Technological process and resonator design optimization of Ir/LGS high temperature SAW devices
Photolithography together with ion beam etching was used for fabrication of high temperature SAW devices. Ir thin film of 0.3 μm thick was deposited by magnetron sputtering without additional adhesion layers and than Ir film was annealed after electrode patterning in different conditions. The resistivity of magnetron sputtered thick Ir films drops noticeably after annealing. However, this process requires special care in order to avoid delaminating of the film due to developing high stress during such procedures. We have annealed the substrates with Ir films in different regimes and in different gas/vacuum conditions. The results of these studies have shown that annealing in air up to about 500 °C decreases the Ir film resistivity 1.5-2 times. Vacuum annealing did not show much improvement in comparison to open air annealing. Magnetron sputtered thin Ir films have somewhat porous structure allowing oxygen to diffuse from the substrate surface through Ir films. Resonator structures with thick Ir electrodes were prepared and tested. Examples of the resonator structures show very promising properties, such as high conductance and high Q-factor.
Theoretical and experimental investigation of langasite as material for wireless high temperature SAW sensors
Different cuts of langasite were investigated theoretically and experimentally as candidates for high temperature sensors utilizing SAW resonators and reflecting SAW tags. Single port SAW resonators with central frequencies close to 170, 200 and 433 MHz with W, Ir and Pt electrodes of different thickness were fabricated and their characteristics were measured as functions of temperature. An approach to SAW device encapsulation, which helps to avoid stress development during heating to high temperatures, was suggested and tested. The damage of the langasite surface during heating to high temperature is strong in the cut family with Euler angles (0°, 138.5°, ψ), while orientations with Euler angles (0°, 90°, ψ) and (0°, 22°, ψ) were found to be more resistant to heating. In the latter cut family, two cuts, (0°, 22°, 31.5°) and (0°, 22°, 90°) can provide zero power flow angle and sufficient piezoelectric coupling. COM parameters of SAW resonators with W, Ir and Pt electrodes, including complex reflection coefficient, were calculated as functions of electrode thickness and measured in the wide temperature range. The frequency responses were described by COM equations and the fitted COM-parameters were compared to their simulated values. Resonators show high Q and their performance is perfectly described by COM equations
EFFECT OF SAMPLE PREPARATION ON WATER TREE RESISTANCE OF XLPE/SEBS BLENDS
The effects of an aromatic polymer, such as poly[styrene-b-(ethylene-co-butylene)b-styrene] (SEBS), and its preparation processes on water tree resistance, morphology, crystallinity, dielectric constant and dielectric loss tangent of crosslinked polyethylene (XLPE)/SEBS and XLPE/SEBS/ethylene vinyl acetate (EVA) blends were investigated. The XLPE/SEBS samples were characterized by means of differential scanning calorimetry, scanning electron microscopy, dielectric spectral analysis and the accelerated water treeing experiment. The results clearly showed that although SEBS was partially compatible with LDPE and it was dispersed evenly in XLPE matrix, the blends demonstrated excellent dielectric performances, such as dielectric constant and dissipation factor. The crystallinity of XLPE/SEBS blends was decreased with increase in SEBS content and it was further decreased with the addition of EVA. SEBS could effectively improve the water-tree resistance of XLPE and both SEBS and EVA were found to improve the water tree resistance of XLPE synergistically as expected. The differences in sample preparation processes could change the phase morphology and dielectric performance of the blends, and could also influence the dispersion of SEBS in XLPE matrix as well as the crystallinity of the blends. Different preparation processes led to different water tree resistance behaviours of the samples. The improvement of SEBS dispersion in XLPE matrix helped to improve the water tree resistance of XLPE.