Saurabh A. Chandorkar saurabhc at
Wed Jun 11 00:00:51 PDT 2008

Ph.D. Thesis Oral Examination
"Energy Loss Mechanisms in Micromechanical Resonators"
Advisor: Prof. Thomas W. Kenny and Prof. Kenneth E. Goodson

Date: Friday, June 13th
Time: 11:30 pm (Refreshments beforehand)
Venue: CISX-101 (Auditorium)

Keywords: energy loss mechanisms, micromechanical resonators,
thermoelastic dissipation, Akhiezer effect, entropy generation 
minimization, quantum limit


Micromechanical resonators have the potential to replace quartz
crystals for timing and frequency references owing to their small
form factors, better aging stability and CMOS scalability. Quality 
factor, an important performance characteristic of all resonators, 
determines limits for system characteristics like close to carrier phase 
noise, stability and motional impedance.
Thus, for most applications we would like to design for the maximum 
achievable quality factor, and this requires good understanding of the 
energy loss mechanisms that limit the performance of modern 
micromechanical resonators. This work focuses on two such mechanisms: 
Thermoelastic dissipation and Akhiezer effect.

Thermoelastic dissipation refers to the energy lost from a solid
due to flow of heat between regions of different volumetric changes. 
This work presents a comprehensive entropic formulation
for quantifying energy loss due to thermoelastic dissipation. Entropy 
generation minimization, and therefore energy loss minimization, will be 
demonstrated through several case studies including simple fixed-fixed 
beams, simple fixed-fixed beams with
slots, composite beams and various bulk mode structures. We compare
our simulations against experimental evidence for confirmation of
modeling technique.

Certain bulk mode resonator structures will be shown to be immune
to thermoelastic dissipation. Akhiezer effect sets the ultimate
quantum limit of minimum achievable energy loss in dielectric 
micromechanical resonators. It will be shown that the current 
micromechanical resonators found in literature are very close to
this limit. Finally, recent results of microresonators designed
to operate close to Akhiezer effect limit will be discussed.

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