Fengping Wang

Structural and electrical properties of Cu films deposited on glass by DC magnetron sputtering

Abstract Cu films with thicknesses of 290–350xa0nm were deposited on glass substrates without heating by DC magnetron sputtering in pure Ar gas. Ar pressure was maintained in 0.5, 1.0 and 1.5xa0Pa, respectively. The target voltage was fixed at 400xa0V, but the target current increased from 69 to 200xa0mA with increasing Ar pressure. X-ray diffraction, scanning electron microscopy and atomic force microscopy were used to observe the structural characterization of the films. The resistivity of the films was measured using four-point probe technique. At all Ar pressures, the Cu films have mixture crystalline orientations of [1xa01xa01], [2xa00xa00] and [2xa02xa00] in the direction of the film growth. The film deposited at a lower pressure shows a slightly more [1xa01xa01] orientation while that deposited at a higher pressure has a slightly more [2xa02xa00] orientation. The amount of larger grains decreases with an increase in Ar pressure. Roughness of the film surface is about 5xa0nm independent of Ar pressure. The resistivity of the films increases with increasing Ar pressure. The increasing of Ar pressure causes the decrease in both the average energy of reflected Ar atoms and the ratio of energetic Ar atoms to Cu atoms as well as the increase in the deposition rate, resulting in the decrease in grain size and the increase in resistivity of the Cu film.

Effect of annealing on the characteristics of Au/Cr bilayer films grown on glass

Abstract Au layers with thickness of about 110xa0nm were sputter-deposited on unheated glass substrates coated with a Cr layer about 20xa0nm thick. The chamber was evacuated to a pressure of 2xa0Pa and then sputtering was carried out at Ar pressure of 4xa0Pa. The Au/Cr bilayer films were annealed in a vacuum of 5×10 −4 xa0Pa at 170°C, 180°C, 200°C and 250°C for from 5 to 120xa0min, respectively. Atomic force microscopy was used to observe the structural characteristic of the bilayer films. Auger electron spectroscopy was used to analyze the composition inside the Au layers. The sheet resistance of the films was measured using the four-point probe technique. The grain size of the bilayer film gradually increases with an increase in annealing temperature while its average surface roughness ranging from 4.5 to 6.8xa0nm does not show any systematic change with annealing temperature and time. No impurities such as carbon, nitrogen and oxygen are detected inside all of the Au layers. When the annealing temperature reaches 200°C and the annealing time exceeds 30xa0min, chromium atoms markedly diffuse into the Au layer. Furthermore, for the bilayer films annealed at 250°C, chromium atoms have markedly diffused into the Au layer even for annealing time of 5xa0min. Regardless of the increase in grain size of the Au layer, the diffusion of chromium atoms into the Au layer causes an increase in the resistivity of the bilayer film.

Effect of deposition rate on structural and electrical properties of Al films deposited on glass by electron beam evaporation

Abstract Aluminium films with thicknesses of 30–650 nm were deposited on unheated glass substrates by electron beam evaporation. The deposition rate was controlled at 10 and 33 nm/min, respectively. The structural, impure and electrical properties of aluminium films were studied by using atomic force microscopy, Auger electron spectroscopy and by measuring resistivity. The grain size of aluminium film apparently increases and the roughness of the film surface decreases from 2.5 to 1.5 nm with increasing deposition rate. Oxygen as main impurity is detected inside the film and its amount slightly decreases with increasing deposition rate. The resistivity of the films decreases from 5×10−7 to 3×10−8 Ωxa0m as the deposition rate increases from 10 to 33 nm/min. It is considered that the increasing in deposition rate weakens the influence of residual gas atoms on the growing film, resulting in the increase in grain size and the decrease in resistivity of the aluminium film.

MAGNETIC TUNNEL JUNCTIONS BASED ON PARTIALLY-OXIDIZED-IRON ELECTRODES

Partially-oxidized-iron(Fe-O)-based magnetic tunnel junctions with large magnetoresistance have been fabricated. The compositions, and the structural and transport properties of the two Fe-O electrodes are characterized. The top Fe-O layer containing 25%–28% oxygen shows a metallic characteristic with fine grain structure. No crystalline iron oxides are detected in the layer. The bottom Fe-O layer whose surface was oxidized during the oxidation process of the Al layer reveals the formation of α-Fe2O3 at the surface. The α-Fe2O3(104) is likely to be epitaxially grown on the Fe(110) plane. The layer shows a nonmetallic transport feature with negative temperature coefficient of resistance.

Structure and characteristics of large Fe-O/AlOx/Fe-O tunnel junctions

The Fe–O/AlOx/Fe–O tunnel junctions with an area of 1u2002cm2 were fabricated by reactive magnetron sputtering. The structure and properties of the junctions were studied by scanning electron microscopy, scanning Auger microprobe, x-ray diffraction (XRD), cross-sectional transmission electron diffraction (XTED), atomic force microscopy, vibrating specimen magnetometer, and I–V characteristic. The as-deposited and annealed Fe–O layers have disparate crystalline grain structure. Only bcc–Fe structure is observed in the Fe–O layers through XRD and XTED measurement. Most of the oxygen atoms exist as impurity in the films, and large compressive stress (σ≈−7.9×109u2009Pa) is induced in the Fe–O layers. The insulating AlOx layer formed by radio-frequency sputtering directly from the alumina target is dense and shows good insulating property.

Magnetic properties and structure of Ni80Fe20/Ni48Fe12Cr40 bilayer films deposited on SiO2/Si(100) by electron beam evaporation

Abstract Ni80Fe20/Ni48Fe12Gr40 bilayer films and Ni80Fe20 monolayer films were deposited at room temperature on SiO2/Si(100) substrates by electron beam evaporation. The influence of the thickness of the Ni48Fe12Cr40 underlayer on the structure, magnetization, and magnetoresistance of the Ni80Fe20/Ni48Fe12Cr40 bilayer film was investigated. The thickness of the Ni48Fe12Cr40 layer varied from about 1 nm to 18 nm while the Ni80Fe20 layer thickness was fixed at 45 nm. For the as-deposited bilayer films the introducing of the Ni48Fe12Cr40 underlayer promotes both the (111) texture and grain growth in the Ni80Fe20 layer. The Ni48Fe12Cr40 underlayer has no significant influence on the magnetic moment of the Ni80Fe20/Ni48Fe12Cr40) bilayer film. However, the coercivity of the bilayer film changes with the thickness of the Ni48Fe12Cr40 underlayer. The optimum thickness of the Ni48Fe12Cr40 underlayer for improving the anisotropic magnetoresistance effect of the Ni80Fe20/Ni48Fe12Cr40 bilayer film is about 5 nm. With a decrease in temperature from 300 K to 81 K, the anisotropic magnetoresistance ratio of the Ni80Fe20(45 nm)/Ni48Fe12Cr40(5 nm) bilayer film increases linearly from 2.1% to 4.8% compared with that of the Ni80Fe20 monolayer film from 1.7% to 4.0%.

Effect of annealing on the characteristics of Au/Ni50Fe50 bilayer films grown on glass

Abstract Sputter-deposited Au/Ni50Fe50 bilayer films were annealed in a vacuum of 5x10-4 Pa at 523 to 723 K for 30 or 90 min. The characteristics of the bilayer films were determined by Auger electron spectroscopy, field emission scanning electron microscopy. X-ray diffractometry, a four-point probe technique, and an alternating gradient magnetometer. When the annealing temperature and time reached 723 K and 90 min, Ni and Fe atoms markedly diffused into the Au layer. The grain size of the Au layer did not change markedly with the annealing condition. As the annealing time was 30 min and the annealing temperature exceeded 573 K, the resistance of the bilayer film increased with increasing the annealing temperature. Furthermore, the resistance of the bilayer film annealed at 723 K for 90 min was lower than that of the bilayer film annealed at 723 K for 30 min. All the bilayer films showed magnetic hysteresis loops. The as-deposited bilayer film showed a hard magnetization. The bilayer film represented an easy magnetization with increasing the annealing temperature. The Au/Ni50Fe50 film that annealed at 723 K for 90 min had the lowest saturation magnetization.