TeO2 Thin Films Research Articles

Propagation and Resonance Properties of Love-Type Surface Acoustic Wave on Y–X LiTaO3 with TeO2 Thin Film

The propagation characteristics of a Love-type surface acoustic wave (SAW) on Y-cut X-propagating LiTaO3 with an amorphous tellurium dioxide (TeO2) thin film with a low phase velocity were investigated theoretically and experimentally, and an interdigital transducer (IDT) resonator using this structure was fabricated and evaluated. The K2 of the Love-type SAW on TeO2/Y–X LiTaO3 was calculated to be 6.6% at a transition thickness of 0.07λ. The insertion loss of a simple delay line was reduced by loading with TeO2 film because the bulk wave radiation in excitation and/or propagation of the LSAW was markedly suppressed. Beyond the experimental transition thickness of 0.12λ, the suppression of the bulk wave radiation was saturated. According to the propagation characteristics for IDT resonators fabricated using this structure, the admittance ratio increased and the minimum phase decreased until the TeO2 film thickness reached the experimental transition thickness. When the TeO2 film thickness was 0.12λ, such resonance properties as admittance ratio, minimum phase, and resonance quality factor of the Love-type SAW on TeO2/Al/Y–X LiTaO3 were almost equal to those for Au/Y–X LiTaO3 and were better than those for LSAW on Al/39° Y–X LiTaO3, except for the band-width ratio. Moreover, the TCD was initially decreased by loading with TeO2 film but then increased as film thickness increased.

Temperature-Compensated Devices Using Thin$hboxTeO_2$Layer With Negative TCD

This letter evaluates the applicability of TeO2 thin films as an attractive alternative over conventional SiO2 layers in the field of temperature compensation of various devices. It is reported that the processing environment during TeO2 growth plays an important role in defining its negative temperature coefficient of delay (TCD), and the magnitude of TCD increases continuously from -1.862times103 ppmmiddotdegC-1 to -9.883times103 ppmmiddotdegC-1 with an increase in the oxygen percentage from 25% to 100% in the processing gas mixture. A very low thickness of 0.008lambda for the TeO2 over layer (in comparison to the 0.32lambda-thick SiO 2 layer) is required for achieving a zero-TCD device without degrading its performance

Low-temperature metallic behavior of amorphous MoO3–TeO2 thin films

We report that vacuum-deposited amorphous MoO3–TeO2 films of different thickness (469–1185 nm) and compositions show metal-insulator transition (MIT) in the temperature (Tp) range 341–231 K (depending on thickness and composition). Interestingly, the corresponding thick bulk glass plates (∼0.2–0.5-mm thickness) of same compositions behave like the usual semiconducting transition metal oxide glasses over the entire range of temperature (80–400 K) and follow small polaron hopping (SPH) conduction mechanism. Temperature-dependent resistivity curves of the films showed peaks (maxima) around the respective MIT temperature Tp, which shifted to the lower-temperature region with the increase of MoO3 content. Fitting of the conductivity data of the film in the high-temperature (T>Tp) semiconducting phase shows a crossover around Tc(>Tp) from the Mott variable range hopping to SPH behavior, which is in sharp contrast to the behavior of the bulk glass. In these films, the estimated localization length (ξ) diverges as MIT is approached from the high-temperature phase. Low-temperature (T<Tp) magnetic-field-independent metallic part of the resistivity (ρ) data of higher (⩾60%)TeO2 containing films can be fitted with ρ=ρ0+ρ2T2 indicating the importance of electron-electron scattering (second term) mechanism of conduction. The corresponding metallic behavior of the comparatively high-resistive and lower (⩽50%)TeO2 containing film is, however, more complicated. All these different features of these glassy films suggest that their glass network structure is different from that of the corresponding bulk glass (indicating a change of glass network structure in the film phase), which is considered to be responsible for the metallic transition in the films.

Temperature stable LiNbO3 surface acoustic wave device with diode sputtered amorphous TeO2 over-layer

Amorphous TeO2 thin film, sputtered in the O2+Ar(25%+75%) gas environment using a metallic tellurium target, has been identified as an attractive negative temperature coefficient of delay (TCD) material that can yield a temperature stable device when combined with a surface acoustic wave (SAW) device based on positive TCD material such as LiNbO3. The influence of amorphous TeO2 over-layer on the SAW propagation characteristics (velocity and temperature coefficient of delay) of the SAW filters (36 and 70 MHz) based on 128° rotated Y-cut X-propagating lithium niobate (128° Y-XLiNbO3) single crystal has been studied. It is found that 0.042λ thick TeO2 over-layer on a prefabricated SAW device operating at 36 MHz centre frequency, reduces the TCD of the device from 76ppm°C−1 to almost zero (∼1.4ppm°C−1) without deteriorating its efficiency and could be considered as a suitable alternative for temperature stable devices in comparison to conventional SiO2 over-layer.

Structural Modifications in Thin Films Caused by Gamma Radiation

This paper reports on the gamma radiation-induced changes in thin oxide films deposited by thermal vacuum technique. Structures of various oxides thin films, such as In2O3, SiO and TeO2 and their mixtures in different proportions were studied. The influence of gamma radiation on In2O3/SiO films has resulted in significant changes in the microstructure of this film. Some kind of agglomerations with variable sizes in the range 0.5-3 µm has occurred. After a dose of 8160 µSv an evidence of partial crystallisation was observed with X-ray diffraction. Structural changes in TeO2 thin film were explored by means of Raman spectroscopy. After they have been exposed to g- radiation, a strong peak appeared at 448.83 cm-1, indicating further transformation to g-TeO2 modification.

Effect of gamma radiation onto the properties of TeO2thin films

The effects of γ‐radiation on both the optical and the electrical properties of Tellurium dioxide (TeO2) thin films were investigated. TeO2 thin films were fabricated using thermal vacuum deposition method. Samples were exposed to a 60Co γ‐radiation source with a dose rate of 6 Gy/min. Absorption spectra for TeO2 thin films were recorded and values of the optical band gap for as‐deposited and γ‐irradiated films were calculated. Sets of measurements based on Hall effect were carried out. From the data received the dependences of sheet resistance, density of charge carriers, mobility and Hall coefficient with radiation dose were determined.

Gamma Radiation Dosimetry Using Tellurium Dioxide Thin Film Structures

Thin films of Tellurium dioxide (TeO2) were investigated for γ-radiation dosimetry purposes. Samples were fabricated using thin film vapour deposition technique. Thin films of TeO2 were exposed to a 60Co γ-radiation source at a dose rate of 6 Gy/min at room temperature. Absorption spectra for TeO2 films were recorded and the values of the optical band gap and energies of the localized states for as-deposited and γ-irradiated samples were calculated. It was found that the optical band gap values were decreased as the radiation dose was increased. Samples with electrical contacts having a planar structure showed a linear increase in current values with the increase in radiation dose up to a certain dose level. The observed changes in both the optical and the electrical properties suggest that TeO2 thin film may be considered as an effective material for room temperature real time γ-radiation dosimetry.

Processing and characterisation of sol-gel glasses and powders in the system TeO2-TiO2

Sol-gel processing routes have been developed for the production of thin films and powders in the system TeO2-TiO2 from tellurium and titanium alkoxides. The structure and properties of the resultant materials have been characterised as a function of heat treatment temperature. Pure sol-gel derived TeO2 thin films are difficult to prepare with good optical transparency due to the presence of organic impurities and/or a highly dispersed metallic tellurium phase when heated at temperatures up to approximately 340°C, with crystallisation to α-TeO2 occurring when the heat treatment temperature is further increased. Additions of TiO2 were found to retard the crystallisation of the α-TeO2 but promote the formation of other TiO2 or TiTe3O8 phases. However, an optimum composition in the range 0.9TeO2 0.1TiO2 was identified, which allows optically transparent thin films to be prepared with high refractive index and offers the potential for practical device manufacture.