Data Storage Goes Organic

A data-storage system based on a new azo compound could increase the memory capacity of future electronic devices.

Most electronic memory systems use binary data storage, in which data are recorded as a string of zeros and ones. However, a few ternary systems—mostly experimental—have been developed that record data as zero, one, or two. In principle, the additional value means that a ternary system can hold much more data than a binary system does in a given amount of space within a storage device.

Now, Jianmei Lu, Hongwei Gu, and colleagues at Soochow University, in Suzhou, China, have devised a new ternary system (J. Am. Chem. Soc., DOI: 10.1021/ja910243f). The researchers synthesized the azo compound and sandwiched it between indium tin oxide (ITO) and aluminum electrodes. Each aluminum electrode, along with the small region of the azo material and ITO directly below it, serves as a memory storage unit, akin to the individual magnetized patches in which data are stored on a hard-drive disk.

Applying a voltage to an aluminum electrode permanently alters the density of molecular stacking—and the ease with which electrons flow—in the azo material below that electrode. The strength of the applied voltage determines whether that region of the azo layer ends up in a low-, medium-, or high-conductivity state, corresponding to zero, one, or two, respectively.

Lu and Gu’s prototype is a “write once, read many times” device, which is useful for permanent data storage. The researchers are looking for new materials that allow data to be erased and rewritten.

The proof-of-concept device is the first in which an organic molecule reliably provides three distinct, electrically switchable states for nonerasable memory storage, according to University of Pennsylvania materials scientist Ritesh Agarwal. Agarwal’s group previously developed a reliable erasable ternary data-storage system based on inorganic materials that change conductivity as an electric field switches the compounds from an amorphous to crystalline state and back (Nano Lett. 2008, 8, 2056).