Metallization Reliability of GaN-Based High-Voltage Light-Emitting Diodes

Electromigration is one of the most stubborn and serious reliability failure mechanisms in interconnection wires. Specifically, there is a high risk of electromigration in the special metal interconnection electrode structure of high-voltage light-emitting diodes (HV-LEDs). Nevertheless, a systematic investigation on this issue is lacking in literature. Here, simulations and experiments were conducted to systematically investigate the metallization reliability of gallium nitride based HV-LEDs (9 V, 100 mA) which were designed and fabricated in this study. The finite element model of the devices was established by the ANSYS software. Numerical solutions of the interconnected electrodes were obtained by multiphysics field coupling electric-thermal-structure simulation. It was found that the temperature, temperature gradient, current density, and stress all reached maximum at the n-type metal of the interconnected electrode, which provided the theoretical support for the experiment. Then, the accelerated aging experiment was conducted under high temperature (85°C) and high current injection (100 mA, 130 mA, 150 mA, 170 mA). It was found that whiskers started to appear from the sidewalls of the Cr/Al/Cr/Pt/Au n-type electrode after 30 hours of burn-in test. The electromigration was more likely to occur at the n-type electrode, which was consistent with the results of the simulation. Finally, the causes of the HV-LED metallization failure were analyzed. It was determined that high current density and high temperature were the main reasons for the electromigration of the interconnected electrodes in HV-LEDs. This work fills the knowledge gap of metallization reliability study of GaN HV-LEDs and is of value to the design, fabrication and application of the devices.