Microswitches with Sputtered Au, AuPd,Au-on-AuPt, and AuPtCu Alloy Electric Contacts

This paper is the first to report on a new analytic model for predicting microcontact resistance and the design, fabrication, and testing of microelectromechanical systems (MEMS) metal contact switches with sputtered bimetallic (i.e., gold (Au)-on-Au-platinum (Pt), (Au-on-Au-(6.3at%)Pt)), binary alloy (i.e., Au-palladium (Pd), (Au-(3.7at%)Pd)), and ternary alloy (i.e., Au-Pt-copper (Cu), (Au-(5.0at%)Pt-(0.5at%)Cu)) electric contacts. The microswitches with bimetallic and binary alloy contacts resulted in contact resistance values between 1-2Omega. Preliminary reliability testing indicates a 3times increase in switching lifetime when compared to microswitches with sputtered Au electric contacts. The ternary alloy exhibited approximately a 6times increase in switch lifetime with contact resistance values ranging from approximately 0.2-1.8Omeg

5-Bit RF MEMS Phase Shifter Development in Ku Band for Phased Array Applications

MEMS based devices represent an extremely attractive alternative to MESFET devices for realization of the programmable phase shifters. The stable operation of RF MEMS devices is impacted by the actuation voltage, restoration force and the structural stresses. These can induce severe functional deformities into the device leading to operational problems. These parameters can be optimized by the concept of built-in reliability through design. In the present work, the study of Ku band 5-bit MEMS phase shifter was associated with the switch development. The hybrid design topology of switched and loaded line was adopted for the phase shifter. This topology has been the best trade off among large phase shift, low loss and reduced space requirement in the defined frequency band. This approach requires 18 switches per 5-bit phase shifter and all must work simultaneously in order to achieve the phase shifter fully functional. Hence the study was initiated with switch development keeping the focus on the above mentioned parameters

A domain adaptive stochastic collocation approach for analysis of MEMS under uncertainties

This work proposes a domain adaptive stochastic collocation approach for uncertainty quantification, suitable for effective handling of discontinuities or sharp variations in the random domain. The basic idea of the proposed methodology is to adaptively decompose the random domain into subdomains. Within each subdomain, a sparse grid interpolant is constructed using the classical Smolyak construction [S. Smolyak, Quadrature and interpo- lation formulas for tensor products of certain classes of functions, Soviet Math. Dokl. 4 (1963) 240–243], to approximate the stochastic solution locally. The adaptive strategy is governed by the hierarchical surpluses, which are computed as part of the interpolation procedure. These hierarchical surpluses then serve as an error indicator for each subdo- main, and lead to subdivision whenever it becomes greater than a threshold value. The hierarchical surpluses also provide information about the more important dimensions, and accordingly the random elements can be split along those dimensions. The proposed adaptive approach is employed to quantify the effect of uncertainty in input parameters on the performance of micro-electromechanical systems (MEMS). Specifically, we study the effect of uncertain material properties and geometrical parameters on the pull-in behavior and actuation properties of a MEMS switch. Using the adaptive approach, we resolve the pull-in instability in MEMS switches. The results from the proposed approach are verified using Monte Carlo simulations and it is demonstrated that it computes the required statistics effectively

Mixed-Domain Fast Simulation of RF and Microwave MEMS-based Complex Networks within Standard IC Development Frameworks

MS technology (MicroElectroMechanical-System) has been successfully employed since a few decades in the sensors/actuators field. Several products available on the market nowadays include MEMS-based accelerometers and gyroscopes, pressure sensors and micro-mirrors matrices. Beside such well-established exploitation of MEMS technology, its use within RF (Radio Frequency) blocks and systems/sub-systems has been attracting, in recent years, the interest of the Scientific Community for the significant RF performances boosting that MEMS devices can enable. Several significant demonstrators of entirely MEMS-based lumped components, like variable capacitors (Hyung et al., 2008), inductors (Zine-El-Abidine et al., 2003) and micro-switches (Goldsmith et al., 1998), are reported in literature, exhibiting remarkable performance in terms of large tuning-range, very high Q-Factor and low-loss, if compared with the currently used components implemented in standard semiconductor technology (Etxeberria & Gracia, 2007, Rebeiz & Muldavin, 1999). Starting from the just mentioned basic lumped components, it is possible to synthesize entire functional sub-blocks for RF applications in MEMS technology. Also in this case, highly significant demonstrators are reported and discussed in literature concerning, for example, tuneable phase shifters (Topalli et al., 2008), switching matrices (Daneshmand & Mansour, 2007), reconfigurable impedance matching networks (Larcher et al., 2009) and power attenuators (Iannacci et al., 2009, a). In all the just listed cases, the good characteristics of RF-MEMS devices lead, on one side, to very highperformance networks and, on the other hand, to enabling a large reconfigurability of the entire RF/Microwave systems employing MEMS sub-blocks. In particular, the latter feature addresses two important points, namely, the reduction of hardware redundancy, being for instance the same Power Amplifier within a mobile phone suitable both in transmission (Tx) and reception (Rx) (De Los Santos, 2002), and the usability of the same RF apparatus in compliance with different communication standards (like GSM, UMTS, WLAN and so on) (Varadan, 2003). Beside the exploitation of MEMS technology within RF transceivers, other potentially successful uses of Microsystems are in the Microwave field, concerning, e.g., very compact switching units, especially appealing to satellite applications for the very reduced weight (Chung et al., 2007), and phase shifters in order to electronically steer short and mid-range radar systems for the homeland security and monitoring applications (Maciel et al., 2007). Given all the examples reported above, it is straightforward that the employment of a proper strategy in aiming at the RF-MEMS devices/networks optimum design is a key-issue in order to gain the best benefits, in terms of performance, that such technology enables to address. This is not an easy task as the behaviour of RF-MEMS transversally crosses different physical domains, namely, electrical, mechanical and electromagnetic, leading to a large number of trade-offs between mechanical and electrical/electromagnetic parameters, that typically cannot be managed within a unique commercial simulation tool. In this chapter, a complete approach for the fast simulation of single RF-MEMS devices as well as of complex networks is presented and discussed in details. The proposed method is based on a MEMS compact model library, previously developed by the author, within a commercial simulation environment for ICs (integrated circuits). Such software tool describes the electromechanical mixed-domain behaviour typical of MEMS devices. Moreover, through the chapter, the electromagnetic characteristics of RF-MEMS will be also addressed by means of extracted lumped element networks, enabling the whole electromechanical and electromagnetic design optimization of the RF-MEMS device or network of interest. In particular, significant examples about how to acc..

Buckling of Carbon Nanotubes: A State of the Art Review

The nonlinear mechanical response of carbon nanotubes, referred to as their "buckling" behavior, is a major topic in the nanotube research community. Buckling means a deformation process in which a large strain beyond a threshold causes an abrupt change in the strain energy vs. deformation profile. Thus far, much effort has been devoted to analysis of the buckling of nanotubes under various loading conditions: compression, bending, torsion, and their certain combinations. Such extensive studies have been motivated by (i) the structural resilience of nanotubes against buckling and (ii) the substantial influence of buckling on their physical properties. In this contribution, I review the dramatic progress in nanotube buckling research during the past few years.Comment: 38 pages, 21 figure

Continuation-Based Pull-In and Lift-Off Simulation Algorithms for Microelectromechanical Devices

The voltages at which microelectromechanical actuators and sensors become unstable, known as pull-in and lift-off voltages, are critical parameters in microelectromechanical systems (MEMS) design. The state-of-the-art MEMS simulators compute these parameters by simply sweeping the voltage, leading to either excessively large computational cost or to convergence failure near the pull-in or lift-off points. This paper proposes to simulate the behavior at pull-in and lift-off employing two continuation-based algorithms. The first algorithm appropriately adapts standard continuation methods, providing a complete set of static solutions. The second algorithm uses continuation to trace two kinds of curves and generates the sweep-up or sweep-down curves, which can provide more intuition for MEMS designers. The algorithms presented in this paper are robust and suitable for general-purpose industrial MEMS designs. Our algorithms have been implemented in a commercial MEMS/integrated circuits codesign tool, and their effectiveness is validated by comparisons against measurement data and the commercial finite-element/boundary-element (FEM/BEM) solver CoventorWare

Vibration Analysis of Piezoelectric Microcantilever Sensors

The main objective of this dissertation is to comprehensively analyze vibration characteristics of microcantilever-based sensors with application to ultra small mass detection and low dimensional materials characterization. The first part of this work focuses on theoretical developments and experimental verification of piezoelectric microcantilevers, commercially named Active Probes, which are extensively used in most today\u27s advanced Atomic Force Microscopy (AFM) systems. Due to special geometry and configuration of Active Probes, especially multiple jump discontinuities in their cross-section, a general and comprehensive framework is introduced for forced vibration and modal analysis of discontinuous flexible beams. More specifically, a general formulation is obtained for the characteristics matrix using both boundary and continuity conditions. The formulation is then reduced to the special case of Active Probes with intentional geometrical discontinuities. Results obtained from experiment are compared with the commonly used uniform beam model as well as the proposed discontinuous beam model. It is demonstrated that a significant enhancement on sensing accuracy of Active Probes can be achieved using the proposed discontinuous beam model compared to a uniform model when a multiple-mode operation is desired. In the second part of this dissertation, a comprehensive dynamic model is proposed for vector Piezoforce Microscopy (PFM) system under applied electrical loading. In general, PFM is considered as a suspended microcantilever beam with a tip mass in contact with a piezoelectric material. The material properties are expressed in two forms; Kelvin-Voigt model for viscoelstic representation of the material and piezoelectric force acting on the tip as a result of response of material to applied electric field. Since the application of bias voltage to the tip results in the surface displacement in both normal and in-plane directions, the microcantilever is considered to vibrate in all three directions with coupled transversal/longitudinal and lateral/torsional motions. In this respect, it is demonstrated that the PFM system can be governed by a set of partial differential equations along with non-homogeneous and coupled boundary conditions. Using the method of assumed modes, the governing ordinary differential equations of the system and its state-space representation are derived under applied external voltage. The formulation is then reduced to vertical PFM, in which low dimensional viscoelestic and piezoelectric properties of periodically poled lithium niobate (PPLN) material can be detected. For this purpose, the experimental and theoretical frequency responses along with a minimization strategy for the percentage of modeling error are utilized to obtain optimal spring constant of PPLN. Finally, the step input responses of experiment and theory are used to estimate the piezoelectric and damping coefficients of PPLN. Overall in this dissertation, a precise dynamic model is developed for piezoelectric microcantilever for ultra small mass detection purpose. This model can also be utilized in AFM systems to replace laser-based detection mechanism with other alternative transductions. Moreover, a comprehensive model is proposed for PFM system to simultaneously detect low dimensional viscoelastic and piezoelectric properties of materials. This model can also be utilized for data storage purpose in ferroelectric materials

Nematic Liquid Crystal Carbon Nanotube Composite Materials for Designing RF Switching Devices

Radio frequency microelectromechanical systems (RF MEMS) devices are microdevices used to switch or modify signals from the RF to millimeter wave (mmWave) frequency range. Liquid crystals (LCs) are widely used as electro-optic modulators for display devices. An electric field-induced electrical conductivity modulation of pure LC media is quite low which makes it difficult to use for RF MEMS switching applications. Currently, RF MEMS devices are characterized as an excellent option between solid-state and electromechanical RF switches to provide high isolation, low insertion loss, low power usage, excellent return loss, and large frequency band. However, commercial usage is low due to their lower switching speed, reliability, and repeatability. This research presents an electrical conductivity enhancement through the use of carbon nanotube (CNT) doping of LCs to realize a high-performance RF LC-CNT switching device. This thesis presents simulations of an RF switch using a coplanar waveguide (CPW) with a LC-CNT composite called 4-Cyano-4’-pentylbiphenyl multi-walled nanotube (5CB-MWNT) that is suitable for RF applications. The electrical conductivity modulation and RF switch performance of the 5CB-MWNT composite is determined using Finite Element Analysis (FEA). The simulations will present data on the coplanar waveguide’s s-parameters at the input and output ports S11 and S21 to measure return and insertion loss respectively, two key parameters for determining any RF switch’s performance. Furthermore, this thesis presents applications for improving tunable phased antenna arrays using the LC-CNT composite to allow for beam steering with high-gain and directivity to provide a broad 3D scannable coverage of an area. Tunable antennas are an important characteristic for 5G applications to achieve an optimal telecommunication system to prevent overcrowding of antennas and reduce overall system costs. This research investigates various device geometries with 5CB-MWNT to realize the best performing RF device for RF applications and 5G telecommunication systems. This research presents return and insertion loss data for three waveguide device configurations: CPW, coplanar waveguide grounded (CPWG), and finite ground coplanar waveguide grounded (FG-CPWG). The best results are shown using the CPW configuration. The return loss for the LC-CNT device showed a 5 dB improvement from -7.5 dB to -12.5 dB when using the LC-CNT signal line device. The insertion loss for this configuration showed a much more consistent 0 to -0.3 dB insertion loss value with much less noise when using the LC-CNT device compared to the -0.3 to -1 dB insertion loss value with heavy noise when using the Au signal line device. For the other two configurations the return loss and insertion loss value stayed the same indicating there is no loss in performance when using the LC-CNT switching mechanism. This is ideal due to the benefits that the LC-CNT switching mechanism provides like device reliability and increased switching speeds