Thermal Management for Chip-Scale Atomic Clocks

Abstract

Power dissipation of chip-scale atomic clocks is one of the major design considerations. The largest power dissipation is for temperature control of the vertical-cavity surface-emitting laser (VCSEL) and cesium vapor cell. For example, the temperature of the VCSEL and Cs cell have to both be at 70±0.1°C or there will be frequency shift which will ruin the lock of the clock. These temperatures have to be maintained even under a large temperature variation such as −40°C to 50°C. There are three major thermal designs to consider: a) micro-heaters to fine-tune the temperatures of VCSEL and Cs cell, b) use of waste heat from other units to heat the system when outside temperature is low, and c) use of a thermal switch to release any extra waste heat when ambient temperatures are high. These three thermal designs have been incorporated in to a thermal test vehicle, which will be used to develop a thermal management design for the clock. This paper describes the proposed clock design, creation of the thermal test vehicle and development of a bimetallic snap based thermal conduction switch. The switch has been demonstrated to change thermal resistance from 52.9±2.8 K/W when the switch is open to 19.5±1.1 K/W with the switch closed.

Thermal conductance switching based on the actuation of liquid droplets through the electrowetting on dielectric (EWOD) phenomenon

“…These include bolometers with enhanced dynamic ranges [1], pulsed thermoelectric cooling with increased maximum temperature lifts [2], low-power precision temperature control of chip scale atomic clocks [3], solid-state thermal energy harvesting [4], and thermally reconfigurable networks for satellite thermal management [5,6].…”

“…Thermal conductance switches based on phase change materials, such as wax and shape memory alloys, have been widely studied [3,7]. Electrostatic devices [8,9] control heat transfer by electrostatically attracting thin radiator films to the opposing surfaces and thereby switching the heat transfer mode from inefficient radiation to efficient conduction.…”