Mareike Klee

Electrode influence on the charge transport through SrTiO3 thin films

The influence of the electrodes on the dielectric behavior and especially on the leakage behavior of SrTiO3 thin films was investigated by impedance analysis. Based on measurements on thin films with different electrode materials the work function of these materials was found to determine the leakage currents. The main conduction mechanism is thermionic emission of electrons from the cathode into the SrTiO3 thin film. The current–voltage characteristics are influenced by the Schottky effect.

Processing and electrical properties of Pb (ZrxTi1−x)O3 (x=0.2–0.75) films: Comparison of metallo‐organic decomposition and sol‐gel processes

The deposition of thin Pb(ZrxTi1−x)O3 films by sol‐gel and by metallo‐organic decomposition (MOD) processes has been studied. Powders obtained from different precursor solutions were analyzed with respect to their decomposition and crystallization. Using a spin‐coating technique, Pb(ZrxTi1−x)O3 films with zirconium concentrations ranging from x=0.2 to 0.75 have been deposited on Pt‐electroded Si wafers. The lattice constants of the perovskite films and their dielectric and ferroelectric properties (permittivity, remanent polarization, coercive field strength) have been measured as a function of the zirconium concentration. The results are compared to the data obtained on bulk ceramics. For Pb(ZrxTi1−x)O3 films with a composition located at the morphotropic phase boundary (x≊0.53) the influence of the processing and the lead excess of the starting solutions on the film properties was examined. First measurements on the resistance degradation of thin Pb(Zr0.53Ti47)O3 films deposited by the MOD process are r...

Theory of Conduction and Breakdown in Perovskite Thin Films

The mechanism of the dc electrical conduction and breakdown of perovskite-type titanates was investigated by impedance analysis. Based on an acceptor doped SrTiO3 model material, samples of different microstructures-ceramics, single crystals, and thin films-were employed. This approach allows us to distinguish conduction contributions of the bulk lattice, grain boundaries, and electrode interfaces. Based on defect chemistry studies, a predominant ionic contribution due to mobile oxygen vacancies and an additional p-type conduction were revealed for the bulk. At interfaces, space charge depletion layers of 100-500 nm width are formed in which the local conductivity is reduced by approx. four orders of magnitude compared to the bulk. Thin films show a similar depression of the conductivity. The combination of these facts may be indicative for considering thin films as distributed Schottky barriers. The field enhancement of the conductivity of thin films and of the interface depletion layers is compared and ...

Materials for bulk acoustic wave (BAW) resonators and filters

Abstract Thin film bulk acoustic wave (BAW) resonators and filters are appropriate for mobile communication systems operating at high frequencies between 1–10 GHz. The resonance frequency is mainly determined by the thickness of the piezoelectric layer. Piezoelectric films used for this application are, therefore, several 100 nm in thickness (up to approx. 2 μm) depending on frequency. Piezoelectric thin film materials used for bulk acoustic wave devices include AlN, ZnO thin films for small bandwidth applications and also PZT films for wide bandwidth applications. Within Philips piezoelectric AlN and PbZr x Ti 1− x O 3 (PZT) layers are investigated with respect to their potential for RF micro-electronic applications. High quality AlN films with strong c -axis orientation are achieved by optimum sputter deposition conditions and by applying suited nucleation layers. Electromechanical coupling factors k of 0.25±0.03, which are close to the bulk data, have been found in highly c-axis oriented AlN thin films. The relationship between sputter deposition conditions, AlN films structure on the one hand and electromechanical coupling factor k and relevant electrical parameters on the other hand will be discussed. A one-dimensional physical model is used to describe the bulk acoustic wave resonators electrical impedance data accurately. Thin PZT films are grown via sol–gel processing. These films show high electromechanical coupling factor k of 0.3–0.6 and are therefore attractive for wide bandwidth filter applications.

Piezoelectric materials for BAW resonators and filters

Thin film bulk acoustic wave (BAW) resonators and filters are appropriate for mobile communication systems operating at high frequencies between 0.5 and 10 GHz. c-axis orientated AlN films are used for medium bandwidth applications. Electromechanical coupling factors k/sub t/ of 0.25/spl plusmn/0.03, which are close to the bulk data, have been found in AlN thin films using optimum sputter conditions. The correlation between k/sub t/ and AlN film orientation is discussed. Resonator Q values of approx. 450 are reported at 2.6 GHz and a Q of 250 was realized at 9.2 GHz. A physical model is shown to accurately predict the frequency responses of BAW resonators and band-pass filters. For wide bandwidth applications PbZr/sub x/Ti/sub 1-x/O/sub 3/ (PZT) films are investigated. They exhibit large coupling coefficients.

Influence of platinum-based electrodes on the microstructure of sol-gel and MOD prepared lead zirconate titanate films

Abstract The microstructure and preferred orientation of PZT films deposited by spin-coating techniques are shown to depend on the morphology of the Ti/Pt bottom electrode. Annealing of the as-deposited Ti/Pt electrodes results in the formation of hillocks. These hillocks serve as nucleation sites for perovskite formation and thus determine the microstructure and preferred orientation of the crystallized PZT films. The microstructure features are investigated by X-ray diffraction analyses and scanning and transmission electron microscopies.

Electromechanical properties of thin ferroelectric Pb(Zr0.53Ti0.47)o3-layers

Abstract A method is described for improving the possibility and sensitivity of measurements of electromechanical properties of ferroelectric thin layers. This method is especially useful for investigating electrostrictive properties. A nonlinear model for the description of the electrical conductivity is presented. First results on the temperature, electric field and strain dependence of the high signal electrostrictive coefficient Q11 are given.

Superconductivity above 100 K in Bi(Pb)-Ca-Sr-Cu-O films made by thermal decomposition of metal carboxylates

Abstract Superconducting layers in the Bi(Pb)-Ca-Sr-Cu-O system are prepared by thermal decomposition of metal carboxylates. The films are deposited on MgO single crystal and ceramic substrates using a spin-coating and dip-coating process. The Bi-Ca-Sr-Cu-O films consist mainly of the low- T c phase ( c -axis=3.073 nm), whereas partial substitution of Bi by Pb favours the formation of the high- T c phase ( c -axis=3.707 nm). Films deposited on MgO (100) are strong c -axis preferentially oriented grown. While the Bi-Ca-Sr-Cu-O films show a step in the resistance versus temperature curve ( T cf ⋍80 K) due to the presence of the low- T c and the high- T c phase, the Bi(Pb)-Ca-Sr-Cu-O films have an onset at 110 K and are superconducting at 104 K. The temperature dependence of the critical current indicates that in the Bi-Ca-Sr-Cu-O system weak links of superconductor-isolator-superconductor type are present, while in the Bi(Pb)-Ca-Sr-Cu-O samples the contact is formed by normal-metal barriers. Using magnetic fields up to 5 T, the anisotropy of the resistive transition of the high- T c phase was studied. In Bi(Pb)-Ca-Sr-Cu-O films the anisotropy ratio is about 18, and the corresponding coherence lengths are ξ ab (0)⋍3.6 nm and ξ c (0)⋍0.2 nm. These values are nearly the same as in the low- T c phase.

Structure-property relations in polycrystalline titanate thin films

Abstract Ferroelectric Pb(Zr,Ti)O3 films have been deposited by spin-coating techniques, applying a modified sol-gel process. The growth of the thin films as a function of processing has been investigated by structural analyses using XRD, XRF, SEM and TEM methods. The data are the basis for the discussion of the ferroelectric properties of the layers.

TfI14: Ferroelectric thin films for memory applications: Sol-gel processing and decomposition of organo-metallic compounds

Abstract Pb(ZrxTi1–x)O3 (PZT), Bi4Ti3O12 and BaTiO3 films as well as SrTiO3 films are considered for nonvolatile memory applications and high density dynamic random access memories. These perovskite systems are frequently deposited by a sol-gel or MOD technique. Processing and the properties of the thin films are summarized.