Highly (100) oriented Pb(Zr<Subscript>0.52</Subscript>Ti<Subscript>0.48</Subscript>)O<Subscript>3</Subscript>/LaNiO<Subscript>3</Subscript> films grown on amorphous substrates by pulsed laser deposition

Pb(Zr_0.52Ti_0.48)O₃ (PZT)/LaNiO₃ (LNO) thin films with highly (100) out of plane orientation were produced on SiO₂/Si(100) and alkaline earth aluminosilicate glass substrates by pulsed laser deposition (PLD). Orientations of both PZT and LNO films were evaluated using X-ray diffraction. The pure (100)-oriented PZT/LNO films were obtained under optimized deposition conditions. Time of flight-secondary ion mass spectrometry analysis showed that LNO could effectively block interdiffusion between the PZT films and the substrates. Fairly smooth surfaces of the PZT films with roughness of about 4 nm were observed using an atomic force microscope. Cross sectional examination revealed that the films grew in columnar grains. The PZT films grown on both SiO₂/Si and glass substrates demonstrated very good ferroelectric characteristic at room temperature with remnant polarization of up to 26 μC/cm². PACS 79.20.DS; 77.84.DY; 78.70.Ck     

Influence of the substrate on ferroelectric properties of 〈1 1 1〉 oriented rhombohedral Pb(Zr0.6Ti0.4)O3 thin films

〈1 1 1〉-oriented Pb(Zr_0.6Ti_0.4)O₃ thin films were elaborated in the same run by RF multitarget sputtering on Si/SiO₂/TiO₂/Pt(1 1 1) and LaAlO₃/Pt(1 1 1) substrates. PZT thin films were textured, exhibiting 〈1 1 1〉 fibre texture on silicon substrates whereas epitaxial relationships were found when grown on LaAlO₃/Pt(1 1 1). On the latter substrate, values of spontaneous polarization and of dielectric permittivity were measured close to that calculated previously along the 〈1 1 1〉 direction of PZT rhombohedral single crystal. On the contrary, spontaneous polarization and dielectric permittivity measured on PZT thin films deposited on platinized silicon were found deviating from calculated values. These different electrical results are attributed to different ferroelectric domain configurations.     

Study of elemental and phase composition of PZT thin films by auger depth profiling

The composition of PZT thin films deposited by diode HF sputtering of a ceramic target on Pt/Ti/SiO₂/Si substrates was studied. The remanent polarization of grown films was to 22 μC/cm². A technique for verifying the adequacy of elemental and phase composition of thin films to the ferroelectric phase composition was proposed. The problems of reliable contact of Pt electrodes with the PZT layer were considered.     

Enhanced ferroelectric property of (Pb0.95Ca0.05)(Nb0.02Zr0.80Ti0.20)O3 thin films prepared by RF magnetron sputtering

(Pb_0.95Ca_0.05)(Nb_0.02Zr_0.80Ti_0.20)O₃ [PCNZT] thin films were deposited on the Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering with and without a LaNiO₃ [LNO] buffer layer. Ca and Nb elements in PZT films enhance the ferroelectric property, LaNiO₃ buffer layer improves the crystal quality of the PCNZT thin films. PCNZT thin films possess better ferroelectric property than that of PZT films for Ca and Nb ion substitution, moreover, PCNZT thin films with a LNO buffer layer possess (1 0 0) orientation and good ferroelectric properties with high remnant polarization (P_r = 38.1 μC/cm²), and low coercive field (E_c = 65 kV/cm), which is also better than that of PCNZT thin films without a LNO buffer layer (P_r = 27.9 μC/cm², E_c = 74 kV/cm). The result shows that enhanced ferroelectric property of PZT films can be obtained by ion substitution and buffer layer.     

Characterization of 90° domain structure and polarization switching in Pb(Zr0.4Ti0.6)O3 film by piezoresponse force microscope

A lead zirconate titanate Pb(Zr_0.4Ti_0.6)O₃ (PZT40/60) film was deposited on a Pt(111)/Ti/SiO₂/Si(100) substrate by a sol–gel process followed by thermal annealing at 650 °C for 5 min. Piezoresponse force microscope observation revealed a lamellar domain structure in the PZT40/60 grains and we attribute the lamellar domains as 90° ferroelectric domains. The polarization-switching mechanism of the 90° domains in the PZT40/60 film under external electric fields has also been studied and it was revealed that a large-area polarization switching is usually accompanied by the appearance of a new direction of 90° domains in order to reduce the stress in the grains. By contrast, a nanometer-sized polarization switching is believed to be accomplished by generating 180° domains within a single lamellar domain. PACS 77.80.-e; 77.84.-s; 68.55.-a; 68.37.-d     

(111)择优取向的Pb(Zr0.52Ti0.48)O3铁电薄膜的制备及研究

选用不同浓度的Pb(Zr_0.52Ti_0.48)O₃溶胶，用Sol-gel法在Pt/Ti/SiO₂/Si基片上沉积一层厚度不同的Pb(Zr_0.52Ti_0.48)O₃ (PZT52)过渡层，经400℃烘烤、550℃退火等程序后，再用Sol-gel法在PZT52过渡层上沉积Pb(Zr_0.52Ti_0.48)O _{关键词： PZT铁电薄膜 择优取向 过渡层 剩余极化强度}     

Comparison of the effect of PLT and PZT buffer layers on PZT thin films for ferroelectric materials applications

In order to study the effect of different buffer layers on the Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films, 10-nm thick (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) and Pb(Zr_0.52Ti_0.48)O₃ buffer layers have been deposited on the Pt(1 1 1)/Ti/SiO₂/Si substrates by pulsed laser deposition, respectively. The top buffer layers were also deposited on PZT thin films with the same thickness of the seed layers in order to enhance the fatigue characteristics of PZT thin films. We compared the results of dielectric constant, hysteresis loops and fatigue resistance characteristics. It was found that the dielectric properties of PZT thin films with PLT buffer layers were improved by comparing with PZT thin films with PZT buffer layers. The polarization characteristics of PZT thin films with PLT buffer layers were observed to be superior to those of PZT thin films using PZT buffer layers. The remanent polarization of PZT thin films showed 36.3 μC/cm² and 2.6 μC/cm² each in the case of use PLT and PZT buffer layers. For the switching polarization endurance analysis, PZT thin films with PLT buffer layers showed more excellent result than that of PZT thin films with PZT buffer layers.     

Ferroelectric properties of bilayer structured Pb(Zr0.52Ti0.48)O3/SrBi2Ta2O9 (PZT/SBT) thin films on Pt/TiO2/SiO2/Si substrates

Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films with large remanent polarization and SrBi₂Ta₂O₉ (SBT) thin films with excellent fatigue-resisting characteristic have been widely studied for non-volatile random access memories, respectively. To combine these two advantages_, bilayered Pb(Zr_0.52Ti_0.48)O₃/SrBi₂Ta₂O₉ (PZT/SBT) thin films were fabricated on Pt/TiO₂/SiO₂/Si substrates by chemical solution deposition method. X-ray diffraction patterns revealed that the diffraction peaks of PZT/SBT thin films were completely composed of PZT and SBT, and no other secondary phase was observed. The electrical properties of the bilayered structure PZT/SBT films have been investigated in comparison with pure PZT and SBT films. PZT/SBT bilayered thin films showed larger remanent polarization (2P_r) of 18.37 μC/cm² than pure SBT and less polarization fatigue up to 1 × 10⁹ switching cycles than pure PZT. These results indicated that this bilayered structure of PZT/SBT is a promising material combination for ferroelectric memory applications.     

Evidence for muonium emission from an SiO2 layer on n-type Si and the positive muon state in Si

Evidence for the emission of slow muonium atoms from a 3.0-nm-thick SiO₂ layer covered on an n-type Si is reported. Also, upon applying an rf-resonance technique at the muon frequency, a time-differential observation of a delayed state-change from muonium to diamagnetic muon at room temperature was observed. Combining results obtained by use of longitudinal field decoupling and transverse spin rotation methods, the conversion rate was estimated to be 5 to 10 μs⁻¹. Both of the above results, namely the observation of the emission and state-change of muonium, suggest a process in which μ⁺ initially captures an electron from Si, then quickly converts to μ⁺ again during thermal diffusion in the Si towards the SiO₂ layer. Within the oxide layer, muonium is again formed and subsequently is emitted from the SiO₂ surface.     

Effect of buffer layers on the property of Pb(Zr,Ti)O3-Pb(Mn,W,Sb,Nb)O3 thin films grown by pulsed laser deposition

New ferroelectric Pb(Zr,Ti)O₃-Pb(Mn,W,Sb,Nb)O₃ (PZT-PMWSN) thin film has been deposited on a Pt/Ti/SiO₂/Si substrate by pulsed laser deposition. Buffer layer was adopted between film and substrate to improve the ferroelectric properties of PZT-PMWSN films. Effect of a Pb(Zr_0.52Ti_0.48)O₃ (PZT) and (Pb_0.72La_0.28)Ti_0.93O₃ (PLT) buffer layers on the stabilization of perovskite phase and the suppression of pyrochlore phase has been examined. Role of buffer layers was investigated depending on different types of buffer layer and thickness. The PZT-PMWSN thin films with buffer layer have higher remnant polarization and switching polarization values by suppressing pyrochlore phase formation. The remnant polarization, saturation polarization, coercive field and relative dielectric constant of 10-nm-thick PLT buffered PZT-PMWSN thin film with no pyrochlore phase were observed to be about 18.523 μC/cm², 47.538 μC/cm², 63.901 kV/cm and 854, respectively.     

Phase evolution and effect of pre-heating temperature on the characteristics of PZT thin films grown by using a triol sol--gel route

Lead zirconate titanate (PZT) films were fabricated on Pt(111)/Ti/SiO₂/Si(100) using the triol sol--gel method. The effect of the pre-heating temperature on the phase transformations, microstructures, electrical properties and ferroelectric properties of the PZT thin films was investigated. Randomly-oriented PZT thin films pre-heated at 400°C for 10?min and annealed at 600°C for 30?min showed well-defined ferroelectric hysteresis loops with a remanent polarization of 26.57?µC?cm^?2 and a coercive field of 115.42?kV?cm^?1. The dielectric constant and dielectric loss of the PZT films were 621 and 0.0395, respectively. The microstructures of the thin films are dense, crack-free and homogeneous with fine grains about 15–20?nm in size.     

Surface characterisation and interface studies of high-k materials by XPS and TOF-SIMS

High-k dielectric LaAlO₃ (LAO) films on Si(100) were studied by TOF-SIMS and XPS to look for diffusion processes during deposition and additional thermal treatment and for the formation and composition of possible interfacial layers. The measurements reveal the existence of SiO₂ at the LAO/Si interface. Thermal treatment strengthens this effect indicating a segregation of Si. However, thin LAO layers show no interfacial SiO₂ but the formation of a La-Al-Si-O compound. In addition, Pt diffusion from the top coating into the LAO layers occurs. Within the LAO layer C is the most abundant contamination (10²¹ at/cm³). Its relatively high concentration could influence electric characteristics. XPS shows that CO₃²⁻ is intrinsic to the LAO layer and is due to the adsorption of CO₂ of the residual gas in the deposition chamber.     

Texture control and its impact on the properties of SrBi2Ta2O9 thin films prepared by pulsed laser deposition

SrBi₂Ta₂O₉ (SBT) ferroelectric thin films with different preferred orientations were deposited by pulsed laser deposition (PLD). Several methods have been developed to control the preferred orientation of SBT thin films. For SBT films deposited directly on Pt/TiO₂/SiO₂/Si substrates and in situ crystallized at the deposition temperature, the substrate temperature has a significant impact on the orientation and the remnant polarization (Pr) of the films; a higher substrate temperature benefits the formation of (115) texture and larger grain size. The films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C are (115)-oriented and exhibit 2Pr of 6 μC/cm². (115)- and (200)-predominant films can be formed by using a La_0.85Sr_0.15CoO₃ (LSCO) buffer layer or by annealing amorphous SBT films deposited on Pt/TiO₂/SiO₂/Si substrates at 450 °C using rapid thermal annealing (RTA). These films exhibit good electric properties; 2Pr of the films are up to 12 μC/cm² and 17 μC/cm², respectively. The much larger 2Pr of the films deposited on the LSCO buffer layer and of the films obtained by RTA than 2Pr of the films deposited on Pt/TiO₂/SiO₂/Si substrates at 830 °C is attributed to a stronger (200) texture. Received: 30 January 2001 / Accepted: 30 May 2001 / Published online: 25 July 2001     

Low-temperature laser processes for synthesizing (100)-textured Pb(Zr,Ti)O3 thin films on Si substrate

High-performance Pb(Zr,Ti)O₃, PZT, thin films were synthesized on Si substrates by using low-temperature laser-assisted processes, which combine pulsed laser deposition (PLD), laser lift-off (LLO) and laser-annealing (LA) processes. The PZT films were first grown on sapphire substrates at 400 °C, using Ba(Mg_1/3Ta_2/3)O₃, BMT, as seeding layer, by the PLD process, and were then transferred to Si substrates at room temperature by a LLO transferring process. Utilization of the BMT layer is of critical importance in those processes, since it acted as a nucleation layer for the synthesis of the PZT thin films on the sapphire substrates and, at the same time, served as a sacrificial layer during laser irradiation in the LLO process. After the LLO process, the surfaces of the PZT films were recovered by the LA process for removing the damage induced by the LLO process. A thin BMT (∼30 nm) layer is randomly oriented, resulting in non-textured PZT films with good ferroelectric properties, viz. P_r=20.6 μC/cm² and E_c=126 kV/cm, whereas a thick BMT (∼100 nm) layer is (100) preferentially oriented, leading to (100)-textured PZT films with markedly better ferroelectric properties, viz. P_r=34.4 μC/cm² and E_c=360 kV/cm. PACS 81.15.Fg; 77.84.-s     

Structural and electrical properties of polycrystalline PbZr0.5Ti0.5O3 films deposited on La0.5Sr0.5CoO3 coated silicon by sol-gel process

La_0.5Sr_0.5CoO₃ (LSCO) films have been grown on Si (100) by a metalorganic chemical liquid deposition (MOCLD) technique using lanthanum acetate, strontium acetate and cobalt acetate as the starting materials. Subsequent PbZr_0.5Ti_0.5O₃ (PZT) films were deposited onto LSCO films by a modified sol-gel method. Field-emission scanning electron microscopy and X-ray diffraction analysis show that PZT and LSCO films are polycrystalline and entirely perovskite phase. At an applied electric field of 250 kV/cm, the Pt/PZT/LSCO capacitor shows no polarization fatigue after 3×10⁹ switching cycles and an internal electric field; the remnant polarization P_r and the coercive field E_c are about 22 μC/cm² and 73 kV/cm, respectively. The dielectric constant of PZT films is 650 at a frequency of 1 kHz. Received: 20 February 2001 / Accepted: 6 June 2001 / Published online: 30 August 2001     

Picosecond laser ablation of SiO2 layers on silicon substrates

In this work, we report on laser ablation of thermally grown SiO₂ layers from silicon wafer substrates, employing an 8–9 ps laser, at 1064 (IR), 532 (VIS) and 355 nm (UV) wavelengths. High-intensity short-pulse laser radiation allows direct absorption in materials with bandgaps higher than the photon energy. However, our experiments show that in the intensity range of our laser pulses (peak intensities of <2×10¹² W/cm²) the removal of the SiO₂ layer from silicon wafers does not occur by direct absorption in the SiO₂ layer. Instead, we find that the layer is removed by a “lift off” mechanism, actuated by the melting and vaporisation of the absorbing silicon substrate. Furthermore, we find that exceeding the Si melting threshold is not sufficient to remove the SiO₂ layer. A second threshold exists for breaking of the layer caused by sufficient vapour pressure. For SiO₂ layer ablation, we determine layer thickness dependent minimum fluences of 0.7–1.2 J/cm² for IR, 0.1–0.35 J/cm² for VIS and 0.2–0.4 J/cm² for UV wavelength. After correcting the fluences by the reflected laser power, we show that, in contrast to the melting threshold, the threshold for breaking the layer depends on the SiO₂ thickness.     

Simple fabrication of hexagonally well-ordered AAO template on silicon substrate in two dimensions

In this study, thin anodic aluminum oxide (AAO) templates both on silicon substrates (AAO template/SiO₂/Si) and Ti-coated silicon substrates (AAO template/Ti/SiO₂/Si) were developed for design of magnetic, electronic and optoelectronic devices, chemical sensors and chip-scale lithium-ion rechargeable microbatteries. Two types of AAO template were prepared by using a two-step anodization procedure. The templates were characterized by scanning electron microscopy and energy dispersive X-ray spectroscopy. The obtained thin AAO templates were approximately 50 nm in diameter and 700 nm in length with 80-nm interpore distances in a relatively large area of 6 cm². A barrier layer of the AAO templates was removed by a cathodic polarization method in KCl solution for several seconds. The current–time transient during removing the alumina barrier layer of the thin AAO template and the mechanism of electrochemical dissolution of the barrier layer are given in detail.     

Preparation of Nb doped PZT film by RF sputtering

Undoped lead zirconate titanate (PZT) and Nb doped lead zirconate titanate (PNZT) films formed on an Ir/Ti/SiO₂/Si substrate using an RF magnetron sputtering method were studied in detail. Films of about 3–4 μm thickness were deposited at a substrate temperature of 525 ^°C. X-ray diffraction measurement (XRD) shows that the obtained PZT and PNZT films are both strongly uniaxially oriented in the (100) direction of the perovskite structure, and TEM observation shows that the films have columnar structures. The addition of Nb results in changes of film electrical characteristics, particularly dielectric constant and hysteresis characteristics. Sputtered PNZT films (Nb 13 at.%) formed on silicon diaphragm structures generate 2 times more deflections than undoped PZT film formed on the same structure, thus demonstrating a superior piezoelectric performance. A sputtering method to directly form a PNZT film with high piezoelectric constant on a substrate at low temperature via electrodes finds a wide potential use in MEMS applications.     

Study of the interaction of argon and nitrogen ions with the silicon dioxide surface

Angular dependences of the sputtering yield, surface layer composition, and changes in the mass spectra of residual atmosphere upon irradiation of silicon dioxide with argon and nitrogen ions are measured. It is found that the sputtering yield of SiO₂ bombarded by N ₂ ⁺ ions is almost two times higher than for Si. The sputtering yields of SiO₂ and Si irradiated with Ar ions are identical, although the binding energy of atoms in SiO₂ is almost two times higher than in Si. An analysis of the surface composition and residual atmosphere near the sample during its irradiation suggests that a chemical reaction is involved in SiO₂ sputtering. Molecules of SiO and NO gases form in the surface layer, whose subsequent desorption increases the SiO₂ sputtering rate.     

Investigation the effects of the excess Pb content and annealing conditions on the microstructure and ferroelectric properties of PZT (52-48) films prepared by sol-gel method

The effects of the PbO volatilization, excess Pb content of PbZr_0.52Ti_0.48 (PZT) precursor, PbTiO₃ (PT) seeding layers and annealing condition on the microstructures, surface morphologies, preferred orientation and ferroelectric properties of PbZr_0.52Ti_0.48 films were systematically investigated. PZT films with a variety of excess Pb (0-20%) were spin-deposited on Si(1 0 0) and Pt(1 1 1)/Ti/SiO₂/Si(1 0 0) substrates by sol-gel technique. The films composition, Pb/Zr/Ti/O atom rate and Pb loss were semiquantitative analyzed by X-ray photoelectron spectrometer (XPS). When the excess Pb of PZT precursor was 10%, the Pb/Zr/Ti/O atomic rate of the fabricated films was very close to the designed rate of 1:0.52:0.48:3. The XRD and AFM investigations confirmed that PT seeding layer promoted the PZT films perovskite phase transformation and grains growth with (1 1 0) plane preferred orientation, accordingly lowered perovskite phase crystallization temperature and reduced Pb loss. The PZT films annealed in O₂ flow demonstrated better microstructure and ferroelectric properties comparing with films annealed in air by double remnant polarization increase and 8% coercive field increase. The underlying mechanism was also investigated.