Integration of metallic phase change material in power electronics

Abstract

For various pulsed power electronics like, metal oxide semiconductor field-effect transistor (MOSFET), insulating gate bipolar transistor (IGBT), Gate turn-off thyristor (GTO), Integrated gate-commutated thyristor (IGCT), heat loads are often in the range of 10W/cm2 to more than 100W/cm2 for critical cases. The power spikes have to be thermally managed in order to avoid failure and ensure reliability. Most of the solutions consist in active heat sink dissipation that can achieve high heat transfer coefficients using air or liquid cooling. Nevertheless, due to thermal barriers between the hot spots and the heat sinks, temperature excursions that might exceed a critical temperature can occur. To avoid these temperature variations the heat sinks are usually oversized which can be an issue for confined systems. Phase change materials (PCM) embedded in the heat sink have been proposed as an improved solution. However, PCMs are most efficient when placed at the chip level the closer to the heat source. This last solution has important consequences on devices' fabrication and global cost. This study presents both experimental and simulation proof of metallic PCM efficiency in reducing devices' temperature. The PCM is inserted in the chip's, closer to the heat source than the integration inside the heat sink. The proposed integration is more straightforward than the integration at the chip level (silicon). The experimental setup consists of a CO2 laser heat source combined with a long wave infrared (LWIR) camera, spectral range: 7.5 – 13.5 µm for temperature monitoring. The CO2 laser can be controlled in power amplitude and duration as well as laser spot diameter. The reflectance of the used materials has been characterized with a spectrophotometer in order to calculate the emissivity and the absorption for a precise determination of the sample temperature variations. The PCM thermo-physical properties have been also characterized. 3D simulations using COMSOL MULTIPHYSICS were carried out in order to be compared with the experimentally observed thermal behavior. In order to account for the phase change phenomenon, an equivalent temperature dependent specific heat was implemented. Its value was correlated to the latent heat and to the phase change temperature range. Good agreement was found between the model and the experimental results. The model was used as a predictive tool for optimizing PCM container design.