Showing papers by "Craig S. Lent published in 2000"

Bypassing the Transistor Paradigm

Abstract: Current computer technology is based on solid state transistors, in which binary information is carried by switching current between "on" and "off" states. When these devices are shrunk to the molecular scale, they run up against fundamental physical limits, most importantly regarding energy dissipation; as a result, superdense transistor devices would melt as soon as they were switched on. In this Perspective, Lent discusses the advantages of an alternative route to molecular electronics, quantum-dot cellular automata, which store binary information in a charge configuration instead of a current switch.

Quasi-adiabatic Switching for Metal-Island Quantum-dot Cellular Automata

Abstract: Recent experiments have demonstrated a working cell suitable for implementing the Quantum-dot Cellular Automata (QCA) paradigm. These experiments have been performed using metal island clusters. The most promising approach to QCA operation involves quasi-adiabatically switching the cells. This has been analyzed extensively in gated semiconductor cells. Here we present a metal island cell structure that makes quasi-adiabatic switching possible. We show how this permits quasi-adiabatic clocking, and enables a pipelined architecture.

Experimental demonstration of a leadless quantum-dot cellular automata cell

Abstract: We present the experimental characterization of a leadless (floating) double-dot system and a leadless quantum-dot cellular automata cell, where aluminum metal islands are connected to the environment only by capacitors. Here, single electron charge transfer can be accomplished only by the exchange of an electron between the dots. The charge state of the dots is monitored using metal islands configured as electrometers. We show improvements in the cell performance relative to leaded dots, and discuss possible implications of our leadless design to the quantum-dot cellular automata logic implementation.

Experimental demonstration of clocked single-electron switching in quantum-dot cellular automata

Abstract: A device representing a basic building block for clocked quantum-dot cellular automata architecture is reported. Our device consists of three floating micron-size metal islands connected in series by two small tunnel junctions where the location of an excess electron is defined by electrostatic potentials on gates capacitively coupled to the islands. In this configuration, the middle dot acts as an adjustable Coulomb barrier allowing clocked control of the charge state of the device. Charging diagrams of the device show the existence of several operational modes, in good agreement with theory. The clocked switching of a single electron is experimentally demonstrated and advantages of this architecture are discussed.

Quantum Cellular Neural Networks

Abstract: We have previously proposed a way of using coupled quantum dots to construct digital computing elements - quantum-dot cellular automata (QCA) Here we consider a different approach to using coupled quantum-dot cells in an architecture which, rather that reproducing Boolean logic, uses a physical near-neighbor connectivity to construct an analog Cellular Neural Network (CNN)

Signal processing with near-neighbor-coupled time-varying quantum-dot arrays

Abstract: The Nano-Devices Group at the University of Notre Dame proposed a new device that encodes information in the geometrical charge distribution of artificial (or natural) molecules. Functional units are composed by electrostatic coupling. In these units, processing takes place by reshaping the electron density of the molecules, and not by switching currents. Signal processing potential of next-neighbor-coupled cellular nonlinear networks (CNNs) has been recently explored with the conclusion that local-activity of the cells is necessary to exhibit complexity. It will be shown that Coulomb-coupled time-invariant artificial molecules behave like nonlinear locally passive devices, thus signal-power-gain or multiple equilibria cannot be achieved by integrating them. However, the signal input-output relation of strongly nonlinear molecules can be varied in time by adiabatic pumping, called clock control. It will be shown that strongly nonlinear time-varying molecules can transform the necessary amount of clock energy into the signal flow, thereby enabling the network of molecules to perform signal processing.

Modeling nanoelectronic CNN cells: CMOS, SETs and QCAs

Abstract: Summary form only given, as follows. We investigate the use of nanoelectronic structures in cellular neural network (CNN) architectures, for future high-density and low-power CMOS-nanodevice hybrid circuits. We present simulation results for Single Electron Tunneling (SET) transistors configured as a voltage-to-current transducer for CNN cells. We also present an example of quantum-dot cellular arrays which may be used to realize binary CNN algorithms. Nanoelectronics offers the promise of ultra-low power and ultra-high integration density. Several device structures have been proposed and realized experimentally, yet the main challenge remains the organization of these devices in new circuit architectures. Here, we investigate the use of nanodevices in CNN architectures. Specifically, we focus on nanostructures based on SET devices and Coulomb-coupled quantum-dot arrays, the so-called Quantum-Dot Cellular Automata (QCA). CNN-type architectures for nanostructures are motivated by the following considerations: on the one hand, locally-interconnected architectures appear to be natural for nanodevices where some of the connectivity may be provided by direct physical device-device interactions. On the other hand, CNN arrays with sizes on the order of 1000-by-1000 (which are desirable for applications such as image processing) will require the use of nanostructures since such integration densities are beyond what can be achieved by scaling conventional CMOS devices.

Experimental studies of clocked quantum-dot cellular automata devices

Abstract: Devices based on the quantum-dot cellular automata (QCA) computational approach (Lent et al, 1993) use interacting quantum dots to encode and process binary information. In this transistorless approach to computation, logic levels are represented by the configurations of single electrons in coupled quantum-dot systems. In the last few years, significant progress has been made towards the realization of basic QCA elements. However, in these devices, power gain needed for the operation of large QCA arrays was not possible since the only source of energy was the signal input. Recent theoretical work (Lent and Tougaw, 1997) proposed clocked control of the QCA circuitry. Clocked controlled QCA systems have many advantages such as power gain, reduced power dissipation, and pipelined architectures. The original theoretical work applied only to semiconductor implementation of clocked QCA arrays, but recently a scheme for clocked control of metallic QCA cells was proposed (Toth and Lent, 1999; Korotkov and Likharev, 1998). Here an extra dot placed between the two dots of the QCA half-cell acts as a tunable barrier controlled by the clock signal. We present the experimental demonstration of a clocked QCA cell. The device consists of two capacitively coupled half-cells, where each half-cell consists of three micron-size Al islands separated by tunnel junctions, and four electrometers to measure the charge state of the half-cells. The half-cells are leadless, with no DC connection to the environment.