Bistability and Memory

This paper is a report on stable and reproducible current-controlled bistable electrical switching and memory phenomena observed in polycrystalline metal-organic semiconducting films. 

Only a few multinuclear cyanide complexes are known to exhibit spin crossover behavior. In all the cases described in Section IV.D, a gradual spin transition is observed, which can be explained by relatively weak intermolecular interactions in the crystal strucmres of these compounds. It is generally known that stronger interactions between individual SCO centers lead to cooperative behavior, abmpt spin transitions, and thermal hysteresis or bistability over a finite temperature range (276). The latter property renders SCO compounds attractive materials for the development of magnetic sensors and memory devices. It is expected that extended... 

The present chapter is organized in three sections the first section is devoted to basic theoretical backgroimd concerning the spin-crossover phenomenon, viz ligand field theory, thermodynamics and cooperativity the second section reports on some examples that we feel are particularly relevant to illustrate the main directions in which research on synthetic aspects of cooperativity is being directed finally, the third section describes three approaches, up to now reported, concerning spin bistability in supramolecular and molecular systems and memory effect. 

Y. Yang, J. Ouyang, L. Ma, R. J.-H. Tseng, C.-W. Chu, Electrical Switching and Bistability in Organic/Polymeric Thin Films and Memory Devices. Adv. Fund. Mater. 2006,16,1001-1014. 

In conclusion of this chapter it should be stated that bistable and tristable switching of ferro- and antiferroelectric liquid crystals is very fast and provides long memory states. The latter allows one to design displays without semiconductor... 

Finally, doping surface-stabilized ferroelectric liquid crystals with charge-transfer complexes, for example, tetramethyltetra-thiafulvalene/octadecyltetracyano-1,4-qui-nodimethane, has been utilized to improve their bistability [37] Ions from the CT complex form an internal electric field in reverse to the applied pulse. By applying this phenomenon, a ferroelectric liquid crystal cell with perfect bistability and inverted memory characteristics was designed [37]. Ono and Nakanowatari developed a method for the determination of the internal electric field and studied a TCNQ doped ferroelectric liquid crystal [38]. 

All ferroelectric materials are also piezo- and pyroelectric, although there are no known examples of ferroelectric LB films. However, bulk phase phthalocyanine (2) is known to undergo a ferroelectric transition at low temperature. By modifying the structure to achieve reversible spontaneous polarization upon application of an external electric field, it may be possible to produce ferroelectric LB films of such materials at more accessible temperatures. Applications for materials of this type include bistable switching devices and memory storage systems. 

Yang Y, Ouyang J, Ma L, Tseng RJ-H, Chu C-W (2006) Electrical switching and bistability in organic/polymeiic thin films and memory devices. Adv Funct Mater 16 1001-1014... 

Such controlled motion might become even more important, if one realizes that a bistable, controllable rotaxane might be useful as a nanoscale electronic device. One state would then be the "0", the other would represent the 1" state of one bit of a computer memory. Even if we have a long way to go before using these molecules as reliable functional units in electrical circuits minimized to nanometer dimensions, it seems to be of great promise and such promise demands the intense study of ways to synthesize these molecules and the detailed examination of their properties. 

Fulgides have been extensively investigated as erasable and rewritable optical memory systems (see Chapter 4) and these photochromic molecules are attractive candidates for chiroptical switch development.1471 Their bistability is based on the... 

Figure 17.13 Structure formulas of V-shaped rotaxanes 144+ and 154+, and bistable rotaxanes 164+ and 174+, used to construct switchable electronic junctions for memory and logic function purposes.114 118 119 (Adapted with permission from V. Balzani et al., ChemPhysChem 2008, 9, 202-220. Copyright Wiley-VCH Verlag GmbH Co. KGaA.)...

Kouklin, N., Bandyopadhyay, S., Tereshin, S., Varfolomeev, A., and Zaretsky, D., Electronic bistability in electrochemically self-assembled quantum dots A potential nonvolatile random access memory. Appl. Phys Lett. 76, 460 (2000). 

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