W. Biegel

PLD of Pb(Zr,Ti)O3 films: Phase formation on various substrates

Abstract Pulsed laser deposition (PLD) was used to deposit Pb(Zr 52 Ti 48 )O 3 (PZT-5A) thin films on various substrates (SrTiO 3 , MgO, polycrystalline Yttria-stabilized ZrO 2 (YSZ) and Al 2 O 3 ). Furthermore, epitaxial YBa 2 Cu 3 O 7− x on SrTiO 3 /Al 2 O 3 , which is serving as bottom electrode, was covered with PZT by PLD. The phase formation of two phases of PZT, the stable ABO 3 with perovskite structure and the metastable A 2 B 2 O 6 O phase with pyrochlore structure, was investigated by XRD in dependence of substrate material, deposition temperature and film thickness. The ferroelectric P(E)-hysteresis of the films was measured and discussed with respect to the above mentioned points. A favoring of the perovskite phase formation was found on SrTiO 3 , a mixture of perovskite and pyrochlore on MgO, whereas YSZ substrates lead to the growth of 100% pyrochlore films under comparable deposition conditions. On polycrystalline Al 2 O 3 substrates an additional YBCO layer allows the deposition of almost pure perovskite PZT.

Patterning of YBCO thin films by ion implantation and magneto-optical investigations

Abstract YBa 2 Cu 3 O 7− δ thin films deposited by pulsed laser deposition were patterned by ion implantation. The patterning technique is based on the local disordering of the crystal structure due to elastic collisions of the implanted O + -ions and thus on a strong breakdown of superconductivity in the irradiated areas. With this patterning method circular and meandering structures with a size of 1 mm were prepared for investigations regarding high current applications. O + -ions with an energy of 180 keV were used to avoid a contamination of the film. The achieved structures were investigated concerning a dependence on the dose by means of RBS, XRD, AFM and magneto-optical characterization. Using a fluence of 5×10 14 O + /cm 2 a fully planar and stable structure can be obtained. The patterning depth can be adjusted by varying the implantation energy. So this technique was also used successfully on YBCO thin films covered already with a 200 nm Au top layer.

Pulsed laser deposition of YBCO thin films on 7×20-cm2 substrates

Abstract A specially designed and patented setup has been built up for Pulsed Laser Deposition (PLD) of homogeneous YBa 2 Cu 3 O 7− x (YBCO)-films on substrates as large as 7×20 cm 2 . YBCO films have been deposited on small substrates (SrTiO 3 , LaAlO 3 and buffered polycrystalline YSZ). Their structural and superconducting properties have been measured. The mean values of the transition temperatures and the critical current densities at T =77 K and zero magnetic field on single crystal substrates are 90 K and 4.3 MA/cm 2 , respectively. The YBCO films on buffered polycrystalline YSZ substrates reach critical current densities up to 1.1 MA/cm 2 at T =77 K and B =0 T.

Large area magneto-optical investigations of YBCO thin films

A new apparatus for magneto-optical investigations of high temperature superconducting (HTS) films as large as 20×20 cm2 is presented. With this equipment flux penetration of an external magnetic field into YBCO thin films has been studied by scanning the samples through an inhomogeneous magnetic field (magneto-optical scanning technique, MOST). The normal penetration of magnetic flux into a superconductor will be changed drastically in the presence of defects. The apparatus was constructed to realize an effective quality control of large area HTS thin films used for device fabrication. With this technique, a visualization of flux pattern in superconducting films larger than 1×1 cm2 is presented for the first time. The results are compared to inductive jc measurements as well as to micrographs [optical microscope (OM), scanning electron microscopy (SEM)] and show that also in the large area characterization the magneto-optical method is very sensitive to microstructural defects impairing the critical curr...

Large area deposition of YBa2Cu3O7−x films by pulsed laser ablation

A special patented design is built up to produce homogeneous YBa2Cu3O7−x (YBCO) films by pulsed laser deposition (PLD) over areas as large as 7×20 cm2. The use of a line focus (8 cm) reduces the substrate movement to one dimension. The demands on plasma homogenization, substrate scanning and film temperature during the deposition process for large area PLD are discussed and their technical realization is presented. First results of 1×1 cm2 YBCO films at different positions on the substrate holder (11×28 cm2) show homogeneous deposition conditions. The transition temperatures of the deposited YBCO thin films on 1×1 cm2 SrTiO3 substrates are TC=89 K with critical currents of 4×106 A/cm2 at T=77 K. The structural properties of these films (χmin=4.5%) indicate also their high crystalline quality. The variation of film thickness perpendicular to the scanning direction is less than ±9% and along the scanning direction ±7%.

Large area deposition of YBCO-films by pulsed laser deposition for microwave applications

Abstract Pulsed laser deposition (PLD) was used to cover 2-inch-wafers of MgO and LaAlO 3 with YBa 2 Cu 3 O 7− x . The homogeneity of the YBCO-films concerning their structural and superconducting properties was proved by X-ray methods, RBS/channelling and spatially resolved inductive measurements of T c and j c . With regard to microwave applications the surface resistance R s at 19 GHz was measured in a dielectric resonator. The film thickness and the c -axis length show no significant variations over the wafer diameter. The rocking curves of the (005) peak show only slight variations of the FWHM. The critical current density j c (77 K) of 2″-films range between 2–5 MA cm −2 , and the transition temperature T c varies between 89.0 and 90.5 K. Surface resistance values at 19 GHz as low as 0.15 mΩ (4.2 K) and 0.8 mΩ (70 K) have been achieved which stay field-independent up to about 10 and 1 mT, respectively.

Correlation between structural, ferroelectric and dielectric properties of laser ablated (Pb0.92La0.08)(Zr0.65Ti0.35)O3 - thin-films on high-grade steel hastelloy

Abstract High-grade steel Hastelloy was covered with (Pb0.92La0.08)(Zr0.65Ti0.35)O3 (PLZT) by Pulsed Laser Deposition (PLD). The direct deposition of the ferroelectric thin film on the substrate material - without additional buffer layers or bottom electrodes beneath the PZT - leads to a simple bicomponental system. The deposited films were characterized with respect to their structural properties (XRD, AFM) and showed excellent ferroelectric behavior [P(E) hysteresis]. Furthermore the fatigue, retention and ageing behavior of PLZT on Hastelloy was investigated and showed strong correlations to the structural measurements. Dielectric spectroscopy was used to investigate the frequency and temperature dependence of the permittivity ε. These measurements were discussed with respect to the above mentioned points.

Defect visualization in large area YBCO thin films by magneto-optical scanning technique

Flux penetration in large area YBCO thin films has been studied by a magneto-optical scanning technique. With a new apparatus HTS films as large as 20 cm/spl times/20 cm can be investigated by scanning the films through an inhomogeneous magnetic field. The apparatus has been built to realize an effective homogeneity control of the electrical properties of large area HTS thin films used for device fabrication. Magnetic flux penetration into YBCO thin films of different sizes and with intrinsic defects as well as artificial ones have been studied at 50 K. Magneto-optical measurements are compared with optical microscopy (OM) and inductive j/sub c/-characterizations. A correlation between the kind of defect and its influence on the electrical properties has been studied with regard to device applications, YBCO films structured especially for high current applications were investigated magneto-optically. These results will be compared to optical photographs of the quenching process caused by currents I>I/sub c/.

Influence of ion implantation on the ferroelectric properties of Pb(Zr,Ti)O/sub 3/ films

Pulsed laser deposition (PLD) was used to deposit Pb(Zr,Ti)O/sub 3/ (PZT) and (Pb,La)(Zr,Ti)O/sub 3/ (PLZT) thin films on YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO)//MgO and on technical substrates (high-grade steel Hastelloy). As a typical characterization of ferroelectric materials the P(E) hysteresis loop reflects the mobility of ferroelectric domain walls. We investigate the influence of ion implantation on the ferroelectric behaviour of thin PZT-films produced by PLD. The species of implanted ions (O/sup +/,Ca/sup +/) and the doses (10/sup 14/-10/sup 16/ cm/sup -2/, 180 keV) were varied to study the influence of the introduced atoms and defects on the ferroelectric properties. The films were investigated by XRD, RBS/Channeling and a RT-66A ferroelectric tester. The influence of thermal treatment of the implanted PZT-films on their ferroelectric properties will be discussed above the background of the induced structural defects and the implanted ions itself.

Magnetooptical investigations of large transport currents in Y-Ba-Cu-O-thin films

Inhomogeneities in large area YBCO-thin films can be studied in external magnetic fields with a specially designed magnetooptical apparatus. Moreover, an investigation of transport current induced magnetic fields in patterned HTS-thin films is possible as well. In the present work we studied the flux penetration of the current induced fields into YBCO-bridges of 8/spl times/0.7 cm/sup 2/ dimensions as a function of the applied currents at 77 K. For the first time transport currents up to I/sub tr//spl sim/60 A could be investigated magnetooptically in HTS-thin films. Flux penetration starts just above a threshold value of the applied current I/sub tr//I/sub c//spl ges/0.3. The influence of the bridge geometry and of inhomogeneities on flux penetration has been investigated. Flux and therefore current distributions change drastically with increasing bend-angle of the YBCO-path. A magnetic interaction between adjacent bridges with parallel and antiparallel current directions as well as a thermal interaction could be observed.