N. Maffei

Bio: N. Maffei is an academic researcher from Queen's University. The author has contributed to research in topics: Ferroelectricity & Thin film. The author has an hindex of 5, co-authored 6 publications receiving 330 citations.

rf planar magnetron sputtering and characterization of ferroelectric Pb(Zr,Ti)O3 films

Abstract: Ferroelectric films of lead zirconate titanate (PZT) have been fabricated by rf planar magnetron sputtering. Films having a resistivity >106 Ω cm and a dielectric constant >800 at 300 K have been achieved using 100% oxygen as a sputtering medium, 10% excess PbO added to the target, and appropriate post‐deposition annealing. The sputtering rate is in the range 0.2–1.0 μm/h and varies with sputtering pressure and substrate temperature. Post‐deposition annealing affects both crystallinity and grain size, but incipient crystallization formed only in as‐grown films deposited at substrate temperatures >400 °C is essential for this process to be effective. A clear ferroelectric transition is observed at 350 °C, while the activation energy for dc conductivity of around 0.8 eV is consistent with bulk properties of PZT. The spontaneous polarization and coercive field measured from ferroelectric hysteresis loops is 20.75 μC/cm2 and 10 kV/cm, respectively. The optical transmittance of the films is determined by a Pb–Pb charge transfer band near 400 nm and this is a sensitive test of film stoichiometry.

Electrical characteristics of excimer laser ablated bismuth titanate films on silicon

Abstract: Bismuthtitanatethin films were deposited by the excimer laserablation technique directly onto bare silicon substrates. Current‐voltage studies suggested the formation of a heterojunction at the Bi4Ti3O12/Si interface. The current characteristics at voltages ≥1 V were ascribed to trap‐limited space‐charge conduction. Hysteretic capacitance‐voltage data indicated that charge injection was dominant, masking any polarization mode necessary for nonvolatile memory operation. Ferroelectric hysteretic studies, however, indicated that the films were ferroelectric with P r ≂10 μC/cm2 and E c ≂150 kV/cm.

Excimer laser‐ablated bismuth titanate thin films

Abstract: Bismuth titanate thin films were deposited by the excimer laser ablation technique. Process parameters such as substrate temperature, laser fluence, and gas pressure were investigated and correlated to the resulting film properties. Results suggest an intrinsic bombardment effect on the growing film. The permittivity and dissipation factor measured at 100 kHz were 150 and 0.01, respectively. The ferroelectric properties exhibited a dependence on film orientation and films with preferred c‐axis orientation yielded fully saturated hysteresis loops with Pr=7 μC/cm2 and Ec=20 kV/cm.

Growth of ferroelectric oxide thin films by excimer laser ablation

Abstract: The pulsed ultraviolet excimer laser ablation technique was employed to deposit a variety of ferroelectric oxide thin film compositions, including lead zirconate titanate, Pb(Zr,Ti)O3 (multiaxial), bismuth titanate, Bi4Ti3O12 (biaxial), and lead germanate, Pb5Ge3O11 (uniaxial), while maintaining the in situ stoichiometry of films close to that of targets. Growth process parameters such as deposition rates and the stoichiometry of the as‐deposited films were examined and correlated with the ablation fluence, pressure, and substrate temperature. A threshold of ablation energy density has been identified for each type of ferroelectric composition. Evidence of intrinsic bombardment by energetic ablated species, during the thin film deposition, indicated an impact on the composition, structure, and the electrical properties as well. Electrical characterization of the ferroelectric films indicated a dielectric permittivity of 800–1000, a remanent polarization (Pr) of 32 μC/cm2, and a coercive field (Ec) of 100 ...

Process‐property correlations of excimer laser ablated bismuth titanate films on silicon

Abstract: Bismuth titanate thin films were deposited by the excimer laser ablation technique directly onto bare silicon substrates, SiO2 and Si3N4 coated silicon. The impact of process parameters such as gas pressure, laser fluence, processing temperature, and the presence of an oxygen plasma were studied with regards to the ferroelectric‐semiconductor interface. The density of interfacial surface state (Nss) at the flatband voltage was found to be on the order of 1012–1014 eV−1 cm−2. Hysteretic capacitance‐voltage data indicated charge injection from the substrate was the dominant mechanism, masking any polarization mode. Films deposited on SiO2 coated silicon did, however, exhibit polarization type switching.

Ferroelectric thin films for micro-sensors and actuators: a review

Abstract: This paper reviews deposition, integration, and device fabrication of ferroelectric PbZrxTi1-xO3 (PZT) films for applications in microelectromechanical systems. As examples, a piezoelectric ultrasonic micromotor and pyroelectric infrared detector array are presented. A summary of the published data on the piezoelectric properties of PZT thin films is given. The figures of merit for various applications are discussed. Some considerations and results on operation, reliability, and depolarization of PZT thin films are presented.

Preparation of Pb(Zr,Ti)O3 thin films by sol gel processing: Electrical, optical, and electro‐optic properties

Abstract: Crack‐free transparent ferroelectric polycrystalline Pb(Zr,Ti)O3 thin films were prepared by spin‐coating solutions of complex alkoxides. The preparation of stock solution, firing, and annealing of films was described. The coating of the intermediate layer of Al2O3 increased the adhesion between Pb(Zr,Ti)O3 thin films and glass substrates. The crystalline phases of films with varying Zr/Ti ratios were investigated. The dielectric constants were about 260. The remanent polarization and coercive field were 6.6 μC/cm2 and 26.7 kV/cm, respectively. The refractive index of the perovskite Pb(Zr,Ti)O3 films was 2.6 at 6328 A, and the absorption edge was at 3400 A. The quadratic and linear electro‐optic effects were measured with respect to the Zr/Ti ratio from 40/60 to 60/40 for films grown on glass substrates. The quadratic and linear electro‐optic coefficients were about 1×10−18 m2 /V2 and 2.4×10−11 m/V at 6328 A, respectively.

New materials for micro-scale sensors and actuators An engineering review

Abstract: This paper provides a detailed overview of developments in transducer materials technology relating to their current and future applications in micro-scale devices. Recent advances in piezoelectric, magnetostrictive and shape-memory alloy systems are discussed and emerging transducer materials such as magnetic nanoparticles, expandable micro-spheres and conductive polymers are introduced. Materials properties, transducer mechanisms and end applications are described and the potential for integration of the materials with ancillary systems components is viewed as an essential consideration. The review concludes with a short discussion of structural polymers that are extending the range of micro-fabrication techniques available to designers and production engineers beyond the limitations of silicon fabrication technology.

PZT thin films for microsensors and actuators: Where do we stand?

Abstract: This paper reviews deposition, integration, and device fabrication of PbZr/sub x/Ti/sub 1-x/O/sub 3/ (PZT) films for applications in micro-electromechanical systems. An ultrasonic micromotor is described as an example. A summary of the published data on piezoelectric properties is given. The figures of merit for various applications are discussed. Some considerations and results on operation, reliability, and depolarization of PZT thin films are presented. The state of the art allows some preliminary conclusions.

Ferroelectric materials for 64 Mb and 256 Mb DRAMs

Abstract: The authors have studied the feasibility of using ferroelectric materials as the capacitor dielectric in the one-transistor memory cells for 64-Mb and 256-Mb DRAMs. They have performed an intensive literature search and analysis. They discuss the crystal structure of the materials reviewed, their hysteresis curve, temperature dependence of the spontaneous polarization, leakage current, dielectric breakdown, reliability, ageing, and fatigue. The authors examine the charge storage capacity in a 1-T DRAM cell and analyze a number of ferroelectric materials for their potential use as the dielectric in 64-Mb and 256-Mb DRAM capacitors, focusing on projected requirements for the electrical parameters and preferred material characteristics. Of the materials examined, those that appear to hold the greatest promise for 64-Mb and 256-Mb DRAMs are the paraelectric phase compositions of (Pb,La)TiO/sub 3/ (PLT) and (Pb,La)(Zr,Ti)O/sub 3/ (PLZT). Pb(Mg,Nb)O/sub 3/ (PMN) is also attractive because it is paraelectric, but it may not be able to achieve the required charge densities when deposited as a thin film. >