Peak channel temperature determination for an AlGaN/GaN HEMT with Raman Thermography and MTTF extraction for long term reliability

Reliability tests are a decisive step for GaN technology qualification. To evaluate the Mean Time to Failure (MTTF), it is necessary to know well the peak channel temperature (Tpeak) reached at the hottest point of the device. For an AlGaN/GaN High Electron Mobility Transistor (HEMT), this region lies at AlGaN/GaN interface where the two-dimensional electron gas (2DEG) is located near the gate contact. InfraRed (IR) Thermography was performed on our GaN on Si HEMT devices to measure Tpeak. Considering the correction in underestimation of Tpeak temperature, the MTTF was extracted. We also performed Raman measurements and Tpeak was evaluated with the aid of 3-Dimensional thermal simulations. The Tpeak difference between IR and Raman technique is more than 100°C and far from the evaluation of about 40-50°C often found in literature. The reliability measurements show a high robustness and from the Raman approach MTTF is approximately 109 hours instead of the 106 hours estimated with the IR method at Tpeak =200°C.