Nanoelectromechanical Systems Research Articles

Review of: "Nanolithography is used, for example, when nanofabricating advanced semiconductor integrated circuits (nanocircuits), for nanoelectromechanical systems (NEMS)"

Review of: "Nanolithography is used, for example, when nanofabricating advanced semiconductor integrated circuits (nanocircuits), for nanoelectromechanical systems (NEMS)"

Dynamic behaviors of delaminated nanofilms partly bonded on substrates with sub-nanoscale van der Waals dynamic boundaries

Abstract Dynamic buckling-induced delamination of nanofilms on substrates is a universal and essential phenomenon in nanoelectromechanical systems (NEMS). Van der Waals (vdWs) interactions play an important role in the dynamic buckling-induced delamination of nanofilms on substrates due to the interaction distances at nanoscale or even sub-nanoscale in NEMS. Therefore, it is interesting yet challenging to reveal the effect of intermolecular vdWs interactions on dynamic buckling-induced delamination of nanofilms on substrates. By considering sub-nanoscale dynamic boundary effects induced by intermolecular vdWs interactions, a parametric excitation nonlinear vibration model for dynamic buckling-induced delamination of nanofilms partly bonded on substrates is established. Effects of sub-nanoscale vdWs dynamic boundaries on transient and steady-state responses of dynamically delaminated nanofilms on substrates are analyzed. The sub-nanoscale vdWs dynamic boundaries lead the dynamic responses of delaminated-nanofilm/substrate systems very sensitive to initial conditions. The bending and shifting frequency response results demonstrated that the system nonlinearities can be greatly amplified by the sub-nanoscale vdWs dynamic boundary effect. Moreover, the spontaneous symmetry breaking and violent interfacial tearing/healing phenomena can be also triggered in the systems. Based on spontaneous symmetry breaking, a trans-scale relationship between nanofilm equilibrium positions and intermolecular vdWs interactions is established, which can provide a promising route for trans-scale measurements of molecular scale interfacial interactions. The work can also be helpful for the dynamic design of resonant NEMS devices based on nanofilm/substrate systems.

Toward practical mass spectrometry with nanomechanical pillar resonators by surface acoustic wave transduction

Nanoelectromechanical systems (NEMS) have shown outstanding performance in the detection of small masses down to single proton sensitivity. To obtain a high enough throughput for application in practical mass spectrometry, NEMS resonators are arranged in two-dimensional (2D) arrays. However, all state-of-the-art electromechanical transduction methods rely on electrical lines placed close to the mechanical resonators, which drastically restricts the density of 2D resonator arrays. An exception is the transduction by surface acoustic waves (SAWs), which has so far only been shown for the transduction of single nanomechanical pillar resonators. Here, we demonstrate the transduction of pillar pairs by SAWs. The pillars have a diameter of 700 nm and show a mass responsivity of −588 ± 98 ng−1. The distances between the pillar pairs are 70 nm and 14.3 µm. SAW transduction enabled us to measure both pillars of each pair with electrical lines no closer than 300 µm, illustrating the potential of SAWs to transduce dense arrays of pillar resonators, a crucial step toward practical mass spectrometry with NEMS.

Biodielectrics: old wine in a new bottle?

Biodielectrics is a subset of biological and/or bioinspired materials that has brought a huge transformation in the advancement of medical science, such as localized drug delivery in cancer therapeutics, health monitoring, bone and nerve repair, tissue engineering and use in other nanoelectromechanical systems (NEMS). While biodielectrics has long been used in the field of electrical insulation for over a century, polar dielectric properties of biological building blocks have not been well understood at the fundamental building block level. In this review article, we provide a brief overview of dielectric properties of biological building blocks and its hierarchical organisations to include polar dielectric properties such as piezo, pyro, and ferroelectricity. This review article also discusses recent trends, scope, and potential applications of these dielectrics in science and technology. We highlight electromechanical properties embedded in rationally designed organic assemblies, and the challenges and opportunities inherent in mapping from molecular amino acid building blocks to macroscopic analogs of biological fibers and tissues, in pursuit of sustainable materials for next-generation technologies.

(Invited) Wafer Bonding for MEMS Integration and Packaging

Wafer bonding is a critical manufacturing process for a vast number of experimental and commercial microelectromechanical system (MEMS) devices [1-5]. Wafer bonding is used for both the hermetic sealing of MEMS [3-5], and for integrating MEMS with electronic integrated circuits (IC) [1-2]. In this invited talk we present recent examples of wafer bonding approaches targeted at hermetic sealing of emerging MEMS devices such as silicon photonic MEMS [3, 4]. In these processes, the MEMS are sealed by wafer bonding and transferring individual lids, while at the same time keeping the final total die thickness as thin as possible. Furthermore, we also present examples of wafer bonding techniques targeted at integrating MEMS or nanoelectromechanical systems (NEMS) directly on top of electronic integrated circuits (IC), thereby closely packaging the MEMS devices with the electronic circuits that provide an interface to the outside world [1-2]. Ultimately the presented wafer bonding approaches can contribute to further miniaturization and thickness reduction of the final packaged MEMS components. REFERENCES [1] Fischer, A.C., Forsberg, F., Lapisa, M., Bleiker, S.J., Stemme, G., Roxhed, N. and Niklaus, F., 2015. Integrating mems and ics. Microsystems & Nanoengineering, 1(1), pp.1-16.[2] Lapisa, M., Stemme, G. and Niklaus, F., 2011. Wafer-level heterogeneous integration for MOEMS, MEMS, and NEMS. IEEE Journal of Selected Topics in Quantum Electronics, 17(3), pp.629-644.[3] Jo, G., Edinger, P., Bleiker, S.J., Wang, X., Takabayashi, A.Y., Sattari, H., Quack, N., Jezzini, M., Lee, J.S., Verheyen, P. and Zand, I., 2022. Wafer-level hermetically sealed silicon photonic MEMS. Photonics Research, 10(2), pp.A14-A21.[4] Edinger, P., Jo, G., Van Nguyen, C.P., Takabayashi, A.Y., Errando-Herranz, C., Antony, C., Talli, G., Verheyen, P., Khan, U., Bleiker, S.J. and Bogaerts, W., 2023. Vacuum-sealed silicon photonic MEMS tunable ring resonator with an independent control over coupling and phase. Optics Express, 31(4), pp.6540-6551.[5] Wang, X., Bleiker, S.J., Edinger, P., Errando-Herranz, C., Roxhed, N., Stemme, G., Gylfason, K.B. and Niklaus, F., 2019. Wafer-level vacuum sealing by transfer bonding of silicon caps for small footprint and ultra-thin MEMS packages. Journal of microelectromechanical systems, 28(3), pp.460-471. Figure 1

Pulse-Electrodeposition and Growth Mechanism of Nanotwinned Copper Nanowires inside High Aspect-Ratio Anodic Aluminum Oxide

Nanotwinned copper (nt-Cu) has proven to possess many fascinating physical/chemical properties. However, it is still challenging to control the twin density and its orientation especially for high aspect-ratio Cu vias. Here, a matrix of nt-Cu nanowires (aspect ratio > 150) with dense coherent twin boundaries (CTBs) perpendicular to the growth direction were deposited in porous anodic aluminium oxide vias by pulse electrodeposition. We changed the pulse on/off duration to control the degree of (111) growth texture and twin density of the nt-Cu nanowires. A small anodic current in the pulse-off period enhanced (111) crystal texture and CTB formation during the bottom-up filling process. With the analysis of twin density, we proposed that the nanoscale twinning was activated by facet-dependent crystal growth and stress accumulation/relaxation behaviour during pulse electrodeposition. The interplay between on/off period and bias potential could modulate the twin density. Also, the sulfate adsorbates were proved to play an important role in the stress accumulation process. This study could be implemented in fabricating Cu interconnect in nanoelectronic devices and nanoelectromechanical systems. Figure 1

Nonlocal strain gradient‐based nonlinear dynamics of sinusoidal impulsive actuated porous/piezoelectric multilayer energy nanoharvesters

AbstractThe applications of nanoelectromechanical systems integrating simultaneously the mechanical and electrical functionalities at nanoscale have been gotten wider in the last decade. The main objective of this exploration is to analyze the small scale‐dependent nonlinear dynamical feedback of multilayer energy nanoharvesters containing a graded porous passive core coated by piezoelectric facesheets under a sinusoidal impulsive external actuation. For this purpose, the technique of meshless collocation is constructed at the same time the nonlocal stress and strain gradient tensors without any necessary background meshes and integration procedure. It is found that by taking the nonlocal stress tensor into account, the average of extremum points of maximum lateral deflection increases from to , and from to for simply supported and clamped multilayer nanoharvesters, respectively. On the contrary, through considering the strain gradient tensor, the average of extremum values of the maximum lateral deflection reduces from to for the simply supported nanoharvester, and from to for the clamped one.Highlights Development a third‐order shear flexible nonlocal strain gradient (NSG)‐based plate‐type nanoharvester model Incorporating the role of nonlocal stress and strain gradient tensors in nonlinear dynamics of nanoharvesters Time‐histories of achieved voltage of sinusoidal impulsive loaded plate‐type nanoharvesters Influence of porosity on the NSG‐based nonlinear dynamic performance.

Advanced magnetocaloric microwires: What does the future hold?

Magnetic refrigeration (MR) based on the magnetocaloric effect (MCE) is a promising alternative to conventional vapor compression refrigeration techniques. The cooling efficiency of a magnetic refrigerator depends on its refrigeration capacity and operation frequency. Existing refrigerators possess limited cooling efficiency due to the low operating frequency (around tens of Hz). Theory predicts that reducing geometrical effects can increase the operation frequency by reducing the relaxation time of a magnetic material. As compared to other shapes, magnetocaloric wires transfer heat most effectively to a surrounding environment, due to their enhanced surface area. The wire shape also yields a good mechanical response, reducing the relaxation time and consequently increasing the operation frequency of the cooling device. Experiments have validated the theoretical predictions. By assembling microwires with different magnetocaloric properties and Curie temperatures into a laminate structure, a table-like magnetocaloric bed can be created and used as an active cooling device for micro-electro-mechanical system (MEMS) and nano-electro-mechanical system (NEMS). This paper assesses recent progress in the development of magnetocaloric microwires and sheds light on the important factors affecting the magnetocaloric behavior and cooling efficiency in microwire systems. Challenges, opportunities, and strategies regarding the development of advanced magnetocaloric microwires are also discussed.

Observing inter-well and intra-well oscillations in buckled nanomechanical systems enabled by image processing

The scanning electron microscope (SEM) recordings of dynamic nano-electromechanical systems (NEMS) are difficult to analyze due to the noise caused by low frame rate, insufficient resolution, and blurriness induced by applied electric potentials. Here, we develop an image processing platform enhanced by the physics of the underlying system to track the motion of buckling NEMS structures in the presence of high noise levels. The algorithm is composed of an image filter, two data filters, and a nonlinear regression model, which utilizes the expected form of the physical solution. The method was applied to the recordings of a NEMS beam about 150 nm wide, undergoing intra- and inter-well post-buckling states with a transition rate of approximately 0.5 Hz. The algorithm can track the dynamical motion of the NEMS and capture the dependency of deflection amplitude on the compressive force on the beam. With the help of the proposed algorithm, the transition from inter-well to intra-well motion is clearly resolved for buckling NEMS imaged under SEM.

MODAL BEHAVIOUR OF LONGITUDINALLY PERFORATED NANOBEAMS

Nano-electro-mechanical systems (NEMS) require perforated beams for structural integrity. Hole sizes, hole numbers, and scale effects need to be modelled appropriately in their design. This paper presents a new finite element model to investigate the modal behaviour of longitudinally perforated nanobeams (LPNBs) using the classical Euler–Bernoulli beam theory. A symmetric array of holes arranged parallel to the length direction of the beam with equal spacing was assumed for the perforation. The non-local Eringen’s differential form was used to incorporate the nanoscale sizes. The accuracy of the proposed model was verified by comparing the obtained results with the available analytical solutions for fully filled nanobeams. The effects of aspect ratios, non-local parameters, boundary conditions, and perforation characteristics on the modal behaviour of LPNBs were investigated. The non-local parameter reduced the natural frequency owing to a decrease in the stiffness of the structures. However, the perforation filling ratio led to higher values of the fundamental frequency. Furthermore, compared with other boundary conditions, clamped–clamped boundary conditions demonstrated the best performance in terms of the maximum frequency.

Nonreciprocal Antisymmetric Magnetoresistance and Unconventional Hall Effect in a Two-Dimensional Ferromagnet.

Two-dimensional (2D) ferromagnets with high Curie temperatures provide a rich platform for exploring the exotic phenomena of 2D magnetism and the potential of spintronic devices. As a prototypical 2D ferromagnet, Fe5-xGeTe2 has recently been reported to possess a high Curie temperature with Tc ∼ 310 K, making it a promising candidate for advancing 2D nanoelectromechanical systems. However, due to its intricate magnetic ground state and magnetic domains, a thorough study of the transport behavior related to its lattice and domain structures is still lacking. Here, we report a nonreciprocal antisymmetric magnetoresistance in Fe5-xGeTe2 nanoflakes observed under an external magnetic field between 85-120 K. Through a detailed examination of its temperature, field orientation, and sample thickness dependence, we trace its origin to an additional electric field induced by the domain structure. This differs from the previously reported antisymmetric magnetoresistance due to thickness inhomogeneity. Notably, at lower temperatures, we observed an unconventional Hall effect (UHE), which can be attributed to the Dzyaloshinskii-Moriya interaction (DMI) resulting from the non-coplanar magnetic moment structure. The pronounced influence of sample thickness on magneto-transport properties underscores the competition between magnetic anisotropy and DMI in Fe5-xGeTe2 flakes with varying thicknesses. Our findings provide a deeper understanding of the magneto-transport behavior of the exotic magnetic structure in 2D ferromagnetic materials, which may benefit future spintronic device applications.

On shear-dependent vibration of nano frames

In this study, the effect of shear deformation on the atomic size-dependent free vibration of nanoframes is investigated. The equations of motion of axial and bending vibrations are obtained via the variational algebra according to nonlocal elasticity theory. Axial and bending behaviors are expressed by using simple rod theory and first-order shear deformation beam theory, respectively. By combining the nonlocal finite element solutions for the equations of motion, an eigenvalue formulation for the free vibration of nanoframe is developed. In the presentation of numerical results, firstly, some comparison studies are carried out to show the accuracy of the present analysis. Then, the variations of nondimensional frequencies of three different nanoframe structures are investigated with respect to various parameters, and the results are discussed in detail. The focus of this study is to better understand the dynamic behavior of nanostructures that are within the scope of nano-electro-mechanical systems (NEMS) technology and can be modelled with discrete members.

QMU Analysis of Flexoelectric Timoshenko Beam by Evidence Theory

In recent years, with the rapid development of nanotechnology, a new type of electromechanical coupling effect similar to the piezoelectric effect, the flexoelectric effect, has gradually come into the public’s view. The flexoelectric beam that is the main structural unit of the flexoelectric signal output has broad application prospects in the next generation of micro- and nanoelectromechanical systems. Therefore, the investigation of flexoelectric materials and structures has important scientific and engineering application significances for the design of flexoelectric devices. In this paper, a model of flexoelectric Timoshenko beam is established, the deflection, rotation angle, and dynamic electrical signal output of the forced vibration are taken as the system response, and the density ρ , shear correction factor κ , and frequency ratio λ are selected as the key performance parameters of the system. The combination of available data and engineers’ experience suggests that there are random and cognitive uncertainties in the parameters. Therefore, the probability distribution of the system performance response is expressed by the likelihood function and belief function through the quantification of margins and uncertainties (QMUs) analysis methodology under the framework of evidence theory, and the system reliability or performance evaluation is measured by the calculated confidence factors. These results provide a theoretical basis for accurate analysis of flexoelectric components and provide guidance for the design of flexoelectric components with excellent performance.

Resonant Transducers Consisting of Graphene Ribbons with Attached Proof Masses for NEMS Sensors.

The unique mechanical and electrical properties of graphene make it an exciting material for nanoelectromechanical systems (NEMS). NEMS resonators with graphene springs facilitate studies of graphene's fundamental material characteristics and thus enable innovative device concepts for applications such as sensors. Here, we demonstrate resonant transducers with ribbon-springs made of double-layer graphene and proof masses made of silicon and study their nonlinear mechanics at resonance both in air and in vacuum by laser Doppler vibrometry. Surprisingly, we observe spring-stiffening and spring-softening at resonance, depending on the graphene spring designs. The measured quality factors of the resonators in a vacuum are between 150 and 350. These results pave the way for a class of ultraminiaturized nanomechanical sensors such as accelerometers by contributing to the understanding of the dynamics of transducers based on graphene ribbons with an attached proof mass.

Mechanical Behaviors of the Single Crystal Two-Dimensional Silicon Carbide (SiC): A Molecular Dynamics Insight

This paper focuses on the two-dimensional silicon carbide (2D-SiC), which has an excellent opportunity to be used as an alternative to graphene in nanotechnologies such as in nanoelectronics, nanoelectromechanical systems (NEMS), nano-sensors, nano-energy harvesting devices, and nano-composites due to its unique structural, mechanical, electronic, and thermal properties. Their mechanical properties characterize the stability of the nanodevices. This study performs molecular dynamics (MD) simulation to examine the mechanical properties based on optimized Tersoff potential of the single crystal 2D-SiC at different temperatures, strain rates, point vacancies, and edge cracks. At room temperature (300 K), the obtained elastic modulus and fracture strength are 423 GPa and 68.89 GPa, respectively, along the armchair direction. As the temperature rises from 100 K to 800 K, the fracture stress falls by 21.96% and the fracture strain by 36.90%. An approximate linear reduction in fracture strength is noticed as the temperature rises from 100 K to 800 K. The elastic modulus also falls as the temperature rises but is not significant. Although the elastic modulus is unchanged, the fracture stress increases by 1.84% while the fracture strain increases by 5.84% for a change in strain rate from 0.0001 ps-1 to 0.005 ps-1. The fracture stress and strain are significantly reduced, primarily due to the edge crack, as the concentration of point vacancy grows from 0.1% to 0.6% and the edge crack size increases from 0.5 nm to 1.5 nm. Moreover, anisotropic behavior is also evaluated at 300 K temperature and 0.001 ps-1 strain rate. These findings would offer a deep understanding of the fracture mechanics of 2D-SiC and also help to address the mechanical instability issue with SiC-based nanodevices.

Simplified top-down fabrication of sub-micron silicon nanowires

Abstract Silicon nanowires are among the most promising nanotechnology building blocks in innovative devices with numerous applications as nanoelectromechanical systems. Downscaling the physical size of these devices and optimization of material functionalities by engineering their structure are two promising strategies for further enhancement of their performance for integrated circuits and future-generation sensors and actuators. Integration of silicon nanowires as transduction elements for inertial sensor applications is one prominent example for an intelligent combination of such building blocks for multiple functionalities within a single sensor. Currently, the efforts in this field are marred by the lack of batch fabrication techniques compatible with semiconductor manufacturing. Development of new fabrication techniques for such one-dimensional structures will eliminate the drawbacks associated with assembly issues. The current study aims to explore the limits of batch fabrication for a single nanowire within a thick Si layer. The objective of the current work goes beyond the state of the art with significant improvements to the recent viable approach on the monolithic fabrication of nanowires, which was based on a conformal side-wall coating for the protection of the nanoscale silicon line followed by deep etch of the substrate transforming the protected layer into a silicon nanowire. The newly developed fabrication approach eliminates side wall protection and thereby reduces both process complexity and process temperature. The technique yields promising results with possible improvements for future micro and nanofabrication processes.

0D van der Waals interfacial ferroelectricity

The dimensional limit of ferroelectricity has been long explored. The critical contravention is that the downscaling of ferroelectricity leads to a loss of polarization. This work demonstrates a zero-dimensional ferroelectricity by the atomic sliding at the restrained van der Waals interface of crossed tungsten disufilde nanotubes. The developed zero-dimensional ferroelectric diode in this work presents not only non-volatile resistive memory, but also the programmable photovoltaic effect at the visible band. Benefiting from the intrinsic dimensional limitation, the zero-dimensional ferroelectric diode allows electrical operation at an ultra-low current. By breaking through the critical size of depolarization, this work demonstrates the ultimately downscaled interfacial ferroelectricity of zero-dimensional, and contributes to a branch of devices that integrates zero-dimensional ferroelectric memory, nano electro-mechanical system, and programmable photovoltaics in one.

Analysis of Temperature Effect on the Mechanical Behavior of Euler–Bernoulli Nanocantilever Using Molecular Dynamics Simulation Method

Due to the various applications of nanocantilevers as nanosensors and nanoactuators in nanoelectromechanical systems, understanding their behavior is of particular importance. In operating environments, nanocantilevers are simultaneously exposed to mechanical forces and heat. This study aims to examine the behavior of an Euler–Bernoulli nanocantilever when it is placed under mechanical loads and exposed to heat at the same time. The effects of size, temperature, and force on the flexural behavior of the nanocantilever were investigated and the following characteristics were obtained via molecular dynamics simulation: nanocantilever displacement versus time, maximum bending, nanocantilever yielding time, and the minimum acceptable working frequency range for nanocantilever-based nanoswitches. It was found that applying forces greater than 0.00005[Formula: see text]eV/A, the studied nanocantilevers would rapidly undergo plastic deformation. For applied forces less than 0.00005[Formula: see text]eV/A, the nanocantilevers with length of 40[Formula: see text]nm, 30[Formula: see text]nm and 20[Formula: see text]nm can withstand upto 750[Formula: see text]K, 600[Formula: see text]K and 300[Formula: see text]K in 200[Formula: see text]ns to more than 1.5[Formula: see text][Formula: see text]s time period, respectively.

Multiple internal resonance couplings and quasi-periodicity patterns in hybrid-shaped micromachined resonators

Micro- and nano-electromechanical systems may experience internal resonances, which are inherently strengthened by the systems' nonlinearities. In the present paper, we investigate the dynamics of a hybrid resonator, combining straight and initially curved microbeam shapes. The curved part length is tailored to monitor the three lowest natural frequencies and induce simultaneous internal resonances between first and second modes and second and third modes. We examine the nonlinear interaction of dual hardening and softening bending of the fundamental frequency response curves. Due to the specific frequency ratios, different types of subcombination internal resonances emerge, with quasi-periodic energy transfer among the modes. The subcombination may result in frequencies closely-spaced, which leads to quasi-periodic beating among the frequencies involved and, due to the strong nonlinearities, to the emergence of intermodulation products. We analyze the different patterns underlying the quasi-periodicity, which are intrinsically related to the frequency ratios and deeply affected by the nonlinearities.

Microelectronics-compatible reduced graphene oxide based nanomechanical resonators capable of all-electrical actuation and read-out

Photolithographic patterning and deterministic transfer of reduced graphene oxide (rGO) are key innovations that can give way to cost-effective batch processing of nanoelectromechanical system (NEMS)-based resonators with high throughput. Here, by implementing the same, we report a facile fabrication process for NEMS-based resonators consisting of rGO as the active material for the structural layer. The structural properties of rGO thin film are confirmed using Raman spectroscopy and X-ray diffraction analysis. Temperature-dependent current–voltage characteristics of rGO film ensure the typical 2D Mott variable range hopping (VRH) transport with ambipolar charge conduction, further supporting the effectiveness of the fabrication process. All-electrical actuation and readout of the fabricated resonators are performed using both frequency modulation (FM) downconversion and piezoresistive mixing methods adeptly to achieve a resonance frequency of around 28–32 MHz. The fabrication process is compatible with the current microelectronic technology and can foster the prospect of on-chip implementation of rGO NEMS toward possible applications such as molecular sensors, mass detectors, etc.