Tadaomi Daibou

Lower-current and fast switching of a perpendicular TMR for high speed and high density spin-transfer-torque MRAM

We investigate extremely low programming current and fast switching time of a perpendicular tunnel-magnetoresistance (P-TMR) for spin-transfer torque using a P-TMR cell of 50 nm-diameter. A L10-crystalline ordered alloy is used as a free layer that has excellent thermal stability and a damping constant of about 0.03. The programming current of 49 uA and the switching time of 4 nsec are also demonstrated.

Tunnel Magnetoresistance Over 100% in MgO-Based Magnetic Tunnel Junction Films With Perpendicular Magnetic L1

Perpendicular L1₀-FePt/MgO/Fe/L1₀ -FePt magnetic tunnel junction (MTJ) films with the (001) texture were successfully developed to obtain a large tunnel magnetoresistance (TMR) above 100 % at room temperature. The TMR ratio in the L1₀-FePt/MgO/Fe/L1₀-FePt MTJ was strongly dependent on the Fe interfacial layer thickness. The lattice mismatch between the MgO(001) barrier layer and the L1₀ -FePt(001) layer is too large for the MgO barrier layer to grow epitaxially on the L1₀-FePt(001) layer. The insertion of the Fe interfacial layer improves the quality of the MgO(001) barrier layer and achieves an epitaxy in the L1₀-FePt/MgO/Fe/L1₀-FePt stack. As a result, the optimization of the Fe interfacial layer thickness is a key to obtain the large TMR ratio in the MgO-based MTJ with the L1₀-FePt electrodes.

_{0}

We demonstrated lower power consumption of mobile CPU by replacing high-performance (HP)-SRAMs with spin transfer torque (STT)-MRAMs using perpendicular (p)-MTJ. The key points that enable the low power consumption are adapting run time power gating architecture (shown in Fig. 1), and satisfying both fast and low-power writing, namely, 3 nsec and 0.09 pJ, of p-MTJ cell (shown in Fig. 3). As shown in Table 1, only our developed p-MTJ has achieved 3 nsec, 0.09 pJ. Thanks to the fast and low-power p-MTJ, the power consumption of cache memory could be reduced by over 80% without degradation of performance.

-FePt Electrodes

We report on the spin-transfer magnetization switching properties of CoFe/Pd-based perpendicularly magnetized giant magnetoresistive cells over a wide current pulse duration time range. Analytic expressions without empirical parameters like attempt frequency are tested experimentally for the thermally assisted and precessional regimes. Good agreement with the experiment data is obtained using a common parameter set in both regimes, which leads to a comprehensive understanding of the switching properties including the origin of the attempt frequency.

Impact of ultra low power and fast write operation of advanced perpendicular MTJ on power reduction for high-performance mobile CPU

We studied the spin-transfer switching probability (Psw) in giant magnetoresistance (GMR) device with perpendicular magnetizations using short nanosecond and sub-nanosecond current pulses. A switching time of 510 picoseconds was achieved with the application of 7.5 mA, which is 4.3 times larger than the critical current at 0 K, without the application of an assisting magnetic field. Experiments with longer pulses revealed an exponential decay of the nonswitching probability (1-Psw) as a function of pulse width. Extrapolation of the results predicts an error rate of 10-19 for a pulse width of about 4.8 ns. To understand the observed pulse width dependence of Psw, we developed a formula using a macro spin model for the perpendicular magnetization system which includes the influence of thermal fluctuations in the initial magnetization direction of the free layer. The formula easily reproduces the qualitative nature of the observed Psw distributions in all time ranges.

Unified understanding of both thermally assisted and precessional spin-transfer switching in perpendicularly magnetized giant magnetoresistive nanopillars

Patterning damage at the sidewall in a magnetic tunnel junction (MTJ) was observed precisely using a rectangular MTJ where deterioration in crystallinity is easier to identify than in the case of a dot-shaped conventional MTJ. A 200-500 nm-square rectangular MTJ was patterned by a 200 eV ion beam (IB). Cross-sectional transmission electron microscopy was used for damage observation. A bright-field image showed that crystallinity deteriorated to a depth of

High-Speed Spin-Transfer Switching in GMR Nano-Pillars With Perpendicular Anisotropy

\sim 1.3

Precise Damage Observation in Ion-Beam Etched MTJ

nm in the MgO-barrier layer. A Fourier transform mapping image and a dark-field transmission electron microscopy image indicated the existence of an amorphous region at the patterning edge in the MgO layer. IB etching is one of the strong candidates for magnetic random access memory (MRAM) fabrication. However, a typical IB etching energy, e.g., 200 eV, introduces a damage depth of several monolayers at the patterned surface. Since nearly damage-free-patterned surface would be needed for high-density MRAM with nanoscale MTJs of

Spin-RAM for Normally-Off Computer

\sim 10

MgGa2O4 spinel barrier for magnetic tunnel junctions: Coherent tunneling and low barrier height

nm in diameter, IB etching with much lower energy would be necessary for fabrication.