Fabrication and characterization of a 20 MHz ultrasonic transducer using soft mold process
Poster presented at Joint IEEE International Symposium on the Applications of Ferroelectrics, European Conference on Applications of Polar Dielectrics & Workshop on Piezoresponse Force Microscopy, ISAF/ECAPD/PFM 2016, Darmstadt, 21.-25.8.2016
High frequency ultrasonic transducers based on fine scale 1-3 piezocomposites enable high resolution in medical or material imaging. As increasing frequency requires decreasing pillar size and kerf width, the conventional dice-and-fill technique is limited by blade thickness and becomes more sophisticated with smaller dimensions. In contrast, the soft mold technique allows for fine-scale piezoceramic arrays with free design of pillar geometry and spatial distribution. Basis of the procedure are net-shaped master molds fabricated by structuring techniques known from microsystems technology, like deep reactive ion etching (DRIE) or LIGA process. From these, soft plastic templates are taken which are reusable. Therein a ceramic slurry based on lead zirconate titanate (PZT) is casted and demolded after drying. After debindering, sintering and filling with an epoxy polymer resulting 1-3 piezocomposites are lapped to the desired thickness, electroded and poled.In this contribution, the development of a 20 MHz ultrasonic transducer based on a 1-3 piezocomposite with circular pillars in hexagonal arrangement and sintered dimensions of 34 mm diameter, 160 mm height and 10 mm spacing is reported. 1-3 piezocomposites made of these structures show coupling coefficients kt = 0.6 at the thickness resonance of 20 MHz. First lateral resonance is measured at anuncritical frequency of 37 MHz. A single element ultrasonic probe has been manufactured by selection of appropriate backing and matching layers. For characterization of sensitivity and bandwidth pulse-echo curves have been investigated and will be presented. Manufacturing technique as well as experimental results on dielectric, electromechanical and acoustic properties will be explained in detail.