Cooling Hot Spots by hexagonal Boron Nitride Heat Spreaders

Other conference contribution, 2015

According to ITRS, the trend for microelectronics systems is towards smaller size, smaller package footprint and more functionality. As a consequence of this development, heat dissipation is becoming one of the major bottlenecks in limiting further growth and development of microelectronics systems. Therefore, there is a great demand for integrating into electronic devices highly efficient heat spreaders for reducing the temperature of local hot spots. Many different heat spreader materials have been developed for addressing the problem. Metallic materials like copper and aluminum are widely used due to their high thermal conductivity. However, the thermal performance of metal films decreases dramatically when their thicknesses are reduced into nanoscale. On the contrary, the thermal conductivity of thin hBN nano-ribbons can be as high as 2000 W/mK. Therefore, hBN films could find applications in the thermal management of high power electronics and displays, in particular in applications where carbon-based materials may not be appropriate. In this invited talk, the use of heat spreaders based on layered hBN films for reducing excess hot spot temperatures at the chip level in high power devices like light-emitting diodes will be reviewed. Different methods for synthesizing hBN flakes will be shown, with the main focus on liquid phase exfoliation (LPE). Examples of electron (SEM, TEM) and Raman spectroscopy characterization of the fabricated hBN films will be shown. After characterization, the hBN films were directly attached to the target power chips. The power chips were integrated with temperature sensors in order to analyze the thermal performance of the hBN heat spreader. Resistor temperature detectors and IR cameras were used to capture the hot spot temperature and the heat spreading effects of the hBN material by monitoring the temperature distribution around the hot spot. At a hot spot heat flux of 600 W/cm2 a hot spot temperature decrease of almost 20oC (from 95 to 75oC) was found compared to samples without hBN heat spreaders. In summary, our work so far shows signs of a promising future for the use of hBN heat spreaders for cooling hot spots in microelectronic systems. This presentation is based on work performed at the BioNano Systems Laboratory, Department of Microtechnology and Nanoscience, Chalmers University of Technology, the SMIT Center, School of Automation and Mechanical Engineering and Key State Laboratory of New Displays and System Applications, Shanghai University, and the SHT Company, Gothenburg, Sweden, by my colleagues Yifeng Fu, Lilei Ye, Johan Liu, and graduate students Shuangxi Sun, Wei Mu, Jie Bao, and Shirong Huang.