Dry release for ultrasensitive mass sensors
Significant advances have been made in the microsystem and nanotechnology fields regarding the development of mechanical mass sensors. Pivotal in this research was work accomplished during the European funded NANOMASS II project. The overall project objective was to combine CMOS (Complementary metal-oxide-semiconductor) circuitry with nanotechnological processes to develop advanced molecular sensors. Industrial application of the device as a very compact and sensitive environmental or biochemical sensor was also evaluated. Due to the technological advancements achieved, the sensors have an unprecedented level of accuracy in terms of mass resolution and spatial sensitivity. The basis of the mechanism is an array of nanoscale silicon cantilevers. Array fabrication makes it possible to optimise the function of the devices by differential detection and allowing the specific detection of single molecules. In order to increase the throughput of functional cantilever devices, the project team at Mikroelektronik Centret in Denmark worked on a new protocol to produce suspended nanostructures. The process involved a dry release method. This utilised a layer of light-sensitive material, photoresist, which was then removed through an oxygen ashing system using a plasma source. A fluorocarbon film, which acted as an anti-stiction coating, was deposited in a single reactive ion etching sequence. This newly developed process has multiple advantages. It is contamination free and lends itself to batch processing. The resultant products can be stored long-term without the development of undesirable stiction, namely static friction. This is due to the deposition of an anti-stiction layer through the merging of the dry release method and plasma deposition. Fabrication-induced stiction is eliminated by means of this anti-stiction layer, as well as friction phenomena during mechanical operation (in-use static friction). The application of nanotechnology and resultant nanodevices is on the verge of conferring a huge economical advantage in the combination of CMOS and nanotechnology. Projects of this nature are set to realise the potential of demonstrations once confined to a laboratory to a productive industrial setting instead. For interested parties, more information is available on the website at http://einstein.uab.es/_c_nanomass/nanomass.html
