Nonlinear behavior of AlN in BAW and CRF devices for high RF electric field

In this work, we study for the first time the nonlinearity of AlN piezoelectric material subjected to high RF electric field (E). Nonlinear effects in BAW (Bulk Acoustic Wave) resonators are seen as a frequency shift and an amplitude variation at the resonance (f_r) and anti-resonance (f_a) frequencies. Moreover the coupling factor increases for high power measurements (high E). By model fittings, these nonlinear effects are produced by two main changes in the real parts of piezoelectric e₃₃ and elastic c₃₃ coefficients. These coefficients rise of 7% for real (c₃₃) and 18% for e₃₃ and become independent of the electric field at AlN layer saturation. The variation laws of both parameters are then applied to CRF (Filter of Coupled BAW Resonators) model and compared to IP₃ measurements. The model doesn´t converge unless we add an extra-nonlinear parameter: the real part of the permittivity ε₃₃ that only appears in case of intermodulation distortion. Thus, nonlinearity affects dielectric, piezoelectric and acoustic sections in AlN piezoelectric material.