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Craig Lent

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Papers by Craig Lent

Signal Processing with Near-Neighbor-Coupled Time-Varying Quantum-Dot Arrays

by Árpád Csurgay and Craig Lent

IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—I: FUNDAMENTAL THEORY AND APPLICATIONS, VOL. 47, NO. 8, AUGUST 2000, 2000

Abstract—The Nano-Devices Group at the University of Notre Dame proposed a new device that encod... more 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 [1]. Signal processing
potential of next-neighbor-coupled cellular nonlinear networks
(CNN’s) has been recently explored with the conclusion that
local-activity of the cells is necessary to exhibit complexity [2].
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.

Experimental studies of quantum- dot cellular automata devices

by Alexei Orlov and Craig Lent

The ultimate nanodevice is the "quantum dot" since that implies confinement in all three dimensio... more The ultimate nanodevice is the "quantum dot" since that implies confinement in all three dimensions. Heretofore, no Boolean logic scheme has been proposed that is based on coupling of quantum dots. A team of researchers at the University of Notre Dame has devised and demonstrated the fundamental properties of a computing paradigm called "Quantum-dot Cellular Automata (QCA)" QCA could be accomplished in several different material systems, including semiconductor dots, metal dots, nanomagnets, or molecules. In this paper we review a series of experiments demonstrating the fundamental properties of QCA devices implemented in metal dots. Devices include basic cell, majority and other logic gates, latches, and shift registers. The chapter concludes with a discussion of sources of errors in QCA logic circuits.

format_quoteQCA latch's performance has a static bit error rate (BER) of ~10^-9 at 100 MHz clock rate, demonstrating reliable electron retention.format_quote

Fanout gate in quantum-dot cellular automata

We present an experimental demonstration of a fanout gate for quantum-dot cellular automata (QCA)... more We present an experimental demonstration of a fanout gate for quantum-dot cellular automata (QCA), where a signal applied to a single input cell is amplified by that cell and sent to two output cells. Each cell is a single-electron latch composed of three metal dots, which are connected in series by tunnel junctions. Binary information is represented by an excess

Experimental test of Landauer's Principle at the sub-kBT level

ABSTRACT Landauer&#39;s principle connects the logical reversibility of computational operati... more ABSTRACT Landauer&#39;s principle connects the logical reversibility of computational operations to physical reversibility and hence to energy dissipation, with important theoretical and practical consequences. We report the first experimental test of Landauer&#39;s principle. For logically reversible operations we measure energy dissipations much less than kB Tlog 2, while irreversible operations dissipate much more than kB Tlog 2. Measurements of a logically reversible operation on a bit with energy 30 kB T yield an energy dissipation of 0.01 kB T.

Hydrogen-bonded clusters of 1, 1′-ferrocenedicarboxylic acid on Au(111) are initially formed in solution

by Craig Lent, John Christie, and Kenneth Henderson

The Journal of Chemical Physics, 2015

Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of fer... more Low-temperature scanning tunneling microscopy is used to observe self-assembled structures of ferrocenedicarboxylic acid (Fc(COOH)2) on the Au(111) surface. The surface is prepared by pulse-deposition of Fc(COOH)2 dissolved in methanol, and the solvent is evaporated before imaging. While the rows of hydrogen-bonded dimers that are common for carboxylic acid species are observed, the majority of adsorbed Fc(COOH)2 is instead found in six-molecule clusters with a well-defined and chiral geometry. The coverage and distribution of these clusters are consistent with a random sequential adsorption model, showing that solution-phase species are determinative of adsorbate distribution for this system under these reaction conditions.

Self-assembly of hydrogen-bonded two-dimensional quasicrystals

by Craig Lent, John Christie, and Kenneth Henderson

Nature, 2014

The process of molecular self-assembly on solid surfaces is essentially one of crystallization in... more The process of molecular self-assembly on solid surfaces is essentially one of crystallization in two dimensions, and the structures that result depend on the interplay between intermolecular forces and the interaction between adsorbates and the underlying substrate. Because a single hydrogen bond typically has an energy between 15 and 35 kilojoules per mole, hydrogen bonding can be a strong driver of molecular assembly; this is apparent from the dominant role of hydrogen bonding in nucleic-acid base pairing, as well as in the secondary structure of proteins. Carboxylic acid functional groups, which provide two hydrogen bonds, are particularly promising and reliable in creating and maintaining surface order, and self-assembled monolayers of benzoic acids produce structure that depends on the number and relative placement of carboxylic acid groups. Here we use scanning tunnelling microscopy to study self-assembled monolayers of ferrocenecarboxylic acid (FcCOOH), and find that, rather than producing dimeric or linear structures typical of carboxylic acids, FcCOOH forms highly unusual cyclic hydrogen-bonded pentamers, which combine with simultaneously formed FcCOOH dimers to form two-dimensional quasicrystallites that exhibit local five-fold symmetry and maintain translational and rotational order (without periodicity) for distances of more than 400 ångströms.

Experimental demonstration of electron switching in a quantum-dot cellular automata (QCA) cell

We present an experimental demonstration of electron switching in a quantum-dot cellular automata... more We present an experimental demonstration of electron switching in a quantum-dot cellular automata (QCA) cell. The four-dot QCA cell is constructed of two capacitively-coupled double-dots. Polarization switching of the cell is accomplished by applying biases to the gates of the input double-dot and is experimentally verified from the conductances of electrometers capacitively coupled to the output double-dot. Theoretical simulations of the QCA switching show excellent agreement with experiment. We include preliminary results of a modified cell design that show improved performance.

A two-stage shift register for clocked Quantum-Dot Cellular Automata

by Craig Lent and Alexei Orlov

Journal of nanoscience and nanotechnology

Quantum-Dot Cellular Automata (QCA) is a computational scheme utilizing the position of interacti... more Quantum-Dot Cellular Automata (QCA) is a computational scheme utilizing the position of interacting single electrons within arrays of quantum dots ("cells") to encode and process binary information. Clocked QCA architectures can provide power gain, logic level restoration, and memory features. Using arrays of micron-sized metal dots, we experimentally demonstrate operation of a QCA latch-inverter and a two-stage shift register.

A functional cell for quantum-dot cellular automata

AbstractÐWe present experimental demonstration of a basic cell of Quantum-dot Cellular Automata, ... more AbstractÐWe present experimental demonstration of a basic cell of Quantum-dot Cellular Automata, a transistorless computation paradigm which addresses the issues of device density and interconnection. The devices presented consist of four and six-dot quantum-dot cellular systems where the metal dots are connected by capacitors and tunnel junctions. The operation of a basic cell is con®rmed by the externally controlled polarization change of the cell. The cell exhibits a bistable response and voltage gain. We present an experimental technique which cancels the parasitic cross-talk capacitors in the system. #

format_quoteMeasurements show clear correlation between electron switching and potential changes in QCA, validating performance theories at low temperatures.format_quote

Experimental demonstration of quantum-dot cellular automata

We present the experimental demonstration of a basic cell of quantum-dot cellular automata (QCA),... more We present the experimental demonstration of a basic cell of quantum-dot cellular automata (QCA), a transistorless computation paradigm which addresses the issues of device density and interconnection. The device presented is a six-dot quantum-dot cellular system consisting of a four-dot QCA cell and two electrometer dots. The system is fabricated using metal dots which are connected by capacitors and tunnel junctions. The operation of a basic cell is confirmed by the externally controlled polarization change of the cell. The cell exhibits a bistable response, with more than 80% polarization of the charge within a cell.

format_quoteQCA devices implement combinational logic functions with simplified interconnects, requiring only nearest neighbor communication, reducing complexity.format_quote

Observation of switching in a quantum-dot cellular automata cell

The notion of quantum-dot cellular automata (QCA) as a possible replacement paradigm for conventi... more The notion of quantum-dot cellular automata (QCA) as a possible replacement paradigm for conventional transistor-based logic is reviewed. Experiments using metal tunnel structures demonstrating a functional QCA cell are presented. It is shown that single electron tunnelling transistors used as electrometers verify proper switching of the QCA cell. Additionally, we provide evidence for a QCA cell switching frequency of 14 MHz, and a calculated upper limit of more than 5 GHz.

format_quoteA QCA full adder composed of 10 nm dots occupies less than 1.5 µm² and replaces 30 transistors, showcasing significant area efficiency.format_quote

External charge state detection of a double-dot system

by Craig Lent and Alexei Orlov

We report direct measurements of the charging diagram of a nanoscale series double-dot system at ... more We report direct measurements of the charging diagram of a nanoscale series double-dot system at low temperatures. Our device consists of two metal dots in series, with each dot capacitively coupled to another single dot serving as an electrometer. This configuration allows us to externally detect all possible charge transitions within a double-dot system. In particular, we show that transfer of an electron between two dots, representing a polarization switch of the double dot, can be most prominently detected by our differential sensing scheme. We also perform theoretical calculations of the device characteristics and find excellent agreement with experiment. We discuss possible applications as an output stage for quantum-dot cellular automata architecture.

Quantum-dot cellular automata: Review and recent experiments

An introduction to the operation of quantum-dot cellular automata is presented, along with recent... more An introduction to the operation of quantum-dot cellular automata is presented, along with recent experimental results. Quantum-dot cellular automata ͑QCA͒ is a transistorless computation paradigm that addresses the issues of device density and interconnection. The basic building blocks of the QCA architecture, such as AND, OR, and NOT are presented. The experimental device is a four-dot QCA cell with two electrometers. The dots are metal islands, which are coupled by capacitors and tunnel junctions. An improved design of the cell is presented in which all four dots of the cell are coupled by tunnel junctions. The operation of this basic cell is confirmed by the externally controlled polarization change of the cell.

Quantum computing with quantum-dot cellular automata

Physical Review A, 2001

Quantum-dot cellular automata (QCA), arrays of coupled quantum-dot devices, are proposed for quan... more Quantum-dot cellular automata (QCA), arrays of coupled quantum-dot devices, are proposed for quantum computing. The notion of coherent QCA (CQCA) is introduced in order to distinguish QCA applied to quantum computing from classical digital QCA. Information is encoded in the spatial state of the electrons in the multidot system. A line of CQCA cells can work as a quantum register.

There is no Landauer Limit: Experimental tests of the Landauer principle

2012 12th IEEE International Conference on Nanotechnology (IEEE-NANO), 2012

ABSTRACT Power dissipation is one of the most important factors limiting the development of integ... more ABSTRACT Power dissipation is one of the most important factors limiting the development of integrated circuits. This work will explore the limits of energy dissipation in computation and show that there is no &quot;Landauer Limit&quot; at k(B)T ln2 as long as information is preserved. Experimental data is presented that demonstrates a dissipation of 0.04 k(B)T, well below kBT ln2. Simulation results for adiabatically clocked reversible circuits are presented showing dramatic reductions of power dissipation.

Power gain in a quantum-dot cellular automata (QCA) shift register

Proceedings of the 2001 1st IEEE Conference on Nanotechnology. IEEE-NANO 2001 (Cat. No.01EX516), 2001

Experimental studies of clocked quantum-dot cellular automata devices

58th DRC. Device Research Conference. Conference Digest (Cat. No.00TH8526), 2000

The ultimate nanodevice is the "quantum dot" since that implies confinement in all three dimensio... more The ultimate nanodevice is the "quantum dot" since that implies confinement in all three dimensions. Heretofore, no Boolean logic scheme has been proposed that is based on coupling of quantum dots. A team of researchers at the University of Notre Dame has devised and demonstrated the fundamental properties of a computing paradigm called "Quantum-dot Cellular Automata (QCA)" QCA could be accomplished in several different material systems, including semiconductor dots, metal dots, nanomagnets, or molecules. In this paper we review a series of experiments demonstrating the fundamental properties of QCA devices implemented in metal dots. Devices include basic cell, majority and other logic gates, latches, and shift registers. The chapter concludes with a discussion of sources of errors in QCA logic circuits.

Experimental demonstration of a QCA shift register and analysis of errors

Digest. International Electron Devices Meeting,, 2002

Demonstration of a functional quantum-dot cellular automata cell

by Alexei Orlov and Craig Lent

Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 1998

We report an experimental demonstration of a functional cell for quantum-dot cellular automata ͑Q... more We report an experimental demonstration of a functional cell for quantum-dot cellular automata ͑QCA͒, a transistorless approach to implement logic functions. The four-dot QCA cell is defined by a pair of series-connected, capacitively coupled input and output double dots. We demonstrate that, at low temperature, an electron switch in the input double dot induces an opposite electron switch in the output double dot, resulting in a complete polarization change of the QCA cell. Switching is verified by electrometer signals which are coupled to the output double dot. Experimental results suggest that electron motion in the coupled double dots is strongly correlated and can support high operating frequencies. Agreement between theoretical predictions and experimentally measured values of the dot potentials is excellent.

Irreversible bit erasures in binary multipliers

2011 IEEE International Symposium of Circuits and Systems (ISCAS), 2011

Nanocircuits will suffer from heat dissipation due to irreversible information erasure, which is ... more Nanocircuits will suffer from heat dissipation due to irreversible information erasure, which is a potential new limiting factor for the maximum operating frequencies of the future circuit technologies. This paper estimates the degree of information loss in the binary multiplier structures and demonstrates that the standard hardware approaches are sub-optimal, by several orders of magnitude in comparison with the determined theoretical limit of the multiplication operation. The hardware analysis is based on the arithmetic units proposed for implementation with quantum-dot cellular automata (QCA), a circuit technology reaching molecular device densities and extremely high signal energy conservation. The results are generally applicable to all other emerging technologies based on the majority logic gate.