Tech Briefs

Promising results are reported for memory devices and solar photovoltaic cells.

A program of research has addressed multiple topics in the field of electronic and optoelectronic devices based on polymers and other organic substances, with special attention to memory devices and solar photovoltaic cells. The accomplishments of this research are summarized as follows:

  • Polymer/metal nanocomposite memory devices.

Applied Potential and Current Response of an experimental polymer/metal nanocomposite memory device were measured over several cycles of writing (W), erasure (E), and reading (R).
Electrically, these devices are characterized as bistable in that they can be switched between a high-electrical-conductance and a low-electrical conductance state. A basic device of this type comprises a polymer/ metal nanocomposite film sandwiched between two metal electrodes. In one successful experiment, the electrodes were made of aluminum, and the polymer/metal nanocomposite comprised 8 hydroxyquinoline, polystyrene, and gold nanoparticles capped with 1 dodecanethiol. The gold nanoparticles were prepared in a two-phase arrested-growth process and had sizes ranging from 1.6 to 4.4 with an average of 2.8 nm. The device was fabricated in a relatively simple process: The first layer of aluminum was deposited on a glass substrate by thermal evaporation in a vacuum. The polymer/ nanoparticle composite was deposited by spin coating with a 1,2-dichlorobenzene solution of the aforementioned polymeric and nanoparticle ingredients. The second layer of aluminum was deposited on the polymer/nanoparticle composite by thermal evaporation in a vacuum.

The figure presents measurement data from an experiment that demonstrated switching between the high- and low-conductance states, which could be taken to represent binary "1" and "0," respectively. The device was written, read, and erased repeatedly: A potential of 5 V was applied to write "1"; that is, to switch the device to the high-conductance state. The state was read by applying a lower potential (1.1 V). The current during the reading of the "1" state was 10-7 A. The "1" state was erased by applying a potential of -2.3 V, which switched the device to the low-conductance "0" state. Upon application of the reading potential of 1.1 V, the device responded at a "0"-state current of the order of 10-9 A. These write-read-erase cycles demonstrate that the device could be used as a nonvolatile memory device. Other measurements, not illustrated in the figure, have been interpreted as signifying that reading and writing can be accomplished by pulses as short as 25 ns.