Vitaly Leus

On the Dynamic Response of Electrostatic MEMS Switches

The undamped dynamic response of electrostatic MEMS switches that are driven by a step-function voltage is investigated. A systematic analysis using energy methods is presented. An analytic expression for switching time is derived and this expression may be used as a design rule for electrostatic switches. The analytic predictions are validated experimentally using test structures with parallel-plates actuators. It is shown that the analysis is also applicable for switches with more general geometry.

How slender can comb-drive fingers be?

In this work, the electromechanical stability of individual comb-drive fingers is considered. Previous studies have shown that optimal design of elastic suspensions can prevent the side pull-in instability of comb-drive rotors. In this work it is shown that side pull-in can nevertheless occur in individual comb fingers, if they are exceedingly slender. To this end, the critical electromechanical state of individual comb fingers is analytically solved. This solution is in good agreement with finite elements simulations. The analytic solution can be used to design comb-drives in which side pull-in of individual fingers is avoided.

Optimizing the Dynamic Response of RF MEMS Switches using Tailored Voltage Pulses

This paper presents analytic modeling, simulations, and experimental validation of RF MEMS switch actuation using tailored voltage waveforms. This actuation scheme can eliminate impact bouncing during switch activation and can significantly reduce harmonic oscillations during switch release.

Switching time, impact velocity and release response, of voltage and charge driven electrostatic switches

In this work we analyze the undamped response of charge-driven and voltage-driven electrostatic switches. We show that charge actuation can drastically reduce the impact velocity between the movable and fixed electrodes and reduce unwanted vibrations during switch release. In voltage-driven switches, a considerable reduction of the impact velocity and switch-release vibrations can only be achieved by damping forces, which inevitably increase the switching time. We also show that in capacitive switches, charge actuation considerably reduces the maximal electrostatic field within the dielectric layer. This suggests that charge actuation can be used to reduce dielectric charging of capacitive switches.

Electromechanical Sensing of Charge Retention on Floating Electrodes

It is demonstrated theoretically and experimentally, that charge on floating electrodes can be measured by its effect on the electromechanical response of an electrostatic actuator. Charged, electrostatically-floating electrodes can be used as a DC bias source or for memory storage. Charge on a floating electrode must be measured indirectly because any direct measurement (e.g. measuring the voltage of the floating electrode) would cause discharge.

A Novel Tilting Micromirror with a Triangular Waveform Resonance Response and an Adjustable Resonance Frequency for Raster Scanning Applications

We present a novel tilting micro-mirror that has a triangular waveform resonance response, and a resonance frequency that can be continuously and reversibly adjusted. The triangular waveform and the adjustability of the resonance frequency are crucially important for raster-scanning applications. Although the mirror is driven by electrostatic forces, the triangular waveform is achieved by mechanical means. Our micro-mirror is driven by up to 60 Volts whereas to achieve the same waveform without the novel mechanical design would require extremely high voltages.

A New Efficient Method for Simulating the Dynamic Response of Electrostatic Switches

This paper presents a new efficient technique for simulating the dynamic response of electrostatic micro switches. It is demonstrated that the dynamic response of a switch can be well predicted based on only a few static states of the system. Using energy methods the deformation of the system is approximated by a single adaptive mode, such that time integration is performed on a scalar equation of motion. Due to the high computational efficiency of the proposed method, it can be used to motivate the functional form of damping forces and extract damping parameters, by fitting experimentally measured dynamic responses.

Predicting the switching time of electrostatic actuators

In this work, new analytic expressions for the frequency of large vibrations and for the switching time, of electrostatic actuators, are presented. These expressions predict that the frequency and switching time are linearly related to specific measures of the applied voltage, on a logarithmic scale. Test devices were designed, fabricated, and characterized, and measurements are shown to be in very good agreement with predictions. These linear relations are important and relevant as design rules for development of fast and accurate switches.

Electromechanical sensing of charge retention on floating electrodes

This paper considers the electromechanical response of electrostatic actuators that are driven by both voltage and charge. The model system is an electrostatic actuator in which the suspended electrode is subjected to a driving voltage and the fixed electrode, which is electrostatically floating, is loaded by charge. The response of the system is analyzed using energy methods, and it is shown that the system has two distinct pull-in voltages. It is also shown that the amplitude of charge on the floating electrode is proportional to the average of these two pull-in voltages. Test-actuators were designed, fabricated, and characterized, and their measured response validates the theoretical predictions. A nondisruptive measurement of charge is proposed and demonstrated which enables to monitor charge decay over time.