Magnetic-Core and Air-Core Inductors on Silicon: A Performance Comparison up to 100 MHz

What is the future of integrated inductor design on silicon for power conversion applications at frequencies up to 100 MHz-is it magnetic-core or air-core inductors. This study presents measured results for two microfabricated inductors (magnetic core and air core), which have been designed to operate at 20 MHz and occupy a substrate area of less than 10 mm(2). The inductor technology and design are briefly discussed. An optimized inductor design study is, then, presented. Both magnetic-core and air-core inductor designs are compared and evaluated, in terms of inductance and efficiency per unit area for frequencies up to 100 MHz. The design of the microinductors is discussed and an analytical design optimization program is used to model the devices for the maximum efficiency and inductance. The introduction of laminations with high-frequency core inductors will also be examined within the study. A 100 MHz magnetic-core inductor design with three laminations gives a 36 nH inductance, with 96.4% efficiency and an area of 3 mm(2). A comparable air-core design also gives a 36 nH inductance, with 93.45% efficiency and an area of just 2.6 mm(2).