  Microresonator frequency combs (microcombs) hold great potential for
precision metrology within a compact form factor, impacting a wide range of
applications such as point-of-care diagnostics, environmental monitoring,
time-keeping, navigation and astronomy. Through the principle of self-injection
locking, electrically-driven chip-based microcombs with minimal complexity are
now feasible. However, phase-stabilisation of such self-injection-locked
microcombs, a prerequisite for metrological frequency comb, has not yet been
attained. Here, we address this critical need by demonstrating full
phase-stabilisation of a self-injection-locked microcomb. The microresonator is
implemented in a silicon nitride photonic chip, and by controlling a pump laser
diode and a microheater with low voltage signals (less than 1.5 V), we achieve
independent control of the comb's offset and repetition rate frequencies. Both
actuators reach a bandwidth of over 100 kHz, enabling phase-locking of the
microcomb to external frequency references. These results establish photonic
chip-based, self-injection-locked microcombs as low-complexity yet versatile
sources for coherent precision metrology in emerging applications.
