Chip-Scale Molecular Clocks: Evolvement Towards Widely Deployable "Atomic Clock" Grade Time Standards

An affordable, miniaturized time standard with "atomic clock" grade stability is in an urgent need for numerous applications. For instance, the 5G wireless infrastructure demands precise timing synchronization for massive Multi-Input-Multi-Ouput (MIMO) antennas. In addition, high performance clocks in micro-positioning, navigation and timing (µPNT) devices under GPS denied environment are experiencing a rapid growth. This paper reviews the development of chip scale molecular clocks (CSMC), which is a new timebase employing rotational spectra in sub-terahertz region of polar gaseous molecules for frequency servo-stabilization. CSMC is a promising alternative of chip-scale atomic clocks (CSAC) and miniaturized atomic clocks (MAC) for massive deployment.