Surface acoustic wave (SAW) devices have been in commercial use for more than 60 years. The telecommunications industry is the largest consumer, accounting for ~3 billion acoustic wave filters annually, primarily in mobile telephones and base stations. Important emerging applications of SAW devices are chemical- and mass sensors with large potential markets as well. The key element of a SAW device is the interdigital transducer (IDT), an array of intertwined metallic fingers, used to convert electrical energy into mechanical energy and vice versa. Both in telecommunications and sensing there is a strong drive towards higher frequencies for enhanced performance. The IDTs thus need to possess smaller finger sizes and spacings, down to the sub-50 nanometer range.
The moving periodic deformation results in a piezoelectric potential accompanying the SAW, which offers the possibility to transport electrons, holes and spins at a well-defined frequency. Especially this feature is explored in our group.
High-frequency SAW devices fabricated by nano imprint lithography
We have developed a reproducible method for fabricating interdigital transducers (IDTs) with characteristic dimensions well below 100nm. To this end, we have employed a recent and exciting lithographic technique: nano-imprint lithography (NIL), currently the most sophisticated form of nano-pattern reproduction by means of ‘printing’ or ‘stamping’. The application of NIL ensures (i) access to large numbers of nanostructured samples from single masters, (ii) easy translation into different semiconductor and non-semiconductor materials, (iii) a large number of degrees of freedom for patterning, such as feature height and pattern inversion.
We have succeeded in fabricating high-quality IDTs generating SAWs up to 16 GHz. Presently devices are being explored for charge transport in Si and GaAs.
High-quality global hydrogen silsequioxane contact planarization for nanoimprint lithography
S. Büyükköse, B. Vratzov and W.G. van der Wiel
J. Vac. Sci. Technol. B 29, 021602 (2011).
This project is in collaboration with the Paul-Drude-Institut Berlin and part of the NanoArrays project, financed by the Netherlands Science and Technology Foundation (STW).
Look here for a cool animation: http://www.utwente.nl/ewi/ne/media/saw.avi