3I-1 A Lateral Field Excited Sensor Array on a Single Piezoelectric Substrate

Bulk acoustic wave sensors such as the quartz crystal microbalance (QCM) and lateral field excited (LFE) [Hu, et. al., 2004] device have been used for sensing applications in liquid and air. Typical bulk acoustic wave sensing arrays consist of sensors on separate substrates linked by interconnects. Fabricating several sensors on a single piezoelectric substrate offers a simple, reproducible alternative that could potentially reduce the size and cost of multi-parameter sensors. Realizing such an array however can be problematic in terms of acoustic interference between sensing areas for QCM sensors which require electrodes on the sensing surface. In contrast, LFE sensors, which use the transverse shear mode (TSM) as the sensing element, have no electrodes on the sensing surface and are excited by electrodes on the surface opposite the sensing surface. In order to isolate the excited TSM fields for each LFE sensor a heat treatment process proposed by T. Uno [Uno, 1996] is performed. This process inverts the direction of the x-axis of AT-cut quartz in the treated region. Heat treating a piezoelectric crystal focuses and confines acoustic energy at the sensing surface providing the means of constructing an acoustically isolated LFE sensor array on a single piezoelectric substrate