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.
P2N-3 Single Port SAW Resonators Design for Arbitrary Reflection Phase
This work deals with some aspects of resonator performance improvement on unidirectional substrates with arbitrary reflection angle. A design concept is proposed based on the use of resonators with slight (by about 1-2%, depending on the material properties) frequency increase (or decrease, for opposite phase) of the IDT pitch in the transducer center for bi-directional substrates. For naturally unidirectional orientations properly placed linear chirp transducers with pitch variation of the same order of magnitude are found to give practically useful results, while for arbitrary phase angles in between of these two extreme cases the position of the transducer pitch maximum (minimum for opposite phase) is shifted from the center to the corresponding side of the transducer in accordance with the phase. Relevant the results are compared with experimental data on langasite substrates
Design method for SAW resonators using natural SPUDT substrates
Several new materials for SAW devices exhibit the natural SPUDT (N-SPUDT) effect, which causes an SAW transducer to generate waves with different amplitudes in the two directions. In general, SAW devices on such materials need to be designed allowing for the complications introduced by this effect. A design method for one-port resonators is derived, valid if the resonance frequency and the Bragg frequencies of the transducer and gratings are all different. The design is versatile enough to remain valid if the N-SPUDT effect is absent.