Microsanj at IMS 2021

Nanoscale and Ultrafast Thermal Imaging of Gan RF Devices

Device performance requirements for today’s microwave devices are leading to shrinking device geometries, new materials such as GaN, Ga2O3, and more complex 3D structures. Since high temperatures and high-temperature gradients contribute to mean-time to failure (MTTF), it is essential that one have a thorough understanding of both static and dynamic thermal performance.  

Fortunately, recent advancements in thermal characterization techniques, such as femtosecond pump-probe laser and thermal imaging techniques have enabled the extraction of accurate thermal properties of the substrate and thin films down to 10’s of nanometers, and interface materials at time scales of 100’s of femtoseconds.  

For advanced electronic devices, we had to abandon Ohm’s law long ago, as ballistic electrical transport and quantum confinement have been present in commercial devices in the last 20 years or so.  Interestingly, Fourier law, which is Ohm’s equivalent for thermal transport, is still widely used to predict the thermal behavior of advanced devices using “effective” thermal conductivity or interface thermal resistances that can vary as a function of the size of the heat source or its frequency. Based on detailed electrothermal experimental and theoretical results, we show that quasi-ballistic non-Fourier heat conduction can be present in devices with feature sizes in the submicron range or at short time intervals  (below 10-100 nanoseconds at room temperature. Deviations from Fourier law can be as large as one order of magnitude in the cross-talk between neighboring heat sources.  

Experimental results for nanoscale heat sources on a GaN high electron mobility transistor (HEMT), are presented. Thermoreflectance imaging is used to study transient temperature distribution of active devices. By combining lock-in imaging with advanced image processing techniques, one can achieve far-field sub-diffraction limit resolution of 100-200nm. 

Presented by

Dr. Peter Aaen (Professor & Head of Electrical Engineering Department, Colorado School of Mines)

Dr. Ali Shakouri (Microsanj LLC & Director of Birck Nanotechnology Center & Professor of Electrical Engineering at Purdue University)