Sub-100 Μm Research Articles

Micro 3D Printing Using a Digital Projector and its Application in the Study of Soft Materials Mechanics

Buckling is a classical topic in mechanics. While buckling has long been studied as one of the major structural failure modes1, it has recently drawn new attention as a unique mechanism for pattern transformation. Nature is full of such examples where a wealth of exotic patterns are formed through mechanical instability2-5. Inspired by this elegant mechanism, many studies have demonstrated creation and transformation of patterns using soft materials such as elastomers and hydrogels6-11. Swelling gels are of particular interest because they can spontaneously trigger mechanical instability to create various patterns without the need of external force6-10. Recently, we have reported demonstration of full control over buckling pattern of micro-scaled tubular gels using projection micro-stereolithography (PμSL), a three-dimensional (3D) manufacturing technology capable of rapidly converting computer generated 3D models into physical objects at high resolution12,13. Here we present a simple method to build up a simplified PμSL system using a commercially available digital data projector to study swelling-induced buckling instability for controlled pattern transformation. A simple desktop 3D printer is built using an off-the-shelf digital data projector and simple optical components such as a convex lens and a mirror14. Cross-sectional images extracted from a 3D solid model is projected on the photosensitive resin surface in sequence, polymerizing liquid resin into a desired 3D solid structure in a layer-by-layer fashion. Even with this simple configuration and easy process, arbitrary 3D objects can be readily fabricated with sub-100 μm resolution. This desktop 3D printer holds potential in the study of soft material mechanics by offering a great opportunity to explore various 3D geometries. We use this system to fabricate tubular shaped hydrogel structure with different dimensions. Fixed on the bottom to the substrate, the tubular gel develops inhomogeneous stress during swelling, which gives rise to buckling instability. Various wavy patterns appear along the circumference of the tube when the gel structures undergo buckling. Experiment shows that circumferential buckling of desired mode can be created in a controlled manner. Pattern transformation of three-dimensionally structured tubular gels has significant implication not only in mechanics and material science, but also in many other emerging fields such as tunable matamaterials.

Giant-Amplitude, High-Work Density Microactuators with Phase Transition Activated Nanolayer Bimorphs

Various mechanisms are currently exploited to transduce a wide range of stimulating sources into mechanical motion. At the microscale, simultaneously high amplitude, high work output, and high speed in actuation are hindered by limitations of these actuation mechanisms. Here we demonstrate a set of microactuators fabricated by a simple microfabrication process, showing simultaneously high performance by these metrics, operated on the structural phase transition in vanadium dioxide responding to diverse stimuli of heat, electric current, and light. In both ambient and aqueous conditions, the actuators bend with exceedingly high displacement-to-length ratios up to 1 in the sub-100 μm length scale, work densities over 0.63 J/cm(3), and at frequencies up to 6 kHz. The functionalities of actuation can be further enriched with integrated designs of planar as well as three-dimensional geometries. Combining the superior performance, high durability, diversity in responsive stimuli, versatile working environments, and microscale manufacturability, these actuators offer potential applications in microelectromechanical systems, microfluidics, robotics, drug delivery, and artificial muscles.

Electrospun fibro-porous polyurethane coatings for implantable glucose biosensors

This study reports methods for coating miniature implantable glucose biosensors with electrospun polyurethane (PU) membranes, their effects on sensor function and efficacy as mass-transport limiting membranes. For electrospinning fibres directly on sensor surface, both static and dynamic collector systems, were designed and tested. Optimum collector configurations were first ascertained by FEA modelling. Both static and dynamic collectors allowed complete covering of sensors, but it was the dynamic collector that produced uniform fibro-porous PU coatings around miniature ellipsoid biosensors. The coatings had random fibre orientation and their uniform thickness increased linearly with increasing electrospinning time. The effects of coatings having an even spread of submicron fibre diameters and sub-100 μm thicknesses on glucose biosensor function were investigated. Increasing thickness and fibre diameters caused a statistically insignificant decrease in sensor sensitivity for the tested electrospun coatings. The sensors' linearity for the glucose detection range of 2–30 mm remained unaffected. The electrospun coatings also functioned as mass-transport limiting membranes by significantly increasing the linearity, replacing traditional epoxy-PU outer coating. To conclude, electrospun coatings, having controllable fibro-porous structure and thicknesses, on miniature ellipsoid glucose biosensors were demonstrated to have minimal effect on pre-implantation sensitivity and also to have mass-transport limiting ability.

Compact and fast photonic crystal silicon optical modulators

We demonstrate the first sub-100 μm silicon Mach-Zehnder modulators (MZMs) that operate at >10 Gb/s, by exploiting low-dispersion slow-light in lattice-shifted photonic crystal waveguides (LSPCWs). We use two LSPCW-MZM structures, one with LSPCWs in both arms of the MZM, and the other with an LSPCW in only one of the arms. Using the first structure we demonstrate 10 Gb/s operation with a operating bandwidth of 12.5 nm, in a device with a phase-shifter length of only 50 μm. Using the second structure, owing to a larger group index as well as lower spectral noise, we demonstrate 40 Gb/s operation with a phase-shifter length of only 90 μm, which is more than an order-of-magnitude shorter than most 40 Gb/s MZMs.

Evaluation of mucoadhesive coatings of chitosan and thiolated chitosan for the colonic delivery of microencapsulated probiotic bacteria

Probiotic bacteria were previously encapsulated in sub-100 µm Ca2+ alginate microcapsules for enhanced survival in human gastrointestinal tract. The aim of this study is to evaluate the altered mucoadhesive property of the probiotic delivery system by coating it with mucoadhesive chitosan or thiolated chitosan, for prolonged retention in human colon. The results confirmed that cross-linking with calcium ions reduced the mucoadhesive property of alginate hydrogel, thus questioning the intrinsic mucoadhesiveness of uncoated systems. In contrast, chitosan and thiolated chitosan were found to be adsorbed on sub-100 µm Ca2+ alginate microcapsules, and substantially improved the mucoadhesion performance of the system. The adhesion performance was correlated to the amount of mucoadhesive coating polymer adsorbed on the surface of the system. The coated system was demonstrated on HT29-MTX colonic epithelial monolayer to deliver markedly higher amount of probiotic bacteria to the in vitro model of colonic mucosa. Additionally, the coatings were also found to exert significantly stronger mucoadhesion to colonic mucosa tissue at slight acid neutral pH with less ambient water, which conforms to the physiological environment of the colon, thus supporting prolonged retention in this region.

Experimental Analysis of Within-Die Process Variation in 65 and 180 nm Complementary Metal–Oxide–Semiconductor Technology Including Its Distance Dependences

As the very large scale integration (VLSI) circuits move deeper into the range of sub-100 µm processes due to the continued scaling efforts, designers increasingly face the variations of design parameters as major roadblocks. These variations include the deviation of process, voltage, and temperature values from the nominal specifications and are of paramount concern as they result in a deviation of the performance of ICs from the originally intended design. Thus, variations reduce the yield of the chip production and increase design cost and the design timing schedule. In this paper, we are presenting location-based within-die variation trends in 65 nm technology across the die, which are derived from measured delays of adjustable ring oscillators. The measured data of the test chips in a 65 nm complementary metal–oxide–semiconductor (CMOS) technology indicate that the magnitude of the position based relative variation is 3–7 times larger than for 180 nm technology. At low voltage (0.7 V), this relative variation is significantly increased (>3 times) in comparison to the variation at nominal supply voltage.

The effect of immobilization of probiotic Lactobacillus reuteri DPC16 in sub-100 μm microcapsule on food-borne pathogens

The aim of this study was to evaluate whether immobilizing a probiotic strain Lactobacillus reuteri DPC16 in chitosan-coated alginate microcapsules affected their inhibitory performance against food-borne pathogens. The probiotic strain was encapsulated in sub-100μm alginate microspheres which were further coated with chitosan. This type of probiotic microcapsules was investigated in a co-culture model for its effect against two food-borne pathogenic bacteria. The results confirmed the comparable inhibitory performances between the planktonic and the microencapsulated DPC16 in terms of the medium acidification and the reuterin production in the presence of sufficient nutrients. However, if an infertile condition was present, in which energy source was limited, the planktonic DPC16 tended to instantly accumulate a higher concentration of reuterin but at the cost of substantial viability loss, whereas immobilization in the chitosan-coated alginate microcapsules extended the survival of DPC16, albeit with a significantly lower reuterin production. In conclusion, no attenuated antimicrobial effect was observed for the immobilized DPC16 in the co-culture model. Microencapsulation rendered an enhanced protection on the embedded probiotics, but it may also induce an altered availability of substrates to those microorganisms.

Development of a novel probiotic delivery system based on microencapsulation with protectants

The establishment of the health-promoting benefits of probiotics is challenged by the antimicrobial bio-barriers throughout the host's gastrointestinal (GI) tract after oral administration. Although microencapsulation has been frequently utilised to enhance the delivery of probiotics, microcapsules of sub-100 μm were found to be ineffective and therefore questioned as an effective delivery vehicle for viable probiotics despite the sensory advantage. In this study, four probiotics strains were encapsulated in chitosan-coated alginate microcapsules of sub-100 μm. Only a minor protective effect was observed from this original type of microcapsule. In order to enhance the survival of these probiotics, sucrose, a metabolisable sugar, and lecithin vesicles were added to the wall material. Both of the ingredients could be readily encapsulated with the probiotics, and protected them from stresses in the simulated GI fluids. The metabolisable sugar effectively increased the survival of the probiotics in gastric acid, mainly through energizing the membrane-bound F1F0-ATPases. The lecithin vesicles proved to alleviate the bile salt stress, and hence notably reduced the viability loss at the elevated bile salt concentrations. Overall, three out of the total four probiotics in the reinforced sub-100 μm microencapsules could significantly survive through an 8-h sequential treatment of the simulated GI fluids, giving less than 1-log drop in viable count. The most vulnerable strain of bifidobacteria also yielded a viability increase of 3-logs from this protection. In conclusion, the sub-100 μm microcapsules can be a useful vehicle for the delivery of probiotics, as long as suitable protectants are incorporated in the wall matrix.

Current concepts in transarterial chemoembolization of hepatocellular carcinoma

Transarterial chemoembolization (TACE) has the potential to improve survival in patients with intermediate stage hepatocellular carcinoma (HCC). Careful selection of patients is mandatory to gain survival benefit and safe quality of life. Basic principles of TACE in HCC include selective treatment via intrahepatic and extrahepatic arteries, proper management of side effects and continuation of treatment guided by imaging. After conventional TACE, based on delivery of cytotoxic drugs emulsified in iodized oil and embolization of various types of particles, has been used for more than 20 years, the new concept of drug-eluting microspheres has been introduced. This technology effectively combines enhanced local drug delivery and ischemic embolization effects. Clinical studies showed intensified local necroses and reduced systemic toxic side effects compared to conventional TACE. Embolization of HCC with sub-100 μm particles penetrating deeply into the tumor vascular bed is another promising new option. Very effective devascularization of HCC nodules has been shown after 40 μm bland embolizations, however, potential risks like passage of particles into hepatic veins and systemic circulation have to be considered. Today the indication for TACE in intermediate stage HCC patients is widely accepted; however, there is no clear methodical standard so far. Further studies are necessary to define how to adapt various available methods to individual HCC and patients characteristics.

Sub-100 μm scale on-chip inductors with CoZrTa for GHz applications

On-chip inductors with magnetic material are fabricated with complementary metal-oxide semiconductor processes. The inductors use copper metallization and amorphous CoZrTa thinfilms. Enhancements of 3.5X in inductance and 3X for the quality factor at frequencies as highas 3 GHz have been successfully demonstrated by using a continuous CoZrTa-ring structure in spiral inductors at the 100 μm scale. Further improvement of the frequency response of inductance up to 6 GHz was achieved by micro-patterning the magnetic film. The effect ofincreasing the film thickness on the performance of strip line inductors was measured and modeled. This work demonstrates significantly larger increases in inductance and quality factor atabove 1 GHz as compared to prior efforts, thereby making the added processing cost worthwhile.

Fully voltage-controlled electrohydrodynamic jet printing of conductive silver tracks with a sub-100 μm linewidth

Silver microtracks with excellent electrical functionality were created by electrohydrodynamic jet (e-jet) printing of commercial metallo-organic ink. Novel e-jet printing was performed in a fully voltage-controlled fashion. By using a 20 μm nozzle and reducing the printing distance to 50 μm, metallic tracks with a sub-100 μm linewidth were successfully achieved on Si substrates. The physical properties of the printed tracks were characterized by means of scanning electron microscopy, atomic force microscopy, energy-dispersive x-ray spectrum analysis, and electrical measurements. A low resistivity in the range (2–4)×10−8 Ω m, 1.7–2.4 times of the theoretical value of silver, was obtained for the printed microtracks. A uniform fine track with a 35 μm feature size was produced by pulsed jet printing operating at low voltage, and a drop-on-demand capability of ∼7 pl/drop was estimated.

Advanced condition monitoring of tapered roller bearings, Part 1

A new condition monitoring technique is under development which is based on electrostatic charge. This was originally employed for the detection of debris in the gas path of jet engines and gas turbines, and is now being developed for lubricated systems. Previous investigations have demonstrated the viability of this technique in dry and lubricated tribo-contacts using laboratory-based equipment. This paper reports on the evolution of wear during a tapered roller bearing test, using a suite of condition monitoring techniques, that incorporated electrostatic wear-site sensors to identify charge during surface wear and oil-line sensors to detect debris in oil scavenge lines. The multi-sensor arrangement also included a vibration accelerometer, thermocouples, inductive and ferromagnetic particle counters. Additionally, oil samples were taken during various stages of the test and were analysed for sub-100 μm debris content. Off-line debris analysis included optical particle counting, ferrography, spectrometric oil analysis and electron microscopy. Further tribological assessments included mass loss calculations and photographic evidence of damage. During the initial 7 h, running-in wear was identified by dynamic wear site charge, acceleration and temperature. Also at this time, increases in oil-line charge correlated with debris detection by the inductive sensor, optical particle counter and ferrographic analysis. Following running-in, benign wear was indicated by a reduction in wear site charge, acceleration and temperature, as well as reductions in oil-line charge, inductive and optical particle counts. Around 42 h, increases in inductive and optical particle count were considered to be an early indicator (or precursor) of the impending wear out phase. At 53.5 h, wear out was identified by increases in wear site charge, acceleration and temperature. Evidence of wear debris was shown by increases in oil-line charge, inductive and ferromagnetic particle count. The debris was further corroborated by optical particle count, ferrography and spectrometry. The test was then stopped after 63 h and post-test analysis confirmed outer race and roller spallation.

Sub-100 μm SnAg Solder Bumping Technology and the Bump Reliability

Lead-free solder bumping and its related interconnection and reliability are becoming one of the important issues in today’s electronic packaging industry. In this paper, alloy electroplating was used as SnAg solder bumping process. Multiple reflow was preformed on as-plated solder bumps. Scanning electron microscopy and energy dispersive X-ray analysis were used to investigate the intermetallic compound and microvoids of cross-sectioned solder bump. Shear test was used to evaluate the reliabilities of the SnAg bumps. The 13×13 area-array Sn/3.0Ag solder bumps of 70 μm in height and 90 μm in diameter were fabricated with a smooth and shiny surface and with a uniform distribution of Ag. During multireflow, the scalloped Cu6Sn5 phase grows by a ripening process. Volume shrinkage was the main reason for the formation of microvoids during multireflow. The average shear strength of solder bumps on TiW/Cu under bump metallurgy (UBM) increased with reflow times. The electroplating process is suitable for mass production of well-controlled geometry and uniformity of SnAg solder bumps. Microvoids have trivial negative impacts on the solder bonds. The combination of TiW/Cu UBM and SnAg solder is reliable.

Integrating bulk piezoelectric materials into MEMS for high authority actuators

A new technique was developed under the European Aeromems II project to produce integrated, thin (<100 µm) piezoelectric bimorph structures to be used in MEMS applications requiring large forces and displacements. The process employs machining, low-temperature bonding and standard microfabrication techniques to build up a laminated actuator structure. The process is believed to be a major improvement over existing techniques used to produce PZT layers in the sub-100 µm thickness range. It is an inherently low-temperature (<250 °C) process and allows the high piezoelectric activities of bulk-processed ceramics to be utilized on a MEMS scale. This is in contrast with conventional thick and thin film deposition techniques, which commonly result in reduced piezoelectric properties, use high processing temperatures and can lead to undesirable tensile stresses due to shrinkage. Prototype microvalves were fabricated using this process and the testing and evaluation of these devices is the subject of this paper. A microvalve based on a 4 mm × 1 mm × 70 µm bimorph cantilever element achieved tip displacements in excess of 100 µm at a driving voltage of 90 V. As the device does not depend on resonance it is possible for it to operate over a wide range of frequencies and duty cycles. Tests showed the microvalve to be capable of modulating a supply pressure of 80 kPa from dc to 1 kHz and to be operable at pressure differentials in excess of 100 kPa at frequencies up to 400 Hz. When operated at high pressure differentials with a 200 µm diameter orifice the microvalve was capable of producing jet velocities in excess of 300 m s−1. These high authority capabilities suggest that this device would meet the requirements for a wide range of practical applications.

HIGH PERFORMANCE SIGEC/SI NEAR-IR ELECTROOPTIC MODULATORS AND PHOTODETECTORS

Numerical simulations are performed for SiGeC/Si electrooptic modulators and photodetectors operating at near-IR wavelengths. The addition of carbon provides the ability to lattice match layers with high germanium composition to silicon, which is shown to allow structures with a substantial increase in the optical confinement factor. In addition, SiGeC/Si heterostructures provide strong confinement of large electron and hole concentrations. The large optical confinement factor and strong carrier confinement enable broadband electrooptic modulators with sub-100 μm lengths and switching times below 0.5 ns with 25 mA current as well as photodetectors with quantum efficiencies as high as 90% for 300 μm length.

Computational modelling for reliable flip-chip packaging at sub-100 μm pitch using isotropic conductive adhesives

This paper presents the assembly process using next generation electroformed stencils and Isotropic Conductive Adhesives (ICAs) as interconnection material. The utilisation of ICAs in flip-chip assembly process is investigated as an alternative to the lead and lead-free solder alloys and aims to ensure a low temperature ( T < 100 °C) assembly process. The paper emphasizes and discusses in details the assembly of a flip-chip package based on copper columns bumped die and substrate with stencil printed ICA deposits at sub-100 μm pitch. A computational modelling approach is undertaken to provide comprehensive results on reliability trends of ICA joints subject to thermal cycling of the flip-chip assembly based on easy to use damage criteria and damage evaluation. Important design parameters in the package are selected and investigated using numerical modelling techniques to provide knowledge and understanding of their impact on the thermo-mechanical behaviour of the flip-chip ICA joints. Sensitivity analysis of the damage in the adhesive material is also carried out. Optimal design rules for enhanced performance and improved thermo-mechanical reliability of ICA assembled flip-chip packages are finally formulated.

Fabrication and Characterization of Sub-100 µm Diameter Gallium Phosphide Solid Immersion Lens Arrays

Fabrication and testing of a sub-100 µm gallium phosphide solid immersion lens is described with suitable sphericity (<160 nm deviation) to a marginal ray angle of 42° for NA up to 2.2 inside the material.

Functional integration of microdevices by field assisted manipulation and trapping

A novel programmable force field method is presented which enables controlled electric field assisted transport and localization of microdevices at silicon chip substrates. Electrically addressable chips bearing n×n arrays of receptor electrode sites are developed and field directed assembly methods are optimized for on-chip transport, trapping and integration of sub-100 μm discrete GaAs-based optoelectronic devices. Tweezer-less field assisted manipulation and trapping of discrete 50 μm diameter 670 nm emitting GaAs-based light emitting diodes is achieved. Following assembly in this manner, the LED devices are permanently integrated by solder reflow bonding to the receptor sites enabling direct device electrical characterization and successful demonstration of light emission.

Particle size analysis of material removed during CO2 laser scabbling of concrete for filtration design

This article examines the particles formed during optimized laser scabbling of concrete in order to help determine an effective filtration strategy for the process. The laser scabbling technique has been developed for noncontact removal of radioactive contaminated surface concrete layers. Surface layer removal is effected using a high power carbon dioxide laser beam to generate stresses in the substrate (caused by temperature gradients and dehydration) which break up the surface. The material removed will be contaminated with radionuclides and its efficient collection must be ensured to prevent the escape of radioactive contaminated particles. The filtration methods selected depend on the size of the particles produced and transport characteristics in an airflow. The particles removed were examined using a laser diffraction particle sizer (for particles below 80 μm physical diameter) and sieving (above 150 μm physical diameter) to determine the particle size distribution. Scanning electron microscope (SEM) analysis was used to identify the components present. The study found that particles removed were constituents of the parent concrete, there were no signs of melting and a small volume fraction (less than 1%) of sub-100 μm physical particle diameter. Particles with aerodynamic diameters under 100 μm are airborne and those between 1 and 30 μm are inhaled into the thoracic and bronchial tracts and lungs. Efficient filtration is required to capture these particles. However, filtration is difficult in the 0.1–1 μm aerodynamic diameter range, which comprises only 0.02% by volume of the removed material. It is considered that laser scabbling of concrete using this method will produce no additional risks than the use of other surface removal mechanisms.

Capture of particles in hypervelocity impacts in aerogel

Abstract— The capture in aerogel of 106 μm diameter glass beads is investigated for impact speeds of 1 to 7.5 km s−1. Three different aerogel densities were used, 60,96 and 180 kg m−3. It was found that the length of the penetration track in the aerogel increases with speed until a maximum is reached. Above the maximum speed the track length decreases. This behaviour is similar to that which has previously been observed for particles impacting polystyrene foams and porous alumina. Whilst track length was not found to be an unambiguous indicator of impact speed, the excavated track volume was found to be a suitable indictor of speed. Further, it was possible to estimate the original particle size by measurements of the track volume and entrance hole size. In addition sub‐100 μm diameter particles composed of various minerals were fired into aerogel and the characterisation of the particles in situ by use of a Raman spectrometer was evaluated. This was found to work well, giving vibrational spectra essentially similar to those of the bulk minerals, thus providing a mineralogical rather than an elemental signature for the captured particles.