  The heterogeneous integration of lithium niobate photonic waveguide devices
onto a silicon nitride waveguide platform via a transfer-printing approach has
been demonstrated for the first time. A fabrication process was developed to
make free-standing lithium niobate membrane devices compatible with back-end
integration onto photonic integrated circuits. Micro-ring resonators in
membrane format were lithographically defined by using laser direct writing and
plasma dry etching. The lithium niobate micro-ring resonators were then
transferred from their host substrate and released onto a silicon nitride
waveguide chip. An all-pass ring resonator transmission spectrum was obtained
in the 1.5 {\mu}m to 1.6 {\mu}m wavelength range, with a measured loaded
Q-factor larger than 32000.
