RAYTUM PHOTONICS LLC — Department of Defense SBIR Phase II: N212-D05

Description

The high performance, ultra-narrow bandpass optical thin film interference filter is a key optical component for the applications of LIDAR, bio-sensing and many other merging applications. Optical thin film interference filters are traditionally manufactured by physical vapor deposition (PVD) technique. However it is subject to intrinsic drawbacks of poor large area uniformity, especially on curved surface, difficulty in thickness control and high cost associated with vacuum technology and thickness monitoring tools. Atomic layer deposition (ALD) on the other hand has been well established for precise thickness control in atomic scale, excellent large area uniformity and conformity for coatings on complex surface, and low growth temperatures. Therefore it is well suited for precise optical coatings and related applications on large area optical glasses. A wide range of high quality dielectric materials (oxides, nitrides, fluorides, carbides, etc.) with high, medium and low refractive indexes are available by ALD, most of which can be deposited in a single batch ALD reactor thus complexity and production cost can be reduced. These merits provide an excellent solution to manufacturing various high performance bandpass filters required very tight uniformity <0.1% for multiple dielectric layer coatings to minimize wavelength shift and bandwidth broadening. Other advantages of ALD coatings include defect-free thus low optical loss, and super moisture/environmental resistance. Special ALD tools for handing large area up to sub-meter size, and multiple wafers up to hundreds/hour were demonstrated commercially. We propose the state of the art ALD technique to manufacture such filters and demonstrate larger area (100-300mm) uniformity (<0.1%) using an innovative batch reactor capable of handling a volume of minimal 10 units.  The unit cost can be reduced far below the program goal of $50,000 with a high yield. A clear path for commercialization is also presented.  During the phase 1 proof of feasibility work Raytum Photonics has accomplished the following tasks: Established key ALD process for high quality dielectric oxides such as Al2O3, TiO2, and SiO2. Demonstrated that coating uniformity <0.3-0.4% on 4-8” substrates are readily achievable by commercial ALD systems. Concept-proven that an innovative ALD reactor design with a step rotation mechanism can further reduce uniformity <0.1%. The initial optical filter designs to meet the specs were conducted using an optical coating design tool as our guide for material selections and ALD process improvement. During DP2 period we will refine filter designs, optimize ALD process and fabricating technique to deliver the desired optical filters at the end of the base period. We will also develop the batch prototype ALD reactor to manufacture such high performance optical interference filters with a volume of minimal 10 units on 12” optical glasses expected to be delivered at the end of the DP2 option period.