Damage Analysis in Proton-Irradiated Barium Titanate Single Crystal Using Rutherford Backscattering Spectrometry/Ion Beam Channeling

Ferroelectric materials such as barium titanate (BaTiO₃/BTO) have garnered enormous interest for various applications, such as in semiconductor devices, and nonlinear optics due to their remarkable properties that include large pockel coefficients, high dielectric constant, and good thermal stability. These properties enable its use in high optical switching devices, fabrication of transducers, and fast modulation in photonic devices like interferometers and biosensors. In order to optimize the optical modulator performance metrics such as RF loss and optical loss, a thin membrane of BTO with ~500 nm thickness is bonded to a waveguide patterned silicon-on-insulator (SOI) wafer. Over the last couple of decades, ion beam exfoliation or smart cut techniques have been employed in Si, InP, SiC, LiNbO₃, SrTiO₃, and BTO crystals to lift-up thin layers from single-crystal wafers [1-2]. In general, this technique employs an energetic light ion beam (typically H or He ions) to induce damage at a certain depth inside the crystal which is later exfoliated as a thin film. Since it uses an energetic ion beam, the damage and artifacts are introduced inside the region of interest as a by-product of ion irradiation affecting the crystalline nature of the film which needs to be studied carefully before any further application. For the damage or crystallinity analysis, Rutherford Backscattering Spectrometry in channeling orientation (RBS/C) is an excellent technique to characterize elemental compositional depth profile and their crystalline quality. RBS/C involves aligning substrates along their crystallographic axis with the incident ion beam (typically 1-3 MeV He⁺) direction which reduces the backscattering yield drastically. The ratio between the backscattering yield in a channeling direction and a random direction provides a quantitative analysis of the crystallinity and the degree of damages caused by ion implantation/irradiation. In the present work, proton implantation at 300 keV with varying fluences has been studied in the BTO sample to create targeted damage layers (in the range of 500-1500 nm) for thin film exfoliation. Additionally, the nature of damages, defects and recovery in crystallinity of the sample with thermal annealing is further analyzed with subsequent in-situ ion channeling technique. The results from this study will help in optimizing the fabrication procedure for the thin film BTO.<br/>[1] Yuechen Jia, Lei Wang, and Feng Chen, Ion-cut lithium niobate on insulator technology: Recent advances and perspectives, Applied Physics Reviews 8, 011307 (2021).<br/>[2] T. Izuhara, I.-L. Gheorma, R. M. Osgood, Jr., A. N. Roy, H. Bakhru, Y. M. Tesfu, M. E. Reeves, “Single-crystal barium titanate thin films by ion slicing”, Appl. Phys. Lett. 82, 616 (2003).