The development of retinal prostheses requires a method for interconnecting an imaging system to the retina. Such a system must be able to individually address and stimulate retinal neurons, a significant advance from current technology. As a step toward this goal, we present a novel electronic-to-biologic interface using microfabricated apertures in a silicon substrate. Apertures are created in a thin silicon nitride membrane, after which the surface is appropriately modified to support cell growth. Excitable cells are seeded on the device and imaged using Ca2+-sensitive fluorescent dyes in either an inverted or confocal microscope. Using rat pheochromocytoma (PC12) cells, we show the ability to stimulate locally through the apertures. The device allows for the stimulation of cells at precise locations, a necessary requirement for future high-resolution retinal prostheses.

This paper presents an overview of the development of novel disposable smart plastic fluidic biochips for clinical diagnostic applications. The biochip is manufactured using a low-cost, rapid turn around injection molding/embossing process on a plastic substrate. The plastic fluidic biochip uses a novel sPROMs (structurally programmable microfluidic system) approach to achieve passive control of fluidic sequencing [1-2]. The plastic biochip also uses an on-chip pressurized air source for fluidic movement thus eliminating the need for active driving mechanisms and allowing for a truly disposable approach. Furthermore, electrochemical biosensors are also integrated on-chip to analyze various metabolically significant parameters such as PO2(partial pressure of oxygen), Glucose, Lactate,and pH. The fluidic biochip is being developed for point-of-care health monitoring applications where parameters such as small size, simplicity of operation, disposability, reduced cross-contamination are vital. The issues mentioned above are successfully addressed using the approach of this work and are discussed in this paper.

This paper reports on the design and simulation of micro-fabricated 0.5 MHz Si-based ultrasonic nozzles that consist of multiple sections of Fourier horns of half wavelength design. Such high frequency ultrasonic nozzles should produce 10-15μm-diameter uniform precursor drops for nanoparticle synthesis by means of spray pyrolysis at ambient pressure. Results of 3-D simulation using a commercial FEM program, ANSYS, show existence of one resonant frequency of pure longitudinal vibration, which is very close to the design value. The results also show that at this resonant frequency increase in vibration amplitude at the nozzle tip is very close to the theoretical values of 2n, where n is the number of horn section. Therefore, the required electric drive power should be drastically reduced and the transducer failure in ultrasonic atomization can be more readily avoided.

A process was developed for patterning thin films of environmentally sensitive hydrogels onto silicon microcantilevers. Microcantilevers have been shown to be ultra-sensitive transducers for chemical, physical, and biological microsensors. By patterning environmentally sensitive hydrogels onto silicon microcantilevers, novel microsensors were prepared for MEMS and BioMEMS applications. Specifically, a cross-linked poly(methacrylic acid) (PMAA) network containing significant amounts of poly(ethylene glycol) dimethacrylate (PEGDMA) was studied. This hydrogel exhibits a swelling dependence on pH. By increasing the environmental pH above the pKa of PMAA to cause ionization of the carboxylic acid groups, electrostatic repulsion is produced along the main polymer chain causing the polymer network to expand and swell. Therefore, a pH change induces swelling or shrinking of the polymer network and creates stress on the microcantilever surface causing it to bend. In this study, silicon microcantilevers were fabricated on p-type (100) SOI wafers. Covalent adhesion was gained between the polymer and the silicon surface through the modification of the silicon surface with γ-methacryloxypropyl trimethoxysilane. Hydrogels were patterned onto the silicon microcantilevers utilizing a mask aligner to allow for precise positioning. The micropatterned hydrogels were analyzed using optical microscopy and profilometry. The bending response of patterned cantilevers with a change in environmental pH was observed, providing proof-of-concept for a MEMS/BioMEMS sensor based on microcantilevers patterned with environmentally sensitive hydrogels.

Microfabricated crevice corrosion samples have been employed in experiments that provided important information necessary for developing an accurate, comprehensive, and reliable crevice corrosion model. Acquiring real-time spatial information of crevice corrosion is also essential in analyzing corrosion processes. Integration of arrays of solid-state microsensors, such as conductometric sensors, pH and other ion concentration potentiometric sensors, into the crevice corrosion samples will allow for in-situ real-time data acquisition. In the present work, crevice corrosion samples with conductometric sensor arrays are made using the techniques developed for thin film semiconductor processing and microelectromechanical systems (MEMS) fabrication. The crevice corrosion testing sample is constructed by coupling a crevice former to a crevice substrate and has a uniform crevice gap. A conductometric sensor array built on a silicon wafer is incorporated into the crevice former. Each of these sensors is composed of a pair of thin film gold electrodes, which enables in-situ spatial conductivity analysis of crevice corrosion. Information about metal ion concentration and active chemistry inside the crevice can also be obtained.

We have investigated a nanopillar-based surface enhanced Raman scattering (SERS) for future multiplexed nanofluidic SERS (nanoSERS) arrays. Without using e-beam or focus ion beam method, we have accomplished this simple and batch processed nanoSERS arrays on a chip, which is economical and mass producible. The polysilicon nanopillar structures are fabricated on top of a silicon wafer using optical lithography, reactive ion etching and passivation steps. High aspect ratio pillar-like nanostructures and spacing are controlled by the reactive ion etching gas and passivation steps. The heights of nanopillars ranged from 0.1 μm to 0.3 mm and their diameters ranged from 20 nm to 100 nm. A thin gold (10-20 nm) layer is evaporated on top of the nanopillar surfaces for further surface enhancements. The Raman shifts were measured for 10-3 M of 4, 6-diamidino-2-phenylindole dihydrochloride dye in solution using a 500 mW near infrared laser (785 nm). A direct correlation between the density of nanopillars and the intensity of Raman enhancement is observed. The SERS spectra through thin PyrexTM glass and polydimethylsiloxane (PDMS) are characterized to find the optimized nanofluidic materials for an autonomous multiplexing biomolecular detection schemes.

In this paper, we present object manipulation methodologies in microfluidic devices based on object-photon interactions. Devices were fabricated by polydimethylsiloxane (PDMS) elastomer molding of channel structures over photolithographically defined patterns using a thick negative photoresist. Inorganic objects including polystyrene spheres and organic objects including live cells were transferred into fluidic channels using a syringe pump. The objects were trapped and manipulated within the fluidic channels using optical tweezers formed by VCSEL arrays, with only a few mW of optical power. We have also shown that it is possible to manipulate multiple objects as a whole assemble by using an optically-trapped particle as a handle, or an “optical handle”. Optical manipulation will have applications in biomedical devices for drug discovery, cytometry and cell biology research.

We present the use of a microfabricated device for impedance-based detection of a few live bacterial cells. Impedance-based detection relies on measuring changes in the AC impedance of two electrodes immersed in a liquid were the bacteria are cultured, caused by the release of ionic species by metabolizing bacterial cells. Rapid detection of a few cells (1 to 10) is possible if the cells are confined into a volume on the order of nanoliters. A microfluidic biochip prototype has been fabricated to test this miniaturized assay. The conductance of the bacterial suspensions is extracted from measuring their complex impedance in a 5.27 nl chamber in the biochip, at several frequencies between 100 Hz and 1 MHz. Measurements on suspensions of the bacteria Listeria innocua, Listeria monocytogenes, and Escherichia coli in a low conductivity buffer demonstrate that, under the current experimental conditions, the minimum detection level is between 50 and 200 live cells, after two hours of off-chip incubation. Work is in progress to develop techniques for selective capture of bacteria inside the chip, and to minimize background changes in impedance during on-chip incubation.

In this paper, we review the approaches developed in our laboratory for polymer-based micro/nanofabrication. For fabrication of microscale features, UV-LIGA (UV-lithography, electroplating, and molding) technology was applied for low-cost mass production. For fabrication of sub-micron or nanoscale features, a novel nano-manufacturing protocol is being developed. The protocol applies a novel nano-lithography imprinting process on an ultra-precision motion-control station. It is capable of economically producing well-defined pores or channels at the nanometer scale on thin polymer layers. The formed thin layers can be used as nano-filters for chemical or bio-separation. They can also be integrated into miniaturized devices for cell immunoprotection or tissue growth. For bonding of polymer-based microfluidic platforms, a novel resin-gas injection-assisted technique has been developed that achieves both bonding and surface modification. This new approach can easily seal microfluidic devices with micron and sub-micron sized channels without blocking the flow path. It can also be used to modify the channel shape, size, and surface characteristics (e.g., hydrophilicity, degree of protein adsorption). By applying the masking technique, local modification of the channel surface can be achieved through cascade resin-gas injection.

A wafer level packaging technique that involves anodic bonding of Pyrex wafers to released surface micromachined wafers is demonstrated. Besides providing a hermetic seal, this technique allows full wafer release, provides protection during die separation, and offers the possibility of integration with optoelectronic devices. Anodic bonding was performed under applied voltages up to 1000 V, and temperatures ranging from 280 to 400°C under vacuum (10-4Torr). The quality of the bonded interfaces was evaluated using shear strength testing and leak testing. The shear strength of Pyrex-to-polysilicon and aluminum bonds was ∼10-15 MPa. The functionality of surface micromachined polysilicon devices was tested before and after anodic bonding. 100% of thermal actuators, 94% of torsional ratcheting actuators, and 70% of microengines functioned after bonding. The 70% yield was calculated from a test sample of 25 devices.

A novel dry etching technique of amorphous silicon is proposed to suspend the metal membrane of RF MEMS tunable capacitors. The proposed fabrication process is simple and excludes all the drawbacks related to a wet process. Moreover, it has the advantage of being fully compatible with CMOS post-processing. Experimental results demonstrate that the capacitor suspension beams design with meanders can reduce the tuning voltage to less than 5 to 10 V.

This paper presents a micro-fluxgate magnetic sensor composed of a rectangular-ring shaped magnetic core and solenoid excitation and pick-up coils. In order to improve the sensitivity of sensing element, the excitation and pick-up Cu coils are formed as a closely coupled structure. This unique coil structure allows to excite the magnetic core in an optimal condition with reduced excitation current. The 11 μm thick excitation and pick-up Cu coils were electroplated using Cr (300 Å) / Au (1500 Å) seed layer. The 2.9 μm thick Ni0.8Fe0.2 (permalloy) magnetic core layer was also electroplated with photoresist frame using sputtered Ni0.8Fe0.2 seed layer. The rectangular-ring shaped core was covered by photoresist and wet etching using dilute sulfuric acid. The magnetic core has a DC permeability of ∼1100 and coercive field of 0.1 Oe. The magnetic core is easily saturated due to the low coercive field and closed magnetic path for the excitation field. The chip size of the fabricated sensing element is 1.3 × 1.0 mm2. Excellent linear response over the range of –100 μT to +100 μT is obtained with 14 V/T sensitivity at excitation sine wave of 3 VP-P and 150 kHz. This low magnetic field sensing element is very useful for various applications such as: portable navigation systems including north-up and map data scrolling, military research, medical research, and space research.

In this work, we present for the first time, the fabrication of a fully biodegradable microfluidic device with features of micron-scale precision. This implantable MEMS device is a transition from poorly defined porous scaffolds to reproducible precision scaffolds with built-in convective conduits. First, conventional photolithography is used to create a master mold by bulk micromachining silicon. Next, polydimethylsiloxane (PDMS) silicone elastomer is replica molded to form a flexible inverse mold. The commonly used biodegradable polymer Poly-lactic-co-glycolic acid (PLGA 85:15) is then compression micromolded onto the PDMS to form micropatterned films of the biodegradable polymer. Finally, a thermal fusion bonding process is used to seal the biodegradable PLGA films, forming closed microfluidic channels at the capillary size-scale. Film thicknesses from 100μm-1mm are demonstrated with features having 2μm resolution and 0.2μm precision. Scanning electron micrographs of bonded biodegradable films reveal no observable bond interface and no significant pattern deformation. Bonded microfluidic channels are capable of supporting more than 30psi during flow studies, and we have used the processes to develop complex microfluidic networks for cell culture and implantation as well as simple channels to verify the fluid dynamics in the degradable microchannels. The processes described here are high resolution and fully biodegradable. In addition, they are fast, inexpensive, reproducible, and scalable, making them ideal for both rapid prototyping and manufacturing of tissue engineering scaffolds.

An approach for measuring force-dependent properties of microscopic structures commonly found in MEMS has been developed. The system has the capability of measuring forces and deflections of the order of micro-newtons and micro-meters, respectively. By implementing a visual inspection system, force is applied to localized areas on a beam, and the resulting force-deflection characteristic can be obtained. From this beam stiffness and effective elastic modulus can be calculated. These results were compared to simulation, which was performed using ANSYS FEM code. In addition, by applying a known mechanical force, direct correlation to voltage and thus electrostatic force can be obtained, which also elucidates the magnitude of the electrostatic feedback effect. Characterization of other force-dependent parameters such as DC contact resistance and isolation/insertion loss at RF and microwave frequencies was obtained experimentally, from which parameters such as lumped capacitance can be extracted.

We present a new method of increasing the effective electrode surface for improved neural recording. To optimize the electrode, the impedance can be decreased by introducing surface roughness or nanostructures on the electrode. High aspect ratio pillar-like polysilicon nanostructures are created in a reactive ion etch. Nanostructure robustness in cell culture is examined.

In our research, PZT film actuated micro-machined Si substrates are being developed for numerous applications in which membranes are actuated primarily in flexural mode. Silicon wafers, 3-inches in diameter, underwent boron doping in order to act as an etch stop. Approximately 200-nm of SiO2 was grown on the boron-doped side of the wafers. Photolithography and backside etching using EDP resulted in 2-μm thick membranes. Using reactive ion etching (RIE), beam structures resulted from the membranes. Nano-mechanical testing of the beams indicated that there were substantial residual tensile stresses in these structures. Initial calculations reveal a tensile stress of 57.7 MPa in the Si/SiO2 beams. The residual tensile stress subsequently caused the overall beam stiffness to be two orders of magnitude higher than it would be without stress. After stripping the oxide with a buffered oxide etchant (BOE), a residual stress of 26.5 MPa was measured, which is presumably caused from the remaining boron concentration. The aim of this paper is to understand influences of boron doping and processing variables on residual stresses.

Cell separation and sorting in micro-assay devices must be performed using minimal sample sizes and few processing steps. To meet these requirements, a biomimetic approach to cell sorting is proposed based on adhesive rolling of cells along surfaces. This type of interaction is mediated by a special class of adhesion proteins on cell membranes and is responsible for localizing cells to particular tissues in vivo. To perform cell capture in a microdevce, raw sample can be flowed through microstructured fluidic channels, which serve as chromatographic “separation columns” and whose surfaces are coated with adhesion proteins. Targeted cells are captured by the flow structures and are permitted to roll slowly under shear from passing fluid. Among captured cells, differences in rolling speed provide the basis for segregating different populations. In this study, two prospective designs for microstructured fluidic channels were coated with E-selectin IgG chimera. The capture and enrichment of HL-60 and U-937 cells from flowing samples were demonstrated. Additionally, the difference in transit speed through one of the fluidic channels indicates that separation of enriched populations of these cells is feasible.

MEMS manufacturing in general and the litho step in particular could benefit tremendously from an enhanced focus range of waferstepper alignment systems. This would help the MEMS community to cope with large substrate topography or extreme thick resist films. In this study the performance range over which of the alignment system of an ASML PAS5000/50 system operates has been investigated.

A test device that requires bulk micro machining was designed and processed. The required front to backwafer alignment (FTBA) was performed on alignment markers in cavities etched through a 100mm wafer. On the test device the FTBA overlay was measured electrically as well as optically using the metrology capability of the stepper alignment system. The results obtained demonstrate the capabilities of an existing alignment system to deal with high topographies. The overlay errors observed were dominated by the bulk micro machining processing.

The influence of high temperature post-processes on the microstructural, electrical, and mechanical properties of evaporated platinum thin films with tantalum as adhesion layer was investigated. Post-processes, such as deposition of a silicon nitride passivation layer by LPCVD and annealing at high temperature (up to 830°C) in an inert or reactive gaseous atmosphere, were performed separately or successively on platinum/tantalum films having different thickness. An abnormal grain growth and a grain reorientation occurred in the platinum films during the heat treatments, with more severe hillocks formation when performed in air at temperatures higher than 500°C. Another parameter influencing the electrical characteristics (resistivity, temperature coefficient of resistance) of these films, in addition to the post-processing temperature and time, was the thickness of the platinum film.

A passivation made of LPCVD silicon nitride film was shown to stabilise the electrical properties of the Pt/Ta films before post-processing or operating them at high temperatures, up to the deposition temperature of the passivation film. However, if the passivation is removed, postprocessing of the Pt films at a higher temperature than 500°C in air induced more or less severe hillocks formation and adhesion problems could occur, related to the oxidation of tantalum. The adhesion of the Pt/Ta films was found to depend on the thickness of the LPCVD silicon nitride film deposited, which was removed before annealing in air. The Pt/Ta films properties depend on the annealing conditions, time and temperature, and on the history of the film, if the annealing was performed just after its deposition or after successive thermal processes.

This paper describes recent research on LPCVD processes for the fabrication of high-quality micro-mechanical structures on foundry CMOS wafers. In order to avoid damaging CMOS electronics with either aluminum or copper metallization, the MEMS process temperatures should be limited to a maximum of 450°C. This constraint rules out the conventional polycrystalline silicon (poly-Si) as a candidate structural material for post-CMOS integrated MEMS. Polycrystalline silicon-germanium (poly-SiGe) alloys are attractive for modular integration of MEMS with electronics, because they can be deposited at much lower temperatures than poly-Si films, yet have excellent mechanical properties. In particular, in-situ doped p-type poly-SiGe films deposit rapidly at low temperatures and have adequate conductivity without post-deposition annealing. Poly-Ge can be etched very selectively to Si, SiGe, SiO2 and Si3N4 in a heated hydrogen peroxide solution, and can therefore be used as a sacrificial material to eliminate the need to protect the CMOS electronics during the MEMS-release etch. Low-resistance contact between a structural poly-SiGe layer and an underlying CMOS metal interconnect can be accomplished by deposition of the SiGe onto a typical barrier metal exposed in contact windows. We conclude with directions for further research to develop poly-SiGe technology for integrated inertial, optical, and RF MEMS applications.