Peter J. Hesketh

Impedance based sensing of the specific binding reaction between Staphylococcus enterotoxin B and its antibody on an ultra-thin platinum film

Immunobiosensing techniques to measure specific antigen-antibody binding reactions are important in the development of biosensor applications in biotechnology, in vitro diagnosis, medicine and food technology. An immunobiosensor was constructed to measure the specific binding reaction between Staphylococcus enterotoxin B (SEB) and anti-SEB antibodies. The biosensor comprised an anti-SEB bioactive layer covalently immobilized on an ultra-thin platinum (Pt) film sputtered onto a 100 nm thick silicon dioxide layer on a silicon chip. The Pt film was discontinuous with a normal thickness of 25 A. The impedance of the Pt film decreased during the binding of the anti-SEB to SEB in phosphate buffered saline (PBS) at room temperature. The impedance decreases were irreversible in PBS before saturation of the specific binding sites. When saturated, the impedance at 100 Hz was 14% of the value obtained for the fresh anti-SEB layer in PBS. The magnitude of the impedance (Z) decrease followed a simple relationship with SEB concentration in the range between 0.389 and 10.70 ng/ml SEB. The specificity of the biosensor was demonstrated by showing that no irreversible impedance decreases occurred when the sensor was exposed to 100 ng/ml kappa-casein, or alpha-lactalbumin, in PBS.

Rapid thermal processing of semiconductors

1. Transient Heating of Semiconductors by Radiation -- 2. Recrystallization of Implanted Layers and Impurity Behavior in Silicon Crystals -- 3. Crystallization, Impurity Diffusion, and Segregation in Polycrystalline Silicon -- 4. Component Evaporation, Defect Annealing, and Impurity Diffusion in the III–V Semiconductors -- 5. Diffusion Synthesis of Silicides in Thin-Film Metal—Silicon Structures -- 6. Rapid Thermal Oxidation and Nitridation -- 7. Rapid Thermal Chemical Vapor Deposition -- References.

An ultrathin platinum film sensor to measure biomolecular binding.

A sensitive conductimetric immunosensor has been demonstrated based on an ultrathin platinum film on an oxidized silicon base. The film is about 25 A thick and is seen to consist of a discontinuous layer with channels 20-30 A wide. Monoclonal antibodies were bound to the sensor surface using conventional biosensor chemistry. Impedance at fixed frequencies across the film was used to track modification and binding at the surface. Impedance increased 55% at 20 Hz during the activation of the surface with anti-alkaline phosphatase (anti-AP). Binding of alkaline phosphatase (AP) to the prepared surface results in a further increase of 12%. p-Nitrophenyl phosphate hydrolysis confirmed binding and activity of the AP. About 40 amol AP were bound on the 0.5 cm(2) electrode. Non-specific binding of horseradish peroxidase caused an impedance change <6%. Control experiments showed small impedance changes and trace enzyme activity. Since the mechanism of electrical conduction of the thin film was not established, modeling of thin-film response was used to distinguish between redox processes, capacitance and tunneling mechanisms. The data fit well with the diffusion distributed elements (DE) model as well as a transmission line distribution element (DX) model. The first model, DE, is distributed elements for diffusion. The second DX model represents a transmission line. The sensors behave in a distributed network or like a transmission line.

Measurements of the anisotropic etching of a single-crystal silicon sphere in aqueous cesium hydroxide

Abstract A mechanically polished single-crystalline silicon sphere with a diameter of 0.25in is etched in 40% cesium hydroxide solution to study the orientation dependence of the anisotropic etching of silicon in three dimensions. The characteristic structures formed on the surface of the sphere after etching are examined under the scanning electron microscope. The slow-etching planes, {111} and {100}, as well as fast-etching planes, {110}, are identified from the micrographs. Most importantly, the {311} planes are found to be the most significant amongst the higher-order crystal planes.

A positive displacement micropump for microdialysis

Abstract Miniature fluid pumps, measuring 15×4×1 mm, have been microfabricated with silicon, glass, and polyimide. Pumps have been tested with deionized water and 10% glycerol solutions as the working solutions. The pumps have been operated with a pneumatic drive or a piezoelectric drive. Flow rates from 0.1 to 110 μl min−1 have been achieved. The maximum pressure generated by the pumps was 56 cm of water. Pumps have been operated with a dialysis probe and with a microchannel load. The pump lifetime is limited by the degradation in the performance of the polyimide components in the pump. The power consumption was less than 1 mW at a drive frequency of 10 Hz.

Finite-element analysis of thermal stresses in a silicon pressure sensor for various die-mount materials

Abstract The performance of a silicon micromachined pressure sensor can be significantly affected by the die-attach material and the mounting configuration of the die in its package. Packaging stresses transmitted to the piezoresistive element implanted in the sensing die can induce an error in the voltage output of the sensor. A finite-element model is developed to analyse the effects of different die-mounting configurations, die-attach materials and sensor-element constraints. The model calculates the temperature-induced stress affecting the piezoresistive element ion-implanted on the surface of the pressure-sensing die. Aluminium nitride produces the minimum offset. The 110 mil glass constraint provides better mechanical isolation from the stresses produced by the thermal mismatch between the silicon/glass component and the substrate.

High index plane selectivity of silicon anisotropic etching in aqueous potassium hydroxide and cesium hydroxide

Abstract Mechanically fabricated single-crystal silicon spheres with diameters of 0.25 in were etched in 40 wt.% aqueous potassium hydroxide at 75 °C and 50 wt.% aqueous cesium hydroxide at 50 °C. The post-etching shapes of both etched spheres show that the 〈111〉 and 〈100〉 directions were the slowest etching directions in both cases. The characteristic structures formed on the surface of these etched spheres were examined under the scanning electron microscope to study the high index plane selectivity. The 〈311〉 directions were found to be the most significant among the higher order crystal planes in both cases. Directions close to 〈023〉 were concluded to be the fastest etching in aqueous KOH; however, the 〈110〉 directions were the fastest in aqueous CsOH.

Etching High Aspect Ratio (110) Silicon Grooves in CsOH

In a previous study the authors developed a fabrication process for a single-crystal silicon X-ray analyzer for use at the Advanced Photon Source, a 6 GeV synchrotron accelerator ring under construction at Argonne National Laboratories. The bent silicon crystal will be used as an analyzer to collect and focus a monochromatic beam of X-rays by Bragg reflection with an energy resolution better than 10 meV for the (hhh) planes (H>6) for diffraction near backscattering. The cross-sectional geometry produced by anisotropic etching high aspect ratio (height/width = 115) silicon grooves with CSOH was studied as a function of the solution concentration. At 50 weight percent (w/o) CSOH straight sidewalls are produced, but at 15 and 25 w/o re-entrant tapered profiles are produced. The etch rates are increased in the groove by 25--100% indicating diffusion effects. The etch rate of the surface was in agreement with previous studies of CSOH etching, but unable to predict the dimensional changes in the grooves.

Biosensors and Microfluidic Systems

Tribological issues have received little attention in microfabricated system. Although work on miniature mechanical devices was initiated in the early 1970’s with the suspended beam and rotating electrostatic motor, issues of surface interactions in these structures has prevented their reliable operation. The application of the technology for the miniaturization of integrated circuits has also found utility in the miniaturization of chemical analysis systems (Manz et al., 1995). Semi-automated chemical analysis systems have been commercialized (Ruzicka and Hansen, 1988) and the key advantages of further reduction in size is the higher through-put of analyses can be achieved resulting in lower cost per analysis. Therefore application of microfabrication technologies facilitates the fabrication of miniature analysis systems. Furthermore, the economic benefits from batch fabrication processes will make miniature, light weight, portable, low cost analysis systems possible. In fluidic devices, the range of scaling does not offer the benefits as the volume of analyte becomes too small. Two issues arise, that of increased surface tension and pressure drop in miniature channels, and the fact that statistically there needs to be enough of the analyte molecule for the sensor to function. Many assays in biomedical analysis are at low concentration and hence volumes of at least 10 nL are required. The issues of control of sample volume without loss due to evaporation and sample reproducibility are important to solve in designing these systems. Miniature fluid handling systems can be applied to a variety of applications. Those in which the fluid is the primary component in microdialysis and drug delivery, for miniature hydraulics for the transmission of power, and in precision manufacturing for dispensing fluids in a controlled manner. The range of chemical analysis systems that can be miniaturized is likewise very broad.

Rapid Thermal Oxidation and Nitridation

In both ULSI and VLSI the sizes of MOS transistors have been scaled to submicron and micron gate widths such that the requisite dimensions of the gate dielectric films are typically less than 200 A. Rapid thermal processing (RTP) of thin dielectrics has therefore become a topic of great interest for achieving good electrical properties with a reduced thermal budget for the manufacture of these circuits. This has had particular impact in manufacturing memory devices where very high packing density is required. For example, dynamic random-access memories (DRAMs) [1], electrically programmable readonly memory (EPROM) [2], electrically erasable programmable read-only memory (EEPROM) [3], and greater than 64-Mbit random-access memory (RAM). The presence of oxide charge is clearly demonstrated by the threshold voltage shifts and leakage currents. These effects become more pronounced as the gate oxide thickness decreases and the gate capacitance increases. In EEPROMs Fowler-Nordheim (FN) tunneling current, which is used to charge and discharge the gate of the memory cell, can slowly degrade the gate dielectric properties through trapped charges in the gate dielectric. The resultant shift in the threshold voltage and increase in the leakage current reduces the time a bit of information is held in the memory cell, thus leading to electrical failure of the device. A second advantage of RTP is incorporating nitrogen into the dielectric to reduce boron penetration which occurs when p+-polysilicon is used in the fabrication of the gate electrode in p-channel MOSFETs.