  Low-noise microwave oscillators are cornerstones for wireless communication,
radar and clocks. Optical frequency combs have enabled photonic microwaves with
unrivalled noise performance and bandwidth. Emerging interest is to generate
microwaves using chip-based frequency combs, namely microcombs. Here, we
demonstrate the first, fully integrated, microcomb-based, microwave oscillator
chip. The chip, powered by a microelectronic circuit, leverages hybrid
integration of a DFB laser, a nonlinear microresonator, and a high-speed
photodetector. Each component represents the best of its own class, yet allows
large-volume manufacturing with low cost in CMOS foundries. The hybrid chip
outputs an ultralow-noise laser of 6.9 Hz linewidth, a microcomb of 10.7 GHz
repetition rate, and a 10.7 GHz microwave of 6.3 mHz linewidth -- all three in
one entity of 76 mm$^2$ size.The microwave phase noise reaches -75/-105/-130
dBc/Hz at 1/10/100 kHz Fourier offset frequency. Our results can reinvigorate
our information society for communication, sensing, timing and precision
measurement.
