Design and Analysis of Vertical Nanoparticles-Magnetic-Cored Inductors for RF ICs

Abstract

We report the design and analysis of the first vertical magnetic-cored inductors in CMOS backend for radio-frequency (RF) ICs, which includes theoretical and experimental studies of device architecture, equivalent circuit model with parameter extraction technique, process development, and device characterization. Vertical magnetic cores with multiple-layer stacked-spiral structures are designed to realize compact inductive devices in RF ICs. A CMOS-compatible post-CMOS backend process module (CMOS +) and optimized high-permeability nanoparticles are utilized to achieve a high inductance-to-coil-area ratio ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -density) in gigahertz range. The prototype six-layer inductors with NiZnCu ferrite nanoparticles-magnetic-core were fabricated in a commercial foundry 0.18-μm six-metal RF CMOS technology. A high <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</i> -density of over 700 nH/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> to multigigahertz was obtained, with an 80% chip size reduction from the reference planar magnetic inductors. An equivalent circuit model with parameter extraction technique is developed to analyze magnetic enhancement effects. This work demonstrates the potential of design and integration of compact high-performance vertical magnetic-cored inductive devices into CMOS backend for high-quality and low-cost RF systems-on-a-chip.