Effect of stress on a bimorph piezoelectric micromachined ultrasound transducer

A bimorph piezoelectric micromachined ultrasound transducer (pMUT) is presented. The bimorph comprises molybdenum and aluminum nitride (AlN) layers in both the top and bottom sections of the device. Residual stresses were included in both the top and bottom sections of the simulation model. Simulation results show that a progression from compressive to tensile stress leads to an increase in the fundamental resonant frequency of the pMUT. Deriving inspiration from Stoney´s equation, a mathematical model is proposed to extract the value of the residual stresses from the experimental data. The residual stresses obtained agree well with the hypothesized inverse relationship between the radius of curvature and the stress difference between the top and bottom sections of the pMUT.