We report on magnetotransport properties of arrays of cobalt/aluminum-oxide/permalloy tunnel junctions with lateral dimensions in the range of 100ϫ200 nm 2 . Due to the small capacitances, these devices show simultaneously a pronounced Coulomb blockade behavior at low temperatures and spin-dependent tunneling transport. The Coulomb blockade energies range from 0.1 to 2.6 meV. All tunnel junctions exhibiting Coulomb blockade behavior did also show a strong dependence of the tunnel current on an external magnetic field, i.e., a tunneling magnetoresistance. At temperatures below 100 K, the resistance changes up to 17% in magnetic fields of ϳ500 Oe. In addition to the known slight increase of the tunneling magnetoresistance with decreasing bias voltage, we found a strong enhancement in the Coulomb blockade regime. This enhancement is explained by cotunneling effects. Considerations towards possible application in devices are given.
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RAPID COMMUNICATIONS
R8894PRB 58 H. BRÜ CKL et al.
RAPID COMMUNICATIONS
R8896PRB 58 H. BRÜ CKL et al.
Tantalum carbonitride thin films were deposited by plasma-enhanced atomic layer deposition using the metallorganic precursor tert-butylimido tris (diethylamido) tantalum and hydrogen/argon direct plasma with 600 W radio frequency power. Within the atomic layer deposition temperature window, which ranges from below 200 to
260°C
, films grow with
∼0.35Å/cycle
. At a substrate temperature of
250°C
, the process yields
Ta2CN
films with an oxygen impurity content of below 5 atom %. These films have a cubic nanocrystalline structure, a high density of
13–14g/cm3
, as well as an excellent low resistivity of
160μΩcm
. Furthermore, the films show copper diffusion barrier performance comparable to stoichiometric physical vapor deposition TaN and a feasible wetting on multiwall carbon nanotubes. The interface between the tantalum carbonitride film and the silicon substrate was investigated using analytical electron microscopy and shows nitrogen and carbon agglomeration.
Galfenol Fe 83 Ga 17 films are sputtered on Si wafers without, and with Ti or Ti/Cu metallic seed layers in order to obtain a magnetoelastic layer which is sensitive to bending deformations of the compound structure. The layer thicknesses range from 100 nm to 5 μm. Layer morphology, texture, and the Villari effect are examined. The texture of the Galfenol films is strongly influenced by the seed layer. No low-index texture components are found for films directly deposited on Si and SiO 2 . On Ti, a (111) texture is formed on layers with more than 1000 nm thickness. A favorable (110) fiber texture is formed on Ti/Cu. Deforming the bimorphs (Si + layer system) by 0.012%, the Villari effect is detected due to the change in relative permeability. The maximum change occurs for Galfenol films with a thickness of 1 μm on a Ti/Cu buffer layer. The films open a route to the incorporation of magnetoelastic films into integrated magnetoelastic sensor devices.
The effects of crystal orientation and doping on the surface energy, γT, of native oxides of Si(100) and Si(111) are measured via Three Liquid Contact Angle Analysis (3LCAA) to extract γT, while Ion Beam Analysis (IBA) is used to detect Oxygen. During 3LCAA, contact angles for three liquids are measured with photographs via the “Drop and Reflection Operative Program (DROP™). DROP™ removes subjectivity in image analysis, and yields reproducible contact angles within < ±1°. Unlike to the Sessile Drop Method, DROP can yield relative errors < 3% on sets of 20-30 drops. Native oxides on 5 x 1013 B/cm3 p- doped Si(100) wafers, as received in sealed, 25 wafer teflon boats continuously stored in Class 100/ISO 5 conditions at 24.5°C in 25% controlled humidity, are found to be hydrophilic. Their γT, 52.5 ± 1.5 mJ/m2, is reproducible between four boats from three sources, and 9% greater than γT of native oxides on n- doped Si(111), which averages 48.1 ± 1.6 mJ/m2 on four 4” Si(111) wafers. IBA combining 16O nuclear resonance with channeling detects 30% more oxygen on native oxides of Si(111) than Si(100). While γT should increase on thinner, more defective oxides, Lifshitz-Van der Waals interactions γLW on native oxides of Si(100) remain at 36 ± 0.4 mJ/m2, equal to γLW on Si(111), 36 ± 0.6 mJ/m2, since γLW arises from the same SiO2 molecules. Native oxides on 4.5 x 1018 B/cm3 p+ doped Si(100) yield a γT of 39 ± 1 mJ/m2, as they are thicker per IBA. In summary, 3LCAA and IBA can detect reproducibly and accurately, within a few %, changes in the surface energy of native oxides due to thickness and surface composition arising from doping or crystal structure, if conducted in well controlled clean room conditions for measurements and storage.
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