Temperature (K)427.2
5.6 Chapter Summary
In this chapter, we have investigated the dissipation in single-crystal 3C-SiC nanomechanical resonators operating at ultra-high frequencies, to gain understanding and develop engineering solutions that make optimal trade-offs between scaling up resonance frequency and attaining high Q’s for UHF NEMS resonators. It is found that the temperature dependence of the dissipation in the 3C-SiC NEMS resonators studied follows Q-1∝Tα, with α≈0.3. It is clear that in-depth theoretical models and analyses are needed to reveal the underlying microscopic mechanisms. The magnetomotive damping effect can be appreciable, but it is relatively well understood and (to some
extent) controlled. Thermoelastic dissipation is found to be negligible for the devices of this study. The losses from metallization layers contribute ≤1% of the observed total dissipation. However, a major source of the dissipation is clamping losses through the supports for these doubly-clamped beam UHF resonators. The measured data show that the theoretical prediction Qclamp-1∝(w/L)3 provides a rough but reasonable model for these clamping losses. Verifying and understanding the dominant clamping losses can lead to new designs and optimization guidelines for UHF NEMS enabling attainment of high Q’s.
Moreover, because SiC can be deposited both in polycrystalline form as well as in several single-crystal polytypes with excellent properties (including 3C-SiC, 6H-SiC, 4H-SiC and 2H-SiC), it represents a particularly promising material for NEMS applications.
Future collective studies of dissipation in SiC NEMS with all these SiC variations would be beneficial.
For future Q-engineering while scaling the frequency up, we propose and are exploring the following possibilities and promising solutions.
(i) Geometric mechanical design and optimization: By engineering and optimizing the anchoring, supports and vibrational modes (e.g., free-free beams, tuning-forks, disks with wine-glass and extensional modes), the clamping losses can be reduced or minimized.
(ii) Processes engineering: By developing suitable annealing process [39], high-temperature and high-vacuum encapsulation packaging process [40,41], surface loss, interfacial loss at inhomogeneous interfaces, metallization layer dissipation and thermoelastic damping are expected to be alleviated.
(iii) Materials engineering: The development of highly-doped conducting single-crystal materials, metallic single-crystal nanowires, very-low internal loss
metallization layers, can also be anticipated to reduce the surface and interfacial losses, the internal friction in metallization and the thermoelastic damping effects.
(iv) Electrical design: In the electrical domain, engineering and development of the transduction schemes and circuit models are expected to create technologies in which the loaded-Q effects are minimized.
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