Showing papers by "Alexei O. Orlov published in 2005"

Magnetic Logic Devices Based on Field-Coupled Nanomagnets

Abstract: Nanomagnets that exhibit two distinct stable states of magnetization can be used to store digital bits. This phenomenon is already applied in today’s magnetic random access memories (MRAM). In addition, interacting networks of such nanomagnets, with physical spacing on the order of 10 nm between them, have been proposed to propagate and process binary information by means of magnetic coupling. The application of field-coupled nanomagnets for digital logic circuits was described in a concept called magnetic quantumdot cellular automata (MQCA) [1][2]. MQCA offer very low power dissipation and high integration density of functional devices. In addition, it can operate over a wide temperature range from near absolute zero to the Curie temperature of the employed ferromagnetic material. We introduce a logic gate similar to that proposed by Parish and Forshaw [3], which performs majority-logic operation. The nanomagnets are arranged in a cross-geometry as shown in Fig. 1, where the dipole coupling between the nanomagnets produces ferromagnetic and antiferromagnetic ordering of the magnetic states. Consider that the magnetic state of nanomagnets A, B, and C can be set by some inputs, and that a horizontal external magnetic field, called the clock-field, can allow the system to relax to its ground state. Then, majority logic operation can be performed by the central nanomagnet M, and the result can be transferred to another nanomagnet labeled as “out”. The cross-geometry can be extended, and inputs can be provided by adding nanomagnets that are oriented along the clock-field. Varying the position of these horizontally elongated nanomagnets, all eight input combinations in the majority-logic truth table can be tested. Figure 1. (a) An elongated polycrystalline NiFe alloy nanomagnet exhibits two stable magnetic states in the direction of its longest axis. (b) Majority gate geometry built up from nanomagnets. We demonstrate room temperature operation of majority gates made of NiFe alloy and fabricated by electron-beam lithography on silicon. Dipolar ordering in the nanomagnetnetworks is imaged by magnetic force microscopy (MFM), and the operation is explained by means of micromagnetic simulations. Figure 2 introduces a particular majority gate, in which the magnetic state of A is set to be the opposite to that of B and C. In this gate, A, B, and C all exert torque on the central dot’s magnetic moment in the same direction. Simulations show that, as the clock-field is reduced, the switching of the nanomagnets inside the gate begins at the input dots. The central dot switches after A, B, and C, and the switching propagates along the antiferromagnetically-coupled chain to the right. The figure demonstrates the final states after two independent experiments, in which the clock-field was applied in opposite directions. The MFM data shows the correct alignment of the magnetic moments in both cases.

Fanout in quantum dot cellular automata

Abstract: In this report, we describe the fabrication and experimental demonstration of fanout in QCA. Fanout is important as it is necessary for complex digital logic circuits and is essential for generating compact designs, as multiple cells can be then driven by a single driver cell. Fanout in QCA is also a direct demonstration of power gain in QCA circuits. The device is realized using metal islands (as quantum dots) and multiple tunnel junctions (MTJs) fabricated using Dolan bridge technique (Fulton, 1987). The circuit consists of three latches, with the latch in the first stage (L1) capacitively coupled to the two latches of the second stage (L2 and L3). The goal of the experiment is to switch L2 and L3 simultaneously using L1 as an input driving both L2 and L3. Each latch is formed by three quantum dots with the middle dot being connected to the end dots by MTJs

Field-coupled nanomagnets for logic applications

Abstract: Nanomagnets that exhibit only two stable states of magnetization can be used to store digital bits. This concept is already applied in today’s magnetic random access memories. Interacting networks of such nanomagnets with physical spacing on the order of 10 nm between them have been proposed to propagate and process binary information by means of magnetic coupling. These networks, called magnetic quantum-dot cellular automata (MQCA), offer very low power dissipation and high integration density of functional devices. In addition, MQCA can operate over a wide temperature range from sub-Kelvin to the Curie temperature of the applied ferromagnetic material. We demonstrate room temperature operation of logic gates made of NiFe alloy and fabricated by electron-beam lithography on silicon. Dipolar ordering in the nanomagnet-networks is imaged by magnetic force microscopy, and the operation is explained by means of micromagnetic simulations.