Abstract
In this paper, the piezoelectric coefficient d33 of AlN thin films for MEMS applications was studied by the piezoresponse force microscopy (PFM) measurement and finite element method (FEM) simulation. Both the sample without a top electrode and another with a top electrode were measured by PFM to characterize the piezoelectric property effectively. To obtain the numerical solution, an equivalent model of the PFM measurement system was established based on theoretical analysis. The simulation results for two samples revealed the effective measurement value d33-test should be smaller than the intrinsic value d33 due to the clamping effect of the substrate and non-ideal electric field distribution. Their influences to the measurement results were studied systematically. By comparing the experimental results with the simulation results, an experimental model linking the actual piezoelectric coefficient d33 with the measurement results d33-test was given under this testing configuration. A novel and effective approach was presented to eliminate the influences of substrate clamping and non-ideal electric field distribution and extract the actual value d33 of AlN thin films.
Highlights
In micro-electromechanical systems (MEMS) devices, especially MEMS resonators, AlN material has great potential due to the excellent acoustic properties, piezoelectric properties, and good compatibility with other microelectronic technologies
33 of an actual the equivalent model verified by the accordance between and the The d33-test of would be smaller thanhave the been intrinsic piezoelectric coefficient d33the of simulation an actual results rationality of in theprevious equivalent model have been verified by the accordance between the simulation results and the reports in previous literatures
piezoresponse force microscopy (PFM) measurement and the finite element method (FEM) simulation were performed for two samples
Summary
In micro-electromechanical systems (MEMS) devices, especially MEMS resonators, AlN material has great potential due to the excellent acoustic properties, piezoelectric properties, and good compatibility with other microelectronic technologies. There are many methods to determine the piezoelectric coefficient quantitatively, such as the Berlincourt method [1], capacitance measurement [2,3], laser interferometer [4,5,6,7], and piezoresponse force microscopy (PFM) method [8,9,10,11,12] Among these methods, the Berlincourt method is a standard method to determine the piezoelectric properties. There are many different measurement values of AlN thin films reported in the literature, it is difficult to make a fair comparison between them as they all ignore the influences of the substrate and electric field distribution. By comparing experimental results of AlN films with the values calculated by FEM, a novel and effective method to extract the actual piezoelectric coefficient d33 was given. Due to a good agreement between the extracted values d33 of two different samples made from the same wafer, the accuracy and rationality of the method were verified
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