Three dimensional integration of GaN-HEMT-based DC-DC converter using planar inductor as a substrate

The three dimensional (3D) integration technology using planar inductor as a substrate for power converter is a promising method to improve the power density. But it introduces additional parasitic inductance, not good for the application of GaN semiconductor devices. So a conductive shield layer was introduced between the magnetic substrate and GaN-based 12V/3.3V synchronous buck converter circuit to reduce loop inductance. Based on the selected split capacitors layout of power loop for 3D integration, the effects of shield layer thickness and insulator thickness on parasitic inductance were investigated and optimized. The comparison of eight cases shows that 3D integrated split-capacitors layout with shied layer can realize the parasitic loop inductance of 0.26nH at inductor current of 10A, which is much smaller than 0.89nH of conventional lateral layout in 2D integration structure. At last, considering all the power losses, thermal analyses were performed on the 3D integrated split-capacitors layout with shield, 3D integrated split-capacitors layout without shield and 2D integrated split-capacitors layout with shield. The results demonstrate the effectiveness of shield on heat dissipation, and an acceptable operating temperature of proposed 3D integrated module was obtained. Thus the feasibility of 3D integrated structure using planar inductor as a substrate for power converter is verified.