3D Integrated Physics Package using MEMS Alkali Vapor Cell for Miniature Atomic Clocks

The 3D integration of MEMS alkali vapor cell for physics package of atomic clocks with function of thermal management and magnetic field control are presented. The physics package consists of MEMS alkali vapor cell, vertical-cavity surface-emitting laser (VCSEL), photo-diode and c-field coil. For thermal management, MEMS heaters and resistance temperature detectors (RTDs) are integrated into MEMS vapor cell and VCSEL subsystem. In order to integrate the MEMS vapor cell, VCSEL, photo-diode, each sub-system is mounted on the flexible substrate and they are 3-dimensionally integrated and interconnected by folding of flexible substrate. The Helmholtz coil and mu-metal foil are also embedded into physics package for magnetic field control. The integrated physics package is attached on ceramic substrate using solder-ball based inter-connection and sealed by using KOVAR lid and preform. The prototype of chip-scale physics for MEMS atomic clocks has a volume of 1 cm ³ and results in power consumption of 150 mW and stability of 2.2×10 ^-10 @ 10s.