Fig. 1. Perspective view of the MOSCAP modulator and microscope images of the fabricated device. (a) Full three-dimensional rendering of the modulator structure as designed; (b) device cross section, showing internal structure of the resonator, doping profiles of c-Si body and p-Si gate device layers, placement of metal contacts, and optical mode profile; (c) optical micrograph of the fabricated device; (d) TEM of the full device cross section, showing the resonator structure, bus waveguide, and lower four metal layers; (e) TEM zoom-in on the guiding core of the resonator and ring-bus coupling region.

Fig. 2. Experimental data from passive optical and DC EO device characterization (device with 32 kΩ/□ gate sheet resistance). (a) Optical transmission response of the MRM in O-band showing two resonances spaced by 8.5 THz or 48 nm FSR; (b) modulator optical response for gate voltages between −3 and 0 V, showing resonance blueshift due to free carrier inversion; (c) optical response for gate voltages between 0 and 4 V, showing resonance blueshift due to carrier accumulation.

Fig. 3. Experimental data from DC electrical and EO device characterization for different p-Si gate doping concentrations. (a) Dependence of gate sheet resistance on acceptor concentration; (b) resonance frequency shift versus gate voltage, showing up to 90 GHz shift for gate voltages between 0 and 4 V; (c) modulator shift efficiency at different bias points, showing 30 GHz/V resonance modulation efficiency above 2 V; (d) resonance intrinsic quality factor versus gate voltage.

Fig. 4. Experimental results from high-speed EO characterization of modulators. (a) Normalized EO response of the modulator with gate sheet resistance of 32 kΩ/□; (b) dependence of EO 3 dB bandwidth on gate bias voltage for a few modulator variants with different gate doping concentrations; (c)–(e) optical eye diagrams at 5 Gbps acquired at several bias points of gate voltage and laser wavelength; (f) illustration of the MOSCAP cross section with half the capacitance of the original device; (g) eye diagram (10 Gbps) of the MRM with 2 times smaller capacitance; (h) illustration of the MOSCAP cross section with additional implants introduced for reducing series resistance while preserving resonance quality factor.