Citation:
Glenn Leighton and Zhaorong Huang, Accurate measurement of the piezoelectric coefficient of thin films by
eliminating the substrate bending effect using spatial scanning laser vibrometry, 2010 Smart Materials and Structures, Volume 19, Number 6, 065011.
Abstract:
One of the major difficulties in measuring the piezoelectric coefficient d(33,f)
for thin films is the elimination of the contribution from substrate bending. We
show by theoretical analysis and experimental measurements that by bonding thin
film piezoelectric samples to a substantial holder, the substrate bending can be
minimized to a negligible level. Once the substrate bending can be effectively
eliminated, single-beam laser scanning vibrometry can be used to measure the
precise strain distribution of a piezoelectric thin film under converse
actuation. A significant strain increase toward the inside edge of the top
electrode (assuming a fully covered bottom electrode) and a corresponding strain
peak in the opposite direction just outside the electrode edge were observed.
These peaks were found to increase with the increasing Poisson's ratio and
transverse piezoelectric coefficient of the piezoelectric thin film. This is due
to the non-continuity of the electric field at the edge of the top electrode,
which leads to the concentration of shear stress and electric field in the
vicinity of the electrode edge. The measured d(33,f) was found to depend not
only on the material properties such as the electromechanical coefficients of
the piezoelectric thin films and elastic coefficients of the thin film and the
substrate, but also on the geometry factors such as the thickness of the
piezoelectric films, the dimensions of the electrode, and also the thickness of
the substrate.
