Advancing all Silicon MOSCAP Ring Modulators with Ultra-thin sub-5 nm Insulator

We demonstrate silicon/SiO <tex-math notation="LaTeX">₂</tex-math> /polysilicon lateral MOS-Capacitor (MOSCAP) RRM operating above 50GHz with modulation amplitude enhanced by a large plasma absorption within the MOS junction. A MOSCAP ring resonator modulator (RRM) model has been built using Lumerical software, in which the plasma effect is defined by adopting a reported superlinear rather than linear plasma absorption equation, which aligns well with our experimental results. The performance of the MOSCAP RRMs has been analyzed with different thicknesses of insulator oxide ( <tex-math notation="LaTeX">tₒₓ</tex-math> ). The modulation performance is enhanced with thinner <tex-math notation="LaTeX">tₒₓ</tex-math> down to 3 nm, giving a lower insertion loss and larger optical modulation amplitude (OMA) when benchmarked with a conventional depletion type RRM with a low <tex-math notation="LaTeX"> {equation*} VπL {equation*} </tex-math> of 2.6-4.0 V <tex-math notation="LaTeX">·</tex-math> mm under a bias voltage <tex-math notation="LaTeX">Vb</tex-math> 0-3V. High-speed operation of the MOSCAP RRM with radius 15 <tex-math notation="LaTeX">μ</tex-math> m demonstrated an average power insertion loss (IL <tex-math notation="LaTeX">ₐᵥₑ</tex-math> ) of 3.5 dB and one level insertion loss (IL <tex-math notation="LaTeX">ₒₙₑ</tex-math> ) of 2 dB for achieving a 3 dB dynamic ER at a data rate of 30 Gb/s and bit-error-rate (BER) <tex-math notation="LaTeX"> {equation*} < 1 × 10⁻¹² {equation*} </tex-math> . The same performance is possible at 50 Gb/s when feed-forward-equalization is enabled on the detection side. We also show the possibility of operating at 224 Gb/s using 4-level pulse amplitude modulation (PAM-4) for a MOSCAP RRM incorporating two active segments. The MOSCAP RRM provides an attractive solution to surpass the performance of the conventional depletion-type RRM, for which future performance scaling is limited with increased doping density towards <tex-math notation="LaTeX">1 × 10¹⁹ cm⁻³</tex-math> .