Volume 92, Issue 2, 15 July 2002
Index of content:
- DEVICE PHYSICS (PACS 85)
92(2002); http://dx.doi.org/10.1063/1.1488252View Description Hide Description
The voltage dependence of magnetoresistance(MR) and the low-frequency voltage fluctuation were studied in magnetic tunnel junctions with an AlN or an barrier formed by plasmanitridation or oxidation. The junctions consist of free and pinned NiFe layers by a FeMn antiferromagnetic layer. For the junction, the variation of half-reduction voltage of MR is about 50 mV from 401.3 mV in maximum to 351.4 mV in minimum depending upon the oxidation time. For the AlN junction, the less nitrided junction with a nitridation time of 120 s shows the higher-half-reduction voltage by about 100 mV than for optimally nitrided or oxidized ones. From the low-frequency voltage noise data, the less nitrided AlN junction shows larger noise magnitude compared with other junctions with an optimal condition, implying more defect states in the barrier due to unnitrided Al metals. In order to investigate the influence of nitrogen on ferromagnetic layer, another junction with an barrier was made after the pinned NiFe layer was exposed to plasma for 10 s. This junction reveals a lower MR and worse bias voltage dependence than any junctions studied here. The voltage dependence of MR, therefore, is likely influenced by the interface state rather than the defects in the barrier, although the two factors play an important role in determining MR.
Optimization of Al interlayer thickness for the multilayer diffusion barrier scheme in Cu metallization92(2002); http://dx.doi.org/10.1063/1.1486039View Description Hide Description
The TiN(5 nm)/Al/TiN (5 nm) structure is fabricated by sequential sputtering for the diffusion barrier application against Cudiffusion. Al is used as an interlayer with an expectation that it will favor stuffing of TiN grain boundaries by reacting with in the structure. In one phase of experiments, the upper TiN layer is exposed to air and preannealed in ambient for better stuffing. In another phase, the preannealing is not performed for the sake of reducing process steps. The Al layer thickness is varied to find out the optimized value. The diffusion barrier performance is investigated by x-ray diffraction, sheet resistance measurement, secco etching and cross sectional transmission electron microscopy after stressing the structure in temperature range of 350–700 °C at vacuum for 30 min. It is found that the barrier property is improved remarkably with the introduction of an Al layer between two TiN layers as compared to that of a single TiN layer with the same thickness. The results indicate that the barrier performance is enhanced proportionally with increasing Al thickness (from 0.5 to 2 nm) in the case that upper TiN is preannealed, showing the best result for 2 nm thick Al interlayer. On the other hand, in not preannealed upper TiN, barrier property is at its best when Al thickness is 1 nm but above this value the barrier performance deteriorates drastically.
Plasma-enhanced chemical vapor deposition and characterization of high-permittivity hafnium and zirconium silicate films92(2002); http://dx.doi.org/10.1063/1.1487911View Description Hide Description
Deposition of hafnium silicate films with various hafnium contents was tried by plasma-enhanced chemical vapor deposition using tetraethoxysilane and a hafnium alkoxide. From x-ray photoelectron spectroscopy, the depositedfilms are confirmed to be silicate with Hf–O–Si bonds but without any Hf–Si bonds. The permittivity calculated from the capacitance of the accumulation layer increases monotonically with an increase in the hafnium content, whereas the optical band gapenergy estimated from vacuum ultraviolet absorption spectra decreases. Similar results were obtained from zirconium silicate filmsdeposited using tetraethoxysilane and a zirconium alkoxide. If we compare the films with the same hafnium or zirconium content, the hafnium silicate exhibits a higher permittivity and a larger band gapenergy than the zirconium silicate.
Exposure characteristics of cobalt fluoride self-developing electron-beam resist on sub-100 nm scale92(2002); http://dx.doi.org/10.1063/1.1487914View Description Hide Description
We have studied electron-beam exposure of cobalt fluoride thin films by real-time high-resolution transmission electron microscopy and by electron energy-lossspectroscopy. We were able to remove fluorine completely from an irradiated area and retain metallic cobalt by exposing the area at low dose rate and elevated temperature. The structures were composed of separated single-crystalcobaltnanoparticles with dimensions on the order of 5–10 nm.
92(2002); http://dx.doi.org/10.1063/1.1479755View Description Hide Description
A reciprocating cantilever utilizing emitted charges from a millicurie radioisotope thin film is presented. The actuator realizes a direct collected-charge-to-motion conversion. The reciprocation is obtained by self-timed contact between the cantilever and the radioisotope source. A static model balancing the electrostatic and mechanical forces from an equivalent circuit leads to an analytical solution useful for device characterization. Measured reciprocating periods agree with predicted values from the analytical model. A scaling analysis shows that microscale arrays of such cantilevers provide an integrated sensor and actuator platform.