Detection of Charge Storage on Molecular Thin Films of Tris(8-hydroxyquinoline) Aluminum (Alq3) by Kelvin Force Microscopy: A Candidate System for High Storage Capacity Memory Cells

• Published in: Nano letters Vol. 12; no. 3; pp. 1260 - 1264
• Main Authors: Paydavosi, Sarah, Aidala, Katherine E, Brown, Patrick R, Hashemi, Pouya, Supran, Geoffrey J, Osedach, Timothy P, Hoyt, Judy L, Bulović, Vladimir
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 14.03.2012
• Subjects: Aluminum; Charge; Computer Storage Devices; Condensed matter: structure, mechanical and thermal properties; Diffusion in nanoscale solids; Diffusion in solids; Durability; Energy Transfer; Equipment Design; Equipment Failure Analysis; Exact sciences and technology; Gates; Macromolecular Substances - chemistry; Materials Testing; Membranes, Artificial; Memory (computers); Microscopy; Microscopy, Atomic Force - methods; Molecular Conformation; Nanostructure; Nanostructures - chemistry; Nanostructures - ultrastructure; Organometallic Compounds - chemistry; Particle Size; Physics; Static Electricity; Storage capacity; Surface Properties; Thin films; Transport properties of condensed matter (nonelectronic); tris(8-hydroxyquinoline) aluminum; nonvolatile; Alq3; Kelvin force microscopy; Flash memory; charge storage; molecules; organic; Charge storage; Atomic force microscopy; Force measurement; Charge carriers; Capacitors; Hole density; High density; Aluminium compounds; Quinoline derivatives; Aluminium; Flash memories; Thin films; Charge density; Charge carrier trapping; Charge injection; Non volatile memory; Gallium tellurides; Electron density; Diffusion; Gates; Hysteresis; Via hole
• DOI: 10.1021/nl203696v
• ISSN: 1530-6984

Retention and diffusion of charge in tris­(8-hydroxyquinoline) aluminum (Alq3) molecular thin films are investigated by injecting electrons and holes via a biased conductive atomic force microscopy tip into the Alq3 films. After the charge injection, Kelvin force microscopy measurements reveal minimal changes with time in the spatial extent of the trapped charge domains within Alq3 films, even for high hole and electron densities of >1012 cm–2. We show that this finding is consistent with the very low mobility of charge carriers in Alq3 thin films (<10–7 cm2/(Vs)) and that it can benefit from the use of Alq3 films as nanosegmented floating gates in flash memory cells. Memory capacitors using Alq3 molecules as the floating gate are fabricated and measured, showing durability over more than 104 program/erase cycles and the hysteresis window of up to 7.8 V, corresponding to stored charge densities as high as 5.4 × 1013 cm–2. These results demonstrate the potential for use of molecular films in high storage capacity nonvolatile memory cells.