Fabrication of robust Bi3.25La0.75Ti3O12 thin film resistant to hydrogen damage

Ferroelectric bismuth lanthanum titanate (Bi_3.25La_0.75Ti₃O₁₂; BLT) thin films were deposited on Pt/TiO₂/SiO₂/Si substrate by chemical solution deposition method. The films were crystallized in the temperature range of 600–700 °C. The spontaneous polarization (P_s) and the switching polarization (2P_r) of BLT film annealed at 700 °C for 30 min were 22.6 μC/cm² and 29.1 μC/cm², respectively. Moreover, the BLT capacitor did not show any significant reduction of hysteresis for 90 min at 300 °C in the forming gas atmosphere.     

Improved fatigue properties of lead zirconate titanate films made on oxygen-implanted platinum electrodes

Pb(Zr_0.3Ti_0.7)O₃ (PZT) thin film capacitors fabricated on an oxygen-implanted Pt bottom electrode were studied. Oxygen was implanted at a low acceleration voltage (40 kV) and dose (1×10¹⁵ cm⁻²). Structural examination by grazing-incident X-ray diffraction (GIXD) and chemical analysis by X-ray photoelectron spectroscopy (XPS) revealed that the implantation generated a very thin amorphous top surface layer (approx. 20 nm), which contained approximately 7% of oxygen that stayed in the film in the form of PtO bonding. The amorphous layer, however, resumed the crystalline structure accompanied by the dissociation of PtO under the rapid thermal annealing at 600 °C for 5 min. The remnant polarization of sol–gel derived Pb(Zr_0.3Ti_0.7)O₃ (PZT) films fabricated on the oxygen-implanted Pt was slightly reduced from 11.92 μC/cm² for the PZT capacitors fabricated on a Pt electrode without implanted oxygen to 9.07 μC/cm². Nevertheless, the fatigue endurance was significantly increased. The switching polarization of PtO_x/PZT/Pt (O-implanted) capacitors remained within 95% of the starting value after 4×10¹⁰ switching cycles, which is comparable to that of PZT capacitors made with other conducting oxides.     

Structure and electrical properties of (100)-oriented Pb(Zn1/3Nb2/3)O3–Pb(Mg1/3Nb2/3)O3–PbTiO3 thin films on La0.7Sr0.3MnO3 electrode by chemical solution deposition

(100)-oriented 0.462Pb(Zn_1/3Nb_2/3)O₃–0.308Pb(Mg_1/3Nb_2/3)O₃–0.23PbTiO₃ (PZN-PMN-PT) perovskite ferroelectric thin films were prepared on La_0.7Sr_0.3MnO₃/LaAlO₃ (LSMO/LAO) substrate via a chemical solution deposition route. The perovskite LSMO electrode was found to effectively suppress the pyrochlore phase while promote the growth of the perovskite phase in the PZN-PMN-PT film. The film annealed at 700 °C exhibited a high dielectric constant of 2130 at 1 kHz, a remnant polarization, 2P_r, of 29.8 μC/cm², and a low leakage current density of 7.2 × 10^− 7 A/cm² at an applied field of 200 kV/cm. The ferroelectric polarization was fatigue-free at least up to 10¹⁰ cycles. Piezoelectric coefficient, d₃₃, of 48 pm/V was also demonstrated. The results showed that much superior properties could be achieved with the PZN-PMN-PT thin films on the solution derived LSMO electrode than on Pt electrode by sputtering.     

Effect of the microwave oven on structural, morphological and electrical properties of SrBi4Ti4O15 thin films grown on Pt/Ti/SiO2/Si substrates by a soft chemical method

Thin films of SrBi₄Ti₄O₁₅ (SBTi), a prototype of the Bi-layered-ferroelectric oxide family, were obtained by a soft chemical method and crystallized in a domestic microwave oven. For comparison, films were also crystallized in a conventional method at 700 °C for 2 h. Structural and morphological characterization of the SBTi thin films were investigated by X-ray diffraction (XRD) and atomic force microscopy (AFM), respectively. Using platinum coated silicon substrates, the ferroelectric properties of the films were determined. Remanent polarization P_r and a coercive field E_c values of 5.1 μC/cm² and 135 kV/cm for the film thermally treated in the microwave oven and 5.4 μC/cm² and 85 kV/cm for the film thermally treated in conventional furnace were found. The films thermally treated in the conventional furnace exhibited excellent fatigue-free characteristics up to 10¹⁰ switching cycles indicating that SBTi thin films are a promising material for use in non-volatile memories.     

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

We report on the properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi₂Ta₂O₉. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi₃TaTiO₉ content in the solid solution. Ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films were significantly improved compared to SrBi₂Ta₂O₉. For example, the observed remanent polarization (2P_r) and coercive field (E_c) values for films with 0.7SrBi₂Ta₂O₉–0.3Bi₃TaTiO₉ composition, annealed at 650°C, were 12.4 μC/cm² and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 10¹⁰ switching cycles and good memory retention characteristics after about 10⁶ s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi₂Ta₂O₉–xBi₃TaTiO₉ thin films compared to SrBi₂Ta₂O₉, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.     

Enhanced ferroelectric properties of multilayer SrBi2Ta2O9/SrBi2Nb2O9 thin films for NVRAM applications

Ferroelectric SrBi₂Ta₂O₉/SrBi₂Nb₂O₉ (SBT/SBN) multilayer thin films with various stacking periodicity were deposited on Pt/TiO₂/SiO₂/Si substrate by pulsed laser deposition technique. The X-ray diffraction patterns indicated that the perovskite phase was fully formed with polycrystalline structure in all the films. The Raman spectra showed the frequency of the O–Ta–O stretching mode for multilayer and single layer SrBi₂(Ta_0.5Nb_0.5)₂O₉ (SBNT) samples was 827–829 cm⁻¹, which was in between the stretching mode frequency in SBT (813 cm⁻¹) and SBN (834 cm⁻¹) thin films. The dielectric constant was increased from 300 (SBT) to 373 at 100 kHz in the double layer SBT/SBN sample with thickness of each layer being 200 nm. The remanent polarization (2P_r) for this film was obtained 41.7 μC/cm², which is much higher, compared to pure SBT film (19.2 μC/cm²). The coercive field of this double layer film (67 kV/cm) was found to be lower than SBN film (98 kV/cm).     

The effect of rapid thermal annealing on structural and electrical properties of TiB2 thin films

This work reports on the effect of post-deposition rapid thermal annealing on the structural and electrical properties of deposited TiB₂ thin films. The TiB₂ thin films, thicknesses from 9 to 450 nm, were deposited by e-beam evaporation on high resistivity and thermally oxidized silicon wafers. The resistivity of as-deposited films varied from 1820 μΩ cm for the thinnest film to 267 μΩ cm for thicknesses greater than 100 nm. In the thickness range from 100 to 450 nm, the resistivity of TiB₂ films has a constant value of 267 μΩ cm.

A rapid thermal annealing (RTA) technique has been used to reduce the resistivity of deposited films. During vacuum annealing at 7 × 10⁻³ Pa, the film resistivity decreases from 267 μΩ cm at 200 °C to 16 μΩ cm at 1200 °C. Heating cycles during RTA were a sequence of 10 s. According to scanning tunneling microscopy analysis, the decrease in resistivity may be attributed to a grain growth through polycrystalline recrystallization, as well as to an increase in film density.

The grain size and mean surface roughness of annealed films increase with annealing temperature. At the same time, the conductivity of the annealed samples increases linearly with grain size. The obtained results show that RTA technique has a great potential for low resistivity TiB₂ formation.     

Structural, electrical, and optical studies on rapid thermally processed ferroelectric BaTiO3 thin films prepared by metallo-organic solution deposition technique

Polycrystalline BaTiO₃ thin films having the perovskite structure were successfully produced on platinum coated silicon, bare silicon, and fused quartz substrate by the combination of the metallo-organic solution deposition technique and post-deposition rapid thermal annealing treatment. The films exhibited good structural, electrical, and optical properties. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) and metal-ferroelectric-semiconductor (MFS) capacitors. The typical measured small signal dielectric constant and dissipation factor at a frequency of 100 kHz were 255 and 0.025, respectively, and the remanent polarization and coercive field were 2.2 μC cm⁻² and 25 kV cm⁻¹, respectively. The resistivity was found to be in the range 10¹⁰–10¹² Ω·cm, up to an applied electric field of 100 kV cm⁻¹, for films annealed in the temperature range 550–700 °C. The films deposited on bare silicon substrates exhibited good film/substrate interface characteristics. The films deposited on fused quartz were highly transparent. An optical band gap of 3.5 eV and a refractive index of 2.05 (measured at 550 nm) was obtained for polycrystalline BaTiO₃ thin film on fused quartz substrate. The optical dispersion behavior of BaTiO₃ thin films was found to fit the Sellmeir dispersion formula well.     

Preparation, electrical and optical properties of (Pb,Ca)TiO3 thin films using a modified sol-gel technique

Calcium modified lead titanate sol was synthesized using lead acetate trihydrate, calcium nitrate tetrahydrate and titanium tetra-n-butoxide as starting materials, methanol and ethanolamine were selected as solvent and stabilizing or complexing agent, respectively. (Pb_0.76Ca_0.24)TiO₃ thin films were prepared on platinum-coated silicon and fused silica substrates with the solution using the spinning method. The surface morphology and crystal structure, surface compositions and chemical states, electrical and optical properties of the thin films were investigated. The films have good composition homogeneity and thickness uniformity. The dielectric constant and dissipation factor of 1 kHz at room temperature were found to be 280 and 0.027, respectively, for thin films with 0.5 μm thickness annealed at 600°C for 1 h. The remanent polarization and coervive field were 15 μC/cm² and 64 kV/cm, respectively. The thin films exhibited good optical transmissitivity, and had optical direct transitions. The dispersion relation of refractive index and wavelength followed the single electron oscillation model. The band gap of the film which annealed at 650°C was 3.68 eV. The results also confirmed that ethanolamine was very effective in preparing uniform and dense oxide films, owing to the superior stability of the sols during hydrolytic polycondensation.     

Ferroelectric properties of BiFeO3 films grown by sol–gel process

Several methods have been used to prepare ferroelectromagnetic BiFeO₃ films. In this paper, we adopted a sol–gel process to fabricate BiFeO₃ films on indium tin oxide (ITO)/glass substrates. X-ray diffraction pattern indicated that the samples are randomly oriented. Cross section scanning microscopy showed that the thicknesses of both films were about 1.2 μm and no apparent diffusion between the BiFeO₃ films and ITO/glass substrates. Remnant polarization of 2.0 and 1.75 μC/cm² were identified by the measuring of electric hysteresis loops for the films annealed at 500 and 600 °C respectively at an applied field of 108 kV/cm. Dielectric property and loss factor were investigated as a function of frequency. In addition, magnetism was detected at 77 K.     

Investigation of stress behaviors and mechanism of void formation in sputtered TiSix films

We have investigated the stress behaviors and a mechanism of void formation in TiSi_x films during annealing. TiSi_x thin films were prepared by DC magnetron sputtering using a TiSi_2.1 target in the substrate temperature range of 200–500 °C. The as-deposited TiSi_x films at low substrate temperature (<300 °C) have an amorphous structure with low stress of 1×10⁸ dynes/cm². When the substrate temperature increases to 500 °C, the as-deposited TiSi_x film has a mixture of C49 and C54 TiSi₂ phase with stress of 8×10⁹ dynes/cm². No void was observed in the as-deposited TiSi_x film. Amorphous TiSi_x film transforms to C54 TiSi₂ phase with a random orientation of (311) and (040) after annealing at 750 °C. The C49 and C54 TiSi₂ mixture phase transforms to (040) preferred C54 TiSi₂ phase after annealing over 650 °C. By increasing substrate temperature, the transformation temperature for C54 TiSi₂ can be reduced, resulting in relieved stress of TiSi₂ film. The easy nucleation of the C54 phase was attributed to an avoidance of amorphous TiSi_x phase. We found that amorphous TiSi_x→C54 TiSi₂ transformation caused higher tensile stress of 2×10¹⁰ dynes/cm², resulting in more voids in the films, than C49→C54 transformation. It was observed that void formation was increased with thermal treatment. The high tensile stress caused by volume decreases in the silicide must be relieved to retard voids and cracks during C54 TiSi₂ formation.     

Semiconducting and structural properties of CrSi2 A-type epitaxial films on Si(111)

Chromium disilicide (CrSi₂) films 1 000 Å thick have been prepared by molecular beam epitaxy on CrSi₂ templates grown on Si(111) substrate. The effect of the substrate temperature on the structural, electrical and optical properties of CrSi₂ films has been studied by transmission and scanning electron microscopies, optical microscopy, electrical resistivity and Hall effect measurements and infrared optical spectrometry. The optimal temperature for the formation of the epitaxial A-type CrSi₂ film have been found to be about 750°C. The electrical measurement have shown that the epitaxial A-type CrSi₂ film is p-type semiconductor having a hole concentration of 1 × 10¹⁷cm⁻³ and Hall mobility of 2 980 cm² V⁻¹ s⁻¹ at room temperature. Optical absorption coefficient data have indicated a minimum, direct energy gap of 0.34 eV. The temperature dependence of the Hall mobility (μ) in the temperature range of T = 180–500 K can be expressed as μ = 7.8 × 10¹⁰T⁻³cm²V⁻¹s⁻¹.     

Highly conducting indium tin oxide (ITO) thin films deposited by pulsed laser ablation

Highly conducting and transparent indium tin oxide (ITO) thin films were prepared on SiO₂ glass and silicon substrates by pulsed laser ablation (PLA) from a 90 wt.% In₂O₃-10 wt.% SnO₂ sintered ceramic target. The growths of ITO films under different oxygen pressures (P_O2) ranging from 1×10⁻⁴–5×10⁻² Torr at low substrate temperatures (T_s) between room temperature (RT) and 200°C were investigated. The opto-electrical properties of the films were found to be strongly dependent on the P_O2 during the film deposition. Under a P_O2 of 1×10⁻² Torr, ITO films with low resistivity of 5.35×10⁻⁴ and 1.75×10⁻⁴ Ω cm were obtained at RT (25°C) and 200°C, respectively. The films exhibited high carrier density and reasonably high Hall mobility at the optimal P_O2 region of 1×10⁻² to 1.5×10⁻² Torr. Optical transmittance in excess of 87% in the visible region of the solar spectrum was displayed by the films deposited at Po₂≥1×10⁻² Torr and it was significantly reduced as the P_O2 decreases.     

Preparation of highly c-axis-oriented Bi4Ti3O12 thin films and their crystallographic, dielectric and optical properties

Bismuth titanate (Bi₄Ti₃O₁₂) thin films with a high c-axis orientation up to 99% were prepared on (100)-oriented silicon wafers by r.f. planar magnetron sputtering using a Bi₂TiO₅ ceramic target at a substrate temperature of 600 °C. From the Auger electron spectroscopy depth profile of the film, there is no evidence of interdiffusion of a specific element between the film and the substrate. Relative dielectric constant of these films depends on film thickness. The behavior was explained assuming a low-dielectric-constant interface layer. Using this assumption, the relative dielectric constant of Bi₄Ti₃O₁₂ film was estimated to be approximately 140. This value is close to that along the c axis in a bulk form. The remanent polarization and the coercive field were 0.8 μC cm⁻² and 20 kV cm⁻¹, respectively.     

Electrical properties of sol-gel processed barium titanate films

The sol-gel technique has been used to prepare ferroelectric barium titanate (BaTiO₃) films. The electrical properties of the films have been investigated systematically. The room temperature dielectric constant (ε) and loss tangent (tanδ) at 1 kHz were respectively found to be 370 and 0.012. Both ε and tanδ showed anomaly peaks at 125°C. The room temperature remanant polarization (P_r) and coercive field (E_c) were found to be 3.2 μC/cm² and 30 kV/cm, respectively. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics also showed hysteresis effect. The temperature variation of C–V and G–V characteristics also confirms the ferroelectric to paraelectric phase transition at 125°C.     

Effect of deposition temperature on the structural and thermoelectric properties of bismuth telluride thin films grown by co-sputtering

Thermoelectric bismuth telluride thin films were prepared on SiO₂/Si substrates by radio-frequency (RF) magnetron sputtering. Co-sputtering method with Bi and Te targets was adopted to control films' composition. Bi_xTe_y thin films were elaborated at various deposition temperatures with fixed RF powers, which yielded the stoichiometric Bi₂Te₃ film deposition without intentional substrate heating. The effects of deposition temperature on surface morphology, crystallinity and electrical transport properties were investigated. Hexagonal crystallites were clearly visible at the surface of films deposited above 290 °C. Change of dominant phase from rhombohedral Bi₂Te₃ to hexagonal BiTe was confirmed with X-ray diffraction analyses. Seebeck coefficients of all samples have negative value, indicating the prepared Bi_xTe_y films are n-type conduction. Optimum of Seebeck coefficient and power factor were obtained at the deposition temperature of 225 °C (about − 55 μV/K and 3 × 10^− 4 W/K²·m, respectively). Deterioration of thermoelectric properties at higher temperature could be explained with Te deficiency and resultant BiTe phase evolution due to the evaporation of Te elements from the film surface.     

Growth of lithium doped silver niobate single crystals and their piezoelectric properties

Lithium doped silver niobate (Ag_1−xLi_xNbO₃, 0 < x < 0.1) is one of the candidate materials for lead-free piezoelectric materials. In this study, Ag_1−xLi_xNbO₃ single crystals were successfully grown by a slow cooling method. Crystal structure was assigned to perovskite-type orthorhombic (monoclinic) phase. Dielectric properties were measured as a function of temperature. As a result, with increasing lithium contents, the phase transition at around 60 °C was shifted to lower temperature while the phase transition at around 400 °C was shifted to higher temperature. On the basis of these peak shifts, the lithium contents in Ag_1−xLi_xNbO₃ single crystals were determined. Moreover, P–E hysteresis measurement revealed that pure silver niobate crystal was weak ferroelectrics with P_r of 0.095 μC/cm² while Ag_0.9Li_0.1NbO₃ (ALN10) crystal was normal ferroelectrics with P_r of 10.68 μC/cm². About this ALN10 crystal, polling treatment was performed and finally piezoelectric properties were measured. As a result, high electromechanical coupling coefficient k₃₁ over 70% was observed.     

Ba(Zr0.15Ti0.85)O3厚膜的介电与铁电性能研究

本研究采用流延法制备Ba(Zr_0.15Ti_0.85)O₃(BZT)厚膜样品。采用扫描电子显微镜分析样品形貌; 采用LCR测试仪和Sawyer-Tower电路法测量样品的介电与铁电性能。结果表明, BZT厚膜具有明显的介电弛豫特征, 击穿电场强度可达60 kV/cm以上, 饱和极化强度可达58.1 μC/ cm², 剩余极化强度(Pr)为20.9 μC/ cm²。     

Influencing factors on the pyroelectric properties of Pb(Zr,Ti)O3 thin film for uncooled infrared detector

Zr-rich PZT thin films were synthesized by metallorganic decomposition and their dielectric and pyroelectric properties were investigated with different ratios of zirconium/titanium and poling condition. All the films became effectively (1 1 1) textured and well crystallized at the annealing temperature of 700 °C. With increasing Zr content, coercive field increased and voltage dependent capacitance curve appeared asymmetrical, indicating the presence of antiferroelectric phase, PbZrO₃, in film composition. The pyroelectric coefficient in the practically applicable temperature ranges of 20–60 °C was found to be maximum for the thin film with 0.85 mol of zirconium in PZT. Further increase in zirconium content led to severe deterioration in pyroelectric properties. The values of pyroelectric coefficient and figures of merit were greatly influenced by poling direction and temperature. The result was explained in terms of electric phase and state of polarization in film.