Design and Characterization of Package-Embedded Solenoidal Magnetic Core Inductors for High-Frequency and High-Efficiency SIP Integrated Voltage Regulators

In this article, the design and characterization of package-embedded solenoid inductors for a high-efficiency, four-phase system-in-package (SIP) buck-type integrated voltage regulator (IVR) switching at 100 MHz is discussed. The IVR enables three conversion ratios (5, 3, and 1.7-1 V) with a minimum inductance of 25 nH/phase and a load current of 10 A (2.5 A/phase). Two inductor designs (one with a rectangular core made of an epoxy dielectric/NiZn ferrite composite magnetic material/epoxy dielectric stack and one with an elliptical core of NiZn ferrite composite magnetic material only) were optimized and compared based on the highest achievable IVR efficiency. At high-load conditions (>5 A), the elliptical core inductor showed higher efficiency than the rectangular core inductor over the frequency range investigated (10-100 MHz). The elliptical core inductors were fabricated using a novel fabrication process combining core printing, noncontact photolithography, and copper electroplating. Two simple deembedding techniques which use a single thru structure and its equivalent circuit model as well as a cascade-based two-port analysis were introduced for the characterizations of the fabricated inductors. The accuracy of these deemebedding techniques was assessed using commercial, fixed-air core inductors and standard THRU and thru-reflect-line (TRL) deembedding for comparison purpose. Less than 5% difference was observed between the TRL and the introduced deembedding techniques for the inductance and ac resistance for both the fixed air core and package-embedded magnetic core inductors. The extracted electrical parameters of the fabricated inductors were compared with the modeling results and a good correlation was observed at 100 MHz.