Design and analysis of a PZT-based micromachined acoustic sensor with increased sensitivity

The ever-growing applications of lead zirconate titanate (PZT) thin films to sensing devices have given birth to a variety of microsensors. This paper presents the design arid theoretical analysis of a PZT-based micro acoustic sensor that uses interdigital electrodes (IDE) and in-plane polarization (IPP) instead of commonly used parallel plate-electrodes (PPE) and through-thickness polarization (TTP). The sensitivity of IDE-based sensors is increased due to the small capacitance of the interdigital capacitor and the large and adjustable electrode spacing. In addition, the sensitivity takes advantage of a large piezoelectric coefficient d/sub 33/ rather than d/sub 31/, which is used in PPE-based sensors, resulting in a further improvement in the sensitivity. Laminated beam theory is used to analyze the laminated piezoelectric sensors, and the capacitance of the IDE is deduced by using conformal mapping and partial capacitance techniques. Analytical formulations for predicting the sensitivity of both PPE- and IDE-based microsensors are presented, arid factors that influence sensitivity are discussed in detail. Results show that the IDE and IPP can improve the sensitivity significantly.