# Low Loss Aluminum Nitride Waveguide Fabrication: Propagation Loss Reduction Through ALD and RTA

## TL;DR

This paper demonstrates a reproducible fabrication process for low-loss aluminum nitride waveguides on sapphire, achieving record propagation loss of 2 dB/cm at 852 nm through process optimization including ALD passivation and RTA.

## Contribution

It introduces the first detailed report of ALD passivation and RTA in AlN waveguides, significantly reducing propagation loss.

## Key findings

- Record low propagation loss of 2 dB/cm at 852 nm
- Systematic process optimization improves waveguide performance
- Quantitative analysis of loss reduction techniques

## Abstract

Aluminum nitride (AlN) has emerged as a leading platform for integrated photonics in the visible and ultraviolet spectral ranges, particularly for quantum information applications involving trapped atoms. However, achieving low propagation loss in tightly confining single-mode AlN waveguides remains a challenge, especially at sub-micron wavelengths where scattering losses scale unfavorably. In this work, we present a reproducible and detailed fabrication process for low-loss AlN waveguides on sapphire, achieving a record loss of 2~dB/cm at 852~nm. Our results are enabled by systematic process optimization including high-resolution electron beam lithography with shape-based proximity effect correction, atomic layer deposition (ALD) of \ce{Al2O3} for waveguide surface passivation, and post-fabrication rapid thermal annealing (RTA). We provide a study of the contributions of each technique to propagation loss reduction and support our findings with quantitative loss measurements and comparison with an exhaustive literature review. This work represents the first detailed report of ALD passivation and post-cladding RTA applied to AlN waveguides.