Date of Award

Fall 12-21-2018

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science in Electrical Engineering (MSEE)

Department

Electrical and Computer Engineering

Advisor

Mauricio Pereira Da Cunha

Second Committee Member

John Vetelino

Third Committee Member

Nuri Emanetoglu

Abstract

Accurate knowledge of the surface acoustic wave (SAW) properties propagating at the surface of a piezoelectric substrate with thin films, electrodes or temperature compensated films, is critical in SAW filter design to meet the target frequency response, power durability and performance prior to device fabrication. While reliable material constants exist for substrates such as LiNbO3 used in SAW filters, the absolute elastic constants associated with operational thin films used for electrodes or temperature compensation do not exist. Although the bulk values of the constituent materials are known, the composite film/substrate properties are difficult to predict since they depend strongly on film deposition parameters, substrate type, and orientation.

This work investigates a method for evaluating the effective stiffness of a composite thin metal film by assuming an equivalent isotropic film model for an electron-beam evaporated Cu- based thin film on a crystal substrate close to the 128°-Y cut LiNbO3, Euler angles (φ, θ, ψ) = (0°, 38°, ψ). Two orientations on the same crystal cut were used, ψ = 0° and ψ = 53°, where the 53° orientation provided an alternative sensitivity to shear-type waves, thus allowing the unique determination of the effective isotropic thin film elastic constants, C11 and C44, through a reverse computational procedure while considering the error propagation from physical measurement uncertainty. SAW delay lines in the range of 550 to 900 MHz were fabricated with and without metal film on the delay path on a single wafer, with multiple identical devices dispersed over the wafer and multiple wafers used for statistical analysis. The metallized SAW velocities for each device wavelength were measured using differential delay lines with the same interdigital transducer configuration to account only for the SAW propagation in the layered delay path. The obtained results show promise for using a single wafer cut on LiNbO3 to characterize metal thin films to be used for SAW filter design simulations.

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