Clipsham, Timothy Jack (2010)
Ph.D. thesis, University of Birmingham.
1-3 Piezocomposites show significant improvements over conventional, monolithic transducers. However, a 10 MHz piezocomposite would require a pillar array structure with an aspect ratio of > 9 and a feature size of < 30 μm; which makes fabrication difficult and increasing the operating frequency challenging. Several processes have been developed to improve on the industry standard, dice and fill, but they remain laboratory based. Viscous polymer (VP) embossing has been demonstrated as a route to smaller feature sizes and higher aspect ratios, but the process is limited by the availability of suitable moulds, which must be replicated to make the process cost effective. This thesis reviews the micro replication and fabrication processes necessary to produce moulds for 1-3 piezocomposites, and characterises the replication process from hot embossing to a functioning 1-3 piezocomposite. It demonstrates that the Bosch process and electroforming can be combined to produce a master with a deeper array structure than has been previously demonstrated by these two processes. Piezocomposites have also been made which have pillar widths that are not possible by dice and fill, by filling hot embossed moulds that have aspect ratios of 14 and feature sizes of 30 μm.
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