Showing papers by "Alexei O. Orlov published in 2006"

Majority Logic Gate for Magnetic Quantum-Dot Cellular Automata

Abstract: We describe the operation of, and demonstrate logic functionality in, networks of physically coupled, nanometer-scale magnets designed for digital computation in magnetic quantum-dot cellular automata (MQCA) systems. MQCA offer low power dissipation and high integration density of functional elements and operate at room temperature. The basic MQCA logic gate, that is, the three-input majority logic gate, is demonstrated.

Flux-Closure Magnetic States in Triangular Cobalt Ring Elements

Abstract: Ferromagnetic ring elements on the micrometer and submicrometer scale exhibit flux-closure magnetic vortex states in an intermediate step of their magnetization reversal. These clockwise or counterclockwise flux-closure states are of interest for applications that encode binary information in magnetic elements. Here, we study the magnetization reversal process of triangular cobalt rings made by e-beam lithography and lift-off. We demonstrate that full control over the direction of flux-closure magnetic states can be achieved solely by homogeneous external magnetic fields applied in particular directions. We have extracted statistical experimental data pertaining to the range of critical field values that trigger magnetization reversal from magnetic force microscopy images, and we explain the results on the basis of micromagnetic simulations

Implementations of Quantum-dot Cellular Automata

Abstract: An introduction to quantum-dot cellular automata (QCA) is presented along with experimental implementations. QCA is a transistorless nanoelectronic computation paradigm that addresses the issues of device and power density, which are becoming increasingly important in the electronics industry. Scaling of CMOS is expected to come to an end in the next 10-15 years, with perhaps the most important limiting problem being the power density and the resulting heat generated. QCA offers the possibility of circuitry that dissipates many orders of magnitude less power than CMOS, is scalable to molecular dimensions, and provides the power gain necessary to restore signal levels.

Strong cotunneling suppression in a single-electron transistor with granulated metal film island

Abstract: Macroscopic quantum tunneling (cotunneling) is a major source of errors in single-electron devices that require the transfer of a precise number of electrons. The authors present a single-electron transistor (SET) where the suppression of cotunneling is achieved by using a granulated metal film as the material of the SET island. In this device a characteristic charging energy is defined by the Al∕AlOx junctions while the cotunneling is suppressed by electron scattering in the granulated metal island. The authors discuss possible applications of this solution for single-electron latches and pumps.

Single-electron devices with granulated film cotunneling suppressors

Abstract: Single-electron devices where a well-determined number of electrons can be controllably transferred continue to attract significant attention as one of the promising devices for applications in future digital circuits and metrology. However, the family of devices based upon precise transfer of single electrons (single-electron pumps, turnstiles, traps, latches and Quantumdot Cellular Automata (QCA) ) suffers from errors caused by cotunneling [1]. Cotunneling, a macroscopic quantum process, impairs the operation of devices where charge transfer is actuated by controllable Coulomb barriers, because it opens a classically prohibited channel for charge transfer under that barrier. A traditional way to reduce the cotunneling [2] is to increase the number of tunnel junctions in the device, N, because cotunneling current scales as I V 2N-1. For small biases the cotunneling current is thus significantly reduced. In practice, this approach has a significant drawback due to the inevitable presence of random background charges on the islands of the array. The need to individually adjust the random offset charges drastically complicates the operation and tuning of the devices. Here we present a different approach to suppress the cotunneling using a granulated metal film (Cr evaporated in 02 ambient) (Fig. 1) with weakly insulating properties. First, we fabricated and tested a single-electron transistor (SET) where suppression of the cotunneling is achieved by replacing the traditional metal island with a granulated metal film (Fig. 2). The SET has a characteristic charging energy defined by the welldefined Al/AlOx junctions while strongly suppressing the cotunneling by electron scattering in the granulated metal island (Fig 3). The value of the charging energy of the SET, EcSET z 0.27 meV exceeds the activation energy within the film, AE, by more than one order of magnitude. Therefore, with respect to the external gate, the granulated metal island can be viewed as a "good" metal and CBOs are completely defined by the larger scale parameter, EcSET >> AE. Second, using this design, we fabricated and tested a single-electron latch which utilizes this technology to achieve cotunneling suppression. A single-electron latch [3] consists of three dots connected in series by tunnel junctions. To achieve memory function in a latch the cotunneling must be suppressed. In previous demonstrations of single electron latches lithographically defined multiple tunnel junctions (MTJ) were used to connect the dots in a latch. The use of MTJs, however, requires complicated cancellation of the background charges affecting parasitic islands of the MTJs. In this work we use a granulated metal oxide film as the material for the middle dot (Fig. 4) that also acts as a cotunneling suppressor, replacing lithographically defined MTJs. The granulated metal film acts as a network of tunnel junctions and thus hampers the cotunneling while the presence of random offset charges localized in the oxidized grain boundaries makes this network of junctions insensitive to the external gate [4]. The experiments demonstrate the operation of the latch at low temperature (Fig. 5), with latching times greater than 1 s, and unlike devices fabricated using lithographically defined MTJs, no background charge compensation is required. This work was supported by the MRSEC Center for Nanoscopic Materials Design of the National Science Foundation under Award No. DMR-0080016.