Molecular Memory

Electronic musicians are familiar with some of the prefixes that indicate data-storage capacity. For example, the maximum amount of RAM in the original
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Electronic musicians are familiar with some of the prefixes that indicate data-storage capacity. For example, the maximum amount of RAM in the original IBM PC was a whopping 640 kilobytes (thousands or 103 bytes). Today, of course, RAM is measured in megabytes (106 bytes) and gigabytes (109 bytes), and hard drives and RAID arrays are now available with one or more terabytes (1012 bytes) of capacity.

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FIG. 1: ZettaCore''s molecular memory uses molecules measuring 1nm across to store data bits. Multiple molecules at each memory location provide redundant defect tolerance and high signal-to-noise -characteristics.

If we learn anything from history, it should be that the need for storage capacity inevitably increases over time, and new prefixes must be added to the vernacular once in a while. So what comes after terabytes? The next step is petabytes (1015), followed by exabytes (1018), zettabytes (1021), and yottabytes (1024). Who could possibly use so much memory? That's what they asked about the original IBM PC, and look how far we've come since then.

One company that understands this better than most is ZettaCore (, a startup based in Denver, Colorado. Founded in 2001 by scientists from the University of California at Riverside and North Carolina State University, ZettaCore is developing molecular memory — that is, digital memory using individual molecules to store bits of data. This approach has the potential to create memory devices that are far smaller, with far greater density, and that use far less power than conventional semiconductor technology can achieve.

The molecules used in ZettaCore's research are called multiporphyrin nanostructures. They consist of several hundred atoms and measure only a few nanometers in size. Data is represented by removing or adding a few electrons and then detecting the molecule's charge state, which consumes much less power than conventional memory.

The molecules are designed to exhibit certain well-defined charge states called oxidation potentials, which are the energy levels required to remove one or more electrons. ZettaCore has designed molecules with up to eight oxidation potentials, allowing as many as three data bits to be stored in a single memory location.

Another critical property of ZettaCore's molecules is chemical self-assembly, which causes them to attach only to the desired materials, such as silicon or gold. In addition, they automatically pack tightly together and align themselves to operate as intended. That allows the use of equipment and techniques that are already common in the semiconductor industry; the molecules are applied to entire wafers, but they adhere only to the exposed surfaces they are designed for.

As with most solid-state memory, individual memory locations are arranged in a 2-D array (see Fig. 1). Each location contains between a few thousand and a million molecules, depending on the required size of the memory elements. This high degree of scalability is made possible by the fact that the properties of the molecules remain constant, even at very small sizes, unlike conventional semiconductor memory. The presence of many molecules at each location provides high signal-to-noise characteristics and redundancy-based defect tolerance.

ZettaCore's initial efforts are targeted at the DRAM and SRAM market, but the potential of this technology goes way beyond that — for example, solving the problem of long-term archival storage, which is especially important for musicians and other digital-media artists. The capacity of optical discs and other current forms of storage is quickly being outstripped by the ever-larger files generated by these artists. And who can say how long those storage solutions will survive or when they will become obsolete? Molecular memory devices with zettabytes or yottabytes of capacity and an unlimited lifespan could keep all the music in the world safe and available for the foreseeable future. ZettaCore's molecular-memory prototypes are nowhere near that capacity yet, but the way these things progress, it might not be long before they are.