Scalability of spin FPGA: A Reconfigurable Architecture based on spin MOSFET

Scalability of Field Programmable Gate Array (FPGA) using spin MOSFET (spin FPGA) with magnetocurrent (MC) ratio in the range of 100% to 1000% is discussed for the first time. Area and speed of million-gate spin FPGA are numerically benchmarked with CMOS FPGA for 22nm, 32nm and 45nm technologies including 20% transistor size variation. We show that area is reduced and speed is increased in spin FPGA owing to the nonvolatile memory function of spin MOSFET.Comment: 3 pages, 7 figure

Spin Transfer from a Ferromagnet into a Semiconductor through an Oxide barrier

We present results on the magnetoresistance of the system Ni/Al203/n-doped Si/Al2O3/Ni in fabricated nanostructures. The results at temperature of 14K reveal a 75% magnetoresistance that decreases in value up to approximately 30K where the effect disappears. We observe minimum resistance in the antiparallel configurations of the source and drain of Ni. As a possibility, it seems to indicate the existence of a magnetic state at the Si/oxide interface. The average spin diffusion length obtained is of 650 nm approximately. Results are compared to the window of resistances that seems to exist between the tunnel barrier resistance and two threshold resistances but the spin transfer seems to work in the range and outside the two thresholds

Crossover from Kondo assisted suppression to co-tunneling enhancement of tunneling magnetoresistance via ferromagnetic nanodots in MgO tunnel barriers

Recently, it has been shown that magnetic tunnel junctions with thin MgO tunnel barriers exhibit extraordinarily high tunneling magnetoresistance (TMR) values at room temperature1, 2. However, the physics of spin dependent tunneling through MgO barriers is only beginning to be unravelled. Using planar magnetic tunnel junctions in which ultra-thin layers of magnetic metals are deposited in the middle of a MgO tunnel barrier here we demonstrate that the TMR is strongly modified when these layers are discontinuous and composed of small pancake shaped nanodots. At low temperatures, in the Coulomb blockade regime, for layers less than ~1 nm thick, the conductance of the junction is increased at low bias consistent with Kondo assisted tunneling. In the same regime we observe a suppression of the TMR. For slightly thicker layers, and correspondingly larger nanodots, the TMR is enhanced at low bias, consistent with co-tunneling.Comment: Nano Letters (in press

Proposal and analysis of a ferromagnetic triple-barrier resonant-tunneling spin filter

A novel spin filter consisting of a triple-barrier resonant tunneling system in the form F/I/N/I/F/I/F is proposed, where F, I, and N represent a ferromagnetic material, an insulator, and a nonmagnetic material, respectively. The spin-dependent tunneling current in the triple-barrier resonant tunneling system is calculated theoretically on the basis of a Tsu-Esaki formula to investigate the output tunnel current polarization. Detailed calculations using the GaMnAs/AlAs/GaAs material system show that the two clear split peaks originating from up- and down-spin holes appear in the current-voltage (I-V) curve due to spin splitting of the energy levels formed in the ferromagnetic quantum well. The polarization can reach more than 98% at the peak positions in the I-V curve

Four-State Magnetoresistance in Epitaxial CoFe-Based Magnetic Tunnel Junctions

A four-state magnetic random access memory (MRAM) was developed using an epitaxial Co50Fe50-MgO-Co50Fe 50 magnetic tunnel junction (MTJ) with a tunnel magnetoresistance (TMR) ratio of 145% at room temperature (RT). Four remanent magnetization states in the single-crystalline Co50Fe50 electrode, due to the cubic anisotropy with easy axes of the lang110rang directions, result in four possible angular-dependent TMRs, each separated by more than 20% at RT. Analysis of the asteroid curve for Co50Fe50 indicated that the magnetic field along 22.5deg from the lang110rang directions made it possible to change the magnetization direction of the selected cell without disturbing those of the half-selected cells

Exchange Bias Effect in Full-Heusler Alloy Co2Cr0.6Fe0.4Al Epitaxial Thin Films

We fabricated trilayer structures consisting of a Co-based full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) layer, a Ru ultrathin film, and a Co90Fe10 layer, and demonstrated well-established antiferromagnetic coupling in the fabricated structures. Furthermore, we observed a clear exchange bias effect in a CCFA/Ru/Co90Fe10/IrMn layer structure with a typical exchange bias field of about 430 Oe at room temperature. These results indicate that the use of a CCFA thin film in antiferromagnetically coupled trilayers is advantageous for obtaining a strong exchange bias field

Highly Spin-Polarized Tunneling in Fully Epitaxial Magnetic Tunnel Junctions Using Full-Heusler Alloy Co2Cr0.6Fe0.4Al Thin Film and MgO Tunnel Barrier

Highly spin-polarized tunneling with tunnel magnetoresistance (TMR) ratios of 90% at room temperature and 240% at 4.2 K was demonstrated for fully epitaxial magnetic tunnel junctions fabricated using a cobalt-based full-Heusler alloy Co2Cr0.6Fe0.4Al (CCFA) thin film having a composition close to the stoichiometric one and a MgO tunnel barrier. A high tunneling spin polarization of 0.79 at 4.2 K was obtained for the epitaxial CCFA films from the TMR ratios. This adds to the promise of the fully epitaxial MTJ as a key device structure for utilizing the intrinsically high spin polarizations of Co-based full-Heusler alloy thin films

Fabrication of Fully Epitaxial Co2Cr0.6Fe0.4Al/MgO/Co2Cr0.6Fe0.4Al Magnetic Tunnel Junctions

Fully epitaxial magnetic tunnel junctions (MTJs) of Co2Cr0.6Fe0.4Al (CCFA)/MgO/CCFA with exchange biasing were fabricated. The fabricated MTJs showed clear exchange-biased tunnel magnetoresistance (TMR) characteristics due to the CCFA/Ru/Co90Fe10/IrMn exchange-biased synthetic ferrimagnetic layer. The TMR characteristics were investigated as a function of in situ annealing temperature (Ta) for the upper CCFA layer. We obtained TMR ratios of 60% at room temperature (RT) and 238% at 4.2 K for MTJs with Ta of 400 degC, while those for MTJs with Ta of RT (i.e., having an as-deposited upper CCFA layer) were 17% at RT and 80% at 4.2 K. These results clearly suggest that the spin polarization of the as-deposited upper CCFA layer was significantly increased by in situ annealing

Epitaxial Growth of Full-Heusler Alloy Co2MnSi Thin Films on MgO-Buffered MgO Substrates

Full-Heusler alloy Co₂MnSi (CMS) thin films were epitaxially grown on MgO-buffered MgO substrates through magnetron sputtering. The films were deposited at room temperature and subsequently annealed in situ at 600℃. X-ray pole figure measurements of the annealed films showed 111 peaks with fourfold symmetry, providing direct evidence that these films were epitaxial and crystallized in the L2₁ structure. The annealed films had sufficiently flat surface morphologies with root-mean-square roughness of about 0.22 nm at a film thickness of 50 nm. The saturation magnetization of the annealed films was 4.5μ B/f.u. at 10 K, corresponding to about 90% of the Slater–Pauling value for CMS

Spin-dependent tunneling characteristics of fully epitaxial magnetic tunneling junctions with a full-Heusler alloy Co[sub 2]MnSi thin film and a MgO tunnel barrier

Fully epitaxial, exchange-biased magnetic tunnel junctions (MTJs) were fabricated with a Co-based full-Heusler alloy Co2MnSi (CMS) thin film as a lower electrode, a MgO tunnel barrier, and a Co50Fe50 upper electrode. The microfabricated CMS/MgO/Co50Fe50 MTJs exhibited relatively high tunnel magnetoresistance ratios of 90% at room temperature and 192% at 4.2 K. The bias voltage dependence of differential conductance (dI/dV) for the parallel and antiparallel magnetization configurations suggested the existence of a basic energy gap structure for the minority-spin band of the CMS electrode with an energy difference of about 0.4 eV between the bottom of the vacant minority-spin conduction band and the Fermi level. ©2006 American Institute of Physic