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High coupling KNbO3 width-extensional vibrators with a polar multidomain structure

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3 Author(s)
Koyama, Hirokatsu ; Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan ; Nakamura, K. ; Takano, T.

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The longitudinal piezoelectric coupling factor for the width-extensional mode of a thin KNbO3 plate, k11, has theoretically been predicted to be as high as 82.4% for the 43.5° rotated Z cut about the Y axis. To experimentally confirm the predicted value we fabricated a width-extensional vibrator using a 45° rotated Z cut plate about the Y axis, which is close to the maximum k11 cut. However, the measured value of k11 was 71.3%, appreciably lower than the predicted value. It is clarified that the lower coupling factor can be ascribed to the tilt of the electric-field vector from the major face of the plate, which results from an off-diagonal component of the dielectric tensor. To prevent the electric-field tilt, a polar multidomain structure consisting of two kinds of 90° domains is introduced into the width-extensional vibrator instead of a single-domain structure. It is demonstrated by finite element method simulations that the coupling factor approaches the predicted value (82.4%) as the number of domains formed in the vibrator increases. The measured coupling factor of a width-extensional vibrator with a polar multidomain structure is as high as 79.4%, which is close to the predicted value. An additional advantage of using this domain structure is its lower spurious response.

Published in:

Journal of Applied Physics  (Volume:97 ,  Issue: 6 )