Microtransformer on silicon with CoFeB magnetic core for high-frequency signal applications

This paper presents the development, characterization and application of a microtransformer with a bar magnetic core fabricated on silicon substrate using thin-film technology. The magnetic core, coils, and insulation layers were deposited using only sputtering PVD (physical vapor deposition) or CVD (chemical vapor deposition) processes. As insulation materials, silicon dioxide and silicon nitride are only used. The device is small with a chip size of 1600 µm x 800 µm. The transformer has a turns ratio of 1:1 and achieves a self-inductance of about 40 nH. The minimum measured breakdown voltage of the microtransformer is 1250 V(DC). The microtransformer device is applicable for frequencies up to 20 MHz. The device was fabricated on 12-inch silicon substrates on mass production equipment.