The influence of transducer metalization on SAW resonator electrical performance

The results of an investigation to establish whether the interdigital transducer (IDT) finger metalization was the source of observed flicker (1/f) noise levels in high performance SAW resonator devices are described. Several alterations to the basic IDT finger metal deposition technique were used in order to vary the grain size in copper-doped aluminum thin-films. Grain size was varied over approximately a 3:1 range (~0.25 μm to ~0.09 μm) by changing the background O₂ pressure during transducer metal deposition. In addition, the influence of grain size was examined in conjunction with compositional differences through the addition of Si or Ti as dopants in the copper-doped aluminum thin-films. The electrical performance (e.g., residual flicker (1/f) noise, loaded-Q, unloaded-Q, and turn-over temperature) for more than one-hundred devices was characterized, and a number of samples were analyzed using transmission electron microscopy (TEM) to examine the corresponding microstructure of the transducers´ finger metalization. Although a correlation between average grain size and residual flicker (1/f) noise was not found, the experimental techniques provide the basis for further investigations into the source, or sources, of flicker (1/f) noise in SAW resonator devices