This PDF file contains the editorial “How does a reviewer make a difference?” for JM3 Vol. 8 Issue 03

We report on a comparison between a full-physical resist model that was calibrated to experimental line/space (L/S) critical dimension (CD) data under the flat-mask (also called "thin-mask" or "Kirchhoff") approximation with the model obtained when using a mask 3-D calculation engine (i.e., one that takes into account the mask-topography effects). Both models were tested by evaluating their prediction of the CDs of a large group of 1-D and 2-D structures. We found a clear correlation between the measured-predicted CD difference and the magnitude of the mask 3-D CD effect, and show that the resist model calibrated with a mask 3-D calculation engine clearly offers a better CD predictability for certain types of structures.

This PDF file contains the editorial “Guest Editorial: Reliability, Packaging, Testing, and Characterization of MEMS and MOEMS” for JM3 Vol. 8 Issue 03

Parameters such as dimensions, edge parallelism, and edge defect are important in separating good rectangular bars from bad ones. This work proposes a Fourier-optics-based noninvasive quality assessment tool for a rectangular bar ranging from a few micrometers to submillimeters thick. Our design concept relies on a transmissive optical architecture to reduce the effect of an object's angle misalignment that can introduce a significant measurement error. From the far-field diffraction pattern of the bar, the thickness of the bar can be determined from the distance between the two adjacent diffracted order beams. In addition, because all diffracted order beams are aligned, we use the resulting slope to determine edge parallelism. The amount of edge defect on the sample can be investigated by evaluating the distribution of the optical intensity inside diffracted order beams. Our experiment using a 635-nm wavelength laser diode, a 150-mm focal length lens, and an image sensor with 8.4-µm pixel pitch for 22 sample bars with an average thickness of 238 µm shows that our approach can simultaneously evaluate the thickness and the edge parallelism of the bar samples, as well as distinguish nicely edged bars from poorly edged bars. Other key features include low cost, ease of implementation, robustness, and low component counts.

The sensitivity of microelectromechanical system (MEMS) devices to radiation is reviewed, with an emphasis on radiation levels representative of space missions rather than of operation in nuclear reactors. As a purely structural material, silicon has shown no mechanical degradation after radiation doses in excess of 100 Mrad. MEMS devices, even when excluding control/readout electronics, have, however, failed at doses of only 20 krad, though some devices have been shown to operate correctly for doses greater than 10 Mrad. Radiation sensitivity depends strongly on the sensing or actuation principle, device design, and materials, and is linked primarily to the impact on device operation of radiation-induced trapped charge in dielectrics. MEMS devices operating on electrostatic principles can be highly sensitive to charge accumulation in dielectric layers, especially for designs with dielectrics located between moving parts. In contrast, thermally and electromagnetically actuated MEMS are much more radiation tolerant. MEMS operating on piezoresitive principles start to slowly degrade at low doses, but do not fail catastrophically until doses of several Mrad. A survey of all published reports of radiation effects on MEMS is presented, as well as a summary of techniques that can improve their radiation tolerance.

This study focuses on the design, simulation, fabrication, and test of the in-plane microgenerator to obtain a high-power output. The microgenerator comprises multilayer planar silver (Ag) microcoil of low-temperature cofired ceramics (LTCC) and multipole hard magnet of Nd/Fe/B (neodymium, iron, and boron). The LTCC process is an approach that saves costs and time to fabricate the microcoil. The multipole hard magnet of Nd/Fe/B provides the large magnetic energy product to contribute to the power. Finite element simulations have been carried out using COMSOL Multiphysics® to observe electromagnetic information. The induced voltages of coils in different basic geometric shapes, including square-shaped coils, circle-shaped coils, and sector-shaped coils, are simulated separately in this study. A prototype of the microgenerator is <1 cm³ in volume size. The simulated result can be compared to the experimental one. The results of simulation reveal that this microgenerator with a sector-shaped microcoil generates a maximum effective value of the induced voltage of 232.7 mV and the power of 2.5 mW. And the 1-µm gap between the microcoil and the magnet achieved is the value that is mentioned above. Experimental measurement shows close agreement with finite element simulations.

An experimental study of the dc breakdown voltage for planar MEMS interdigitated aluminum electrodes with gaps ranging from 10 to 500 µm is presented. Unlike most research on the breakdown in MEMS electrodes that was performed at atmospheric pressure, this work focuses on the effect of gas pressure and gas type on breakdown voltage, because this is central for chip-scale plasma generation and for reliable operation in aerospace applications. The breakdown voltage is measured in helium, argon, and nitrogen atmospheres for pressures between 10² to 8.10⁴ Pa (1 to 800 mbar). For higher values of the pressure P, or of the gap d (i.e., for high values of the Paschen reduced variable P_red=P·d), classical Paschen scaling is observed. For lower values of P_red, however, significant deviations are seen: the V_bd versus. Pd curve shows an extended flat region rather than a narrow dip. These differences cannot be attributed to field emission, but are due to the many length scales effectively present in a planar geometry (on-chip and even off-chip) that leads to the superposition of several Paschen curves. Guidelines are formulated for low-pressure operation of MEMS to avoid or encourage breakdown.

A 440-MHz wireless and passive surface acoustic wave (SAW) microsensor was developed for simultaneous measurement of CO₂ and relative humidity (RH). The developed SAW microsensor was composed of SAW reflective delay lines structured by an interdigital transducer (IDT) and several shorted grating reflectors, CO₂, and water vapor-sensitive films. A theoretical model was established to predict the response mechanism of the polymer-coated SAW gas sensor. Infusion of CO₂ into the chamber and humidity changes induced large phase shifts in the reflection peaks. Good linearity and repeatability were observed in the CO₂ concentration of 0~400 ppm and 20~80% RH. The obtained sensitivity was ~2° ppm⁻¹ for CO₂ detection and 7.45°/%RH for humidity sensing. Temperature and humidity effects were also investigated during the sensitivity evaluation process.

Key types of microelectromechanical systems (MEMS) sensors need vacuum or other controlled ambients in order to operate properly. Examples include MEMS infrared sensors and sensitive MEMS gyros. Steps to attain and maintain the vacuum ambient include: (i) Proper processing to reduce trapped gasses in the package, (ii) hermetically sealing the package, and (iii) providing a means to pump away gasses that outgas into the package. Proper package processing and getter technology are key to success in this endeavor. Although many aspects of package processing and assembly are proprietary, the key items to control include leaks (i.e., obtaining a hermetic package) and outgassing from materials within the vacuum cavity. Once gas loads are minimized as much as possible, the actual service life of a package depends on pumping away any internal gases built up through outgassing, leaks, or permeation. This pumping is done by a class of materials called getters. Gettering technology is discussed in relation to vacuum-packaged MEMS/MOEMS. With proper materials and processes, controlled ambients to include vacuum can be obtained in MEMS/MOEMS packages. Not only can they be obtained, they can be maintained for the desired system lifetime.

We present the progress in the development of a 4096-element microelectromechanical systems (MEMS) deformable mirror, fabricated using polysilicon surface micromachining manufacturing processes, with 4 µm of stroke, a surface finish of <10 nm rms, a fill factor of 99.5%, and a bandwidth of >5 kHz. The packaging and high-speed drive electronics for this device, capable of frame rates of 22 kHz, are also presented.

The deposited thin films in surface micromachining have a lot of residual stress, and it is essential to measure this for both process development and monitoring. We estimate residual stress by electrical measurements on a series of fixed-fixed polysilicon beams designed to deflect laterally due to stress. To minimize errors in estimation during parameter extraction, the device dimensions also have to be measured accurately. Surface micromachining of an oxide-anchored polysilicon cantilever beam can result in beam undercut, reduction in beam thickness, and increase in the gap between the beam and the substrate. The undercut in the beam is estimated from the resonance frequency of the cantilever beam and also by using polysilicon resistors. Final device thickness is obtained by measuring the resistance in fixed-fixed beams.

This PDF file contains the editorial “Guest Editorial: Computational Lithography” for JM3 Vol. 8 Issue 03

To support the successful implementation of extreme ultraviolet (EUV) lithography for high volume manufacturing, a spectrum of simulation tools is needed. For investigation of new materials and geometries, rigorous but computationally expensive simulations are required. For faster simulations, a new method, rapid absorber defect interaction computation for advanced lithography (RADICAL), is introduced. RADICAL is a modular program, that uses separate methods to simulate the absorber pattern and defective multilayer. Two different methods are used to simulate the multilayer within RADICAL: ray tracing and single surface approximation (SSA). Ray tracing can accurately simulate arbitrary multilayer geometries. SSA is only accurate for defects shorter than 4.5 nm on the multilayer surface. With ray tracing, RADICAL is nearly 1000 times faster than finite difference time domain (FDTD) for simulating line-space patterns over buried defects. RADICAL with SSA is nearly 25,000 times faster than FDTD. The accuracy of RADICAL is shown to be excellent for simulating defects in focus, and for simulating defects smaller than 2.5 nm through focus. The error can be as high as 4 nm in predicting CD change for larger defects out of focus due to the complexities of modeling the phase of buried defects. But this error is predictable and will likely be acceptable for most applications considering the huge speed advantages of RADICAL.

We apply a newly developed parallel generalized eigen-oscillation spectral element method (GeSEM) for rigorous simulations of 2-D phase-shift masks (PSMs). The GeSEM combines highly parallel Schwarz-domain decomposition iterations and an eigen-oscillation-based spectral method to model high-frequency oscillatory electromagnetic fields in PSMs with dispersive chrome materials in the PSMs. The performance of the GeSEM has been compared to the popular plane wave-based waveguide method for 2-D masks. The numerical results have clearly demonstrated the GeSEM's advantages in modeling the effects of nonperiodic structures such as optical images near mask edges, and its speedup through parallel implementations, which makes the simulation of a large-scale mask possible in whole-chip mask modeling.

We introduce the new concept of orientation Zernike polynomials, a base function representation of retardation and diattenuation in close analogy to the wavefront description by scalar Zernike polynomials. We show that the orientation Zernike polynomials provide a complete and systematic description of vector imaging using high numerical aperture lithography lenses and, hence, a basis for an in depth understanding of both polarized and unpolarized imaging, and its modeling.

We analyze the uniqueness of the solutions of inverse lithographical problems, stated as optimization problems, and optical images. By considering a band-limitedness argument, examples of ill-posed problems are constructed with multiple solutions in the domain of real non-negative passive masks. We conclude that the necessary condition for the solution m to be unique is to touch (or to pass infinitely close to) the boundary of the constraint 0 ≤ m ≤ 1. In the domain of binary masks, we propose a procedure to construct two nonunique solutions from a possibly unique one. We prove the existence of unique binary solutions in some class of optical systems and suggest a thresholding procedure to generate a unique solution from a possibly nonunique one.

We present the basic concept of a fast mask optimization method that utilizes target-intensity back propagation. This method decomposes the target-intensity using a two-dimensional (2-D) transmission cross coefficient. After applying normal incidence approximation to the decomposed target intensity, the spectrum of the mask is optimized in the pupil plane. Since the optimization is performed in the pupil plane, one can use relatively small sampling points, leading to a fast optimization. By setting a high-contrast target intensity, we can obtain an approximation of a phase shifting mask, whereas a low-contrast target intensity approximates a binary intensity mask or attenuated phase shifting mask.

In photolithography, aerial image simulation of the mask has become mandatory. To compute aerial images, transmission cross coefficients (TCCs), drawn from Hopkins optical system transmission function, are arranged as a four-way array (four-entry table) called a fourth-order tensor. To estimate the kernels using the linear algebra-based methods, the existing algorithms unfold this tensor into a matrix. To reduce the computational load, this matrix is approximated by lower rank order matrix owing to the singular value decomposition (SVD). We propose to adopt the multilinear algebra tools to the tensor of TCC values in order to keep this data tensor as a whole entity. For runtime improvement, we use a fixed point algorithm to estimate only the needed eigenvectors. To estimate the optimal number of needed eigenvectors, two well-known criteria of signal processing and information theory are adopted. This tensorial approach leads to a fast and accurate algorithm to compute aerial images.

The concepts of dynamical scaling in the study of kinetic roughness are applied to the problem of photoresist development. Uniform, open-frame exposure and development of photoresist corresponds to the problem of quenched noise and the etching of random disordered media and is expected to fall in the Kadar-Parisi-Zhang (KPZ) universality class. To verify this expectation, simulations of photoresist development in 1+1 dimensions were carried out with random, uncorrelated noise added to an otherwise uniform development rate. The resulting roughness exponent α and the growth exponent β were found to match the 1+1 KPZ values exactly.

In this paper we study interactions of double patterning technology (DPT) with lithography, optical proximity correction (OPC) and physical design flows for the 22-nm device node. DPT methods decompose the original design intent into two individual masking layers, which are each patterned using single exposures and existing 193-nm lithography tools. Double exposure and etch patterning steps create complexity for both process and design flows. DPT decomposition is a critical software step that will be performed in physical design and also in mask synthesis. Decomposition includes cutting (splitting) of original design intent polygons into multiple polygons, where required, and coloring of the resulting polygons. We evaluate the ability to meet key physical design goals, such as reduce circuit area, minimize relayout effort, ensure DPT compliance, guarantee patterning robustness on individual layer targets, ensure symmetric wafer results, and create uniform wafer density for the individual patterning layers.

The most accurate width measurements in a scanning electron microscope (SEM) require raw images to be corrected for instrumental artifacts. Corrections are based on a physical model that describes the sample-instrument interaction. Models differ in their approaches or approximations in the treatment of scattering cross sections, secondary electron generation, material properties, scattering at the surface potential barrier, etc. Corrections that use different models produce different width estimates. We have implemented eight models in the Java Monte Carlo simulator for secondary electrons (JMONSEL) SEM simulator. Two are phenomenological models based on fitting measured yield versus energy curves. Two are based on a binary scattering model. Four are variants of a dielectric function approach. These models are compared to each other in pairwise simulations in which the output of one model is fit to the other by using adjustable parameters similar to those used to fit measured data. The differences in their edge position parameters is then a measure of how much these models differ with respect to a width measurement. With electron landing energy, beam width, and other parameters typical of those used in industrial critical dimension measurements, the models agreed to within ±2.0 nm on silicon and ±2.6 nm on copper in 95% of comparisons.

We investigate a novel nanofabrication process called soft ultraviolet (UV) nanoimprint lithography (NIL), for nanopatterning of compound semiconductors. We use flexible stamps with three layers and analyze their performance with wafers composed of III-V semiconductors. The developed stamp configuration is in many ways advantageous for the fabrication of precise gratings for various applications in photonics. We describe how to handle the deformation in both lateral and vertical directions by tuning the softness of the stamp and using a two step imprint process. As an application of the UV-NIL, we demonstrate a fabrication process for a laterally corrugated distributed feedback laser. Our laser fabrication process is free from regrowth and therefore easily adaptable to various material compositions and emission wavelengths. Because of the cost-effective full-wafer NIL, these lasers are attractive in various applications where low-cost, single-mode laser diodes are required. Our development work improves the design freedom of the NIL fabrication process of the laser diodes and improves the quality of the transferred patterns. To the best in our knowledge, this is the first demonstration of a single-mode laser diode fabricated by soft UV-NIL.

We discuss the methodology of physical resist model calibration for a rigorous lithography simulator under various aspects and assess the resulting predictive accuracy. The study is performed on an extensive optical proximity correction (OPC) dataset, which includes several thousands of critical dimensions (CDs) values obtained with immersion lithography for the 45-nm half-pitch technology node. We address practical aspects such as speed of calibration versus size of calibration dataset, and the role of pattern selection for calibration. In particular, we show that a small subset of the dataset is sufficient to provide accurate calibration results. However, the overall predictive power can strongly be enhanced if a few critical patterns are additionally included into the calibration dataset. Also, we demonstrate a significant impact of the illumination source shape (measured versus nominal top hat) on the resulting model quality. Most importantly, it is shown that calibrated resist models based on a 3-D (topographic) mask description perform better than resist models based on a 2-D (Kirchhoff) mask approximation. Also, we show that a resist model calibrated with one-dimensional (lines and spaces) structures only can successfully predict the printing behavior of two-dimensional patterns (end-of-line structures).

Optical immersion lithography using fluids with refractive indices greater than that of water (1.436) can enable numerical apertures of 1.55 or above for printing sub-45-nm lines. Two second-generation immersion fluid candidates, IF132 and IF169, both have indices above 1.64 and have been optimized to absorb less than 0.1 cm⁻¹ at 193.4 nm. These fluids, although meeting the requirements of index and absorption, must also be compatible with current resists and processes to image the required fine line patterns. Results of fluid-resist interactions, with water and high-index fluids on four commercial resists, are shown. Photoacid generator (PAG) leaching measurements reveal much less leaching into both high-index fluids than into water, and in two water-immersion dedicated resists, no leaching is detected with the high-index immersion fluids. Little resist thickness change and swelling is detected by a quartz crystal microbalance (QCM) on contact with the fluids. Resist profile and line height changes due to pre- and postexposure fluid contact varies from one resist to the next, but overall the changes are minimal. Misting defects from high-index fluid-resist contact show lower counts than for water, and imaging on an immersion interference printer produces 36-nm half-pitch lines. We find no serious impediments to the use of high-index liquids based on these results.

We have constructed a hotspot management flow and applied the flow to large-scale integration (LSI) manufacturing in the ultralow k1 lithography era. This flow involves three main management steps: hotspot reduction, hotspot extraction, and hotspot monitoring. Hotspot reduction works with lithography-friendly restricted design rule (RDR) and manufacturability check (MC). Hotspot extraction is carried out with a view to realizing short operation time and accurate extraction. Hotspot monitoring is achieved with tolerance-based verification in the mask fabrication process and wafer process (lithography and etching). These technology elements could be integrated into the LSI fabrication flow for reduction of total cost, quick turnaround time (TAT), and ramp-up to volume production. In addition to discussion of the technology elements in hotspot management, we also provide typical applications for important decisions in LSI fabrication: photomask availability for any exposure tools ("exposure tool yokoten") and process condition updates in LSI fabrication.

According to the International Technology Roadmap for Semiconductors 2008 (http: www.itrs.net) overlay error should be controlled under 12 nm for sub-60-nm memory devices. To meet such a tight requirement, lot-to-lot high-order wafer correction (HOWC) and per-shot correction (PSC) is evaluated for the gate and contact layers of dynamic random access memory. A commercial package is available from scanner makers, such as ASML, Canon, and Nikon. In this study, HOWC is investigated for wafer correction, whereas PSC is considered for scan direction-dependent overlay correction. Experimental results verify 1-3 nm of overlay improvement by applying HOWC. However, the amount of improvement is layer (process) dependent. It turned out that HOWC is not an overall solution. It should be applied carefully for certain process conditions. In addition, if scan direction is different (mixture of up, down, left, right) due to wafer stage routing path, then overlay performance could be degraded. To solve this problem, PSC is also evaluated. Detailed experimental results are discussed.

Ni films, replacing photoresists, serve as masks in the selective deposition of optical thin films by electron-beam gun evaporation at a substrate temperature of 300°C. Photolithography is adopted herein to define the growth of Ni films by electroforming. Mosaic patterns with a width of 20 µm are employed as red color filters, which are longwave pass. These red filters are formed from alternate SiO₂ and TiO₂ layers and have a mean transmittance of >90%. The experimental results show that the combined use of photolithography, electroforming, and electron-beam gun evaporation can deposit miniaturized multilayer dielectric coatings with high light transmittance in a hot process.

We demonstrated fabricating a needle array of polycarbonate (PC) and polymethyl methacrylate (PMMA) by using a 3-D LIGA (lithografie, galvanoformung, abformung) process. The diameter of the bottom of the needle was about 50 µm, and the height was 135 µm. Although the LIGA process is commonly applied for making structures with vertical sidewalls, the use of an x-ray grayscale mask in the LIGA process has made it possible to fabricate needle-shaped structures. The x-ray grayscale mask was composed of a Si x-ray absorber and an SU-8 membrane. The sidewall of the x-ray absorber was diagonally processed by Si tapered-trench-etching technology such that the transmission intensity of x rays could be changed locally. The x-ray lithography experiment was executed by using this x-ray grayscale mask on a beamline BL-4 in the TERAS synchrotron radiation facility at National Institute of Advanced Industrial Science and Technology (AIST). By using this facility, a PMMA resist master with three-dimensional (3-D) structures was made. A Pt layer was then sputter-deposited as a seed layer on the PMMA resist master, and a Ni mold was fabricated by electroforming technology. In addition, a needle array of PC and PMMA was produced by hot embossing technology. Self-assembled monolayers (SAMs) of a release agent were required on the surface of the mold pattern to achieve a complete molding. Thus, we succeeded in extending the LIGA process to three dimensions by the use of an x-ray grayscale mask.

We report the development of a silicon microelectrode array for brain machine interfaces and neural prosthesis fabricated in a commercial microelectromechanical systems (MEMS) process. We demonstrate high-aspect ratio silicon microelectrodes that reach 6.5 mm in length while having only 10 µm thickness. The fabrication of such elongated neural microelectrodes could lead to the development of cognitive neural prosthetics. Cognitive neural signals are higher level signals that contain information related to the goal of movements such as reaching and grasping and can be recorded from deeper regions of the brain such as the parietal reach region (PRR). We propose a new concept of reinforcing the regions of the electrodes that are more susceptible to breakage to withstand the insertion axial forces, retraction forces, and tension forces of the brain tissue during surgical implantation. We describe the design techniques, detailed analytical models, and simulations to develop reinforced silicon-based elongated neural electrodes. The electrodes are fabricated using the commercial MicraGem process from Micralyne, Inc. The use of a commercial MEMS fabrication process for silicon neural microelectrodes development yields low-cost, mass-producible, and well-defined electrode structures.

The influence of backside illumination and temperature on the fabrication of large and high aspect ratio silicon microchannel plates (MCPs) by photoelectrochemical (PEC) process is described. Backside illumination is provided by three 150-W tungsten halogen lamps with a feedback loop, keeping a constant current density. The etching temperature is maintained by a circulation system. Proper backside illumination and the lower temperature can provide better integrated etching conditions compared to that without illumination and temperature control. Etching under the improved conditions results in smoother undercutting and better surface topography for large (effective diameter of about 80 mm for 4-inch silicon substrates) silicon microchannel plates. Enhancing the backside illumination within the etching temperature range ensures that the aspect ratio is more than 40, boding well for applications of silicon microchannel plates.

We examine the necessary technologies to be mastered in order to build a practical microarray-based immunoassay cassette and its processing station for protein analysis. The interdependence of surface chemistry, dye stability, and imaging are outlined, showing why a treated 100-nm film of nitrocellulose adhered by an intervening layer to glass offers an efficacious surface for immobilizing an array of protein probes. The properties of a storage surface to support in desiccated form, fluidize and transport additional reagents are outlined, and a practical solution proposed. Wet and dry imaging are compared. The steps and functions expected for an assay platform comprising a processing station and biochip cassette are identified. The performance of a successful benchtop automated multiplex immunoassay system is briefly described.

In order to implement cell surgery on a chip-based system, we have been developing microneedle arrays capable of introducing desired biomolecules (nucleic acids, proteins, etc.) into living cells and the parallel extracting biomolecules expressed in the cells. An array of hollow silicon dioxide (SiO₂) microneedles with a sharp tip radius of less than 0.5 µm was successfully fabricated by using a micromachining technique. In order to investigate the mechanical stability of fabricated microneedle arrays, insertion tests with a gelatin as an artificial cell were performed. The results indicated that the microneedles are expected to be sufficiently stiff to insert into living cells without fracture. In addition, bending behavior was characterized by both finite element method (FEM) analysis and experimental fracture test. Needle insertion performance into gelatin was also evaluated. The displacement required for needle insertion increased linearly with an increase in surface area at the needle tip, resulting in the relative value of estimated insertion stresses being approximately constant. Moreover, the results showed that the mechanical oscillation with an amplitude of 0.6 µm was effective and that increasing oscillation frequency decreased remarkably the displacement probably due to an increase in the viscous resistance of a viscoelastic material.

We propose an approximate analytical solution to the pull-in voltage of a microcurled cantilever beam. The analytical model considers the realistic situations, which include stress gradient, nonideal boundary conditions, and fringing field capacitance. The proposed analytical model can be used at wafer level for extracting the Young's modulus of the thin film of which the cantilever beam is made. The approximate analytical solution is obtained based on the Euler's beam model and the minimum energy method. The accuracy of the proposed model is verified to be more accurate than the other published models. The model presented in this work can be used for wafer-level evaluation of the material properties through simple electrical testing and is also expected to find use in the design of microelectromechanical devices.

The vertical comb electrodes capacitive sensor (VCECS) has been widely used in inertia sensors, resonant sensors, and pressure sensors, etc. In this paper, we present an improved microspring, called a W-form spring, that provides a large stiffness ratio in an out-of-plane direction while retaining a long sensing range for a VCECS. The stiffness ratio, defined as the ratio of the stiffness in the lateral direction to the out-of-plane direction, is an important parameter for determining the stability of the VCECS. To realize the properties of the W-form spring, such as the spring constant and stiffness ratio, theoretical analysis and numerical simulations are performed. In addition, VCECSs with W-form and other springs have been fabricated using microelectromechanical systems (MEMS) micromachining technology. The spring constants of the sensor have been calculated from simulations and measured results. The characteristics among different suspension springs are compared. According to the numerical simulations and experiment results, the working range and stability of the device are both improved for the VCECS by using the W-form suspension spring.

The effect of residual stress on the nanoindentation property of Si/C/Si multilayers has been investigated. Sandwiched Si/C/Si multilayers were deposited on Si(100) substrates by means of ultrahigh-vacuum ion-beam sputtering at room temperature (RT). Four structures with different Si top-layer thickness of 5, 10, 25, and 50 nm and the constant thickness of C/Si underlayer at 100/50 nm were investigated in this study. The residual stress of the Si/C/Si (5/100/50 nm/nm/nm thick) film was about −17.76 GPa under compression, and its hardness was 20.39 GPa at RT. The compressive residual stress was decreased to −5.54 GPa with the increased thickness of Si toplayer up to 50 nm, and its hardness was reduced to ~16.22 GPa at RT. The effect of Si top-layer thickness (5-50 nm) on Si/C/Si residual stress on the nanoindentation property were also discussed. The results showed that the thicker was the Si toplayer, the lower was the residual stress and hardness, which was good for the suppression of the buckling or wrinkling in the C/Si-nanocomposite film.

Implementing the capability to perform fast ignition experiments, as well as, radiography experiments on the National Ignition Facility (NIF) places stringent requirements on the control of each of the beam's pointing and overall wavefront quality. One quad of the NIF beams, four beam pairs, will be utilized for these experiments and hydrodynamic and particle-in-cell simulations indicate that for the fast ignition experiments, these beams will be required to deliver 50% (4.0 kJ) of their total energy (7.96 kJ) within a 40-µm-diam spot at the end of a fast ignition cone target. This requirement implies a stringent pointing and overall phase conjugation error budget on the adaptive optics system used to correct these beam lines. The overall encircled energy requirement is more readily met by phasing of the beams in pairs but still requires high Strehl ratios and root-mean-square tip/tilt errors of approximately 1 µrad. To accomplish this task we have designed an interferometric adaptive optics system capable of beam pointing, high Strehl ratio, and beam phasing with a single pixilated microelectromechanical systems deformable mirror and interferometric wavefront sensor. We present the design of a testbed used to evaluate the performance of this wavefront sensor along with simulations of its expected performance level.

Although solid-state microreference electrodes (µREs) have been developed for electrochemical and biomedical sensing applications for more than one decade, there are very few studies devoted to improving their performance through packaging. Using planar technology and a silicon cap sealing method, we implement a packaged Ti/Pd/Ag/AgCl/KCl-gel µRE with a total dimension of only 9 mm (L)×6 mm (W)×1 mm (H), a hundredfold less than the commercial Ag/AgCl reference electrode (RE). Compared with the unpackaged µRE, the presented chip-level packaged µRE demonstrates many improved characteristics, including a very stable cell potential (5-mV drift voltage in 30,000 s), an approximately zero offset voltage (−7 mV), a very low impedance (1.50 kΩ) and phase shift (8.98 deg) at 1-kHz operation frequency, a very small double-layer capacitance (0.04 µF), and a very high reproducibility (±3.1-mV).

Whispering-gallery (WG) modes in photonic microdevices made of dielectric circularly planar resonators are analyzed. The wave equation is solved by using the method of separation of variables based on the eigenvalue technique. The resonant frequency at an azimuthal mode is decided by iteration using the bisection method based on the continuity conditions at the resonator peripheral boundary. The radial mode is determined by the critical points of the field intensity profile in the radial direction via the first derivative test. The resonance frequencies as well as the E-field distributions in two exemplary small resonators are presented for a variety of modes. Comparison with numerical predictions is conducted, and a good agreement is found. The geometric optics method is found inappropriate for small resonators.

Since porous silicon (PS) has a much lower Young's modulus than single crystalline silicon, Si/PS composite membranes deflect more and can be used to fabricate pressure sensors with improved sensitivity. However, PS has some drawbacks, like weaker structural stability and being more susceptible to humidity due to its large surface-to-volume ratio. We discuss the fabrication and testing of Si/PS composite membrane pressure sensors with MicroPS and MacroPS of varying porosity. For the same porosity, the composite membranes with Si/MicroPS show higher sensitivity than Si/MacroPS. The sensor output is linear and repeatable at pressures less than 1 bar. The deformation of composite membranes measured up to 10 bar showed that it saturates at high pressure and is irreversible. Composite membranes also exhibit higher offset voltage than single crystal silicon membranes, which could be attributed to the stress developed in the membrane during PS formation and subsequent processing. The composite membrane pressure sensors were packaged on TO 39 headers, and the effect of humidity and temperature variation were investigated.

We have reported a novel optical sensor based on whispering gallery mode (WGM) resonance for measuring thermal deformation in microelectromechanical systems (MEMS) devices. New asymptotic expressions for transverse electric and transverse magnetic waves are developed based on electromagnetic theory derivations for the large size parameter (π times diameter divided by wavelength of light) limits. The optical thermal deformation sensor is characterized both theoretically and experimentally by considering the fact that the size parameter of the microspheres is very large at optical wavelengths. As a prototype thermal deformation sensor, an optical fiber experimental setup with tunable laser diode has been used for realizing the effect of WGM resonances due to change in surrounding temperature of a dielectric microsphere made of BK-7 glass. The quality factor of experimental resonance spectra observed in the laboratory is calculated approximately on the order of 10⁴, which is sensitive enough for detecting micro or nano level deformation changes in the surrounding medium. The novel optical sensor can measure the thermal deformation in the MEMS devices as small as the submicron or nanometer level. This sensor could potentially be used for nanotechnology, MEMS devices, biomedical applications, and other microdevices.

We present the control of magnetostriction and magnetization of the magnetostrictive thin film via additional electric field with original low magnetic field for microelectromechanical systems (MEMS) application. To examine the electric field effect on the magnetostrictive thin film deposited on each substrate, Si and polyimide (Kapton, Dupont Corp.) substrates are used. During the measurement of magnetization and magnetostriction, 0-to 50-V electric fields are applied under 0.5-T magnetic fields. As a result, 3% of magnetostriction is enhanced compare with no electric field.