Transient Simulation for the Thermal Design Optimization of Pulse Operated AlGaN/GaN HEMTs.

Huaixin Guo,Tangsheng Chen,Shang Shi

doi:10.3390/mi11010076

Abstract

The thermal management and channel temperature evaluation of GaN power amplifiers are indispensable issues in engineering field. The transient thermal characteristics of pulse operated AlGaN/GaN high electron mobility transistors (HEMT) used in high power amplifiers are systematically investigated by using three-dimensional simulation with the finite element method. To improve the calculation accuracy, the nonlinear thermal conductivities and near-junction region of GaN chip are considered and treated appropriately in our numerical analysis. The periodic transient pulses temperature and temperature distribution are analyzed to estimate thermal response when GaN amplifiers are operating in pulsed mode with kilowatt-level power, and the relationships between channel temperatures and pulse width, gate structures, and power density of GaN device are analyzed. Results indicate that the maximal channel temperature and thermal impedance of device are considerably influenced by pulse width and power density effects, but the changes of gate fingers and gate width have no effect on channel temperature when the total gate width and active area are kept constant. Finally, the transient thermal response of GaN amplifier is measured using IR thermal photogrammetry, and the correctness and validation of the simulation model is verified. The study of transient simulation is demonstrated necessary for optimal designs of pulse-operated AlGaN/GaN HEMTs.

Highlights

AlGaN/GaN high electron mobility transistors (HEMTs) have recently been researched intensively and are considered prospective for high-power RF applications, owing to the advantages such as wide bandgap, high breakdown voltage, and high electron mobility [1,2,3,4]
For the high-power amplifiers used in radar and communication system, the GaN HEMTs are often operated in pulsed mode, performance is typically pulse width for the purpose of thermal management, and to maintain the operating channel temperature within a safe limit to avoid thermally activated degradation of the device performance
It is noteworthy that the thermal impedance of device increases with the rise of pulse width shown in the inset Figure 4b, the relation between pulse width and duty cycle is decided by the formula in the inset Figure 4b, and we find that this increase (∆Z)

Summary

Introduction

AlGaN/GaN high electron mobility transistors (HEMTs) have recently been researched intensively and are considered prospective for high-power RF applications, owing to the advantages such as wide bandgap, high breakdown voltage, and high electron mobility [1,2,3,4]. High power applications require high power densities in the active region of GaN devices, which leads to highly localized Joule self-heating and potentially high peak temperatures. To exploit the full potential of GaN devices, especially high-power amplifiers, a great concern is the thermal management both from a performance point of view and more importantly to ensure adequate device reliability [2,3,4,5,6,7,8]. For the high-power amplifiers used in radar and communication system, the GaN HEMTs are often operated in pulsed mode, performance is typically pulse width for the purpose of thermal management, and to maintain the operating channel temperature within a safe limit to avoid thermally activated degradation of the device performance. The relation between typically pulse width and channel temperature is influenced by thermal design of GaN HEMTs, including the Micromachines 2020, 11, 76; doi:10.3390/mi11010076 www.mdpi.com/journal/micromachines

Methods

Discussion

Conclusion