Sub-Volt High-Speed Silicon MOSCAP Microring Modulator Driven by High Mobility Conductive Oxide

TL;DR

This paper introduces a silicon microring modulator driven by a high-mobility conductive oxide MOSCAP, achieving sub-volt operation and high-speed data transmission suitable for energy-efficient optical systems.

Contribution

It presents a novel heterogeneously integrated MOSCAP microring modulator using titanium-doped indium oxide, significantly reducing the required driving voltage and enhancing modulation efficiency.

Findings

Achieved 117 pm/V electro-optic modulation efficiency.

Demonstrated 25 Gb/s data rate with 53 fJ/bit energy efficiency.

Operates at 0.8 V Vpp with potential for 52 GHz bandwidth.

Abstract

Low driving voltage (Vpp), high-speed silicon microring modulator plays a critical role in energy-efficient optical interconnect and optical computing systems owing to its ultra-compact footprint and capability for on-chip wavelength-division multiplexing. However, existing silicon microring modulators usually require more than 2 V of Vpp, which is limited by the relatively weak plasma dispersion effect of silicon and the small capacitance density of the reversed PN-junction. Here we present a highly efficient metal-oxide semiconductor capacitor (MOSCAP) microring modulator through heterogeneous integration between silicon photonics and titanium-doped indium oxide, which is a high-mobility transparent conductive oxide (TCO) material with a strong plasma dispersion effect. The device is co-fabricated by Intel's photonics fab and TCO patterning processes at Oregon State University, which exhibits a high electro-optic modulation efficiency of 117 pm/V with a low VpiL of 0.12 Vcm, and consequently can be driven by an extremely low Vpp of 0.8 V. At a 11 GHz modulation bandwidth where the modulator is limited by the high parasitic capacitance, we obtained 25 Gb/s clear eye diagrams with energy efficiency of 53 fJ/bit and demonstrated 35 Gb/s open eyes with a higher driving voltage. Further optimization of the device is expected to increase the modulation bandwidth up to 52 GHz that can encode data at 100 Gb/s for next-generation, energy-efficient optical communication and computation with sub-volt driving voltage without using any high voltage swing amplifier.