Showing papers in "Advanced Materials in 1990"

Electroceramics: Characterization by Impedance Spectroscopy

Abstract: Electroceramics are advanced materials whose properties and applications depend on the close control of structure, composition, ceramic texture, dopants and dopant (or defect) distribution. Impedance spectroscopy is a powerful technique for unravelling the complexities of such materials, which functions by utilizing the different frequency dependences of the constituent components for their separation. Thus, electrical inhomogeneities in ceramic electrolytes, electrode/electrolyte interfaces, surface layers on glasses, ferroelectricity, positive temperature coefficient of resistance behavior and even ferrimagnetism can all be probed, successfully, using this technique.

Electrochromic Materials for optical switching devices

Abstract: The basic principles of electrochromism have been reported and discussed using the example of WO3, and some other important electrochromic materials have been described which have a number of interesting technical applications. Both compounds and materials used in ECDs were discussed and the principles of device design were portrayed, using as an example a reflective ASSD. By continuing the search for new electrochromic compounds and by further improving device design and cost optimization the applications of these materials are bound to increase.

Chemically modified metal surfaces—a new class of composite materials

Abstract: This promising method of chemically modifying reactive metal surfaces with organic molecules prior to the attachment of polymers could have a significant impact on work aimed at the optimization of the performance of composite materials. Strong chemical bonds can be formed between a suitably prepared metal surface and certain monomers, which resist even an electrochemical polarization of the interface at large cathodic or anodic overpotentials. These chemical bonds can, however, only be achieved if a suitable structure and reactivity is generated, for example, by using electrochemical techniques. Therefore, further technological progress in this important area requires the cooperation of scientists from rather different scientific disciplines like electrochemistry, surface science and organic chemistry, in order to optimize the structure of the organic monomers and to provide the best possible bonds to the different metals in use, taking into account the rather different reactivity of technologically important media.

Langmuir–blodgett films for electronic applications

Abstract: The present status of research on Langmuir-Blodgett (LB) films is outlined in relation to specific properties for electronic applications. The fundamentals of LB films are briefly described such as preparation techniques, film types, structure, and suitable compounds for functional amphiphiles, unconventional film-forming materials and polymers. Stress is laid on novel functional LB films exhibiting either photochemical and thermal reactivity, or electroactive properties such as electrical conduction, redox activity, electrochromism, nonlinear optical properties, and pyroelectric activity. The current status of LB films with regard to electronic applications is described, e.g. as photo- or e-beam resists, information storage systems, barrier layers, chemisensors, frequency converters and modulators, optical switches, guided wave structures or infrared sensors. Prospects for future molecular electronic devices are also briefly discussed.

The transduction of host‐guest interactions into electronic signals by molecular systems

Abstract: Synthetic receptor molecules that selectively bind charged guests can store chemical information. The transduction of this information into electronic signals connects the chemical and electronic domains. Field effect transistors (FETs) are attractive transducing elements because these microdevices are able to register and amplify chemical changes at the gate oxide surface of the semiconductor chip. Integration of molecular receptors and field effect transistors into one chemical system gives a device that can communicate-changes of substrate activities in aqueous solution. Simulations of a system in which the receptor molecules are directly attached to the FET gate oxide indicate serious limitations with respect to sensitivity, dynamic range and extreme requirements for complex stability. Therefore we have concentrated on the integration of covalently attached thin membranes. The problem of the thermodynamically ill-defined oxidemembrane ipterface has been solved by applying a covalently linked hydrophilic polyhydroxyethylmethacrylate (polyHEMA) gel between the sensing membrane and the silylated gate oxide. A buffered aqueous electrolyte solution in the hydrogel renders the surface potential at the gate oxide constant via the dissociation equilibrium of the residual silanol groups. The subsequent attachment of a polysiloxane membrane that has the required dielectric constant, glass transition temperature Tg, and receptor molecule, provides a stable chemical system that transduces the complexation of cationic species into electronic signals (CHEMFET). The response to changing K concentrations in a solution of 0.1 M NaCl is fast (<1 sec) and linear in the concentration range of 10-5-1.0 M (55-58 mV /decade). A reference FET (REFET) based on the same technology is obtained when the intrinsic sensitivity to changes in ion concentration is eliminated by the addition of 2.10-5 mol g-1 of didodecyldimethyl ammonium bromide to the ACE membrane. Differential measurements with a REFET/CHEMFET combination showed excellent linear K response over long periods of time. All chemical reactions used are compatible with planar IC technology and allow fabrication on wafer scale.

Photoreactive polymers for electronics

Abstract: Light-induced changes of the properties of materials are of major imprtance in electronics. This will be illustrated by examples showing the photoresists presently used to produce submicron structures, phot-patternable insulating materials, and UV-curable reactive resins.