Abstract
In the study, an acoustic sensor for a high-resolution acoustic microscope was fabricated using zinc oxide (ZnO) piezoelectric ceramics. The c-cut sapphire was processed into a lens shape to deposit a ZnO film using radio frequency (RF) magnetron sputtering, and an upper and a lower electrode were deposited using E-beam evaporation. The electrode was a Au thin film, and a Ti thin film was used as an adhesion layer. The surface microstructure of the ZnO film was observed using a scanning electron microscope (SEM), the thickness of the film was measured using a focused ion beam (FIB) for piezoelectric ceramics deposited on the sapphire wafer, and the thickness of ZnO was measured to be 4.87 μm. As a result of analyzing the crystal growth plane using X-ray diffraction (XRD) analysis, it was confirmed that the piezoelectric characteristics were grown to the (0002) plane. The sensor fabricated in this study had a center frequency of 352 MHz. The bandwidth indicates the range of upper (375 MHz) and lower (328 MHz) frequencies at the −6 dB level of the center frequency. As a result of image analysis using the resolution chart, the resolution was about 1 μm.
Highlights
We found the optimal growth conditions for zinc oxide (ZnO) films using radio frequency (RF) magnetron sputtering
An acoustic sensor for high-resolution acoustic microscopy with sub μm resolution was fabricated using ZnO piezoelectric ceramics, which can be used for surface microstructure analysis and subsurface inspection of micro/nano scale thin-film structures
The upper and lower electrodes of Ti and Au thin films were fabricated using E-beam evaporation, and Ti was used as an adhesion layer for the Au thin films with poor bonding properties
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Non-destructive methods are used to obtain surface structures of thin films and subsurface micro-faults, and the material properties are limited. ZnO is classified as a group II-VI semiconductor, and is a material used in electronic, optoelectronic, and laser technology due to its wide energy band, high bonding energy, and high thermal as well as mechanical stability [7,8] It is attracting attention in the ceramic industry due to its hardness, rigidity, and piezoelectric constant, and has low toxicity, biocompatibility, biodegradability, biomedicine, and a pro-ecological system [9,10]. An acoustic sensor for high-resolution acoustic microscopy with sub μm resolution was fabricated using ZnO piezoelectric ceramics, which can be used for surface microstructure analysis and subsurface inspection of micro/nano scale thin-film structures
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