  Microring resonators are critical photonic components used in filtering,
sensing and nonlinear applications. To date, the development of high
performance microring resonators in LNOI has been limited by the sidewall
angle, roughness and etch depth of fabricated rib waveguides. We present large
free spectral range microring resonators patterned via electron beam
lithography in high-index contrast $Z$-cut LNOI. Our microring resonators
achieve an FSR greater than 5 nm for ring radius of 30 $\mu$m and a large 3 dB
resonance bandwidth. We demonstrate 3 pm/V electro-optic tuning of a 70
$\mu$m-radius ring. This work will enable efficient on-chip filtering in LNOI
and precede future, more complex, microring resonator networks and nonlinear
field enhancement applications.
