Y. Nemirovsky

Pull-in study of an electrostatic torsion microactuator

Pull-in study of an electrostatic microactuator is essential for making the electrostatic actuation more effective. In this paper, pull-in analysis is presented for an electrostatic torsion microactuator. The torsion microactuator can be used as a microtorsion mirror. A polynomial algebraic equation for the pull-in voltage and pull-in angle of a torsion microactuator is derived. Two types of microactuators fabricated using bulk micromachining are presented. Measurements done on the fabricated microactuators are reported, showing deviations within 1% error from the calculations.

A methodology and model for the pull-in parameters of electrostatic actuators

This paper presents a generalized model for the pull-in phenomenon in electrostatic actuators with a single input, either charge or voltage. The pull-in phenomenon of a general electrostatic actuator with a single input is represented by an algebraic equation referred to as the pull-in equation. This equation directly yields the pull-in parameters, namely, the pull-in voltage or pull-in charge and the pull-in displacement. The model presented here permits the analysis of a wide range of cases, including nonlinear mechanical effects as well as various nonlinear, nonideal, and parasitic electrical effects. In some of the cases, an analytic solution is derived, which provides physical insight into how the pull-in parameters depend upon the design and properties of the actuator. The pull-in equation can also yield rapid numerical solutions, allowing interactive and optimal design. The model is then utilized to analyze analytically the case of a Duffing spring, previously analyzed numerically by Hung and Senturia, and captures the variations of the pull-in parameters in the continuum between a perfectly linear spring and a cubic spring. Several other case studies are described and analyzed using the pull-in equation, including parallel-plate and tilted-plate (torsion) actuators taking into account the fringing field capacitance, feedback and parasitic capacitance, trapped charges, an external force, and large displacements.

1/f noise reduction of metal-oxide-semiconductor transistors by cycling from inversion to accumulation

A new experimental setup for the study of 1/ f noise of metal‐oxide‐semiconductor transistor under nonsteady state conditions is presented. The noise measurements demonstrate for the first time that, by interposing periods of negative bias corresponding to accumulation between the monitored periods of positive bias corresponding to inversion, the low‐frequency noise sampled in the positive bias intervals is reduced.

Infrared optical absorption of Hg1−xCdxTe

The absorption near the fundamental absorption edge of Hg1−xCdxTe was measured over the composition range 0.205⩽x⩽0.220 at temperatures from 80 to 300 K. The dispersion of the index of refraction of Hg1−xCdxTe was obtained from the interference pattern. It was found that the absorption tail obeys a modified Urbach’s rule and is expressed by α=α0 exp[σ (E−E0)/(T+T0)] for 20⩽α (cm−1) ⩽1000. The fitting parameters α0, σ, T0, and E0 vary regularly with x. The expression is used to obtain the absorption coefficient and the temperature coefficient of the gap as a function of x and T. Evidence is presented to show that these parameters may be extrapolated to calculate the absorption beyond the measured composition range.

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.

Passivation of mercury cadmium telluride surfaces

The practical aspects of HgCdTe surface passivation, as related to devices and applications, are reviewed. Currently used technologies are classified in two categories: thick deposited dielectrics and a two‐layer combination of a thin native film with a thick deposited dielectric film. The first category includes ZnS, low‐temperature photochemical vapor deposited SiO2 (photox), and electron cyclotron resonance plasma deposited SiNx. The second category includes anodic oxide, plasma oxide, photochemical native oxide, anodic sulfide, and anodic fluorides. The unique behavior of HgCdTe surfaces, metal‐insulator semicoductor structures, and gate‐controlled p–n junctions are reviewed. The surface requirements of HgCdTe devices of interest for present and next‐generation focal plane arrays are discussed in terms of the reviewed technologies.

1/f Noise in CMOS transistors for analog applications from subthreshold to saturation

Abstract Detailed noise measurements of the 1/ f noise in p - and n -mos transistors for analog applications are reported under various bias conditions ranging from subthreshold to saturation. The CMOS transistors under study have a relatively large area, exhibit long channel behavior and are fabricated in a commercial “low noise process”, as prescribed for analog applications. A clear methodology and useful models for the power spectral densities of the gate voltage and drain current are presented and are based on recent studies in sub-micron transistors that have established the physical origin of 1/ f noise in MOS transistors. In saturation, it is found that it is advisable to limit the bias voltages to values that are experimentally determined from the transconductance characteristics and correspond to a nearly constant channel mobility. The experimentally observed reduction in channel mobility indicates the existence of strong fields that induce additional oxide charging and hence an increase in the effective density of oxide traps and the noise. In the bias voltages where channel mobility is nearly constant, the measured input-referred noise power is practically constant. Below threshold voltage, a reduction is observed in the input-referred noise as gate voltage is decreased, corresponding to the prediction of the model and due to the exponential reduction of the inversion capacitance with gate voltage. This behavior is observed for both n -mos and p -mos transistors.

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.

Measurement of band offsets and interface charges by the C–V matching method

The present article describes a novel application of capacitance–voltage measurements to determine simultaneously the band discontinuities (ΔEV, ΔEC) and interface charge density (σ) of heterojunctions. The method, which we refer to as C–V matching, complements the most versatile C–V profiling technique proposed by Kroemer and successfully applied by others. In contrast to the C–V profiling which is limited to isotype heterojunctions, the new method is applicable to p-n heterojunctions as well. The methodology is based on three cardinal equations which are not controversial—the lineup of the bands relative to the common Fermi level (at equilibrium) or the quasi-Fermi levels (when voltage is applied), the charge neutrality and the expression for the total capacitance of the heterostructure. The three equations are formulated for equilibrium as well as nonequilibrium conditions, using quasi-Fermi levels and the quasi-equilibrium approximation. The three cardinal equations are defined by the two constant (al...

Design considerations of rectangular electrostatic torsion actuators based on new analytical pull-in expressions

An important design issue of electrostatic torsion actuator is the relative locations of the actuating electrodes, where the bias voltage is applied. These geometrical design parameters affect both the pull-in angle as well as the pull-in voltage. In this paper, a new approximated analytical solution for the pull-in equation of an electrostatic torsion actuator with rectangular plates is derived. The analytical expression is shown to be within 0.1% of the one degree of freedom (1DOF) lumped-element model numerical simulations. Moreover, the analytical expressions are compared with the full coupled-domain finite-elements/boundary-elements (FEM/BEM) simulations provided by MEMCAD4.8 Co-solve tool, showing excellent agreement. The approach presented here provides better physical insight, more rapid simulations and an improved design optimization tool for the actuator.