Research On Flexible Integration Process Of Yttrium Iron Garnet Film Based On Transfer Printing

In recent years,flexible electronic devices have attracted much attention due to the potential applications in the fields of the Internet of Things and bioelectronics.The integration of functional oxide materials in flexible polymers has proven to be an effective way to achieve high performance flexible electronic devices.On the other hand,yttrium iron garnet(Y₃Fe₅O₁₂,YIG)thin films are widely used in spintronic devices and magneto-optical isolators due to the excellent magnetic and magneto-optical properties.However,YIG thin films can only be prepared at high temperature,limiting their back-end process compatibility and system integration with semiconductor materials.Therefore,the development of YIG thin film integration on flexible substrates is an important issue in the field.So,this paper studies the flexible integration process of YIG thin films,the contents are divided into the following three parts.The first part is the study of transfer printing YIG film based on etching a sacrificial layer of SiO₂.Square array YIG films and hole-shape YIG films were fabricated on SiO₂/Si substrates by pulsed laser deposition（PLD）and microfabrication,and then etched the SiO₂ sacrificial layer in HF solution.By controlling HF solution concentration and etching time,YIG films were successfully transferred by using Si substrates or Polydimethylsiloxane（PDMS）seals.The results of optical microscopy and scanning electron microscopy（SEM）showed that we can transfer square YIG film of 0.5mm×0.5mm and hole-shaped YIG film of 2mm×2mm from the SiO₂/Si substrate onto the Si substrate,but the YIG films were severely corroded by the HF solution and had many cracks.The second part is the transfer printing of YIG thin film based on MoS₂/SiO₂ Van der Waals heterojunction.We prepared Si/SiO₂/MoS₂/SiO₂/YIG thin films on SiO₂/Si substrate by PLD and magnetron sputtering.Based on the different hydrophobic and hydrophobic properties of MoS₂ and SiO₂ films,we can dissociate the MoS₂/SiO₂ van der Waals heterojunction interface by using deionized water,and transfer printing the YIG films from Si/SiO₂/MoS₂/SiO₂/YIG to PI flexible substrates.SEM result shows that MoS₂film is separated from sputtered SiO₂ film by deionized water,and MoS₂ film remains on the original SiO₂/Si substrate.XRD results show that there is no difference in the crystal structure of the YIG film before and after transfer printing.The Vibrating sample magnetometer（VSM）results show that the saturation magnetization of the YIG film transferred onto the PI is 115 emu/cm³,and the coercivity of in-plane and out-of-plane is31Oe and 75Oe,respectively.The third part is the transfer printing of other functional oxide films based on MoS₂/SiO₂ Van der Waals heterojunction.We successfully transferred VO₂ and Fe₂O₃thin films onto different substrates by using the process of transfer printingYIG in the second part.XRD results show that there is no difference in the crystal structure of VO₂（Fe₂O₃）films before and after transfer printig.Temperature-dependent Raman spectrum and infrared reflectance spectrum demonstrate the good metal-insulator transition（MIT）performance of VO₂ films before and after transfer printing.This method is proved to be universal.