Method For Fabrication Of Devices Research Articles

Development of a Photochemical Microfluidics Platform

Abstract In an effort to utilize microfluidics to enable photochemistry, we have devised a method for fabrication of devices with UV-transmissive glass. The photochemical device is successfully incorporated into a system utilizing high-pressure capillary mercury lamps and cooling system. We have demonstrated the ability to carry out photochemical transformations with substantial rate acceleration. Furthermore, we highlight the ability to carry out analytical-scale reactions on a pulse flow automated system while modulating wavelength and residence time to identify optimal photochemical reaction conditions. The analytical conditions were also successfully converted to continuous-flow preparative scale.

Phase Change Line Memory Cell Based on Ge2Sb2Te5 Fabricated Using Focused Ion Beam

Using focused-ion-beam-deposited SiO2 as a hard mask, a new phase change line memory cell fabrication method was developed in this work. A phase change line memory cell with a length of 150 nm and width of 100 nm was fabricated and electrical characterization was performed. Reversible phase transition between amorphous (RESET) and polycrystalline (SET) states was realized. Threshold current of the device is only 0.5 µA, which is considerably low owning to the line structure. The reset operation was achieved by applying a voltage pulse with a magnitude of 3.5 V and duration of 50 ns, and the set operation was achieved by applying 1.6 V for 1000 ns. The dynamic resistance switching ratio (off/on ratio) was nearly 104. The device fabrication method enables simplified scaling to ultrasmall phase change device dimensions.

Introduction: Advances in Optical Materials (AIOM) feature

Innovation of solid-state sources of coherent radiation, including lasers and nonlinear optical frequency convertors, has long been a materials-limited field. That is why advances in optical materials offer opportunities improvements in performance and new applications. In this special issue, we focus on laser and nonlinear materials with new device fabrication methods and designs for new light sources.

Nanoengineering and interfacial engineering of photovoltaics by atomic layer deposition

Investment into photovoltaic (PV) research has accelerated over the past decade as concerns over energy security and carbon emissions have increased. The types of PV technology in which the research community is actively engaged are expanding as well. This review focuses on the burgeoning field of atomic layer deposition (ALD) for photovoltaics. ALD is a self-limiting thin film deposition technique that has demonstrated usefulness in virtually every sector of PV technology including silicon, thin film, tandem, organic, dye-sensitized, and next generation solar cells. Further, the specific applications are not limited. ALD films have been deposited on planar and nanostructured substrates and on inorganic and organic devices, and vary in thickness from a couple of angstroms to over 100 nm. The uses encompass absorber materials, buffer layers, passivating films, anti-recombination shells, and electrode modifiers. Within the last few years, the interest in ALD as a PV manufacturing technique has increased and the functions of ALD have expanded. ALD applications have yielded fundamental understanding of how devices operate and have led to increased efficiencies or to unique architectures for some technologies. This review also highlights new developments in high throughput ALD, which is necessary for commercialization. As the demands placed on materials for the next generation of PV become increasingly stringent, ALD will evolve into an even more important method for research and fabrication of solar cell devices.

Thermoplastic elastomers for microfluidics: Towards a high-throughput fabrication method of multilayered microfluidic devices

Multilayer soft lithography of polydimethylsiloxane (PDMS) is a well-known method for the fabrication of complex fluidic functions. With advantages and drawbacks, this technique allows fabrication of valves, pumps and micro-mixers. However, the process is inadequate for industrial applications. Here, we report a rapid prototyping technique for the fabrication of multilayer microfluidic devices, using a different and promising class of polymers. Using styrenic thermoplastic elastomers (TPE), we demonstrate a rapid technique for the fabrication and assembly of pneumatically driven valves in a multilayer microfluidic device made completely from thermoplastics. This material solution is transparent, biocompatible and as flexible as PDMS, and has high throughput thermoforming processing characteristics. We established a proof of principle for valving and mixing with three different grades of TPE using an SU-8 master mold. Specific viscoelastic properties of each grade allow us to report enhanced bonding capabilities from room temperature bonding to free pressure thermally assisted bonding. In terms of microfabrication, beyond classically embossing means, we demonstrate a high-throughput thermoforming method, where TPE molding experiments have been carried out without applied pressure and vacuum assistance within an overall cycle time of 180 s. The quality of the obtained thermoplastic systems show robust behavior and an opening/closing frequency of 5 Hz.

Thermoplastic microfluidic devices and their applications in protein and DNA analysis

Microfluidics is a platform technology that has been used for genomics, proteomics, chemical synthesis, environment monitoring, cellular studies, and other applications. The fabrication materials of microfluidic devices have traditionally included silicon and glass, but plastics have gained increasing attention in the past few years. We focus this review on thermoplastic microfluidic devices and their applications in protein and DNA analysis. We outline the device design and fabrication methods, followed by discussion on the strategies of surface treatment. We then concentrate on several significant advancements in applying thermoplastic microfluidic devices to protein separation, immunoassays, and DNA analysis. Comparison among numerous efforts, as well as the discussion on the challenges and innovation associated with detection, is presented.

Die-to-Die Adhesive Bonding for Evanescently-Coupled Photonic Devices

Heterogeneous integration of III-V semiconductor materials on the SOI (silicon-on-insulator) platform is a promising method for fabrication of active photonic devices. It requires a reliable and robust bonding procedure that also enables an effective optical coupling between III-V layers and SOI waveguides. Molecular bonding is usually used for this purpose, but due to its strict requirements for contamination-free and smooth bonding surfaces, it might not be sufficiently robust for industrial-scale fabrication. As an alternative technique, in this paper we present an adhesive bonding procedure based on the use of DVS-BCB. We developed a die-to-die adhesive bonding procedure, resulting in less than 100nm-thick bonding layers thereby enabling evanescent optical coupling between III-V layers and silicon waveguides. The process shows very good robustness and bonding strength (brake-down shear stress of 2MPa). In perspective, we plan to scale-up the process to a multiple die-to-wafer bonding procedure which would be suitable for industrial-scale fabrication.

High-Temperature Thermoelectric Characterization of III–V Semiconductor Thin Films by Oxide Bonding

A device fabrication and measurement method utilizing a SiO2–SiO2 covalent bonding technique is presented for high-temperature thermoelectric characterization of thin-film III–V semiconductor materials that suffer from the sideeffect of substrate conduction at high temperatures. The proposed method includes complete substrate removal, high-temperature surface passivation, and metallization with a Ti-W-N diffusion barrier. A thermoelectric material, thin-film ErAs:InGaAlAs metal/semiconductor nanocomposite grown on a lattice-matched InP substrate by molecular beam epitaxy, was transferred onto a sapphire substrate using the oxide bonding technique at 300C, and its original InP substrate, which is conductive at high temperatures, was removed. Electrical conductivities and Seebeck coefficients were measured from room temperature to 840 K for this material on both the InP and sapphire substrates, and the measurement results clearly show that the InP substrate effect was eliminated for the sample on the sapphire substrate. A strain experiment has been conducted to investigate the effect of strain on electrical conductivity.

A simple photolithography method for microfluidic device fabrication using sunlight as UV source

A straightforward method for microfluidic devices fabrication using sunlight as the ultraviolet (UV) source is established in this work. This method is based on photolithography, but obviates the need for specialized UV exposure facility. Substrates coated with photoresist were placed directly under sun in a perpendicular direction to the sunlight for exposure. Exposure conditions were optimized for patterning features with different kinds of photoresist, photoresist of different thicknesses and dimensions. Exposure time can be adjusted to obtain designed features on a mask with good lateral structure according to the energy measured by UV meter (with a constant intensity of UV in sunlight). Masters produced under optimum exposure conditions were used for the fabrication of several microfluidic devices with different materials, structures, or functions. Resultant devices were shown eminently suitable for microfluidic applications such as electrophoretic separation, multiple gradient generator, and pneumatic valve-based cell culture. This photolithographic method is simple, low cost, easy to operate, and environmental friendly. Especially, the masters can be obtained in parallel simultaneously, which is suitable for chip fabrication for mass production. It is also more attractive for the laboratories, in which the support for photolithographic facility is not available.

Progress in patterned paper sizing for fabrication of paper-based microfluidic sensors

In this paper, we report the progress in using paper sizing chemistry to fabricate patterned paper for chemical and biological sensing applications. Patterned paper sizing uses paper sizing agents to selectively hydrophobize certain area of a sheet. The hydrophilic-hydrophobic contrast of the pattern so created has an excellent ability to control capillary penetration of aqueous liquids in channels of the pattern. Incorporating this idea with digital ink jet printing technique, a new fabrication method of paper-based microfluidic devices is established. Ink jet printing can deliver biomolecules and chemicals with precision into the microfluidic patterns to form biological/chemical sensing sites within the patterns, forming the complete sensing devices. This study shows the potential of combining paper sizing chemistry and ink jet printing to produce paper-based sensors at low cost and at commercial volume.

Fabrication of paper-based microfluidic sensors by printing

A novel method for the fabrication of paper-based microfluidic diagnostic devices is reported; it consists of selectively hydrophobizing paper using cellulose reactive hydrophobization agents. The hydrophilic–hydrophobic contrast of patterns so created has excellent ability to control capillary penetration of aqueous liquids in paper channels. Incorporating this idea with digital ink jet printing techniques, a new fabrication method of paper-based microfluidic devices is established. Ink jet printing can deliver biomolecules and indicator reagents with precision into the microfluidic patterns to form bio-chemical sensing zones within the device. This method thus allows the complete sensor, i.e. channel patterns and the detecting chemistries, to be fabricated only by two printing steps. This fabrication method can be scaled up and adapted to use high speed, high volume and low cost commercial printing technology. Sensors can be fabricated for specific tests, or they can be made as general devices to perform on-demand quantitative analytical tasks by incorporating the required detection chemistries for the required tasks.

Printing Fabrication of a Bucky Gel Actuator/Sensor and Its Application to Three-Dimensional Patterned Devices

A bucky gel actuator is a novel electro-active polymer (EAP), which is a low-voltage-driven dry soft actuator. In addition, the bucky gel device generates electromotive force when bending and then it can also be used as a sensor. Its device has a bimorph structure with polymer-supported bucky gel electrodes and a polymer-supported ionic gel electrolyte. It can be fabricated by layer-by-layer casting to easily form any shape. In this paper, we demonstrate an automatic fabrication method of bucky gel devices based on a printing method. By using a dispensing machine, we construct the printing system and the manual forming process is replaced with automatic printing. We investigate the printing of complicated shapes and three-dimensional electrode patterns through experiments.

Batch fabricated long throw bi-stable electromagnetic micro-actuator

A long throw bi-stable electromagnetic micro-actuator is presented. Its configuration was easy to be batch fabricated. According to the experiment results, when the actuator was applied with a 5 V voltage pulse, the bi-stable switch was realised and the output displacement was larger than 150 µm. Its overall size is 6×6×3 mm. The device structure, principle and fabrication method are also presented.

Optimization of power and energy densities in supercapacitors

Supercapacitors use nanoporous electrodes to store large amounts of charge on their high surface areas, and use the ions in electrolytes to carry charge into the pores. Their high power density makes them a potentially useful complement to batteries. However, ion transport through long, narrow channels still limits power and efficiency in these devices. Proper design can mitigate this. Current collector geometry must also be considered once this is done. Here, De Levie's model for porous electrodes is applied to quantitatively predict device performance and to propose optimal device designs for given specifications. Effects unique to nanoscale pores are considered, including that pores may not have enough salt to fully charge. Supercapacitors are of value for electric vehicles, portable electronics, and power conditioning in electrical grids with distributed renewable sources, and that value will increase as new device fabrication methods are developed and proper design accommodates those improvements. Example design outlines for vehicle applications are proposed and compared.

Fast Benchtop Fabrication of Laminar Flow Chambers for Advanced Microscopy Techniques

BackgroundFluid handling technology is acquiring an ever more prominent place in laboratory science whether it is in simple buffer exchange systems, perfusion chambers, or advanced microfluidic devices. Many of these applications remain the providence of laboratories at large institutions with a great deal of expertise and specialized equipment. Even with the expansion of these techniques, limitations remain that frequently prevent the coupling of controlled fluid flow with other technologies, such as coupling microfluidics and high-resolution position and force measurements by optical trapping microscopy.MethodHere we present a method for fabrication of multiple-input laminar flow devices that are optically clear [glass] on each face, chemically inert, reusable, inexpensive, and can be fabricated on the benchtop in approximately one hour. Further these devices are designed to allow flow regulation by a simple gravity method thus requiring no specialized equipment to drive flow. Here we use these devices to perform total internal reflection fluorescence microscopy measurements as well as position sensitive optical trapping experiments.SignificanceFlow chamber technology needs to be more accessible to the general scientific community. The method presented here is versatile and robust. These devices use standard slides and coverslips making them compatible with nearly all types and models of light microscopes. These devices meet the needs of groups doing advanced optical trapping experiments, but could also be adapted by nearly any lab that has a function for solution flow coupled with microscopy.

Three‐Dimensional Interconnected Silica Nanotubes Templated from Hyperbranched Nanowires

Figure 1. Flowchart of the fabrication process for interconnected silica nanotubes from hyperbranched PbSe nanowires. Inorganic nanofluidic devices, such as nanopores, nanochannels, and nanotubes (NTs) have been actively studied in bioseparation, bioanalysis, fluidic transistors, power generation, and fast mass transport. Compared to biological nanopores, inorganic nanofluidic devices have been demonstrated to be robust, to have easily tuned surfaces and to be integrable into arrays. One of the most powerful nanofluidic device fabrication methods is templating against a porous membrane or chemically synthesized or lithographically patterned nanowires (NWs). NTs or nanochannels made in this way have controllable dimensions, with diameters down to several nm and lengths up to tens of mm. Herein, we exploit hyperbranched PbSe NWs as templates to produce 3D interconnected hyperbranched silicon dioxide (silica) NTs by simple coating and etching steps. The obtained NTs with a thick enough shell retain the orientation of the original hyperbranched arrays and are either parallel or perpendicular to each other. These hyperbranched NTs afford interesting opportunities for constructing new 3D nanofludic devices. The fabrication process for silica hyperbranched NTs is shown in Figure 1. Hyperbranched PbSe NWs were grown on Si (100) substrates using vapor transport growth. Each hyperbranched PbSe NW exhibits 908 orientation between branches because of the epitaxial relationship. The details of hyperbranched NW growth can be found elsewhere. The samples with hyperbranched NWs were then coated by plasma enhanced chemical vapor deposition (PECVD) of silica. The deposition temperature was 350 8C. The growth rate for a silicon oxide layer based on thin-film deposition on silicon (100) substrate is around 6 nm min . Silica layers with different thickness (30 nm and 80 nm) were deposited on different samples of hyperbranchedNWs to evaluate the effect of silica thickness on the morphologies of the final silica NTs.

Development of a Nanoelectronic 3-D (NEMO 3-D ) Simulator for Multimillion Atom Simulations and Its Application to Alloyed Quantum Dots

Material layers with a thickness of a few nanometers are common-place in today's semiconduc- tor devices. Before long, device fabrication methods will reach a point at which the other two device dimensions are scaled down to few tens of nanometers. The total atom count in such deca-nano devices is reduced to a few million. Only a small finite number of free electrons will operate such nano-scale devices due to quantized electron energies and electron charge. This work demon- strates that the simulation of electronic structure and electron transport on these length scales must not only be fundamentally quantum mechanical, but it must also include the atomic granularity of the device. Various el- ements of the theoretical, numerical, and software foun- dation of the prototype development of a Nanoelectronic Modeling tool (NEMO 3-D) which enables this class of device simulation on Beowulf cluster computers are pre- sented. The electronic system is represented in a sparse complex Hamiltonian matrix of the order of hundreds of millions. A custom parallel matrix vector multiply al- gorithm that is coupled to a Lanczos and/or Rayleigh- Ritz eigenvalue solver has been developed. Benchmarks of the parallel electronic structure and the parallel strain calculation performed on various Beowulf cluster com- puters and a SGI Origin 2000 are presented. The Be- owulf cluster benchmarks show that the competition for memory access on dual CPU PC boards renders the util- ity of one of the CPUs useless, if the memory usage per node is about 1-2 GB. A new strain treatment for the

Mechanical Properties and Adhesion of CdTe/CdS Thin Film Solar Cells Deposited on Flexible Foil Substrates

AbstractCadmium telluride (CdTe) is a leading thin film photovoltaic (PV) material due to its near ideal band gap of 1.45 eV, its high optical absorption coefficient and availability of various device fabrication methods. Superstrate CdTe solar cells fabricated on glass have to-date exhibited efficiencies of 16.5%. Work on substrate devices has been limited due to difficulties associated with the formation of an ohmic contact with CdTe. Foil substrate curvature, flaking, delamination and adhesion as a result of compressive strain due to the coefficient of thermal expansion (CTE) mismatch between the flexible foil substrate and the solar cell films has been studied. Thin films have been characterized by AFM, XRD, SEM, ASTM D3359-08 tape test, and solar cells have been characterized using J-V and spectral measurements. Adhesion improves by minimizing the mismatch of the CTE . A CdCl2 treatment is important for high efficiency solar cells. The treatment influences the microstructure and interface properties of the layers. The effect of the current CdCl2 chemical treatment increases flaking and has to be optimized for the CdTe substrate cell on foil. We have also fabricated solar cells on tantalum, molybdenum and tungsten foils, all with lower CTEs than SS430. We are currently producing solar cells with a VOC of 630mV, a 50% fill factor and over 6.0% efficiency.

MICROFABRICATION TECHNOLOGY OF POLYMERIC MICROFLUIDIC DEVICE

In this paper, possibility of using laser ablation (LA) and thermal bonding methods for polymeric microfluidic device fabrication was studied. The experimental dependencies of the channel profiles cut in polymethylmetacrylate (PMMA) matrices with different parameter settings and corresponding dependencies after thermal bonding were obtained. It was shown that at purpose choose of LA and thermal bonding parameters channel with reproducible sizes from 50 to 170 μm could be obtained.

STI Post CMP Cleaning Solution Development

Shallow Trench Isolation (STI) is the standard isolation method for fabrication of submicron CMOS devices. Ceria based slurries are often used for the chemical mechanical planarization (CMP) of STI structures. It is essential therefore, to clean the structure after the CMP process to remove the ceria and other organic residues, usually resulting from the slurry. In this paper, post CMP cleaning of STI wafers with a specially formulated clean solution has been discussed.