Integrated PNZT film structures for MEMS gyroscopes

During the last decade there has been an explosion of interest in microelectromechanical systems (MEMS), since MEMS technology has become increasingly important for various industries like medical, chemical, automotive and aerospace.; The efficiency of MEMS devices based on piezoelectric thin films largely depends upon the piezoelectric constants and the electrical properties of the films. The purpose of this research has been to develop a sol-gel growth process of niobium doped lead zirconate titanate (PNZT) thin films and to quantify the electrical and mechanical properties of the PNZT films for MEMS-gyroscope applications. Two different schemes for annealing of the sol-gel PNZT films were used and the measured properties of the two types of samples were measured and compared. High dielectric strength, low dielectric loss, small leakage current, high dielectric constant, and long term stability of the piezoelectric PNZT films were obtained, making them compatible for microelectronics and micromechanical applications. The self-polarization in the thin films was very stable leading to high piezoelectric coefficients in the as-grown PNZT films.; The choice of the piezoelectric material for an actuator is mainly determined by the piezoelectric coefficient d₃₁, which determines the magnitude of the actuation which is possible for a given drive voltage. The piezoelectric properties of PNZT films were characterized using the cantilever beam technique. The d₃₁ piezoelectric coefficient was determined by measuring the deflection of cantilevers actuated by PNZT films at resonance and in a quasistatic regime.; The effective piezoelectric coefficient $eeff31$ was measured using the direct piezoelectric effect; i.e. electric charges were collected from a cantilever bent in a quasistatic regime. The aging of the piezoelectric response was studied as a function of driving voltages and solutions for lowering the aging of the piezoelectric response have been proposed.; Piezoelectrically excited cantilevers were used to determine the Young's modulus of the composite substrate and of the PNZT thin film since these values are needed to evaluate the piezoelectric coefficients of the films. The multilayer cantilevers were excited into vibration and the resonance frequencies of the cantilevers could then be utilized in a composite beam model to extract the Young's modulus for each layer.