It is a "Schottky-barrier indium-gallium-zinc-oxide thin-film transistor operating in the deep subthreshold regime." According to the original article in Scien

It is a "Schottky-barrier indium-gallium-zinc-oxide thin-film transistor operating in the deep subthreshold regime." According to the original article in Science Mag. the currents involved are significantly lower then of the other possible technologies. It's not only that the OFF current is apparently an order of magnitude lower (as a property of the use of that material, IGZO) it's that the transistor does the useful work in the "almost off" state (as they operate it in that regime). The low currents typically mean also "slow" but for the applications intended it could be exactly what's enough, and the advantages huge. I don't see that they give any exact estimate of some real life application, it can be that the practical uses technologically introduce some limitations that aren't discussed. At least it looks promising.