Characterization and Modeling of Frequency-Dependent On-Resistance for GaN Devices at High Frequencies

The switching frequencies of the GaN-based power converters have been pushed to several megahertz and even higher. At such high frequencies, the on-resistances of the GaN devices might be much higher than their dc values, especially for the devices with low on-resistances. The frequency-dependent characteristics of the on-resistance are studied through the electrical and thermal experiments for the first time in this article. A device model for the finite element simulation is proposed to illustrate the mechanism. The results show that the frequency-dependent characteristics of the on-resistance are closely related to the current distribution inside the GaN device and affected by the layout. A 4-depth ladder circuit model is proposed to describe the frequency-dependent on-resistance of the GaN devices, and it proves a good accuracy in the frequency range of interest. Beside, two GaN-based 10 MHz dc-dc converters were designed, the only difference of which comes from the layout around GaN devices. The experimental results show that the efficiency of the converter with the optimized layout can be improved by around 2%.