Search

W–C thin films were prepared by non-reactive magnetron co-sputtering simultaneously from pure tungsten and carbon targets in an argon atmosphere at room temperature on Si(100) substrate. The main purpose of the present work was to investigate the influence of deposition method and annealing process on structural and electrical properties of the tungsten carbide thin films. The experimental results show that the growth rate of films was about 5.46 nm/min; the films have spherical granular structure. Hexagonal W2C appeared when the annealing temperature was 700 and 800°C and W : C atomic ratio of 1.18. Moreover, grain size of W2C films was about 8.1 and 11.7 nm after annealing at 700 and 800°C, respectively. Resistivity of films was relatively high, possibly due to the presence of excess carbon in the films not bound with tungsten, verified by the Raman spectrum.

Titanium carbide (TiC) thin films were prepared by non-reactive simultaneous double magnetron sputtering. After deposition, all samples were annealed at different temperatures under high-vacuum conditions. This paper mainly discusses the influence of deposition methods and annealing temperatures on microstructure, surface topography, bonding states and electrical resistivity of TiC films. XRD (X-ray diffraction) results show that TiC thin films can still form crystals without annealing, and the crystallinity of thin films is improved after annealing. The estimated grain size of the TiC films varies from 8.5 nm to 14.7 nm with annealing temperature. It can be seen from SEM (scanning electron microscope) images that surfaces of the films are composed of irregular particles, and when the temperature reaches to 800 °C, the shape of the particles becomes spherical. Growth rate of film is about 30.8 nm/min. Oxygen-related peaks were observed in XPS (X-ray photoelectron spectroscopy) spectra, which is due to the absorption of oxygen atoms on the surface of the film when exposed to air. Raman spectra confirm the formation of TiC crystals and amorphous states of carbon. Resistivity of TiC films decreases monotonically from 666.73 to 86.01 μΩ·cm with the increase in annealing temperature. In brief, the TiC thin films prepared in this study show good crystallinity, thermal stability and low resistivity, which can meet the requirements of metal gate applications.

Carbon rich Nano-crystalline grain size tantalum carbide (Ta-C) thin films were prepared by non- reactive simultaneously dual magnetron sputtering. The main purpose of the current work was to investigate the influence of deposition method, deposition power, film thickness and annealing temperature on structural, surface morphology and electrical resistivity of TaC thin films. The experimental result shows that the growth rate of film was about 6.7 nm min−1 and films are growth like spherical structure. The atomic percentage of elements in the films were very sensitive to the deposition power, which even if the small amount of increases in the deposition power of Ta lead the increase of Ta content. However, a small change in Ta percentage did not result in a change in film structure and surface morphology. Annealing temperature did not cause structural changes in the films, but lead small changes in the grain size (range from 7.0 to 9.1 nm) and surface roughness. Resistivity variation of deposited TaC films on the annealing temperature shows random behavior which may cause by the deposition method. Nevertheless, the resistivity of the film decreases first and then increases when the thickness increases from 79.2 nm to 134 nm. Minimum resistivity of film appears at the thickness of 79.2 nm, about 235.2 μΩ.cm. In the end, deposited TaC thin films shows good thermal stability and low enough resistivity for gate electrode application.

In order to explore new nonlinear optical (NLO) crystals with superior performance, it is greatly desirable to understand the intrinsic relationship between the microscopic structural features and macroscopic optical properties of crystals. In this paper, the electronic structures and optical properties of Mg3B7O13Cl (MBOC), which contains B7O13 functional building blocks, were investigated to understand the structure — optical property relationship by first-principles calculation. Our calculated results show that the large band gap and the moderate second-harmonic generation (SHG) coefficient of MBOC (8.43 eV and d32 = 0.41 pm/V) are comparable to those of KBe2BO3F2 (8.64 eV and d11 = 0.46 pm/V). The origin of the large band gap and the moderate SHG response of MBOC were explained by combining electronic structure analysis and the SHG density method.

Direction detection of a magnetic field by spin-valve-type magnetic tunnel junction (MTJ) has been investigated at temperatures ranging from room to 150/spl deg/C, concentrating on the magnetic property of the pinned layer. Angular dependencies of resistance curves show that detection errors from cosine curve increase with rising temperatures in MTJ with the IrMn/CoFe pinned layer. Measurements of the magnetization curves of the pinned layer found that detection errors are caused by rotation of the pinned layer magnetization. Direction detection of a magnetic field by MTJ with a IrMn/CoFe/Ru/CoFe of synthetic antiferromagnetic (SyAF) pinned layer, in which magnetizations of two CoFe layers nearly cancel each other, was also investigated. We confirmed that the pinned layer of SyAF structure in MTJ effectively reduces the dependence of detection errors on temperature.

The read-cycle endurance of a magnetic tunneling junction (MTJ) has been investigated, focusing on the spin-dependent tunneling current at high temperatures. The MTJ structure used in this study consisted of Ta-NiFe-CoFe-AlOx-CoFe-IrMn-NiFe-Ta prepared on a thermally oxidized Si wafer. Both the tunneling current and tunneling magnetoresistance ratio showed no significant degradation during the 1E9 read-cycle test using unipolar voltage pulses of 0.5 V at room temperature. Temperature dependence of the MTJs resistance calculated from the measured tunneling current has also been examined in a temperature range from room temperature to 175/spl deg/C. Furthermore, in the case of read-cycle tests for thermally stressed MTJs, the variation of the tunneling current was less than 2% after 1E9 cycles at a stress temperature of 175/spl deg/C. This indicates that MTJs have sufficient read-cycle endurance under high-temperature operation.

We have experimentally investigated a method of controlling the magnetization direction of a CoFe pinned layer in a spin-valve-type magnetic tunnel junction (MTJ) with an IrMn layer. Arbitrary control of the direction of the pinned layer magnetization was performed by a postannealing process in conditions above the blocking temperature of IrMn and in a magnetic field to saturate the magnetization of the pinned layer. The results show that it is possible to control and to uniformly rearrange the direction of the pinned layer magnetization in MTJs with a postannealing process in the magnetic random access memories manufacturing process.