In memory cells, a bit of information is either a zero or a one. One way to cram more data into a fixed region on a data-storage device is to store more than one bit in each memory cell. The current record holder is silicon flash memory, with two bits per cell; going beyond that is difficult due to device compexities. Now, a team led by Chongwu Zhou (University of Southern California) has used self-assembled molecular electronics to build working three-bit memory cells. In a nanowire transistor, they coated the 10-nm × 2-µm wire with certain molecules and manipulated parcels of charge placed in the molecules. The resulting memory cell had three different controllable bit states, with a total of 8 (23) distinct levels. The multilevel molecular memory unit charges or discharges the molecules into different chemically reduced or oxidized (redox) states. The stored information is...

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