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 (ɛr) of fine-scale lead zirconate titanate (PZT) rods was developed. This new method made it easy to control ɛr of 1-3 piezoelectric composites, 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 μm square, 250 μm and 25%, respectively. The new method consists of a plasma treatment applied before sintering of the PZT rods. By controlling the output RF power and duration of the plasma treatment, ɛr could be controlled between 250 and 400. Although extended plasma etching reduced ɛr, there were no changes in the piezoelectric properties and no defects in the sintered body. The ability to control ɛr of piezoelectric composites allows good electrical impedance matching with the electric circuit of diagnostic systems, thereby reducing signal transmission losses. Changing ɛr by varying the piezoelectric material or the sintering conditions requires lengthy process optimization. In contrast, controlling ɛr to establish a good impedance match can be done relatively easily with this new plasma technique because the piezoelectric properties are not affected.