Zoom-in on organic memory

Nano Lett.http://doi.org/hqp (2012)

In memory capacitors, a floating charge-storage layer is sandwiched between two insulator layers. The memory state of these cells can be modified by applying a high voltage across the stack, which induces a tunnelling current that changes the stored charge. The miniaturization of such devices relies on the identification of storage materials that can maintain high charge densities over long times. Sarah Paydavosi and colleagues now use Kelvin force microscopy to investigate the microscopic charge-storage properties of the organic semiconductor tris(8-hydroxyquinoline) aluminium (Alq₃). The researchers modify the technique, in which a microscope tip is scanned over a surface to measure variations in the local potential, by injecting charges in Alq₃ films, which they then monitor over time. They find that both electrons and holes in these films remain highly localized with decay times on the order of several hours. Building on this result, the researchers successfully apply 3-nm-thick Alq₃ storage layers in prototype memory capacitors, leading to charge densities of up to 5 × 10¹³ cm⁻² and reversible programmability over more than 100,000 cycles.