Demonstration of the mass-producible feature of a Cs vapor microcell technology for miniature atomic clocks

Abstract

We report on the characterization of Cs vapor microcells based on pill dispensers and fabricated in a MEMS foundry according to a process compatible with mass-production. More than three quarters of cells from 6-inch wafers are successfully filled with Cs vapor. Various cells of a given wafer have been characterized using coherent population trapping (CPT) spectroscopy, demonstrating similar buffer gas (Ne) pressure with a standard deviation of about 2.5% and CPT resonances with similar linewidth and contrast properties. In addition, frequency drifts mainly attributed to cell inner atmosphere variations have been investigated onto several cells over 250–500 h measurements. The corresponding contribution at 1 day averaging time to a clock fractional frequency stability is estimated to be about 10−11 or lower. In a last section, the fractional frequency stability of a clock prototype using one fabricated Cs-Ne microcell is measured to be 2.5 × 10−11 τ−1/2 up to 200 s averaging time and better than 2 × 10−11 at 105 s. The clock frequency stability is mainly limited at short-term by the frequency-to-amplitude (FM-AM) noise conversion process and the laser amplitude (AM) noise. The mid-term stability is mainly affected by temperature-induced light shift effects. These performances tend to demonstrate that this vapor cell technology, compatible with mass-production, is suitable for miniature quantum clocks or sensors.