Research progress on energy dissipation mechanisms in micro- and nano-mechanical resonators

Abstract

Advances in micro- and nanofabrication technologies have enabled the development of micro- and nano-mechanical resonators which have attracted significant attention due to their advantages of ultra-high resonance frequency, quality factor and sensitivity, and growing potential for physical sensing, biological and chemical detection, radio frequency communications and energy harvesting applications. It has become one of the emphases and hotspots in micro- and nano-electromechanical systems (MEMS/NEMS). Energy dissipation is always the key problem and significant bottlenecks, which restricts its performance improvement and application development. Energy dissipation in a mechanical resonator represents the relaxation or loss of energy contained in a resonant mode to the external environment coupled to the resonator structure as well as to the other resonant modes. In micro- and nano-mechanical resonators, a key performance metric is the quality factor ( Q ), which is the ratio of stored mechanical energy to the dissipated energy. Furthermore, energy dissipation has various and complicated mechanisms, which are uncertainty and scaling with system size. It is of great importance to understand the dissipation mechanisms. There exists a host of identifiable mechanisms, both intrinsic and extrinsic, which play an important role in the energy dissipation in micro- and nano-mechanical resonators. This article provides an overview on the progress of energy dissipation mechanisms and nonlinear damping effects in micro- and nano-mechanical resonators. Both intrinsic and extrinsic mechanisms, including thermoelastic damping, phonon interaction, viscous damping, support loss, surface and interface losses, are reviewed and discussed. The energy dissipation caused by viscous damping environments needs to be taken into account in initial design process. Different damping mechanisms are distinguished as the ambient air pressure varies based on the Knudsen number and various models for evaluating air damping mechanisms in different vibration structures from viscous flow regime to molecular flow mechanism have been paid more attention. Furthermore, the quality factor is limited by the thermal physics and specific energy loss mechanisms including thermoelastic, Akhieser, and Landau-Rumer damping in well-optimized designs of mechanical resonators. Support loss occurs because of the strain at the connection to the support structure and must be considered in order to understand the interaction and energy transmission between the resonator-support coupled systems. The support losses become detrimental as the resonator size is reduced but can be suppressed with appropriate device design. As the mechanical resonators become thinner or narrower, the surface- to-volume ratio grows and the surface properties start to play a significant role in the dissipation. Understanding the effect of each mechanism is very important for their application in predicting adequately the quality factor and operation characteristics of micro- and nano-mechanical resonators. In addition, the mergence of nonlinear dissipation mechanisms becomes more and more important in predicting and determining the device performance and discerning the dominant contribution to energy dissipation in resonator devices. Specifically, it reveals the physical mechanisms and the methods of dissipation reduction used in each strategy and provides design guidelines for the development of high-performance resonators. The purpose of this review is to understand, sort, and categorize dominant energy dissipation sources and to determine their significance with respect to physics processes and engineering applications.