Mass sensing AlN sensors for waste water monitoring
2014
Monitoring the presence of nanomaterials in waste water from semiconductor facilities is a critical task for public health
organizations. Advanced semiconductor technology allows the fabrication of sensitive piezoelectric-based mass sensors
with a detection limit of less than 1.35 ng/cm 2 of nanomaterials such as nanoparticles of alumina, amorphous silica,
ceria, etc. The interactions between acoustic waves generated by the piezoelectric sensor and nanomaterial mass
attached to its surface define the sensing response as a shift in the resonant frequency. In this article the development and
characterization of a prototype AlN film bulk acoustic resonator (FBAR) are presented. DC reactive magnetron
sputtering was used to create tilted c-axis oriented AlN films to generate shear waves which don’t propagate in liquids
thus minimizing the acoustic losses. The high acoustic velocity of AlN over quartz allows an increase in resonance
frequency in comparison with a quartz crystal microbalance (QCM) and results in a higher frequency shift per mass
change, and thus greater sensitivity. The membrane and electrodes were fabricated using state of the art semiconductor
technology. The device surface functionalization was performed to demonstrate selectivity towards a specific
nanomaterial. As a result, the devices were covered with a “docking” layer that allows the nanomaterials to be selectively
attached to the surface. This was achieved using covalent modification of the surface, specifically targeting ZnO
nanoparticles. Our functionalization approach was tested using two different types of nanoparticles, and binding
specificity was confirmed with various analytical techniques.
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