Thin-film Metal Electrodes Research Articles

Fluidic Microchannel Arrays for the Electrophoretic Separation and Detection of Bioanalytes using Electrochemiluminescence

In this paper a low cost, multi-channel separation and detection system is reported for use in fast, high throughput screening of bioanalytes. Applications include genetic engineering and drug discovery, particularly combinatorial chemistry. A prototype detection system is presented which is comprised of an array of 50 microchannels fabricated on 25 mm×75 mm glass substrates with planar, thin film metal electrodes for electrophoresis and electrochemiluminescence excitation. Fluidic interconnects to the microchannels via standard tubing provide quick and facile interfacing to external macro components, controllers and/or other microsystems. The fabrication process is readily scalable to higher density arrays.

Adsorbed state of pyridine, uracil and water on gold electrode surfaces

Attenuated total reflection (ATR) IR spectroscopy was applied to thin film metal electrodes deposited onto Si and ZnSe half-spherical prisms. Optimum conditions for the largest enhancement were quite similar for these prism materials, while their surface morphology is substantially different. In addition to a large enhancement factor of ca. 100, surface selectivity of the ATR-IR spectroscopy was confirmed by spacer experiments that give the decay length of ca. 4 nm even for smooth Ag films on ZnSe prism. Adsorbed pyridine (Py) and uracil on Au electrodes were studied with respect to their hydrophilicity. Two adsorbed states with different vibrational frequencies were observed for uracil in 0.1 M LiClO 4 solution, which have pronounced interaction with water molecules and electrolyte ions. In contrast, no evidences were obtained for distinct adsorbed states for Py, while water molecules were eliminated from the electrode surface upon Py adsorption. Furthermore, three distinct water species were observed on the Au electrode with different hydrogen bonding properties in 1 mM alkali metal halide solution.

Low Temperature Hydrogen Induced Degradation of (Ba,Sr)TiO3 Thin Film Capacitors

AbstractWe have used electrical characterization and secondary ion mass spectroscopy (SIMS) to investigate the influence of hydrogen or deuterium (H/D) on the degradation of the electrical properties of metal/Ba0.7Sr0.3TiO3/metal (M/BSTO/M) thin film capacitors after forming gas annealing (FGA). Leakage and dielectric relaxation currents increase after FGA at temperatures as low as 23C. SIMS profiling shows that at 23C H/D diffuses through thin film metal electrodes and accumulates at electrode interfaces. The location (top or bottom electrode interface) of H/D accumulation is dependent on the type of electrodes and capacitor structure. The resulting asymmetric distribution of H/D leads to large voltage offsets in the C-V characteristic, asymmetric leakage currents, and increased dielectric relaxation currents. Possible mechanisms for increased leakage and relaxation currents after FGA are discussed.

High field characteristics of thin-film metal electrodes

In order to investigate prebreakdown and breakdown characteristics of micrometric vacuum gaps relevant to field emission displays, a specially designed thin film electrode structure, easy to fabricate, was developed to closely simulate electrode gaps in field emission displays (FEDs). An extra-low light detection three-dimensional-imaging system using an intensified charge-coupled device camera was used to diagnose and record the different prebreakdown phases and the breakdown between planar metal film electrodes. Experimental results showed that the prebreakdown activity occurred mostly along the edge of the smaller diameter electrode and obeyed Fowler–Nordheim behavior. Breakdown of the gap at relatively larger gap distances (750 μm) caused damage to the thin-film electrodes; there was no significant damage for small gap distances (250 μm). The extent of electrode damage strongly depended on the film deposition temperature and was believed to be caused by the high-energy electron bombardment. The hold-off voltage of thin-film vacuum gaps was relatively high (>18.0 kV for a Ni/Cr 750 μm gap) which could be improved significantly by direct current glow discharge treatment. The insulation capability of such a vacuum gap was mainly limited by the edge effect and the thin-film quality. The high field characteristics of micrometric thin-film gaps, relevant to FEDs, are reported for the first time in the literature. These results can be used to define the theoretical limits to which actual gaps can be stressed in vacuum microelectronic devices and provide a basis for the design of the phosphor anode and the gate edges of the FEAs.

Surface resistance measurements at the metal/electrolyte interface of Ag(100) and Ag(111) thin film electrodes

The conductivity of thin film metal electrodes with a thickness of the order of the mean free path of the conduction electrons (∼50 nm at 300 K) is sensitive to several processes on the metal surface (e.g. adsorption and desorption of ions). We developed epitaxially grown Ag(100)/MgO(100) and Ag(111)/TiO 2(110) electrodes of 20 nm thickness. The change in the surface resistance of Ag(100) thin film electrodes during adsorption of the halide ions Cl −, Br − and I − shows the different strengths of specific adsorption. We investigated the phase transition of thiocyanate (SCN −) on Ag(100) electrodes by combining the surface resistance method with voltammetric, capacitance and ex-situ XPS measurements. The influence of adsorbed uracil on the resistance of Ag(100) films was demonstrated. The surface resistance is very sensitive to small concentrations of metal cations (e.g. Tl +). The surface resistance of Ag(100) and Ag(111) thin film electrodes shows the typical difference in the stripping potential of Tl + of about 100 mV.

Long Optical Path Length Cell for Thin-Layer Spectroelectrochemistry

This paper describes the design and construction of a thin-layer spectroelectrochemical cell with a long optical path length. This cuvette-based cell, which can be reproducibly filled by capillary action, facilitates the use of metal thin-film electrodes such as those constructed on glass, silicon, and mica substrates. Electrochemical and spectroscopic data are presented that demonstrate the thin-layer behavior of the cell and other important performance characteristics (e.g., optical sensitivity, electrolysis time, and oxygen exclusion capability).

Chemical microsensor systems for medical applications in catheters

Abstract For the synthesis of chemical parameters in human blood, miniaturised sensors have been developed and implemented in common catheter systems. Based on the principle of amperometric sensors, enzyme chips for lactate and glucose determination have been constructed by depositing a thin-film noble metal electrode and a reference electrode at one side of the silicon chips. The enzymes are entrapped into poly-urethane films which are directly attached to the chip surface and optimised by chemical surface modification. The potentiometric sensors have silicon micromachined grooves containing ion-selective ionophores in modified poly(vinyl chloride) (PVC) and electrodes located on both sides of the silicon chip. By means of an intelligent analyte management system the exposure time of the sensors to serum or blood was reduced to about one min/hour. The sensors are conditioned and calibrated immediately before each blood measurement. The analyte and calibrant handling and the signal treatment are controlled by a microprocessor. The sensors assembled in the catheter tip respond reproducibly and accurately to the respective analytes in human serum for more than 70 h.

Properties of interdigital electrode arrays with different geometries

Interdigital array (IDA) microelectrodes have been fabricated by photolithographic and electron-beam lithographic techniques on silicon substrates. Thin-film noble metal electrodes have been deposited on a titanium-adhesion layer. The electrode width and space varied between 1 and 2 μm and between 300 nm and 1 μm, respectively. These IDA electrodes were applied to voltammetric and chronoamperometric measurements of reversible redox species using a home-build free programmable multipotentiostat. The multiple oxidation and reduction of these compounds result in an increased current generation, where the collection efficiencies and the signal amplification of reversible redox molecules have been determined. Both parameters are dependent on average diffusion length. The measurement conditions, such as ionic strength and buffer composition, influence the amplification rate. Time resolved redox recycling experiments showed that the diffusion equilibrium strongly depends on the distance between generator and collector electrode. A high redox recycling rate and collection efficiency of the IDA spacing in the nm-range enable electrochemical measurements to be performed more sensitive and faster than conventional measurements. These measuring principle is attractive to enhance the sensitivity of biosensor based microsystems.

Microfabricated glucose, lactate, glutamate and glutamine thin-film biosensors

Glucose, glutamate and lactate oxidase as well as glutaminase were covalently immobilized on thin-film metal electrodes employing a polyimine gel obtained by polymerization of amines and aldehydes. The gel matrix having ion-exchange properties serves an an excellent suppression layer for electrochemically interfering compounds. A glutamine sensor was obtained using the glutamate sensor in combination with highly purified immobilized glutaminase from Escherichia coli, pig kidney and Bacillus subtilis. Sensor thus obtained showed rapid response, high stability, excellent suppression of interfering substances and short regeneration time. These sensors were designed for fermentation control in bioreactors using flow-injection-analysis device (FIA). The sensors were also applied for assaying in plasma and whole blood.

積層型電子セラミックス素子の残留熱応力の解析

Recently, multilayer electronic ceramic devices such as chip capacitors, ceramic actuators or chip inductors have been used in electronic circuit . Mutually sandwiched layers of electronic ceramics and metallic thin film electrodes are usually sintered simultaneously. Accordingly, thermal expansion mismatch stresses occur in them owing to difference in thermal expansion between their ceramic and metal layers. These stresses may result in crack or fracture formation in their ceramic layers, decrease in their capacitances or inductances, or troubles during actuator operation.This paper describes analytical treatment of these stresses as a function of their layer number on the basis of theoretical discussion given elsewhere for residual thermal stresses in ceramic-to-metal joints .

Thin-film conductometric biosensors for glucose and urea determination

The characteritics of the developed conductometric biosensors for urea and glucose determination are described. Conductometric transducers based on thin-film interdigitated metal (Au, Cr, Cu, Ni) electrodes were studied, and enzymes urease and glucose oxidase were used for the selective membranes formation on the chips having gold electrodes. The influence of ionic strength and buffer capacity of the samples on the biosensors response in kinetic and steady-state modes of measurements was thoroughly tested. It was shown that the kinetic response of the sensors does not depend on the buffer capacity of the analyzed sample. In basic features the performance of the developed biosensors is rather close to that of respective enzyme field effect transistor, though the former are much superior when the technological complexity of the transducer itself is considered and taking into account that conductometric sensors require no reference electrode.

Chip biosensors on thin-film metal electrodes

A set of amperometric, impedimetric, potentiometric and reference thin-film metal electrodes (TFMEs) in silicon technology, which may be combined in different shapes and sizes, has been constructed as transducers for biosensors. The chips inserted in test strips or flow-through devices are covered by the enzyme included in surface-crosslinked polyurethane layers. Improved selectivity for glucose, lactose, lysine and urea sensors as well as reduced protein adsorption from real blood samples have been achieved by using chemically modified polymer surfaces.

Second generation biosensors

Enzyme-membrane electrodes using glucose oxidase in combination with peroxide detection dominate in the field of laboratory analyzers for diluted samples. Using the same indication principle, extremely fast responding glucose sensors have been fabricated by covering thin film metal electrodes with a porous enzyme layer. In the second generation auxiliary enzymes and/or co-reactants are coimmobilized with the analyte converting enzyme in order to improve the analytical quality and to simplify the performance. Following this line oxidizable interferences are suppressed by using a glucose oxidase/peroxidase complex which communicates with the electrode at a low working potential. Furthermore, fluctuations of pH or buffer capacity are ineffective when using a glucose oxidase/peroxidase layer covered fluoride FET in the potentiometric glucose determination. Enzymatic recycling of the analyte and/or accumulation of intermediates increase the sensitivity by several orders of magnitude. Inclusion of NAD bound to PEG in the glucose dehydrogenase layer allows a reagentless glucose measurement.

Dependence of the pressure sensitivity of a quartz oscillator on its size

The dependence of the pressure sensitivity of a tuning-fork-shaped quartz oscillator on its size has been studied experimentally and theoretically. It was experimentally found that the oscillator has a maximum pressure sensitivity when the ratio of the thickness to the length is about 0.1, and the maximum sensitivity is approximately proportional to the length (or the thickness). These results were theoretically analyzed on the basis of the string-of-beads model of a quartz oscillator. The theoretical results strongly suggest that the energy dissipation takes place mainly in the thin film metal electrodes on the surface of the quartz.

A new solid oxide fuel cell design based on thin film electrolytes

A novel solid oxide fuel cell (SOFC) design that can be fabricated entirely using low-temperature, thin-film processing is described. Potential advantages of the cell are reduced materials costs and improved fuel-cell characteristics. The critical design feature is the use of thin (≈ 50 nm), catalytically-active oxide layers on a < 10 μm thick yttria-stabilized zirconia (YSZ) supported electrolyte to minimize reaction overpotentials and ohmic losses. Doped ceria at the fuel electrode side and doped bismuth oxide at the oxygen electrode side are proposed for the surface layers. The surface reaction rates and overall electrolyte conductance in this design are high enough at < 750 °C to allow efficient SOFC operation. This operating temperature is low enough that low-resistance, thin-film metal electrodes, Ni at the fuel side and Ag at the oxygen side, can be used to provide low ohmic losses. The overpotential behavior of the proposed cell is estimated on the basis of literature data and leads to fuel efficiencies > 50% at a power density of ≈ 0.5 W/cm 2 when operated at 750 °C. The thin film monolithic design will lead readily to the incorporation of the cells into stacks with high power-to-weight and power-to-volume ratios. Methods for cell fabrication are discussed.

Plasma-Polymerized Thin Films for Enzyme Immobilization in Biosensors

Abstract Polymer films deposited on thin film noble metal electrodes on silicon chips, utilizing plasma polymerization are shown to be suited for immobilization of enzymes. Glucose oxidase is covalently coupled via amino- or carboxyl-groups of polymer films made by plasma polymerization of 2-amino-benzotrifluoride, acrylic or methacrylic acid. The concentration of these active surface groups increases by after-treatment in an ammonia- or oxygen-plasma. A biosensor consisting of a thin film metal electrode, plasma polymer film and immobilized glucose oxidase shows an amperometric response to glucose with a fast response time.

Near IR interband transitions and optical parameters of metal-germanium contacts

A theoretical and experimental study of the zero-bias quantum efficiency eta(0) for metal (Au, Cu, Ag)-Ge Schottky barrier photodetectors in the near IR range (1.1 microm < lambda < 1.8 microm) has been performed. By an interactive computer programming technique, the optical parameters of the metal thin film electrodes (index of refraction n and extinction coefficient k) as a function of wavelength and of film thickness are determined. Starting with a two-layer calculation of the reflectance R, transmittance T, and absorptance A of the metal electrode, it is found that the eta(0) in this near IR range is dominated by the band-to-band excitation of electrons in the Ge substrate. Using the minority carrier diffusion length L(p) as an adjustable parameter, good agreement between theoretical and experimental results was found for L(p) approximately 150 microm; this value was obtained independent of choice of metal or metal thickness justifying the above procedure.

A Multichannel Depth Probe Fabricated Using Electron-Beam Lithography

A multielectrode probe structure is described in which several thin-film metal electrodes are defined on the outer surface of a glass micropipette using electron-beam lithography. Electrode geometries are controlled to within one micron, resulting in electrode recording characteristics which are extremely well matched. Recording sites are 5 , um wide rings spaced 100 , um apart in depth. Analysis and characterization show the structure to be capable of accurately recording tissue potentials with a minimum of tissue damage. Use of these probes in current source-density (CSD) analysis of extraceliular current flow is described.

A novel transparent electrode process

A novel process for the formation of thin-film, optical-quality conductive electrodes for use in electrophoretic deposition of high-resolution phosphor screens is described. The thin-film metal electrodes can be removed from under the phosphor either chemically or by vacuum sublimation leaving a completely transparent interface. The metal electrodes show good adherence to substrates and are low in pinhole density. High condensation rates are obtained through the use of nucleation techniques.

Avalanche-Induced Negative Resistance in Thin Oxide Films

A current-controlled negative resistance phenomenon, similar to that exhibited by a gas discharge tube, has been observed in suitably prepared thin oxide films of Nb, Ta, and Ti, sandwiched between thin-film metal electrodes, at frequencies up to 1 Mc/sec. The voltage required to sustain the negative resistance in both directions of current is independent of the electrode materials, apparent area and thickness (up to 500 Å) of the oxide film, and is about 0.4, 1.3, and 3.5 V for Ti, Nb, and Ta oxide films, respectively. The corresponding electric fields are approximately 0.8×106, 3×106, 9×106 V/cm. These values increase slightly with decrease of temperature. Experimental evidence supports the interpretation of the phenomenon in terms of avalanche multiplication of carriers in a thin region of the oxide film attended by space-charge-limited flow conditions.