Variable thermal resistor for low power temperature regulation of CSAC

It is essential for a chip-scale atomic clock (CSAC) development to make an efficient thermal isolation structure as well as to use low power for temperature controlling due to the low-power requirements (near 30 mW total power consumption in the presence of -40~50°C of ambient temperature variation). There have been several efforts on the thermal management of a CSAC to keep the temperature of a vapor cell in a CSAC at 75°C with low power using thermal isolation structures; however, this is the first study that shows the ability of thermal resistance change in multiple stages to control a CSAC temperature in a range of ambient temperature variation. We developed a variable thermal resistor (VTR) for the purpose of changing the thermal resistance of a CSAC package according to the ambient temperature variation.;The current VTR is comprised of thermal isolation structures (polyimide posts) and an array of ten electrostatic actuators (suspended gold beams). The top silicon die which has ground electrode for vertical electrostatic actuator is separated by three 30 mum tall polyimide posts. Ten 1.6 mum thick gold suspended beams are placed between the top and the bottom dies while they keep the distance to the top die 5+/-1 mum at zero bias. When 100 V of electrical potential is applied to the gold beams, they bend up and make contact with the top die. As a consequence, the thermal resistance of VTR decreases. The 0.5 mum SiO2 passivation layer on the top die prevents electrical contact between ground electrode and the gold beams.;In addition to the current design of VTR, we also discuss passive actuation type VTR which is actuated by the ambient temperature variation. An improved thermal resistance measurement method we have developed is also introduced and evaluated.;The current version of VTR demonstrates thermal resistance variation from 200°C/W to 1200°C/W with 100+/-20°C/W of resolution. As a room temperature thermal switch that deals with low heat load, VTR may serve as a high thermal resistance package solution for any low-power and high-temperature electric device.