Highly oriented ZnO thin films deposited by grazing ion-beam sputtering: Application to acoustic shear wave excitation in the GHz range

In-plane and out-of-plane oriented (112̄0) ZnO thin films are attractive for acoustic shear wave excitation in the GHz range. In this study it is proposed that highly oriented and submicron-thick (112̄0) ZnO thin films can be fabricated using an ion beam sputter-deposition system with grazing incidence to the substrate surface. The formation of the (112̄0) texture cannot only be attributed to the well-known ion-channeling effect or to the self-shadowing effect since the ion beam incidence direction in the system does not correspond to the ion-channeling direction of the ZnO film (the [112̄0] or [112̄0] direction). The full width at half-maximum (FWHM) values of the φ- and ψ-scan profile curves of the (112̄2) X-ray diffraction poles were measured to be 5 and 28°, respectively. A shear-wave transducer with a 0.9-μm-thick film exhibited a one-way conversion loss of less than 20 dB at 1-2 GHz and a 3 dB fractional bandwidth of 100%, without any longitudinal wave excitation.