Single-electron transistor

Article By:

Tiwari, Sandip Thomas J. Watson Research Center, IBM Corporation, Yorktown Heights, New York.

Last reviewed:1999

DOI:https://doi.org/10.1036/1097-8542.YB990795

Single-electron transistors are devices whose critical dimensions are extremely small: tens of atoms to a hundred atoms across, that is, in the nanometer range. Associated with these dimensions is an extremely small capacitance. This small capacitance, in turn, magnifies the energy required for a single electron to charge the volume defined by the critical dimension, causing this charging energy to become comparable to or larger than the thermal energy. Consequently, conduction is prevented if not enough energy is available to the electron attempting to traverse this island, and the transistor exhibits characteristics sensitive to transport and storage of single electrons. In semiconductors, at these small dimensions, device operation also becomes sensitive to quantum confinement effects. Hence, both single-electron and quantum effects help determine the device behavior, and result in a large nonlinearity in the relation of current to applied voltage and the quantization of electrons in a small volume. Such devices can be coupled to a less confined region, namely, a channel of a field-effect transistor, resulting in a memory element. Because of their smaller dimensions, low voltages, operation with a limited number of electrons, and use of silicon as the semiconductor medium, these memory elements offer a very high areal density of storage, compatibility with present-day microelectronic practice, and low-power operation. The devices cover a large design range, including high-speed elements (with write times measured in tens of nanoseconds) that require refreshing similar to that of dynamic random-access memories, and medium-speed elements (having microsecond write times) that display nonvolatility similar to that of electrically erasable and programmable memories and flash memories. Conventional dynamic memories now in production are 64 megabits in size and occupy approximately 1 cm² (0.16 in.²) of silicon chip area. Because of their significantly smaller size, the density of the new memories can exceed tens of gigabits in the same chip area; that is, they offer improvement in density by many orders of magnitude, and a large reduction in power density.

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