Diffusion-Driven Exfoliation of Magneto-Optical Garnet Nanosheets: Implications for Low Thermal Budget Integration in Si Photonics

Karthik Srinivasan, Andrew Schwarz, Jason C. Myers, Nicholas C.A. Seaton, Bethanie J.H. Stadler

Research output: Contribution to journalArticlepeer-review

Abstract

Rare-earth iron garnets are instrumental in the development of integrated nonreciprocal passive devices such as isolators and circulators in silicon photonics. Unfortunately, monolithic integration of garnet on-chip requires annealing temperatures much higher than the thermal budget of a semiconductor foundry. Here, we report the mechanical exfoliation of large area (0.2 mm × 0.2 mm) nanosheets of a high-gyrotropy cerium-doped terbium iron garnet (CeTbIG) enabled by a strain-enhanced vacancy diffusion process that follows the Nabarro-Herring (lattice diffusion) model. Diffusivities calculated from the strain rate-stress data (1.13 × 10-18 m2s-1) identify iron and rare-earth cations as the rate-determining lattice diffusants. Cross-section scanning transmission electron microscopy reveals an exfoliation gap located ∼30 nm into the film, comparable to the cation diffusion length, which appears to verify the model. With a saturation magnetization of 18 emu cc-1 and a Faraday rotation of -2900°cm-1 at 1550 nm, the magnetic and optical properties of the nanosheets are comparable to their thin-film values. Diffusion-driven exfoliation will open foundry-acceptable pathways for heterogeneous integration of garnets on photonic waveguides and protect devices from the high-temperature processes used in crystallizing garnet films.

Original languageEnglish (US)
Pages (from-to)11888-11894
Number of pages7
JournalACS Applied Nano Materials
Volume4
Issue number11
DOIs
StatePublished - Nov 26 2021

Bibliographical note

Funding Information:
Parts of this work were carried out in the Characterization Facility and the Minnesota Nano Center, University of Minnesota, which receives partial support from the NSF through the MRSEC (Award Number DMR-2011401), and the Nanotechnology Coordinated Infrastructure (NNCI) program under Award Number ECCS-2025124. K.S. would like to acknowledge the support from Doctoral Dissertation Fellowship 2020-2021 awarded by the Graduate School, University of Minnesota.

Publisher Copyright:
© 2021 American Chemical Society. All rights reserved.

Keywords

  • diffusion creep
  • ferrimagnetic insulators
  • garnet nanosheets
  • magneto-optical materials
  • mechanical exfoliation
  • rare-earth iron garnets

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