A highly sensitive Pb(Zr,Ti)O3 thin film ultrasonic micro-sensor with a grooved diaphragm

A highly sensitive piezoelectric ultrasonic micro-sensor with a grooved multilayer membrane was developed by a Si-based MEMS technique. The groove was located at one-quarter of the distance away from the edge of the membrane and opened into piezoelectric layer. The piezoelectric layer Pb(Zr,Ti)O(3) (PZT) was 2.2 microm thick and was prepared by a sol-gel method. The prepared PZT film was pure perovskite and showed a highly (100) textured structure. The sensitivity of the fabricated piezoelectric ultrasonic sensor without the groove structure was 100 microV/Pa. In comparison, the sensitivity of the ultrasonic sensor with the groove structure was about 500 microV/Pa, which is 5 times that without the groove structure. The diaphragm having grooves showed a corrugate-like structure that was formed by residual stress. The high sensitivity of the membrane with the grooved diaphragm is considered to relate to the corrugate-like structure.     

Preparation of (001)-oriented Pb(Zr,Ti)O/sub 3/ thin films and their piezoelectric applications

Preparation of (001)-oriented Pb(Zr,Ti)O₃ (PZT) thin films and their applications to a sensor and actuators were investigated. These thin films, which have a composition close to the morphotropic phase boundary, were epitaxially grown on (100)MgO single-crystal substrates by RF magnetron sputtering. These (001)-oriented PZT thin films could be obtained on various kinds of substrates, such as glass and Si, by introducing (100)-oriented MgO buffer layers. In addition, the (001)-oriented PZT thin films could be obtained on Si substrates without buffer layers by optimizing the sputtering conditions. All of these thin films showed excellent piezoelectric properties without the need for poling treatment. The PZT thin films on the MgO substrates had a high piezoelectric coefficient, d₃₁, of -100 pm/V, and an extremely low relative dielectric constant, epsiv_r, of 240. The PZT thin films on Si substrate had a very high d₃₁ of -150 pm/V and an epsiv_r = 700. These PZT thin films were applied to an angular rate sensor with a tuning fork in a car navigation system, to a dual-stage actuator for positioning the magnetic head of a high-density hard disk drive, and to an actuator for an inkjet printer head for industrial on-demand printers.     

Optical Properties of Pb(Zr,Ti)O/sub 3/Films Prepared by Aerosol Deposition

The optical properties and related band structure of ferroelectric lead zirconate titanate [PZT, Pb(Zr_0.6Ti_0.4)O₃] films prepared on glass substrates at room temperature by aerosol deposition were investigated. The reflectance and transmittance of the PZT films were measured in the wavelength range from UV to near-infrared. The measured optical spectra were analyzed using dielectric function models that describe optical transitions in the band gap region. Optical absorption of the as-deposited PZT films was found to be larger than that of the annealed PZT films in the near-infrared wavelength range. The analyzed results indicated that post-deposition annealing increased the band gap energy of the PZT films, corresponding to a decrease in optical absorption.     

Characterization of sol-gel Pb(Zr0.53Ti0.47O3) in thin film bulk acoustic resonators

The behavior of {f111g}-textured Pb(Zr(0.53Ti0.47O3) (PZT) deposited by the sol-gel technique in thin film bulk acoustic resonators (TFBAR's) was investigated at a resonance frequency of about 1 GHz. The resonators were fabricated on Si wafers using deep silicon etching to create a membrane structure and using platinum as top and bottom electrodes. The best response of the resonators was observed at a bias voltage of -15 kV/cm with values of about 10% for the coupling constant and about 50 for the quality factor. This voltage corresponds to optimal values of piezoelectric constant d33 and dielectric constant measured as a function of the electric field. The influence of a bias voltage on the resonance frequency, antiresonance frequency, and coupling constant were observed. Both the resonance and antiresonance frequency show a hysteretic change with applied bias. This effect can be used to shift the whole band of a filter by applying a voltage. The TFBAR structure also allowed us to extract values for materials parameters of the PZT film. Dielectric, piezoelectric, and elastic properties of the f111g-textured PZT film are reported and compared to direct measurements and to literature values.     

Characterization of Pb(Zr,Ti)O3 thin films obtained by MOD

Pb(Zr, Ti)O₃ thin films were deposited by dip-coating on polycrystalline alumina substrates by using an MOD method. The thickness and homogeneity of the films were measured as a function of dip rates and solution concentration. Heating and cooling schedules determined the main structure of the crystallized films. Rheology measurements and Fourier transform-infrared spectra were carried out to obtain a better knowledge of the solution features. A microstructural development study and some ferroelectric measurements were also carried out.     

Phase evolution of electron-beam evaporated Pb(Zr,Ti)O3 thin films

Solid phase reactions among electron-beam deposited PbO, ZrO₂ and TiO₂ in the thin film state as distinct from those occurring in the bulk state are described under varied annealing conditions leading to growth of perovskite PZT phase. Loss of PbO by direct high temperature (700 °C) anneal led to the growth of cubic A₂B₂O_7−x pyrochlore as well as an AB₃O₇ phase of monoclinic structure. A lower temperature initial anneal at 600 °C in O₂ ambient minimises PbO loss through phase transformation to tetragonal Pb₃O₄ and better crystallised oxide phases partially react to form pyrochlore as well as perovskite PZT. This partial reaction is kinetically driven as it goes to completion in ∼4 h resulting in transformation of pyrochlore to perovskite phase. At high temperature (800 °C) A₂B₂O_7−x phase converts to PZT perovskite and the AB₃O₇ dissociate to yield TiO₂ secondary phase inclusion in the PZT film.     

Preparation of spherical Pb(Zr,Ti)O3 powders by ultrasonic spray pyrolysis

Spherical Pb(Zr,Ti)O₃ powders were prepared from the aqueous acetate-base solution by ultrasonic spray pyrolysis. The raw materials were Pb(C₂H₃O₂)-3H₂O, ZrO(C₂H₃O₂)₂ and a mixture of Ti(C₃H₇O)₄ and C₅H₇O₂. A single-phase PZT was formed at 900 C in air and at 700 C in O₂ atmosphere. The PbTiO₃ phase, as an intermediate product, was observed in the formation of PZT and no PbZrO₃ phase was detected under our experimental conditions. The intensity of the PbTiO₃ peak decreased with increasing reaction temperature in air, while the reverse effect of reaction temperature was observed in O₂. Spherical and irregular-shaped particles coexisted in the powder containing the minor PbTiO₃ phase, while the particles of a single-phase PZT have spherical morphology with little evidence of irregular-shaped particle formation.     

LaNiO3缓冲层对Pb(Zr,Ti)O3铁电薄膜的影响

采用化学溶液法在Pt／Ti／SiO2／Si衬底上制备了PbZr0．4Ti0.6O3／LaNiO3(PZT／LNO)多层薄膜。X射线衍射测量表明LNO缓冲层的引入使PZT薄膜(111)择优取向度减小,(100)取向增加。原子力显微镜测量表明引入LNO缓冲层使得PZT薄膜表面更加平整、致密。在LNO缓冲层上制备的PZT薄膜具有优良的铁电特性和介电特性：LNO缓冲层厚度为40nm时,500kV／cm的外加电．场下。剩余极化(Pr)为37．6μC／cm^2,矫顽电场(Ec)为65kV／cm;100kHz时,介电常数达到822,并且发现LNO缓冲层的厚度为40nm,PZT的铁电、介电特性改进最为显著。     

Preparation of (001)-oriented Pb(Zr,Ti)O3 thin films and their piezoelectric applications

Preparation of (001)-oriented Pb(Zr,Ti)O(3) (PZT) thin films and their applications to a sensor and actuators were investigated. These thin films, which have a composition close to the morphotropic phase boundary, were epitaxially grown on (100)MgO single-crystal substrates by RF magnetron sputtering. These (001)-oriented PZT thin films could be obtained on various kinds of substrates, such as glass and Si, by introducing (100)-oriented MgO buffer layers. In addition, the (001) oriented PZT thin films could be obtained on Si substrates without buffer layers by optimizing the sputtering conditions. All of these thin films showed excellent piezoelectric properties without the need for poling treatment. The PZT thin films on the MgO substrates had a high piezoelectric coefficient, d(31), of -100 pm/V, and an extremely low relative dielectric constant, epsilon(r), of 240. The PZT thin films on Si substrate had a very high d(31) of -150 pm/V and an epsilon(r) = 700. These PZT thin films were applied to an angular rate sensor with a tuning fork in a car navigation system, to a dual-stage actuator for positioning the magnetic head of a high-density hard disk drive, and to an actuator for an inkjet printer head for industrial on-demand printers.     

Asymmetric switching behavior of Ni/Pb1.1(Zr0.3Ti0.7)O3/Pt thin films

An asymmetric behavior of P–E response was observed in Ni/Pb_1.1(Zr_0.3Ti_0.7)O₃/Pt multilayer thin films where Ni was used as top electrode. This interesting phenomenon was investigated by comparative analysis of the hysteresis loops and dynamic pyroelectric responses. The PZT thin films were prepared under the same conditions but different Ni and Pt top electrodes were used in the hysteresis loop measurement, and the Pt was used as the common bottom electrode. It is believed that this asymmetric behavior in hysteresis loop is originated from the strong domain pinning near the top Ni electrode. Dynamic pyroelectric response to 633 nm radiation of the Ni/Pb_1.1(Zr_0.3Ti_0.7)O₃/Pt thin films with polarization up and down was carried out. Higher dynamic pyroelectric response was observed in the positively poled film, in which the direction of the polarization was from the top to bottom electrode. It provides further evidence that the domain pinning near the top electrode dominates the asymmetric switching behavior.     

Pb(Zr0.5, Ti0.5)O3 nanofibres by electrospinning

Lead zirconate titanate Pb(Zr_0.5, Ti_0.5)O₃ nanofibres with diameters ranging from 200–300 nm have been synthesized by calcination of the electrospun lead zirconate titanate/polyvinyl acetate composite fibres. The morphology and crystalline phase features of these lead zirconate titanate (PZT) nanofibres have been studied by various physico-chemical methods such as SEM, AFM, XRD and FT–IR. The formation of perovskite PZT phase was observed at temperatures as low as 550 °C.     

Measurement and modeling of dielectric properties of Pb(Zr,Ti)O3 ferroelectric thin films

In this study, the real and imaginary parts of the complex permittivity of lead zirconate titanate ferroelectric thin films are studied in the frequency range of 100 Hz to 100 MHz. The permittivity is well fitted by the Cole-Cole model. The variation of the relaxation time with the temperature is described by the Arrhenius law and an activation energy of 0.38 eV is found. Because of its nonlinear character, the dielectric response of the ferroelectric sample depends on the amplitude of the applied ac electric field. The permittivity is composed of three different contributions: the first is due to intrinsic lattice, the second is due to domain wall vibrations, and the third is due to domain wall jumps between pinning centers. This last contribution depends on the electric field, so it is important to control the field amplitude to obtain the desired values of permittivity and tunability.     

From lighting-ferroelectric to photovoltaic properties of Pb(Zr,Ti)O_3(PZT) thin film with symmetric/asymmetric interface energy barrier

正Recently,ferroelectric(FE)materials have been intensively investigated for photovoltaic(PV)applications due to the existence of internal polarization field which acts as a drive force to separate electron-hole pair.Lead zirconate titanate,Pb(Zr,Ti)O3(PZT),as one of the most commonly used ferroelectric materials,has been extensively studied because     

A study of vacancy-related defects in (Pb,La)(Zr,Ti)O(3) thin films using positron annihilation

The formation of vacancy-type defects in La-doped lead zirconate titanate (PLZT) thin films (Zr/Ti=20/80) was studied as a function of lanthanum doping and after cooling in an oxygen-reduced ambient. The changes in the Doppler-broadening S parameter are consistent with the progressive introduction of Pb-vacancies upon La-doping. Cooling of PLZT thin films with 0 and 10% La doping in 10(-5) Torr oxygen partial pressure after growth exhibits an increase in the density of vacancy-type defects compared to films cooled in 760 Torr. It is proposed that the defects formed are likely cation-oxygen vacancy complexes.     

Compositionally graded Pb(Zr,Ti)O3 thin films with different crystallographic orientations

Compositionally graded ferroelectric PbZr_xTi_1−xO₃ (PZT) films were deposited using a sputtering method and crystallized in situ at 500 °C. The films showed purely (100) or (111) crystallographic orientation when grown on Si/SiO₂/TiO₂/Pt substrates, while they exhibited c-axis epitaxial microstructure when prepared on MgO/Pt substrates. Their crystallographic orientation was controlled owing to a thin TiO_x layer sputtered on substrates prior to PZT deposition. Analysis performed by Auger depth profile clearly confirmed the variation of composition in the films. Coercive fields from 80 kV/cm to 200 kV/cm and remnant polarization as large as 45 μC/cm² were obtained. However, no typical offset was observed on hysteresis loops, unlike previous works related to graded PZT films.     

Conduction at domain walls in insulating Pb(Zr0.2 Ti0.8)O3 thin films

Domain wall conduction in insulating Pb(Zr(0.2) Ti(0.8))O(3) thin films is demonstrated. The observed electrical conduction currents can be clearly differentiated from displacement currents associated with ferroelectric polarization switching. The domain wall conduction, nonlinear and highly asymmetric due to the specific local probe measurement geometry, shows thermal activation at high temperatures, and high stability over time.     

Influence of annealing on the ferroelectric properties of Pt/Pb(Zr,Ti)O3/Pt thin film capacitors

The deformation in the hysteresis loop of Pt/Pb(Zr,Ti)O₃/Pt capacitors has been investigated by varying the annealing temperature after patterning the top sputter-deposited electrode using reactive ion etching (RIE) with Ar gas. It was observed that as-patterned capacitors were positively poled by the dc plasma potential during RIE of Pt. Voltage shift and slant in the hysteresis loop are found to be due to space charges trapped at domain boundaries during both sputtering and RIE rather than a nonferroelectric second phase. As Zr:Ti ratio decreases, internal bias field increases, and annealing temperature, at which maximum in polarization occurs, also increases due to lower permittivity and higher Curie temperature.