Advanced Thermal Characterization

GaN Electronics

Gallium Nitride (GaN)-based electronics are one of the most exciting semiconductor technologies for high power, high frequency power amplifiers and high voltage power switching devices. However, the very high power densities enabled by the excellent electrical properties of GaN and its related alloys lead to high device temperatures and degraded performance. Due to recent advances in the design of heat sinks, thermal spreaders, and interface materials, the thermal resistance within the first ~100 µm of the electrical junction may be the dominant thermal resistance in the system [1]. This very challenging thermal management problem requires a paradigm shift from the traditional thermal stack to embedded cooling solutions.

At the Device Research Laboratory, we are investigating thermal issues in GaN devices. We are developing electro-thermal and thermal modeling tools to aid in understanding the relationship between the electrical operation and thermal transport in GaN-based devices. Although often limited to simple 2D configurations, electro-thermal models give valuable information about the heat source and the dependence of the heat source size and shape on the bias condition and device geometry [2]-[3]. On the other hand, more flexible thermal models provide the 3D temperature and heat flux distributions for predicting device temperature and optimizing the device design.

Our most recent work has included computationally-efficient, analytical thermal models for GaN epitaxial structures and high electron mobility transistors (HEMTs) [4]-[5]. These models are helpful in parametric studies to understand the key dependencies of temperature rise on device structure and layout. In addition, we are pursuing thermal metrology techniques based on micro-Raman and infrared microscopy and in-situ thermal sensors [6]. Our future goal is to develop an innovative, near-junction thermal management strategy based on high thermal conductivity solid materials and liquid-vapor phase change cooling.

  1. “Near Junction Thermal Transport (NJTT)”, DARPA Broad Agency Announcement DARPA-BAA-11-09, Nov. 2011.
  2. K. R. Bagnall, O. I. Saadat, T. Fujishima, Y. Nam, T. Palacios, and E. N. Wang, “Electro-thermal modeling of heat generation in AlGaN/GaN HEMTs,” Proc. International Workshop on Nitride Semiconductors, Sapporo, Japan, Oct. 2012.
  3. K. R. Bagnall, T. Fujishima, O. I. Saadat, Y. Nam, T. Palacios, and E. N. Wang, “Quantitative analysis of heat generation in GaN-based electronics based on electro-thermal modeling,” ASME 2013 Summer Heat Transfer Conference, Minneapolis, MN, Jul. 2013.
  4. Y. S. Muzychka, K. R. Bagnall, and E. N. Wang, “Thermal spreading resistance and heat source temperature in compound orthotropic systems with interfacial resistance,” To be published in IEEE Trans. Components, Packaging, and Manufacturing Technology, Mar. 2013.
  5. K. R. Bagnall, Y. S. Muzychka, and E. N. Wang, “Kirchhoff transformations for conduction problems with heterogeneous temperature-dependent thermal conductivity relationships,” To be presented at ASME 2013 Summer Heat Transfer Conference, Minneapolis, MN, Jul. 2013.
  6. O. I. Saadat, K. R. Bagnall, T. Fujishima, D. Piedra, J. R. Lachapelle, E. N. Wang, and T. Palacios, “Schottky diode based in-situ temperature sensors for AlGaN/GaN HEMTs,” Proc. International Workshop on Nitride Semiconductors, Sapporo, Japan, Oct. 2012.