Organic Chip-Scale Physics Packages for MEMS Atomic Clocks

The organic chip-scale physics package for MEMS atomic clocks with function of thermal management and magnetic field control is presented. The organic package consists of MEMS alkali vapor cell, vertical-cavity surface-emitting laser (VCSEL), photo-diode, and rigid-flexible organic frame for package. The alkali vapor cell is fabricated by conventional bulk-micromachining. For thermal management of vapor cell, the micro-heater and resistance temperature detector (RTD) are integrated on the glass lid of vapor cell by using Ti/Pt thin film with typical lift-off process. In order to integrate of MEMS vapor cell, VCSEL, and photo-diode, each device is mounted on the organic substrate with area of 1 cm2 and they are vertically stacked and inter-connected. To increase the thermal resistance of physics package, the rigid-flexible PCB is applied for the suspension of alkali cell and VCSEL. The FEA analysis resulted 1300 K/W of thermal resistance and temperature difference within 100mK. For magnetic field control, the Helmholtz coil and folded mu-metal foil are embedded into stacked PCB to generate C-field and magnetic shielding. The magnetic field gradient of proposed coil was 120nT/cm. The mockup of proposed organic chip-scale physics had a volume less than 1 cm3 and the electro-thermal analysis presented the power consumption of 50 mW for operating temperature of 80°C from room temperature under 20 mTorr of vacuum environment.