Quantum-dot cellular automata (QCA) is an emerging nanotechnology, with the potential for faster speed, smaller size, and lower power consumption than transistor-based technology. Quantum-dot cellular automata has a simple cell as the basic element. The cell is used as a building block to construct gates and wires. Previously, adder designs based on conventional designs were examined for implementation with QCA technology. That work demonstrated that the design trade-offs are very different in QCA. This paper utilizes the unique QCA characteristics to design a carry flow adder that is fast and efficient. Simulations indicate very attractive performance (i.e., complexity, area, and delay). This paper also explores the design of serial parallel multipliers. A serial parallel multiplier is designed and simulated with several different operand sizes.

Adder and Multiplier Design in Quantum-Dot Cellular Automata

Quantum-dot cellular automata (QCA) is an emerging nanotechnology for electronic circuits. Its advantages such as faster speed, smaller size, and lower power consumption are very attractive. The fundamental device, a quantum-dot cell, can be used to make gates, wires, and memories. As such it is the basic building block of nanotechnology circuits. While the physical nature of the nanoscale materials is complicated, the circuit designer can concentrate on the logical and structural design, so the design effort is reduced. Because of its novelty, the current literature shows only simple circuit structures. So this paper broadens the QCA circuit designs with larger circuits and shows analyses based on those designs. This paper proposes three kinds of adder designs in QCA. Ripple carry adders, carry lookahead adders, and conditional sum adders are designed and simulated with several different operand sizes. The designs are compared according to complexity, area, and delay

Adder Designs and Analyses for Quantum-Dot Cellular Automata

In this work we present a novel probabilistic modeling tool (QCAPro) to estimate polarization error and non-adiabatic switching power loss in Quantum-dot Cellular Automata (QCA) circuits. The tool uses a fast approximation based technique to estimate highly erroneous cells in QCA circuit design. QCAPro also provides an estimate of power loss in a QCA circuit for clocks with sharp transitions, which result in non-adiabatic operations and provides an upper bound of power expended. QCAPro can be used to estimate average power loss, maximum and minimum power loss in a QCA circuit during an input switching operation. This work will provide a good platform for researchers who wish to study polarization error and power dissipation related issues in QCA circuits.

QCAPro - An error-power estimation tool for QCA circuit design

The Physics of Low-dimensional Semiconductors: An Introduction; J.H. Davies, Cambridge University Press, UK, ISBN 0-521-48491-X, $44.95

We use a coplanar QCA crossover architecture in the design of QCA full adders that leads to reduction of QCA cell count and area consumption without any latency penalty. This crossover uses non-adjacent clock zones for the two crossing wires. We further investigate the impact of these gains on carry flow QCA adders. These designs have been realized with QCADesigner, evaluated, and tested for correctness. For better performance comparison with previous relevant works, we use a QCA-specific cost function, as well as the conventional evaluation method. We show 23% cell count and 48% area improvements over the best previous QCA full adder design. Similar results for 4-, 8-, 16-, 32-, and 64-bit adders are 29% (22%), 24% (51%), 19% (54%), 13% (69%), and 9% (49%) cell count reduction (less area consumption), respectively.

Coplanar Full Adder in Quantum-Dot Cellular Automata via Clock-Zone-Based Crossover

This paper describes a project to create a novel design and simulation tool for quantum-dot cellular automata (QCA), namely QCADesigner. QCA logic and circuit designers require a rapid and accurate simulation and design layout tool to determine the functionality of QCA circuits. QCADesigner gives the designer the ability to quickly layout a QCA design by providing an extensive set of CAD tools. As well, several simulation engines facilitate rapid and accurate simulation. This tool has already been used to design full-adders, barrel shifters, random-access memories, etc. These verified layouts provide motivation to continue efforts toward a final implementation of QCA circuits.

QCADesigner: a rapid design and Simulation tool for quantum-dot cellular automata

We examine a novel quantum-dot cellular automata device concept using the interaction of resonant tunneling currents through a system of four quantum wells. The interaction of resonant tunneling currents forces the total current to flow predominantly in the wells along one of the two diagonals, effectively polarizing the cell. We refer to this device concept as split current quantum cellular automata (SCQCA). A free cell will settle to a random diagonal, whereas charge interactions between adjacent cells will cause the polarization to synchronize between cells. In contrast with the standard QCA cell, this device does not require tunneling between dots. Electron tunneling occurs along the vertical direction, where highly controllable deposition techniques are able to deposit very thin films and effectively tune the device parameters. Clocking of an SCQCA cell is performed by controlling the bias across the device, and none of the potential barriers between the dots need to be controlled. We believe this device concept lends itself to fabrication using currently available fabrication technologies.

Split current quantum-dot cellular automata-modeling and simulation

This paper investigates the simulation of charging a semiconductor quantum-dot cellular automata (QCA) cell in the presence of impurity atoms. The complete configuration space of the cell and the impurities is analysed using the canonical partition function. Limits on the size and location of the impurity region are determined. Within these limits, it is shown that the semiconductor QCA cell can be controllably charged. Using these results, it is shown that a short wire consisting of three QCA cells can operate with high logical correctness at cryogenic temperatures.

Impurity charging in semiconductor quantum-dot cellular automata

In this paper, we propose an alternative heterostructure device geometry to realize a semiconductor quantum cellular automata (QCA) cell. This device, called a split current quantum cellular automata (SCQCA) cell, has some attractive features which may enable the fabrication and circuit realization of QCA systems with current fabrication technologies. We present the device model and simulation results by incorporating this model in QCADesigner, a design and simulation tool for QCA. The simulations consist of the two cell interaction, showing the nonlinear cell-cell response function, a short wire, as well as the majority gate created with a cross pattern of five QCA cells.

R.A. Budiman

Papers

QCADesigner: a rapid design and Simulation tool for quantum-dot cellular automata

Split current quantum-dot cellular automata-modeling and simulation

Impurity charging in semiconductor quantum-dot cellular automata

Split current quantum cellular automata: device and logic gates