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Experimental SAW resonator structures with iridium electrodes were fabricated on Y-cut of langasite with few different propagation directions and their characteristics were measured in a wide temperature interval, up to 700ºC, and compared with simulations. Between two sets of material constants reported by Bungo one set was selected as providing much better agreement with experiments, for the analyzed orientations. Further improvement of simulation accuracy was achieved via after-correction of the calculated temperature characteristics using auxiliary function extracted from experimental data. This approach was used to predict resonator characteristics in orientation with Euler angles (0º, 22º, 90º), in which Bluestein-Gulyaev wave propagates, and provided excellent agreement between experiments and simulations, in a wide temperature interval.

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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SAW resonators were patterned on CTGS wafers with different orientations at different propagation angles. Ir was used as a metal without additional adhesion layers. Resonator responses were acquired with a network analyzer. Resonance frequencies of the responses were measured and processed to obtain temperature behavior. For the cut with Euler angles (0, 90°, 0) almost linear behavior was observed with TCF close to -35 ppm/°C. The turnover point of the fitted parabolic curve gradually changed with propagation angle ψ (0, 90°, ψ) from negative temperatures up to about +550°C at (0, 90°, 90°). This also means that this material gives orientations (close to (0, 90°, 40°)) with the turnover point near the room temperature. Surrounding orientations should probably be same useful (the turnover point change is about 0.5°C with ψ angle change by 1' for these orientations). The coefficient at the quadratic term (with Ir metal) has a low value of about -30 ppb/°C 2 . This value is several times lower than that of most langasite cuts and is close to that of ST-quartz. The material seems to be chemically stable at high temperatures. CTGS shows great potential and useful properties for devices operating in a wide temperature range. Similar to ST-quartz, CTGS can serve for temperature compensated resonators and filters at room temperature. It can also work in devices operating at temperatures up to several hundred degrees C.

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This paper reports an investigation of the freesurface SAW velocity homogeneity of 4-inch langasite wafers. The technique employed is fast, cheap, and nondestructive. The method is based on the determination of the SAW propagation time between two interdigital transducers (IDT), separated by a fixed distance. The measurement setup consists of an acoustic system comprising a sensor, the piezoelectric substrate under investigation, and a vector network analyzer HP-3577A. The sensor is fabricated on a non-piezoelectric substrate, with two split-electrode IDTs. The piezoelectric substrate to be studied is placed in intimate contact with the transducer system. The complex frequency response of the acoustic system measured by the vector network analyzer is the product of the input and output IDT responses including the phase. It is then possible to determine the impulse response of the acoustic system accurately with the help of the Fourier transform. The total error (data processing and acoustic system imperfections) amounts to 35 ppm of the measured velocity. The method described was used to carry out an inspection of the SAW velocity uniformity of quartz, langasite and lithium niobate substrates. SAW velocity measurements on 3" and 4" langasite wafers have shown that the mean square deviation of SAW velocity is less than 120 ppm. Information on the velocity variation over the area of 3" and 4" langasite wafers has been used to improve the inhouse manufacturing process for the growth of large-size langasite crystals in batch production. A filter employing slanted fingers was designed and fabricated on wafers of LGS. This device required very small IDT dimensions and displayed exceptional repeatability of performance. The advantages of langasite devices are discussed.