Influence of step-like portions on the surface of ZnO/glass SAW filters on their frequency characteristics

• Published in: IEEE transactions on ultrasonics, ferroelectrics, and frequency control Vol. 44; no. 3; pp. 658 - 665
• Main Authors: Kadota, M., Kondoh, C.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.05.1997; Institute of Electrical and Electronics Engineers
• Subjects: Acoustic wave devices, piezoelectric and piezoresistive devices; Acoustic waves; Applied sciences; Electrodes; Electronics; Exact sciences and technology; Filters; Fingers; Frequency; Glass; Rough surfaces; Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices; Surface acoustic waves; Surface roughness; Zinc oxide; Frequency characteristic; Binary compound; Interdigital transducer; Glass; Surface wave; Zinc Oxides; Experimental study; Acoustic wave filter
• ISSN: 0885-3010; 1525-8955
• DOI: 10.1109/58.658325

The frequency amplitudes of surface acoustic wave (SAW) filters mass produced of zinc oxide (ZnO) films on glass were found to be different among the filters even when their center frequencies are the same. We attempted various experiments In order to reduce the deviation of amplitudes. We accidentally found that the frequency characteristics and the amplitude deviation could be improved by mirror-polishing the ZnO film surface. In a SAW filter with a ZnO/interdigital transducer (IDT)/glass substrate structure, periodic step-like portions due to the thickness of the finger electrode of IDT and fine roughness were present on the ZnO film surface. As a result of investigating the effect of surface structure on amplitude deviation, the step-like portions did not affect the electromechanical coupling factors but reduced the SAW phase velocities, experimentally and theoretically. In addition, it was clarified that the step-like portions due to the finger electrodes and fine roughness on the ZnO surface caused deviations in the SAW velocities and their reflections, causing the deviation in the amplitude characteristics.