The usual way to cram more storage capacity into memory chips is to shrink the bits that hold the 1s and 0s of computer information. Researchers from the University of Southern California and NASA have built a prototype molecular memory device that puts more memory into one place by storing three bits in the same spot.

A memory chip based on the researchers' prototype would be able to hold 40 gigabits -- about a DVD's-worth of data -- per square centimeter, and the method has the potential to produce memory that holds 10 times that. Today's flash memory chips hold about 1 gigabit per square centimeter.

The multilevel molecular memory could be used to make memory chips for computers and cameras, and can be integrated into flexible substrates like smart cards, according to the researchers.

Each memory cell consists of a field-effect transistor made from a 10-nanometer-diameter indium oxide wire. Current applied to a gate electrode produces an electric field around the nanowire, which lowers the nanowire's electrical resistance, allowing current to flow through the nanowire.

The nanowire in the memory cell is covered in molecules of an organic compound that adjust the nanowire's electrical conductance to eight discrete levels. These levels represent the eight possible combinations of three bits: 000, 001, 010, 011, 100, 101, 110 and 111.

The multilevel molecular memory could be used practically in 5 to 10 years, according to the researchers. They published the research in the March 15, 2004 issue of Applied Physics Letters.