Improved sensitivity prediction method for FBAR transducer

Defects in efficiency or usability have come into being when using the maximum stress on FBAR structure as the reference stress or using the so called "Calculus-like analysis method" to calculate the sensitivity of FBAR transducer. The former does not consider the influence of the strain in the thickness direction, which overestimates the sensitivity. The latter learns from FEM, but it is too complicate and heavy-workload. In order to eliminate these deficiencies, the improved sensitivity prediction method for FBAR transducer is put forward. The whole calculation process is completed with COMSOL (R) FEM software to avoid the complex data processing. The energy weighted average method is used to calculate the average strain of every single layer in FBAR and the average internal pressure of piezoelectric layer. The average strain is used to modify the thickness of FBAR, and the internal pressure is used to modify the elastic constant of piezoelectric material. Then the eigenfrequency solving method is carried out to solve the eigenfrequency of FBAR. The former improves the speed of solving, and the latter enhance the accuracy of the calculation results. The sensitivity of both circular membrane type FBAR transducer and FBAR micro-accelerometer can be calculated through the improved method. The expected sensitivity of the membrane type FBAR transducer is 46.5 MHz/N, which is close to the experimental result, 50 MHz/N. However, due to unawareness of the actual structure parameters, the expected sensitivity of the micro-accelerometer is 27 kHz/g, which is different from the experimental result, 100 kHz/g. The two calculation cases indicate that the improved sensitivity prediction method for FBAR transducer is both effective and available.