Nuri Emanetoglu, David Frankel, Andre Khalil, Mark Haggerty
Medical and environmental needs have served as a catalyst for the development of sensors that can probe the molecular level and below. This study addresses the practicality of highly sensitive aluminum nitride (AlN) thin film bulk acoustic wave resonators (FBARs) as sensors from theoretical and experimental points of view. Theoretically, COMSOL Multiphysics simulations predict that lateral field excitation of AlN produces an electric field perpendicular to the c-axis, with the electrical energy density being concentrated in the active area of the sensor. An analysis of the piezoelectrically stiffened Christoffel equation shows that the shear mode can be excited by an applied electric field in the x − y plane. Several thin films were deposited on various substrates such as borosilicate glass, silicon, sapphire, and fused silica using RF reactive magnetron sputtering and e-beam evaporation. To characterize film structure and composition, x- ray diffraction and x-ray photoelectron spectroscopy were used. An Agilent network analyzer was used to assess the performance of the sensor in air and water. In the most successful case, c-axis AlN films with a FWHM of 1.5 degrees were fabricated with quality factors between 33-36 in air and water. The magnitude of the admittance did not change appreciably when the film was exposed to water, indicating a shear mode was excited. Overall, a building block to a realizable AlN sensor was established.
FitzGerald, Michael R., "A Lateral Field Excited Thin Film Bulk Acoustic Wave Sensor" (2013). Honors College. 631.