Effect of Sb2O3 addition on the varistor characteristics of ZnO-Bi2O3-ZrO2-MtrO (Mtr = Mn, Co)

Effect of Sb₂O₃ addition on the varistor characteristics of pyrochlore-free ZnO-Bi₂O₃-ZrO₂-M_trO (M_tr = Mn, Co) system previously proposed has been studied. With Sb₂O₃ up to 0.1 mol%, a gradual enhancement of densification and the grain growth inhibition were seen in the system sintered between 900 and 1200^∘C. In X-ray diffraction patterns, small amount of pyrochlore appeared in the specimens doped with Sb₂O₃ (>0.06 mol%), which is thought responsible for the sintering behavior. Enhanced values of non linear coefficient (α) were obtained in ZnO-Bi₂O₃-ZrO₂ (ZBZ) doped with 0.001 mol% Sb₂O₃, but was leveled off at higher concentrations. In ZBZ added with M_trO (M_tr = Mn, Co), significant increase of nonlinear coefficient (α > 30) along with low leakage current (I _L ≪ 100 μA/cm²) was attained. The α-enhancement effect of Sb₂O₃, however, was not observed in high-α ZBZ added with M_trO. As for degradation, addition of a trace amount (0.001 mol%) of Sb₂O₃ to ZBZM_tr was efficient, especially in I _L.     

Effects of Al2O3 on the piezoelectric properties of Pb(Mn1/3Nb2/3)O3-PbZrO3-PbTiO3 ceramics

Piezoelectric properties of Al₂O₃-doped Pb(Mn_1/3Nb_2/3)O₃-PbZrO₃-PbTiO₃ ceramics were investigated. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with Al₂O₃. The highest sintered density of 7.8 g/cm³ was obtained for 0.2 wt% Al₂O₃-doped specimen. Grain size increased by doping Al₂O₃ up to 0.3 wt%, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping Al₂O₃ up to 0.2 wt%, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in O^{2 −} ion sites and the substitution of Al³⁺ ions.     

Effects of molten salt synthesis (MSS) parameters on the morphology of Sr3Ti2O7 and SrTiO3 seed crystals

A two-step molten salt synthesis process was utilized to fabricate Sr₃Ti₂O₇ and SrTiO_3. High aspect ratio SrTiO₃ seed crystals were developed by optimizing processing conditions such as temperature, salt-to-oxide ratio, and flux type in a systematic fashion. Sr₃Ti₂O₇ seeds were synthesized at temperatures ranging from 1050–1350°C, using salt-to-oxide ratios of 3:1, 1:1, and 1:3, and various salt types, including NaCl, KCl, and a 1:1 combination of NaCl and KCl. Sr₃Ti₂O₇ seeds synthesized at 1250°C with a 1:1 salt-to-oxide ratio in 100% NaCl salt resulted in a majority of higher aspect ratio platelets and elongated platelets as opposed to lower aspect ratio cubic-like and tetragonal-like morphologies. The seeds were 10–40 μm in length with aspect ratios of highly elongated platelets as high as 25:1. A second MSS step was used to synthesize SrTiO₃ seeds of the proper composition by TiO₂ addition to the Sr₃Ti₂O₇ seeds and heat treatment at 1100°C. These studies showed that highly anisotropic SrTiO₃ seeds could be produced at 1250°C using a 1:1 salt-to-oxide ratio in 100% NaCl flux. XRD studies of the resulting SrTiO₃ seeds revealed that the increase in aspect ratio for these particular seeds also resulted in the enhancement of (200) peaks, which are of major interest for texturing of PMN-PT.     

Ferroelectric-Gate Field Effect Transistors Using (Y,Yb)MnO3/Y2O3/Si(111) Structures for 1T-Type FeRAMs

Fabrication and characterization of metal-ferroelectric-insulator-semiconductor field-effect-transistors (MFIS FETs) using (Y,Yb)MnO₃/Y₂O₃/Si structures were introduced for the first time. P-channel MFIS FETs were fabricated on n-type Si(111) substrates, in which an Y_0.5Yb_0.5MnO₃(200 nm)/Y₂O₃(25 nm) structure was used as gate insulator. The Y_0.5Yb_0.5MnO₃ and Y₂O₃ films were prepared by chemical solution deposition. A fabricated MFIS FETs showed the hysteresis loop due to spontaneous polarization in the I_D-V_GS characteristic, in which the memory window was about 0.9V when the applied gate voltage was swept between 8 V and ?8 V. Especially, the alternative drain current was retained after applying a single voltage pulse with a magnitude of +9 V or ?9 V.     

Ferroelectric Properties of (Bi, Sm)4Ti3O12 (BST) Thin Films Fabricated by a Metalorganic Solution Deposition Method

Ferroelectric properties of samarium substituted Bi₄Ti₃O₁₂ films, Bi_3.15Sm_0.85Ti₃O₁₂ (BST), were evaluated for use as lead-free thin film ferroelectrics for FeRAM applications. The BST films were fabricated on the Pt/Ti/SiO₂/Si(100) substrates by a metalorganic solution deposition method. The measured XRD patterns revealed that the BST films showed only a Bi₄Ti₃O₁₂-type phase with a random orientation. The BST film capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700C, 2P_r of 64.2 C/cm² and 2E_c of 101.7 kV/cm at applied electric field of 150 kV/cm were observed. The capacitor did not show any significant fatigue up to 1.5 × 10⁸ read/write switching cycles at a frequency of 1 MHz, which suggests that the samarium should be considered for a promising lanthanide elements to make a good thin ferroelectric film for memory applications.     

Pulsed Laser Deposited Ba(Mg1/3Ta2/3)O3 Microwave Dielectric Thin Films

Ba(Mg_1/3Ta_2/3)O₃ (BMT) microwave dielectric thin films were successfully synthesized by a modified pulsed laser deposition (PLD) process, which includes low temperature (200°C) deposition and high temperature (>500°C) annealing. Crystalline structured BMT thin films were obtained when the PLD-deposited films were post-annealed at a temperature higher than 500°C in oxygen atmosphere. The characteristics of BMT thin film, including crystallinity, grain size, film roughness, and dielectric properties were improved with annealing temperature, achieving dielectric constant K = 23.5 and dissipation factor tan δ = 0.015 (at 1 MHz) for the 800°C-annealed films.     

Growth and characterization of epitaxial SrBi2Ta2O9 films on (110) SrTiO3 substrates

Abstract

SrBi₂Ta₂O₉ (SBT) is an attractive material for nonvolatile ferroelectric memory applications. In this paper we report on the deposition of highly epitaxial and smooth SrBi₂Ta₂O₉ films on (110) SrTiO₃substrates. The films were grown by pulsed laser deposition at temperatures ranging from 600 to 800°C and at various laser fluences from a Bi-excess SBT target. The background oxygen pressure was maintained at 28 Pa during the film deposition. Structural characterization of the films was performed by x-ray diffraction. Atomic force microscopy was used to investigate morphology and growth of the films. The films grew with preferred (115) or (116) orientation. The roughness was of the order of unit cell height. The films display a growth pattern resulting in corrugated film morphology.     

Growth and characterization of non-c-axis-oriented SrBi2Ta2O9 epitaxial thin films on Si(100) substrates with SrRuO3 bottom electrodes

Abstract

We have successfully grown non-c-axis-oriented epitaxial ferroelectric SrBi₂Ta₂O₉ (SBT) films with (116) and (103) orientations on Si(100) substrates using epitaxial (110)- and (111)-oriented SrRuO₃ (SRO) bottom electrodes, respectively. The SRO orientations have been induced by coating the Si(100) substrates with epitaxial YSZ(100) and MgO(111)/ YSZ(100) buffer layers, respectively. All films were sequentially grown by pulsed laser deposition. Specific in-plane orientations of the epitaxial SBT films were found, which are in turn determined by specific in-plane orientations of the epitaxial SRO bottom electrodes. These include a diagonal rectangle-on-cube epitaxy of SRO(110) on YSZ(100) and a triangle-on-triangle epitaxy of SRO(111) on MgO(111).     

Influence of B2O3/SiO2 Ratio on the Fabrication of Nd:YAG Ceramics

B₂O₃/SiO₂ are used as composite sintering aids to fabricate Nd:YAG ceramics by solid-state reaction and vacuum sintering method at 1750°C for 5h using Nano-Al₂O₃, Y₂O₃, Nd₂O₃ as starting materials. In this article, we focus on the influence of B₂O₃/SiO₂ ratio on grain size, porosity and relative density. Finally, with the increase of B₂O₃/SiO₂ ratio, the density and shrinkage rate of transparent ceramics increase, the grain size becomes uniform and the porosity reduces, for the reason that B³⁺ begins to vaporize at 1300°C and is reduced to trace levels by 1600°C. The best B₂O₃/SiO₂ ratio is 4: 1.     

Crystal Growth and Dielectric Properties of New Ferroelectric Barium Titanate: BaTi2O5

Single crystals of the ferroelectric BaTi₂O₅ and BaTiO₃ were prepared from a solution of 33-mol% BaO and 67-mol% TiO₂ by a rapid cooling method. The dielectric constant () and dielectric loss tangent (tan) were measured in a wide temperature range of 10–860 K and in a frequency range of 0.1–3,000 kHz. The along the b-axis of the BaTi₂O₅ crystal, prepared in air, shows a sharp dielectric anomaly reaching 30,000 at the ferroelectric Curie temperature of T_C = 752 K. By contrast, the crystal prepared in a reducing atmosphere shows a diffuse phase transition near T_C = 703 K. The values of and tan are compared between these three crystals consisting of two kinds of BaTi₂O₅ and one BaTiO₃.     

Electrically tunable Ag(Ta,Nb)O3 thin film structures on oxide substrates

Abstract

We report on design, fabrication, and comparative test of three different types of voltage-variable interdigital capacitors made on ferroelectric Ag(Ta,Nb)O₃ films deposited on MgO and A1₂O₃ substrates. X-ray diffraction patterns show that ATN films pulsed laser deposited on MgO(001) and Al₂O₃(0112) single crystals have preferential (00/) and (0kk) orientation. Capacitance and loss tangent in interdigital capacitors were measured as the functions of frequency and applied dc voltage bias. Loss tangent was as low as 0.0025 and 0.0034 and AT-factor (tunability/tanδ) was around 26.2 and 20.0 for MgO and A1₂O₃, respectively, @ ± 40 V (maximum electric field 200 kV/cm), 300 K, and 1 MHz. Both of polarization and steady leakage currents were observed in the current-time domain measurements. 0.1 pF interdigital capacitors have pA leakage current level @ ± 40 V.     

Thermal and dielectric properties of ZnO-B2O3-MO3glasses (M = W, Mo)

Glasses in the ZnO-B₂O₃-MO₃(M = W, Mo) ternary were examined as potential replacements to PbO-B₂O₃-SiO₂-ZnO glass frits with the low firing temperature (500–600^∘C) for the dielectric layer of a plasma display panels (PDPs). Glasses were melted in air at 950–1150^∘C in a narrow region of the ternary using standard reagent grade materials. The glasses were evaluated for glass transition temperature (T _g ), softening temperature (T _d ), the coefficient of thermal expansion (CTE), dielectric constant (ε _r ), and optical property. The glass transition temperature of the glasses varied between 470 and 560^∘C. The coefficient of thermal expansion and the dielectric constant of the glasses were in the range of 5–8 × 10^{− 6}/^∘C and 8–10, respectively. The addition of MO₃to ZnO-B₂O₃binary could induce the expansion of glass forming region, the reduction of T _g and the increase in the CTE and the dielectric constant of the glasses. Also, the effect of the addition of MO₃to ZnO-B₂O₃binary on the transmittance in the visible-light region (350–700 nm) was investigated.     

Acid-catalysed Al2O3 sol and its gel material: influence of HNO3 content and stability

Abstract

A series of Al₂O₃ sols were prepared by HNO₃ catalysis of aluminum isopropoxide (AIP), using different molar ratios of HNO₃/AIP (n_H). The changes in sol densities, viscosities, refractive indices, stability and particle sizes were reported. Derived properties such as Gibbs energies (ΔG*) and the reaction rate constant (k) have been calculated from the experimental density and viscosity data. The phase-chemical structures of Al₂O₃ materials were characterized using Fourier transform infrared (FTIR) and X-ray diffraction (XRD) measurement. The results show that, when the molar ratio of HNO₃/AIP is 0.25, the prepared Al₂O₃ sol was transparent, uniform and stable, and the sol average particle size gets the minimum. The chemical structure of the non-calcined Al₂O₃ gel material is dominated by Al–O–H and Al–O bonds. After calcination at 350?°C, the Al–O–H bond will break and is transformed into Al–O bonds, and the phase structure is changed from γ-AlOOH to γ-Al₂O₃.     

Microwave dielectric properties of B2O3-added Li2MgTiO4 ceramics for LTCC applications

Li₂MgTiO₄ (LMT) ceramics which are synthesized using a conventional solid-state reaction route. The LMT ceramic sintered at 1250°C for 4 h had good microwave dielectric properties. However, this sintering temperature is too high to meet the requirement of low-temperature co-fired ceramics (LTCC). In this study, the effects of B₂O₃ additives and sintering temperature on the microstructure and microwave dielectric properties of LMT ceramics were investigated. The B₂O₃ additive forms a liquid phase during sintering, which decreases the sintering temperature from 1250°C to 925°C. The LMT ceramic with 8 wt% B₂O₃ sintered at 925°C for 4 h was found to exhibit optimum microwave dielectric properties: dielectric constant 15.16, quality factor 64,164 GHz, and temperature coefficient of resonant frequency -28.07 ppm/°C. Moreover, co-firing of the LMT ceramic with 8 wt% B₂O₃ and 20 wt% Ag powder demonstrated good chemical compatibility. Therefore, the LMT ceramics with 8 wt% B₂O₃ sintered at 925°C for 4 h is suitable for LTCC applications.     

Dielectric properties of Pb[(Mg1/3Nb2/3),Ti]O3 with Bi modification

Bi(Mg_2/3Nb_1/3)O₃ was partially substituted into a Pb(Mg_1/3Nb_2/3)O₃⋅PbTiO₃ perovskite system and resultant changes in the phase developments and dielectric properties were investigated. Two major structures of columbite and rutile, along with a small fraction of Mg₄Nb₂O₉ (α-Al₂O₃ structure), were developed in the B-site precursor system, whereas only a perovskite was observable after the addition of PbO and Bi₂O₃. The replacement of Bi for Pb resulted in a great reduction in the maximum dielectric constants as well as a substantial decrease in the dielectric maximum temperatures.     

Structural and Multiferroic Properties of Bi3.4La0.6Ti3O12/CoFe2O4 Composite Thin Films

Bi_3.4La_0.6Ti₃O₁₂ and CoFe₂O₄ were synthesized by chemical solution route, and Bi_3.4La_0.6Ti₃O₁₂/CoFe₂O₄ multilayers were deposited by spin coating on Pt substrate. X-ray diffraction of multilayer structures reveals composite-like polycrystalline film. Leakage current is less than 10^?5 A at electric field < 90 KV/cm and follows the Ohmic behavior. Dielectric response shows relaxation and the loss (tan δ) is below 3% at 10⁶ Hz. Room temperature ferrroelectric polarization (P_r) = 20.2 μC/cm² and ferromagnetic memory (M_r) = 46.5 emu/cm³ has been obtained. Co-existence of FE and FM response can be attributed to stress and different permeability and permittivity involved in multilayer structures.     

Phase Formations and Electrical Properties of Various (Bi, La)4Ti3O12 Thin Films by Chemical Solution Deposition

The phase formation and electrical properties of (Bi, La)₄Ti₃O₁₂ (BLT) thin film and V-, Sm-doped BLT thin films prepared by the chemical solution deposition method on Pt/TiO₂/SiO₂/Si substrates have been investigated. It was observed that the microstructure and electrical properties of BLT thin films dramatically varied with V- and Sm-doping. The crystallinity and grain size of BLT thin films were definitely increased by V- and Sm-doping into BLT films, which resulted in the enhancement of remanent polarization in doped BLT films. The remanent polarization (Pr) of Sm-doped BLT films annealed for 3 min by an RTA system was about 9 C/cm². The V- and Sm-doped BLT films also exhibited good fatigue characteristics under bipolar stressing to 10¹⁰ cycles.     

Laser ablation preparation and property of bismuth-layer-structured SrBi2Ta2Ta2O9 and Bi4Ti3O12 ferroelectric thin films

Abstract

Bismuth-layer-structured ferroelectric thin films, SrBi₂Ta₂O₉ and Bi₄Ti₃O₁₂, have been prepared by laser ablation method on both Pt sheets and Si wafers at low temperatures of 400 ～ 500°C. These thin films have been characterized by XRD, XPS, AFM, C-V, D-E hysteresis and J-V measurement. SrBi₂Ta₂O₉ thin films have a good (105) preferential orientation, and Bi₄Ti₃O₁₂ thin films have (117) and c-axis orientation on these substrates. Ferroelectric film-SiO₂-Si structures show good C-V hysteresis curve owing to Si surface potential controlled by the D-E hysteresis. D-E hysteresis is obtained in Bi₄Ti₃O₁₂ thin film prepared on Pt sheet, and the remnant polarization and the coercive force are 7.5 μC/cm² and 72 kV/cm, respectively.     

Electrical properties of Ga2O3-based dielectric thin films prepared by plasma enhanced atomic layer deposition (PEALD)

Ga₂O₃ and Ga₂O₃-TiO₂ (GTO) nano-mixed thin films were prepared by plasma enhanced atomic layer deposition with an alternating supply of reactant sources, [(CH₃)₂GaNH₂]₃, Ti(N(CH₃)₂)₄ and oxygen plasma. The uniform and smooth Ga₂O₃ and GTO thin films were successfully deposited. Excellent step coverage of these films was obtained by chemisorbed chemical reactions with oxygen plasma on the surface. The dielectric constant of GTO thin film definitely increased compared to Ga₂O₃ film, and the leakage currents of GTO films were comparable to Ga₂O₃ films. The leakage current density of a 40-nm-GTO film annealed at 600^∘C was approximately 1×10⁻⁷ A/cm² up to about 600 kV/cm.     

Integration of H2 barriers for ferroelectric memories based on SrBi2Ta2O9 (SBT)

Abstract

In this study, integration of an hydrogen barrier into a FeRAM process flow is investigated. It is reported in the literature that ferroelectric properties can be maintained after hydrogen annealing by using IrO_x as a top electrode [16][17][18]. Advantage of materials like IrO_x is less catalytic activity compared to Pt. However, we found that IrO_x is not a promising candidate for top electrode barrier. (Pt)/IrO_x/SBT/Pt capacitors are prone to shorting or exhibit high leakage. IrO_x films are very easily reduced by reducing ambient which will result in peeling off. Also, IrO_x films tend to oxidize Ti or TiN layers immediately. Therefore, other barrier materials or layer sequences like Ir/IrO_x have to be considered.

For protection of the entire capacitor an Encapsulation Barrier Layer (EBL) is required. In this study, LPCVD SiN is used. LPCVD SiN is a standard material in CMOS technology. Production tools are available and it is well known as hydrogen barrier. By modifying the deposition process and using a novel process sequence, no visual damage of the capacitors after SiN-deposition and FGA is seen. Also, no degradation of electrical properties after capacitor formation as well as after SiN-deposition and FGA is observed. However, after metal 1 and metal 2 processing, 2P_r values at 1.8V are reduced from 12μC/cm²to 2μC/cm². Polarization at 5.0V is not affected.