# Germanium-Based Optical Coatings for Aesthetic Enhancement with Low Radiofrequency Attenuation

## TL;DR

This paper introduces new optical coatings using germanium that look good and allow radiofrequency signals to pass through with minimal interference.

## Contribution

The novel use of germanium in optical coatings enables aesthetic design while maintaining low radiofrequency signal loss.

## Key findings

- Germanium-based coatings can produce metallic gray, black, or colorful appearances while transmitting visible light.
- The coatings show negligible radiofrequency attenuation compared to traditional metallic coatings.
- Multilayer structures with SiAlNx and germanium were successfully designed and characterized.

## Abstract

This work focused on developing optical coatings for decorative applications that remain transparent in the radiofrequency range. To achieve this, a combination of dielectric material (silicon-aluminum nitride, SiAlNx) and low-electrical-conductivity semiconductor material (germanium) was utilized. Germanium plays a crucial role in providing absorption in the visible spectrum, facilitating the design of coatings with various aesthetic appearances, while allowing for control over their transmittance. The optical properties of thin germanium layers were thoroughly characterized and leveraged to create multilayer designs with diverse aesthetic features. Different multilayer structures were designed, fabricated, and optically characterized, resulting in coatings with metallic gray, black, or various colors in reflection, while retaining the ability to transmit visible light for illumination and signaling applications. Finally, the radiofrequency attenuation of the developed coatings was measured, revealing negligible attenuation; this is in stark contrast to the metallic coatings used for decorative purposes, which can attenuate by up to 30 dB.