Design and fabrication of nanoscale ultrasonic transducers

The development of nanometre sized ultrasonic transducers is important in both biological and industrial applications. The small size can be important in its own right or necessary in order to generate acoustic waves with nanometric wavelengths. Potential applications of nanotransducers range from embedded sensors through to sub optical wavelength acoustic imaging. In this paper we discuss the design and fabrication of nanoscale ultrasonic transducers. The transducers rely on optical and mechanical resonances, they can be used to generate and detect high frequency ultrasound in a sample. The mechanical and optical performance of the devices have been extensively modelled using both analytical techniques and finite element modelling. This allows the fine tuning of the design parameters to ensure optimised performance for the experimental configuration. The devices can be fabricated in a number of ways, we present one method for building these types of devices, a 'top down' approach where plate structures are built up and patterned using standard photolithographic techniques. This method produces nanoscale devices in one dimension only (the others being a few microns) but produces excellent devices for testing in situ and for comparison to the models as they are easy to handle and measure. Approaches for reducing the other dimensions to the nanoscale will also be considered.