Low-power voltage controlled oscillators in 90nm CMOS using high-quality thin-film post-processed inductors

IMEC realized a 5GHz and 15GHz low-power voltage controlled oscillator (VCO) by post-processing high-quality (Q) inductors on top of 90nm RF CMOS devices using a thin-film wafer-level packaging (WLP) technology. These results prove that IMEC’s WLP technology is a promising solution for the integration of low-power high-performance RF and microwave systems.

As transistor dimensions scale down and CMOS and SiGe are increasingly replacing GaAs for microwave and mm-wave applications, circuit performance becomes increasingly determined by the on-chip passive component quality. However, in the attempt to pace up with this evolution, thinner on-chip metals and dielectrics have a troubling effect on the Q factor of on-chip passives. A cost-effective and attractive solution is to realize inductors using thin-film WLP techniques.

IMEC’s thin-film technology uses alternating layers of BCB (benzo-cyclobutene dielectric) and thick electroplated Cu layers deposited on top of the passivation. The post-processing is compatible with both Cu and Al back-end. The technology is cost-effective and consumes no additional Si real estate. Measurements performed on MOS transistors and back-end interconnects show no important performance shifts after post-processing. The WLP inductors have increased performance and resonance frequency as compared to back-end versions enabling the design of high-performance low-power circuits such as VCOs.

IMEC applied this technology to realize a 5GHz and 15GHz low-power VCO in 90nm CMOS. The 5GHz and 15GHz VCOs use respectively a 3nH and a 0.6nH WLP inductor without ground shielding resulting in a differential Q factor of respectively 40 and 55. The Q factor can even be increased by applying a polysilicon ground shield. The 5GHz and 15GHz VCOs show a low core power consumption of respectively 0.33mW and 2.76mW, a phase-noise of –115 and –105dBc/Hz (at 1MHz offset) and a tuning range of 148MHz and 469MHz. For comparison, a 6.3GHz 90nm VCO using a back-end inductor with patterned ground shield has a core power consumption of 5.9mW with a phase noise of -118dBc/Hz at 1MHz.

The thin-film technology can be applied both on active wafers (WLP) as on an intermediate glass or high-resistivity Si substrate (thin-film system-in-a-package (SiP) or MCM-D). These results prove that thin-film technology allows integrating high-Q passives in miniaturized system-on-chip (SoC) and SiP for wireless telecommunication applications covering the 1 to 5GHz mobile-phone standards up to 77GHz automotive radar.

Explore further

Natural gas used in homes contains hazardous air pollutants, shows Boston-area study

Citation: Low-power voltage controlled oscillators in 90nm CMOS using high-quality thin-film post-processed inductors (2005, February 11) retrieved 25 September 2022 from https://phys.org/news/2005-02-low-power-voltage-oscillators-90nm-cmos.html
This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.

Feedback to editors