Ferroelectric nanoparticles, wires and tubes: synthesis, characterisation and applications

Nanostructured materials are central to the evolution of future electronics and information technologies. Ferroelectrics have already been established as a dominant branch in the electronics sector because of their diverse application range such as ferroelectric memories, ferroelectric tunnel junctions, etc. The on-going dimensional downscaling of materials to allow packing of increased numbers of components onto integrated circuits provides the momentum for the evolution of nanostructured ferroelectric materials and devices. Nanoscaling of ferroelectric materials can result in a modification of their functionality, such as phase transition temperature or Curie temperature (TC), domain dynamics, dielectric constant, coercive field, spontaneous polarisation and piezoelectric response. Furthermore, nanoscaling can be used to form high density arrays of monodomain ferroelectric nanostructures, which is desirable for the miniaturisation of memory devices. This review article highlights some research breakthroughs in the fabrication, characterisation and applications of nanoscale ferroelectric materials over the last decade, with priority given to novel synthetic strategies

Pyroelectric effect enhancement in laminate composites under short circuit condition

The pyroelectric coefficients of laminate composites under short circuit condition have been investigated by analytical modeling and numerical simulations. Indicators for various pyroelectric/non-pyroelectric material pairs that can be utilized to determine their pyroelectric coefficient enhancement credentials have been identified. Six pyroelectric materials were paired with six non-pyroelectric/elastic materials and their pyroelectric coefficient enhancement potential and figure of merit for efficiency were investigated. The best performing partnership out of the 36 pairs was lead zirconate titanate (PZT5H)-chlorinated polyvinyl chloride thermoplastic (CPVC) for thickness ratios (R) below 0.09 and PZT5H-zinc for R larger than 0.09 with both demonstrating total pyroelectric coefficient of approximately -20x10(-4) C m(-2) K(-1) at R=0.09, which corresponds to approximately 300% increase in the coefficient. PZT5H-CPVC also showed maximum of 800% rise in the pyroelectric coefficient while figure of merit for efficiency indicated up to twentyfold increase in its electrical response output per given thermal stimuli when compared to that of PZT5H by itself

Novel piezoelectric thick film actuators

Planar-spiral piezoelectric-unimorph-actuators, that deflect out-of-their-plane, were modelled, designed and fabricated. A range of other planar piezoelectric-device designs has also been made. These include spokes, multi-arms, plates and swastikas. All these devices consisted of a mechanical support in the plane with a piezoelectric layer deposited on top. Impedance spectra demonstrated that a fabricated device was piezoelectrically active. Finite-element (FE) models of straight and spiral piezoelectric- unimorph-actuators were constructed. The mechanical stiffness of the spiral-beam was increased with the curvature of the beam; consequently, the inner coils exhibited virtually no deflection and appeared to be redundant. The advantage of the spiral-actuators is that they allow large actuator lengths to be contained compactly without the loss of mechanical stiffness. Fabrication of the above devices necessitated the development of new fabrication technologies. The active-piezoelectric and mechanical-support were a lead zirconate titanate (Pb(Tii_XZrx)O3 - PZT) thick-film and a-platinised-silicon-wafer respectively. Vias were opened in the PZT with wet etching, and this was completed without damaging the back electrode. Powder blasting allowed any 2-dimensional-shape to be cut into the device wafer. Devices were released from the Si support with deep-reactive-ion-etching (DRIE). The PZT thick films were fired with a Cu20-PbO eutectic additive. Pb and Cu were considered to dope on A and B lattice sites (of PZT) respectively, when the PZT was sintered at high oxygen-partial-pressure (p02). The electrical conductivity of PZT thick films was increased when they were sintered at low P02, and this was moderated by the presence of Cu' as an acceptor ion. A lead-platinum intermetallic and lead silicate glass phase simultaneously formed under sintering conditions of low pot, and this simultaneous formation, was accounted for by a six-stage mechanism. Step 1, residual C in the thick film reduces PbO to Pb followed by step 2 where Pb diffuses into the Pt back electrode. In step 3, Pt3Pb formation occurs in the intermetallic layer followed by step 4 in which PtPb forms. Step 5 occurs with saturation of the intermetallic layer as Pb continues to diffuse from the thick film. There is additional diffusion of Pb into the underlying Si substrate. Finally step 6 occurs at some later point, when P02 has risen, Pb is oxidised to PbO, and Si is oxidised to Si02. PbO and Si02 can flux to form PbSiO3 The glass was found to undermine film/substrate adhesion.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

The structural and piezoresponse properties of c-axis-oriented Aurivillius phase Bi5Ti3FeO15 thin films deposited by atomic vapor deposition

The deposition by atomic vapor deposition of highly c-axis-oriented Aurivillius phase Bi 5Ti 3FeO 15 (BTFO) thin films on (100) Si substrates is reported. Partially crystallized BTFO films with c-axis perpendicular to the substrate surface were first deposited at 610°C (8 excess Bi), and subsequently annealed at 820°C to get stoichiometric composition. After annealing, the films were highly c-axis-oriented, showing only (00l) peaks in x-ray diffraction (XRD), up to (0024). Transmission electron microscopy (TEM) confirms the BTFO film has a clear layered structure, and the bismuth oxide layer interleaves the four-block pseudoperovskite layer, indicating the n 4 Aurivillius phase structure. Piezoresponse force microscopy measurements indicate strong in-plane piezoelectric response, consistent with the c-axis layered structure, shown by XRD and TEM

Surface roughness assisted growth of vertically oriented ferroelectric SbSI nanorods

We report the catalyst-free synthesis of arrays of c-axis oriented antimony sulfoiodide nanorods on anodic aluminum oxide (AAO) substrates by vapor phase deposition. The surface roughness of the AAO substrates played a decisive role in the orientation control of the SbSI nanorods produced. The as-grown SbSI nanorods were single-crystalline and ⟨001⟩ oriented, as revealed from the X-ray diffraction and transmission electron microscopy analysis. Switching spectroscopy-piezoresponse force microscopy experiments demonstrated, for the first time, the presence of switchable ferroelectricity and piezoelectricity in individual SbSI nanorods. Ferroelectric switching in the SbSI nanorods was found to occur via a 180° domain reversal, because of the preferred orientation of the nanorods along their polar c-axis

Atomic vapor deposition of bismuth titanate thin films

c-axis oriented ferroelectric bismuth titanate (Bi4Ti 3O12) thin films were grown on (001) strontium titanate (SrTiO3) substrates by an atomic vapor deposition technique. The ferroelectric properties of the thin films are greatly affected by the presence of various kinds of defects. Detailed x-ray diffraction data and transmission electron microscopy analysis demonstrated the presence of out-of-phase boundaries (OPBs). It is found that the OPB density changes appreciably with the amount of titanium injected during growth of the thin films. Piezo-responses of the thin films were measured by piezo-force microscopy. It is found that the in-plane piezoresponse is stronger than the out-of-plane response, due to the strong c-axis orientation of the films

Nanoscale ferroelectric and piezoelectric properties of Sb2S3 nanowire arrays

We report the first observation of piezoelectricity and ferroelectricity in individual Sb2S3 nanowires embedded in anodic alumina templates. Switching spectroscopy-piezoresponse force microscopy (SS-PFM) measurements demonstrate that individual, c-axis-oriented Sb2S3 nanowires exhibit ferroelectric as well as piezoelectric switching behavior. Sb2S3 nanowires with nominal diameters of 200 and 100 nm showed d33(eff) values around 2 pm V–1, while the piezo coefficient obtained for 50 nm diameter nanowires was relatively low at around 0.8 pm V–1. A spontaneous polarization (Ps) of approximately 1.8 μC cm–2 was observed in the 200 and 100 nm Sb2S3 nanowires, which is a 100% enhancement when compared to bulk Sb2S3 and is probably due to the defect-free, single-crystalline nature of the nanowires synthesized. The 180° ferroelectric monodomains observed in Sb2S3 nanowires were due to uniform polarization alignment along the polar c-axis

Piezoresponse force microscopy investigations of Aurivillius phase thin films

The sol-gel synthesis and characterization of n≥3n≥3 Aurivillius phase thin filmsdeposited on Pt/Ti/SiO2–SiPt/Ti/SiO2–Si substrates is described. The number of perovskite layers, nn, was increased by inserting BiFeO3BiFeO3 into three layered Aurivillius phase Bi4Ti3O12Bi4Ti3O12 to form compounds such as Bi5FeTi3O15Bi5FeTi3O15 (n=4)(n=4). 30% of the Fe3+Fe3+ ions in Bi5FeTi3O15Bi5FeTi3O15 were substituted with Mn3+Mn3+ ions to form the structureBi5Ti3Fe0.7Mn0.3O15Bi5Ti3Fe0.7Mn0.3O15. The electromechanical responses of the materials were investigated using piezoresponse force microscopy and the results are discussed in relation to the crystallinity of the films as measured by x-ray diffraction

Room temperature electromechanical and magnetic investigations of ferroelectric Aurivillius phase Bi5Ti3(FexMn1−x)O15 (x = 1 and 0.7) chemical solution deposited thin films

Aurivillius phase thin films of Bi5Ti3(FexMn1−x)O15 with x = 1 (Bi5Ti3FeO15) and 0.7 (Bi5Ti3Fe0.7Mn0.3O15) on SiO2-Si(100) and Pt/Ti/SiO2-Si substrates were fabricated by chemical solution deposition. The method was optimized in order to suppress formation of pyrochlore phase Bi2Ti2O7 and improve crystallinity. The structuralproperties of the films were examined by x-ray diffraction, scanning electron microscopy, and atomic force microscopy. Optimum crystallinity and pyrochlore phase suppression was achieved by the addition of 15 to 25 mol. % excess bismuth to the sols. Based on this study, 17.5 mol. % excess bismuth was used in the preparation of Bi2Ti2O7-free films of Bi5Ti3FeO15 on SrTiO3(100) and NdGaO3(001) substrates, confirming the suppression of pyrochlore phase using this excess of bismuth. Thirty percent of the Fe3+ ions in Bi5Ti3FeO15 was substituted with Mn3+ ions to form Bi2Ti2O7-free thin films of Bi5Ti3Fe0.7Mn0.3O15 on Pt/Ti/SiO2-Si, SiO2-Si(100), SrTiO3(100), and NdGaO3(001) substrates. Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15thin films on Pt/Ti/SiO2-Si and SiO2-Si(100) substrates were achieved with a higher degree of a-axis orientation compared with the films on SrTiO3(100) and NdGaO3(001) substrates. Room temperature electromechanical and magnetic properties of the thin films were investigated in order to assess the potential of these materials for piezoelectric,ferroelectric, and multiferroic applications. Vertical piezoresponse force microscopy measurements of the films demonstrate that Bi5Ti3FeO15 and Bi5Ti3Fe0.7Mn0.3O15thin films are piezoelectric at room temperature. Room temperature switching spectroscopy-piezoresponse force microscopy measurements in the presence and absence of an applied bias demonstrate local ferroelectric switching behaviour (180°) in the films. Superconducting quantum interference device magnetometry measurements do not show any room temperature ferromagnetic hysteresis down to an upper detection limit of 2.53 × 10−3 emu; and it is concluded, therefore, that such films are not mutiferroic at room temperature. Piezoresponse force microscopy lithography images of Bi5Ti3Fe0.7Mn0.3O15thin films are presented

Pyroelectric response of lead zirconate titanate thin films on silicon: Effect of thermal stresses

Ferroelectric lead zirconate titanate [Pb(ZrxTi1-xO)(3), (PZT x:1-x)] has received considerable interest for applications related to uncooled infrared devices due to its large pyroelectric figures of merit near room temperature, and the fact that such devices are inherently ac coupled, allowing for simplified image post processing. For ferroelectric films made by industry-standard deposition techniques, stresses develop in the PZT layer upon cooling from the processing/growth temperature due to thermal mismatch between the film and the substrate. In this study, we use a non-linear thermodynamic model to investigate the pyroelectric properties of polycrystalline PZT thin films for five different compositions (PZT 40:60, PZT 30:70, PZT 20:80, PZT 10:90, PZT 0:100) on silicon as a function of processing temperature (25-800 degrees C). It is shown that the in-plane thermal stresses in PZT thin films alter the out-of-plane polarization and the ferroelectric phase transformation temperature, with profound effect on the pyroelectric properties. PZT 30:70 is found to have the largest pyroelectric coefficient (0.042 mu C cm(-2)degrees C-1, comparable to bulk values) at a growth temperature of 550 degrees C; typical to what is currently used for many deposition processes. Our results indicate that it is possible to optimize the pyroelectric response of PZT thin films by adjusting the Ti composition and the processing temperature, thereby, enabling the tailoring of material properties for optimization relative to a specific deposition process. (C) 2013 AIP Publishing LLC