Fabrication and characterization of PDMA inductors

Integration of inductors onto a silicon chip is the main challenge in realizing monolithic dc-dc converters. Planar spiral inductors can be fabricated with top metal layer of any standard CMOS IC process. These inductors have high series resistance due to low thickness of the metal layer. As the series resistance of inductor is directly related to converter efficiency, a custom process is to be devised in order to fabricate spiral inductors with higher metal thickness. In this paper, we present a MEMS based process called plastic deformation and magnetic assembly (PDMA) for fabricating inductors directly on to silicon chip. We detail the key fabrication steps in building these PDMA inductors. We also derive empirical expressions for estimating inductance and series resistance of these PDMA inductors from measured data. Finally, we compare these inductors with planar spiral inductors and present the advantages of using PDMA inductors in monolithic dc-dc converters.