Study On Epitaxial Growth And Modification Of PZT Thin Films For Piezoelectric MEMs

In recent years, with the development of micro-electric-mechanical technology(MEMS), a lot of MEMS devices are manufactured, but how to power them becomes one of the most important problems. The materials that advantage performance MEMS devices constitute require high reliability with the structures and properties. That is reason why the piezoelectric PZT based thin films have paid much more attentions in MEMS applications is those excellent properties for their piezoelectric, ferroelectric and dielectric. In this thesis, magnetron sputtering technology was utilized to deposite PZT(50/50) and(1-x) Pb(Zr1/2Ti1/2)O3-x Pb(Ni1/3Nb2/3)O3(PZT-PNN, x=0~0.15) thin films. Studies have been focused on the effect of different deposition conditions and relaxor ferroelectrics PNN doping on the crystalline phases,surface topography,ferroelectric and piezoelectric properties.High-quality polycrystalline PZT(50/50) thin films were successively grown onto(111)Pt/Ti O2/Si O2/Si substrate from the powder target using sputtering method. The crystallization and flatness of the films was enhanced by increasing the substrate temperature. However, the Pb O volatilized with temperature continuing increased, which caused the reduction of piezoelectric and ferroelectric properties. The excess Pb O in target could compensate the likely loss of this volatile component in the subsequent thin film preparation. It was revealed that excess 10 mol.% Pb O is appropriate to grow the perovskite crystalline thin films. The PZT thin films deposited at 750? in the ambient of 0.6Pa and at Ar/O=20/1 atmosphere had better electric properties. Moreover, the high-quality epitaxial PZT thin films were successively deposited on(001)Sr Ti O3(STO) and(001)Mg O single crystal substrates. The more strong upward ferroelectric self-poling, enhanced polarization switching and piezoelectric response characteristics were confirmed in epitaxial PZT films with compressive strains on(001) Mg O substrate.Polycrystalline(1-x) PZT-x PNN(x=0.05, 0.10, 0.15) thin films were also prepared via rf magneton sputtering technology, and X-ray diffraction showed that they are all well crystallized perovskite structure, free of impure phases. The crystal structure tetragonality increased with the addition of PNN. The composition of thin film 0.95PZT-0.05 PNN located on the region near the morphotropic phase boundary(MPB) of PZT-PNN Solid-solution system thin films. Thin films are dense and uniform with no obvious pores, both the grain size and root-mean-square(RMS) surface roughness increased with the increase of PNN content. Almost saturated ferroelectric hysteresis loop and better dielectric property were obtained from the sample when x=0.05, with the remnant polarization of 99.1?C/cm2, saturated polarization of 124?C/cm2, smaller coercive field values of 57.5k V/cm, relative dielectric constant of 2030 and low leakage current density. It is shown that 0.95PZT-0.05 PNN thin film exhibit better upward polarization and more excellent piezoelectric respone.