P2P-7 Design, Fabrication and Characterisation of High Frequency Piezoelectric Micromachined Ultrasonic Transducers

High frequency bending mode membranes are fabricated using a 1 mum PZT thick film deposited by sol-gel. Finite element analysis (FEA) is used to tailor the membrane radius to a resonant frequency in the 5-10 MHz frequency range. Using a radius of 16 and 24 mum, devices are produced as individual cells as well as 3 times 3 and 5 times 5 arrays. The arrays are designed so that the bottom electrode is common to all cells whereas the top electrode is only common to a column of 5 or 3 cells depending on the type of arrays. Within a column each cell was separated by a wall of silicon (having the length of the substrate of silicon) in order to sustain the array, reduce parasitic vibrations, hence cross-talk. A 16 mum radius membrane shows a resonant frequency of 9 MHz and a coupling coefficient of 11%. Suspended cells are also investigated to increase frequency further. Two arms-suspended cells resonate at 8.1 MHz for a 24 mum radius membrane