GaN-Based Power Transistors for Future Power Electronic Converters

Gallium Nitride (GaN) is increasingly considered a viable semiconductor material in future power electronic converters. The benefical properties of GaN, being the result of its wide bandgap and the possibility to form heterostructures, make a further optimization of the power conversion possible. Although GaN power devices are still in an early phase, they have already overtaken the silicon counterparts. The expectations are that figures of merits (FOM) of at least an order of magnitude better than those of existing state of the art silicon MOSFETs are feasible in the future. The preference of GaN over other wide bandgap materials like Silicon Carbide (SiC) and Diamond is a matter of ’cost-effective’ revolutionary performance. Beside an overview of the properties and advantages of GaN semiconductors, their benefits are demonstrated by a hard switching boost converter that was constructed using E-mode DHFET prototypes on silicon. The low on-resistance (Ron ≈ 0.23 Ω) and low gatecharges (e.g. Qg ≈ 15 nC at Vds = 200 V) result in minor transistor losses. Together with a proper design of the passives and the use of SiC diodes, high overall efficiencies are reached. Measurements show a high conversion efficiency of 96% (Pout = 106 W, 76 to 142 V at 512 kHz). This is, to our knowledge, the highest efficiency reported for an E-mode GaN DHFET on Si in this frequency range. Allowing higher positive drive voltages can increase the efficiency even further at high frequencies.