Superconductor electronic devices

The prospective applications ofmolecular assemblies seem so wide that their limits are difficult to set. The sizes of electronic devices in the computer industry are close to their lower limits. One simply cannot fit many more electronic elements into a cell since the walls between the elements in the cell would become too thin to insulate them effectively. Thus further miniaturization of today s devices will soon be virtually impossible. Therefore, another approach from bottom up was proposed. It consists in the creation of electronic devices of the size of a single molecule or of a well-defined molecular aggregate. This is an enormous technological task and only the first steps in this direction have been taken. In the future, organic compounds and supramolecular complexes will serve as conductors, as well as semi- and superconductors, since they can be easily obtained with sufficient, controllable purity and their properties can be fine tuned by minor adjustments of their structures. For instance, the charge-transfer complex of tetrathiafulvalene 21 with tetramethylquinodimethane 22 exhibits room- temperature conductivity [30] close to that of metals. Therefore it could be called an organic metal. Several systems which could serve as molecular devices have been proposed. One example of such a system which can also act as a sensor consists of a basic solution of phenolophthalein dye 10b with P-cyciodextrin 11. The purple solution of the dye not only loses its colour upon the complexation but the colour comes back when the solution is heated [31]. 

In 1962 a postgraduate student, Brian Josephson, working in the University of Cambridge, and later to win a Nobel Prize, predicted that Cooper pairs should be able to tunnel through a thin (approximately 1 nm) insulating barrier from one superconductor to another with no electrical resistance [46]. This quantum tunnelling was confirmed by experiment and is known as the Josephson effect . The superconducting electronic devices exploit Josephson junctions. 

Achievements in the field of organic conductors and superconductors have promoted the development of the field of molecular electronics as well. The latter is a nascent field of research, suggesting the use of organic molecules with the tunability of their electronic structure, instead of conventional inorganic microelectronics. It has been suggested that molecular electronic devices could utilize a variety of optoelectronic and conductivity phenomena of organic substances at the nanometer level. Whereas the conductivity and superconductivity of organic metals is a result of bulk electrical behavior of lower-dimensional systems, molecular electronics deals... 

But wire, monoliths, cables, and coils are not the only shapes of interest to materials scientists trying to shape the new superconductors into some useful form. Thin films, the form that the ceramic oxides would take in advanced computers and a host of electronic devices, are actually further along than the ceramic wire and indeed may be the very first of the new superconductors to see a practical application. 

Radebaugh, R., (2003) Cryocoolers and Fhgh-rc Devices, Handbook of High-Temperature superconductor Electronics, N. Khare (ed.), Marcel Dekker, New York, pp. 379-424. 

This chapter is intended as a convenience to those readers actively engaged in the investigation of high Tc superconductors by transmission electron microscopy (TEM). A future possible application of the newly discovered high Tc superconductors is their use in electronic devices. The electrical properties of a device strongly depend on their microstructure, since grain boundaries in these materials can behave as weak links as reported by Dimos et al. [4.1], Therefore, TEM is an important tool in the study of the relationship between the microstructure and the electrical properties. 

At first sight, metals, ceramics and polymers have little in common. This is because of two main factors - the chemical bonding holding the atoms together and the microstructure of the solids themselves - that are quite different in representative examples of each material. However, the difference is illusory. Many ceramics can be considered as metals, for example the ceramic superconductors. Many polymers show electronic conductivity greater than metals and have use in lightweight batteries and electronic devices. The material in this and later chapters will allow these apparent anomalies to be understood. 

The application of high-temperature oxide superconductors for electronic devices is being successfully performed for superconducting quantum... 

In principle, molecules can be either passive or active electronic components, either singly or in parallel as a one-molecule-thick monolayer array. This may lead to electronic devices with dimensions of 1-3 nm. Unimolecular electronics (UE) or molecular electronics sensu stricto, or molecular-scale electronics evolved from studies of organic crystalline metals, superconductors, and conducting polymers the idea is to exploit the electronic energy levels of a single molecule, and most importantly its HOMO (highest occupied molecular orbital) and LUMO (lowest unoccupied molecular orbital), which can be tuned, or modified by incorporation of electron-donating... 

Pulsed Laser Deposition. A pulsed laser (e.g. a Kr-F excimer laser) is used to vaporise material from a target, and deposit it to form a coating on a substrate. The technique is particularly applicable to the production of electronic devices using high temperature superconductors. 

Fig. 37.2 (A) Schematic illustration showing a conductive polymer/high-temperature superconductor sandwich device. To create such a structure, a YBa2Cu307-s thin film is deposited onto a MgO(lOO) substrate via laser ablation, a microbridge is patterned on the central portion of the film, and a conductive polymer layer is deposited electrochemi-cally onto the microbridge area. (B) Cyclic voltammetry (5 mV/s) recorded at room temperature in 0.1 M Et4NBp4/ acetonitrile for a YBa2Cu307-s thin-film electrode assembly coated with polypyrrole. Well-behaved voltammetry is observed, indicating that electronic charge flows readily between the superconductor and the polymer layer. (Adapted from Ref. 11.)...

When a normal metal and a superconductor are in intimate contact with each other, there can be a leakage of the superconducting Cooper pairs from the superconductor to the normal metal and quasiparticle (normal electron) leakage from the metal to the superconductor. This effect is known as the superconducting proximity effect and is an important phenomenon that can be used in practical applications such as in electronic devices and as a tool to better understand superconductivity [64J. The proximity effect can occur over distances that are quite large compared to molecular dimensions. Cooper pairs typically extend into normal metals for distances on the order of 100 nm and, in some cases, considerably further. 

Superconductors exhibit a number of properties such as zero resistance, the Meissner effect, Josephson tunneling, the proximity effect, and persistent currents (12 ) that make them well suited for use in electronic devices and sensors. Accordingly, superconducting electronic devices are particularly attractive due to the ultra-low power dissipation and ultra-fast response times that can be achieved from such substances (13). 

---