  To develop a new generation of high-speed photonic modulators on
silicon-technology-based photonics, new materials with large Pockels
coefficients have been transferred to silicon substrates. Previous approaches
focus on realizing stand-alone devices on dedicated silicon substrates,
incompatible with the fabrication process in silicon foundries. In this work,
we demonstrate monolithic integration of electro-optic modulators based on the
Pockels effect in barium titanate (BTO) thin films into the back-end-of-line of
a photonic integrated circuit (PIC) platform. Molecular wafer bonding allows
fully PIC-compatible integration of BTO-based devices and is, as shown,
scalable to 200 mm wafers. The PIC-integrated BTO Mach-Zehnder modulators
outperform conventional Si photonic modulators in modulation efficiency,
losses, and static tuning power. The devices show excellent V{\pi}L (0.2 Vcm)
and V{\pi}L{\alpha} (1.3 VdB), work at high speed (25 Gbps), and can be tuned
at low static power consumption (100 nW). Our concept demonstrates the
possibility of monolithic integration of Pockels-based electro-optic modulators
in advanced silicon photonic platforms.
  {\c} 2019 Optical Society of America. Users may use, reuse, and build upon
the article, or use the article for text or data mining, so long as such uses
are for non-commercial purposes and appropriate attribution is maintained. All
other rights are reserved.
  https://www.osapublishing.org/jlt/abstract.cfm?URI=jlt-37-5-1456
  Publication date: March 1, 2019
  This work was supported in part by the European Union (EU) under Horizon 2020
grant agreements no. H2020-ICT-2015-25-688579 (PHRESCO) and
H2020-ICT-2017-1-780997 (plaCMOS).
