Date of Award

Summer 2007

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)

First Advisor

Joshi, Shrinivas G.

Second Advisor

Richie, James E.

Third Advisor

Johnson, Michael T.

Abstract

This thesis presents theoretical and experimental investigation of acoustic waves propagating in thin piezoelectric plates. A unique matrix approach is described that readily solves for propagation characteristics of the waves under various sets of electrical and mechanical boundary conditions. The electromechanical coupling coefficient K2 has been calculated from the obtained short circuit and open circuit velocities. Analysis shows that very strong coupling can be obtained for the SHo plate wave mode. For example, it is found that values of K2 as high as 0.44 can be obtained for SHo waves propagating along the X axis of 30° rotated Y cut lithium niobate plates. This is nearly ten times the maximum value of K2 that can be obtained for surface acoustic waves in this material. The high value of K2means that the wave can be efficiently excited by the interdigital transducer IDT and it is also very sensitive to electrical perturbations at the surface. The latter property is confirmed by studying propagation characteristics of plate waves when a thin film of arbitrary conductivity is deposited on one of the plate surfaces. It is found that the film produces significant change in the velocity and attenuation of the wave. The case of plate waves propagating in contact with a conducting liquid is also investigated. The analysis described above confirms the many attractive properties of plate waves for device applications. However, in order to exploit these properties, one will need to fabricate devices on very thin plates, typically of thickness less than 150 um. A suitable fabrication method that can be used to realize devices on such thin plates has been developed. It has been used to fabricate devices on plates of thickness less than 110 um operating at fundamental resonant frequencies greater than 25 MHz. The performance of these devices has been measured and compared with theoretical calculations.

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