Organic materials are attractive for memory applications: they can be ideally scaled down to molecular size, they are processed at a temperature close to ambient temperature, they can be deposited in layered structures on a large number of substrates, silicon included. Therefore organic materials address correctly the issues of next generation memory devices, that is minimum size of the cell and 3-dimentional stacking for maximum density, without forgetting the lower cost of fabrication and the ecological advantage of a very low energetic budget during production. These potentialities have since long solicited the investigation of memory effects in organic materials, leading to interesting results on both molecular and bulk bistable devices.
The research at DEI (initiated with the European Community project Nosce Memorias IST-2002-2.3.1.1) is focused on a new class of organic memory devices based on phenol substituted bithiophenes whose conductivity can be switched between two stable values upon electric pulses.
A simple two terminal memory device has been made that can store information in a non-volatile way by means of two well distinct conductance states that can be programmed and read electronically.
The devices have shown to operate both in air and in vacuum with low programming voltages of about 4V, to retain the information for largely more than 48 hours in each state and to sustain multiple write&erase cycles in excess to 200 if pristine and in excess to 1000 when blended in a matrix of polystirene, without degradation in the active material volume as testified by infrared spectroscopy.
Although questions still remains on the basic switching mechanisms and on the role of the electrodes, organic-based devices have proved to merit large attention toward the realisation of scaled memory cells.