Study On The YIG Crystal Growth And Liquid Phase Epitaxy Equipment

YIG is a garnet material with excellent magnetic,magneto-optical and microwave properties,which is widely used in various optical devices,magneto-optical devices and microwave devices.Especially in the context of the current rapid development of 5G,we have a major demand for non-reciprocal optical devices based on magneto-optical isolators,and need high-quality YIG magneto-optical crystals.On the other hand,the development of spintronics heavily depend on the control of the spin polarization current which carry the spin angular momentum,and spin polarization current can be through the spin transfer process to manipulate magnetic moment.As a ferromagnetic insulating material with extremely low magnetic damping coefficient,high-quality nano-scale YIG thin film plays a very important role in the preparation of spintronic devices,and has been widely concerned by industry and academia.YIG crystal growth is extremely difficult and requires flux to obtain a garnet phase.At present,regardless of bulk single crystal or thin film,more successful growth techniques are focused on the LPE method.However,all the YIG crystals required for my country’s communications industry and national defense construction rely on imports.Foreign countries have strictly sealed the LIG equipment and technology of YIG crystals.Therefore,the development of domestic LPE equipment and the growth of YIG crystals are important topics to break through the technical blockade and ensure industrial safety.Therefore,this paper focuses on the development of liquid phase epitaxy growth equipment for YIG crystal growth,and has carried out a little preliminary work on the choice of flux for preparing YIG crystal by liquid phase epitaxy.The research results obtained are as follows:（1）We developed the liquid phase epitaxy equipment,which can be used for the growth of YIG crystal.The long-term operating temperature of the equipment is about 1200℃,and the temperature control accuracy is within ±0.1℃,which meets the growth temperature requirements of YIG single crystal.The heating area adopts multi-stage heating,and each heating program is independently coordinated and controlled;the furnace stainless steel shell,insulation brick,crucible and platform are designed with concentric circles;the substrate can realize automatic forward and reverse rotation,and the crucible is equipped with a reflective cover of Pt.Its function is to reduce air heat convection and heat radiation and maintain the stability of the melt temperature.Through this design,the temperature field can be better controlled.The temperature measurement in the experiment is divided into multi-stage furnace body and melt temperature measurement.The melt temperature measurement method is based on the crucible bottom temperature measurement,and the melt direct temperature measurement is supplemented to obtain a more accurate and reliable temperature.The overall use of PLC control system,computerized operation,easy to program programming,automatic data recording and network communication.At the same time,the equipment is equipped with a CCD phase-forming system,which can monitor the internal conditions of the furnace in real time.In summary,the equipment is completely suitable for preparing YIG single crystal by liquid phase epitaxy.（2）Bi₂O₃-B₂O₃ lead-free flux can be used as a flux system for growing YIG crystals by liquid phase epitaxy,and pure phase YIG crystals can be obtained.Under air atmosphere,Pt crucible is suitable for crystal growth under this system.Pure phase YIG polycrystalline material was synthesized by solid-phase method,and optimized synthesis conditions determined 1350℃/12 h as the polycrystalline material synthesis condition for liquid phase epitaxy method;By changing the quality of n（Fe/Y）and B₂O₃,it was found that the crystal phase obtained from pure phase YIG（n（Fe/Y）=1.67）to Fe2O3（main）+YIG phase（n（Fe/Y）=1.67）with the continuous increase of n（Fe/Y）=1.67,2,2.5,4 in the melt,indicating that adding too much Fe will affect the generation of YIG phase;at the same time,when n（Fe/Y）=1.67,the mass of B₂O₃ was increased from 3% to 5%.Excessive B₂O₃ consumed too much Y2O3,which caused the imbalance of Fe and Y in the melt,resulting in the appearance of YIG+Fe2O3 phase.In general,the flux system is completely suitable for the growth of YIG crystals by liquid phase epitaxy,but the theoretical research on the growth of YIG crystals in the flux system still needs to be strengthened,and the growth process needs to be further optimized.