Monolithic integrated SAW filter based on AlN for high-frequency applications

Integrated AlN/SiO2/Si (1 0 0) delay lines for Rayleigh surface acoustic waves (SAWs) with resonant frequencies up to 3.4 GHz were fabricated using a new CMOS compatible concept. Different thicknesses of textured AlN films with wurtzite structure were deposited on tungsten-based interdigital transducers embedded in a SiO2 layer by reactive pulse dc-sputtering at a temperature of 200 °C. Rocking curves of the films indicate c-axis (0 0 0 1) oriented, textured piezoelectric AlN films with a full-width at half-maximum of 1.88°. The determined propagation loss and coupling factor K2 of these SAW devices are 0.07 dB/λ and 0.78%, respectively. Different Rayleigh modes with acoustic velocities up to 5770 m s−1 are observed. By varying the wavelength, number of fingers as well as the length (i.e., the separation between the transducers) of the delay lines, the impact of several physical parameters on the frequency responses (S11, S21) was studied. The influence of the AlN thickness and of the orientation of the delay lines on the silicon (1 0 0) wafers was also investigated. Finite element method simulations were applied to model the resonant frequencies, giving resonant frequencies in reasonable agreement with the experimental data.