Gary H. Bernstein

Quantum cellular automata

The authors formulate a new paradigm for computing with cellular automata (CAS) composed of arrays of quantum devices-quantum cellular automata. Computing in such a paradigm is edge driven. Input, output, and power are delivered at the edge of the CA array only; no direct flow of information or energy to internal cells is required. Computing in this paradigm is also computing with the ground state. The architecture is so designed that the ground-state configuration of the array, subject to boundary conditions determined by the input, yields the computational result. The authors propose a specific realization of these ideas using two-electron cells composed of quantum dots. The charge density in the cell is very highly polarized (aligned) along one of the two cell axes, suggestive of a two-state CA. The polarization of one cell induces a polarization in a neighboring cell through the Coulomb interaction in a very non-linear fashion. Quantum cellular automata can perform useful computing. The authors show that AND gates, OR gates, and inverters can be constructed and interconnected.

Nanocomputing by field-coupled nanomagnets

Demonstrates through simulations the feasibility of using magnetically coupled nanometer-scale ferromagnetic dots for digital information processing. Microelectronic circuits provide the input and output of the magnetic nanostructure, but the signal is processed via magnetic dot-dot interactions. Logic functions can be defined by the proper placements of dots. We introduce a SPICE macromodel of interacting nanomagnets and use this tool to design and simulate the proposed nanomagnet logic units. This SPICE model allows us to simulate such magnetic information processing devices within the same framework as conventional electronic circuits.

Experimental demonstration of a binary wire for quantum-dot cellular automata

Experimental studies are presented of a binary wire based on the quantum-dot cellular automata computational paradigm. The binary wire consists of capacitively coupled double-dot cells charged with single electrons. The polarization switch caused by an applied input signal in one cell leads to the change in polarization of the adjacent cell and so on down the line, as in falling dominos. Wire polarization was measured using single islands as electrometers. Experimental results are in very good agreement with the theory and confirm there are no metastable states in the wire.

Sub-10 nm electron beam lithography using cold development of poly(methylmethacrylate)

We investigate poly(methylmethacrylate) (PMMA) development processing with cold developers (4–10 °C) for its effect on resolution, resist residue, and pattern quality of sub-10 nm electron beam lithography (EBL). We find that low-temperature development results in higher EBL resolution and improved feature quality. PMMA trenches of 4–8 nm are obtained reproducibly at 30 kV using cold development. Fabrication of single-particle-width Au nanoparticle lines was performed by lift-off. We discuss key factors for formation of PMMA trenches at the sub-10 nm scale.

Quantum-Dot Cellular Automata at a Molecular Scale

Abstract: Quantum‐dot cellular automata (QCA) is a scheme for molecular electronics in which information is transmitted and processed through electrostatic interactions between charges in an array of quantum dots. QCA wires, majority gates, clocked cell operation, and (recently) true power gain between QCA cells has been demonstrated in a metal‐dot prototype system at cryogenic temperatures. Molecular QCA offers very high device densities, low power dissipation, and ways to directly integrate sensors with QCA logic and memory elements. A group of faculty at Notre Dame has been working to implement QCA at the size scale of molecules, where room‐temperature operation is theoretically predicted. This paper reviews QCA theory and the experimental measurements in metal‐dot QCA systems, and describes progress toward making QCA molecules and working out surface attachment chemistry compatible with QCA operation.

Operation of a quantum-dot cellular automata (QCA) shift register and analysis of errors

Quantum-dot cellular automata (QCA) is a digital logic architecture that uses single electrons in arrays of quantum dots to perform binary operations. A QCA latch is an elementary building block which can be used to build shift registers and logic devices for clocked QCA architectures. We discuss the operation of a QCA latch and a shift register and present an analysis of the types and properties of errors encountered in their operation.

Experimental demonstration of a leadless quantum-dot cellular automata cell

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.

On-Chip Clocking for Nanomagnet Logic Devices

We report local control of nanomagnets that can be arranged to perform computation in a cellular automata-like architecture. This letter represents the first demonstration of deterministically placed quantum-dot cellular automata (QCA) devices (of any implementation), where devices are controlled by on-chip local fields.

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

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.

Clocking structures and power analysis for nanomagnet-based logic devices

Logical devices made from nano-scale magnets have many potential advantages - systems should be non-volatile, dense, low power, radiation hard, and could have a natural interface to MRAM. Initial work includes experimental demonstrations of logic gates and wires and theoretical studies that consider their power dissipation. This paper looks at power dissipation too, but also considers the circuitry needed to drive a computation. Initial results are very encouraging and indicate that clocked magnetic logic could - in the worst case - match equivalent low power CMOS circuits and - in the best-case - potentially provide more than 2 orders of magnitude improvement when one considers energy per operation.