  This work demonstrates the capabilities of an entangled photon-pair source at
telecom wavelengths, based on a photonic integrated Si$_3$N$_4$ microresonator
with monolithically integrated piezoelectric frequency tuning. Previously,
frequency tuning of photon-pairs generated by microresonators has only been
demonstrated using thermal control, however these have limited actuation
bandwidth, and are not compatible with cryogenic environments. Here, the
frequency-tunable photon-pair generation capabilities of a Si$_3$N$_4$
microresonator with a monolithically integrated aluminium nitride layer are
shown. Fast-frequency locking of the microresonator to an external laser is
demonstrated, with a resulting locking bandwidth orders of magnitude larger
than reported previously using thermal locking. These abilities will have
direct application in future schemes which interface such sources with quantum
memories based on e.g. trapped-ion or rare-earth ion schemes.
