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In this paper some alternative approaches to SAW tag chevron-type electrode reflectors (as in RAC devices) design and coding are discussed. The first idea is to use for reflecting "taps". One of the advantages of the use of oblique reflectors is that there is no multiple reflection in such a system even if many reflectors are placed in the same acoustic channel.It is also important for the 2.5 GHz frequency range that the minimal size of electrode in oblique reflectors is roughly 1.4 larger than for normal reflectors. The small size of the device is another attractive feature.A further idea to he discussed is the possibility to code a tag device simply by the time positioning of the reflectors, which allows calibration problems to be avoided and simplifies the reading system since the phase of the pulses does not need to be measured. Measurements of propagation and reflection of SAW a t 2 GHz frequency range and tag prototype characteristics are presented.

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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.

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