneous Integration) GaN HEMTs are presented and contrasted: IR microscopy and micro Raman spectroscopy. The QFI IR system uses a per-pixel material emissivity flat temperature calibration when the device is in an off-state, and then calculates operating temperatures by CCD exposure. Two separate QFI systems with differing CCD resolutions were used to collect thermal data and are compared. Raman Thermometry by contrast, is a laser point measurement of the frequency shift in scattered photons due to phonon vibrational modes whose frequencies are temperature dependent. Differences in measurements between the two methods arising from the stack of materials used in the DAHI process and their transparency are discussed. A method for measuring the surface temperature of the devices through Raman by the use of TiO2 nanoparticles is also presented in conjunction with a profile of the HEMT. Measurements are presented alongside thermal simulation results using prototype software Mentor GraphicsTM Calibre®.