The ongoing thrust in big data mining and artificial intelligence is critically demanding the high-density and fast access data storage, which cannot be fulfilled with current computation architecture due to the slow access speed of memory. Using the nonvolatile memory (NVM) element with high density and high speed can potentially tackle this impasse in the journey of next-generation computing [1] . Among several others, magnetic random-access memory (MRAM) is one of the promising NVM elements [2] . The basic building block of MRAM is a magnetic tunnel junction (MTJ), where the resistance state of the device can be modulated by manipulating the spin state of the magnetic layers via the current or magnetic field. Magnetization manipulation by voltage is an attractive alternative as it reduces the energy consumption by orders of magnitude with faster write/read operation and provides a higher density memory solution compared with current-controlled devices. The common route to use the voltage for this purpose is by exploiting the voltage-controlled magnetic anisotropy (VCMA) effect at the magnetic layer/ MgO interface [3] . Upon the application of voltage, the modification of the electronic occupation states of the d orbitals of the ferromagnetic electrode at the interface modulates the magnetic anisotropy. Additionally, the electric field-induced magnetic dipole moment and the Rashba effect are also proposed mechanisms for the origin of the VCMA effect [4] . In addition to the large VCMA effect for the writing operation, high perpendicular magnetic anisotropy (PMA) is required for thermal stability of data retention in MRAM devices [5] . The enhancement in PMA and VCMA effect in the CoFe/MgO system has resulted from the insertion of a thin metallic dusting layer (e.g. Ir, Mg, Pd, Hf) at the CoFe/MgO interface but at the expense of reducing magnetic moment [6] . In this work, we have demonstrated a large enhancement in PMA, the coercive field of the CoFe layer, and the VCMA effect with the insertion of thin, novel metallic dusting layers between CoFe and MgO layers without any reduction in magnetic moment. These results demonstrate that the engineering of the ferromagnet/MgO interface with the insertion of a suitable metallic dusting layer can provide a pathway to develop high-density voltage-driven spintronic devices.
Directed self-assembly (DSA) of block copolymers (BCPs) is a leading strategy to pattern at sublithographic resolution in the technology roadmap for semiconductors and is the only known solution to fabricate nanoimprint templates for the production of bit pattern media. While great progress has been made to implement block copolymer lithography with features in the range of 10–20 nm, patterning solutions below 10 nm are still not mature. Many BCP systems self-assemble at this length scale, but challenges remain in simultaneously tuning the interfacial energy atop the film to control the orientation of BCP domains, designing materials, templates, and processes for ultra-high-density DSA, and establishing a robust pattern transfer strategy. Among the various solutions to achieve domains that are perpendicular to the substrate, solvent annealing is advantageous because it is a versatile method that can be applied to a diversity of materials. Here we report a DSA process based on chemical contrast templates and solvent annealing to fabricate 8 nm features on a 16 nm pitch. To make this possible, a number of innovations were brought in concert with a common platform: (1) assembling the BCP in the phase-separated, solvated state, (2) identifying a larger process window for solvated triblock vs diblock BCPs as a function of solvent volume fraction, (3) employing templates for sub-10-nm BCP systems accessible by lithography, and (4) integrating a robust pattern transfer strategy by vapor infiltration of organometallic precursors for selective metal oxide synthesis to prepare an inorganic hard mask.
Abstract The spin‐coated thin‐film morphology of poly(4‐vinylpyridine) has been studied by AFM; the dark lines or disks (circular holes) in the AFM height images correspond to the depressed regions. An epitaxy‐like “nano‐trench” pattern was observed in the noncrystalline polymer film deposited on the crystalline graphite substrate. The transition from surface‐templated to isotropic dewetting occurs during 3 nm of the film thickness increase. This study presents an example of ordered nanopatterns emerging from the chaotic spin‐coating process. The well‐defined “nano‐trench” morphology offers an opportunity for the study of the nanoconfinement effect and provides a unique means for surface patterning and nanolithography. magnified image
The influence of solvents (alcohols and binary mixtures of alcohol and water) on the structure and permeability of self-assembled layer-by-layer polyelectrolyte multilayers (PEMs) has been investigated by in situ atomic force microscopy (AFM), cyclic voltammetry (CV), and confocal laser scanning microscopy (CLSM). A decrease in the dielectric constant of the solvent medium increases the strength of electrostatic interactions between the polyelectrolyte chains because the Coulombic force is inversely proportional to the dielectric constant. The stronger attractions as a result of increased alcohol volume percentage in water drive the polyelectrolyte chains to contract, collapse, and coagulate. Consequently, subtle changes in the PEM film structure are observed. AFM images show that the originally smooth surface of the PEM film becomes rougher with aggregates and holes developing with increasing alcohol amount. The diffusion of Fe(CN)63-/4- through PEM films is promoted upon solvent treatment. The entrapment of Fe(CN)63-/4- in the film occurs at a high amount of ethanol content (>60%). The permeability of large macromolecules, i.e., dextran with molecular weight of 66 kDa, to polymeric capsules is also enhanced by solvent treatment. By the methods of "additional PEM coating" and solvent treatment, the mesh size of capsules becomes tunable as does the capsule permeability. The conversion between microporous capsules to mesoporous capsules has a potential application in smart encapsulation and controlled delivery.
Directed self-assembly is emerging as a promising technology to define sub-20nm features. However, a straightforward path to scale block copolymer lithography to single-digit fabrication remains challenging given the diverse material properties found in the wide spectrum of self-assembling materials. A vast amount of block copolymer research for industrial applications has been dedicated to polystyrene-b-methyl methacrylate (PS-b-PMMA), a model system that displays multiple properties making it ideal for lithography, but that is limited by a weak interaction parameter that prevents it from scaling to single-digit lithography. Other block copolymer materials have shown scalability to much smaller dimensions, but at the expense of other material properties that could delay their insertion into industrial lithographic processes. We report on a line doubling process applied to block copolymer patterns to double the frequency of PS-b-PMMA line/space features, demonstrating the potential of this technique to reach single-digit lithography. We demonstrate a line-doubling process that starts with directed self-assembly of PS-b-PMMA to define line/space features. This pattern is transferred into an underlying sacrificial hard-mask layer followed by a growth of self-aligned spacers which subsequently serve as hard-masks for transferring the 2x frequency doubled pattern to the underlying substrate. We applied this process to two different block copolymer materials to demonstrate line-space patterns with a half pitch of 11nm and 7nm underscoring the potential to reach single-digit critical dimensions. A subsequent patterning step with perpendicular lines can be used to cut the fine line patterns into a 2-D array of islands suitable for bit patterned media. Several integration challenges such as line width control and line roughness are addressed.
Abstract Spin transfer torque magnetic random access memory (STT-MRAM) is a promising candidate for next generation memory as it is non-volatile, fast, and has unlimited endurance. Another important aspect of STT-MRAM is that its core component, the nanoscale magnetic tunneling junction (MTJ), is thought to be radiation hard, making it attractive for space and nuclear technology applications. However, studies on the effects of ionizing radiation on the STT-MRAM writing process are lacking for MTJs with perpendicular magnetic anisotropy (pMTJs) required for scalable applications. Particularly, the question of the impact of extreme total ionizing dose on perpendicular magnetic anisotropy, which plays a crucial role on thermal stability and critical writing current, remains open. Here we report measurements of the impact of high doses of gamma and neutron radiation on nanoscale pMTJs used in STT-MRAM. We characterize the tunneling magnetoresistance, the magnetic field switching, and the current-induced switching before and after irradiation. Our results demonstrate that all these key properties of nanoscale MTJs relevant to STT-MRAM applications are robust against ionizing radiation. Additionally, we perform experiments on thermally driven stochastic switching in the gamma ray environment. These results indicate that nanoscale MTJs are promising building blocks for radiation-hard non-von Neumann computing.
Segmented polyether-polyester polyurethanes with an amorphous hydrophilic soft segment phase were prepared from 4,4'-diphenylmethane diisocyanate (MDI), polybutylene adipate glycol 2000 (PBA2000) and polyethylene glycol 1000 (PEG1000) with 1,4-butanediol (BDO) as the chain extender.Furthermore, the micro phase separation structure of the polyurethanes was studied.The studies show, the micro-structure of nonionic polyurethane has been remarkable influenced by the structure, molecule and concentration of its soft segments.
Directed self-assembly (DSA) of block copolymer thin films remains a promising alternative to achieve the resolution gains needed to enable dense patterning with sub-10 nm critical dimensions (CD). Yet, some significant challenges remain. Among others, two challenges stand out: one relating to the thermodynamic and kinetic conditions that lead to finite defect densities while the second relates to a scalability challenge to harness simultaneous gains in both resolution metrics: minimum line width and minimum pitch. Here we present a self-registered self-assembly process that employs a two-step DSA to address both the energetics of defect formation and the scalability limitations to achieve simultaneous gains in both pitch and line width when compared to the guiding patterns.
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