Abstract
The wafer-level integration technique of PageWafer® (SAES Getters’ solution for getter film integration into wafer to wafer bonded devices) has been tested in hermetically sealed miniature glass-Si-glass cells filled with Cs and Ne, e.g. for microelectromechanical systems (MEMS) atomic clock applications. Getter effects on the cell atmosphere are analyzed by quadruple mass spectroscopy and coherent population trapping (CPT) spectroscopy. The quadruple mass spectroscopy revealed that the residual gases (H2, O2, N2 and CO2) that are attributed to anodic bonding process are drastically reduced by the getter films while desirable gases such as Ne seem to remain unaffected. The impurity pressure in the getter-integrated cells was measured to be less than 4 × 10−2 mbar, i.e. pressure 50 times lower than the one measured in the cells without getter (2 mbar). Consequently, the atmosphere of the getter-integrated cells is much more pure than that of the getter-free cells. CPT signals obtained from the getter-integrated cells are stable and are, in addition, similar to each other within a cell batch, suggesting the strong potential of applications of this getter film and especially for its wafer-level integration to MEMS atomic clocks and magnetometers.
Highlights
Hermetical sealing of microelectromechanical systems (MEMS) structures is one of the important fabrication steps in order to generate miniature devices such as alkali-vapor cells-based MEMS atomic sensors, i.e.atomic clocks [1], spectrometers [2] or magnetometers [3]
We report the integration of PageWafer R to Cs–Ne cells for micro atomic clock applications, which have been developed within the European project ‘MEMS atomic clocks for timing, frequency control and communications (MAC-TFC)’
In the related micro atomic clock, the coherent population trapping (CPT) resonance is obtained in a microcell containing Cs and a single buffer gas, i.e. Ne [13]
Summary
Hermetical sealing of microelectromechanical systems (MEMS) structures is one of the important fabrication steps in order to generate miniature devices such as alkali-vapor cells-based MEMS atomic sensors, i.e.atomic clocks [1], spectrometers [2] or magnetometers [3] These devices require MEMS cells which contain a precisely controlled atmosphere that stays stable for short and long-term use. A CPT atomic clock using such a Cs–Ne microcell achieved a short-term frequency stability of 1.5 × 10−10 τ −1/2 until 30s [16] and more recently 3.8 × 10−11 τ −1/2 until 1000 s [17] using a laser resonant with the Cs D1 line In these experiments, a possible explanation of the clock frequency shift occurring after 1000s integration time is the variation of the cell atmosphere that could be related to reactions between very reactive alkali atoms such as Cs and impurities. The getter-integrated Cs–Ne cells were further examined through CPT spectroscopy
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