The work is based on a microwave generator that exploits thickness extensional (TE) vibration in a piezoelectric thin film. The approach is said to be suitable for mechanical resonance at GHz frequencies and to remove the need for frequency multipliers and off chip quartz oscillators.
Combining researchers from the Japanese National Institute of Information and Communications Technology, Tohoku University and Tokyo Institute of Technology, the team says it has exploited the TE mode and developed a microwave generator oscillating at 3.4GHz; the clock transition frequency of Rubidium-87. In comparison with a module-sized atomic clock, the researchers say that chip area and power consumption could be reduced by 30% and 50%, respectively.
While a chip-scale atomic clock was commercialised in 2011, the team says it contains a number chips inside, adding that most of the board area and power in the device are taken up by a microwave generator, with a complicated PLL system acting as a major source of power consumption.
‘Our approach could reduce the size, cost, and power consumption of atomic clocks deployed to high-end systems such as satellites or base stations’, the researchers note. ‘Transferring this technology to practical applications will make it possible to incorporate the atomic clock into smartphones or other wireless devices’.
The work features rubidium gas contained in a silicon-based microcell. A feedback loop stabilises the frequency of the microwave generator, enabling atomic clock operation. Short-term frequency instability is said to be 10 -11, with an averaging time of 1s. This, says the team, is more than an order of magnitude better than commercialised module-sized atomic clocks.
