Performance of Monolayer Graphene Nanomechanical Resonators with Electrical Readout

The enormous stiffness and low density of graphene make it an ideal material for nanoelectromechanical (NEMS) applications. We demonstrate fabrication and electrical readout of monolayer graphene resonators, and test their response to changes in mass and temperature. The devices show resonances in the MHz range. The strong dependence of the resonant frequency on applied gate voltage can be fit to a membrane model, which yields the mass density and built-in strain. Upon removal and addition of mass, we observe changes in both the density and the strain, indicating that adsorbates impart tension to the graphene. Upon cooling, the frequency increases; the shift rate can be used to measure the unusual negative thermal expansion coefficient of graphene. The quality factor increases with decreasing temperature, reaching ~10,000 at 5 K. By establishing many of the basic attributes of monolayer graphene resonators, these studies lay the groundwork for applications, including high-sensitivity mass detectors

CAREER: advanced temperature compensation techniques for integrated bulk-mode micro and nano mechanical resonators

Issued as final reportNational Science Foundation (U.S.

Mechanical resonating devices and their applications in biomolecular studies

To introduce the reader in the subjects of the thesis, Chapter 1 provides an overview on the different aspects of the mechanical sensors. After a brief introduction to NEMS/MEMS, the different approaches of mechanical sensing are provided and the main actuation and detection schemes are described. The chapter ends with an introduction to microfabrication. Chapter 2 deals with experimental details. In first paragraph the advantages of using a pillar instead of common horizontal cantilever are illustrated. Then, the fabrication procedures and the experimental setup for resonance frequencies measurement are described. The concluding paragraph illustrates the technique, known as dip and dry, I used for coupling mechanical detection with biological problems. In Chapter 3, DNA kinetics of adsorption and hybridization efficiency, measured by means of pillar approach, are reported. Chapter 4 gives an overview of the preliminary results of two novel applications of pillar approach. They are the development of a protein chip technology based on pillars and the second is the combination of pillars and nanografting, an AFM based nanolithography. Chapter 5 starts with an introduction about the twin cantilever approach and of the mechanically induced functionalization. Fabrication procedure is described in the second paragraph. Then the chemical functionalizations are described and proved. Cleaved surface analyses and the spectroscopic studies of the mechanically induced functionalization are reported. In Appendix A there is an overview of the physical models that are used in this thesis

Mechanical reliability of silicon microstructures

In this article, an overview of the mechanical reliability of silicon microstructures for micro-electro-mechanical systems is given to clarify what we now know and what we still have to know about silicon as a high-performance mechanical material on the microscale. Focusing on the strength and fatigue properties of silicon, attempts to understand the reliability of silicon and to predict the device reliability of silicon-based microstructures are introduced. The effective parameters on the strength and the mechanism of fatigue failure are discussed with examples of measurement data to show the design guidelines for highly reliable silicon microstructures and devices

INVESTIGATION OF THERMOELASTIC LOSS MECHANISM IN SHELL RESONATORS

ABSTRACT Maximizing quality (Q) factor is key to enhancing the performance of micro mechanical resonators, which are used in a wide range of applications such as gyroscopes, filters, and clocks. There are several energy loss mechanisms commonly associated with micro resonators including anchor loss through the substrate, squeeze film damping, thermoelastic dissipation (TED), and surface loss. This work focuses on the thermoelastic loss as one of the major energy dissipation mechanisms of micro shell resonators. In this article, the effects of material properties, thickness, conductive coating and operating temperature on the Q-factor of micro shell resonators are investigated. Numerical simulation shows shell resonators have higher Q-factors when they are operating at lower temperatures. Although, the magnitude of the simulated Q-factors of an uncoated bare resonator made from fused silica is more than 70 million and so it is too high to have a remarkable effect on the total Q-factor, our study shows that even a thin layer of some conductive coatings like gold on the surface of a bare shell reduces Q-factor significantly. The sensitivity of the coated shell resonator design to the TED phenomenon provides useful information for the development of new micro shell resonators with improved performance and Q-factors

RADIO FREQUENCY SIGNAL PROCESSING WITH MICROELECTROMECHANICAL RESONATING SYSTEMS

This thesis presents a study of the dynamics and applications of a high frequency micromechanical (MEMS) resonator. Mechanical systems, which have been scaled in dimension to the micron scale, show promise for replacing electrical resonant systems, which have larger physical size and lower performance. MEMS resonators can also be integrated into a chip containing conventional field effect transistors. A process incorporating both frequency dependent resonant systems as well as analog and digital electronics will enable all hardware in a communication architecture to be placed on a single silicon chip. In this study, a micron-sized circular membrane, suspended in the middle and clamped on the periphery, forms the basis of the resonant mechanical system. A small degree of curvature is fabricated into the resonator, which serves to stiffen the device and hence increase the frequency range. A microheater, defined in proximity to the resonator, is used to induce motion in the membrane. The frequency dependent response of the membrane is then detected through either interferometric or piezoresistive techniques. Resistive actuation and detection allow the membrane and actuators to be fabricated into a single plane of silicon, facilitating integration of the complete MEMS system. It is demonstrated how both the resonators and transducers can be implemented into two CMOS processes. Both designs incorporate the mechanical system as well as the solid-state electronics for output signal detection into a single fabrication process. Finally, the dynamics of the MEMS resonator, both in the linear and non-linear regime, are explored. The micron-sized mechanical system is demonstrated to perform several types of signal processing that are critical for wireless communication architectures. These studies shed new light on how the nonlinear dynamics of these systems may be characterized and harnessed for new applications

Multiphysics modelling and experimental validation of microelectromechanical resonator dynamics

The modelling of microelectromechanical systems provides a very challenging task in microsystems engineering. This field of research is inherently multiphysics of nature, since different physical phenomena are tightly intertwined at microscale. Typically, up to four different physical domains are usually considered in the analysis of microsystems: mechanical, electrical, thermal and fluidic. For each of these separate domains, well-established modelling and analysis techniques are available. However, one of the main challenges in the field of microsystems engineering is to connect models for the behavior of the device in each of these domains to equivalent lumped or reduced-order models without making unacceptably inaccurate assumptions and simplifications and to couple these domains correctly and efficiently. Such a so-called multiphysics modelling framework is very important for simulation of microdevices, since fast and accurate computational prototyping may greatly shorten the design cycle and thus the time-to-market of new products. This research will focus on a specific class of microsystems: microelectromechanical resonators. MEMS resonators provide a promising alternative for quartz crystals in time reference oscillators, due to their small size and on-chip integrability. However, because of their small size, they have to be driven into nonlinear regimes in order to store enough energy for obtaining an acceptable signal-to-noise ratio in the oscillator. Since these resonators are to be used as a frequency reference in the oscillator circuits, their steady-state (nonlinear) dynamic vibration behaviour is of special interest. A heuristic modelling approach is investigated for two different MEMS resonators, a clamped-clamped beam resonator and a dog-bone resonator. For the clamped-clamped beam resonator, the simulations with the proposed model shows a good agreement with experimental results, but the model is limited in its predictive capabilities. For the dogbone resonator, the proposed heuristic modelling approach does not lead to a match between simulations and experiments. Shortcomings of the heuristic modelling approach serve as a motivation for a first-principles based approach. The main objective of this research is to derive a multiphysics modelling framework for MEMS resonators that is based on first-principles formulations. The framework is intended for fast and accurate simulation of the steady-state nonlinear dynamic behaviour of MEMS resonators. Moreover, the proposed approach is validated by means of experiments. Although the multiphysics modelling framework is proposed for MEMS resonators, it is not restricted to this application field within microsystems engineering. Other fields, such as (resonant) sensors, switches and variable capacitors, allow for a similar modelling approach. In the proposed framework, themechanical, electrical and thermal domains are included. Since the resonators considered are operated in vacuum, the fluidic domain (squeeze film damping) is not included. Starting from a first-principles description, founded on partial differential equations (PDEs), characteristic nonlinear effects from each of the included domains are incorporated. Both flexural and bulk resonators can be considered. Next, Galerkin discretization of the coupled PDEs takes place, to construct reduced-order models while retaining the nonlinear effects. The multiphysics model consists of the combined reduced-order models from the different domains. Designated numerical tools are used to solve for the steady-state nonlinear dynamic behaviour of the combined model. The proposed semi-analytical (i.e. analytical-numerical) multiphysics modeling framework is illustrated for a full case study of an electrostatically actuated single-crystal silicon clamped-clamped beam MEMS resonator. By means of the modelling framework, multiphysics models of varying complexity have been derived for this resonator, including effects like electrostatic actuation, fringing fields, shear deformation, rotary inertia, thermoelastic damping and nonlinear material behaviour. The first-principles based approach allows for addressing the relevance of individual effects in a straightforward way, such that the models can be used as a (pre-)design tool for dynamic response analysis. The method can be considered complementary to conventional finite element simulations. The multiphysics model for the clamped-clamped beam resonator is validated by means of experiments. A good match between the simulations and experiments is obtained, thereby giving confidence in the proposed modelling framework. Finally, next to themodelling approach for MEMS resonators, a technique for using these nonlinear resonators in an oscillator circuit setting is presented. This approach, called phase feedback, allows for operation of the resonator in its nonlinear regime. The closedloop technique enables control of both the frequency of oscillation and the output power of the signal. Additionally, optimal operation points for oscillator circuits incorporating a nonlinear resonator can be defined

Thin-film piezoelectric-on-substrate resonators and narrowband filters

A new class of micromachined devices called thin-film piezoelectric-on-substrate (TPoS) resonators is introduced, and the performance of these devices in RF and sensor applications is studied. TPoS resonators benefit from high electromechanical coupling of piezoelectric transduction mechanism and superior acoustic properties of a substrate such as single crystal silicon. Therefore, the motional impedance of these resonators are significantly smaller compared to typical capacitively-transduced counterparts while they exhibit relatively high quality factor and power handling and can be operated in air. The combination of all these features suggests TPoS resonators as a viable alternative for current acoustic devices. In this thesis, design and fabrication methods to realize dispersed-frequency lateral-extensional TPoS resonators are discussed. TPoS devices are fabricated on both silicon-on-insulator and thin-film nanocrystalline diamond substrates. The performance of these resonators in simple and low-power oscillators is measured and compared. Furthermore, a unique coupling technique for implementation of high frequency filters is introduced in which dual resonance modes of a single resonant structure are coupled. The measured results of this work show that these filters are suitable candidates for single-chip implementation of multiple-frequency narrow-band filters with high out-of-band rejection in a small footprint.Ph.D.Committee Chair: Farrokh Ayazi; Committee Member: James D. Meindl; Committee Member: John D. Cressler; Committee Member: Nazanin Bassiri-Gharb; Committee Member: Oliver Bran

Microelectromechanical Systems and Devices

The advances of microelectromechanical systems (MEMS) and devices have been instrumental in the demonstration of new devices and applications, and even in the creation of new fields of research and development: bioMEMS, actuators, microfluidic devices, RF and optical MEMS. Experience indicates a need for MEMS book covering these materials as well as the most important process steps in bulk micro-machining and modeling. We are very pleased to present this book that contains 18 chapters, written by the experts in the field of MEMS. These chapters are groups into four broad sections of BioMEMS Devices, MEMS characterization and micromachining, RF and Optical MEMS, and MEMS based Actuators. The book starts with the emerging field of bioMEMS, including MEMS coil for retinal prostheses, DNA extraction by micro/bio-fluidics devices and acoustic biosensors. MEMS characterization, micromachining, macromodels, RF and Optical MEMS switches are discussed in next sections. The book concludes with the emphasis on MEMS based actuators