Jordan E. Massad

A Soft-Landing Waveform for Actuation of a Single-Pole Single-Throw Ohmic RF MEMS Switch

A soft-landing actuation waveform was designed to reduce the bounce of a single-pole single-throw (SPST) ohmic radio frequency (RF) microelectromechanical systems (MEMS) switch during actuation. The waveform consisted of an actuation voltage pulse, a coast time, and a hold voltage. The actuation voltage pulse had a short duration relative to the transition time of the switch and imparted the kinetic energy necessary to close the switch. After the actuation pulse was stopped, damping and restoring forces slowed the switch to near-zero velocity as it approached the closed position. This is referred to as the coast time. The hold voltage was applied upon reaching closure to keep the switch from opening. An ideal waveform would close the switch with near zero impact velocity. The switch dynamics resulting from an ideal waveform were modeled using finite element methods and measured using laser Doppler vibrometry. The ideal waveform closed the switch with an impact velocity of less than 3 cm/s without rebound. Variations in the soft-landing waveform closed the switch with impact velocities of 12.5 cm/s with rebound amplitudes ranging from 75 to 150 nm compared to impact velocities of 22.5 cm/s and rebound amplitudes of 150 to 200 nm for a step waveform. The ideal waveform closed the switch faster than a simple step voltage actuation because there was no rebound and it reduced the impact force imparted on the contacting surfaces upon closure

A Domain Wall Model for Hysteresis in Ferroelastic Materials

We develop a model that quantifies constitutive nonlinearities and hysteresis inherent to ferroelastic compounds, with emphasis placed on shape memory alloys. We formulate the model in two steps. First, we use the Landau theory of phase transitions to characterize the effective Gibbs free energy for single-crystal and polycrystalline ferroelastics. The resulting nonlinear equations model equilibrium material behavior in the absence of impurities. Second, we incorporate pinning losses to account for the energy required to move domain walls across material inclusions. The full model is analogous to those developed by Jiles and Atherton for ferromagnetic compounds and Smith and Hom for ferroelectric materials. We illustrate aspects of the model through numerical simulations and comparisons with experimental stress-strain data.

Modeling, simulation, and testing of the mechanical dynamics of an RF MEMS switch

Mechanical dynamics can be a determining factor for the switching speed of radio-frequency microelectromechanical systems (RF MEMS) switches. This paper presents the simulation of the mechanical motion of a microswitch under actuation. The switch has a plate suspended by springs. When an electrostatic actuation is applied, the plate moves toward the substrate and closes the switch. Simulations are calculated via a high-fidelity finite element model that couples solid dynamics with electrostatic actuation. It incorporates non-linear coupled dynamics and accommodates fabrication variations. Experimental modal analysis gives results in the frequency domain that verifies the natural frequencies and mode shapes predicted by the model. An effective 1D model is created and used to calculate an actuation voltage waveform that minimizes switch velocity at closure. In the experiment, the switch is actuated with this actuation voltage, and the displacements of the switch at various points are measured using a laser Doppler velocimeter through a microscope. The experiments are repeated on several switches from different batches. The experimental results verify the model.

Structural Dynamics of an RF MEMS Switch

The radio-frequency micro-electromechanical system (RF MEMS) switch comprises a plate suspended by four double-cantilever springs. When electrostatic actuation is applied, the plate moves toward the substrate and closes the switch. This article discusses how simulation and experimental methods improve the performance of the switch by suppressing mechanical rebounds and thus electrical signal discontinuities. To accurately simulate the mechanical motion of the switch, a high-fidelity three-dimensional finite element model is created to couple the solid dynamics with the electrostatic actuation. The displacement of the switch at various points is measured using a laser Doppler velocimeter through a microscope. The operational deflection shapes agree with the model. The three-dimensional model produces the necessary information for an effective one-dimensional model. The latter model is used to calculate an actuation voltage waveform to minimize switch velocity at closure, thereby suppressing switch rebound. The waveforms can be refined experimentally to compensate for switch property variations. Laboratory tests indicate that the waveform suppresses or eliminates rebound events.© 2005 ASME

A free energy model for thin-film shape memory alloys

Thin-film shape memory alloys (SMAs) have become excellent candidates for microactuator fabrication in MEMS. We develop a material model based on free energy principles combined with stochastic homogenization techniqies. In the first step of the development, we construct free energies and develop phase fraction and thermal evolution laws for homogeneous, single-crystal SMAs. Second, we extend the single-crystal model to accomodate material inhomogeneities and polycrystalline compounds. The combined model predicts rate-dependent, uniaxial SMA deformations due to applied stress and temperature. Moreover, the model admits a low-order formulation that is suitable for subsequent control design. We illustrate aspects of the model through comparison with thin-film NiTi superelastic hysteresis data.

Domain wall model for SMA characterization

We develop a model that quantifies constitutive nonlinearities and hysteresis inherent to ferroelastic compounds, with emphasis placed on shape memory alloys. We formulate the model in two steps. First, we use the Landau theory of phase transitions to characterize the effective Gibbs free energy for both single-crystal and polycrystalline ferroelastics. The resulting nonlinear equations model ideal material behavior in the absence of impurities. Second, we incorporate pinning losses to account for the energy required to move domain walls across material inclusions. We illustrate aspects of the model through comparison with experimental stress-strain data.

Front end of line integration of high density, electrically isolated, metallized through silicon vias

We have developed a complete process module for fabricating front end of line (FEOL) through silicon vias (TSVs). In this paper we describe the integration, which relies on using thermally deposited silicon as a sacrificial material to fill the TSV during FEOL processing, followed by its removal and replacement with tungsten after FEOL processing is complete. The uniqueness of this approach follows mainly from forming the TSVs early in the FEOL while still ultimately using metal as the via fill material. TSVs formed early in the FEOL can be formed at comparatively small diameter, high aspect ratio, and high spatial density. We have demonstrated FEOL-integrated TSVs that are 2 µm in diameter, over 45 µm deep, and on 20 µm pitch for a possible interconnect density of 250,000/cm2. Moreover, thermal oxidation of silicon can be used to form the dielectric isolation. Thermal oxidation is conformal and robust in the as-formed state. Finally, TSVs formed in the FEOL alleviate device design constraints common to vias-last integration.

Analytical and Experimental Studies of Orthotropic Corner-Supported Plates With Segmented In-Plane Actuators

This paper outlines a model for a corner-supported, thin, rectangular bimorph actuated by a two-dimensional array of segmented, orthotropic PVDF laminates; it investigates the realization and measurement of such a bimorph. First, a model is derived to determine the deflected shape of an orthotropic laminate for a given distribution of voltages over the actuator array. Then, boundary conditions are realized in a laboratory setup to approach the theoretical corner-supported boundary condition. Finally, deflection measurements of actuated orthotropic PVDF laminates are performed with Electronic Speckle Pattern Interferometry and are compared to the model results.

Modeling aspects concerning THUNDER actuators

This paper summarizes techniques for modeling geometric properties of THUNDER actuators which arise in the fabrication process. These actuators are high performance composites comprised of layers of piezoceramics in combination with aluminum, stainless steel, brass or titanium bonded with hot- melt adhesive. During the construction process, the assembly is heated under pressure to high temperatures, cooled and repoled to restore the actuator capabilities. This process provides the actuators with the robustness necessary to withstand the high voltages required for large displacement and force outputs. The process also provides the actuators with their characteristic curved shape. In this paper, relations between the thermal and electrostatic properties of the material and the final geometric configuration are quantified. This provides an initial model that can be employed in control applications which employ THUNDER actuators.

Uncertainty Enabled Design of an Acceleration Switch

A mechanical acceleration switch has been developed to synchronize instrumentation during a destructive acceleration test. The tests are of short durations and involve very high velocities and accelerations, and a destructive impact. Therefore, accurately synchronized instrumentation is critical. When the switch detects a desired acceleration time history, the switch closes to complete a circuit for instrument activation. Preliminary tests on the proposed switch have shown that switch-to-switch variations exist due to fabrication and assembly tolerances, and that combinations of variations may lead to a switch that does not respond properly. If the switch does not close at the proper time, improper data may be collected; or, at worst, no data may be collected before destructive impact. In this paper, a nonlinear model of the switch closing dynamics is developed in order to investigate the effect of uncertainty on its operation. In particular, the propagation of uncertainty from the switch parameters to the switch dynamics is quantified, and then the design is optimized such that the operation of the switch is insensitive to the variation and uncertainty. The results of the analysis elucidate the parameters that significantly impact switch operation, quantify the reliability of the existing switch design, and ultimately are used to recommend a design that could significantly improve reliability.Copyright