We investigate the Gilbert damping and the magnetization switching of perpendicularly magnetized FeCoB-based free layers (FLs) embedded in magnetic tunnel junctions adequate for spin-torque-operated ...magnetic memories. We first study the influence of the boron content in MgO/FeCoB/Ta systems alloys on their Gilbert damping parameter after crystallization annealing. Increasing the boron content from 20% to 30% increases the crystallization temperature, thereby postponing the onset of elemental diffusion within the FL. This reduction of the interdiffusion of the Ta atoms helps maintaining the Gilbert damping at a low level of 0.009 without any penalty on the anisotropy and the magnetotransport properties up to the 400 °C annealing required in CMOS back-end-of-line processing. In addition, we show that dual MgO FLs of composition MgO/FeCoB/Ta/FeCoB/MgO have a substantially lower damping than their MgO/FeCoB/Ta counterparts, reaching damping parameters as low as 0.0039 for a 3 Å thick tantalum spacer. This confirms that the dominant channel of damping is the presence of Ta impurities within the FeCoB alloy. On optimized tunnel junctions, we then study the duration of the switching events induced by spin-transfer torque. We focus on the sub-threshold thermally activated switching in optimal applied field conditions. From the electrical signatures of the switching, we infer that once the nucleation has occurred, the reversal proceeds by a domain wall (DW) sweeping though the device at a few 10 m/s. The smaller the device, the faster its switching. We present an analytical model to account for our findings. The DW velocity is predicted to scale linearly with the current for devices much larger than the wall width. The wall velocity depends on the Bloch DW width, such that the devices with the lowest exchange stiffness will be the ones that host the DWs with the slowest mobilities.
We propose a field-free switching SOT-MRAM concept that is integration friendly and allows for separate optimization of the field component and SOT/MTJ stack properties. We demonstrate it on a 300 mm ...wafer, using CMOS-compatible processes, and we show that device performances are similar to our standard SOT-MTJ cells: reliable sub-ns switching with low writing power across the 300mm wafer. Our concept/design opens a new area for MRAM (SOT, STT and VCMA) technology development.
We study nanosecond-scale spin-torque-induced switching in perpendicularly magnetized tunnel junctions. Although the switching voltages match with the macrospin instability threshold, the electrical ...signatures of the reversal indicate the presence of domain walls in junctions of various sizes. In the antiparallel (AP)-to-parallel (P) switching, a nucleation phase is followed by an irreversible flow of a wall through the sample at an average velocity of 40 m/s with back-and-forth oscillation movements indicating a Walker propagation regime. A model with a single wall locally responding to the spin torque reproduces the essential dynamical signatures of the reversal. The P-to-AP transition has a complex dynamics with dynamical back-hopping whose probability increases with voltage. We attribute this back-hopping hopping to the instability of the nominally fixed layers.
The requirements and development of high-
k dielectric films for application in storage cells of future generation flash and Dynamic Random Access Memory (DRAM) devices are reviewed. Dielectrics with
...k-value in the 9–30 range are studied as insulators between charge storage layers and control gates in flash devices. For this application, large band gaps (>6
eV) and band offsets are required, as well as low trap densities. Materials studied include aluminates and scandates. For DRAM metal–insulator–metal (MIM) capacitors, aggressive scaling of the equivalent oxide thickness (with targets down to 0.3
nm) drives the research towards dielectrics with
k-values >50. Due to the high aspect ratio of MIMCap structures, highly conformal deposition techniques are needed, triggering a substantial effort to develop Atomic Layer Deposition (ALD) processes for the deposition of metal gates and high-
k dielectrics. Materials studied include Sr- and Ba-based perovskites, with SrTiO
3 as one of the most promising candidates, as well as tantalates, titanates and niobates.
We investigate whether smile mimicry and emotional contagion are evident in non-text-based computer-mediated communication (CMC). Via an ostensibly real-time audio-visual CMC platform, participants ...interacted with a confederate who either smiled radiantly or displayed a neutral expression throughout the interaction. Automatic analyses of expressions displayed by participants indicated that smile mimicry was at play: A higher level of activation of the facial muscle that characterizes genuine smiles was observed among participants who interacted with the smiling confederate than among participants who interacted with the unexpressive confederate. However, there was no difference in the self-reported level of joviality between participants in the two conditions. Our findings demonstrate that people mimic smiles in audio-visual CMC, but that even though the diffusion of emotions has been documented in text-based CMC in previous studies, we find no convincing support for the phenomenon of emotional contagion in non-text-based CMC.
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