Browsing by Author "Corkovic, Silvana"

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    Compaction of lead zirconate titanate sol-gel coatings.
    (Elsevier Science B.V., Amsterdam., 2006-06-01T00:00:00Z) Khan, Mikael A.; Kurchania, Rajnish; Corkovic, Silvana; Zhang, Qi; Milne, Steven J.
    A novel method for the densification of sol-gel films is presented. After elimination of organic decomposition products by heat-treatment at 350 °C and 450 °C, the films are isopressed prior to crystallisation at 550 °C. Consequently, porous lead zirconate titanate films, ~0.7 m in thickness with pore sizes of ~0.1 m could be transformed into dense 0.2 m fil
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    ItemOpen Access
    Densification of lead zirconate titanate sol-gel coatings
    (Elsevier Science B.V., Amsterdam., 2006-06-01T00:00:00Z) Khan, Mikael A.; Kurchania, Rajnish; Corkovic, Silvana; Zhang, Qi; Milne, Steven J.
    A novel method for the densification of sol-gel films is presented. After elimination of organic decomposition products by heat-treatment at 350 °C and 450 °C, the films are isopressed prior to crystallisation at 550 °C. Consequently, porous lead zirconate titanate films, ~0.7 um in thickness with pore sizes of ~0.1 um could be transformed into dense 0.2 um fil
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    Development of residual stress in sol-gel derived Pb(Zr,Ti)O3 films: An experimental study
    (American Institute of Physics, 2008-04-30T00:00:00Z) Corkovic, Silvana; Zhang, Qi
    Residual stresses develop in the sol-gel-derived ferroelectric thin films during the transformation of the metalorganic gel to the metal oxide upon thermal treatment and due to the thermal and elastic mismatch between the Pb(Zrx,Ti1-x)O3 (PZT) film and the substrate materials during cooling. In this study, residual stresses were determined using the wafer curvature method after the deposition of multilayer PZT film on platinized (100) silicon wafers. A multilayer model for stress analysis was used to calculate the residual stress in PZT films of three different compositions, x=0.4, x=0.52 and x=0.6. Orientation dependent residual stresses were found in compositions containing the tetragonal phase, with x=0.4 and x=0.52. Depending on the fraction of (100) orientated domains low compressive or low tensile stress was found in Pb(Zr0.4Ti0.6)O3 (PZT 40/60). Higher residual stress was found in PZT films consisting of only rhombohedral crystallographic structure (PZT 60/40) while the residual stress in PZT films with morphotropic boundary composition (PZT 52/48) was significantly dependent on the film orientation and the phase composition and could range from 17 MPa to 90 MPa. The effect of the film orientation on residual stress was found to be a function of the anisotropic thermal expansion coefficient of PZT. The contribution of the thermal and elastic properties of materials to the total wafer curvature was investigated and discussed. Finally, the residual stress results calculated with the four layers model were compared to the results calculated using the Stoney equation.
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    Enhanced pyroelectric coefficient of antiferroelectric-ferroelectric bilayer thin films
    (American Institute of Physics, 2009-12-31T00:00:00Z) Corkovic, Silvana; Zhang, Qi
    In this study, the pyroelectric coefficient and the figure of merit (FOM) of the ferroelectric PbZr0.3Ti0.7O3 (PZT 30/70) thin films were found to be greatly enhanced by introducing a thin antiferroelectric PbZr0.95Ti0.05O3 (PZT 95/05) layer underneath the ferroelectric film and thus creating a bi-layer structure on platinised silicon substrates. The film properties were investigated as a function of the ferroelectric layer thickness when the thickness of antiferroelectric layer remained unchanged. The highest pyroelectric coefficient of 1 mm thick PZT 30/70 film was 3.18 x10-4 Cm-2K-1. However, the highest pyroelectric coefficient for 1 mm thick bi-layer film was 3.5 x10-4 Cm-2K-1 or 2.5 x10-4 Cm-2K-1 for only 280 nm thick bi-layer film. The enhancement of pyroelectric coefficient suggests switching of antiferroelectric (AF) into ferroelectric (FE) phase during poling and following stabilization of FE phase at room temperature. The reduction of dielectric constant in bi-layer films after poling, compared to pure PZT 30/70, showed a FOM of 2.94 x10-5 Pa-0.5 which is the double of the FOM for pure PZT 30/70 films of similar thickness (1.45 x10-5 Pa-0.5).
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    Piezoelectric thick films for microelectromechanical systems application
    (Cranfield University, 2007-03) Corkovic, Silvana; Zhang, Qi
    This thesis concerns the processing and characterization of thick PZT sol-gel films for potential applications in MEMS devices. The deposition method was spin-coating. The aim was to reduce the number of coatings in the film processing by increasing the thickness of a single coating, with the restriction that the processed films must be crackfree and dense. Only by retaining the thick film dense, pore-free and crack-free one can obtain the piezoelectric properties in thick films that make the PZT thin sol-gel films attractive for the MEMS applications. Three PZT compositions, PZT 40/60, PZT 60/40 and PZT 52/48 were investigated. Each one of these PZT compositions has different crystallographic structure and thus differences in the piezoelectric properties were expected. The processing of thickness-increased sol-gel films was investigated. A combination of analysis techniques was employed. The stress development was monitored via ex-situ wafer deflection measurement after various fabrication steps. The ongoing processes in the sol-gel film were identified and correlated to certain temperature ranges and to the stress that is induced with each process in the film. It was found that crack-free films could be fabricated if a stress-controlled heating profile was applied. The PZT films were deposited on platinised silicon substrate and it was found that stress-related recrystallization was taking place in the platinum electrode which affected the total stress. After the platinum recrystallization the stress state in the bottom electrode and in the substrate was stable. Films up to 5 μm thick were obtained by repeated deposition of 200 nm thick single layers. The maximum thickness of a single coating was increased to 500 nm and a 2.5 μm film was fabricated by only 5 repeated coatings. The crystallographic orientation of all three employed PZT compositions was studied systematically on Pt/Si substrate at different thicknesses. Also, individual PZT films were deposited onto platinised sapphire substrates, or on LNO/Si substrate. It was found that the orientation of the films changes gradually with each coating. The residual stresses in all three PZT compositions were studied. A stress model for composite structures was applied for the first time in PZT films stress analysis. The results have shown that the residual stress at the room temperature is due to thermal expansion mismatch between the individual layers. Furthermore, a large orientation dependent stress variation was found in PZT 52/48 films that could be only explained if anisotropic thermal expansion in PZT were considered. The lattice parameters of all PZT compositions were determined and were in good agreement with the residual stress results. Thus, using the stress model it was possible to understand the origin of stress in PZT films. Finally, the electrical properties of the PZT films were determined. It was found that the piezoelectric, dielectric and ferroelectric properties of PZT films vary with PZT composition, film thickness and depend on the substrate type. Based on the finding it was proposed that there must be an interfacial layer that is responsible for domain wall pinning and thus reduced PZT properties in films below 5 μm thickness. In thick PZT 40/60 films enhanced piezoelectric properties were found making these PZT compositions very promising candidates for MEMS application.