Thermal characterisation and analysis of GaN power devices

• Main Author: Wirna
• Other Authors: Ng Geok Ing
• Format: Final Year Project
• Language: English
• Published: 2018
• Subjects: DRNTU::Engineering::Electrical and electronic engineering
• Online Access: http://hdl.handle.net/10356/76291
• Institution: Nanyang Technological University

The main objective of this final year project is to do thermal analysis of the high-voltage AlGaN/GaN high-electron-mobility transistors (HEMTs) on Silicon (Si), Silicon Carbide (SiC) and CVD-Diamond (Dia) substrate. The measurements in this project were all done on fabricated 0.25 µm gate CPW GaN HEMTs on Si, SiC and Dia substrate. In this work, electrical and pulse measurements of the HEMTs were done and it was observed that GaN-on-Si device has largest current reduction, GaN-on-Dia has the lowest current reduction with GaN-on-SiC in between. After which, junction temperature measurements were carried out. It was found that GaN-on-Si device has the largest delta temperature increase as compared to the other two substrates and GaN-on-Dia has the smallest delta temperature increase. This shows that Silicon device has the largest device self-heating due to the lowest thermal conductivity. Diamond substrate having the highest thermal conductivity, the self-heating of the device is lowest. Finally, the lifetime of both Silicon and Silicon Carbide substrate devices from the degradation rate derived from short term step temperature stress test was evaluated. Instead of using the conventional failure rate to calculate the activation energy, the rates of drain current degradation of Silicon and Silicon Carbide devices were used. With the activation energy plot, the lifetime can be derived from any junction temperature. With the same output power and similar bias conditions, Device fabricated on Silicon Carbide had cooler junction temperature than Silicon. This in turn resulted in slower degradation rate and longer device lifetime. Studies on different types of substrates to achieve the best performance is increasing. Most of the studies are to explore the types of substrate that allow quick dissipation of heat under high power application, to enable high output power, high efficiency and low energy consumption. This project present the test methodology used to test and evaluate three different substrates by measuring and evaluating the performance of GaN HEMT devices grown on each type to determine the best substrate material for power amplifier devices.