Hybrid Integration of a Low-Voltage, High-Current Power Supply Buck Converter With an LTCC Substrate Inductor

Miniaturization of hybrid integrated buck converters is impeded by the difference in growth laws in current rating for silicon and for inductors as current rating increases. In the 20 A range, this leads to the attractive feasibility of planarizing the output inductor as the largest component by utilizing low-temperature cofired ceramic technology in the form of the (magnetic) substrate to carry the rest of the converter circuit. The presence of a magnetic substrate below the circuitry creates additional parasitic inductances, which results in low-frequency oscillations. From simulation, the presence of a conductive shield reduces trace inductances and improves circuit performance. There is a minimum shield thickness required to minimize losses associated with ringing. High-shield conductivity is necessary to lower the trace inductance and minimize power loss. Traces should be placed close to the shield to minimize inductance. Experimental results on converters with ceramic-based shield layers and organics-based shield layers bear out the theoretical expectations and establish the practical viability of the proposed hybrid integration technology.