Microfabrication and characteristics of double-rectangular spiral type thin-film inductors with an upper NiFe magnetic core

Simple, double-rectangular spiral-type thin-film inductors with an upper Ni81Fe19 core for 5 MHz drive dc–dc converter application were investigated. Copper films 10-μm-thick covered by a 3-μm-thick NiFe film were used as the coils. The inductors fabricated in this study are 2.5×3.4–3.5×5.5 mm2. The inductors developed, with a small size of 2.97×3.1 mm2, exhibit L of 1.43 μH, quality factor of 15.8, and resistance of 2.88 Ω at 5 MHz, and show results comparable to those reported in recent literature for similar inductors sandwiched by more complex magnetic core materials. An analysis of the experimental data suggests an equivalent circuit of the fabricated inductors. From the equivalent circuit analysis, C was shown to have a negligibly small effect over the frequency ranges used. The calculated data obtained from the equivalent circuit and the well-known equation of Q described the high-frequency data of the L, Q, and impedance of the inductors developed well.