Carmen Pradas Guerrero

Pulsed laser deposition of epitaxial PbZrxTi1-xO3 ferroelectric capacitors with LaNiO3 and SrRuO3 electrodes

It is commonly accepted that, in order to solve the fatigue problem in PbZr x Ti 1-x O 3 (PZT) ferroelectric capacitors, oxide electrodes have to be used. However, clear criteria for the choice of an electrode material have not given yet. Here we report on the deposition and ferroelectric properties of epitaxial pulsed laser deposited PZT capacitors with SrRuO 3 and LaNiO 3 perovskite bottom electrodes, and aluminium top electrodes. Remarkable improvement of the ferroelectric properties, i.e. remanent polarization increasing from 7.5 to 37 μC/cm 2 , is observed when the bottom electrode material is changed from SrRuO 3 to LaNiO 3 . This improvement is attributed to a smoother ferroelectriclelectrode interface and the formation of the tetragonal phase of PZT instead of the rhombohedral one.

High-quality epitaxial LaNiO3 thin films on SrTiO3(100) and LaAlO3(100)

Abstract.LaNiO3 thin films have been deposited by pulsed laser deposition on SrTiO3(100) and LaAlO3(100) substrates. The processing conditions have been investigated in order to optimize electrical resistivity, crystal quality, and surface morphology. Excellent properties are achieved at moderate substrate temperature and relatively low oxygen pressure, without the need for annealing. Thickness exerts an important influence on electrical transport, as the electrical resistivity increases quickly in films thicker than a few tens of nanometer. The surface of the films on LaAlO3 is very flat in all the studied thickness range, but the films on SrTiO3 develop a pattern of boundaries and even cracks as the thickness is higher. Below the critical thickness, high-quality epitaxial films with very smooth surface and low electrical resistivity are obtained under the optimum conditions of substrate temperature and oxygen pressure. The optimum processing conditions are different depending on the substrate, and control is especially critical in films deposited on SrTiO3.

Epitaxial SrRuO3 thin films on LaAlO3(100) and Si(100)

Abstract Epitaxial SrRuO 3 (SRO) thin films were deposited by pulsed laser deposition on LaAlO 3 (100) and Si(100) substrates. A study of the influence of substrate temperature and oxygen partial pressure on the structural and electrical properties is presented for films deposited on LaAlO 3 (100). The dependence of the properties of SRO on film thickness was also studied. The crystal properties improved when a SrTiO 3 (STO) seed layer was used, although the surface of the SRO films deposited on this layer had a high density of outgrowths. SRO thin films deposited on Si(100) were epitaxial when an yttria-stabilised zirconia (YSZ) buffer layer was used. The crystal structure and morphology of these films was determined.

Pulsed laser deposition of epitaxial ferroelectric PbZrxTi1−xO3/SrTiO3 and PbZrxTi1−xO3/SrRuO3 bilayers

Epitaxial ferroelectric PbZrxTi1−xO3 (PZT) thin films have been deposited by pulsed laser deposition on LaAlO3 (001) substrates. The substrates were covered in situ with a thin SrTiO3 seed layer before the PZT deposition. Wide ranges of substrate temperature and oxygen partial pressure have been investigated in order to optimise structure and morphology. X-ray diffraction measurements revealed that epitaxial films with high crystalline quality were obtained at temperatures ranging from 600°C to 750°C and oxygen pressures from 0.03 to 0.2 mbar. Within this range, flat morphologies with rms roughness below 1 nm were observed by scanning electron and atomic force microscopies, whenever oxygen pressure was kept below 0.1 mbar and the films were 100 nm thick or less. A rougher columnar microstructure is obtained for thicker films and greater oxygen pressures. Ferroelectricity of the films has been tested in samples deposited on conductive SrRuO3 electrodes. Typical remanent polarisations of 13 μC/cm2 and coercive fields of 47 kV/cm are obtained.

Excimer laser irradiation of SrRuO3 epitaxial thin films

Abstract Single and multishot excimer laser ablation of SrRuO 3 (SRO) epitaxial thin films has been studied, aiming at selective removal of SRO electrodes in device applications. High quality SRO epitaxial thin films were grown by pulsed laser deposition on LaAlO 3 (001) substrates; subsequent irradiation was performed by an excimer laser at 248 nm wavelength. Inspection of the ablated surfaces by scanning electron microscopy shows the existence of two well-defined regimes above damage threshold depending on the laser fluence, namely exfoliational and hydrodynamical, which closely correspond to the different mechanisms responsible for material emission. The role of spot size and film thickness with regard to improved edge definition and damage-free substrates has been studied.