Analysis of constrained piezoelectric thin film sensor

Abstract

A three dimensional electro-mechanical continuum field model is developed to analyze the constrained boundary effects on the transduction performance of thin Piezoelectric films. The model proposed in this paper for Piezoelectric thin film is based on 3D continuum mechanics under plane-stress condition. The plane-stress condition is justifiable for the fact that the thickness of the piezoelectric film is of the order of microns(in 'z' direction); and hence, very small in comparison to the other two dimensions(in 'x' and 'y' directions) of the film. The film, and its proposed model, are intended to be used for Structural Health Monitoring of any structural component, such as, wing of an aircraft. The thin film is surface-mounted on this structural component, and this component will be termed as Host structure, henceforth. When the host structure is strained under the action of loads, the displacement vector field that is generated acts as an input to the thin film in this model. The performance of the thin film in terms of its voltage response, capacitance, and effect of residual stresses on capacitance and output voltage are studied here. The results show significant variation of the same as compared to conventional design and analysis based on electro-statics. The voltage distribution and its variation over the film when a crack is initiated in the host structure under mode-I and mode-II loadings are also presented. It has been observed that in microelectronic devices, various process-induced stresses such as intrinsic stress, epitaxial stress, thermal stress etc., play crucial role in the device performance. The model presented here is capable of handling such stresses while designing the sensor itself.