A Novel Reliability Model for GaN Power FET

The existing standard reliability models for power devices are not satisfactory and they fall short of predicting failure rates or wear-out lifetime of semiconductor products. This is mainly attributed to two reasons; the lack of a unified approach for predicting device failure rates and the fact that all commercial reliability evaluation methods relay on the acceleration of one dominant failure mechanism. Recently, device reliability research programs are aimed to develop new theoretical models and experimental methods that would result at a better assessment of the device lifetime as well as point out on the dominating failure mechanism for particular operating conditions. A novel model, named Multi-failure mechanism, Overstress Life test (MOL) has been introduced and posed a better understanding of the dominating failure mechanisms under various stressed conditions in advanced FPGA devices (for 45nm and 28nm technologies). More recently, we have presented, for the first time, the implementation of the MOL model to investigate the reliability of silicon power MOSFET devices. Both, LT Spice simulation and experimental data were presented for a test circuit of a ring oscillator, based on CMOS-FET, NMOS-FET and PMOS-FET. The monitored data was acquired in-situ in form of the ring frequency or Vds values that enabled to assess the lifetime and determine the dominating mechanism during accelerated wear-out by temperature, applied bias voltage, thermal cycling, gamma and electron irradiation. In this paper, we extend our study to investigate GaN HEMT reliability by our newly developed MOL model. Complex RO circuits containing all GaN devices and mixed (GaN HEMT-Si MOSFET) have been tested. Rds-on monitoring circuit has also been operated during thermal cycling of the tested component and the acceleration factor was derived for various operational parameters. It is noted that the presented data is the first attempt to monitor the GaN device degradation rate in-situ, during accelerated wear-out conditions. However, we are still working to extend the experimental results, aimed to determine the full multi mechanism matrix.