The crystalline orientation of thin films gradually improves as the growth proceeds. Especially in the non-epitaxial growth, its initial layer is often unoriented. Because the unoriented layer degrades the performance of the device, the degree of crystalline orientation in depth direction is a very important issue. We propose a non-destructive method for predicting the thickness of the unoriented layer, making use of piezoelectricity distribution of films. An electromechanical resonator consisting of the single highly oriented layer excites a fundamental mode, but does not excite a second-overtone mode. The unoriented layer, on the other hand, exhibits little piezoelectric effect. A bilayer resonator consisting of the highly oriented layer on the unoriented layer excites a second-overtone mode because of the deference of piezoelectricity in these layers. In this study, the electromechanical resonance characteristics of Cu/ZnO(0 0 0 1)/Ti(0 0 0 1)/SiO2, Cu/ZnO(0 0 0 1)/AZO(0 0 0 1)/Ti(0 0 0 1)/SiO2 and Cu/ZnO(112̄0) /Al/SiO 2 were experimentally observed. These results were compared with the theoretical estimations by a mechanical transmission line model to determine the thicknesses of the piezoelectrically inactive layers in the (0 0 0 1) or(112̄0) oriented ZnO films. The inactive layer thickness in(112̄0) the oriented ZnO film was in good agreement with the unoriented layer thickness observed by the cross-sectional transmission electron microscopy and electron diffraction.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Acoustics and Ultrasonics
- Surfaces, Coatings and Films