Gyorgy Csaba

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.

The Bistable Ring PUF: A new architecture for strong Physical Unclonable Functions

This paper introduces a new architecture for circuit-based Physical Unclonable Functions (PUFs) which we call the Bistable Ring PUF (BR-PUF). Based on experimental results obtained from FPGA-based implementations of the BR-PUF, the quality of this new design is discussed in different aspects, including uniqueness and reliability. On the basis of the observed complexity in the challenge-response behavior of BR-PUFs, we argue that this new PUF could be a promising candidate for Strong PUFs. Our design shows noticeable temperature sensitivity, but we discuss how this problem can be addressed by additional hardware and protocol measures.

A computing architecture composed of field-coupled single domain nanomagnets clocked by magnetic field

SUMMARY Next neighboureld coupling of nanodevices is emerging as an alternative way to integrate nano- electronic devices (Nanotechnology 1993; 4:49). In this paper, integrated circuits composed of single domain nanomagnets are proposed. New magneticeld-coupled devices with multiple equilibrium states are introduced. The devices are made locally active by exposing them to external magneticelds. Non- reciprocity is achieved by proper design of the nanomagnets shape together with its clocking. We demonstrate that (i) digital signal can propagate along a line of coupled single domain nano- magnets; (ii) and a family of logic circuits (inverter, majority gate, etc.) can be realized. Based on these observations we envision a new nanoelectronic computing architecture as a two-dimensional ar- ray ofeld-coupled nanomagnets. We estimate an integration density of 10 10 device=cm 2 , few hundred MHz operation speed, straightforward fabrication technology and robust operation in a wide temperature range. Copyright ? 2003 John Wiley & Sons, Ltd.

Behavior of Nanomagnet Logic in the presence of thermal noise

We use numerical simulations to analyze the behavior of Nanomagnet Logic (NML) in the presence of room-temperature thermal fluctuations and discuss simple models to estimate temperature-induced error rates in these devices. Our calculations show that small NML gates — composed of sub-100 nm size dots — are sufficiently stable against temperature fluctuations, but thermal noise imposes design constraints for structures with long signal paths.

Majority Gate for Nanomagnetic Logic With Perpendicular Magnetic Anisotropy

A majority gate for nanomagnetic logic with perpendicular magnetic anisotropy is presented. A novel technique of local focused ion beam irradiation generating artificial domain wall nucleation centers is used to enable directed signal flow and logic computation in an array of field-coupled nanomagnets. The switching behavior of the majority gate is characterized and logic operation is experimentally proven using magneto-optical and magnetic force microscopy. The findings are supported by numerical and micromagnetic simulations. Tolerance margins for fabrication and computing frequencies for correct operation are explored. The presented majority gate allows for complex, non-volatile logic with synchronous global clocking at room-temperature.

Simulation of Field Coupled Computing Architectures Based on Magnetic Dot Arrays

In this paper, we demonstrate that field-coupled nanomagnets can be used for digital information processing. The operation of logic devices is based on a QCA-like architecture, where information propagates by magnetostatic interaction between individual magnetic dots. Micromagnetic simulations indicate that simple logic gates function properly. Efficient design tools, based on the single-domain approximation are developed.

Coupled-Oscillator Associative Memory Array Operation for Pattern Recognition

The operation of an array of coupled oscillators underlying the associative memory function is demonstrated for various interconnection topologies (cross-connect and star-coupled). Three types of nonlinear oscillators (Andronov-Hopf, phase-locked loop, and spin torque) and their synchronization behavior are compared. Frequency-shift keying scheme of encoding input and memorized data is introduced. The speed of synchronization of oscillators and the evolution of the degree of match are studied as a function of device parameters.

Magnetic Ordering of Focused-Ion-Beam Structured Cobalt-Platinum Dots for Field-Coupled Computing

This paper presents an experimental and computational study of dipolar ordering phenomena in ion-beam patterned Co/Pt multilayers. The fabrication and the patterning of the layers were chosen to achieve single-domain dots, which show strong magnetic coupling and are uniform in their magnetic properties. We find that antiferromagnetic-like ordering can extend to as many as several hundred adjacent dots. Micromagnetic simulations reproduce the experimentally observed ordering and suggest that such multilayers are promising candidates for field-coupled computing devices.

Experimental Demonstration of a 1-Bit Full Adder in Perpendicular Nanomagnetic Logic

In this paper a 1-bit full adder realized in perpendicular nanomagnetic logic (pNML) is presented for the first time. The theory of NML with perpendicular magnetic anisotropy is introduced illustrating the great benefit of the universal majority decision. The working principle of complex logic circuits is experimentally demonstrated utilizing the presented full adder. Partial focused ion beam irradiation is used to control the anisotropy locally and tailor the magnetic behavior of the nanomagnets. A full adder structure consisting of 3 majority gates and 4 inverters is realized on an area of 17 um . Global, alternating field pulses with constant amplitude are used as power clock. MFM measurements demonstrate the functionality of the structure and the validity of the introduced theory. The presented work proves the working principle of non-volatile, field-coupled logic and demonstrates the feasibility of complex logic circuits in perpendicular nanomagnetic logic.

Spin torque oscillator models for applications in associative memories

We present physics-based models for both individual and coupled spin torque nano oscillators (STNOs). Such STNOs may become as building blocks for CNN-like dynamic computing architectures. We discuss a hierarchy of models, extending from micromagnetic models, which include the detailed geometry and physics, to compact models, which are based on parameters extracted from the underlying physical description. These simulations also include coupling between individual STNOs, both via spin waves and via electrical interconnects. Using this modeling approach, we demonstrate frequency entrainment and phase synchronization between STOs in the array, which enable computing functions.