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Cited by 1Advanced MEMS and NEMS TechnologiesPhotonic and Optical DevicesOptical Coatings and Gratings

High Reflectivity, Compact, and Widely Tunable Distributed Bragg Reflector Based on Silicon-Rich SiNx-SiOy at 80 °C PECVD

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Rodríguez Lamoso, Irene, Preu, Sascha·2025·Applied Sciences
DOI 10.3390/app15063330
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Abstract

This study investigates the mechanical and optical characteristics of silicon nitride thin films deposited with PECVD at 80 °C for tunable silicon-rich SiNx-SiOy-based MEMS optical cavities. Varying the deposition parameters using SiH4 and N2 as precursor gases for silicon-rich SiNx thin films allows us to tune the refractive index to a value as high as 2.40 ± 0.013 at an extinction coefficient of only 0.008, an extremely low surface roughness of only 0.26 nm, and a compressive stress of about 150 MPa. We deposited 6.5-layer pairs of silicon-rich SiNx/SiOy-distributed Bragg reflector (DBR) micro-electro-mechanical system (MEMS) mirror that covers the whole 1300 and 1550 nm range. Cavity architectures of 6.5 top and 6 bottom layer-pairs were fabricated in the clean room providing a variety of cavity lengths between 0.615 µm and 2.85 µm. These lengths were then simulated in order to estimate the Young’s Modulus of silicon-rich SiNx, obtaining values from 56 to 92 GPa. One of the designs was characterised electro-thermally providing a tuning range of at least 86.7 nm centred at 1585 nm. The tunable filters are well suitable for implementation as tuning element in lasers for optical coherence tomography.

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  • Dielectric thin films are better suited than metallic coatings for applications where metallic counterparts fail, owing to low optical losses (reflectivity over 99.9%), angular and spectral engineering, superior laser-induced damage threshold, and superior mechanical and chemical stability.

    “However, a robust way to overcome these limitations is to use dielectric thin films. Known also as optical interference coatings [11], dielectric ones are better suited for applications where metallic counterparts fail. This advantage comes from their specific properties, such as low optical losses that result in a reflectivity of over 99.9%, angular and spectral engineering through alternating”

    From Metal Oxide Thin Films for Advanced Photonic Applications (2026) · cites this paper as [14]

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Authors
Rodríguez Lamoso, I., & Preu, S.
Affiliations
  • Terahertz Devices and Systems, Technical University of Darmstadt; Merckstrasse 25, 64283 Darmstadt, Germany
  • Technische Universität Darmstadt (DE)
ORCID
Preu, Sascha
Venue
Applied Sciences
Publisher
MDPI AG
Published
2025-03-18
Volume
15
Issue
6
Pages
3330
ISSN
2076-3417 (ISSN-L)
DOI
10.3390/app15063330
OpenAlex
W4408571170
Cited by
1
References
29
Citations by year
2025: 1
FWCI
0.23
Type
journal article
Language
en
Open access
Licence
Locations
  • Applied Sciences (publishedVersion, cc-by)
  • Preprints.org (acceptedVersion, cc-by)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Funders
  • Marie-Curie-Sklodowska Actions ITN “NETLAS” (GA 860807)
  • Open Access Fund of the German Research Foundation through TU Darmstadt (GA 860807)
Topics
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Advanced MEMS and NEMS Technologies
  • Physical Sciences › Engineering › Electrical and Electronic Engineering › Photonic and Optical Devices
  • Physical Sciences › Materials Science › Surfaces, Coatings and Films › Optical Coatings and Gratings
Keywords
distributed Bragg reflector, silicon-rich silicon nitride, tunable optical filter, low-temperature PECVD, refractive index tuning, compressive stress, surface roughness, Young's modulus, MEMS mirror

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