Mémoires Organiques Supramoléculaires – SUPRAMEM

This project is devoted to the development of original approaches for rewritable organic non-volatile memories with a density close to 1 bit per 20nm2 (30 Tbit per in2), stable at room temperature and under air pressure. - These devices will be based on: - 1) bottom-up construction of organic nanowires on a semi conductive surface acting as a template, - 2) development of self-organized architectures stable under air pressure and at room temperature, - 3) cis-trans isomerisation of N=N double bond by domino effect induced by STM tip, - 4) reading of data by STM, EFM or AFM, - 5) erasing of data by heating. - We propose a new concept which takes the advantages of the large density obtained with organic molecules and the addressing of wire-type arrangement for the development of an innovative non-volatile memory with high density, and operating at room temperature under air atmosphere and compatible with CMOS technology. - In order to circumvent the problem of traditional silicon surface reactivity with p-conjugated molecules, an original reconstructed semi-conductive substrate Si-B will be used. The main property of this interface is to exhibit depopulated dangling bonds due to boron atoms under the top silicon layer. Consequently, p-conjugated organic molecules would weakly interact with pz depopulated dangling orbitals of the surface and thus preserve their electronic structure after deposition. In addition, the total potential resulting on the SiB surface has been calculated and the results show a positive contour along the main diagonal of the Si-B reconstruction. This implies that electron-rich p-conjugated organic molecules can be specifically adsorbed on the Si-B reconstruction by superimposing their rich-electron moieties onto two electron-poor silicon atoms localized at the extremity of the main diagonal of this interface to form nanowires. Consequently, an original organisation of the organic supramolecular network will be achieved by template effects of the underlying Si-B surface. The cis-trans isomerisation of N=N bond in azobenzene derivatives will be the site of the data storage. The compounds will be deposited on SiB surface, and form supramolecular wires in order to facilitate data addressing and reading on such a network. All target molecules will exhibit N=N double bond and will lie flat on the semi-conductive interface due to the functional groups created for their self-assembly. Moreover, an original solution which consists in the formation of organic nanowire with N=N double bond organised perpendicularly to the main axis of the nanowires is proposed to reinforce the stability of the network of nanowires. The writing process will be obtained by the STM tip which is able to isomerise all N=N bonds in the nanowire by domino effect. To overcome the limitations of the nanopositionning of the open-loop scanners currently available for STM, AFM and SPM, the addressing will be obtained by a commercial ultra-high performance scanner (capacitive feedback) used for nanoimprinting, nanolithography and nano-surface-metrology applications, capable of 50 picometers resolution for a 5x5x5 micrometer travel range. STM or EFM will act as the reading process. Finally, the complete erasing of the data will also be possible by a strong heating of the substrate. - The main results expected are (i) the fabrication of organic nanowires on Si-B surface, stable at room temperature and (ii) the experimental validation of our innovative concept of complete isomerisation of organic nanowires induced by STM tip. Theses two points will be the start of a major breakthrough for the introduction of nanotechnologies in memories with densities larger than 10Tbit/in2 instead of few Gbit/in2 for the best devices commercially available today. - ...