Effect of 1-3 Piezocomposite Layout on Resonance Behavior of High-frequency Ultrasonic Transducers

High frequency ultrasonic transducers based on 1-3 piezocomposites are essential prerequisite for medical diagnostics and non-destructive testing. In order to achieve superior image resolution, operating frequencies have to be... [ view full abstract ]

High frequency ultrasonic transducers based on 1-3 piezocomposites are essential prerequisite for medical diagnostics and non-destructive testing. In order to achieve superior image resolution, operating frequencies have to be increased, which requires reduction of transducer thickness. Furthermore, lateral layout dimensions have to be adjusted to prevent spurious resonance frequencies. Accordingly, these requirements for high-resolution imaging put high challenges on the manufacturing process of appropriate ultrasonic transducers.

In this contribution, the development of ultrasonic transducers with operating frequencies above 20 MHz is reported. For fabrication of fine-scale piezoceramic arrays, soft mold technique is used. The basis of this process are master molds structured by microsystems technologies like LIGA, SU8 and deep reactive ion etching (DRIE). In contrast to conventional dice-and-fill technique, these processes allow for free design of pillar geometry and spatial distribution. Master molds with circular pillars in hexagonal arrangement and different combinations of pillar diameters (40, 30, 20 µm) and interpillar spacings (10, 7.5, 5 µm) have been fabricated. Manufacturability of fine-scale 1-3 piezocomposites based on these master molds has been tested to shift spurious modes to frequencies approximately twice as operating frequency. Influence of pillar diameter and interpillar spacing on resonance modes are investigated by analyzing resulting transducers in respect of their frequency spectra. Experimental results will be explained in detail and compared to modelled data.