Flexible Hybrid Approach for a 3D Integrated Physics Package of Chip-Scale Atomic Clocks

To realize the chip-scale atomic clocks (CSACs) for atomic reference with miniaturization and low power consumption, there are technological challenges in the physics package for compact and stable frequency standards. Here, the precise thermal management and the exact magnetic-field control of the physics package are required for accurate clocks. Also, high thermal resistance for the physics package helps to considerably reduce power consumption of the CSAC. Thus, in this study, a compact physics package with embedded magnetic shielding has been developed by using flexible hybrid approach for a chip-scale atomic clock. The vertical-cavity surface-emitting laser (VCSEL) and the MEMS hotplate on a flexible circuit board (FPCB) are vertically stacked and bound with a QWP and a MEMS vapor cell by aluminum foil. The aluminum bound structure is suspended by the polyimide core of the FPCB for high thermal resistance. Also, the mu-metal fixture is applied for magnetic shield and FPCB suspension, while the MEMS hotplate with a resistance heater and an amorphous Si based thermistor is adopted for thermal management of the physics package. Then, the planar integrated FPCB is folded and stacked vertically at an intersection with the mu-metal fixture. As a result, the CSAC incorporating the proposed physics package reveals the CPT linewidth of 5.6 kHz and low power consumption of about 200mW. The measured frequency short-term stability is about 5.2×10
^-12
τ
^-1/2
at 1000-second integration. The observed results demonstrate promising performances of the flexible hybrid physics package for its use in miniaturized atomic clocks.