Solution-based fabrication and electrical properties of CaBi4Ti4O15 thin films

Ferroelectric CaBi₄Ti₄O₁₅ (CBT) thin films were prepared by spin coating technology using solution-based fabrication. The as-deposited CBT thin films were crystallized below 600 °C and the layered perovskite were crystallized at 700 °C using CFA processing in air. The enhancement of ferroelectric properties in CBT thin films for MFIS structures were investigated and discussed. Compared the Bi₄Ti₃O₁₂ (BIT), the CBT showed the better physical and electrical characteristics. The 700 °C annealed CBT thin films on SiO₂/Si substrate showed random orientation and exhibited large memory window curves. The maximum capacitance, memory window and leakage current density were about 250 pF, 2 V, and 10^?5 A/cm², respectively.     

Structural and electrical properties of Pb(Zr0.53Ti0.47)O3 films prepared on La0.5Sr0.5CoO3 coated Si substrates

PbZr_0.53Ti_0.47O₃ (PZT) thin films with thickness of 0.9 μm were prepared on La_0.5Sr_0.5CoO₃ (LSCO) coated Si substrates. Both PZT and LSCO were prepared by the sol–gel method. The concentration of LSCO sol was varied from 0.3 to 0.1 mol/L, which could modify the preferential orientation of PZT thin films and consequently affect the dielectric and ferroelectric properties. The LSCO electrode layers derived from lower sol concentration of 0.1 mol/L have much more densified structure, which facilitates the formation of (1 0 0) textured PZT films with smooth and compact columnar grains. PZT thin films prepared on the optimized LSCO films exhibit the enhanced dielectric constant and remnant polarization of 980 and 20 μC/cm², respectively.     

Dip-coated La2Ti2O7 as a buffer layer for growth of Bi3.25La0.75Ti3O12 films with enhanced (0 1 1) orientation

Thin-films of La₂Ti₂O₇ were obtained by dip-coating process using a precursor salt in nitric acid solution. The effects of solution concentration, withdrawal speed, post-annealing duration and temperature were investigated both on grain size and orientation of the La₂Ti₂O₇ thin layers. In addition, a target with the required stoichiometry for PVD deposition of La-substituted Bi₄Ti₃O₁₂ (BLT) was successfully sintered by spark plasma sintering (SPS) at 750 °C. Finally (0 1 1)-oriented BLT ferroelectric films have been grown by RF sputtering on (1 1 0)-oriented La₂Ti₂O₇ polycrystalline thin-film. A preferential orientation of BLT thin films has been obtained after annealing at a temperature lower than 650 °C.     

Effect of annealing temperature on ferroelectric electron emission of sol–gel PZT films

In this work, the influence of annealing temperature on the ferroelectric electron emission behaviors of 1.3-μm-thick sol–gel PbZr_0.52Ti_0.48O₃ (PZT) thin film emitters was investigated. The results revealed that the PZT films were crack-free in perovskite structure with columnar-like grains. Increasing annealing temperature led to the growth of the grains with improved ferroelectric and dielectric properties. The remnant polarization increased slightly from 35.3 to 39.6 μC/cm² and the coercive field decreased from the 56.4 to 54.6 kV/cm with increasing annealing temperature from 600 to 700 °C. The PZT film emitters exhibited remarkable ferroelectric electron emission behaviors at the threshold voltage above 95 V. The film annealed at 700 °C showed a relatively lower threshold voltage and higher emission current, which is related to the improved ferroelectric and dielectric properties at higher annealing temperature. The highest emission current achieved in this work was around 25 mA at the trigger voltage of 160 V.     

Structural and electrical properties of Na0.5Bi4.0RE0.5Ti4O15 (RE=Tm,Yb and Lu) thin films

In the current study, a series of lanthanide ions, Tm, Yb and Lu, were used for doping at the Bi-site of the Aurivillius phase Na_0.5Bi_4.5Ti₄O₁₅ (NaBTi) to investigate the structural, electrical and ferroelectric properties of the thin films. In this regard, Na_0.5Bi_4.5Ti₄O₁₅ and the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5i₄O₁₅ (RE=Tm, Yb and Lu, denoted by NaBTmTi, NaBYbTi, and NaBLuTi, respectively) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. Formations of the Aurivillius phase orthorhombic structures for all the thin films were confirmed by X-ray diffraction and Raman spectroscopic studies. Based on the experimental results, the rare earth metal ion-doped Na_0.5Bi_4.0RE_0.5Ti₄O₁₅ thin films exhibited a low leakage current and the improved ferroelectric properties. Among the thin films, the NaBLuTi thin film exhibited a low leakage current density of 6.96×10⁻⁷ A/cm² at an applied electric field of 100 kV/cm and a large remnant polarization (2P_r) of 26.7 μC/cm² at an applied electric field of 475 kV/cm.     

Enhanced ferroelectric properties of 0.95Pb(Sc0.5Ta0.5)O3–0.05PbTiO3 thin films with Pb(Zr0.52,Ti0.48)O3 seed layer

0.95Pb(Sc_0.5Ta_0.5)O₃–0.05%PbTiO₃ (PSTT5) thin films with and without a Pb(Zr_0.52,Ti_0.48)O₃ (PZT52/48) seed layer were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrates by RF magnetron sputtering. X-ray diffraction patterns indicate that the PSTT5 film with a PZT52/48 seed layer exhibited nearly pure perovskite crystalline phase with highly (4 0 0)-preferred orientation. Piezoresponse force microscopy observations reveal that a large out-of-plane spontaneous polarization exists in the highly (4 0 0)-oriented PSTT5 thin film. The PSTT5/PZT(52/48) possesses good ferroelectric properties with large remnant polarization P_r (12 μC/cm²) and low coercive field E_c (110 kV/cm). Moreover, The perfect butterfly-shaped capacitance–voltage characteristic curve and the relative dielectric constant as high as 733 is obtained in this PSTT5 thin film at 100 kHz.     

Effects of Ta-substitution on the dielectric properties of Ba6Ti2(Nb1−xTax)8O30 thin films

Tunable Ba₆Ti₂(Nb_1−xTa_x)₈O₃₀ (BTN-xTa; x = 0, 0.25, 0.4) thin films with a tetragonal tungsten bronze structure (TTB) were deposited on platinized Si substrates using the pulsed laser deposition (PLD) technique and their properties were investigated from the viewpoint of orientation and ferroelectric phase transition. Crystal structures and dielectric properties were characterized using an X-ray diffractometer and an impedance analyzer. Pure BTN (BTN-0Ta) thin films showed tunability as high as 60% and the tunability decreased as the amounts of Ta-substitution increased at 150 kV/cm and at 1 MHz. The dielectric constants also decreased from 436 to 88 at 1 MHz through the Ta-substitution. The low tunability and dielectric constants of Ta-substituted thin films were mainly ascribed to the lowered ferroelectric transition temperature (T_c). Ferroelectric BTN (BTN-0Ta) thin films may have been changed into a paraelectric state through the Ta-substitution since the T_c of BTN thin films were shifted to temperatures far below room temperatures (approximately −60 °C).     

Dielectric and optical properties of electroceramic PBZNZT thin films prepared by pulsed laser deposition process

The 0.6[0.94Pb(Zn_1/3Nb_2/3)O₃ + 0.06BaTiO₃] + 0.4[0.48(PbZrO₃) + 0.52(PbTiO₃)], PBZNZT, thin films were synthesized by pulsed laser deposition (PLD) process. The PBZNZT films possess higher insulating characteristics than the PZT (or PLZT) series materials due to the suppressed formation of defects, therefore, thin-film forms of these materials are expected to exhibit superior ferroelectric properties as compared with the PZT (or PLZT)-series thin films. Moreover, the Ba(Mg_1/3Ta_2/3)O₃ thin film of perovskite structure was used as buffer layer to reduce the substrate temperature necessary for growing the perovskite phase PBZNZT thin films. The PBZNZT thin films of good ferroelectric and dielectric properties (remanent polarization P_r = 26.0 μC/cm², coercive field E_c = 399 kV/cm, dielectric constant K = 737) were achieved by PLD at 400 °C. Such a low substrate temperature technique makes this process compatible with silicon device process. Moreover, thus obtained PBZNZT thin films also possess good optical properties (about 75% transmittance at 800 nm). These results imply that PBZNZT thin films have potential in photonic device applications.     

Lead zirconium titanate thin films prepared by thermal annealing of multilayer structures composed of PbO,ZrO2 and TiO2

Lead zirconium titanate [Pb(Zr_xTi_1?x)O₃ or PZT] thin films were prepared by the thermal annealing of multilayer films composed of binary oxide layers of PbO, ZrO₂ and TiO₂. The binary oxides were deposited by metal organic chemical vapor deposition. An interdiffusion reaction for perovskite PZT thin films was initiated at approximately 550 °C and nearly completed at 750 °C for 1 h under O₂ annealing atmosphere. The composition of Pb/Zr/Ti in perovskite PZT could be controlled by the thickness ratio of PbO/ZrO₂/TiO₂ where the contribution of each binary oxide at the same thickness was 1:0.55:0.94. The electrical properties of PZT (Zr/Ti = 40/60, 300 nm) prepared on a Pt-coated substrate included a dielectric constant ?_r of 475, a coercive field E_c of 320 kV/cm, and remnant polarization P_r of 11 μC/cm² at an applied voltage of 18 V.     

Light controlled resistive switching and photovoltaic effects in ferroelectric 0.5Ba(Zr0.2Ti0.8)O3-0.5(Ba0.7Ca0.3)TiO3 thin films

In this work, the structural and ferroelectric properties of 0.5Ba(Zr_0.2Ti_0.8)O₃-0.5(Ba_0.7Ca_0.3)TiO₃ (0.5BZT-0.5BCT) thin films deposited at different pulse repetition rates were studied. The films deposited at pulse repetition rate of 1 Hz display the optimum values of ferroelectric polarization and dielectric permittivity and are chosen for the investigation of resistive switching and photovoltaic studies. The Pt/0.5BZT-0.5BCT/ITO capacitors show the electroforming free resistive switching (RS) and is explained based on the polarization modulation of the Schottky barrier at the 0.5BZT-0.5BCT/ITO interface. Furthermore, it is shown that the RS ratio and switching voltage can be tuned with white light illumination. The capacitors display photovoltaic effect with the open circuit voltage ≈0.8 V and the short circuit current density ≈72.6 μAcm⁻². The photovoltaic efficiency is found to be ≈0.010% and is greater than that of other perovskite ferroelectric thin films. The underlying mechanism for enhanced RS and photovoltaic effects is highlighted.     

Structural,dielectric and piezoelectric properties of (Bi0.5Na0.5)TiO3–(Bi0.5K0.5)TiO3–Bi(Zn0.5Ti0.5)O3 thin films prepared by sol–gel method

Lead free (1−x)(0.8Bi_0.5Na_0.5Ti_0.5O₃–0.2Bi_0.5K_0.5TiO₃)–xBiZn_0.5Ti_0.5O₃ (x=0–0.06) (BNT–BKT–BZT) thin films were deposited on Pt(111)/Ti/SiO₂/Si(100) substrates by a sol–gel processing technique. The effects of BZT content on the structural, dielectric, ferroelectric and piezoelectric properties of the BNT–BKT–BZT thin films were investigated systematically. The BNT–BKT–BZT thin films undergo a transition from ferroelectric to relaxor phase with increasing temperature. The phase transition temperature decreases with the increase of BZT content. The BNT–BKT–BZT thin film with x=0.04 exhibits the best ferroelectric properties (P_max=40 µC/cm² and P_r=10 µC/cm²), largest dielectric constant (ε=560) and piezoelectric constant (d₃₃=40 pm/V). This finding demonstrates that the BNT–BKT–BZT thin film has an excellent potential for demanding high piezoelectric properties in lead free films.     

Pulsed laser deposition BTS thin films: The role of substrate temperature

BaSn_0.15Ti_0.85O₃ (BTS) thin films were deposited on Pt/Ti/SiO₂/Si(1 0 0) substrate by pulsed laser deposition and the effects of substrate temperature on their structure, dielectric properties and leakage current density were investigated. The results indicate that the substrate temperature has a significant effect on the structural and dielectric properties of the BTS thin films which exhibit a polycrystalline perovskite structure if the substrate temperature ranges within 550–750 °C. The dielectric constant and loss tangent of the BTS thin films deposited at 650 °C are 341 and 0.009 at 1 MHz, respectively, the tunability is 72.1% at a dc bias field of 400 kV/cm, while the largest figure of merit (FOM) is 81.1. The effect of the substrate temperature on the leakage current of the BTS thin films is discussed.     

Optical scattering of nanocrystalline Pb(ZrxTi1−x)O3 films

Optical characterization methods, like spectrophotometry at UV–vis-NIR wavelengths and prism-coupler method, were applied to polycrystalline Pb(Zr_xTi_1?x)O₃ thin films at various thicknesses. Thin films were deposited at room temperature by pulsed laser deposition on MgO (1 0 0) substrates and post-annealed at different temperatures. X-ray diffraction and atomic force microscopy were used to characterize the crystal structure and surface morphology of the thin films, respectively.Well oscillating transmission with a sharp fall near the absorption edge was found in films with high orientation and low surface roughness. Changes in the surface morphology and crystal orientation were found to modulate optical interference maxima and minima of the transmittance spectra and to increase the width of the TE₀ mode (Δβ ≈ 0.06) indicating an increase in the scattering losses of the films. Single-phase oriented films had sharpest coupling values (Δβ ≈ 0.005) of the TE₀ mode.     

The microstructure,ferroelectric and dielectric behaviors of BiFeO3-Na0.5Bi0.5TiO3 based solid solution thin films

BiFe_0.98Zn_0.02O₃-Na_0.5Bi_0.5Ti_0.98W_0.02O₃ solid solution thin films with two thicknesses (300 nm and 1.2 μm) were fabricated on indium tin oxide/glass substrates via metal organic decomposition. The effects of the thickness on crystallization, microstructure morphology, ferroelectric and dielectric properties were investigated. Compared with the 300-nm-thick film, 1.2 μm- film exhibits standard ferroelectric hysteresis loop with slim feature and larger dielectric constant due to the improvements of crystallinity and insulating property. Moreover, obvious aging behavior, manifested by pinched-like ferroelectric hysteresis loop and abnormal butterfly dielectric constant-electric field curve, can be observed in the film with 1.2 μm thickness. The aging behavior can be explained by the formation of the defect complex.     

Electrical properties of chemical solution deposited (Bi0.9RE0.1)(Fe0.975Cu0.025)O3−δ (RE=Ho and Tb) thin films

Pure BiFeO₃ (BFO) and (Bi_0.9RE_0.1)(Fe_0.975Cu_0.025)O_3?δ (RE=Ho and Tb, denoted by BHFCu and BTFCu) thin films were prepared on Pt(111)/Ti/SiO₂/Si(100) substrates by using a chemical solution deposition method. The BHFCu and BTFCu thin films showed improved electrical and ferroelectric properties compared to pure BFO thin film. Among them, the BTFCu thin film exhibited large remnant polarization (2P_r), low coercive field (2E_c) and reduced leakage current density, which are 89.15 C/cm² and 345 kV/cm at 1000 kV/cm and 5.38×10^?5 A/cm² at 100 kV/cm, respectively.     

Impact of Sr-doping on structural and electrical properties of Pb(Zr0.52Ti0.48)O3 thin films on RuO2 electrodes

In this paper, we investigated the impact of Sr-doping on the structural properties and electrical characteristics of lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films deposited on RuO₂ electrodes by a sol-gel process and spin-coating technique. We used X-ray diffraction, atomic force microscopy, X-ray photoelectron spectroscopy, and field-emission transmission electron microscopy to explore the structural, morphological, chemical, and microstructural features, respectively, of these films as a function of the growth condition (strontium doping concentrations varied from 1, 3, and 5 mol%). The PZT thin film processed at the 3 mol% Sr exhibited the best electrical characteristics, including a low leakage current of 2.27×10⁻⁷ A/cm² at an electric field of 50 kV/cm, a large capacitance value of 2.74 μF/cm² at a frequency of 10 kHz, and a high remanent polarization of 37.95 μC/cm² at a frequency of 5 kHz. We attribute this behavior to the optimal amount of strontium in the PZT film forming a perovskite structure and a thicker interfacial layer at the PSZT film-RuO₂ electrode interface.     

Structural,electrical and optical properties of molybdenum-doped TiO2 thin films

Molybdenum doped TiO₂ (MTO) thin films were prepared by radio frequency (RF) magnetron sputtering at room temperature and followed by a heat treatment in a reductive atmosphere containing 90% N₂ and 10% H₂. XRD and FESEM were employed to evaluate the microstructure of the MTO films, revealing that the addition of molybdenum enhances the crystallization and increases the grain size of TiO₂ films. The optimal electrical properties of the MTO films were obtained with 3 wt% Mo doping, producing a resistivity of 1.1×10^?3 Ω cm, a carrier density of 9.7×10²⁰ cm^?3 and a mobility of 5.9 cm²/Vs. The refractive index and extinction coefficient of MTO films were also measured as a function of film porosity. The optical band gap of the MTO films ranged from 3.28 to 3.36 eV, which is greater than that of the un-doped TiO₂ film. This blue shift of approximately 0.14 eV was attributed to the Burstein–Moss effect.     

Fabrication and characterization of intergrown Bi4Ti3O12-based thin films using a metal-organic precursor solution

Ferroelectric intergrowth-structured Bi₄Ti₃O₁₂-based thin films have been fabricated by chemical solution deposition. Bi₄Ti₃O₁₂–SrBi₄Ti₄O₁₅ (BiT–SBTi) and SrBi₂Nb₂O₉–Bi₄Ti₃O₁₂ (SBN–BiT) precursor films crystallized in the desired intergrown BiT–SBTi and SBN–BiT structures on Pt/TiO_x/SiO₂/Si substrates by optimizing the processing conditions. Synthesized BiT–SBTi and SBN–BiT thin films exhibited ferroelectric P–E hysteresis loops. The BiT–SBTi thin films crystallized at 750 °C showed a 2P_r value approximately 20 μC/cm². Although a little smaller P_r value was observed for the SBN–BiT thin films, the squareness of a P–E hysteresis loop was superior to that of BiT–SBTi thin films. Also, the SBN–BiT thin films had a smoother surface morphology compared with BiT–SBTi thin films.     

Low voltage resistive memory devices based on graphene oxide–iron oxide hybrid

Low cost resistive switching memory devices using graphene oxide–iron oxide (GF) hybrid thin films, sandwiched between platinum (Pt) and indium-tin-oxide (ITO) electrodes, were demonstrated. The fabricated devices with Pt/GF/ITO structure exhibited reliable and reproducible bipolar resistive switching performance, with an ON/OFF current ratio of 5 × 10³, excellent retention time longer than 10⁵ s, SET voltage of 0.9 V, and good endurance properties. In all aspects of the device characteristics, the GF based devices outperformed graphene oxide (GO) based devices. Ohmic conduction was found to be dominant current conduction mechanism in all switching regions except for the high voltage regime where space charge limited conduction and trap charge limited conduction were found to be the main current conduction mechanism. X-ray photoelectron spectroscopy and transmission electron microscopy/selected area diffraction analysis revealed γ-Fe₂O₃ and Fe₃O₄ iron oxide phases coexist in the hybrid films. While the desorption/adsorption of oxygen-related functional groups on the GO sheets is the dominant resistive switching mechanism in Pt/GO/ITO devices, the formation/rupture of multiple highly conducting Fe₃O₄ filaments at the iron oxide/GO interface additionally facilitate the switching in the present Pt/GF/ITO devices. Thereby, excellent electrical switching performance was achieved.     

Ferroelectric properties of Pb(Zr0.52Ti0.48)O3–Bi3.25La0.75Ti3O12 ceramics

The ceramic samples of compound (1 ? x)Pb(Zr_0.52Ti_0.48)O₃–xBi_3.25La_0.75Ti₃O₁₂ (when x = 0, 0.03, 0.05, 0.07, 0.10, 0.15 and 0.20) were prepared by a solid-state mixed oxide method. X-ray diffraction analysis showed that complete solid solutions occurred for all compositions. Perovskite phase with tetragonal crystal structure and corresponding lattice distortion was observed. Scanning electron micrographs of sample surfaces showed equiaxed grains for all compositions. Ferroelectric measurements revealed that the addition of small amount of BLT (x = 0.03) showed high remanent polarization (～33.5 μC cm^?2) and low coercive field (～2.74 kV mm^?1). Further increasing BLT content could maintain ferroelectric properties of PZT–BLT ceramics. Based on this study, ferroelectric properties of this PZT–BLT ceramic system can be improved for being further used in ferroelectric memory applications.