Modeling interdigitated piezoelectric thin-film micro-actuators

As Microelectromechanical Systems (MEMS) become more practical and useful, there exists a need to properly characterize and model the behavior of these devices. Smart materials such as shape memory alloys and piezoelectric materials are most commonly used for micro-actuation in MEMS devices. Piezoelectric thin film micro-actuators for use in MEMS micro-pumps has become a large topic of study. This dissertation deals with the development of models of piezoelectrically actuated diaphragms. Two types of diaphragms, planar capacitor and interdigitated, most suitable for MEMS micro-pump applications are studied.The study starts with developing a model using a multi-physics finite element modelling package and validating the results with well known classical analytical results. Three dimensional one quarter, three dimensional 10o slice, and two dimensional axissymmetric models of piezoelectrically actuated diaphragms were modelled and simulated using the multi-physics FEM package. Good agreements were obtained with the analytical results.As the next step, two planar capacitor samples were modelled as a unimorph diaphragm with sandwiched piezoelectric material. Simulation with one-quarter symmetry model of the planar capacitor yielded a static deflection in the range of 71 to 150 nm. Both the static deflection and the harmonic frequencies obtained were in agreement with the known experimental results obtained earlier at Northrop Grumman. This level of deflection is not enough for many micro-actuator applications. This FEM model can serve as a valuable tool to develop better devices.Finally, the interdigitated diaphragms were modeled and evaluated. The interdigitated configuration allows us to take advantage of the d 33 constant. Two-dimensional axis-symmetric models were developed using the material properties and boundary conditions established by literature and through collaboration from Northrop Grumman and Pennsylvania State University. Several individual models were developed to model the different design parameters of piezoelectric thickness, electrode pitch and width, center disk diameter and number of electrodes. By design, the models coupled several of the parameters, in particular, center disk diameter and number of electrodes. The parametric analysis served as a very good predictor of the design parameters and offered a valuable knowledge that a user could use to choose a suitable design. It should be noted that although individual parameters were varied, several of the parameters were naturally coupled, such as the electrode width and electrode separation, center disk diameter and number of electrodes that will require further study. Although the experimental devices differed in material configuration to the proposed and initially modelled devices, successful 2-D interdigitated axis-symmetric models were developed.These models will be able to predict the behavior of piezoelectric actuated diaphragms most suitable for MEMS micropump applications. Even though the models are not exhaustive, they can serve as a valuable tool to design and analyze piezoelectric diaphragm actuators leading to both economical and technological benefits.