A nanoscale transistor based on gate-induced stochastic transitions

A nanoscale device consisting of a metal nanowire, a dielectric, and a gate is proposed. A combination of quantum and thermal stochastic effects enable the device to have multiple functionalities, serving alternately as a transistor, a variable resistor, or a simple resistive element with I −V characteristics that can switch between ohmic and non-ohmic. By manipulating the gate voltage, stochastic transitions between different conducting states of the nanowire can be induced, with a switching time as short as picoseconds. With an appropriate choice of dielectric, the transconductance of the device can significantly exceed the conductance quantum G0 = 2e2/h, a remarkable figure of merit for a device at this lengthscale. Variable resistors are commonly used circuit elements in many electronic applications. However, their large size and slow response time have heretofore limited their use primarily to the To whom correspondence should be addressed †Department of Physics and Astronomy, California State University, Sacramento ‡Department of Physics, University of Arizona ¶Department of Physics and Courant Institute of Mathematical Sciences, New York University 1 human-circuit interface. In this article, we describe how the exploitation of quantum and stochastic effects at the nanoscale1 allows one to combine what would ordinarily be distinct macroscale circuit elements into a single nanoscale device with multiple functionalities, and to achieve response times on the order of picoseconds. The device architecture we propose is illustrated in Figure 1. The physics behind its operation is the following: A metal nanowire is the active circuit element, and is embedded in a dielectric sheath, surrounded by an outer conductor of comparable dimensions, referred to as the gate. A positive/negative voltage applied to the gate enhances/depletes the density of carriers in the nanowire. This results in a shift of the electronic Fermi energy EF , which alters the electron-shell structure of the nanowire.1–4 This in turn changes the energy barriers that determine the rates of stochastic transitions5,6 between different conducting states of the nanowire. The idea is that a sufficient voltage applied at the gate will make the energy barrier small enough to be comparable to the thermal energy kT , thus making a stochastic transition all but certain. Figure 1: Diagram of the proposed device Such a device would require as active element a nanowire where electron-shell effects dominate over atomic-shell effects.7 This has been shown8 to be the case for wires of conductance between a few and about a hundred conductance quanta G0 = 2e2/h. Such nanowires with lengths below or around a few nanometers have been fabricated using various techniques, including scanning tunneling microscopy (STM),9,10 mechanically-controllable break junctions (MCBJ),11,12 thin-film