In this work, we present a new-generation atomic layer deposition (ALD) technology that revolutionizes the production of conformal optical coatings: the spatial ALD. In spatial ALD, the substrate is rotated across successive process zones to achieve ultra-fast, high-precision and conformal thin film deposition. We present our latest results obtained with our novel C2R spatial ALD system, including the fabrication of SiO2, Ta2O5, Al2O3 and TiO2 with deposition rates reaching > 1 µm/h. We also show that these materials exhibit low surface roughness (<1 Å RMS), low optical loss (<10 ppm @ 1064 nm) and excellent uniformity (< 2% over 200 mm)
Over the last decades, rare-earth-doped materials such erbium, holmium and thulium have been extensively studied as a cost-efficient solution for optical amplification and lasing on the silicon photonic platform. When combined with suitable host medium and integrated circuit design, rare-earth doped materials can be tailored into efficient and low-noise integrated devices such as waveguide amplifiers and lasers with relatively straightforward and cheap fabrication techniques. Despite their superior properties and potential, rare-earth-doped waveguide technology still remains relatively immature when it comes to the production of competitive building blocks for the silicon photonics industry. Further improvements, such as higher gain, scalable fabrication process and lower deposition temperatures need to be pursued for ultimate cost-efficiency and silicon photonic circuit compatibility. In this work, we present a novel waveguide amplifier design that combines silicon nitride strip waveguides and multiple spatially engineered erbium-doped active layers to improve the gain characteristics of hybrid waveguide amplifiers fabricated on silicon with cost-effective and mass-scalable methods. By spatially controlling the erbium-ion distribution of the proposed multilayer waveguide amplifier such that it matches the transverse intensity distribution of the fundamental mode propagating within the device, we show up to 30% enhanced optical gain when compared to an amplifier design that utilizes only a single gain layer. The design, enabled by atomic layer deposition, opens a completely new approach in developing silicon-integrated waveguide amplifiers and lasers with as high efficiency extracted from the active section as possible.
We present a new-generation atomic layer deposition (ALD) technology that revolutionizes the production of conformal optical coatings: the spatial ALD. In spatial ALD, the substrate is rotated across successive process zones to achieve ultra-fast and high-precision thin film deposition. We present our latest results obtained with our novel C2R spatial ALD system, including the fabrication of SiO2, Ta2O5 and Al2O3 with deposition rates reaching > 1 µm/h. We also show that these materials exhibit low surface roughness (<1 Å RMS), low optical loss (<10 ppm @ 1064 nm), excellent uniformity (< 2% over 200 mm) and high damage threshold (up to 40 J/cm2).
Since its invention in 1974, atomic layer deposition (ALD) has shown tremendous performance in depositing thin film structures for various applications in physical, chemical, biological and medical sciences. The unique layer-by-layer growth mechanism of ALD enables exceptional uniformity, conformality and accurate control of film thickness for a plethora of materials. In physical sciences, especially in optical systems, these properties are of utmost importance as sustaining optical performance not only requires a high degree of uniformity, but also excellent conformality when it comes to complex micro- or macrostructures. To reach a high level of uniformity and conformality on complex macro shapes, such as highly curved lenses or spherical domes, effort needs to be made to specifically twist, turn, rotate or otherwise move the structures. For the traditional physical vapor deposition, this comes with an extensive load of mechanical work and process optimization, ultimately leading to a tight control of the process parameters. In the end, the optimized processes may still not lead to a sufficiently homogeneous film deposition on the most challenging structures. In this work, we demonstrate that we have been able to overcome these constraints by utilizing our P-series ALD batch tools to deposit various optical coatings on complex 3D macrostructures. As example structures, we use a topless cube (length, height, width = 150 mm) and a hemispherical dome (diameter = 155 mm). By depositing various low-loss oxide materials (SiO2, Al2O3, HfO2, TiO2 and Ta2O5) and by measuring their resulting thickness distributions from various locations throughout the 3D bodies, we have been able to achieve non-uniformities ranging from less than 1 % to 2.5 % over the entire structures. In addition, we have designed and deposited anti-reflective, highly reflective and edge-pass coatings on these structures and verified that excellent spectral responses from 400 to 2500 nm can be obtained. Ultimately, our results demonstrate an exceptional method to realize high-quality optical coatings on the most challenging surfaces, paving the way for the mass production of critical optical components in macroscale for a variety of applications ranging from military to microscopy.
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