Passive alignment and mounting of LiNbO3 waveguide chips on Si substrates by low-temperature solid-state bonding of Au

Ryo Takigawa, Eiji Higurashi, Tadatomo Suga, Tetsuya Kawanishi

Research output: Contribution to journalArticlepeer-review

37 Citations (Scopus)


In this study, passive alignment and mounting of lithium niobate (LiNbO3) chips, with a large mismatch in the coefficient of thermal expansion with most semiconductors, are demonstrated for hybrid-integrated optical devices. LiNbO3 chips were aligned passively using the visual index alignment method and were subsequently bonded on the Si substrates by low-temperature solid-state bonding with Au microbumps, which allow for electrical connections and heat dissipation. Au-Au bonding was carried out at 100 °C in ambient air after surface activation by argon RF plasma. The vertical bonding accuracy was determined by assessing the height variations of the Au microbumps due to the plastic deformation in the bonding process. The bonding accuracies in the horizontal and vertical directions were estimated to be within ±1 μm. Average excess loss due to misalignment between titanium-diffused single-mode LiNbO3 waveguides and V-groove-guided single-mode fibers was about 0.5-dBm per interface (wavelength: 1.55 μm).

Original languageEnglish
Article number5713807
Pages (from-to)652-658
Number of pages7
JournalIEEE Journal on Selected Topics in Quantum Electronics
Issue number3
Publication statusPublished - 2011 May
Externally publishedYes


  • Hybrid integration
  • lithium niobate
  • microbumps
  • passive alignment
  • surface activated bonding
  • visual index alignment

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Electrical and Electronic Engineering


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