Distinguished Seminar: Samuel Graham, Ph.D., Engineering Interfaces to Improve Thermal Performance of Wide Bandgap Semiconductors

Abstract: Wide bandgap electronics made from Gallium Nitride (GaN), Gallium Oxide (Ga2O3), and Hafnium Oxide (HfO2) are currently under development due to their potential to create some of the most advanced RF, power electronics, and neuromorphic computing devices in the world. However, the performance and reliability of these devices are often controlled by their electrothermal response during device operation.  A key feature which limits thermal control of the peak temperature is the thermal resistance that is encountered at material interfaces with these devices.  In general, thermal energy is created through joule heating and must be dissipated by transport across interfaces within the devices (e.g., GaN HEMTs) or across contacts to the devices (e.g., in Ga2O3 and HfO2).  Thus, an understanding of the interfacial thermal transport and methods to create low thermal resistance interfaces is of key concern in the development of future electronic devices from these materials.

In this talk we will discuss advancements in thermal characterization techniques that have allowed new insights into the impact of interfaces on the thermal response of GaN and  Ga2O3 electronic devices.  Thermal interfacial resistance and thermal conductivity have been measured by time domain thermoreflectance and provide critical properties for the electrothermal modeling of both power and RF devices.  Recent advancements in growth have shown near theoretically high values of thermal conductivity for materials such as AlN, in excellent agreement with DFT calculations.  While such high thermal conductivity substrates like AlN, SiC or diamond have promise for heat dissipation from wide bandgap materials, their integration must be performed in a manner that limits the interfacial thermal resistance.  This integration can be done through growth processes with inherent defects at the interface or through bonding.  Recent results have shown ultralow interfacial thermal resistance for the heterogenous integration of materials through plasma activated bonding.  The integration of GaN on Si, GaN on diamond, and GaN on SiC have shown that interfaces of excellent quality can be produced by this method, allowing for excellent heat dissipation.  Finally, for power electronics, the packaging solutions for the thermal management of ultrawide bandgap devices will be presented, allowing for the future implementation of this technology.

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Bio: Samuel Graham is the Eugene C. Gwaltney, Jr. Professor and Chair of the Woodruff School of Mechanical Engineering at the Georgia Institute of Technology.  He leads the Electronics Manufacturing and Reliability Laboratory which is focused on the electrical and thermal characterization, packaging, and reliability of wide bandgap semiconductors, solar cells, and flexible electronics.  He also holds a courtesy appointment in the School of Materials Science and Engineering at Georgia Tech, a joint appointment with Oak Ridge National Laboratory, and is a Visiting Professor at Nagoya University in Nagoya, Japan. He is a Fellow of ASME, a member of the Engineering Sciences Research Foundation Advisory Board of Sandia National Laboratories, Air Force Scientific Advisory Board, and the JASONs Advisory Group.