Advancing All Silicon MOSCAP Ring Modulators With Ultra-Thin Sub-5 nm Insulator

We demonstrate silicon/SiO
$_{2}$
/polysilicon lateral MOS-Capacitor (MOSCAP) RRM operating above 50 GHz 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 (
$t_{\text{ox}}$
). The modulation performance is enhanced with thinner
$t_{\text{ox}}$
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
$V_{\pi }L$
of 2.6–4.0 V
$\cdot$
mm under a bias voltage
$V_{\text{b}}$
0–3 V. High-speed operation of the MOSCAP RRM with radius 15 μm demonstrated an average power insertion loss (IL
$_{\text{ave}}$
) of 3.5dB and one level insertion loss (IL
$_{\text{one}}$
) of 2dB for achieving a 3dB dynamic ER at a data rate of 30 Gb/s and bit-error-rate (BER)
$<\! 1 \times 10^{-12}$
. 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
$1 \times 10^{19}$
cm
$^{-3}$
.