Traditional Fabrication Techniques Research Articles

Ultrafast-laser-inscribed 3D integrated photonics: challenges and emerging applications

AbstractSince the discovery that tightly focused femtosecond laser pulses can induce a highly localised and permanent refractive index modification in a large number of transparent dielectrics, the technique of ultrafast laser inscription has received great attention from a wide range of applications. In particular, the capability to create three-dimensional optical waveguide circuits has opened up new opportunities for integrated photonics that would not have been possible with traditional planar fabrication techniques because it enables full access to the many degrees of freedom in a photon. This paper reviews the basic techniques and technological challenges of 3D integrated photonics fabricated using ultrafast laser inscription as well as reviews the most recent progress in the fields of astrophotonics, optical communication, quantum photonics, emulation of quantum systems, optofluidics and sensing.

Manipulation of Nanoscale Pattern Formation in Photoelectrochemically Deposited Chalcogenide Films Using Multiple Beam Illumination

Photoelectrochemical deposition of semiconducting chalcogenide films resulted in the spontaneous generation of ordered nanostructures wherein the pattern developed is a function of the illumination utilized during growth. Film adopted an ordered, highly anisotropic lamella-type pattern when deposited under conformal illumination with polarized light. Feature size and pitch were controlled the illumination wavelength, direction of anisotropy by the polarization vector and the growth direction by the incident light vector. In order to progress toward generation of intricate, 3-dimensional architectures for specific applications, the manipulation of the pattern formation by utilizing simultaneous illumination from multiple discrete beams during deposition has been investigated. Illumination with two parallel polarized, narrowband sources with two discrete mean wavelengths resulted in patterns with periods that were intermediate of those that would be expected for either source alone and a function of the relative source intensities. The use of two linearly polarized sources with polarization vectors separated by an acute angle produced structures oriented in a direction between the two polarization vectors: this direction was a function of the relative intensities and mean wavelengths of the sources. Illumination with orthogonally polarized sources provided for the generation of mesh-type structures wherein the periodicity and height of pattern in the two orthogonal, in-plane directions could be controlled independently by varying the intensities and wavelengths of the sources. Modeling of the growth was achieved with a Monte Carlo process wherein the probability of mass-addition was weighted based on simulations of the light-matter interactions in the films. This photoelectrochemical deposition process is unique from other methods of generating ordered mesostructures with electrochemical means as no photomask, no photoactive substrate, no physically patterned substrate, nor any chemical templating agents (ligands, surfactants) were utilized. Additionally, tuning the deposition potential and electrolyte along with the illumination has enabled control of the material composition. The same general morphology was observed for a range of varying materials. Thus, this process displays significant, increasing potential to possibly enable the generation of complex morphologies for functional materials without some of the limitations imposed by traditional fabrication techniques.

Diffraction Properties for 1000 Line/mm Free-Standing Quantum-Dot-Array Diffraction Grating Fabricated by Focused Ion Beam

The traditional fabrication technique of quantum-dot-array diffraction grating (QDADG) is a hybrid lithography method that includes electron-beam lithography and x-ray lithography. In this work, 1000 line/mm free-standing QDADG has successfully been fabricated by focused ion beams (FIBs) for the first time. The diffraction patterns of the grating are measured in the 250–450 nm wavelength range from the xenon lamp source. In consequence, the QDADG in this experiment can be used to disperse light without high-order diffraction. The present inspiriting result demonstrates the prospect of FIB fabrication for high energy QDADG in the soft x-ray region.

Untangling Fashion for Development

Latin American cultural memories and historical narratives, embodied in traditional symbols, designs, and fabrication techniques, have been leveraged by fashion enterprises seeking to address development issues. Through fashion, these enterprises have built a presence within the development space. Fashion for Development entrepreneurship models, ranging from one-for-one purchasing to sustainable artisanal workshops, present a new approach to target persistent development problems. By providing consumers the ability to directly support frameworks that encourage social change, they are democratizing the capacity to make a difference. This article questions dominant discourses associated with Fashion for Development and attempts to spotlight veiled narratives hidden behind overtly positive narratives and imagery. It employs an interdisciplinary approach to critically analyze and deconstruct online discourse and design adopted by three Fashion for Development enterprises: TOMS Shoes, the Faire Collection, and MARIO TESTINO FOR MATE. The article investigates the role of brands and their fashion products as mechanisms for the construction of identities, the perpetuation of discourses of power and privilege, and the deconstruction and deterritorialization of culture and history. The article highlights the need for further research to untangle impacts from the numerous processes and factors associated with Fashion for Development on both fashion and development theoretical approaches.

Device Isolation in Hybrid Field-Effect Transistors by Semiconductor Micropatterning Using Picosecond Lasers

Leakage currents are the bugaboo of thin-film electronics. In this study field-effect transistors, made of either ZnO film or bilayers of tellurium and organic oligomer, are machined using picosecond laser pulses, leaving the SiO${}_{2}$ substrate beneath unharmed, due to its different optical absorption. This approach (1) provides almost no variation in structure or performance from device to device, (2) enables patterning of novel materials that may be soft or easily damaged, and, critically, (3) drastically reduces gate leakage compared to traditional fabrication techniques.

Characteristics of Precipitation-formed Polyethylene Glycol Microgels Are Controlled by Molecular Weight of Reactants

This work describes the formation of poly(ethylene glycol) (PEG) microgels via a photopolymerized precipitation reaction. Precipitation reactions offer several advantages over traditional microsphere fabrication techniques. Contrary to emulsion, suspension, and dispersion techniques, microgels formed by precipitation are of uniform shape and size, i.e. low polydispersity index, without the use of organic solvents or stabilizers. The mild conditions of the precipitation reaction, customizable properties of the microgels, and low viscosity for injections make them applicable for in vivo purposes. Unlike other fabrication techniques, microgel characteristics can be modified by changing the starting polymer molecular weight. Increasing the starting PEG molecular weight increased microgel diameter and swelling ratio. Further modifications are suggested such as encapsulating molecules during microgel crosslinking. Simple adaptations to the PEG microgel building blocks are explored for future applications of microgels as drug delivery vehicles and tissue engineering scaffolds.

Fabrication of polydimethylsiloxane microlens array on spherical surface using multi-replication process

In comparison to traditional planar optical devices, compound-eye structured optical elements can reduce the number of components and their volume when being applied to wide-field imaging and sensing systems. However, the fabrication process for microstructures on a curvilinear surface has many difficulties since traditional fabrication techniques are planar. In this paper, we present a cost-effective method to fabricate microlenses on a spherical surface. Microlenses, of which the fill factor was about 78%, were formed using the thermal reflow technique, followed by multiple replication processes to transfer the microlenses from the planar substrate onto a spherical surface. We produced a curved mold with concave microlenses, and it allowed this method to be replicable. A polydimethylsiloxane elastomer was employed as the material for both the microlenses and the mold. The radius of curvature of the spherical surface was approximately 6.1 mm. The variation of the microlenses was analyzed, demonstrating high uniformity. The imaging performance of the microlenses is also presented. The curved microlens arrays were combined with image sensors, and sub-images of objects at various distances are shown. The experimental results demonstrate a high potential for curved microlens arrays being applied to compact mobile camera lenses.

A Variable-Impedance Prosthetic Socket for a Transtibial Amputee Designed from Magnetic Resonance Imaging Data

ABSTRACTThis article evaluates the design of a variable impedance prosthetic (VIPr) socket for a transtibial amputee using computer-aided design and manufacturing (CAD/CAM) processes. Compliant features are seamlessly integrated into a three-dimensional printed socket to achieve lower interface peak

The Application of Diamond-based Electrodes for Efficient EDMing of Silicon Wafers for Freeform MEMS Device Fabrication

Using EDM technology in conjunction with traditional MEMS fabrication techniques offers great advantages in the creation of freeform features silicon wafers. The ability to mass produce features, however, is often limited by high electrode wear rates due to poor EDMing stability based on silicon's material properties. By investigating the use of novel diamond-based electrode materials, high productivity and low wear rates can be achieved simultaneously. First, the feasibility of applying diamond-based electrodes is presented through the rough EDMing of 200 hemispherical features. Second a two-step EDM roughing and finishing process is applied in order to achieve high quality and axisymmetric hemispherical features. Using only an EDM roughing process, 200 hemispherical features were successfully fabricated in 80minutes with virtually zero electrode end wear. The two-step EDM roughing and finishing process resulted in the fabrication of 15 highly axisymmetric hemispherical features with only 15 microns of total electrode end wear. A case study is presented in the fabrication of hemispherical shell structures, where the EDMed hemispherical features are used as a mold for MEMS device fabrication.

Nanofibers in thin-film composite membrane support layers: Enabling expanded application of forward and pressure retarded osmosis

Re-engineering the support layers of membranes for forward and pressure retarded osmosis is critical for making these technologies commercially viable. Real-world applications of forward and pressure retarded osmosis, especially those involving natural and waste waters, will require membranes to withstand significant stresses. Therefore, structural changes to the support layer, which are necessary in minimizing internal concentration polarization, must not compromise its critical abilities to resist mechanical stress and provide a suitable surface for the interfacial polymerization of a robust and selective active layer. Electrospinning can provide nanofibers for support layers to potentially overcome the limitations of traditional membrane fabrication techniques in fulfilling these challenging design criteria. In this work, we present the fabrication and evaluation of thin-film composite membranes composed of electrospun polyethylene terephthalate nanofibers, a phase separation formed microporous polysulfone layer, and a polyamide selective layer formed by interfacial polymerization. These membranes have active and support layer transport properties that are suitable for engineered osmosis, with water permeability of 1.13Lm−2h−1bar−1 (3.14×10−7ms−1bar−1), salt permeability of 0.23Lm−2h−1 (6.4×10−8ms−1), and a structural parameter of 651μm. Relevant and easily reproducible tests for membrane resistance to mechanical stress were performed. The use of electrospun fibers in the support layer enhanced membrane resistance to delamination at high cross-flow velocities because the 340nm diameter electrospun fibers enmesh with the microporous polysulfone layer. A broader discussion of the most promising approaches for using electrospun materials to improve membranes for engineered osmosis is provided.

An optimized hollow microneedle for minimally invasive blood extraction

The healthcare system relies widely on biochemical information obtained from blood sample extracted via hypodermic needles, despite the invasiveness and pain associated with this procedure. Therefore, an alternative micro-scale needle for minimally invasive blood sampling is highly desirable. Traditional fabrication techniques to create microneedles do not generate needles with the combined features of a sharp tip, long length, and hollow structure concurrently. Here, we report the fabrication of a microneedle long enough to reach blood vessels and sharp enough to minimize nerve contact for minimally invasive blood extraction. The microneedle structure was precisely controlled using a drawing lithography technique, and a sharp tip angle was introduced using a laser-cutting system. We investigated the characteristics of a microneedle with a length of 1,800μm length, an inner diameter of 60μm, a tip diameter of 120μm, and a 15° bevel angle through in-vitro liquid extraction and mechanical strength analysis. We demonstrated that the proposed structure results in blood extraction at a reasonable rate, and that a microneedle with this geometry can reliably penetrate skin without breaking. We integrated this microneedle into a blood extraction device to extract a 20μl volume of mouse blood in-vivo. Our optimized, hollow microneedle can potentially be incorporated with other cutting-edge technologies such as microactuators, biosensors, and microfluidic chips to create blood analysis systems for point-of-care diagnostics.

ENGINEERING CURRICULUM DEVELOPMENT IN MICROSYSTEMS

Microsystems are a rapidly developing technology that integrates Micro-electro-mechanical systems (commonly known as MEMS) and microfluidics devices with microelectronics and optoelectronics circuits. Due to increasing demand and opportunities from these fields, universities are introducing or have introduced MEMS/Microfluidics courses to their students at undergraduates and graduate levels. By its nature, the field is multidisciplinary and requires various backgrounds when integrating all components of Microsystems as described above. The current challenges in this area are design, fabrication and testing the microsystem devices. This brings various constraints on both the instructors and the students from the point of teaching and learning aspects. Designing a typical microsystem requires the use of modeling and simulation tools from multi energy domains (circuit simulators, multiphysics analysis, 3D modeling, fluidic flows etc). Fabrication methods have recently been evolved from traditional microelectronics fabrication techniques to more complicated micromachining technologies (bulk vs. surface micromachining, LIGA vs. Deep Reactive Ion etching etc). Testing of Microsystems goes beyond traditional electrical testing to the motion analysis of the moving parts on the microsystems. In recent years, the application of microsystems have also been moving away from traditional telecommunication and entering into new areas like health care, energy, environment, automobile and biotechnology. This makes the teaching of microsystem technologies more challenging to fulfill the needs of students entering in Microsystems from existing disciplines (electrical, mechanical, physics, etc.) with limited background on all parts of microsystems. In addition to the multidisciplinary nature of Microsystems, limited resources (small number of design platforms versus large number of students), absence of supportive funding vs. high cost of prototyping, limited time frame vs. long fabrication periods, restrictive opportunities for students to have hands-on design experience make it difficult to offer such courses at graduate and undergraduate levels. In this paper, we discuss developing a new Microsystems course curriculum with emphasis on MEMS in university environment, particularly at Queen’s University in Canada. This curriculum is designed in a team project-based manner but in modular form. The lecture will be delivered by two main instructors and some guest instructors for different topics. The team members for each project have complementary background or coming from different discipline. The pertinent resources at Queen’s University, including such in CMC Microsystems will be available to the students which solves the shortage of resources for teaching.

Printed Fuel Cell Electrodes with Engineered Porosity

Solid Oxide Fuel Cells (SOFC's) are complex electrochemical devices whose designs require consideration of mass transport, electronic and ionic conductivity, and thermal management. Traditional SOFC fabrication techniques produce electrodes whose random pore geometries are not necessarily ideal with respect to the cell's functional requirements. This paper details initial experimentation involving novel multi-material direct-write printing techniques whose aim is to produce anode and cathode layers in which pore size and shape have been tailored to improve cell performance. Optical and electron microscopy are used to characterize the direct-write printed porous electrodes.

CubeSat Fabrication through Additive Manufacturing and Micro-Dispensing

Fabricating entire systems with both electrical and mechanical content through on-demand 3D printing is the future for high value manufacturing. In this new paradigm, conformal and complex shapes with a diversity of materials in spatial gradients can be built layer-by-layer using hybrid Additive Manufacturing (AM). A design can be conceived in Computer Aided Design (CAD) and printed on-demand. This new integrated approach enables the fabrication of sophisticated electronics in mechanical structures by avoiding the restrictions of traditional fabrication techniques, which result in stiff, two dimensional printed circuit boards (PCB) fabricated using many disparate and wasteful processes. The integration of Additive Manufacturing (AM) combined with Direct Print (DP) micro-dispensing and robotic pick-and-place for component placement can 1) provide the capability to print-on-demand fabrication, 2) enable the use of micron-resolution cavities for press fitting electronic components and 3) integrate conductive traces for electrical interconnect between components. The fabrication freedom introduced by AM techniques such as stereolithography (SL), ultrasonic consolidation (UC), and fused deposition modeling (FDM) have only recently been explored in the context of electronics integration and 3D packaging. This paper describes a process that provides a novel approach for the fabrication of stiff conformal structures with integrated electronics and describes a prototype demonstration: a volumetrically-efficient sensor and microcontroller subsystem scheduled to launch in a CubeSat designed with the CubeFlow methodology.

Scaffolds with a standardized macro-architecture fabricated from several calcium phosphate ceramics using an indirect rapid prototyping technique

Calcium phosphate ceramics, commonly applied as bone graft substitutes, are a natural choice of scaffolding material for bone tissue engineering. Evidence shows that the chemical composition, macroporosity and microporosity of these ceramics influences their behavior as bone graft substitutes and bone tissue engineering scaffolds but little has been done to optimize these parameters. One method of optimization is to place focus on a particular parameter by normalizing the influence, as much as possible, of confounding parameters. This is difficult to accomplish with traditional fabrication techniques. In this study we describe a design based rapid prototyping method of manufacturing scaffolds with virtually identical macroporous architectures from different calcium phosphate ceramic compositions. Beta-tricalcium phosphate, hydroxyapatite (at two sintering temperatures) and biphasic calcium phosphate scaffolds were manufactured. The macro- and micro-architectures of the scaffolds were characterized as well as the influence of the manufacturing method on the chemistries of the calcium phosphate compositions. The structural characteristics of the resulting scaffolds were remarkably similar. The manufacturing process had little influence on the composition of the materials except for the consistent but small addition of, or increase in, a beta-tricalcium phosphate phase. Among other applications, scaffolds produced by the method described provide a means of examining the influence of different calcium phosphate compositions while confidently excluding the influence of the macroporous structure of the scaffolds.

Influence of tool fabrication process on characteristics of hot embossed polymer microfluidic chips for electrospray

Fabrication techniques for mass manufacture of disposable polymer microfluidic chips are important for electrospray application used in mass spectrometry. Hot embossing offers advantages over traditional MEMS fabrication techniques and is the focus of this research. The aim of the paper is to evaluate hot embossed open channel polymer chips using two different hot embossing tools. One tool was fabricated in nickel using the electroforming process, and the other in high carbon bright steel by laser machining technique using a pulsed Nd:YAG laser that is normally used for conventional applications. Process parameters are determined and measurement of dimensions and surface roughness of tools and chips are presented. Depending on the fabrication method, each tool exhibits its own characteristic profile feature and surface roughness. Polystyrene and polycarbonate substrates embossed with the electroformed tool exhibited lowest surface roughness of 48 nm compared to 450 nm for the laser machined tool. The embossed microfluidic chips were tested for fluid flow and electrospray and showed good performance.

Experimental investigation into the performance of heat pipe with micro grooves fabricated by Extrusion–ploughing process

Heat pipe with groove--shaped capillary structure always shows smaller heat transfer limit. It is because that traditional fabrication technique leads to the difficulty in minimizing the geometric dimension of grooves. As a result, novel fabrication technique is of great importance. In this paper, we will discuss some heat transfer characteristics of heat pipe fabricated by novel Extrusion–ploughing process. Owing to the extrusion from tools in the fabrication course, two kinds of grooves, namely leading grooves and secondary grooves, are formed in this kind of heat pipe. This feature will polish the groove geometric structure. Furthermore, considering the fact of parallel combination of these two kinds of grooves, excellent heat transfer performance of novel heat pipe fabricated by novel Extrusion–ploughing process can be expected. The experiments of testing temperature changes versus time at evaporator sector and condenser sector at different work temperature are conducted. The temperature distribution along axial direction of this kind of novel heat pipe at its steady stage is also tested. The experimental results prove that the heat pipe fabricated by Extrusion–ploughing process exhibits ideal isothermal performance and excellent heat respond speed. When compared with normal axially grooved heat pipe, this novel kind of heat pipe also shows larger final heat transfer limit.

Structural Electronics through Additive Manufacturing and Micro-Dispensing

Implementing electronics systems that are conformal with curved and complex surfaces is difficult if not impossible with traditional fabrication techniques, which require stiff, two dimensional printed circuit boards (PCB). Flexible copper based fabrication is currently available commercially providing conformance, but not simultaneously stiffness. Consequently, these systems are susceptible to reliability problems if bent or stretched repeatedly. The integration of Additive Manufacturing (AM) combined with Direct Print (DP) micro-dispensing can provide shapes of arbitrary and complex form which incorporate 1) miniature cavities for insetting electronic components and 2) conductive traces for electrical interconnect between components. The fabrication freedom introduced by AM techniques such as stereolithography (SL), ultrasonic consolidation (UC), and fused deposition modeling (FDM) have only recently been explored in the context of electronics integration. Advanced dispensing processes have been integrated into these systems allowing for the introduction of conductive inks to serve as electrical interconnect within intricately-detailed dielectric structures. This paper describes a process that provides a novel approach for the fabrication of stiff conformal structures with integrated electronics and describes several prototype demonstrations: a body conformal helmet insert for detection of Traumatic Brain Injury (TBI), a 3D magnetic flux sensor with LED indicators for magnitude and direction and a floating sensor capable of detecting impurities in water while maintaining orientation through density gradients.

Microfabricated FSCV-compatible microelectrode array for real-time monitoring of heterogeneous dopamine release.

Fast scan cyclic voltammetry (FSCV) has been used previously to detect neurotransmitter release and reuptake in vivo. An advantage that FSCV has over other electrochemical techniques is its ability to distinguish neurotransmitters of interest (i.e. monoamines) from their metabolites using their respective characteristic cyclic voltammograms. While much has been learned with this technique, it has generally only been used in a single working electrode arrangement. Additionally, traditional electrode fabrication techniques tend to be difficult and somewhat irreproducible. Described in this report is a fabrication method for a FSCV compatible microelectrode array (FSCV-MEA) that is capable of functioning in vivo. The microfabrication techniques employed here allow for better reproducibility than traditional fabrication methods of carbon fiber microelectrodes, and enable batch fabrication of electrode arrays. The reproducibility and electrochemical qualities of the probes were assessed along with crosstalk in vitro. Heterogeneous release of electrically evoked dopamine was observed in real-time in the striatum of an anesthetized rat using the FSCV-MEA. The heterogeneous effects of pharmacology on the striatum were also observed and shown to be consistent across multiple animals.

Three-Dimensional Porous Biodegradable Polymeric Scaffolds Fabricated with Biodegradable Hydrogel Porogens

We have developed a new fabrication technique to create three-dimensional (3D) porous poly(epsilon-caprolactone fumarate) (PCLF) scaffolds using hydrogel microparticle porogens, as an alternative to overcome certain limitations of traditional scaffold fabrication techniques such as a salt leaching method. Both natural hydrogel, gelatin, and synthetic hydrogel, poly(ethylene glycol) sebacic acid diacrylate, were used as porogens to fabricate 3D porous PCLF scaffolds. Hydrogel microparticles were prepared by a single emulsion technique with the particle size in the range of 100-500 microm after equilibrium in water. The pore size distribution, porosity, pore interconnectivity, and spatial pore heterogeneity of the 3D PCLF scaffolds were assessed using micro-computed tomography and imaging analysis. Scaffolds fabricated with the hydrogel porogens had higher porosity and pore interconnectivity as well as more homogeneous spatial pore distribution, compared to the scaffolds made from the salt leaching process. Compressive moduli of the scaffolds were also measured and showed that lower porosity yielded greater modulus of the scaffolds. Overall, the new fabrication technology using hydrogel porogens may be beneficial for certain tissue engineering applications.