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High-resistivity silicon to reduce substrate noise coupling in 28 nm FD-SOI VCOs

Published online by Cambridge University Press:  07 August 2025

Youssef Bendou*
Affiliation:
ICTEAM, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Dimitri Lederer
Affiliation:
ICTEAM, Université catholique de Louvain, Louvain-la-Neuve, Belgium
Andreia Cathelin
Affiliation:
STMicroelectronics, Crolles, France
Jean-Pierre Raskin
Affiliation:
ICTEAM, Université catholique de Louvain, Louvain-la-Neuve, Belgium
*
Corresponding author: Youssef Bendou; Email: youssef.bendou@uclouvain.be
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Abstract

This paper explores the impact of handle silicon substrate resistivity on substrate noise coupling and its influence on the spectral purity of voltage-controlled oscillators (VCOs). Three VCOs were designed using the 28 nm fully depleted silicon-on-insulator (FD-SOI) technology and fabricated on process-of-reference wafer featuring a handle Si substrate resistivity value of 10 Ω.cm and also on high-resistivity (HR) Si handle wafer of 1 kΩ.cm. The output spectrum of the VCOs was measured under two conditions: with and without a 0 dBm noise signal injected into the substrate. The results demonstrate that passivated HR substrates achieve more than 26 dB reduction in parasitic spurs induced by substrate noise. To the best of the authors’ knowledge, this work presents the first fabrication and measurement of VCOs on HR substrates in FD-SOI technology, highlighting their effectiveness in mitigating substrate noise coupling.

Information

Type
Research Paper
Creative Commons
Creative Common License - CCCreative Common License - BYCreative Common License - NCCreative Common License - ND
This is an Open Access article, distributed under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives licence (http://creativecommons.org/licenses/by-nc-nd/4.0), which permits non-commercial re-use, distribution, and reproduction in any medium, provided that no alterations are made and the original article is properly cited. The written permission of Cambridge University Press must be obtained prior to any commercial use and/or adaptation of the article.
Copyright
© The Author(s), 2025. Published by Cambridge University Press in association with The European Microwave Association.
Figure 0

Figure 1. Noise coupling mechanism through the substrate.

Figure 1

Figure 2. HR-SOI substrates and passivation solutions. (a) No passivation. (b) PN implants passivation. (c) Field effect, and (FE) passivation.

Figure 2

Figure 3. Depiction of the four VCOs designed and taped-out for this study.

Figure 3

Figure 4. LC tank VCO architecture.

Figure 4

Figure 5. Stand-alone inductors used in the two types of VCOs.

Figure 5

Figure 6. Implementation of PN junctions passivation in the case of a CPW line and an inductor. (a) Top view for a CPW line. (b) 3D view for a CPW line. (c) Top view for an inductor.

Figure 6

Figure 7. VCO layout with PN passivation.

Figure 7

Figure 8. VCO layout with FE passivation.

Figure 8

Figure 9. Simulated ${H_{sub}}$ as a function of frequency for different SOI substrates.

Figure 9

Figure 10. Photograph of the fabricated VCOs.

Figure 10

Figure 11. Measurement results of the inductors. (a) The inductance value l, (b) the series resistance ${R_S}$, and (c) the inductor quality factor Q.

Figure 11

Figure 12. Measurement results of the tuning range and phase noise of the four VCOs. (a) Tuning range and (b) phase noise.

Figure 12

Table 1. Measured performance of the four VCOs designed

Figure 13

Figure 13. The output spectrum of the VCOs with and without the injection of a 0 dBm power 5 MHz frequency noise signal. (a) POR VCO, (b) PSC VCO, (c) PN VCO, and (d) FE VCO.

Figure 14

Figure 14. Power of the first spur as a function of (a) VCO type and noise signal frequency ${f_{noise}}$ at ${V_{ctrl}} = 0\,V$, (b) control voltage and VCO type at ${f_{noise}} = 40\,MHz$.