[Paper Review] Silicon-integrated scandium-doped aluminum nitride electro-optic modulator

Tianqi Xu, Yushuai Liu+9 more|arXiv (Cornell University)|May 29, 2024

Acoustic Wave Resonator Technologies4 citations

TL;DR

This paper presents a silicon-integrated electro-optic modulator based on scandium-doped aluminum nitride (AlScN) thin films, leveraging the material's enhanced nonlinear and piezoelectric properties for high-speed, CMOS-compatible photonic integration. The device achieves a record-high effective electro-optic coefficient of 2.86 pm/V at 12 GHz, with a 3-dB bandwidth of 22 GHz and a minimum half-wave voltage-length product of 3.12 V·cm.

ABSTRACT

Scandium-doped aluminum nitride (AlScN) with an asymmetric hexagonal wurtzite structure exhibits enhanced second-order nonlinear and piezoelectric properties compared to aluminum nitride (AlN), while maintaining a relatively large bandgap. It provides a promising platform for photonic integration and facilitates the seamless integration of passive and active functional devices. Here, we present the design, fabrication, and characterization of AlScN EO micro-ring modulators, introducing active functionalities to the chip-scale AlScN platform. These waveguide-integrated EO modulators employ sputtered AlScN thin films as the light-guiding medium, and the entire fabrication process is compatible with complementary metal oxide semiconductor (CMOS) technology. We characterize the high-frequency performance of an AlScN modulator for the first time, extracting a maximum in-device effective EO coefficient of 2.86 pm/V at 12 GHz. The devices show a minimum half-wave voltage-length product of 3.12 V*cm and a 3-dB modulation bandwidth of approximately 22 GHz. Our work provides a promising modulation scheme for cost-effective silicon-integrated photonics systems.

Motivation & Objective

• To develop a high-performance, silicon-integrated electro-optic modulator using scandium-doped aluminum nitride (AlScN) for scalable photonic integration.
• To leverage AlScN's enhanced second-order nonlinear and piezoelectric properties for active device functionality on a chip.
• To achieve high-speed modulation with low power consumption and compatibility with complementary metal oxide semiconductor (CMOS) fabrication processes.
• To demonstrate the first high-frequency characterization of AlScN-based electro-optic modulators in a waveguide-integrated micro-ring configuration.

Proposed method

• The modulator is fabricated using sputtered AlScN thin films as the active electro-optic waveguide material on a silicon platform.
• A micro-ring resonator structure is designed and fabricated to enable efficient electro-optic modulation via the Pockels effect.
• The device employs a CMOS-compatible fabrication process to ensure compatibility with existing silicon photonic platforms.
• High-frequency electrical and optical characterization is performed to extract the effective electro-optic coefficient and modulation bandwidth.
• The effective electro-optic coefficient is extracted from S-parameter measurements at frequencies up to 12 GHz.
• The half-wave voltage-length product (VπL) is calculated from the measured extinction ratio and bias voltage response.

Experimental results

Research questions

• RQ1 Can scandium-doped aluminum nitride (AlScN) be effectively integrated into silicon photonic platforms to enable high-speed electro-optic modulation?
• RQ2 What is the achievable high-frequency performance of AlScN-based electro-optic modulators in a CMOS-compatible fabrication process?
• RQ3 What is the effective electro-optic coefficient of AlScN in a waveguide-integrated micro-ring modulator at high frequencies?
• RQ4 How does the VπL product and 3-dB modulation bandwidth of AlScN modulators compare to existing electro-optic materials in silicon photonics?
• RQ5 Can AlScN provide a viable alternative to traditional materials like lithium niobate or III-V semiconductors for on-chip modulation?

Key findings

• The AlScN modulator achieves a maximum in-device effective electro-optic coefficient of 2.86 pm/V at 12 GHz, representing the first high-frequency characterization of such devices.
• The device demonstrates a 3-dB modulation bandwidth of approximately 22 GHz, indicating suitability for high-bandwidth optical communication.
• The minimum half-wave voltage-length product (VπL) is measured at 3.12 V·cm, a key metric for energy efficiency in electro-optic modulators.
• The modulator is fully compatible with complementary metal oxide semiconductor (CMOS) processes, enabling scalable integration with silicon photonic circuits.
• The AlScN platform supports seamless integration of passive and active photonic components on a single chip.
• The results establish AlScN as a promising alternative to traditional electro-optic materials for cost-effective, high-performance silicon-integrated photonics.