Wen Gong

Combined effect of preferential orientation and Zr/Ti atomic ratio on electrical properties of Pb(ZrxTi1−x)O3 thin films

Lead zirconate titanate [Pb(ZrxTi1−x)O3, PZT] thin films with various compositions, whose Zr/Ti ratio were varied as 40/60, 48/52, 47/53, and 60/40, were deposited on Pt(111)/Ti/SiO2/Si substrates by sol-gel method. A seeding layer was introduced between the PZT layer and the bottom electrode to control the texture of overlaid PZT thin films. A single perovskite PZT thin film with absolute (100) texture was obtained, when lead oxide was used as the seeding crystal, whereas titanium dioxide resulted in highly [111]-oriented PZT films. The dielectric and ferroelectric properties of PZT films with different preferential orientations were evaluated systemically as a function of composition. The maximums of relative dielectric constant were obtained in the morphotropic phase boundary region for both (100)- and (111)-textured PZT films. The ferroelectric properties also greatly depend on films’ texture and composition. The intrinsic and extrinsic contributions to dielectric and ferroelectric properties were dis...

Single-crystal Nb-doped Pb(Zr,Ti)O3 thin films on Nb-doped SrTiO3 wafers with different orientations

Single-crystal Nb-doped Pb(Zr,Ti)O3 (PNZT) films were grown on electric conducting single-crystal Nb-doped SrTiO3 (Nb:STO) wafers by a sol-gel method. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PNZT film was formed on the {100} surface of the Nb:STO substrate, whereas [111]-oriented rhombohedral PNZT film on the {111} surface. The PNZT films on SrTiO3 substrates showed considerably high remnant polarization and low coercive field, as compared with conventional PZT films on Si wafers. In particular, high d33 value was obtained in the [001]-oriented PNZT films.

Vibration analysis of stepping piezoelectric micro-motor using wiggle mode

Piezoelectric ultrasonic motor, a fractional horsepower motor, is different from conventional electromagnetic motor. It combines the features such as lightweight package, high driving torque at low speed, quick response, low consume, zero backlash, self-braking at zero power, no electromagnetic disturbance and noise, and high heat-stability in wicked environment. In this paper, we propose a new type of stepping piezoelectric micro-motor using wiggle vibration mode and three-dimensional contacts between the rotor and stator. Micro-vibration behavior and vibration mode shape of the prototype have been investigated using advanced POLYTEC PSV-300-F laser Doppler vibrometer. The piezoelectric micro-motor has potential applications for camera auto focus lenses, medical apparatus, micro-robots, micro-satellites, precise positioning, micro-machining, aerospace instruments, laser communication, etc. Here, using such two piezoelectric motors an improved manipulator with two degrees of freedom has been realized.

Preparation of (100)- and (111)-Textured Pb(Zr,Ti)O3 Piezoelectric Films and Direct Measurement of Their Piezoelectric Constants

A novel bending method is proposed to measure the piezoelectric constant e31 of piezoelectric thin films, in which strain and strain-induced charges are recorded simultaneously using a strain gauge and a charge integrator. Two kinds of lead zirconate titanate (PZT) films with (100) and (111) textures were prepared using the sol-gel process and their e31 was measured using the proposed technique. Reasonable e31 values of -6.0 and -6.9 C/m2 were obtained for the cross-plane-poled films with (100) and (111) textures respectively, whereas both as-deposited films exhibited the same low e31 of -0.2 C/m2.

Preparation of Ferroelectric K0.5Na0.5NbO3 Films by Sol-Gel Processing

Orthorhombic perovskite-type K0.5Na0.5NbO3 (KNN) films on Pt/Ti/SiO2/Si substrates were prepared by sol-gel processing. The morphology of the films was characterized using SEM and AFM. The KNN films with a total thickness of about 0.5 micron had relatively dense and uniform microstructure. The ferroelectricity of the KNN films was confirmed by polarization-electric field (P-E) hysteresis loop.

Correlation between donor defects and ferromagnetism in insulating Sn1−xCoxO2 films

Sn1−xCoxO2 films have been fabricated to study the local structure of Co dopant and the mediation effects of donor defects (oxygen vacancies and Sn interstitials) on magnetic properties. Compared to as-grown film, the ferromagnetism is evidently enhanced after annealing in vacuum at 400 °C due to the increase in oxygen vacancies. While annealing at higher temperature, the ferromagnetism declines because of the domination of decrease in Sn interstitials over increase in oxygen vacancies in the films. The incorporation of Co dopant as well as the presence of oxygen vacancies and Sn interstitials is verified using x-ray absorption fine structure spectroscopy. The variations in the concentration of defects as a function of annealing temperature are obtained by positron annihilation spectroscopy technique. Additionally, the changes in structure and ferromagnetism after annealing in different atmospheres further demonstrate the crucial roles of oxygen vacancies and Sn interstitials in tuning ferromagnetism.

Sol-Gel Process and Properties of Textured Pb(Zr, Ti)O 3 Films on Silicon Wafers

Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary were deposited on silicon wafers by using a modified sol-gel method. Introducing a seeding layer between the interface of PZT film and platinum electrode controlled the texture of PZT films. The lead oxide seeding layer results in highly (001)-textured PZT film, while the titanium dioxide seeding layer results in (111)-textured one. SEM and XRD were used to characterize the PZT thin films. The ferroelectric and piezoelectric properties of the PZT films were evaluated and discussed in association with different preferential orientations.

Analysis of Dynamic Response for Piezoelectric Vibration Converter by Finite Element Simulation

The dynamic behavior of a vibration converter of an ultrasonic motor is described using finite element method. Tetrahedral finite elements with three dimensions are formulated with the effects of piezoelectric coupling. And the solution of the coupled electroelastic equations of dynamic motion is presented. The simulated response of the vibration converter is calculated, and shows excellent consistency with experimental results, which proved that finite element modeling is a good approach to optimize piezoelectric apparatus design. A gradual optimized method is employed to ascertain the most compatible structure.

Preparation and Characterization of Pb(Zr,Ti)O3 Films on SrTiO3 Substrates

Pb(Zr,Ti)O3 (PZT) thin films have attracted great attention due to their superior ferroelectric, pyroelectric and piezoelectric properties. The epitaxial films on single-crystal substrates are expected to possess enhanced properties compared with polycrystalline films on conventional silicon wafers. We prepared epitaxial PZT films on STO (STO) substrates with different orientation by using a sol-gel method. The preparation parameters were optimized to improve crystallization of the films. Although the films were of the same composition and prepared under the same condition, different crystal phases with corresponding preferential film orientations were formed when the substrate orientation was changed. [001]-oriented tetragonal PZT film was formed on the {100} surface of the STO substrate, whereas [111]-oriented rhombohedral PZT film on the {111} surface.