Design and optimization techniques of over-chip bond-wire microtransformers with LTCC core

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Camarda, Antonio
Macrelli, Enrico
Paganelli, Rudi Paolo
Tartagni, Marco
Roy, Saibal
Romani, Aldo
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Institute of Electrical and Electronics Engineers (IEEE)
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This paper describes the realization of bond-wire micromagnetics by using standard bonding wires and a toroidal ferromagnetic low-temperature co-fired ceramic core with high resistivity. The proposed fabrication procedure is suitable for the development of magnetic components on the top of an integrated circuit with a small profile and a small size (<;15 mm 2 ). A transformer is designed and applied over chip, working in the MHz range with high inductance (~33 μH) and high effective turns ratio (~20). Applications include bootstrap circuits and micropower conversion for energy harvesting. Measurements demonstrate a maximum secondary Q-factor of 11.6 at 1.3 MHz, and a coupling coefficient of 0.65 with an effective turns ratio of 19, which are among the highest values reported for toroidal miniaturized magnetics. The achieved inductance density is 2 μH/mm 2 , along with an inductance per unit core volume of 15.6 μH/mm 3 , and a dc inductance-to-resistance ratio of 2.23 μH/Ω. The presented technique allows to obtain over-chip magnetics trough a postprocessing of the core, and it is also suitable for high-density power supply in package and power supply on-chip. Finally, a series of optimization techniques for planar core magnetic devices in order to maximize the inductance per unit area is discussed and applied to the considered case.
Energy harvesting applications , On-chip , Boost converter , Magnetic-core , Power , Inductors , Transformer , Silicon , Fabrication
Camarda, A., Macrelli, E., Paganelli, R. P., Tartagni, M., Roy, S. and Romani, A. (2018) 'Design and optimization techniques of over-chip bond-wire microtransformers with LTCC core', IEEE Journal of Emerging and Selected Topics in Power Electronics, 6(2), pp. 592-603. doi:10.1109/JESTPE.2017.2751745
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