Spray-coated magnetic powder composite planar inductor for compact IoT sensor node

Abstract

A spray coating process of magnetic powder composite material is proposed in this paper for planar inductors and transformers for small DC/DC converter. This is a low temperature (≤150 °C) process that is usable for ferrites and extensively other magnetic powders and flakes. A commercially available Ni-Cu-Zn spinel ferrite particles and epoxy resin composite is applied for a 3 x 3 mm2 planer spiral inductor whose coil has 1 μm-thick, line/space =56/9 μm, and 10 turns made on a Si substrate, and exhibited inductance enhancement from from 157 nH to 205 nH (30%) without any resistance increase, up to 5 MHz. Physical stress by the proposed spray coating process can be negligible, judging from the well increased inductance and low resistance.