On-Chip Out-of-Plane High-Q Inductors
Abstract
Integrating high-Q inductors on semiconductor circuits has been an elusive goal for years due primarily to the eddy current losses and skin effect resistance associated with in-plane spiral inductors. Three-dimensional out-of-plane coils reduce eddy current and skin effect losses by virtue of their geometry and magnetic field orientation. However, out-of- plane coils were not deemed producible by standard semiconductor fabrication methods. This paper reports on a novel use of conventional semiconductor processing techniques to batch-fabricate three-dimensional high-Q inductors on a wide range of insulating or active semiconductor substrates. Thin molybdenum-chromium films are sputter deposited with an engineered built-in stress gradient so that, when patterned and released from their substrate, they curl into circular springs. These springs self-assemble into three-dimensional scaffolds that form highly conductive windings after being copper plated. Quality factors up to 85 are observed at 1GHz on standard CMOS silicon. The in-circuit microcoil performance is also compared in BiCMOS silicon L-C oscillators to that of state-of-the-art planar spirals with slotted grounds. A 12.3dB phase-noise improvement is observed with an earlier coil design that produced a maximum Q of 40, and 14.6dB taking the frequency and power differences into account. A 5micronmeter copper layer underneath the coil boosts the quality factor to 85 and should therefore further improve the phase noise by up to 6dB.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jan 01, 2002
- Accession Number
- ADP015114
Entities
People
- Christopher L. Chua
- David K. Fork
- Jeng-ping Lu
- Koenraad Van Schuylenbergh