Pull-out Voltage Research Articles

Analysis of Ferroelectric Negative Capacitance-Hybrid MEMS Actuator Using Energy–Displacement Landscape

We propose an energy-based framework to analyze the statics and dynamics of a ferroelectric negative capacitance-hybrid Microelectromechanical System (MEMS) actuator. A mapping function that relates the charge on the ferroelectric to displacement of the movable electrode, is used to obtain the Hamiltonian of the hybrid actuator in terms of displacement. We then use graphical energy-displacement and phase portrait plots to analyze static pull-in, dynamic pull-in and pull-out phenomena of the hybrid actuator. Using these, we illustrate the low-voltage operation of the hybrid actuator to static and step inputs, as compared to the standalone MEMS actuator. The results obtained are in agreement with the analytical predictions and numerical simulations. The proposed framework enables straightforward inclusion of adhesion between the contacting surfaces, modeled using van der Waals force. We show that the pull-in voltage is not affected, while the pull-out voltage is reduced due to adhesion. The proposed framework provides a physics-based tool to design and analyze negative capacitance based low-voltage MEMS actuators.

A Noise Immune Double Suspended Gate MOSFET for Ultra Low-Power Applications

The purpose of this paper is to develop the design and analytical modelling of a noise immune double suspended gate MOSFET (DSG-MOSFET) for ultra-low power applications. Also, important performance parameters of the proposed structure such as pull-in and pull-out voltages have been thoroughly investigated with respect to the valuable structural parameters. The design methodology used is EKV based analytical approach to calculate the pull-in and pull-out voltages with ingeniously developed boundary conditions which helps achieving reasonably accurate result. Also, the I-V characteristics has been modelled to justify accuracy. The experimental result shows that the pull-in and pull-out voltages are in millivolts and microvolts range and hence it can be used in ultra-low power applications. As the ratio between the pull-out and the pull-in voltage is 10^(+3) range, justifies that the proposed structure is noise immune. The ID-VGS characteristic has hysteresis and this sharp transition in pull-in and pull-out voltage indicates that it can be used as an ideal switch with infinite sub-threshold slope. This paper presents a compact EKV based analytical modelling of pull-in and pull-out voltages for a DSG-MOFET which predict the device characteristics reasonably similar to simulated results. Also, for the first time the noise immunity for a DSGMOSFET has been analyzed.

SPICE-Based Multiphysics Model to Analyze the Dynamics of Ferroelectric Negative-Capacitance–Electrostatic MEMS Hybrid Actuators

We propose a framework to model ferroelectric negative capacitance: electrostatic Micro Electro Mechanical Systems (MEMS) hybrid actuators and analyze their dynamic (step input) response. Using this framework, we report the first proposal for reduction in the dynamic pull-in and pull-out voltages of the hybrid actuators due to the negative capacitance of the ferroelectric. The proposed model also reveals the effect of ferroelectric thickness on the dynamic pull-in and pull-out voltages and the effect of ferroelectric damping on the energy dissipated during actuation. We infer from our analysis that the hybrid actuators are better than the standalone MEMS actuators in terms of operating voltage and energy dissipation. Further, we show that one can trade-off a small part of the reduction in actuation voltage to achieve identical pull-in times in the hybrid and standalone MEMS actuators, while still consuming substantially lower energy in the former as compared to the latter. The circuit compatibility of the proposed hybrid actuator model makes it suitable for analysis and evaluation of various heterogeneous systems consisting of hybrid MEMS actuators and other electronic devices.

MEMS Slow-Wave CPW Phase Shifter for mm-Wave Applications

MEMS-based phase shifters show the best performance in terms of figure of merit, but their footprints are usually large and it is difficult to achieve several bits. This paper demonstrates a miniaturized phase shifter based on slow-wave CPW and MEMS that occupy 0.47 mm2. A total phase shift of 152° was obtained with a maximum insertion loss of 3 dB, resulting in a figure of merit of 50°/dB at 60 GHz. The 3-bit device showed an insertion loss variation of 1.3 dB and return loss better than 13 dB. The pull-in and pull-out voltages were measured to be 17 V and 10 V, respectively. The presented device is well suited for mm-wave phased array applications. Thanks to the proposed concept, more bits could be easily achieved and much higher frequencies could be addressed.

3D modeling of graphene oxide based nanoelectromechanical capacitive switch

The present work deals with 3D modeling of a novel configuration of a double clamped nanoelectromechanical (NEM) capacitive switch. In the proposed work, graphene oxide (GO) as a dielectric has been used as suspended beam material in NEM switch for the first time. Analysis of von Mises stress, pull-in, and pull-out voltages are investigated using COMSOL Multiphysics, for standard and perforated GO NEM switch structures. The actuation voltages of 5.4 V and 3.35 V are evaluated for standard and perforated beam structures respectively for the beam lengths of 1 µm and widths of 0.3 µm. The actuation voltage and von Mises stress value have reduced by making perforations in the beam. The von Mises stress comparative analysis of GO and graphene NEM switch exhibits that GO is a better choice for beam material as GO NEM switch withstand less von Mises stress than graphene NEM switch. The variation in capacitance including the fringing field capacitance is calculated as the beam is pulled down by the actuating electrode.

Bi-stability behavior in electrostatically actuated non-contact based micro-actuator

The nonlinear mechanical response of an electrostatically actuated doubly-clamped micro-actuator assuming a non-contact based actuation arrangement is examined. The electrostatic actuating force is numerically approximated through solving a nonlinear electrical field problem using a finite-elements based analysis. An electro-mechanical model is established within the framework of the Euler–Bernoulli continuous nonlinear beam theory, where both the nonlinear geometric mid-plane stretching and the nonlinear electric forcing effects have been both taken into consideration. Then, assuming a Galerkin’s based modal expansion technique, the structural behavior of the micro-actuator under the effect of the resultant electric out-of-plane fields is solved numerically. The resultant nonlinear reduced-order model equations are examined to get the deflection of the microbeam against an assumed bias voltage for different vertical initial gap sizes. The snap-through and pull-out voltages of the micro-system are calculated for different assumed initial vertical gap separation. Frequency diagrams are analyzed against any applied DC bias voltage through solving a linearized eigenvalue problem. Thorough parametric simulations indicate a prospect of such bi-stable design of the micro-actuator with large stroke and high fundamental frequency enabling it to be potentially useful for MEMS based high frequency energy harvester devices with bi-stable capabilities.

Stability analysis of an electrostatically actuated out of plane MEMS structure

In the present research, stability and static analyses of microelectromechanical systems microstructure were investigated by presenting an out-of-plane structure for a lumped mass. The presented model consists of two stationary electrodes in the same plane along with a flexible electrode above and in the middle of the two electrodes. The nonlinear electrostatic force was valuated via numerical methods implemented in COMSOL software where three-dimensional simulations were performed for different gaps. The obtained numerical results were compared to those of previous research works, indicating a good agreement. Continuing with the research, curves of electrostatic and spring forces were demonstrated for different scenarios, with the intersection points (i.e., equilibrium points) further plotted. Also drawn were plots of deflection versus voltage for different cases and phase and time history curves for different values of applied voltage followed by introducing and explaining pull-in and pull-out snap-through voltages in the system for a specific design. It is worth noting that, at voltages between the pull-in and pull-out snap-through voltages, the system was in bi-stable state. Based on the obtained results, it was observed that the gap between the two electrodes and the applied voltage play significant roles in the number and type of the equilibrium points of the system.

Ferroelectric-Gated Nanoelectromechanical Nonvolatile Memory Cell

A ferroelectric-gated nanoelectromechanical (NEM) nonvolatile random-access memory cell [negative capacitance (NC)-NEM memory] is proposed and investigated. By adjusting the structural parameters of the NEM relay, the pull-in voltage of the NC-NEM memory cell can be reduced, and its pull-out voltage can even become negative. Hence, an NEM relay with a ferroelectric layer in the gate stack can be used as a nonvolatile random-access memory cell. Herein, the device design and operational principles for read/program/erase are introduced in detail. The program/erase voltage and the program delay time of the NC-NEM memory cell have been quantitatively estimated.

Design and simulation of electrostatic NEMS logic gates

PurposeThis paper aims to present a design and simulation of electrostatic nanoelectromechanical system (NEMS)-based logic gates using laterally actuated cantilever with double-electrode structure that can implement logic functions, similar to logic devices that are made of solid-state transistors which operates at 5 V.Design/methodology/approachThe analytical modeling of NEMS switch is carried out for finding the pull-in and pull-out voltage based on Euler-Bernoulli’s beam theory, and its numerical simulation is performed using finite element method computer-aided design tool COVENTORWARE.FindingsThis paper reports analytical and numerical simulation of basic NEMS switch to realize the logic gates. The proposed logic gate operates on 5 V which suits well with conventional complementary metal oxide semiconductor (CMOS) logic which in turn reduces the power consumption of the device.Originality/valueThe proposed logic gates use a single bit NEMS switch per logic instead of using 6-14 individual transistors as in CMOS. One exclusive feature of this proposed logic gates is that the basic NEMS switch is structurally modified to function as specific logic gates depending upon the given inputs.

Dynamic pull-in and pull-out analysis of viscoelastic nanoplates under electrostatic and Casimir forces via sinusoidal shear deformation theory

In the present research, dynamic pull-in and pull-out analysis of viscoelastic nanoplate switch under electrostatic and intermolecular Casimir forces are studied. The Viscoelastic properties of the nanoplate are considered using Kelvin-Voigt model. Sinusoidal shear deformation theory is utilized for mathematical modeling of the structure due to its accuracy of polynomial function than other plate theories. The surface effects are considered based on Gurtin-Murdoch theory to enhance the accuracy of results. Considering size effects based on Eringen's nonlocal theory, motion equations are derived using Hamilton's principle and solved by Galerkin's method. Considering two boundary conditions of clamped in all edges (CCCC) and clamped in two edges and free in tow another edges (CCFF), the influences of various parameters such as small scale effect, surface layer, viscoelastic damping coefficient and applied voltage on the pull-in voltage, pull-in time, pull-in deflection and pull-out voltage are discussed in details. Numerical results indicate that considering small scale effects, the pull-in time and voltage as well as pull-out voltage are increased and decreased, respectively, for CCFF and CCCC boundary conditions. In addition, as the effective gap distance increases, the pull-out voltage tends toward the pull-out voltage. The results of this investigation can be used in control and optimum design of smart nano-electrical devices in advanced applications as smart controller.

Quantification of Uncertainty in Creep Failure of RF-MEMS Switches

We present simulations of the failure of radio-frequency micro-electro-mechanical systems switches due to diffusional creep that include the quantification of uncertainty in the geometry, material parameters, and residual stress. The switch is modeled as an Euler-Bernoulli beam that is actuated electrostatically in a fluid medium. The fluid damping is modeled by a squeeze-film model and the beam model incorporates stretching nonlinearity in addition to Coble creep. The resulting nonlinear dynamic model is solved using a Ritz-Galerkin-based modal expansion and explicit time integration. The focus of this paper is on the effect of creep as a failure mechanism and the implications of uncertainty in the device geometry, material parameters, and boundary conditions. The degradation of the device performance is evidenced by decreases in the pull-in voltage, the pull-out voltage, and the impact velocity. We find that the variability in the experimentally measured pull-in voltage is accounted for by the inclusion of uncertainty in the material and geometric properties.

On the Small-Signal Capacitance of RF MEMS Switches at Very Low Frequencies

This paper presents on-wafer capacitance measurements of silicon-based RF MEMS capacitive switches down to frequencies below 1 Hz. The capacitance-voltage ( C-V ) curve measured at very-low frequency (0.01–10 Hz) deviates from the commonly measured and well-understood high-frequency C-V curve, especially near the pull-in and pull-out voltages. This behavior is explained from the mechanical action of the top electrode. An electrostatic transducer model is used to express the coupling between mechanical and electrical behavior of the device under study. The mechanical action and air damping play an important role at the lower measurement frequencies, as confirmed by vibrometer measurements, FEM modeling and experiments at reduced pressure.

Dynamic Properties of Three-Terminal Tungsten CMOS-NEM Relays Under Nonlinear Tapping Mode

In this paper, we present the electrical characterization of the nonlinear tapping mode of the nanorelays capacitively transduced. Such a characterization is carried out utilizing three-terminal tungsten CMOS-NEM relays. Exciting electrostatically the switching devices near its resonance and detecting its movement by means of capacitive detection, we reveal double-side frequency dynamic-contact characteristics when the displacement is large and the tapping occur in the nonlinear regime. In this way, we take advantage of this periodic contact to evaluate the switching characteristics of the device. We report that the switch stands more than 10 billion of tapping cycles (in a cold switching scenario) without showing any failure. Moreover, we measure current–voltage ( $I$ – $V$ ) curves before and after the cycling test in order to evaluate the changes produced in the ON-state contact resistance and in the pull-in and pull-out voltages. This test reveals that the characterized switch has a consistent and repetitive pull-in voltage without changing its elastic properties. In addition, we observe that the pull-out voltage decreases slightly and the contact resistance diminishes (from an initial value of 2 $\text{G}\Omega $ to a minimum value of 735 $\text{M}\Omega $ ). We eventually attribute this result to the fact that the superficial oxide is broken down due to the continuous tapping of the cantilever tip on the contact electrode.

Partitioning Electrostatic and Mechanical Domains in Nanoelectromechanical Relays

This paper describes the improvement of pull-in stability, contact properties, and reliability of laterally actuated nanoelectromechanical relays by partitioning the mechanical and electrostatic domains in the relay structure. Separation of the two physics allows us to individually optimize the structural stiffness and the actuation voltage to increase the contact pressure and reduce the ON-state resistance without applying excessive drain voltage. The devices can tolerate more than 200% overdrive gate voltage, resulting in near 100% increase in contact force, and reducing the contact resistance from $\sim 10$ G $\Omega $ to $\sim 23$ K $\Omega $ . For a given overall device dimension, tailoring the mechanical and electrostatic elements independently also enables us to control the pull-in and pull-out voltages, which have different design requirements for different applications. The measurement results show that the pull-in/pull-out hysteresis could vary between 30% and 60% of the actuation (pull-in) voltage. Increasing the mechanical force without affecting the device actuation voltage improves the relay reliability by reducing the possibility of failure due to source–drain stiction when the relay is switched ON. As a proof of concept, mechanical relays are fabricated using polycrystalline silicon coated by a titanium nitride layer deposited via plasma enhanced atomic layer deposition. [2014-0018]

Effective Nanometer Airgap of NEMS Devices Using Negative Capacitance of Ferroelectric Materials

Nanoelectromechnical system (NEMS) is seen as one of the most promising candidates for next generation extreme low power electronics that can operate as a versatile switch/memory/sensor/display element. One of the main challenges toward this goal lies in the fabrication difficulties of ultrascaled NEMS required for high density integrated circuits. It is generally understood that fabricating and operating a NEMS with an airgap below a few nanometer will be extremely challenging due to surface roughness, nonideal forces, tunneling, etc. Here, we show that by cascading a NEMS with a ferroelectric capacitor, operating in the negative capacitance regime, the effective airgap can be reduced by almost an order of magnitude, without the need to reduce the airgap physically. This would not only reduce the pull-in voltage to sub-1 V regime, but also would offer a set of characteristics which are difficult/impossible to achieve otherwise. For example, one can reduce/increase the classical travel range, flip the traditional stable-unstable regime of the electrode, get a negative pull-out voltage, and thus, center the hysteresis around zero volt. Moreover, one can also operate the combination as an effective ferroelectric memory with much reduced switching voltages. These characteristics promise dramatic saving in power for NEMS-based switching, memory, and other related applications.

Fabrication and characterization of field-effect transistors with suspended-nanowire channels

Novel field-effect transistors (FETs) configured with suspended-nanowire (NW) channels were fabricated and characterized. Owing to the small aspect ratio of the etched structure, a simple wet etching process was adopted to release the NW channels. Our results show that the stiction issue can be eliminated as the channel length is sufficiently short or the air gap is sufficiently thick. In addition, the specific trends in pull-in and pull-out voltages as well as subthreshold swing (SS) with varying air gap thicknesses were investigated in terms of hysteresis characteristics. Finally, the devices were shown to withstand more than 500 cycles of operation in the cycling tests with repeatable hysteresis characteristics.

Nonlinear nonlocal pull-in instability of boron nitride nanoswitches

In the present study, nonlinear pull-in instability of boron nitride nanoswitches (BNNSs) subjected to electrostatic and van der Waals (vdW) forces is investigated. Based on Euler–Bernoulli beam theory, von Karman geometric nonlinearity, nonlocal piezoelasticity theory and the principle of virtual work, the governing equations are obtained. The differential quadrature method is employed to discretize the nonlinear governing equations, which are then solved by a direct iterative method to obtain the nonlinear pull-in and pull-out voltages for cantilever and fixed–fixed boundary conditions. A detailed parametric study is conducted to elucidate the influences of nonlocal parameter, vdW force, fringing field, beam length and gap distance on the behavior of the pull-in instability voltage. Numerical results indicate that the magnitude of the pull-in voltage increases with increase in the gap distance. Furthermore, as the effective gap distance increases, the pull-out voltage tends toward the electrostatically pull-out voltage.

Investigation of temporary stiction in poly-SiGe micromirror arrays

Stiction, permanent but also temporary, remains one of the most critical reliability concerns for micro-electro-mechanical systems (MEMS). In this paper, we present an investigation of temporary stiction of standard poly-SiGe MEMS. This is done by analyzing the hysteresis in the displacement-versus-voltage characteristics of electrostatically actuated micromirrors. The anomalous widening of the “pull-in window”, caused by stiction-induced delay of the pull-out, is used as an indication of the amount of mirror-to-surface stiction. Differences in the pull-out voltage of micromirrors within an array indicate varying levels of stiction from mirror to mirror. It is shown that a 1H,1H,2H,2H-perfluorodecyltrichlorosilane (FDTS) self-assembled monolayer (SAM) can reduce this in-use stiction. Analytical and finite element methods are used to quantify the stiction forces. Also the impact of the relative humidity and of a vacuum thermal treatment is studied. The results show that humidity at the surface is the main cause of the stiction in these devices.

Dielectric Charging in Capacitive RF MEMS Switches: The Effect of Extended Durations of Electric Stress

By focusing on thermally-activated processes, a straight-forward and reliable method is devised to investigate dielectric charging effects in capacitive RF MEMS switches subjected to extended durations of electric stress. A general model of distributed charge and air gap is adopted and further developed for theoretical formulation. Experiments performed over a wide temperature range agree well with the theoretical model. It is shown that for extended stress periods, the algebraic sum of the pull-out voltages is thermally activated, and follows the same temperature trend as the voltage corresponding to the minimum capacitance of the switch. Since pull-out voltages can be measured accurately with little effort, this discovery significantly simplifies the study of thermally-activated processes in these switches. Finally, it is shown that charging increases with time, following a power-law relation.

Floating electrode microelectromechanical system capacitive switches: A different actuation mechanism

The paper investigates the actuation mechanism in floating electrode microelectromechanical system capacitive switches. It is demonstrated that in the pull-in state, the device operation turns from voltage to current controlled actuation. The current arises from Poole-Frenkel mechanism in the dielectric film and Fowler-Nordheim in the bridge-floating electrode air gap. The pull-out voltage seems to arise from the abrupt decrease of Fowler-Nordheim electric field intensity. This mechanism seems to be responsible for the very small difference with respect to the pull-in voltage.