Substrate Noise Mitigation Using a High Resistivity Substrate: The Case of a 14 GHz VCO on 28nm FD-SOI CMOS

This paper investigates the effect of silicon substrate resistivity on substrate noise coupling and how higher resistivity substrates improve the spectral purity of voltage-controlled oscillators (VCOs). Three VCOs were designed in the 28 nm fully depleted Silicon-on-Insulator (FD-SOI) technology and implemented on process-of-reference (POR) wafers (10 Ω.cm) as well as high-resistivity (HR) wafers (1 kΩ.cm). The output spectrum of the VCOs is measured with and without the injection of a 0 dBm noise signal into the substrate. Results show the highest reduction in the parasitic spurs caused by the noise signal to be more than 26 dBs when using a passivated HR substrate. To the best of the author’s knowledge, this is the first time VCOs are fabricated and measured on HR substrates in FD-SOI technology to explore their effectiveness in the reduction of substrate noise coupling.