Technological Challenges of Making PZT Based Piezoelectric Wafers

Abstract

In recent future, piezoelectric wafers are going to play a pivotal role in nondestructive evaluation (NDE) of structures in defence, aerospace and industrial sectors. Structural health monitoring (SHM) or integrated vehicle health monitoring (IVHM) requires small, light-weight, minimally invasive sensors which can be embedded in or mounted on the surface of the structure. Especially, for the NDE of thin-wall structure, piezoelectric wafers look very promising for Lamb wave excitation and sensing. Incidentally, piezoelectric wafers are normally required in large numbers for NDE of structures and hence, a proven and cost-effective technology of making such wafers is the need of the hour. Though the standard tape casting (doctor-blade) technique is expected to serve the purpose, some typical problems, which crop up during fabrication of PZT based wafers, need to be sorted out to make high performance wafers. Just by following the standard process of fabrication of alumina/zirconia substrates, one does not get quality products in the present case owing to volatilization of lead from PZT at the sintering temperature, warpage and adhesion of the wafers with the setter plate. Such problems are quite alarming in the present case as the effective exposed surface of a single-layer wafer is much higher compared to that of a bulk or stacked multilayered structure. In the present work, important processing parameters to make good quality PZT wafers have been discussed. The dielectric and piezoelectric properties of the wafers have been studied and compared with those of bulk PZT ceramics.