Nanoelectromechanical Research Articles

Development of sacrificial layer wet etch process of TiNi for nano-electro-mechanical device application

We report the wet etching of titanium nickel (TiNi) films for the production of nano-electro-mechanical (NEM) device. SiO 2 and Si 3 N 4 have been selected as sacrificial layers of TiNi metal and etched with polyethylene glycol and hydrofluoric acid (HF) mixed solution. Volume percentage of HF are varied from 10% to 35% and the etch rate of the SiO 2 , Si 3 N 4 and TiNi are reported here. Within the various experiment results, 15% HF mixed polyethylene glycol solution show highest etch ratio between sacrificial layre and TiNi metal. Especially Si 3 N 4 films shows high etch ratio with TiNi films. Wet etching results are measured with SEM inspection. Therefore, this experiment provides a novel method for TiNi in the nano-electro-mechanical device.

Laterally Actuated Platinum-Coated Polysilicon NEM Relays

Laterally actuated polycrystalline silicon nanoelectromechanical (NEM) relays with enhanced electrical properties are presented. Due to surface oxidation of polysilicon in room ambient conditions, the relays have a high contact resistance (> 1 GΩ) that requires high drain bias (3-5 V) to break through. The addition of a platinum sidewall coating reduces the on-resistance and the required drain bias to as low as 3 kΩ and 0.1 V, respectively. The platinum coating's stability is demonstrated by two tests: first, a contact-and-hold test where the relay passes current (~1μA) for up to 155 min and, second, a hot cycling test where the relay survives for over 108cycles . The NEMS relays are simulated using finite-element analysis, and the models are verified against experimental tests. Furthermore, the relays are configured and tested as a 2 : 1 multiplexer to show their potential as a digital logic component.

NEM Relay-Based Sequential Logic Circuits for Low-Power Design

Nanoelectromechanical (NEM) relays are a promising class of emerging devices that offer zero off-state leakage and behaves like an ideal switch. The zero leakage operation has generated lot of interest in low power logic design using these relays [1],[2]. This paper presents various sequential circuit topologies using NEM relays and analyzes their power, performance, and area tradeoffs. The mechanical delay is inversely proportional to the gate-base voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gb</sub> . This paper also presents an integrated voltage doubler-based flip-flop that improves the performance by 2× by overdriving V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">gb</sub> . An electromechanical model which accounts for the mechanical, electrical, and dispersion effects of the suspended gate relay operating at 1 V with a nominal air gap of 5-10 nm has been developed based on published fabrication results in . Three sequential logic benchmark circuits were designed using NEM relays to verify the correctness of operation of the proposed circuits. This study explores different relay-based latch and flip-flop topologies, proposes fast sequential circuits that can operate at a frequency of 1/2t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> (theoretical fastest frequency for NEM relay logic circuits) and further improves speed of sequential circuits by distributed charge boosting.

Adhesive slip process between a carbon nanotube and a substrate

Since their discovery in 1991, carbon nanotubes (CNTs) have been attractive components for nanoelectromechanical (NEM) devices because of their excellent mechanical and electrical properties. Several CNT-based NEM devices have been reported. Experimental investigations have discovered that the force required for a CNT to slip on a SiO2 substrate is almost constant in the range of contact lengths from 140 to 246 nm and increases with the contact length for greater lengths. This study develops a theory based on the continuum mechanics to explain this observed phenomenon. The critical force needed to cause the CNT to slip over the whole substrate is determined by applying a beam theory which includes the bending, shear, and axial deformations of the CNT. At the stick–slip transition, the work of adhesion contributes a concentrated force and a concentrated moment to produce discontinuities in the internal forces and moments of the CNT. The modelling results obtained here provide the external force required for complete slip versus a dimensionless parameter related to the shear stress and the contact length. A comparison of the modelling result and the experimental data from the literature shows good agreement.

Influence of Air Damping on Nanoelectro-Mechanical Switches in Low Vacuum

In order to treat the performance of nano-electro-mechanical (NEM) switches in low vacuum, molecular dynamics model of NEM switches is established and the influence of air damping on NEM switches is investigated. When the pressure in low vacuum is from 100Pa to 1000Pa, we get the gas molecule in low vacuum belong to free molecule flow. Tersoff-Brenner potential function is used to describe the interaction of carbon nanotube atoms. L-J potential function is adopted to state the interaction between carbon nanotube and the base ground. Results show that in low vacuum condition, when the same amplitude change of intensity of pressure, the lower intensity of pressure change will take a more clearly effect for the nano structure than the higher intensity of pressure change. Results also show when the length of carbon nanotube from 200 circles to 50 circles, the beam vibrating amplitude increased gradually. When the length is 50 circles, the vibrating amplitude reach the maximum. With the beam length keep to decrease, the vibrating amplitude becomes weak crossly.

Kondo Force in Shuttling Devices: Dynamical Probe for a Kondo Cloud

We consider the electromechanical properties of a single-electronic device consisting of a movable quantum dot attached to a vibrating cantilever, forming a tunnel contact with a nonmovable source electrode. We show that the resonance Kondo tunneling of electrons amplifies exponentially the strength of nanoelectromechanical (NEM) coupling in such a device and make the latter insensitive to mesoscopic fluctuations of electronic levels in a nanodot. It is also shown that the study of a Kondo-NEM phenomenon provides additional (as compared with standard conductance measurements in a nonmechanical device) information on retardation effects in the formation of a many-particle cloud accompanying the Kondo tunneling. A possibility for superhigh tunability of mechanical dissipation as well as supersensitive detection of mechanical displacement is demonstrated.

Nanoelectromechanics of shuttle devices

A single-electron tunneling (SET) device with a nanoscale central island that can move with respect to the bulk sourceand drain electrodes allows for a nanoelectromechanical (NEM) coupling between the electrical current through the device and the mechanical vibrations of the island. Although the electromechanical “shuttle” instability and the associated phenomenon of single-electron shuttling were predicted more than 15 years ago, both theoretical and experimental studies of NEM-SET structures are still carried out. New functionalities based on quantum coherence, Coulomb correlations and coherent electron-spin dynamics are still of particular interest. In this article we present a short review of recent activities in this area.

A sub-1-volt nanoelectromechanical switching device

Nanoelectromechanical (NEM) switches have received widespread attention as promising candidates in the drive to surmount the physical limitations currently faced by complementary metal oxide semiconductor technology. The NEM switch has demonstrated superior characteristics including quasi-zero leakage behaviour, excellent density capability and operation in harsh environments. However, an unacceptably high operating voltage (4-20 V) has posed a major obstacle in the practical use of the NEM switch in low-power integrated circuits. To utilize the NEM switch widely as a core device component in ultralow power applications, the operation voltage needs to be reduced to 1 V or below. However, sub-1 V actuation has not yet been demonstrated because of fabrication difficulties and irreversible switching failure caused by surface adhesion. Here, we report the sub-1 V operation of a NEM switch through the introduction of a novel pipe clip device structure and an effective air gap fabrication technique. This achievement is primarily attributed to the incorporation of a 4-nm-thick air gap, which is the smallest reported so far for a NEM switch generated using a 'top-down' approach. Our structure and process can potentially be utilized in various nanogap-related applications, including NEM switch-based ultralow-power integrated circuits, NEM resonators, nanogap electrodes for scientific research and sensors.

Mass loading induced dephasing in nanomechanical resonators

This paper presents a study of dephasing of an underdamped nanomechanical resonator subject to random mass loading of small particles. A frequency noise model is presented which describes dephasing due to the attachment and detachment of particles at random points and particle diffusion along the resonator. This situation is commonly encountered in current mass measurement experiments using nanoelectromechanical (NEM) resonators. The conditions which can lead to inhomogeneous broadening and fine structure in the modes’ absorption spectra are discussed. It is also shown that the spectra of the higher-order cumulants of the (complex) vibrational mode amplitude are sensitive to the parameters characterizing the frequency noise process. Hence, measurement of these cumulants can provide information not only about the mass but also about other parameters of the particles (diffusion coefficient and attachment–detachment rates).

나노전기기계 메모리 시뮬레이터의 개발

A nano-electro-mechanical (NEM) memory simulator has been developed by using Matlab. The simulator can be used for the prediction of hysterisis curves, applied forces, steady- or transient-state behavior, program/erase energy consumption and potential energy. Predicting NEM memory behavior by simple user interface, the simulator will make the design of NEM memory cells simpler.

Design Optimization of Pulsed-Mode Electromechanical Nonvolatile Memory

Storage-layer-based nonvolatile memory (NVM) devices, such as Flash, ferroelectric RAM, or magnetic RAM, have limited reliability at high temperature (HT, T >; 200°C). On the contrary, storage-layer-free NVM devices based on a bistable nanoelectromechanical (NEM) mechanism and adhesion forces show excellent reliability at HT. This letter presents design optimization of an electrostatic NEM NVM device. The set/ reset principle is based on the pulsed-mode switching of a mechanically free electrode (the shuttle), which is placed inside a guiding pod, having two stable positions. Based on the shuttle kinematic equation, this letter derives key design and operation parameters, particularly optimization in terms of switching speed and switching energy. The small footprint of the shuttle NEM NVM makes it applicable to ultracompact and reliable data storage at HT.

Controllable Chemical Vapor Deposition Growth of Few Layer Graphene for Electronic Devices

Because of its atomic thickness, excellent properties, and widespread applications, graphene is regarded as one of the most promising candidate materials for nanoelectronics. The wider use of graphene will require processes that produce this material in a controllable manner. In this Account, we focus on our recent studies of the controllable chemical vapor deposition (CVD) growth of graphene, especially few-layer graphene (FLG), and the applications of this material in electronic devices. CVD provides various means of control over the morphologies of the produced graph ene. We studied several variables that can affect the CVD growth of graphene, including the catalyst, gas flow rate, growth time, and growth temperature and successfully achieved the controlled growth of hexagonal graphene crystals. Moreover, we developed several modified CVD methods for the controlled growth of FLGs. Patterned CVD produced FLGs with desired shapes in required areas. By introducing dopant precursor in the CVD process, we produced substitutionally doped FLGs, avoiding the typically complicated post-treatment processes for graphene doping. We developed a template CVD method to produce FLG ribbons with controllable morphologies on a large scale. An oxidation-activated surface facilitated the CVD growth of polycrystalline graphene without the use of a metal catalyst or a complicated postgrowth transfer process. In devices, CVD offers a controllable means to modulate the electronic properties of the graphene samples and to improve device performance. Using CVD-grown hexagonal graphene crystals as the channel materials in field-effect transistors (FETs), we improved carrier mobility. Substitutional doping of graphene in CVD opened a band gap for efficient FET operation and modulated the Fermi energy level for n-type or p-type features. The similarity between the chemical structure of graphene and organic semiconductors suggests potential applications of graphene in organic devices. We used patterned CVD FLGs as the bottom electrodes in pentacene FETs. The strong π-π interactions between graphene and pentacene produced an excellent interface with low contact resistance and a reduced injection barrier, which dramatically enhances the device performance. We also fabricated reversible nanoelectromechanical (NEM) switches and a logic gate using the FLG ribbons produced using our template CVD method. In summary, CVD provides a controllable means to produce graphene samples with both large area and high quality. We developed several modified CVD methods to produce FLG samples with controlled shape, location, edge, layer, dopant, and growth substrate. As a result, we can modulate the properties of FLGs, which provides materials that could be used in FETs, OFETs, and NEM devices. Despite remarkable advances in this field, further exploration is required to produce consistent, homogeneous graphene samples with single layer, single crystal, and large area for graphene-based electronics.

Electron Fluctuation Induced Resonance Broadening in Nano Electromechanical Systems: The Origin of Shear Force in Vacuum

This article presents a study of the poorly understood "shear-force" used in an important class of near-field instruments that use mechanical resonance feedback detection. In the case of a metallic probe near a metallic surface in vacuum, we show that in the 10-60 nm range there is no such a thing as a shear-force in the sense of the nonconservative friction force. Fluctuations of the oscillator resonance frequency, likely induced by local charge variations, could account for the reported effects in the literature without introducing a dissipative force.

Nanoelectromechanical contact switches

Nanoelectromechanical (NEM) switches are similar to conventional semiconductor switches in that they can be used as relays, transistors, logic devices and sensors. However, the operating principles of NEM switches and semiconductor switches are fundamentally different. These differences give NEM switches an advantage over semiconductor switches in some applications--for example, NEM switches perform much better in extreme environments--but semiconductor switches benefit from a much superior manufacturing infrastructure. Here we review the potential of NEM-switch technologies to complement or selectively replace conventional complementary metal-oxide semiconductor technology, and identify the challenges involved in the large-scale manufacture of a representative set of NEM-based devices.

Analytical Model of Nano-Electromechanical (NEM) Nonvolatile Memory Cells

The fringe field effects of nano-electromechanical (NEM) nonvolatile memory cells have been investigated analytically for the accurate evaluation of NEM memory cells. As the beam width is scaled down, fringe field effect becomes more severe. It has been observed that pull-in, release and hysteresis voltage decrease more than our prediction. Also, the fringe field on cell characteristics has been discussed.

Integration of Nanoelectromechanical Relays With Silicon nMOS

Electrostatically actuated nanoelectromechanical (NEM) relays are integrated with silicon nMOS devices. An nMOSFET successfully drives a NEM relay with the MOSFET serving as a pass transistor to control the state of the relay. Silicon MOSFET-NEM relay integration opens up the possibility for applications, where the zero off-state leakage, the sharp on/off transition, and/or the hysteresis of the NEM relay can be used to complement the capabilities of CMOS.

Design and Finite Element Method Analysis of Laterally Actuated Multi-Value Nano Electromechanical Switches

Design and Finite Element Method Analysis of Laterally Actuated Multi-Value Nano Electromechanical Switches

Design and Finite Element Method Analysis of Laterally Actuated Multi-Value Nano Electromechanical Switches

We report on the design and modeling of novel nano electromechanical switches suitable for implementing reset/set flip-flops, AND, NOR, and XNOR Boolean functions. Multiple logic operations can be implemented using only one switching action enabling parallel data processing; a feature that renders this design competitive with complementary metal oxide semiconductor and superior to conventional nano-electromechanical switches in terms of functionality per device footprint. The structural architecture of the newly designed switch consists of a pinned flexural beam structure which allows low strain lateral actuation for enhanced mechanical integrity. Reliable control of on-state electrical current density is achieved through the use of metal-metal contacts, true parallel beam deflection, and lithographically defined contact area to prevent possible device welding. Dynamic response as a function of device dimensions numerically investigated using ANSYS and MatLab Simulink.

High density vertical silicon NEM switches with CMOS-compatible fabrication

Presented is a resistive, vertically oriented, silicon electromechanical cantilever switch, fabricated with a two-mask top-down CMOS-compatible process. The fabricated switch has a vertical height of approximately 500 nm, a tip width of 35 nm, and an airgap of 30 nm between the cantilever and two lateral gates. Preliminary testing results show an initial pull-in voltage of 17 V with contact held by van der Waals forces even in the absence of actuation voltage. Subsequent switching occurs at 25 V. With low-cost fabrication and high integration density, the vertical nanoelectromechanical (NEM) switch is a promising candidate for memory and computing applications.

Hybrid numerical analysis of a high-speed non-volatile suspended gate silicon nanodot memory (SGSNM)

We present a hybrid numerical analysis of a high-speed and non-volatile suspended gate silicon nanodot memory (SGSNM) which co-integrates a nano-electromechanical (NEM) control gate with a MOSFET as a readout element and silicon nanodots as a floating gate. A hybrid NEM-MOS circuit simulation is developed by taking account of the pull-in/pull-out operation of the suspended gate and electron tunnelling processes through the tunnel oxide layer as behavioural models. The signals for programming, erasing and reading are successfully achieved at circuit level simulation. The programming and erasing times are found as short as 2.5 nsec for a SGSNM with a 1-μm-long suspended gate, which is a summation of the mechanical pull-in/pull-out times and the tunnel charging/discharging times.