"[it
is desired to have] a Watch to keep Time exactly: But, by reason of the
Motion of a Ship, the Variation of Heat and Cold, Wet and Dry, and the
difference of Gravity in different Latitudes, such a Watch hath not yet
been made."
Sir Isaac Newton, report to the House of Commons, 1714
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- Thermal Isolation of MEMS Resonators
- High Precision MEMS Digital Temperature Sensor
- Shape Optimization of Micro-Structures
CMOS compatible MEMS resonators are becoming an interesting and viable
technology as a replacement for quartz crystals for timing and frequency
reference applications. Oven controlled silicon and quartz resonators are
used to generate high precision frequency references suitable for high-end
industry and military standards. In this method, the resonator is held at a
fixed temperature to compensate for the temperature dependence of the resonator
frequency. The extent to which the resonator is heated depends on the difference
between the set-point and the ambient temperature. For an ovenized resonator
required to operate within a temperature range of -40°C
to 85°C, the heating has to cover the
range of 125°C. Due to the large volume
of a conventional quartz crystal resonators, which can be up to 1000 mm3,
the power consumption is up to 10W with a warm-up time of approximately 30
minutes. MEMS technology offers miniaturization to sub-mm scales which can
provide substantial power reduction.
This research describes a miniature
thermal isolation design which achieves a
small thermal time constant with low power consumption, and a unique
self-temperature sensing technique
of resonators to achieve our ultimate goal of low-power temperature-stable
resonators. To further increase the thermal isolation and temperature-stability
of the resonator while maintaining a
mechanically stiff structure, an
optimum resonant structure needs to be designed. |