Applied Physics

A Little Bit of Memory

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Science  21 Jun 2002:
Vol. 296, Issue 5576, pp. 2105
DOI: 10.1126/science.296.5576.2105b

How far can memory devices shrink before thermal fluctuations corrupt data. Two groups have shown that a memory element can be fabricated in devices based on a single carbon nanotube (CNT). Fuhrer et al. built a p-type field effect transistor (FET) by growing a CNT onto a silicon substrate with a silicon dioxide insulating layer. At room temperature, the conductance of the CNT could be switched on and off by applying a gate signal of ±10 V, and, at much lower temperatures (20 K), switching the voltage over a smaller range (−1.3 to −3 V) was sufficient to change the conductance of the FET, revealed as a hysteresis in the current-voltage curves. Radosavljevi'c et al. built an n-type ambipolar FET on the same SiO2/Si substrate but with cobalt electrodes. They annealed the FET in the presence of hydrogen, which they suggest improves the coupling of the CNT to the oxide layer. When the gate voltage was switched between ±20 V, charge was injected from the CNT into the oxide layer, or vice versa, thus changing the conductance of the nanotube. This effect was harnessed to create a room temperature-stable nonvolatile memory, which is capable of storing a bit based on the flow of only a few electrons. — MSL

Nano Lett. 10.1021/nl025577o; 10.1021/nl025584c (2002).

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