A new control method for the relative dielectric constant of 1-3 piezoelectric composites realized with the LIGA process

A plasma treatment for controlling the relative dielectric constant (epsilo n(r)) of fine-scale lead zirconate titanate (PZT) rods was developed. This new method made it easy to control epsilon(r) of 1-3 piezoelectric composit es, which were made up of fine-scale PZT rods in epoxy resin. The PZT rods were fabricated using the LIGA process, realizing an array of PZT rods with a cross section, height and volume fraction of 25 mu m square, 250 mu m an d 25%, respectively. The new method consists of a plasma treatment applied before sintering of the PZT rods. By controlling the output RF power and du ration of the plasma treatment, epsilon(r) could be controlled between 250 and 400. Although extended plasma etching reduced epsilon(r), there were no changes in the piezoelectric properties and no defects in the sintered bod y. The ability to control epsilon(r) of piezoelectric composites allows goo d electrical impedance matching with the electric circuit of diagnostic sys tems, thereby reducing signal transmission losses. Changing epsilon(r) by v arying the piezoelectric material or the sintering conditions requires leng thy process optimization. In contrast, controlling epsilon(r) to establish a good impedance match can be done relatively easily with this new plasma t echnique because the piezoelectric properties are not affected.