Multiple Tunnel Junctions Research Articles

Electron pump current by two pulses with phase delay

Electron packet transport through two nodes built between three multiple-tunnel junctions (MTJs) was investigated. Two trapezoidal voltage pulses were applied to each node to transfer the electron packet. A pump current due to sequential transport of the electron packets was observed at a particular phase delay where the backward tail of the first pulse just overlapped the forward tail of the second pulse, whereas synchronized pulses could not carry the current. A dependence on pulse shape was also investigated.

Electronic transport in a series of multiple arbitrary tunnel junctions

Monte Carlo simulations and an analytical approach within the framework of a semiclassical model are presented which permit the determination of Coulomb blockade and single electron charging effects for multiple tunnel junctions coupled in series. The Coulomb gap in the I( V) curves can be expressed as a simple function of the capacitances in the series. Furthermore, the magnitude of the differential conductivity at current onset is calculated in terms of the model. The results are discussed with respect to the number of junctions.

Electron pump in multiple-tunnel junctions

We present measurements of an electron pump based on the Coulomb blockade in two multiple-tunnel junctions (MTJ's) connected in series, utilizing a single source of radio-frequency signal. The electron pump realizes both forward and reverse electron flow. In the reverse flow, the electrons move from the drain to the source in an opposite direction to the bias-voltage polarity. Moreover, the current polarity due to the electron pump can be switched by the two dc side-gate voltages. The bidirectional electron pump is attributed to asymmetric Coulomb blockade gaps at positive and negative sides in the current-voltage characteristics of the MTJ's.

Metal-based single electron transistors

Metal-based single electron transistors operating at liquid nitrogen temperature were fabricated. Multiple tunnel junctions with metal particles of about 3 nm in diameter were used to construct the transistors. In these transistors the gates are placed directly underneath the islands and separated only by a 10-nm-thick dielectric. The capacitance of the islands is less than 1 aF. Clear oscillations induced by gate bias voltage are observed in the current–voltage characteristics at 77 K.

77 K single electron transistors fabricated with 0.1 μm technology

Metal based single electron transistors are fabricated by the step edge cut off process. Titanium metal lines with a width of 0.1 μm are deposited on prepatterned silicon substrates, that serve as the dielectric barriers for the tunnel junctions. In structures with multiple tunnel junctions, clear Coulomb blockade and Coulomb oscillation features can be observed at temperatures up to 77 K.

Novel nanofabrication method of high temperature metallic Coulomb blockade devices

We propose a novel fabrication method to produce nanometric metallic islands with a controlled geometry by using high resolution electron beam lithography on an inorganic resist. We show that the direct vaporisation of a thin AlF3 film by electrons of 200 keV incident energy can lead to the formation of a hole surrounded by an Al metallic ring. Controlling the position of a series of holes between two metallic electrodes, it is then possible to generate small Al rings separated by very thin AlF3 insulator barriers. TEM investigations show that holes of less than 10 nm in diameter can be obtained with surrounding Al grains of less than 4 nm separated by small junctions of 2 nm. The morphology of these Al islands is fully compatible with the observation of high temperature single charge phenomena and the fabrication of multiple tunnel junction devices is described.

Enhancement of Coulomb blockade in semiconductor tunnel junctions

The Coulomb blockade region was measured directly in an experimental single-electron memory device. The device was constructed with multiple-tunnel junctions (MTJ) formed by making a sidegated constriction in δ-doped GaAs. The Coulomb blockade region is defined by electron transfer rates of less than 10 electrons per second. At low values of sidegate voltages in the MTJ an enhancement of the Coulomb blockade is observed and explained by the formation of a nonuniform electrostatic potential in the semiconductor tunnel junctions.

The multiple tunnel junction and its application to single‐electron memories

Single‐electron memories and single‐electron logic circuits are two devices that can be constructed from multiple tunnel junctions (MTJs). The electrical characteristics of this basic building block are described, and the fabrication of very small MTJ devices is outlined. The simple structure of the MTJ and the low power consumption and small size of MTJ devices could open up a new era in electron device technology, with devices being constructed from materials completely different from those used in the present semiconductor industry.

Fabrication of ultrasmall tunnel junctions by electron-beam lithography

Fabrication of a variety of ultrasmall tunneling structures is presented for possible applications in single electronics. Two main structures are described: (i) arrays of nanometer-scale metal dots and (ii) single and multiple linear tunnel junctions formed by overlapping lines. Very large, uniform particle arrays were fabricated by electron-beam lithography (EBL) with particle diameters as small as 25 nm. The advantage of our dot array system is its high degree of uniformity and very small junction size coupled with the use of isolated particles to reduce stray capacitance effects. Single and multiple linear tunnel junctions were fabricated by EBL using single-layer resist and angled evaporations. Our fabrication technique differs from previous ones in its ability to create very small tunnel junctions without the need for multilayer resist systems or precise knowledge of the angle of evaporation.