Piezoelectric nonlinearity in GaN Lamb mode resonators

This paper reports on the measurement of nonlinearity in GaN Lamb mode resonators subjected to power levels between -10 and +10 dBm. In these devices, nonlinearity manifests itself as both frequency shift (Δ/f of 60-128 ppm) and change in motional impedance (ΔR_m/R_m of 13-33%). In this work, we decouple the contributions from self-heating and strain-induced piezoelectric nonlinearity to ΔR_m/R_m, and conclude that strain-induced change in piezoelectric coefficients Δe₃₁ and Δe₃₃ is the dominant cause of ΔR_m/R_m, accounting for 31% of the total 33% observed shift. The result is consistent with 2^nd order nonlinear coefficients previously derived analytically [1].