Evaluation of Frequency-Dependent On-Resistance of GaN Devices at High Frequency

The switching frequency of GaN-based power converters has been pushed to several MHz and even higher. At such high frequencies, this paper finds that the on-resistance of GaN devices may be much higher than their DC values, especially for the devices with low on-resistance. The frequency-dependent characteristics of on-resistance are studied through electrical and thermal experiments for the first time in this paper. A simplified finite-element-simulation model is proposed to illustrate the mechanism of the frequency-dependent characteristics. 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. In addition, two same GaN-based 10MHz DC-DC converters were designed to operate under the same conditions, and the only difference comes from the layout of GaN devices. The experimental results show that the efficiency of the converter with optimized layout is improved by 2% compared to that with conventional layout.