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

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.