Chandra Mohan Jha Thesis Defense - 8:08 am Friday, 08/08/08

Chandra Mohan Jha cmjha at stanford.edu
Mon Aug 4 14:50:38 PDT 2008


Ph.D. Thesis Oral Examination
"Design of Thermally and Mechanically Isolated Ovenized Microresonators"
Advisor: Prof. Thomas W. Kenny

Date: Friday, Aug 8th
Time: 8:08 am (Refreshments beforehand)
Venue: CISX-101 (Auditorium)
http://campus-map.stanford.edu/index.cfm?ID=04-055



Abstract:

Micromechanical resonators are becoming an interesting and viable technology
as a replacement for quartz crystals for timing and frequency reference
applications. For high precision applications in industry and military, oven
controlled resonators are used to compensate for the temperature dependence
of resonator frequency. An oven controlled resonator requires a good
temperature sensor and an efficient heater (oven). However, an external
temperature sensor leads to thermal lag and the ovenization leads to power
consumption.

This work presents a microresonator based digital temperature sensing
technique as well as an efficient local-thermal-isolation method. The
microresonator based thermometry results into a lag-free temperature sensor
for self temperature compensation suitable for high precision oven control
of the resonator. The thermal isolation technique includes the design of an
integrated heater with the microresonator such that the mechanical
suspension, electrical heating and thermal isolation are provided in a
single compact structure. This results in reducing the power consumption by
more than 20x and the thermal time constant by more than 50x. Further
reduction in power consumption requires analysis of the resonator structure
to maintain its mechanical integrity. An improved thermally isolated design
using topology optimization will be described. The final design provides
both the thermal isolation as well as the mechanical isolation with the
overall reduction in power consumption of 40x. Furthermore, these methods
are simple enough to implement it into any existing MEMS fabrication
process.





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