To determine the sound velocity in wurtzite AlxGa1−xN, we have used surface acoustic-wave (SAW) delay lines on AlxGa1−xN/c-Al2O3. AlxGa1−xN films with compositions from x=0 to x=1 were grown by plasma-induced molecular beam epitaxy. Starting from published data, we fine tuned the values of the elastic moduli used in numerical calculations such that the simulated and measured dispersion of the SAW were in good agreement. Based on these values, the surface and bulk acoustic-wave velocities of single-crystal AlxGa1−xN were determined as functions of the composition. The resulting SAW velocities ranged from 3700 to 5760 m/s for GaN and AlN, respectively.

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The technology of surface acoustic wave (SAW) devices allows the integration of signal processing and sensor functions within one product. In the past, SAW sensors have been operated at room temperature or 100 to 200°C at most. Materials related problems become obvious if one attempts to increase this operating temperature to a value as high as 1000°C. First experimental results will be presented based on a variation of the metallization and the use of diffusion barriers. It is expected that the use of these specially taylored materials with particular functional properties will lead to a considerable improvement of the lifetime and reliability of SAW sensors and the development of devices resistant to high temperatures as well as high pressures and chemically aggressive environments. The high-temperature characteristics of such novel devices are investigated by finite element simulation and by experimental deformation analyses. It will also be discussed which assembly, interconnection, and packaging techniques are applicable at 1000°C.

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This paper describes a design of a surface acoustic wave (SAW) ladder-type bandpass filter (BPF) for 2.4-2.5GHz ISM-band, based on the low temperature co-fired ceramic (LTCC) substrate, which can be used in 802.11b/g wireless LAN and Bluetooth applications. It obtains an excellent state-of-the-art performance in the ultra small package. The proposed architecture is based on a combination of SAW and low temperature co-fired ceramic (LTCC) technologies, where the multilayer LTCC substrate is used for integration of matching and passband-driving elements and for obtaining additional transmission zeros. It is comprised of three series and two parallel SAW resonators, realized on the LiTaO 3 piezoelectric substrate and connected accordingly to a ladder-type T-topology circuit design, and an additional resonator to obtain an attenuation at 2.57-2.62 GHz IMT-E (TDD) band. Two input/output matching inductors and three additional inductors, permitting to obtain a sufficient suppression level at 2.11-2.17 GHz UMTS (DL) band and harmonics, are completely integrated within ceramic.The described bandpass filter has ultra small dimensions of 1.1 x 1.4 x 0.9 mm, very low insertion losses of -1.5 dB max in the passband. This fully matched SAW bandpass filter has achieved excellent selectivity performance with the up-to-date smallest package size.Index Terms -Bandpass filter (BPF), ladder-type, surface acoustic wave (SAW), coexistence, low temperature co-fired ceramic (LTCC), wireless local area network (WLAN), systemin-package (SIP).