Room-temperature reactive sputtering of SiO₂ films for high-transmittance linear variable optical filters

To address the limitations of conventional radio frequency (RF) magnetron sputtering using SiO₂ target - particularly low deposition rates and pronounced optical absorption, we developed high-quality SiO₂ thin films via RF reactive magnetron sputtering with a pure silicon target. The room-temperature (RT) deposition process eliminates the need for substrate heating, resulting in enhanced performance, including the removal of optical absorption and a twofold increase in deposition rate (from 1.15 to 2.85 nm/min), as verified by spectroscopic ellipsometry and X-ray photoelectron spectroscopy (XPS) characterization. Building on this advancement, we engineered linear variable optical filters (LVOFs) for spectral operation in the 500-700 nm range by combining the reactive-sputtered SiO₂ and RF sputtered TiO₂. The LVOFs demonstrated remarkable improvement of average transmittance from 67.7% to 93.6%. Temperature-dependent spectral analysis revealed a thermally-induced blue shift of 3.0 nm at 110 °C relative to RT measurements. This work establishes RT reactive magnetron sputtering as an effective fabrication strategy for high-performance optical filters, showing particular promise for applications requiring precise spectral control and thermal stability in ambient temperature deposition processes.