Mikael A. Khan

Large remanent polarization in ferroelectric BiFeO3–PbTiO3 thin films on Pt∕Si substrates

Bismuth ferrite–lead titanate thin films in the region of the morphotropic phase boundary, with compositions of (1−x)BiFeO3–xPbTiO3 (0.3<x<0.5), were prepared by pulsed laser deposition on Pt∕Si substrates. X-ray diffraction confirmed the formation of pure perovskite phase at a substrate temperature of 565°C under 75mTorr of oxygen. The films exhibit remanent polarizations with 2Pr up to 100μCcm−2 for a field amplitude of 820kVcm−1 and switchable polarization up to 80μCcm−2.

Leakage mechanisms in bismuth ferrite-lead titanate thin films on Pt∕Si substrates

(1−x)BiFeO3–xPbTiO3 (0.5<x<0.3) thin films have been reported to exhibit high remanent polarizations but device integration is hindered by the presence of leakage currents. An insight into the nature of leakage mechanisms in the films is presented. Films with x=0.4 and 0.5 exhibit lower leakage currents as compared to x=0.3 films. At applied fields above 190kVcm−1, in the region of the coercive field of these films, x=0.4 and 0.5 exhibit a Poole–Frenkel mechanism while films with x=0.3 exhibit a combination of space charge limited current and the Schottky effect.

Synthesis of the ferroelectric solid solution, Pb(Zr1−xTix)O3 on a single substrate using a modified molecular beam epitaxy technique

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1−xTix)O3 (PZT) on single Pt∕Ti∕SiO2∕Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral to tetragonal symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary at Zr:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis. Results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery.

LASER TRANSFER PROCESSING AND THE INTEGRATION OF FERROELECTRIC FILMS

ABSTRACT Thin films of barium strontium titanate (BST), lanthanum modified bismuth titanate (LBT) and lead zirconate titanate (PZT) were fabricated by sol-gel methods onto sapphire substrates. They were transferred to a second substrate by using UV eximer laser radiation to delaminate the films from the fabrication substrate. Scanning electron microscopy revealed melting at the interfacial region of the LBT and PZT films, thus providing the delamination mechanism, but melting was not observed in the BST films. Only the PZT film, after laser transfer, retained its ferroelectric properties, with remnant polarisation of ∼30 μC/cm2, and a high coercive field of 150 kV/cm.

Ferroelectric BiFeO/sub 3/-PbTiO/sub 3/ thin films on Pt/Si substrates

In this work we report on the preparation and properties of bismuth ferrite lead titanate films [(1-x)BiFeO_3-xPbTiO₃] with tetragonal compositions (x = 0.8 and 0.7) and compare them with compositions close to the morphotropic phase boundary (MPB; x = 0.4 and 0.3). The films were prepared by pulsed laser deposition on Pt/Si substrates, and exhibited a dense columnar grain growth. X-ray diffraction analysis revealed that the films have a perovskite structure with a preferred (111) texture. The dielectric properties, polarization-field hysteresis, and leakage current behavior of the films is also reported. For MPB compositions, the films exhibited remanent polarizations with 2P_r up to 100 muC cm^-2 and E_c ~ 185 kV cm^-1 under a maximum applied field of 500 kV cm^-1, while the tetragonal compositions exhibited 2P_r values in the range of 45-52 muC cm^-2 with a coercive field E_c ~ 118 kV cm^-1.

Ferroelectric BiFeO3-PbTiO3 thin films on Pt/Si substrates.

In this work we report on the preparation and properties of bismuth ferrite lead titanate films [(1-x)BiFeO_3-xPbTiO₃] with tetragonal compositions (x = 0.8 and 0.7) and compare them with compositions close to the morphotropic phase boundary (MPB; x = 0.4 and 0.3). The films were prepared by pulsed laser deposition on Pt/Si substrates, and exhibited a dense columnar grain growth. X-ray diffraction analysis revealed that the films have a perovskite structure with a preferred (111) texture. The dielectric properties, polarization-field hysteresis, and leakage current behavior of the films is also reported. For MPB compositions, the films exhibited remanent polarizations with 2P_r up to 100 muC cm^-2 and E_c ~ 185 kV cm^-1 under a maximum applied field of 500 kV cm^-1, while the tetragonal compositions exhibited 2P_r values in the range of 45-52 muC cm^-2 with a coercive field E_c ~ 118 kV cm^-1.

Synthesis of the Ferroelectric Solid Solution, Pb(Zr 1−x Ti x )O 3 on a Single Substrate Using a Modified Molecular Beam Epitaxy Technique

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1-xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Z:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics.

Impedance Spectroscopy of Mn-Doped BiFeO 3 -PbTiO 3 Ceramics

BiFeO3-PbTiO3-based materials have the potential to be used as high temperature piezoelectrics and are candidate multiferroic materials. Two drawbacks are the significant conductivity and the apparently low mobility of ferroelastic domain walls. Both may be influenced by aliovalent doping. Here we have investigated a number of B-site dopants, including manganese, plus B-site non-stoichiometry (i.e. Fe/Ti ratio) to determine their role in the conduction mechanism. Dense ceramics of 0.7BiFeO3-PbTiO3 were prepared by conventional preparation techniques incorporating the above dopants or stoichiometric adjustments. DC resistivity measurements were carried out as a function of field. AC impedance spectroscopy from 1 mHz to 20 MHz was also employed to determine the extent of heterogeneity in the transport and displacement properties. The results are interpreted in terms of the conventional models of oxygen vacancy and Fe2+:Fe3+ hopping conduction.

Synthesis of the Ferroelectric Solid Solution, Pb(Zr 1-x Ti x )O 3 on a Single Substrate Using a Modified Molecular Beam Epitaxy (MBE) Technique

High-throughput synthesis of the ferroelectric solid solution Pb(Zr1-xTix)O3 (PZT) on single Pt/Ti/SiO2/Si substrates was demonstrated using a modified molecular beam epitaxy (MBE) system. The PZT films exhibited a phase transition from rhombohehdral (R) to tetragonal (T) symmetry as a function of Zr:Ti ratio, across the substrate diagonal. This was consistent with the presence of a morphotropic phase boundary (MPB) at a Z:Ti ratio of 0.64:0.36, different from the value of 0.53:0.47 observed for bulk ceramics. All points on the films exhibited ferroelectric hysteresis loops. The results demonstrate the feasibility of high-throughput MBE for deposition of complex ferroelectric oxides, and pave the way for further materials discovery, in particular Pb-free piezoceramics.

Ferroelectric BiFeO 3 -PbTiO 3 Thin Films on Pt/Si Substrates

In this work we report on the preparation and properties of bismuth ferrite lead titanate films [(1-x)BiFeO_3-xPbTiO₃] with tetragonal compositions (x = 0.8 and 0.7) and compare them with compositions close to the morphotropic phase boundary (MPB; x = 0.4 and 0.3). The films were prepared by pulsed laser deposition on Pt/Si substrates, and exhibited a dense columnar grain growth. X-ray diffraction analysis revealed that the films have a perovskite structure with a preferred (111) texture. The dielectric properties, polarization-field hysteresis, and leakage current behavior of the films is also reported. For MPB compositions, the films exhibited remanent polarizations with 2P_r up to 100 muC cm^-2 and E_c ~ 185 kV cm^-1 under a maximum applied field of 500 kV cm^-1, while the tetragonal compositions exhibited 2P_r values in the range of 45-52 muC cm^-2 with a coercive field E_c ~ 118 kV cm^-1.