Stable, non-volatile computer memory could emerge from research that involves depositing amorphous carbon on to silicon, say US researchers.

While attention has focused recently on graphene, a form of graphite that exists as single sheets, James Tour and colleagues at Rice University have turned to humble amorphous carbon for their experiments in microlithography. [Tour et al., ACS Nano, Article ASAP (2009) 10.1021/nn9006225].

The researchers used industry-standard techniques - chemical vapour deposition and lithography - to deposit nanoscopic discs of amorphous carbon in 10-nanometre-thick strips on a silicon substrate. The technique offers an easy way to fabricate in parallel devices that display voltage-induced switching behaviour useful for two-terminal memory devices. The approach could pave the way for the fabrication of inexpensive reprogrammable gate arrays and non-volatile mass data storage media.

“Over the past decade, there has grown a demand for truly nano-sized electronic switches and memories that can be scaled beyond conventional CMOS counterparts,” the researchers explain. As these devices are based on two terminals rather than the three terminals used in CMOS (complementary metal-oxide semiconductor), the ability to pack these devices into 3D architectures is simplified. They point out that the approach precludes the need to develop the sophisticated manufacturing processes that would be required for devices based on carbon nanotubes, semiconductor nanowires, quantum dots, graphene nanoribbons, and individual organic molecules, by simply exploiting standard methods in a new way.

The researchers used scanning electron microscopy to analyse their depositions and have now tested the electrical properties of their graphitic stripes and found them to be remarkably stable to repeated switching. However, they cannot yet explain why the devices are so stable. Nevertheless, they were able to run a current through a 10-nm-thick layer of graphitic material to make a break in the circuit, a gap just a couple of nanometres across. Another burst of current closes the gap once again and this switching process can be repeated indefinitely at very high rates, the team says. Indeed, they observe ON/OFF ratios implying that the device can be held in the ON state (10 million parts) per one part in the OFF state at the microsecond and 3-4 Volt limits of their tests.

The demonstrated devices could provide researchers with a test bed for further experiments. The approach could lead to blank computer chips that can be rewired using software to control the making or breaking of carbon filled connections between circuit layers.