Progress Report on the Development of an European Chip Scale Atomic Clock at the Femto-ST Institute
GIORDANO, V.¹; DOUAHI, A.¹; HASEGAWA, M.¹; DZIUBAN, P.¹; NIERADKO, L.¹; DZIUBAN, J.²; GORECKI, C.^1
1Femto-ST Institute - CNRS; ²Wroclaw University of Technology

The development of highly miniaturised, battery powered atomic frequency references based on micromachining techniques would enable significant advancements in telecommunication and satellite navigation systems. This new category of atomic frequency standard uses the principle of coherent population trapping (CPT), obtained in an extremely compact vapour microcell of a few mm³.

Signifcant advances have been already realized by the different groups and first prototypes have been already designed and demonstrated. The micro-cell fabrication is one of the main key issues for the realization of a such compact frequency standard. The micro-cell should contain a controled and stable vapor composition and its manufacturing should moreover be compatible with a batch production. Two techniques for introducing cesium and a buffer gas into the cells have been proposed: one based on a chemical reaction, and the other based on direct injection of liquid cesium within a controlled anaerobic environment. In both methods of the alkali atom vapour is introduced inside the micromachined cavity prior to its sealing. The common drawback of both techniques is the high chemical reactivity of cesium, that makes its presence in the cavity essentially non-compatible with most of the subsequent steps of the cell fabrication, and in particular with the anodic bonding step.

At the Femto-ST Institute, we have developped a new type of cesium microcell based on an original technique of microfabrication, in which the conflict of the anodic bonding process with cesium chemistry is fully avoided, making the fabrication of alkali microcells simpler and improving the potentiality of mass production for miniature atomic clocks.
In this paper, our microcell fabrication procedure will be explained. Eventually the latest experimental results on CPT obtained with our micro-cells will be presented.