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

Abstract

We demonstrate silicon/SiO<inline-formula><tex-math notation="LaTeX">$_{2}$</tex-math></inline-formula>/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 (<inline-formula><tex-math notation="LaTeX">$ t_{\text{ox}}$</tex-math></inline-formula>). The modulation performance is enhanced with thinner <inline-formula><tex-math notation="LaTeX">$ t_{\text{ox}}$</tex-math></inline-formula> down to 3 nm, giving a lower insertion loss and larger optical modulation amplitude (OMA) when benchmarked with a conventional depletion type RRM with a low <disp-formula><tex-math notation="LaTeX"> \begin{equation*} V_{\pi }L \end{equation*} </tex-math></disp-formula>of 2.6-4.0 V <inline-formula><tex-math notation="LaTeX">$\cdot$</tex-math></inline-formula> mm under a bias voltage <inline-formula><tex-math notation="LaTeX">$V_{\text{b}}$</tex-math></inline-formula> 0-3V. High-speed operation of the MOSCAP RRM with radius 15 <inline-formula><tex-math notation="LaTeX">$\mu$</tex-math></inline-formula>m demonstrated an average power insertion loss (IL<inline-formula><tex-math notation="LaTeX">$ _{\text{ave}}$</tex-math></inline-formula>) of 3.5 dB and one level insertion loss (IL<inline-formula><tex-math notation="LaTeX">$ _{\text{one}}$</tex-math></inline-formula>) of 2 dB for achieving a 3 dB dynamic ER at a data rate of 30 Gb/s and bit-error-rate (BER) <disp-formula><tex-math notation="LaTeX"> \begin{equation*} &lt; 1 \times 10^{-12} \end{equation*} </tex-math></disp-formula>. 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 <inline-formula><tex-math notation="LaTeX">$1 \times 10^{19} cm^{-3}$</tex-math></inline-formula>.

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