Sputtered AlN thin films on Si and electrodes for MEMS resonators: relationship between surface quality microstructure and film properties

Abstract

Aluminum nitride thin films grown by reactive AC magnetron sputtering are characterized using several metrology techniques to examine the correlation between surface quality, microstructure and piezoelectric properties. Atomic force microscopy, X-ray diffraction and electron microscopy, and are employed to characterize the microstructure. . A range of substrate coatings is explored to understand the impact of topography on film crystallinity and piezoelectric performance. A first order approximation model providing the piezoelectric characteristics as a function of the c-axis misorientation in the mosaic-structured wurtzite AlN films is presented. While the model predicts a only small e 33,eff and kt change for a misorientation distribution of FWHM of less than 5 degrees, it services as a indication of the impact of AlN crystallinity on film piezoelectric properties.

Influence of crystal quality on the excitation and propagation of surface and bulk acoustic waves in polycrystalline AlN films

“…First, it is important to note that a widening of the RC alone does not produce a significant deterioration of the piezoelectric activity, unless other defects are also present in the samples. This result can be predicted by simple geometrical considerations [23]. On the other hand, the presence of inclined grains with orientations others than (00-2) is clearly linked to the reduction of the piezoelectric activity.…”

Low-thickness high-quality aluminum nitride films for super high frequency solidly mounted resonators

“…It can be noticed that AIN films grown on polished substrates exhibit excellent piezoelectric activity, almost independent of the RC of the underlying Ir electrode (ranging from 2° to 5°) and the RC around the (00-2)-AIN reflection (ranging from 1.5° to 3°). The widening of the RCs of both Ir and AIN is very likely related with a "geometrical" effect (growth on tilted surfaces) rather than to a real worsening of the crystalline structure [27], Hence, it was found that it is possible to produce highly oriented AIN films even on Ir electrodes of different quality. The best achievements were AIN films 200 nm-thick with a RC 1.57°-wide grown on Ir substrates with a RC of 3.8°.…”

Solidly mounted BAW resonators with layer-transferred AlN using sacrificial Si surfaces

“…It is evident that the layer on which AlN is deposited has a strong influence on the AlN quality [4]. High c-axis orientation of AlN on smooth crystalline surfaces such as Sapphire [5] and Silicon [4] has been reported.…”