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Open AccessArticle

Residual Stress in Lithium Niobate Film Layer of LNOI/Si Hybrid Wafer Fabricated Using Low-Temperature Bonding Method

1
Graduate School of Information Science and Electrical Engineering, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
2
Graduate School of Science, Tohoku University, 6-3 Aramaki Aza Aoba, Aobaku, Sendai 980-8578, Japan
3
Research Center for Ubiquitous MEMS and Micro Engineering, National Institute of Advanced Industrial Science and Technology (AIST), 1-2-1 Namiki, Tsukuba, Ibaraki 305-8564, Japan
4
Department of Precision Engineering, School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 153-8904, Japan
*
Author to whom correspondence should be addressed.
Micromachines 2019, 10(2), 136; https://doi.org/10.3390/mi10020136
Received: 25 October 2018 / Revised: 1 February 2019 / Accepted: 8 February 2019 / Published: 18 February 2019
(This article belongs to the Special Issue Heterogeneous Integration for Optical Micro and Nanosystems)
This paper focuses on the residual stress in a lithium niobate (LN) film layer of a LN-on-insulator (LNOI)/Si hybrid wafer. This stress originates from a large mismatch between the thermal expansion coefficients of the layers. A modified surface-activated bonding method achieved fabrication of a thin-film LNOI/Si hybrid wafer. This low-temperature bonding method at 100 °C showed a strong bond between the LN and SiO2 layers, which is sufficient to withstand the wafer thinning to a LN thickness of approximately 5 μm using conventional mechanical polishing. Using micro-Raman spectroscopy, the residual stress in the bonded LN film in this trilayered (LN/SiO2/Si) structure was investigated. The measured residual tensile stress in the LN film layer was approximately 155 MPa, which was similar to the value calculated by stress analysis. This study will be useful for the development of various hetero-integrated LN micro-devices, including silicon-based, LNOI-integrated photonic devices. View Full-Text
Keywords: Residual stress in LN film layer; Lithium niobate-on-insulator/Si hybrid wafer; Surface-activated bonding; Low-temperature wafer bonding; Large mismatch of thermal expansion coefficient Residual stress in LN film layer; Lithium niobate-on-insulator/Si hybrid wafer; Surface-activated bonding; Low-temperature wafer bonding; Large mismatch of thermal expansion coefficient
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Takigawa, R.; Tomimatsu, T.; Higurashi, E.; Asano, T. Residual Stress in Lithium Niobate Film Layer of LNOI/Si Hybrid Wafer Fabricated Using Low-Temperature Bonding Method. Micromachines 2019, 10, 136.

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