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New lithographic, deposition, and etching tools for micro fabrication on planar silicon substrates have led to remarkable advances in miniaturization of silicon devices. However silicon is often not the substrate material of choice for applications in which there are requirements for electrically or thermally insulating substrates, low capacitance, resistance to corrosion, or hermetic sealing. Some of the MEMS packaging materials such as ceramics, polymers, and glass are currently being used to fabricate many microdevices. To support the rapid advancements of non-silicon MEMS it is necessary to introduce innovative techniques to process these MEMS packaging materials. In this study we present the application of pulsed laser ablation of ceramics, polymers and glass (MEMS packaging materials) to assist in fabrication of MEMS devices. Microstructuring of Al2O3 ceramic, polymers Poly-Vinyl-Alcohol (PVA), polystyrene (PS), and Pyrex glass were performed and studied by pulsed lasers at 193-nm, 266-nm and 308-nm wavelengths.© (2001) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The morphologies of Si surfaces are modified with single, tightly focused nanosecond laser pulses and characterized by atomic force microscopy (AFM). Dimple-shaped features with diameters $1--4 \ensuremath{\mu}\mathrm{m}$ and depths 1--300 nm are produced by varying the laser-spot diameter and the peak energy densities ${F}_{0}$ in the range $0.4l{F}_{0}l1.3 \mathrm{J} {\mathrm{cm}}^{\ensuremath{-}2}.$ Greater control of the depth of shallow dimples and quantitative comparison of theory and experiment is enabled by first removing the native oxide of Si with dilute HF acid. We develop approximate analytical solutions for two-dimensional fluid-flow driven by gradients in the surface tension; these solutions provide fundamental insight on how the morphology depends on laser parameters and the thermophysical properties of the melt and its surface. Quantitative comparisons between theory and experiment are enabled by using numerical simulations of heat flow in one-dimension as inputs to the analytical fluid-flow equations; we find good agreement with AFM data for the dimple shape and depth.

In this paper a parametric study on the excimer laser micromachining of silicon (Si) is conducted and a Michelson interferometer is used for the in-situ diagnostics of the machining depth on the sub-micron and micron scales. An excimer laser of wave length 308 nm is used for the micromachining process. A He-Ne laser of 632.8 nm wavelength is used as the light source for the interferometer and the setup consists of a beam splitter, beam expander and other optics. The interference patterns caused due to the change in the path length between the two interferometer arms gives the machined depth information. These interference patterns are captured by using a photodiode and an oscilloscope. Results from the interferometer are compared with the actual depth measurements obtained by using a surface profilometer in combination with an optical microscope. It is observed that the depths of machining obtained by the surface profile measurement are in accordance with the interferometer measurements with a very high accuracy. The experimental results demonstrate the feasibility of applying this system for the in-situ monitoring of the micromachining process.

Two polymer materials, PDLA and PVA, have been patterned by ultra-violet (UV) Excimer laser micromachining for biomedical applications. In this work, Parametric investigations were conducted for both PVA and PDLA polymers using a XeCl (Xenon-chloride) Excimer laser of 308 nm wavelength. Laser machined micro-patterns were examined by a high-resolution optical microscope. A surface profilometer was used to measure the actual depths of the micromachined patterns. Results show that it is much easier to pattern PVA than PDLA at 308 nm wavelength. The micro-channels show distinguished edges, indicating that thermal damage to the surrounding polymer is minimized.

This work investigates the transient process of melting and microscale surface deformation upon pulsed Nd:YLF laser heating of Ni-P hard disk substrates. The laser pulse energy is in the range of 1.0 (mu) J to 5.0 (mu) J. The features produced by laser heating have a diameter of approximately 15 micrometers and height in the tens of nanometers range. A laser flash photography system is developed to visualize the transient topography development during the laser texturing process. The system has a nanosecond time resolution and sub-micron spatial resolution. A numerical analysis based on finite difference method is conducted to simulate the microscale energy transport and fluid glow. Comparison between the numerical and the experimental result helps to understand the physical mechanism of the process.

Microelectromechanical systems (MEMS) and nanoelectromechanical systems (NEMS) technologies enable us to create varioius useful sensing and actuating devices integrated with other microelectronic, optoelectronic, microwave, thermal and mechanical devices for advanced microsystems. One of the critical issues for cost-effective integration is MEMS/NEMS packaging, which is often neglected and therefore blocks potential products from a successful market launch. This special issue has a collection of 16 papers covering different challenging aspects in MEMS/NEMS packaging. It begins with an introduction to MEMS/NEMS packaging, followed by wafer-level MEMS packaging and self-assembly for nano-devices. These three papers will help readers understand the field with representative applications and packaging technologies. The next five papers will present studies on MEMS packaging for different applications: bioMEMS, RF MEMS, optical MEMS and MEMS for fluid mixing. The second group of papers will address specific design or technology issues in details. In this group, the first five papers study the use of getters, laser-assisted sealing, glass-to-glass wafer bonding, improved corrosion resistance, and through-wafer vias. The last three papers present thermal and mechanical designs for

Overall performance of a thin film solar cell is determined by the efficiency of converting photons to electrons through light absorption, carrier generation, and carrier collection. Recently, photon management has emerged as a powerful tool to further boost this conversion efficiency. Here we propose a novel nanograting solar cell design that achieves enhanced broadband light absorption and carrier generation in conjunction with the reduced use of active and non-earth-abundant materials. A test using this design for the short circuit current density in CuInxGa(1-x)Se2 (CIGS) thin film solar cells shows up to 250% enhancement when compared to the bare thin film cells. In addition, placing metal strips on top of the nanograting to act as the top electrode reduces the use of non-earth-abundant materials that is normally used as the transparent conducting materials. This novel solar cell design has the potential to become a new solar cell platform technology for various thin film solar cell systems.

A number of studies have investigated the behavior of neurons on microfabricated topography for the purpose of developing interfaces for use in neural engineering applications. However, there have been few studies simultaneously exploring the effects of topographies having various feature sizes and shapes on axon growth and polarization in the first 24 h. Accordingly, here we investigated the effects of arrays of lines (ridge grooves) and holes of microscale (approximately 2 microm) and nanoscale (approximately 300 nm) dimensions, patterned in quartz (SiO2), on the (1) adhesion, (2) axon establishment (polarization), (3) axon length, (4) axon alignment and (5) cell morphology of rat embryonic hippocampal neurons, to study the response of the neurons to feature dimension and geometry. Neurons were analyzed using optical and scanning electron microscopy. The topographies were found to have a negligible effect on cell attachment but to cause a marked increase in axon polarization, occurring more frequently on sub-microscale features than on microscale features. Neurons were observed to form longer axons on lines than on holes and smooth surfaces; axons were either aligned parallel or perpendicular to the line features. An analysis of cell morphology indicated that the surface features impacted the morphologies of the soma, axon and growth cone. The results suggest that incorporating microscale and sub-microscale topographies on biomaterial surfaces may enhance the biomaterials' ability to modulate nerve development and regeneration.

A major problem of current silicon thin film solar cells lies in low carrier collection efficiency due to short carrier diffusion length. Instead of improving the collection efficiency in a relatively thick solar cell, increasing light absorption while still keeping the active layer thin is an alternative solution. Absorption enhancement in a thin film Si solar cell by incorporating a two-dimensional periodic metallic nanopattern was investigated using three-dimensional finite element analysis. By studying the enhancement effect brought by different materials, dimensions, coverage, and dielectric environments of the metal nanopattern, we found that absorption enhancement occurs at wavelength range outside surface plasmons resonance of the nanostructures. The exploitation of the nanostructures also enhances the Fabry-Perot resonance in the active layer. It plays an important role in optimizing the absorption of the solar cell.

Tunable extraordinary transmission via changing temperature of a porous metallic layer on top of a thin layer of dielectric strontium titanate (STO) was studied. The metallic layer has a through-hole array and each hole has a circular converging-diverging channel (CDC) shape, which induces the excitation of surface plasmon polaritons (SPPs) and then results in a controllable extraordinary optical transmission in the terahertz (THz) frequency range. We used a three-dimensional (3D) finite element method to analyze the transmission characteristics of the structure. Location and magnitude of the transmission peaks can be adjusted by hole size, converging angle, and thicknesses of metal and STO layers. Remarkably, the suggested structure presents a strong transmission dependency on temperature, which offers a new approach to actively and externally tune the transmission. This new design could lead to a family of temperature-sensitive devices working in the THz frequency range, promising in many applications including photonics, nanolithography, imaging, and sensing.

We report on the design, fabrication, and analysis of a light-driven micromotor. The micromotor was created from a nanoporous polymer with close-packed gold nanoparticles which generate heat by absorbing light. The blades of the micromotor were curved, forming convex and concave sides. Upon lateral irradiation, by geometric effect the convex side transfers more photon-generated heat to the surrounding gas molecules, causing a convective motion of gas and leading to the rotation of the micromotor. The light-driven motions of gas molecules were analyzed using molecular dynamics modeling.

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In this paper, we report a general method for imprinting nanometer-scale features in low-viscosity photosensitive hydrogels using conventional optical mask aligner technology. We call this method flash imprint lithography using a mask aligner (FILM). The FILM process makes it possible to fabricate nanometer-scale features in ultraviolet (UV)-curable hydrogels quickly, inexpensively and reproducibly. We believe that the FILM process will be useful in many areas of research but is particularly applicable to tissue engineering. Accordingly, we demonstrate the FILM process by imprinting dense arrays of nanostructures in polyethylene glycol dimethacrylate (PEGDMA), a material commonly utilized as a substrate in micro-and nanoscale tissue scaffolds; finite element modeling and contact angle analysis are employed to characterize pattern transfer of low-viscosity polymers (e.g. PEGDMA) in the FILM process.

Microlens array is a key element in the field of information processing, optoelectronics, and integrated optics. Many existing fabrication processes remain expensive and complicated even though relatively low-cost replication processes have been developed. Here, we demonstrate the fabrication of microlens arrays through projection photopolymerization using a digital micromirror device (DMD) as a dynamic photomask. The DMD projects grayscale images, which are designed in a computer, onto a photocurable resin. The resin is then solidified with its thickness determined by a grayscale ultraviolet light and exposure time. Therefore, various geometries can be formed in a single-step, massively parallel fashion. We present microlens arrays made of acrylate-based polymer precursor. The physical and optical characteristics of the resulting lenses suggest that this fabrication technique is potentially suitable for applications in integrated optics.

In this article, we present our study on surface plasmon (SP) assisted contact scheme nanoscale photolithography technique. Sub-100-nm features on a metallic mask, fabricated by e-beam lithography, were successfully transferred to a resist pattern in a setup close to traditional photolithography. Our previous work based on finite difference time domain simulation reveals the mechanism of SP-light coupling in the transferring and confining of light in surface plasmon assisted nanolithography (SPAN), which was demonstrated using 355nm laser light. In this article, we extended our SPAN work to the use of UV light from a mercury lamp, which emits broadband, unpolarized, and incoherent light. Our experimental results show that sub-100-nm features can still be easily transferred using SPAN despite the light source used, proving SPAN to be an alternative nanopatterning technique that is simple, quick, and inexpensive. The experiments also showed interesting SP interference effects at the boundary of the mask.

The transmission of light through a thin Ag film with a periodic subwavelength hole array can be influenced by the presence of the externally applied magnetic field H. Using a three-dimensional finite element method, we show that the spectral locations of the transmission peak resonances can be shifted by varying the magnitude and direction of the H. The transmission peaks have blueshift, and the higher the magnitude of H the larger the blueshift. The shift is due to the change of cavity resonance condition as a result of the magneto-induced anisotropy in the optical properties of the Ag film. Hence, high transmittance for any desired wavelength can be achieved by applying an appropriate H to the metallic film of optimized material and hole parameters.

We describe two techniques for patterning spin-cast thin films of a solution-processable organic semiconductor, triethylsilylethylnyl anthradithiophene (TES ADT), to eliminate parasitic leakage currents and to lower off currents in thin-film transistors. One technique utilizes UV light in the presence of solvent vapors to simultaneously define the active channel and to crystallize TES ADT. The second technique selectively removes TES ADT from the nonchannel regions of the thin-film transistors through direct contact with a poly(dimethylsiloxane) stamp. Both patterning techniques yield thin-film transistors with high charge-carrier mobility (⩾0.1cm2∕Vs), low off currents (10−10–10−11A), and minimal parasitic leakage.

A technique to create nanopatterns on hard-to-machine bulk silicon carbide (SiC) with a laser beam is presented. A monolayer of silica (SiO2) spheres of 1.76-µm and 640-nm diameter are deposited on the SiC substrate and then irradiated with an Nd:YAG laser of 355 and 532 nm. The principle of optical near-field enhancement between the spheres and substrate when irradiated by a laser beam is used for obtaining the nanofeatures. The features are then characterized using a scanning electron microscope and an atomic force microscope. The diameter of the features thus obtained is around 150 to 450 nm and the depths vary from 70 to 220 nm.

We demonstrate that photolithography can be extended to a subwavelength resolution for patterning of virtually any substrate by exciting surface plasmons on both a metallic mask and a substrate. Without any additional equipment or added complexity to mask design, one-to-one pattern transfer has been achieved. In this letter, a polarized laser beam of 355 nm wavelength was used as light source to photoinitiate an 80 nm thick photoresist on a silicon substrate coated with titanium of 80 nm thick. Array of line apertures of 100 nm in width were made on gold film or titanium film deposited on a quartz substrate, serving as the mask. Simulation results by finite-difference time-domain method have shown that surface plasmons excited on both the metallic mask and the Ti shield help to spatially confine the light behind the apertures. Experimental results show a strong dependence of pattern transfer on the polarization of light as well as the energy dosage of the light. The feature size using such method could be...

In this paper, we throw light on current state of advancements in the field of biodegradable polymers and devices targeted at biomedical applications. A short introduction involving biodegradable polymers, various fabrication techniques for patterning biodegradable polymers and an extensive coverage of ultraviolet (UV) laser micromachining of polymers is presented. We also present UV laser micromachining of biodegradable polymers for potential biomedical applications. Micro-holes and microchannels, which are important features in many micro-devices, have been etched on biodegradable polymers by UV lasers. The morphology and surface conditions of the etched micro-features in the polymers are studied using SEM and surface profilometre. The effect of laser parameters such as laser wavelength and pulse energy on the etching quality is also investigated. This work on using UV laser for ablation of biodegradable polymers is the first of its kind.