Ofir Bochobza-Degani

Modeling the Pull-In Parameters of Electrostatic Actuators with a Novel Lumped Two Degrees of Freedom Pull in Model

This paper reports a new approach for the direct calculations of the Pull-In parameters of electrostatic actuators using a lumped two degrees of freedom (L2DOF) Pull-In model. This model benefits from shorter calculation time compared with coupled domains finite-elements simulations and from higher accuracy than the L1DOF Pull-In models. Using this model, the variations of the Pull-In with geometry, such as asymmetries in the beams, can be investigated. The L2DOF Pull-in model results are compared with FEM simulations, provided by MEMCAD™, showing excellent agreement. This provides a fast tool for design optimization of actuators with coupled DOF.

An efficient DIPIE algorithm for CAD of electrostatically actuated MEMS devices

Pull-in parameters are important properties of electrostatic actuators. Efficient and accurate analysis tools that can capture these parameters for different design geometries, are therefore essential. Current simulation tools approach the pull-in state by iteratively adjusting the voltage applied across the actuator electrodes. The convergence rate of this scheme gradually deteriorates as the pull-in state is approached. Moreover, the convergence is inconsistent and requires many mesh and accuracy refinements to assure reliable predictions. As a result, the design procedure of electrostatically actuated MEMS devices can be time-consuming. In this paper a novel Displacement Iteration Pull-In Extraction (DIPIE) scheme is presented. The DIPIE scheme is shown to converge consistently and far more rapidly than the Voltage Iterations (VI) scheme (>100 times faster!). The DIPIE scheme requires separate mechanical and electrostatic field solvers. Therefore, it can be easily implemented in existing MOEMS CAD packages. Moreover, using the DIPIE scheme, the pull-in parameters extraction can be performed in a fully automated mode, and no user input for search bounds is required.

On the Effect of Residual Charges on the Pull-In Parameters of Electrostatic Actuators

In this paper a quantitative model for the effect of residual-charge upon the Pull-In parameters of electrostatic actuators is presented. The model is derived for a general electrostatic actuator with a charge sheet located arbitrarily in a dielectric coating layer. The main interesting new results derived from the model are: (i) the pull-in displacement is unaffected by the residual-charge and the travel range is only extended due to the series dielectric capacitor, (ii) the pull-in voltage is significantly reduced due to the residual charge, independent of the residual charge polarity.

Analytical approach and numerical /spl alpha/-lines method for pull-in hyper-surface extraction of electrostatic actuators with multiple uncoupled voltage sources

This work presents a systematic analysis of electrostatic actuators driven by multiple uncoupled voltage sources. The use of multiple uncoupled voltage sources has the potential of enriching the electromechanical response of electrostatically actuated deformable elements. This in turn may enable novel MEMS devices with improved and even new capabilities. It is therefore important to develop methods for analyzing this class of actuators. Pull-in is an inherent instability phenomenon that emanates from the nonlinear nature of the electromechanical coupling in electrostatic actuators. The character of pull-in in actuators with multiple uncoupled voltage sources is studied, and new insights regarding pull-in are presented. An analytical method for extracting the pull-in hyper-surface by directly solving the voltage-free K-N pull-in equations derived here, is proposed. Solving simple but interesting example problems illustrate these new insights. In addition, a novel /spl alpha/-lines numerical method for extracting the pull-in hyper-surface of general electrostatic actuators is presented and illustrated. This /spl alpha/-lines method is motivated by new features of pull-in, that are exhibited only in electrostatic actuators with multiple uncoupled voltage sources. This numerical method permits the analysis of electrostatic actuators that could not have been analyzed by using current methods.

Experimental verification of a design methodology for torsion actuators based on a rapid pull-in solver

In this work, an experimental and theoretical study of the effect of various geometrical parameters on the electromechanical response and pull-in parameters of torsion actuators is presented. A lumped two-degrees-of-freedom (L2DOF) pull-in model that takes into account the bending/torsion coupling, previously proposed for cantilever suspended actuators, is tailored for the torsion actuators under study. This model is shown to better capture the measured pull-in parameters than previously proposed lumped single-degree-of-freedom (L1DOF) models. The measurements were conducted on torsion actuators with various shapes, fabricated on silicon-on-insulator (SOI) wafers using deep reactive ion etching (DRIE) and flip-chip bonding. Furthermore, a novel rapid solver, for extracting the pull-in parameters of the L2DOF model of the torsion actuators, is proposed. The proposed solver is based on a Newton-Raphson scheme and the recently presented DIPIE algorithm and is shown to be /spl sim/10 times faster than the prevalent voltage iterations based solvers. The rapid and more accurate pull-in extraction of the proposed approach renders it as a tool for extensive analysis and design optimization of torsion actuators.

A novel micromachined vibrating rate-gyroscope with optical sensing and electrostatic actuation

Abstract This paper reports the fabrication and preliminary characterization of a novel vibratory rate-sensor. The sensor employs the modulated integrative differential optical sensing (MIDOS) to detect the output mode amplitude. The mechanical part of the sensor is fabricated by bulk micromachining using a double side anisotropic wet etching process. A CMOS chip containing the detecting photodiodes and their readout electronics is fabricated through MOSIS. Electrical and mechanical integration of the two parts is achieved by using the indium bumps technology. The proof mass is aligned with the detecting photodiodes, so that when at rest, equal portions of the two photodiodes are exposed. Several prototypes have been fabricated and tested on a rotating table. Good linearity (

Optimal performance of CMOS compatible IR thermoelectric sensors

This paper presents a theoretical and empirical study of the optimal performance of CMOS compatible infrared thermoelectric sensors with varying pixel area and different aspect ratio of the pixels for two possible sensor structures: cantilever and bridge types. Optimal performance is analyzed analytically, using simplifying assumptions. This analysis is verified by comparing with the exact simulations as well as by comparing with measured results. The resistance of optimized sensors in the sense of minimal noise equivalent power (NEP) is shown to be independent of aspect ratio, but proportional to the third root of the pixel area. The product of the optimal NEP and the square root of the time constant is shown to be constant with varying aspect ratios, while the same applies with the time constant to the power of 3/8 for varying areas. The measured sensors exhibit NEPs down to 13.5 nW in a 300-Hz bandwidth and time constants up to 30 ms.

A general relation between the ranges of stability of electrostatic actuators under charge or voltage control

Pull-in instability is a crucial effect in electrostatically-actuated microelectromechanical devices. This phenomenon was recently shown to occur under both voltage and charge control. So far, for all known cases, it has been shown that, under charge excitation, electrostatic actuators have a larger range of stability than under voltage excitation. No counter-examples are known, and whether this is a general rule for electrostatic actuators is an open question. In this work, a general proof is presented that shows this is indeed a fundamental rule for general electrostatic actuators.

A novel spiral CMOS compatible micromachined thermoelectric IR microsensor

A novel sensing structure and realization method is proposed for complementary metal-oxide semiconductor (CMOS) compatible thermoelectric uncooled infrared microsensors. The structure enables high sensitivity and excellent thermal isolation in sensor pixels with small dimensions suitable for two-dimensional thermal imaging. Front-side dry micromachining allows fast CMOS post-processing, small pixel pitch and integration with on-chip CMOS readout. Prototype sensors with an area of 70×70 µm2 achieved a measured noise equivalent power of 0.36 nW Hz-1/2 and a response time of 3 ms.

Characterization of a novel micromachined accelerometer with enhanced-MIDOS

This paper reports the successful realization of a novel micromachined accelerometer with a highly sensitive in-plane optical motion sensor. Two arrays of CMOS integrated photodiodes are used to detect the motion of a matching micromachined suspended grid. Sub-angstrom displacements of the suspended grid are detected by the integrated readout electronics that amplify and subtract the resulting photocurrents from each array. The device is fabricated by deep reactive ion etching (DRIE) and then flip-chip bonded on the CMOS chip. A preliminary prototype with a natural frequency of 2500[Hz] exhibited a noise equivalent acceleration (NEA) of /spl sim/40[/spl mu/g//spl radic/(Hz)] and a dynamic range >90[dB] with linearity <0.1%.