Orientation Of PZT Research Articles

Iridium Based Electrodes for Ferroelectric Capacitor Fabrication

AbstractIr and its conductive oxide, IrO2, are candidates to replace Pt as the electrodes in ferroelectric capacitors (FECAPs) because of improved endurance (since e.g. Pt/PZT/Pt shows strong fatigue) and also because of the oxygen barrier properties of Ir/IrO2 stacks that enable the fabrication of stacked FECAPs on top of contact plugs. Two important issues related to these electrodes are the control of the ferroelectric layer orientation on top of these materials, as well as material stability (e.g. oxidation and possible growth of large IrO2 crystallites).In this work, we show that IrO2 bottom electrodes affect the crystallization of sol-gel deposited Pb(Zr,Ti)O3 (PZT). While PZT films deposited on (111) Pt show a (111) preferential orientation, IrO2 electrodes nucleate strongly different oriented PZT. Controlling and changing the microstructure of the bottom electrode allows tuning of these PZT orientations and the resulting grain morphology, and, consequently, their FECAP polarization hysteresis properties.

Orientation controlling of PZT thin films derived from sol-gel techniques

The factors that influence the crystal orientation of lead zirconate titanate (PZT) thin films fabricated by using sol-gel techniques on (111) preferred oriented Pt/Ti/SiO2./Si(100) substrates were systematically investigated. The crystallization treatment of PZT thin films was done at 650 ◦C for 30 min by using rapid thermal annealing (RTA). X-ray diffraction (XRD) analysis was used to identify the orientation of PZT thin films. The morphology was examined by using scanning electron microscopy (SEM). The different ratio of zirconium to titanium, the lead contents in precursor solutions, the modification of the PZT precursor and the thickness of PZT thin films have obviously effects on the formation of (111) or (100) preferred-oriented and random-oriented PZT thin films. It is concluded that controlling the orientation of PZT thin films can be realized by using the sophisticated sol-gel processing and normal (111) Pt/Ti/SiO2./Si(100) substrates. Electrical properties of ferroelectric thin films are strongly dependent on their crystallographic orientation, which determines the magnitude of switchable polarization of a thin film. Among the applications for which highly oriented PZT thin films will be of interest are pyroelectric detectors, optical disk storage system, optical waveguide devices, and spatial light modulators. A further benefit of orientation may be enhancing process integration of ferroelectric thin film and semiconductor technologies. Many studies for the control of a preferred orientation in PZT films are usually based on the substrate used. Most of them use various single crystals as substrates to fabricate the crystal alignment of the PZT thin films. For example, PZT films with (100), (110), and (111) textures can be obtained by using single-crystal SrTiO3 or MgO wafers of the same orientation [1]. But single-crystal substrates have economical problem for applications of the ferroelectric thin films. It is necessary to develop a method for the control of the PZT orientation using relatively cheaper substrates. RF magnetron sputtering [2], metal organic chemical vapor deposition (MOCVD) [3], and pulsed laser deposition (PLD) [4] methods have been widely utilized to produce highly oriented or epitaxial ferroelectric thin films. Chemical process has the advantages of feasible

Pt and RuO2 Bottom Electrode Effects on Pb(Zr,Ti)O3 Memory Capacitors

This study examines the effects of bottom electrodes for metal ferroelectric metal (MFM) capacitor applications. We investigated the following parameters of bottom electrodes and Pb(Zr0.53Ti0.47)O3 (PZT) thin films: substrate temperature, rf power, gas flow rate, Ar/O2 ratio, electrode material, and post-annealing effect. Bottom electrodes grown at 300°C for Pt and 200°C for RuO2 exhibited a film resistivity of 10-4 Ω·cm, had a surface roughness of approximately 55 Å and a preferred crystal orientation. Rapid thermal annealing (RTA) treatments on a Pt electrode at 600°C for 30 s improved the resistivity to 5×10-6 Ω·cm and generated the (111) preferred crystal orientation. PZT films exhibited a strong PZT (101) peak for an optimized Pt bottom electrode and (111), (200), (112) planes without preferred PZT orientations for the RuO2 electrode. A well-fabricated Pd/PZT/Pt capacitor showed a leakage current density in the order of 6×10-5 A/cm2, a dielectric constant (εr) of 365, a remanent polarization (Pr) of 27 µC/cm2, and a coercive field (Ec) of 50.5 kV/cm. This paper discusses the bottom electrode properties as well as their recommended conditions in memory device applications of thin-film PZT capacitors.

Bottom Electrode Effects in Controlling Orientation of Lead Zirconate Titanate Films Deposited by Chemical Solution Deposition

AbstractThe microstructure and electrical properties of lead zirconate titanate Pb(Zr,Ti)O3 (PZT) films prepared by chemical solution deposition (CSD) with and without lead titanate (PT) seed layers were examined as a function of Ir/lr oxide electrode type. The novel PZT CSD solution was prepared from a mixture of zirconium and titanium butoxyethoxides and lead ethylhexanoate dissolved in butoxyethanol. The use of excess-lead (PbxsTi) and stoichiometric PT seed layers was found to promote PZT(111) orientation on Ir but not on Ir oxide. Ir substrate thickness was observed to influence orientation of PZT deposited on stoichiometric PT with greater PZT(111) texturing on thinner Ir(111) substrates. PZT with greater PZT(111) texturing tended to have greater remanent polarization (2Pr, μC/cm2). PZT deposited on stoichiometric PT seed layers on Ir(111) was of higher film quality than PZT deposited on PbxsTi seed layers on Ir(111). The PZT films deposited on stoichiometric PT on Ir(111) had enhanced PZT(111) orientation, a reduced pyrochlore content, and tended to saturate at lower coercive fields, have higher remanent polarization, squarer hysteresis loops with less tilt and greater fatigue endurance. The use of iridium oxide top electrode was demonstrated to significantly improve fatigue endurance compared to use of an iridium top electrode.

Growth and polarization features of highly (100) oriented Pb(Zr0.53Ti0.47)O3 films on Si with ultrathin SiO2 buffer layer

Highly (100) oriented Pb(Zr0.53Ti0.47)O3 (PZT) films were prepared on Si substrates with ultrathin SiO2 buffer layer by pulsed laser deposition. Hysteresis measurements show that saturation polarization, remnant polarization and coercive field of the films reach 26 μC/cm2, 10 μC/cm2 and 70 kV/cm, respectively. The thickness of SiO2 buffer layer is found to play a significant role on phase purity and orientation of PZT as well as the prevention of interdiffusion. It is also found that the grain size and the interdiffusion between PZT and Si are the key factors for the ferroelectric properties of the films, which are discussed together with the synthesis condition in detail.

Characterization of PZT capacitors with SrRuO3 electrodes

Pb(Zr, Ti)O3 [PZT] capacitors were prepared by CSD on sputtered electrodes of SrRuO3(SRO)/Pt on SiO2/Si wafers. The SRO/Pt bottom electrodes were deposited using two different conditions: (1) at 600°C in-situ (abbreviated HT), and (2) at low temperature followed by a post-deposition anneal at 600°C (abbreviated LTA). The PZT orientation and switching pulse polarization, i.e. HT-SRO (43 μC cm-2) and LTA-SRO (32 μC cm-2) were strongly dependent on the bottom electrodes. Yet neither capacitor showed polarization loss resulting from switching 108 times with ± 5 V pulses. These results indicate that the PZT ferroelectric properties are greatly influenced by the SRO bottom electrode processing conditions.

Effect of PbTiO3 Seeding Layer on the Growth of Sol-Gel-Derived Pb(Zr0.53Ti0.47)O3 Thin Film

Lead zirconate titanate (PZT) films prepared by a sol-gel method were deposited on Pt/Ti/SiO2/Si substrates with a seeding layer. A thin PbTiO3 layer, about 30 nm in thickness, was deposited on the Pt surface as the seeding layer to provide a nucleation site for PZT crystallization. Strong (001)-preferred orientation of PZT was observed when the seeding layer was deposited by pulsed laser ablation at room temperature and annealed subsequently. This result was explained by a “two-step growth" model. The texture and microstructure of PZT films can be controlled by the introduction of a thin seeding layer which lowers the crystallization temperature and makes it possible to obtain films composed of very fine grains. The dielectric properties of ferroelectric materials could be controlled by changing the grain size.

Influence of the ferroelectric domain structure and switching properties on the endurance of PZT ferroelectric capacitors

Ferroelectric Pt/PZT/Pt capacitors with different PZT orientations are characterized before and after electrical fatigue. (111)c-oriented, tetragonal PZT is characterized by abrupt 180° switching and very high-quality hysteresis loops but is very prone to electrical fatigue, while the 90° switching which is dominant in unsaturated and/or unpoled (100)c PZT films results in slanted loops with low polarization but high endurance.

Influence of PbTiO3 Buffer Layers on Microstructural Properties of Pb(Zr,Ti)O3 Films Deposited by Sputtering

AbstractPb(Zr,Ti)O3 (PZT) films with very thin PbTiO3 (PT) buffer layers inserted between the film and the Si/SiO2/Ti/Pt substrate were grown by a rf magnetron sputtering technique. The Xray diffraction patterns and the surface morphology of PT as a function of the thickness, in the range of 20 to 400 Å, were first investigated. Such a marked contrast in morphological features was not observed when the thickness was above 400 Å. The films were grown in-situ at 500°C. We found modification of the PT orientation when its thickness varied between 20 Å and 400 Å. This implies a gradual evolution of the lattice parameters in the nucleation stage of PT films. Insertion of these buffer layers was found to exert marked effects. Up to 400 Å the PT was grown with a [100] preferred orientation. The orientation of PZT could be controlled by changing the thickness and then the orientation of PT. The results will be discussed in terms of the effects of the buffer layer on the crystalline structure and the surface morphology of PZ

Effects of the utilization of a buffer layer on the growth of Pb(Zr, Ti)O 3 thin films by metalorganic chemical vapor deposition

Metalorganic chemical vapor deposition (MOCVD) growth of Pb(Zr,Ti)O 3 (PZT) thin films employing a two-step growth process was investigated. In the two-step growth process, the effects of the utilization of a PbTiO 3 buffer layer on the succeeding growth of PZT thin films were observed. The orientation of the PZT thin films was controlled by changing the orientation of the PbTiO 3 buffer layer deposited on the substrate. The degree of orientation of PZT was also influenced by the use of a PbTiO 3 buffer layer. From atomic force microscope (AFM) observations, it was found that the main growth mechanism of (111)-oriented PbTiO 3 was two-dimensional growth and that the PbTiO 3 buffer layer played an important role as dense nuclei in the succeeding PZT growth.