Saurabh Chandorkar Thesis Defense - 12:30pm Friday, 13 June 2008

Saurabh A. Chandorkar saurabhc at stanford.edu
Tue Jun 10 12:05:35 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: 12:30 pm (Refreshments beforehand)
Venue: CISX-101 (Auditorium)
http://campus-map.stanford.edu/index.cfm?ID=04-055

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

Abstract:

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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