Digital Memory: Molecular-Sized Switches

November 3, 2011, By George Lang

Computers and other digital devices (e.g., tablets and smartphones) use digital memory to operate and to store information. They depend on simple on/off switches to store bits of data that can then be manipulated by the processor to perform millions of productive tasks in very short periods of time.

How much memory will fit on a given size chip all depends on how small the on/off switch can be made. Silicon has its limitations. In the 1970s they began to talk about growing biological switches made from single organic molecules. The problem was how to electrically interface with each switch in order to make it useable; i.e., the thinnest visible wire is many thousands of molecules in diameter and is way too big to connect to the molecule-sized switch.

Interfacing with a Single Molecular Switch

Recent technological advances have brought the industry closer to making these connections a reality. “Contacting a single molecule: Scanning electron microscope image of a metallic bridge [see above], used for establishing contact to an individual molecule. Atomic-sized tips, serving as electrodes, are created by stretching and finally breaking this ‘nano’ bridge. The method is called the mechanically controllable break junction (MCBJ). The sketch at the top shows the switching molecule.” Research shows that, “…by applying voltage pulses to the molecule, it can be controllably switched between two distinct ‘on’ and ‘off’ states. These correspond to the ‘0’ and ‘1’ states on which data storage is based” (ERCIM Online News).

Currently, the largest silicon-based flash memory to fit on a Secure Digital or SD card is around 16 Gigabytes (16 x 1000 x 1,000,000 bytes). New SD formats have recently been released for the camera and camcorder industry that hold from 32 to 128 GB of memory (e.g., High Capacity or SDHC and Extended Capacity or SDXC respectively) but very few devices are ready to recognize them. If the industry can successfully and reliably produce molecular digital memory, the amount of memory on an SD size card versus what is currently available would be virtually analogous to the bandwidth potential of fiber optic cable versus coaxial cable.

Another form of stackable memory is also in the works; Graphene molecules with 10 nanometer circuitry compared to current 45 nanometer flash memory, is rapidly reducing chip size and increasing memory potential. Competitive memory manufacturers are chomping at the “bit” to be the first to make it all happen!

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