RF-MEMS Switches Designed for High-Performance Uniplanar Microwave and mm-Wave Circuits

Radio frequency microelectromechanical system (RF-MEMS) switches have demonstrated superior electrical performance (lower loss and higher isolation) compared to semiconductor-based devices to implement reconfigurable microwave and millimeter (mm)-wave circuits. In this chapter, electrostatically actuated RF-MEMS switch configurations that can be easily integrated in uniplanar circuits are presented. The design procedure and fabrication process of RF-MEMS switch topologies able to control the propagating modes of multimodal uniplanar structures (those based on a combination of coplanar waveguide (CPW), coplanar stripline (CPS), and slotline) will be described in detail. Generalized electrical (multimodal) and mechanical models will be presented and applied to the switch design and simulation. The switch-simulated results are compared to measurements, confirming the expected performances. Using an integrated RF-MEMS surface micromachining process, high-performance multimodal reconfigurable circuits, such as phase switches and filters, are developed with the proposed switch configurations. The design and optimization of these circuits are discussed and the simulated results compared to measurements

A High Isolation Series-Shunt RF MEMS Switch

This paper presents a wide band compact high isolation microelectromechanical systems (MEMS) switch implemented on a coplanar waveguide (CPW) with three ohmic switch cells, which is based on the series-shunt switch design. The ohmic switch shows a low intrinsic loss of 0.1 dB and an isolation of 24.8 dB at 6 GHz. The measured average pull-in voltage is 28 V and switching time is 47 μs. In order to shorten design period of the high isolation switch, a structure-based small-signal model for the 3-port ohmic MEMS switch is developed and parameters are extracted from the measured results. Then a high isolation switch has been developed where each 3-port ohmic MEMS switch is closely located. The agreement of the measured and modeled radio frequency (RF) performance demonstrates the validity of the electrical equivalent model. Measurements of the series-shunt switch indicate an outstanding isolation of more than 40 dB and a low insertion loss of 0.35 dB from DC to 12 GHz with total chip size of 1 mm × 1.2 mm

RF-MEMS switches for a full control of the propagating modes in uniplanar microwave circuits and their application to reconfigurable multimodal microwave filters

This is a copy of the author 's final draft version of an article published in the journal Microsystem technologies. The final publication is available at Springer via http://dx.doi.org/10.1007/s00542-017-3379-8In this paper, new RF-MEMS switch configurations are proposed to enable control of the propagating (even and odd) modes in multimodal CPW transmission structures. Specifically, a switchable air bridge (a switchable short-circuit for the CPW odd mode) and switchable asymmetric shunt impedances (for transferring energy between modes) are studied and implemented using bridge-type and cantilever-type ohmic-contact switches, respectively. The switchable air bridge is based in a novel double ohmic-contact bridge-type structure. Optimized-shape suspension configurations, namely folded-beam or diagonal-beam for bridge-type switches, and straight-shaped or semicircular-shaped for cantilever-type switches, are used to obtain robust structures against fabrication-stress gradients. The switches are modelled using a coupled-field 3D finite-element mechanical analysis showing a low to moderate pull-in voltage. The fabricated switches are experimentally characterized using S-parameter and DC measurements. The measured pull-in voltages agree well with the simulated values. From S-parameter measurements, an electrical model with a very good agreement for both switch states (ON and OFF) has been obtained. The model is used in the design of reconfigurable CPW multimodal microwave filters.Peer ReviewedPostprint (author's final draft

Bouncing Dynamics of a Class of MEM/NEM Switching Systems

The aim of the present research is to understand the bouncing dynamic behavior of NEM/MEM switches in order to improve the switch performance and reliability. It is well known that the bouncing can dramatically degrade the switch performance and life; hence, in the present study, bouncing dynamics of a cantilever-based NME/MEM switch has been studied in detail. To this end, a model of a MEM switch that incorporates electrostatic force, squeeze film air damping force as well as asperity-based contact force has been proposed for an electrostatically actuated switch. An actuation force due to piezoelectric effects is further included in an alternative micro-switch model of combined actuation for the purposes of bounce mitigation. For a NEM switch, an asperity-based contact model along with repulsive van der Waals force are incorporated in a nano-switch to capture the contact dynamics. Intermolecular forces, surface effects, and gas rarefication effects are also included in the NEM switch model. Further, an intermolecular force, specifically the Casimir force, is also used to actuate this class of switches in addition to the classical electrostatic actuation. Euler-Bernoulli beam theory and an approximate approach based on Galerkin’s method have been employed for predicting transient dynamic responses. In the present study, performance parameters such as initial contact time, permanent contact time, major bounce height, and the number of bounces have been quantified in the presence of interactive system nonlinearities. For a MEM switch, improvement of bouncing behavior has been investigated using harmonic dither in the actuation voltage of an electrostatically actuated switch or using harmonic dither in the secondary piezoelectric actuator voltage. Improvements have been achieved in both types of switches at specific frequency ranges. Uncertainty quantification of parameters that affect the bouncing is also performed since MEM switches are prone to uncertainties during the fabrication. Measure of performance in terms of second order statistics is predicted, particularly for the beam as well as beam tip parameters and the influence of uncertainty in parameters on the system performance has been quantified. For a NEM switch, the performance parameters are also used to investigate the influence of surface effects and rarefication effects on the performance of an electrostatically actuated switch. Influence of some pull-in parameters on the switch bouncing behavior have also been investigated in the presence of surface effects at different vacuum conditions for purely Casimir actuated NEM switch. Recommended operating conditions or actuation parameters are suggested for the purposes of avoiding excessive bouncing for both types of NEM switches. The present investigation on the bouncing dynamic behavior of a class of MEM/NEM switches is envisaged to yield greater insight into the design, reliability and performance predictions for this class of switches

Dual-Beam Actuation of Piezoelectric AlN RF MEMS Switches Monolithically Integrated with AlN Contour-Mode Resonators

This work reports on piezoelectric Aluminum Nitride (AlN) based dual-beam RF MEMS switches that have been monolithically integrated with AlN contour-mode resonators. The dual-beam switch design presented in this paper intrinsically compensates for the residual stress in the deposited films, requires low actuation voltage (5 to 20 V), facilitates active pull-off to open the switch and exhibits fast switching times (1 to 2 μs). This work also presents the combined response (cascaded S parameters) of a resonator and a switch that were co-fabricated on the same substrate. The response shows that the resonator can be effectively turned on and off by the switch. A post-CMOS compatible process was used for the co-fabrication of both the switches and the resonators. The single-chip RF solution presented herein constitutes an unprecedented step forward towards the realization of compact, low loss and integrated multi-frequency RF front-ends

NONLINEAR INSTABILITIES IN MEM/NEM ELECTROSTATIC SWITCHES

The aim of this thesis is to develop suitable mathematical models for the purpose of investigating nonlinear instabilities in Micro-Electro-Mechanical (MEM) and Nano- Electro-Mechanical (NEM) electrostatic switches. The proposed models capture the influence of electric field fringing, intermolecular forces, surface stress and surface elasticity. Based on Euler-Bernoulli assumptions, a surface elasticity model and the generalized Young-Laplace equation, effects of surface stress and surface elasticity are incorporated in the models, while the intermolecular force effects are modelled using quantum mechanics. The derived governing equation representing static pull-in behaviour of switches is inherently nonlinear due to the driving electrostatic force and intermolecular forces which become dominant at nanoscale. Since no exact solutions are available for the resulting nonlinear differential equation, an approach based on homotopy perturbation method (HPM) is proposed to construct approximate analytical solutions, as well as to characterize the instability behaviour. Numerical solutions obtained via finite difference method (FDM) are employed for validating the analytical results. HPM in conjunction with Adomian decomposition method (ADM) has been employed for approximate analytical predictions. To this end, the solutions for the fourth-order two- point boundary value problem (BVP) representing MEM/NEM electrostatic switches are constructed in terms of a convergent series. The pull-in parameters, including pull-in voltage, detachment length and low-voltage actuation windows, are investigated in detail using the above methods and also via a lumped parameter model. HPM analytical solutions are found to be more accurate and reliable compared to those predicted via the lumped parameter model. HPM solutions also tend to overestimate the static deflection, and underestimate pull-in voltage and detachment length compared to the FDM numerical solutions. However, its relative differences to the FDM numerical solutions are within an acceptable range for design purposes. HPM is concluded to work well for the static pull-in in parameter determination, and is preferred since it is straightforward to implement and could save computation efforts while not losing accuracy. Predictions via HPM and FDM also revealed that the influence of surface effects on the pull-in instability of MEM/NEM switches is significant and the exclusion of surface effects in the analysis may result in an erroneous estimation of the pull-in parameters. Further, the concept of Casimir actuated switches is proposed for the purpose of ensuring the physical realization of a new class of the switchable devices using pure Casmir force actuation. To this end, a new idea of Casimir-force actuation window has been introduced for the purpose of ensuring designs that yield functional Casimir actuated switches. The present study is envisaged to be beneficial for the design and applications of MEM/NEM electrostatic as well as Casimir actuated switches. The methodology presented in this thesis may be also used for the analysis of actuation systems, which may involve other types of nonlinear actuation forces

ELECTRICAL CHARACTERIZATION, PHYSICS, MODELING AND RELIABILITY OF INNOVATIVE NON-VOLATILE MEMORIES

Enclosed in this thesis work it can be found the results of a three years long research activity performed during the XXIV-th cycle of the Ph.D. school in Engineering Science of the Università degli Studi di Ferrara. The topic of this work is concerned about the electrical characterization, physics, modeling and reliability of innovative non-volatile memories, addressing most of the proposed alternative to the floating-gate based memories which currently are facing a technology dead end. Throughout the chapters of this thesis it will be provided a detailed characterization of the envisioned replacements for the common NOR and NAND Flash technologies into the near future embedded and MPSoCs (Multi Processing System on Chip) systems. In Chapter 1 it will be introduced the non-volatile memory technology with direct reference on nowadays Flash mainstream, providing indications and comments on why the system designers should be forced to change the approach to new memory concepts. In Chapter 2 it will be presented one of the most studied post-floating gate memory technology for MPSoCs: the Phase Change Memory. The results of an extensive electrical characterization performed on these devices led to important discoveries such as the kinematics of the erase operation and potential reliability threats in memory operations. A modeling framework has been developed to support the experimental results and to validate them on projected scaled technology. In Chapter 3 an embedded memory for automotive environment will be shown: the SimpleEE p-channel memory. The characterization of this memory proven the technology robustness providing at the same time new insights on the erratic bits phenomenon largely studied on NOR and NAND counterparts. Chapter 4 will show the research studies performed on a memory device based on the Nano-MEMS concept. This particular memory generation proves to be integrated in very harsh environment such as military applications, geothermal and space avionics. A detailed study on the physical principles underlying this memory will be presented. In Chapter 5 a successor of the standard NAND Flash will be analyzed: the Charge Trapping NAND. This kind of memory shares the same principles of the traditional floating gate technology except for the storage medium which now has been substituted by a discrete nature storage (i.e. silicon nitride traps). The conclusions and the results summary for each memory technology will be provided in Chapter 6. Finally, on Appendix A it will be shown the results of a recently started research activity on the high level reliability memory management exploiting the results of the studies for Phase Change Memories

A Review of Micro-Contact Physics for Microelectromechanical Systems (MEMS) Metal Contact Switches

Innovations in relevant micro-contact areas are highlighted, these include, design, contact resistance modeling, contact materials, performance and reliability. For each area the basic theory and relevant innovations are explored. A brief comparison of actuation methods is provided to show why electrostatic actuation is most commonly used by radio frequency microelectromechanical systems designers. An examination of the important characteristics of the contact interface such as modeling and material choice is discussed. Micro-contact resistance models based on plastic, elastic-plastic and elastic deformations are reviewed. Much of the modeling for metal contact micro-switches centers around contact area and surface roughness. Surface roughness and its effect on contact area is stressed when considering micro-contact resistance modeling. Finite element models and various approaches for describing surface roughness are compared. Different contact materials to include gold, gold alloys, carbon nanotubes, composite gold-carbon nanotubes, ruthenium, ruthenium oxide, as well as tungsten have been shown to enhance contact performance and reliability with distinct trade offs for each. Finally, a review of physical and electrical failure modes witnessed by researchers are detailed and examined

Electrostatic Radio Frequency (RF) Microelectromechanical Systems (MEMS) Switches With Metal Alloy Electric Contacts

RF MEMS switches are paramount in importance for improving current and enabling future USAF RF systems. Electrostatic micro-switches are ideal for RF applications because of their superior performance and low power consumption. The primary failure mechanisms for micro-switches with gold contacts are becoming stuck closed and increased contact resistance with increasing switch cycles. This dissertation reports on the design, fabrication, and testing of micro-switches with sputtered bi-metallic (i.e., gold (Au)-on-Au-(6.3at%)platinum (Pt)), binary alloy (i.e., Au-(3.7at%)palladium (Pd) and Au-(6.3at%)Pt), and ternary alloy (i.e., Au-(5at%)Pt-(0.5at%)copper (Cu)) contact metals. Performance was evaluated, in-part, using measured contact resistance and lifetime results. The micro-switches with bi-metallic and binary alloy contacts exhibited contact resistance between 1 - 2 ohms and, when compared to micro-switches with sputtered gold contacts, showed an increase in lifetime. The micro-switches with tertiary alloy contacts showed contact resistance between 0.2-1.8 and also showed increased lifetime. Overall, the results presented in this dissertation indicate that micro-switches with gold alloy electric contacts exhibit increased lifetimes in exchange for a small increase in contact resistance

Classical and fluctuation-induced electromagnetic interactions in micronscale systems: designer bonding, antibonding, and Casimir forces

Whether intentionally introduced to exert control over particles and macroscopic objects, such as for trapping or cooling, or whether arising from the quantum and thermal fluctuations of charges in otherwise neutral bodies, leading to unwanted stiction between nearby mechanical parts, electromagnetic interactions play a fundamental role in many naturally occurring processes and technologies. In this review, we survey recent progress in the understanding and experimental observation of optomechanical and quantum-fluctuation forces. Although both of these effects arise from exchange of electromagnetic momentum, their dramatically different origins, involving either real or virtual photons, lead to different physical manifestations and design principles. Specifically, we describe recent predictions and measurements of attractive and repulsive optomechanical forces, based on the bonding and antibonding interactions of evanescent waves, as well as predictions of modified and even repulsive Casimir forces between nanostructured bodies. Finally, we discuss the potential impact and interplay of these forces in emerging experimental regimes of micromechanical devices.Comment: Review to appear on the topical issue "Quantum and Hybrid Mechanical Systems" in Annalen der Physi