Amorphous Nb2O5 Research Articles

Characteristics of Multilayered Thin-Film Optical Tunable Separators Using Surface Acoustic Waves

New type optical tunable separators consisting of multilayered thin-film optical waveguides are studied. The coupling strength and coupling length can be controlled by surface acoustic waves. For this coupler, amorphous Nb2O5, Ta2O5 and ZnS film waveguides are fabricated on a substrate, Y-cut LiNbO3, by R.F. sputtering method. Tunable and wavelength-selective properties, that are important factors for active wave separators and tunable optical filters in multi-wavelength optical communication systems, are discussed with analysis of propagation properties of surface acoustic waves in film guides.

Switching phenomena and dielectric breakdown in amorphous Nb2O5 films

Repititive switching from the high-to the low-resistance states in thin amorphous Nb2O5 films are investigated. The switching processes are found to be associated with four conduction states. The transitions among the first three states are reversible, exhibiting a cyclic switching behavior. The resistive transitions are abrupt, taking place within a range of less than a millivolt. The switching time from the first conduction state to others is <2 ns, while the switching from the second state occurs with a voltage-dependent delay time. The values of resistivity, thermal activation energy and I–V characteristics of the four conduction states are given and show that the final or irreversible dielectric breakdown process occurs throuh the formation of highly conductive filaments. The current-voltage characteristics for the four conduction states are briefly discussed.

Dielectric properties of amorphous Nb2O5 thin films

The dielectric constant, a.c. resistance and loss tangent tan δ of amorphous Nb2O5 films with Nb electrodes have been investigated in the frequency range 3 Hz to 5 × 106 Hz, as a function of temperature and applied field. The capacitance decreases with frequency ƒ according to a C(ƒ)∝ƒ−0.3 relation in the range 3 Hz<ƒ<800 Hz and remains constant for 800 Hz<ƒ<5 × 106 Hz, giving a dielectric constant εr of approximately 45. The loss tangent tan δ decreases with ƒfor 3 Hz<ƒ<200 Hz and then forms a loss peak centered at 200 Hz and decreases to a constant value of tan δ0&#x0304;.05 for ƒ>2 × 10su5 Hz. The activation energy of a dielectric oscillator is 0.032 eV; C−V, G−V and tan δ−V data are presented. The real and imaginary parts of the complex dielectric constant ε∗ = ε′ − jε″ and polarizability α∗ = α′ − jα″ were calculated from the data. The Cole-Cole (ε″versus ε′), Scaife (α″versus α′) and tan δ versus log ƒ plots indicate the existence of two relaxation times below 8 × 103 Hz. The films are in a thickness range where the principal conduction mechanism is hopping conduction, as shown by the σ(ƒ)∝ƒn relation, with 0.75<n<1 behavior at low fields for 8 × 103 Hz<ƒ<5 × 106 Hz.

Atomic implantation of Nb in amorphous Nb2O5 by rf sputtering

It is shown that amorphous Nb2O5 films 2400 Å thick produced by anodization can be doped with Nb by rf sputtering of Nb atoms at substrate temperatures of 150°C. Large increases in electrical conductivity, reductions in thermal activation energy, and increases in capacitance as function of sputtering voltage in the range 2−5 kV support this interpretation. The high−field conduction process also changes from the Poole−Frankel mechanism often found in insulating films, where the conductance G = G0 exp(KV1/2) to the Poole mechanism where G = G0 exp(KV) found in Nb doped films. The doping concentration for 2400−Å films was calculated using the experimental values of the exponent K and found to be 1019 atoms/cm3 for films sputtered with Nb at an rf voltage of 3 kV. Capacitance variation as a function of voltage and temperature also support these conclusions. These effects are interpreted on the basis of possible implantation and temperature−aided diffusion process.

Phénomènes de pulvérisation et de distribution en profondeur. Partie IV. Pulvérisation cathodique des oxydes Nb2O5, Ta2O5 et WO3

Three different methods have been used to determine the sputtering yield (S) for 2–30 keV Kr ions on the amorphous anodic oxides Nb2O5, Ta2O5, and WO3. The methods were based on (a) the change of interference colors due to ion bombardment, (b) the perforation of a film of free oxide by an intense ion beam, and (c) the loss of weight of the target. Although S for Kr–WO3 was larger than expected, S for Kr–Nb2O5 and Kr–Ta2O5 was similar to what has been found for other oxides. For example, at 4 keV, S lies between 1.1 and 2.4 atoms/ion for Ar or Kr bombardment of Al2O3, Nb2O5, SiO2, Ta2O5, TiO2, and UO2, whereas it is 6.2 atoms/ion for WO3. The results were interpreted first with a modified form of the theory of Rol et al., in which S is equated to K′E/Rm, where K′ is a constant in Å/keV and Rm is the experimental median range. A good fit between experiment and theory was obtained for K′ equal to 25 for Nb2O5, 13 for Ta2O5, and 51 for WO3. The recently formulated theory of Sigmund, which is in principle completely analytical, was also considered. The observed values of S could be made compatible with the predictions of the theory by taking the following values for Eb, the surface binding energy (units of kcal/gram atom): 100–150 for Nb2O5, 200–250 for Ta2O5, and 45–60 for WO3, We would point out that these latter values are similar to the heats of atomization.