Researchers at the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland have created flexible, energy-efficient, high-performance flash memory from graphene and molybdenite.
Molybdenite has received some attention in recent years as a possible replacement for silicon, as it has a structure, bandgap, and charge mobility that enable the creation of small, low-power transistors. Graphene, as you probably know by now, is the most conductive material in the world, making it ideal for use in high-performance electronics — but it isn’t a semiconductor, so it’s proving rather hard to include it in conventional CMOS designs.
Curiously, molybdenite (MoS2) actually looks and feels a lot like graphite/graphene, too — and indeed, given its semiconducting properties, some have suggested that we should be focusing on molybdenite instead of graphene as a silicon replacement. Importantly, both graphene and molybdenite can be cleaved (using the famed sticky tape technique) into layers that are just a single atom thick.
EPFL created the first molybdenite microchip last year, and now it has gone one step further and created floating gate (flash memory) transistors out of molybdenite and graphene. In this setup, molybdenite is the transistor’s channel, assuming silicon’s usual role. Due to molybdenite’s direct bandgap, it can be switched more efficiently than silicon, allowing for lower-power program/erase cycles. The graphene both acts as an electrode/interface to the molybdenite, and as the floating gate, which stores the memory cell’s value (i.e. it retains charge). In this case, graphene’s excellent conductivity allows for faster switching and less power consumption. The most standout feature of the memory cell, though, is a program/erase current ratio that exceeds 104 — basically, this makes it very easy to read and write data, and opens up the possibility of multi-level storage, where multiple bits of data are stored in different floating gates in the same cell.
Due to their nature of being monolayers, graphene and molybdenite are perfectly suited for the manufacture of thin, flexible electronics. They should also allow for more efficient computer chips, which could be a boon for wearable and mobile computing. Whether there will be any actual performance gains from using graphene and molybdenite remains to be seen: Pure graphene transistors are theoretically capable of switching at terahertz frequencies, but molybdenite’s properties are less well known. As far as we’re aware, EPFL seems to be the only major research institution that’s looking into molybdenite — but we’re sure, if EPFL continues its streak of molybdenite breakthroughs, other research groups will surely sit up and notice.
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