Fast estimation of channel temperature in GaN high electron mobility transistor under RF operating conditions

Abstract

Working at high RF power leads gallium nitride (GaN) high electron mobility transistors (HEMT) to self-heating that poses a limit to device performances and reliability. Thermal characterization is therefore of great value for proper design of heat dissipation and also for device reliability studies. The peak power dissipation in HEMT devices is located in the channel near the gate edge, which is typically buried under a field plate. This hot spot is thus inaccessible to direct temperature measurement. Therefore, any method used for temperature measurement has to be augmented by a thermal simulation to calculate the actual temperature in the channel from temperature measured elsewhere. In this work, we used thermal imaging to measure temperature during device operation in various pulsed RF conditions. To obtain the hot spot temperature, we developed a thermal simulation of AlGaN/GaN HEMT transistor on SiC substrate. The simulation estimates the channel temperature using 3D finite element method with multi-parameter input. To calibrate the simulation, we compared simulation results with IR images of a 2 mm AlGaN/GaN HEMT transistor operating at various pulsed RF conditions. The simulation is typically slow. In this work, we used the calibrated simulation to study the hot spot temperature as a function of the working conditions and formulated an approximated equation for the thermal behavior of the transistor as a function of power dissipation, base plate temperature, pulse width, and pulse duty cycle that may be used to estimate the channel temperature in real time.

Unveiling Tmax Inside GaN HEMT Based X-Band Low-Noise Amplifier by Correlating Thermal Simulations and IR Thermographic Measurements

“…The drawback is that they underestimate peak channel temperature due to averaging over the active device region [25], [26]. Optical measurements such as micro-Raman and infrared (IR) thermography [27]- [30] provide information on the surface temperature [18], [19], [31], [32], not the hotspots inside 2DEG buried below the gate of each HEMT. Moreover, spatial resolution limits optical measurements due to diffraction [33].…”

Experimental three-dimensional thermal mapping of a GaN on RF-SOI chip

“…As such, the knowledge of the temperature of the transistors, as well as the surrounding temperature field is a useful tool to ensure the optimal performance of the RF integrated circuit. The most common reported experimental techniques for a thermal analysis of an IC rely on measuring its surface temperature using either an infrared or CCD camera [4], [5], Raman spectroscopy [6], thermocouples or thermometers deposited on top [7], [8], thermal scanning probe [9], liquid crystal technique [10], the temperature dependence of leakage currents [11] and noise Thermometry [12]. Nevertheless, the temperature of the transistor channel may not be the same as that of the surface of the IC.…”