Session: 13-02-01: Design and Fabrication, Analysis, Processes, and Technology for Micro and Nano Devices and Systems

Paper Number: 145319

145319 - Comparison of Electrode Configuration for 0,2 Piezoelectric Ultrasound Transducer 

Microelectromechanical systems (MEMS) based piezoelectric microultrasound transducer (PMUT) are extensively used in numerous applications. The majority of these devices operate in the first acoustic mode (0,1), and the electrode configuration and design of these have been extensively investigated. However, some applications such as vibrating mesh atomizer (VMA) operate in the 0,2 acoustic mode, where the velocity and force generated from the center ring allows liquid to be squeezed through nozzles to produce an aerosol. Therefore, optimizing the electrode configuration is critical to maximize force, displacement and velocity.  However, currently there has not been any investigation into how the electrode configuration affects the dynamics of the membrane. It has been found that optimal atomization occurs when the membrane is excited into the (0,2) mode of vibration, generating sufficient force to propel liquid through the mesh apertures, resulting in efficient atomization. This study focuses on using multiphysics finite element modeling (FEM) to investigate possible electrode configurations to determine their effects on the output performance of these VMA PMUT devices. The devices consist of two thin Pt electrodes, lead zirconate titanate (PZT) piezoelectric layer sandwiched between the electrodes and a Si membrane. This study seeks to find the optimal configuration of the top and bottom electrodes for achieving the highest displacement and velocity of the (0,2) mode. This study also dives deeper into analytically calculating and simulating the stress nodal circles of the (0,2) mode of the Si membrane. A 2D FEM model was created and validated based experimental results from previous research and then the electrode configurations were modified.

Initially, the resonant frequency at the (0,2) mode were determined by doing a sweep, then the frequency was used for further testing. Since the resonant frequency changed slightly due varying mass of the electrodes each device was operated at resonant frequency. Due to the cylindrical axisymmetric advantage of the model and axisymmetric natural frequency mode (0,1) and (0,2), a two-dimensional (2D) model was used to carry out the simulation. A total of seven electrode designs have been designed and compared in terms of membrane amplitude, membrane velocity and area for creating apertures. Schematic 2D model of electrode design for VMA is represented in Fig. 1 (a). The device is made up of 30 µm silicon membrane, a 1 µm PZT-5H that is sandwiched between two 100 nm electrodes, a uniform planar brick type mesh was used to create the computational nodes on the model. The stress nodal circles of mode (0,2) have been calculated and the electrode designs are located at a gap from these nodal circles of volumetric stress. An AC voltage was applied at resonant frequency between the electrodes with a constant 20V.  Increasing the voltage will increase displacement, but this was held constant to compare the results.

Results determined that the electrode configuration does have a significant affect on the displacement, velocity, and force.  It was determined that a single layer circular electrode covering the entire membrane had the lowest displacement. Whereas a multiple ring configuration for the top electrode with the electrode rings located at the nodal circle locations gave the largest output.  The results of this study will be used to experimentally validate the performance and could be useful for design engineers working with 0,2 PMUT devices in the future.

Presenting Author: Ranjith Janardhana University of New Mexico

Presenting Author Biography: Ranjith is a Phd Student studying Micro acoustofluidics at the University of New Mexico

Authors:

Abdul Popal University of New Mexico
Ranjith Janardhana University of New Mexico
Fazli Akram University of New Mexico
Nathan Jackson University of New Mexico