Study of 3-GHz-band Thin-film Bulk Acoustic Resonator Oscillators for Microfabricated Atomic Clocks

Ultracompact and ultrastable clock chips are essential for beyond 5G/6G (b5G/6G) telecommunication systems, and we are studying 3-GHz-band thin-film bulk acoustic resonator (FBAR) oscillators for the development of such clock chips. Good frequency instability of less than 10
⁻¹¹
can be obtained by stabilizing the 3-GHz-band RF signal from the FBAR oscillator with the sharp resonance line called the clock transition of the Rb atom by feedback control. Here, to reduce the cost of such a frequency stabilization system due to mass production, the FBAR oscillator was redesigned using the 180 nm CMOS rule, and its oscillation characteristics were evaluated. We also developed an FBAR two-divider oscillator to simplify the above stabilization loop and elaborately evaluated the locking range of the dividers.