Mitigating Water Absorption in Waveguides Made From Unannealed PECVD SiO₂

Area of Science:

• Materials Science
• Optical Engineering
• Semiconductor Manufacturing

Background:

• Unannealed plasma-enhanced chemical vapor deposition (PECVD) silicon dioxide (SiO2) is used in optical waveguides.
• Water absorption in SiO2 can degrade waveguide performance over time.
• Standard anti-resonant reflecting optical waveguides (ARROWs) and buried ARROWs (bARROWs) were fabricated using PECVD SiO2 films.

Purpose of the Study:

• To evaluate the impact of water absorption on the optical throughput of PECVD SiO2 waveguides.
• To identify waveguide designs and material properties that enhance environmental stability.
• To present a solution for stable waveguides using unannealed PECVD SiO2.

Main Methods:

• Fabrication of standard ARROWs and bARROWs with varying intrinsic stress and refractive index differences.
• Exposure of fabricated waveguides to a heated, high humidity environment.
• Monitoring of optical throughput over time to quantify performance degradation.

Main Results:

• All tested ARROWs showed decreased optical throughput due to water absorption.
• Waveguides with lower intrinsic stress SiO2 exhibited a slower rate of throughput change.
• High index difference bARROWs maintained optical throughput after 40 days in the humid environment.

Conclusions:

• Water absorption significantly affects the performance of unannealed PECVD SiO2 waveguides.
• High index difference bARROWs are a promising solution for environmentally stable optical waveguides.
• Optimizing waveguide design and material properties is crucial for long-term device reliability.