Partial Pressure Differential and Rapid Thermal Annealing for Integrated Yttrium Iron Garnet (Yig)
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PARTIAL PRESSURE DIFFERENTIAL AND RAPID THERMAL ANNEALING FOR INTEGRATED YTTRIUM IRON GARNET (YIG) SANG-YEOB SUNG, XIAOYAUN QI, SAMIR K. MONDAL, AND BETHANIE J. H STADLER In this work, magneto-optical garnets were grown monolithically by low-temperature reactive RF sputtering, followed by an ultra-short (< 15sec) anneal. It was found that in addition to low thermal budgets due to timing, the temperature required (< 750°C) for garnet crystallization was also reduced compared to standard tube furnace annealing (> 1000°C). MgO and fused quartz were used as substrates because they will be useful for future buffer layers and optical claddings. Y-Fe-O films were made with systematically varied compositions and the chemical, structural, and optical properties of the resulting films were analyzed. A solid solution single phase field for YIG was found that spanned a wide range of compositions (30.1 ~ 49.0 atomic % of Fe). The resulting YIG quality was measured by vibrating sample magnetometry (VSM), X-ray diffraction (XRD), and measurements of Faraday rotation (FR). Although the XRD results showed that the films had isotropic crystallinity, the VSM indicated that shape anisotropy dominated the magnetic properties. Out of plane FR measurements yielded up to 0.2°/µm at 632nm rotations. This rotation will be higher in plane. All of these tests demonstrated that the YIG was comparable to YIG grown by standard annealing and also by in-situ crystallization. Introduction The critical active element in optical isolators is a magneto-optical garnet. These isolators are required for integrated light sources as they allow extended lifetimes by blocking backreflected light. However, garnet is difficult to integrate with semiconductors due to the high thermal budget usually required to obtain the garnet crystal structure. For example, current isolator garnets cannot be integrated monolithically into a photonic integrated circuit due to the growth process of liquid phase epitaxy (LPE). Therefore, for semiconductor integration, lowtemperature semiconductor-friendly process, such as reactive RF sputtering, is needed. In addition to this, a buffer layer is also needed when using semiconductor platforms. In previous work [1], Y3Fe5O12 films were successfully fabricated on MgO substrates with single target reactive RF sputtering. MgO is good optical cladding that can also be deposited by sputtering onto semiconductors. However, the conventional gas feed-through of this previous technique led to a slow deposition rate and post-annealing was often required to get the Y3Fe5O12 garnet phase. Non-reactive sputtering of yttrium-iron-garnet (YIG) target has also been reported to have small deposition rate (5nm/min) [2]. Other research reported a higher deposition rate (10.8nm/min) [3], but very high RF power densities (~4.93W/cm2) were required. The use of this high power density is likely to lead to cracking of oxide targets. To improve the deposition rate in a less destructive way and to reduce thermal damage from post annealing, new method
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