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This article has shown the design and characterization of silicon-integrated thin-film micro-transformers and their application in a quasi-resonant flyback converter. Two micro-transformers with different turn ratios of 4:4 and 3:3 were designed. The micro-transformers in this study have elongated spiral shape windings sandwiched between two layers of the thin-film magnetic core, and this structure can leverage the anisotropic core property. The micro-transformers were built on a silicon substrate using micro-electro-mechanical systems (MEMSs) fabrication process to ensure a high integration level and high power density. The inductance of 4:4 and 3:3 micro-transformers are 57.3 and 31.5 nH, respectively, their coupling coefficients are 90.5% and 82.7% at 30–40 MHz, and the measured quality factors are 7.82 at 21 MHz and 8.94 at 35 MHz, respectively. A resonant flyback converter topology deploying with a high electron mobility transistor [Gallium nitride (GaN)] was used to evaluate the electrical performance of two micro-transformers. Two resonant flyback converters operating at zero voltage switching (ZVS) reached the maximum conversion efficiency of 46.4% (3:3) and 45.7% (4:4), respectively, with 3.3 V input. The 3:3 micro-transformer developed in this work achieved the highest power density of 128 mW/mm2 with a similar efficiency compared to other cored micro-transformers. The loss analysis of the flyback conversion circuit shows that the main losses in the circuit are the copper winding loss of the micro-transformer and the eddy current loss of the magnetic core. The conversion efficiency of the circuit will be improved by applying thicker copper and core lamination in the future. [ABSTRACT FROM AUTHOR]

This letter demonstrates an on-silicon integrated thin film coupled inductor using a novel cascade matrix concept to suit multiphase integrated voltage regulator (IVR) applications. The novel cascade matrix coupled (CMC) stripline inductor facilitates all-phase-coupled configuration to reduce the phase ripple current in IVRs. It also shows excellent scalability and neat floor planning. Moreover, the proposed CMC inductor uses double layer metal scheme for windings and interconnects, which significantly reduces the ac winding resistance. A four-phase CMC inductor has been successfully fabricated on-silicon substrate and characterized, which uses conventional thin film magnetic core deposition process to achieve in-plane magnetic uniaxial anisotropy. The device occupies 3.2 × 1.7 mm2 floor area and provides 19.5 nH phase inductance with 120 mΩ dc resistance. The saturation current for each phase is up to 0.4 A when the phase inductance drops by approximately 20%. The coupling coefficient between any two phases of the proposed CMC inductor is 0.27, much higher and more controllable than that of toroid core-based coupled inductors. [ABSTRACT FROM AUTHOR]

In this paper, models that account for the duty cycle and phase shift angle of the applied phase voltages in coupled stripline microinductors are presented and are shown to have a significant impact on harmonic current amplitudes and therefore microinductor efficiency. The impact of a high coupling factor between two windings surrounded by a single core is also investigated. The models are validated using finite-element analysis and measurements. A three-phase-coupled microinductor has been fabricated with a Ni45Fe55 core and analyzed for a number of operating conditions. A prototype 1.6 W, three-phase converter utilizing this inductor has also been measured and is discussed in detail. The coupled microinductor is predicted to have a peak efficiency of 86.6% at 20 MHz in the prototype circuit. [ABSTRACT FROM AUTHOR]