I. Lauks

The extended gate chemically sensitive field effect transistor as multi-species microprobe☆

Abstract This paper describes a multi-species microprobe structure for potentiometric measurements and the appropriate patterning techniques of the chemically-sensitive membranes. The structures consists of an integrated coaxial cable whose signal line is connected to a high input impedance electrometer with the shield boot-strapped in order to reduce capacitive charging effects. The electrometer is an on-chip source follower, designed for minimum input capacitance. The coaxial line, which is an extension of the gate of the transistor, is fabricated with a triple poly-silicon NMOS process. The whole structure is compatible with current IC technology and allows integration of on-chip signal conditioning circuitry. Units of four element probes, each covered with a different membrane, have been fabricated. One important issue in multi-sensor fabrication is the deposition and patterning technique of the membranes. A scheme has been developed which allows successive patterning of both vacuum-deposited inorganics and spin coated polymers and gels. This technique has been successfully applied for a multi-species electrode of IRO 2 (H + ),AgCl(Cl - ) LaF 3 (F - ) and Ag.

pH-sensitive sputtered iridium oxide films

Abstract The results of an extensive series of measurements of the pH response of electrodes consisting of d.c. reactively sputtered iridium oxide on a variety of substrates are reported. After an initial instability, the electrodes behave nearly theoretically between 0 and 100 °C. Preliminary testing has shown these electrodes to be stable in aqueous solutions at temperatures up to 200 °C. Interferences appear to be acceptably small.

Electrically free-standing IrOitx thin film electrodes for high temprature, corrosive environment pH sensing☆

Abstract In this paper we show that electrodes prepared by d.c. reactive sputtering of iridum oxide on to alumina substrates have utility for pH sensing in high temperature/corrosive aqueous environments. The electrode potential pH response, resulting from a potential-determining reaction between protons from solution and the film, is also transmitted along the film, the alumina rod being an inactive support. With this structure interferences resulting from electrochemical reaction between ions from solution and a substrate metal are precluded, and film peeling due to corrosive attack of such a support-metal is also reduced. We report results of measurements in concentrated acids at temperatures T‘ 100°C and atmospheric pressure, and in dilute aqueous systems at 100°‘ T ‘ 200°C and high pressure in an autoclave.

Spin-coated amorphous chalcogenide films: Photoinduced effects

Abstract Photoinduced effects in spin-coated arsenic sulfide films were investigated by UV-visible spectroscopy, X-ray diffractometry, transmission electron microscopy and IR spectroscopy. Reversible effects as well as irreversible effects were observed. The photoinduced decrease in the joint density of states between the conduction and valence bands, which can be recovered by thermal annealing, is believed to be compensated by an increase in the defects in the energy gap. The decomposition, crystallization, oxidation and grain growth of the material under UV illumination were associated with the irreversible photobleaching effect.

Electrochemical Microsensor Arrays For Biomedical Applications

A brief review of recent advances in biosensor technologies which have contributed to the development of state-of-the-art biomedical microsensors is given. This is followed by a discussion of potential medical applications in the area of diagnosis and monitoring. The combination of IC fabrication technologies with membrane science has led to a new class of chemically sensitive devices. Those show promise of having important advantages over the conventional ion selective electrodes for biomedical applications. They are small, rugged, require only a very small sample of analyte, have a fast response, are inexpensive, and are compatible with microelectronic readouts. In the second part, some specific electrochemical microfabricated sensors will be given. The results of an - integrated multispecies sensor chip for the measurement of pH, Cl , K? and Na+in physiological fluids will be discussed.

Multi-Element Thin Film Chemical Microsensors

A review of the science and technology of chemical sensing using planar micro-fabricated thin film potentiometric electrodes is presented. Those aspects of technology of stratified media that are especially peculiar to this class of structures, namely fabrication of thin film composites consisting of inoraanics, organics, gels and heterogeneous mixtures of these on planar electronic substrates are discussed. Problems encountered in patterning of this broad range of materials for the fabrication of chemical sensor arrays are emphasized.

Polyimide survival in high temperature high pressure dilute aqueous solutions

Measurements of the gross properties of polyimides at high temperature and pressures in dilute aqueous environments are reported. The polyimide polymer solution is spun onto SiO/sub 2/ substrates prepared with an aluminum chelated adhesion promoter. The cured films are subjected to temperatures exceeding 150/sup 0/C and pressures of more than 1000 lbf in/sup -2/ in dilute aqueous solutions ranging in pH from 3 to 10 for 2 to 4 h. Film quality, adhesion and water adsorption determined by IR measurements are reported.

Characteristics Of Microfabricated Ion Selective Electrodes

The paper discusses the fabrication and the test results of a blood urea nitrogen sensor (BUN) and a chloride sensor. The BUN sensor consists of a potentiometric ammonium ion sensor covered by a polymer membrane that contains the immobilized enzyme urease. The chloride sensor is a liquid membrane type electrode. Both electrodes are batch fabricated. The sensors are part of a multispecies sensor chip. The results of the sensor in aqueous solutions and blood will be given. Good uniformity and reproducibility is obtained. The BUN sensor has a linear range of 1 to 20 mM urea and a coefficient of variation of 3% in normal blood.