No abstract

We report on the fabrication of a flexible pressure sensitive device based on near-field coupling between silver nanoparticles and an underlying conductor. Visually apparent colour changes can be realized with minimal change in separation owing to the high fields localized to the particle's surface. The use of soft and compliant materials enables actuation of the device at low strain.

Active polymer materials allow the construction of cheap, flexible circuitry using simple printing techniques. A process and devices capable of performing a variety of circuit functions using electrolytic technology have been developed. The process is based on a simple screen printing system that allows the formation of multilayer circuitry with no active layer-to-layer alignment. Using this system, it has been possible to build a number of circuits utilizing transistor-like electrolytic devices and other active devices with novel topologies. Models have been developed that provide the ability to simulate arbitrary device geometries using a standard-cell approach for the basic elements required. These have allowed accurate simulation of the dynamic response of a number of device structures to be performed.

Since the discovery of electrical conduction in polyacetylene in 1977, the field of conducting polymers has progressed at a rapid and accelerating pace. It has been found that the conductivity of many of these polymers can be altered reversibly by electrochemical means. The electrolytic intercalation of ionic species into the polymer can be used to either dope an undoped material or compensate a material that has been previously doped. By varying the level of doping, the materials can be made to act as conductors, semiconductors or essentially insulators. This allows the fabrication of devices that effectively act as "electrolytic transistors" where the polymer "channel" conductivity can be adjusted by applying a potential to a counter-electrode in a liquid, gel or solid electrolyte. The basic operation of such transistors and related structures has been examined in the past [l] and interesting results on planar devices have recently been demonstrated in the literature [2,3].

The effect of replacing a conventional metal with an organic conductive polymer in a metal-insulator-semiconductor (MIS) diode is examined theoretically and experimentally. Two sets of MIS diodes, one with gold and the other with poly(3,4-ethylenedioxythiophene) as the top “metal”, have been manufactured in parallel. Despite the two conductors having similar reported work functions of 5.1 eV to 5.2 eV, the hybrid devices exhibited far lower current densities as compared to their inorganic counterparts. Simulating the device behaviour reveals the limited width of the energy bands in the conductive polymer as the reason for low current density in the hybrid MIS.