High Aspect Ratio Micromirrors With Large Static Rotation and Piston Actuation

A novel method for fabricating a self-aligned electrostatic vertical comb drive using a single layer of a SOI wafer is introduced. The fixed combs are anchored to bimorph cantilevers made of two materials with dissimilar thermal coefficient of expansion, i.e., silicon dioxide and single crystal silicon. The cantilever, which provides the vertical offset between fixed comb and movable comb, is deflected by residual stress during cooling down from oxidation temperature to room temperature. In piston motion, the vertical amplitude at the resonant frequency of 3.5 kHz was 30 /spl mu/m. In torsional motion, the angle of optical deflection at the resonance of 830 Hz was changed by 6.5/spl deg/. The measured resonant frequencies correspond to the results form a finite element analysis within 10%. This vertical comb drive is useful for optical and biophotonic MEMS requiring out-of-plane torsional or piston motion.

A CMOS-compatible magnetically actuated micromachined cantilever device is described. The structure employs the concept of nested cantilevers to enhance the angular deflection produced by Lorentz forces acting at the ends of each cantilever. Devices fabricated by two CMOS processes were tested. Static and dynamic bi-directional deflection responses were measured; static deflections of more than 2.5/spl deg/ and dynamic resonance deflections of 65/spl deg/ were obtained, Resonant frequencies were observed from 4.5 kHz to 56 kHz. Numerical simulations were performed and agree well with experiment.

A rotary pneumatic actuator for the actuation of the exoskeleton knee joint

In this paper, we present the design, fabrication, and measurements of a two-dimensional (2-D) optical scanner with electrostatic angular vertical comb (AVC) actuators. The scanner is realized by combining a foundry-based surface-micromachining process (Multi-User MEMS Processes-MUMPs) with a three-mask deep-reactive ion-etching (DRIE) postfabrication process. The surface-micromachining provides versatile mechanical design and electrical interconnect while the bulk micromachining offers high-aspect ratio structures leading to flat mirrors and high-force, large-displacement actuators. The scanner achieves dc mechanical scanning ranges of /spl plusmn/6.2/spl deg/ (at 55 Vdc) and /spl plusmn/4.1/spl deg/ (at 50 Vdc) for the inner and outer gimbals, respectively. The resonant frequencies are 315 and 144 Hz for the inner and the outer axes, respectively. The 1-mm-diameter mirror has a radius of curvature of over 50 cm. [1454].

Static and free vibration analyses of small-scale functionally graded beams possessing a variable length scale parameter using different beam theories

We describe a novel method for liquid crystal (LC) alignment using nano-patterns of electrically conductive indium–tin oxide (ITO) layers with high resolution (ca< 20 nm) and high aspect ratio (ca 10), fabricated based on the secondary sputtering phenomenon. The ITO pattern developed in this manner not only provides high anchoring energy comparable to that of rubbed polyimides, but also maintains its low resistivity as an electrode. As a result, the patterned ITO can function as an electrode and alignment layer at the same time, which facilitates successful fabrication of bifunctional conductive alignment layer for LC devices. The LC cells fabricated using patterned ITO substrates show highly stable alignment of LCs over large area and good electro-optical responses. Moreover, systematic approach made by the precise control of pattern dimensions allows us to estimate a critical anchoring energy required for an effective LC alignment based on Berreman's theory.

Fe–Ni invar alloy (Fe 64–Ni 36 wt%) has a very low coefficient of thermal expansion (CTE) than any other metals. For this reason, it has been used as fine metal mask (FMM) in RGB patterning of OLED manufacture process. However, as the resolution of OLED display is getting higher, the thickness of FMM is getting thinner and then the conventional extruded invar sheet cannot be used directly. The electrodeposition of invar can be the alternative for fabrication of thin FMM. In this study, the Fe–Ni alloy were electrodeposited varying bath compositions and current density. Also, the effects of ferric ion (Fe3+), produced during electrodeposition on inert anode, on the behavior of deposition were investigated. Finally, the Fe–Ni alloy with 36–40 wt% Ni were obtained at 50 mA/cm2 in 0.30 M Fe2+ bath. The back side and front side composition of the deposits were analyzed to evaluate the composition uniformity of the Fe–Ni alloys. Generally, the Fe content of back side of the deposits were higher than that of front side.Graphical

A closed macroscopic equation for the motion of the two-dimensional adiabatic piston is derived from standard hydrodynamics. It predicts a damped oscillatory motion of the piston towards a final rest position, which depends on the initial state. In the limit of large piston mass, the solution of this equation is in quantitative agreement with the results obtained from both hard disk molecular dynamics and hydrodynamics. The explicit forms of the basic characteristics of the piston's dynamics, such as the period of oscillations and the relaxation time, are derived. The limitations of the theory's validity, in terms of the main system parameters, are established.

Procedure for designing the wind tunnel model of a high aspect ratio (HAR) wing containing geometric nonlinearities is described in this paper. The design process begins with identification of basic features of the HAR wing as well as its design constraints. This enables the design space to be narrowed down and consequently, brings ease of convergence towards the design solution. Parametric studies in terms of the spar thickness, the span length and the store diameter are performed using finite element analysis for both undeformed and deformed cases, which respectively demonstrate the linear and nonlinear conditions. Two main criteria are accounted for in the selection of the wing design: the static deflections due to gravitational loading should be within the allowable margin of the size of the wind tunnel test section and the flutter speed of the wing should be much below the maximum speed of the wind tunnel. The findings show that the wing experiences a stiffness hardening effect under the nonlinear static solution and the presence of the store enables significant reduction in linear flutter speed.

The mechanism for changing selectivity in the process of plasma-chemical etching of the device layer of a micromechanical accelerometer has been studied to improve the manufacturing technology of inertial micromechanical devices, as well as to introduce methods and programs for the development and design of new products of microelectromechanical systems. The objects of study are surface structures formed by plasma etching of the device layer of a micromechanical accelerometer. A method is presented for calculating heat flows for deep reactive ion etching using the Bosch process as input parameters for modeling the heating process of the sensitive element of a micromechanical accelerometer. Finite element modeling of the heating process of the sensitive element of a micromechanical accelerometer makes it possible to determine the temperature of surface structures in the formed instrumental layer of the micromechanical accelerometer. Knowledge of the temperature for surface structures in the device layer of a micromechanical accelerometer is key for determination of the changes in the selectivity of the plasma etching process. The dependence of selectivity on time makes it possible to determine the minimum required mask thickness for the etching process, as well as the possibility of obtaining surface structures with the required geometric accuracy. An experimental study of changes in the mask etching rate during plasma etching of the device layer of a micromechanical accelerometer was carried out and the selectivity of the etching process was determined, as well as an assessment of the convergence with the modeling results. The etching rate of the mask was determined during the etching process using laser interferometry. The result of the study allows to identify the most optimal method of plasma etching of the device layer of a micromechanical accelerometer for the formation of precision surface structures with a high aspect ratio and the required geometric accuracy.

The flexible beam theory is widely applied in engineering, due to that many engineering structures can be regarded as flexible beam. For the flexible beam under large rotation, researches have shown that consideration of geometric nonlinearity is necessary: beam deflection will be erroneously larger or diverge without consideration of geometric nonlinearity. The reason lies on the dynamic stiffening effect caused by geometric nonlinearity. The dynamic stiffening effect of flexible beam under large rotation is well studied already, however, most studies only focus on flexible beam with constant cross section and rarely considers flexible beam without rotation. In view of this, a flexible beam with variable and twisted cross section is adopted to analyze the influence of geometric nonlinearity, and the response of flexible beam without rotation or static response is also analyzed. The results of dynamic beam deflection with and without consideration of geometric nonlinearity is compared, the results of static beam deflection under different load is also compared. On the basis of result comparison, the influence of geometric nonlinearity on static and dynamic response of flexible beam is then explained.

This study outlines active flight control materials, structural arrangements, and several new active flight control methods for rotorcraft, airplanes and missiles. A system-level comparison shows that flight control actuator systems using materials like piezoceramics have approximately double the mass-specific energy and 4 to 6 times the volume specific energy of conventional actuators. New fabrication techniques centered on the principal of directional attachment allow wings and rotor blades to become twist active. Using these new methods, directionally attached piezoelectric (DAP) actuator elements were built into graphite-epoxy sandwich structures. When compared to conventionally attached piezoelectric (CAP) elements, twist deflections (important for flight control) of DAP plates were an order of magnitude greater. By using such twist-active elements in a torque-plate configuration, an active helicopter rotor was built. This Froude-scaled solid state rotor was whirl-stand tested and showed steady blade pitch deflections in excess of plus or minus 8 degrees with good correlation between theory and experiment rates up to 42 Hz (which corresponded to 2.5/rev) and no degradation in deflection as RPM was increased. DAP elements were also used in high aspect ratio subsonic and supersonic wings, demonstrating static twist deflections of plus or minus 2 degrees and plus or minus 6 degrees respectively, with good correlation between experiment and finite element results. The final section compares all-moving active stabilator structural arrangements and pitch deflections, which range up to plus or minus 12 degrees, generating lift coefficient changes in excess of plus or minus 0.8.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

This paper reports on a new type of through-silicon via (TSV) defect, silicon fin defect, which was found after TSV deep-reactive-ion-etching (DRIE) process for TSV integration with front-end-of-line (FEOL) devices. One possible root cause for this defect is that the bulk micro defect (BMD) in silicon substrate serves as a micro-mask during etching and results in silicon fin defects at TSV bottom. These defects have to be eliminated as they are killer TSV defects for several reasons: (1) could serve as a weak point for isolation liner deposition; (2) could be a weak point for barrier/seed layer deposition; and (3) may cause mechanical failures during TSV backside reveal. Previously, silicon fin defects were removed by switching to a non-BMD silicon substrate for interposer application. However, for TSV integration with FEOL devices, the BMD layer serves as an intrinsic gettering layer for devices, therefore, it cannot be removed from the silicon substrate, which makes it challenging to get rid of silicon fin defects. In order to establish a non-destructive in-line detection method of the fin defects, scanning electron microscope (SEM) automatic process inspection (API) was set up to image the fin defects at the bottom of the trench. A special working point with high depth of focus (DoF) and contrast was created to obtain good top-down SEM imaging of the defects at the bottom of this high-aspect-ratio (HAR) structure. Three types of silicon substrates (A, B, and C) were used for this study to investigate the potential root cause. SEM API results show defect rates of 20%, 3.3% and 0% for substrates A, B, and C, respectively. This is in good agreement with both BMD simulation results and benchmarking data in which substrates A, B, and C had normalized BMD densities of 11.7, 5.74, and 1 cm-3, respectively, with a comparable BMD size of 80~90 nm and a denuded zone (DNZ) depth of 10~15 μm. The correlation between BMD density in a silicon substrate and silicon fin defect rate indicates that BMD is a key root cause for silicon fin defects. To eliminate silicon fin defects, an optimized DRIE process has been developed. On the same type of substrate, the DRIE process with a typical voltage bias results in a defect rate of 6.7%, while no silicon fin defect was detected out of 200 TSVs with a polynomial bias ramp to relatively higher final voltage bias during the last 15 μm etch. The hypothesis is that higher voltage bias is able to sputter away BMD and shows potential to get rid of the silicon fin defects at the TSV bottom. In summary, a capable inspection method, a preferred silicon substrate with BMD spec range, and a promising way for DRIE process optimization to eliminate the silicon fin defect at the TSV bottom have been identified and developed in this work. Detailed results and analysis, particularly the fin defect images, statistical inspection results, BMD benchmarking data, simulation results, and TSV profile with optimized process will be discussed in the paper.

Three-dimensional (3D) integration wherein multiple layers of planar devices are stacked and interconnected using through silicon vias (TSV). This technology offers great potential improvement over the traditional 2D planar integrated circuits by many ways. A key issue in 3D integration is fabricating ultrathin wafer with TSV. This paper presents a method to fabricate ultrathin wafer by a locally selective thinning technique. Deep reactive ion etching (DRIE) has been utilized to thin the wafer and to prepare the high aspect ratio vias, which are filled with copper by using bottom-up electroplating technique. This method simplifies the fabricating process of ultrathin wafer, comparing to the conventional technology, which grinds the whole wafer with temporary supporting substrate. The surface of thinned wafer has been examined by shadow moiré co-planarity measuring system and the result is acceptable for following bonding process. The experimental results verify the feasibility of proposed method.

High temperature durability of back side metallization layers for power devices