Thin aluminum nitride film resonators: miniaturized high sensitivity mass sensors

A miniaturized piezoelectric mass sensor has been developed that displays a very high mass sensitivity, S{sub m}. The sensor is based upon thin film resonator (TFR) technology, which is used to produce a gold-coated thin film (5.5 {mu}m) resonator (TFR) of piezoelectric aluminum nitride in the shape of 400-{mu}m squares. At this thickness, the TFRs support a standing bulk acoustic wave in a longitudinal mode at frequencies of {approximately} 1 GHz. Coatings of poly(methyl methacrylate) and spontaneously adsorbed monolayers from alkanethiols (CH{sub 3}-(CH{sub 2}){sub n}SH, n = 3,17) were used for the evaluation of S{sub m}. Results indicated that the S{sub m} ({approximately} -550 cm{sup 2}/g) of the TFRs rivals those of the most sensitive mass sensors currently available, while offering such performance in a markedly smaller device. Coatings were also used to sorb a gaseous analyte (i.e. methanol) at the TFRs to test their potential as gas-phase sensors. Tests conducted using monolayers formed by the chemisorption of a fluorinated thiol (CF{sub 3}(CF{sub 2}){sub 7}(CH{sub 2}){sub 2}-SH) and an acid-terminated thiol (HO{sub 2}C(CH{sub 2}){sub 15}SH) at the gold electrodes demonstrated both the performance of the TFRs and a primitive manipulation of the sorption selectivity of the interfacial structure. Possible applicationsmore » of the TFRs as mass sensors are examined based upon their high mass sensitivity and compatibility for device integration using semiconductor processing technology. 51 refs., 4 figs., 2 tabs.« less