Experimental characterization of metal fill placement and size impact on spiral inductors

This paper experimentally studies the parasitic impact of metal fill on a spiral inductor fabricated in a 180 nm Bi-CMOS process. Metal fill design aspects such as placement (in-plane vs. off-plane) and size are considered. We demonstrate larger impact on the quality factor (Q) and self-resonance frequency for off-plane metal fill compared to in-plane metal fill. A 70% decrease in fill size with unchanged metal density gives a 13% improvement in measured Q.