Ferroelectric properties of Bi<Subscript>4</Subscript>Zr<Subscript>0.5</Subscript>Ti<Subscript>2.5</Subscript>O<Subscript>12</Subscript> thin films prepared on LaNiO<Subscript>3</Subscript> bottom electrode by sol-gel method

The Bi4Zr0.5Ti2.5O12 (BZT) thin films were fabricated on the LaNiO3 bottom electrode using sol-gel method. The structure and morphology of the films were characterized using X-ray diffraction, AFM and SEM. The results show that the films have a perovskite phase and dense microstructure. The 2Pr and 2Vc of the Pt/BZT/LaNiO3 capacitor are 28.2 μC/cm2 and 14.7 V respectively at an applied voltage of 25 V. After the switching of 1×1010 cycles, the Pr value decreases to 87% of its pre-fatigue values. The dielectric constant (ε) and the dissipation factor (tanδ) of the BZT thin films are about 204 and 0.029 at 1 kHz, respectively. The films show good insulating behavior according to the test of leakage current. The clockwise C-V hysteresis curve observed shows that the Pt/BZT/LaNiO3 structure has a memory effect because of the BZT film's ferroelectric polarization.     

Crystallization and Electrical Properties of （Ba0.4Pb0.3）Sr0.3TiO3 Thin Film by Pulsed Laser Deposition

（Ba0.4Pb0.3）Sr0.3TiO3 thin films were fabricated via pulsed laser deposition （PLD） technique on Pt/TiO2/SiO2/Si substrate. The crystallization of the films was characterized by XRD and FSEM, and the experimental results suggested deposition parameters, especially the deposition temperature was the key factor in forming the perovskite structure. The dielectric properties of the film deposited with optimized parameters were studied by an Agilent 4294A impedance analyzer at 1 MHz. The dielectric constant was 772, and the loss tangent was 0.006. In addition, the well-shaped hysteresis loop also showed that the film had a well performance in ferroelectric. The saturated polarization P, remnant polarization Pr and coercive field E were about 4.6 μC/cm2, 2.5 μC/cm2 and 23 kV/cm （the coercive voltage is 0.7 V）, respectively. It is suggested the film should be a promising candidate for microwave applications and nonvolatile ferroelectric random access memories （NvFeRAMs）.     

Reliability of Au/PZT/BIT/p-Si ferroelectric diode

A ferroelectric memory diode that consisted of Au/PZT/BIT/p-Si multilayer configuration was fabricated by pulsed laser deposition (PLD) technique. The reliability issues (I-V characteristics, capacitance retention, fatigue and imprint) were investigated. The I-V curve showed the conventional Schottky diode characteristics with a small current density of - 5.3×10 -10 A/cm2 at a voltage of - 4 V and 6.7×10-8 A/cm2 at a voltage of + 4V, and this characteristic can be maintained below 50℃. The capacitance variety of the ferroelectric diode was only 5 % in 10 hours after withdrawing the applied bias of + 5 V or - 5 V, indicating the diode had good capacitance retention. By applying 100 kHz bipolar pulses of 5 V amplitude, the decay in remanent polarization was only 10% after 109 switching cycles, and meanwhile the increase in coercive field was 12%. After being irradiated for 20 min with a 200 W ultraviolet ray lamp, the remanent polarization and coercive field had both varied, and a voltage shift was obse     

Inducing effect of Pb(Zr0.4Ti0.6)O3 thin film derived by different processes in BiFeO3/Pb(Zr0.4Ti0.6)O3 multilayer capacitor at room temperature

BiFeO₃/PZT multilayer capacitor was prepared on Pt(100)/Ti/SiO₂/Si(100) substrate. PZT buffer layer was derived by MOCVD method (label: PZT₁) and sputtering method (label: PZT₂) respectively. XRD analysis indicated that high (110) orientation of BFO in the BFO/PZT₁ structure was achieved. SEM analysis indicated a better microstructure in the BFO/PZT₁ structure compared with BFO/PZT₂. The remnant polarization of the BFO/PZT₁ was 82.5 μ C/cm² at an applied voltage of 8 V, compared with that of 25.2 μC/cm² in the BFO/PZT₂ structure. The BFO/PZT₁ multilayer exhibited little polarization fatigue (<1.5%) upon 1×10¹⁰ switching cycles, at an applied voltage of 4 V. The leakage current density was about 2×10₋₇ A/cm² at an applied voltage 4 V, in the BFO/PZT₁ capacitor. All the results indicated that PZT can act as an inducing layer to the BFO and the MOCVD derived PZT has more inducing effect to the BFO thin film at room temperature. Supported by the National Natural Science Foundation of China (Grant No. 60601003), Ying Tong Education Foundation (Grant No. 101063), and International Cooperation Project from Ministry of Science and Technology of China (Grant No. 2008DFA12000)     

Effect of Annealing on Ferroelectric Properties of Bi3.25La0.75Ti3O12 Thin Films Prepared by the Sol-gel Method

Bi_3.25La_0.75Ti₃O₁₂(BLT) thin films were prepared on Pt/Ti/SiO₂/Si substrate by the sol-gel method. The effect of annealing on their structures and ferroelectric properties was investigated. The XRD patterns indicate that the BLT films annealed at different temperatures are randomly orientated and the single perovskite phase is obtained at 550°C. The remnant polarization increases and the coercive field decreases with the annealing temperature increasing. The leakage current density of the BLT films annealed at 700°C is about 5.8×10⁻⁸ Al cm² at the electric field of 250 kV/cm. Funded by the National Natural Science Foundation of China (No. 90407023)     

Effect of Pb substitution on the microstructure and ferroelectric properties of Ba<Subscript>0.7</Subscript>Sr<Subscript>0.3</Subscript>TiO<Subscript>3</Subscript> ceramic

Ferroelectric Ba0.7Sr0.3TiO3（BST） and partially Pb^2＋ substituted for Ba^2＋ ceramics （Ba0.7-xPbx）Sr0.3TiO3 （x=0.1-0.4, BPST） were prepared by using conventional solid-reaction method. XRD analysis shows that the samples microstructure changes from cubic phase to tetragonal one with the Pb^2＋ content increasing. ESEM analysis shows that the Pb^2＋ substituted samples have a denser and more uniform surface morphology than that of pure BST. Measured electrical properties suggest that the Pb^2＋ substitution for Ba^2＋ in the BST system enhances the ferroelectric performance obviously when x=0.2. In addition, the substitution increases the samples Curie temperature （To） r （Ba0.5Pb0.2）Sr0.3TiO3 ceramic has good ferroelectric properties measured at a maximal electric field of 30 kV/cm under the condition of room temperature. The corresponding saturated polarization （Ps）, remnant polarization （Pr） and coercive field （Ec） is respectively 15.687 μC/cm^2, 8.100 μ C/cm^2 and 6.611 kV/cm. The measured Tc of （Ba0.5Pb0.2）Sr0.3TiO3 is 117 ℃.     

Microstructures and Electrical Properties of Bi_(0.5)-(Na_(1-x-y)K_xLi_y)_(0.5)TiO_3 Lead-free Piezoelectric Ceramics

The microstructures and electrical properties of Bi0.5(Na1-x-yKxLiy)0.5TiO3 lead-free piezoelectric ceramics were studied.These ceramics were prepared by conventional ceramic technique.XRD analysis reveals that the ceramics possess almost pure perovskite phase when y≤0.2.The SEM results show that,with more amounts of Li+,the crystalline grain growing speed is accelerated,and the sintering temperature can effectively be decreased.The measurements of piezoelectric properties indicate that the ceramics with relatively low amount of Li+ and high amount of K+ have comparatively large piezoelectricity.The dielectric measurements show that the ceramics have properties like relaxor ferroelectrics and diffuse phase transition(DPT) at Td and Tc,respectively.The results of ferroelectric measurements reveal the system has relatively higher remanent polarization Pr(27.6 μC/cm2) and lower coercive field Ec(37.5 kV/cm).     

Performance improvement of <Emphasis Type="Italic">n-i-p</Emphasis> μc-Si:H solar cells by gradient hydrogen dilution technique

High pressure radio frequency plasma enhanced chemical vapor deposition (RF-PECVD) process was adopted to investigate the effect of constant hydrogen dilution technique and gradient hydrogen dilution technique on the structural evolution of intrinsic films and the performance of n-i-p microcrystalline silicon solar cells. The experiment results demonstrated that the grain size and crystalline volume fraction along the growth direction of intrinsic films can be controlled and the performance of solar cells can be greatly improved by gradient hydrogen dilution technique. An initial active-area efficiency of 5.7% (V _oc=0.47 V, J _sc=20.2 mA/cm², FF=60%) for the μc-Si:H single-junction n-i-p solar cells and an initial active-area efficiency of 10.12% (V _oc=1.2 V, J _sc=12.05 mA/cm², FF=70%) for the a-Si:H/μc-Si:H tandem n-i-p solar cells has been achieved. Supported by the National Basic Research Program of China (“973” Program) (Grant Nos. 2006CB202602, 2006CB202603) and the Tianjin Assistant Foundation for the National Basic Research Program of China (Grant No. 07QTPTJC29500)     

Microstructures and fatigue-free properties of the La<Superscript>3+</Superscript> and Nd<Superscript>3+</Superscript> doped Bi<Subscript>4</Subscript>Ti<Subscript>3</Subscript>O<Subscript>12</Subscript> thin films prepared by modified sol-gel technique

Ferroelectric Bi_3.25La_0.75Ti₃O₁₂ (BLT) and Bi_3.15Nd_0.85Ti₃O₁₂ (BNT) thin films were fabricated on Pt/TiO₂/SiO₂/Si (100) substrates by a modified sol-gel technique. X-ray diffraction indicated that these films were of single phase with random polycrystalline orientations. The surface morphologies of the films were observed by scanning electron microscope, showing uniform, dense films with grain size of 50–100 nm. Well-saturated hysteresis loops of the films were obtained in metal-ferroelectric-metal type capacitors with Cu top electrodes at an applied voltage of 400 kV/cm, giving the remanent polarization (2P _r) and coercive field (2E _c) values of the films of 25.1 μC/cm² and 203 kV/cm for BLT, and 44.2 μC/cm² and 296 kV/cm for BNT, respectively. Moreover, these capacitors did not show fatigue behaviors after up to 1.75×10¹⁰ switching cycles at the test frequency of 1 MHz, suggesting a fatigue-free character. The influences of the La³⁺ and Nd³⁺ doping on the properties of the films were comparatively discussed. Supported by the National Key Basic Research and Development Program of China (Grant No. 2006CB932305) and the Natural Science Foundation of Hubei Province, China (Grant No. 2004ABA082)     

Microstructure and microwave dielectric properties of CaO-B2O3-SiO2 glass ceramics with various B2O3 contents

The effects of B2O3 addition on both the sintering behavior and microwave dielectric properties of CaO-B2O3-SiO2 (CBS) glass ceramics were investigated by Fourier transform infrared spectroscopy (FTIR),X-ray diffractometry (XRD) and scanning electron microscopy (SEM).The results show that the increasing amount of B2O3 causes the increase of the contents of [BO3],[BO4] and [SiO4],which deduces the increase of CaB2O4 and α-SiO2 and the decrease of CaSiO3 correspondingly.No new phase is observed throughout the...     

Characterization of PZT/PVC Composites Added with Carbon Black

1Introduction Piezoelectricceramicshavebeenusedastheconven tionalintelligentmaterialsforalongtime.Theirinterest ingpropertiesusedintransducersarehighpiezoelectric straincoefficient(d33),highelectromechanicalcoupling coefficient(Kp)[15].However,therelative…     

Fabrication of sub-micro size PZT array and their ferroelectric properties

The photosensitive PZT sols and their gel films were prepared by sol-gel process. Based on the photosensitivity of the PZT gel films, two-dimensional (2D) array of the PZT gel film was fabricated using twice-exposure of double-beam interference on the gel film. PZT gel films coated on ITO/quartz substrate were exposed to an interference fringe of 325 He-Cd laser beams, the substrate was rotated by 90° between the first and second irradiation steps. Island type periodic 2D array structures with a pitch of 1 μm and cell size of about 480 nm × 480 nm × 40 nm were formed after the irradiation, and followed by leaching with organic solvent, and then by heat treatment at 600℃ for 15 min. The hysteresis loops of the cell in PZT array were in-situ measured by the online-operation of TF analyzer and atomic force microscope (AFM). The probe can be located on the locked cell of PZT array in the AFM image. The alternating voltage applied to the locked cell is supplied by the TF analyzer through the conductive coating probe, and then the test signal is fed back to the TF analyzer to obtain the hysteresis loop of the locked cell of array in the absence of top electrode. The results show that the sub-micro size PZT arrays prepared in this way are of polarization reversal characteristics with the alternating electric fields, thereby exhibiting obvious ferroelectricity.     

The Effect of Bi2O3 on the Structure and Microwave Dielectric Properties of Ba6-3xNd8＋2xTi18O54 System（x=2/3）

The structures and dielectric properties of Ba6-3xNd8＋2xTi18O54 system（x=2/3） doped with different contents of Bi2O3, whose final molecular formula is Ba6-3x（Nd1-yBiy）8＋2xTi18O54 were investigated. It is indicated that the dielectric constant increases greatly whereas Q value（f0=4 GHz） decreases with the increase of Bi2O3 content. However, the temperature coefficient could be controlled below 0±30×10^-6/℃ in the experiment. These phenomena are related to the appearance of a new phase, Bi4Ti3O12, which has high dielectric constant. Also, that Bi^3＋（0.13 nm） substitutes for Nd^3＋（0.099 5 nm） will increase the unit cell volume, which will lead to the enlargement of the octahedron B site occupied by Ti^4＋. So the spontaneous polarization of Ti^4＋ ions will be strengthened. Besides, Bi^3＋ will fill up some vacancies which Ba^2＋ or Nd^3＋ ions leave in two A1 sites and four A2 sites. More positive ions polarize, which also contributes to higher dielectric constant. The samples got with the optimium properties are sintered at 1 200 ℃ for 4 h, when y=0.25, ε≈110, Q≈5 400（f0=4 GHz）, TCC=-4.7×10^-6/℃; When y=0.3, ε≈120, Q≈5 000（f0=4 GHz）, TCC=-24×10^-6/℃.     

Dynamic dam-reservoir interaction analysis including effect of reservoir boundary absorption

The Bi3.25La0.75Ti3O12 thin films were fabricated on the Pt/Ti/SiO2/Si substrates using sol-gel method. The structure and morphology of the films were characterized using X-ray diffraction and atomic force microscopy. The thin films showed a perov- skite phase and dense microstructure. The 2Pr and 2Vc of the Bi3.25La0.75Ti3O12 thin films annealed at 700℃ were 18.6 μC/cm2 and 4.1 V, respectively, under an applied voltage 10 V. After the switching of 1×1010 cycles, the Pr value decreased to 90% of its pre-fatigue values. The films showed good insulating behavior according to the test of leakage current. The dielectric constant and the dissipation factor of the Bi3.25La0.75Ti3O12 thin films were about 176 and 0.046 at 1 kHz, respectively.     

Dielectric and pyroelectric characteristics of the infrared sensitive (Pb1?xSrx)TiO3 ceramics

PST ferroelectric ceramics were fabricated successfully by a two-step method, i e first, PbTiO₃ and SrTiO₃ were sintered respectively, then mixed and sintered together. The process and characteristics of PST ferroelectric ceramics were introduced and researched. Their dielectric and pyroelectric characteristics are as follows dielectric constant 10⁴ order, low dielectric loss (lower than 3.0% in the working frequency range of 1–1 000 kHz), saturation polarization intensity 10⁻¹ C/m² order, and pyroelectric coefficient 10⁻³ C/m²·K order.     

Bursting of Morris-Lecar neuronal model with current-feedback control

The Morris-Lecar (ML) neuronal model with current-feedback control is considered as a typical fast-slow dynamical system to study the combined influences of the reversal potential V _Ca of Ca²⁺ and the feedback current I on the generation and transition of different bursting oscillations. Two-parameter bifurcation analysis of the fast subsystem is performed in the parameter (I, V _Ca)-plane at first. Three important codimension-2 bifurcation points and some codimension-1 bifurcation curves are obtained which enable one to determine the parameter regions for different types of bursting. Next, we further divide the control parameter (V ₀, V _Ca)-plane into five different bursting regions, namely, the “fold/fold” bursting region R1, the “fold/Hopf” bursting region R2, the “fold/homoclinic” bursting region R3, the “subHopf/homoclinic” bursting region R4 and the “subHopf/subHopf” bursting region R5, as well as a silence region R6. Codimension-1 and -2 bifurcations are responsible for explanation of transition mechanisms between different types of bursting. The results are instructive for further understanding the dynamical behavior and mechanisms of complex firing activities and information processing in biological nervous systems. Supported by the National Natural Science Foundation of China (Grant Nos. 10872014 and 10702002)     

Study of GaN MOS-HEMT using ultrathin Al2O3 dielectric grown by atomic layer deposition

We report on a GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) using atomic-layer deposited (ALD) Al₂O₃ as the gate dielectric. Through further decreasing the thickness of the gate oxide to 3.5 nm and optimizing the device fabrication process, a device with maximum transconductance of 150 mS/mm was produced. The drain current of this 0.8 μm gate-length MOS-HEMT could reach 800 mA/mm at +3.0 V gate bias. Compared to a conventional AlGaN/GaN HEMT of similar design, better interface property, lower leakage current, and smaller capacitance-voltage (C-V) hysteresis were obtained, and the superiority of this MOS-HEMT device structure with ALD Al₂O₃ gate dielectric was exhibited. Supported by the National Natural Science Foundation of China (Grant No. 60736033) and the National Basic Research Program of China (“973“) (Grant No. 51327020301)     

Preparation and properties of SrBi2.2 Ta2O9 thin film

SrBi_2.2 Ta₂O₉ (SBT) thin film with thickness of 2 μm was successfully prepared by sol-gel method, using strontium acetate semihydrate [Sr(CH₃ COO)₂ · 1/2H₂O] and bismth subnitrate [BiO(NO₃)], and tantalum ethoxide [Ta(OCH₂CH₃)₅] as source materials, glacial acetic and ethylene glycol as solvents. The X-ray diffraction (XRD) and transmission electron microscope(TEM) results indicate that SBT layer-perovskite phase obtained has to be single phase, SBT thin film is formed after being annealed at 800 °C for for 1 min. The typical hysteresis loop of SBT thin film on Pt/Ti/SiO₂/Si is obtained, and the measured polarization value of the SBT thin film is 4. 2 μ/C/cm². Foundation item: Project (HIT. 2001. 67) supported by the Scientific Research Foundation of Harbin Institute of Technology; project (50172012) supported by the National Natural Science Foundation of China     

Effect of Bi content in precursor solutions on microstructure and ferroelectric properties of bismuth cerium titanate thin films

Sol-gel derived bismuth cerium titanate (BCT) thin films with different Bi contents in precursor solutions were deposited on the Pt/Ti/SiO₂/Si substrates. The effect of Bi content in the precursor solutions on the microstructure and ferroelectric properties of the films was investigated. It is found that with Bi content increasing from 90% to 110% of the nominal value in the precursor solutions, the dissipation factor and leakage current density of the BCT films obtained decrease, while the grain sizes, dielectric constant and remanent polarizations (2Pr) increase, and concurrently, a Bi-deficient phase of Bi₂Ti₂O₇ gradually disappears. The film prepared from solution with 110% of the nominal Bi content exhibits pure Bi-layered Aurivillius polycrystalline phase, and the 2Pr value and coercive field value are 67.1 μC/cm² and 299.7 kV/cm, respectively. Their dielectric constant and the dissipation factor are about 172 and 0.033 at 1 kHz, respectively. Moreover, this film shows no polarization fatigue after 4.46×10⁹ switching cycles. Supported by the Hubei Province Natural Science Foundation (Grant No. 2007ABA309)     

Understanding of the influence of process parameters on the heat transfer behavior at the metal/die interface in high pressure die casting process

The current paper focuses on the influence of the process parameters on the peak values of the inter-facial heat transfer coefficient (IHTC) at metal/die interface during high pressure die casting (HPDC) process. A "step shape" casting and AM50 alloy were used during the experiment. The IHTC was de-termined by solving the inverse thermal problem based on the measured temperature inside the die. Results show that the initial die surface temperature (IDST, TDI) has a dominant influence while the casting pressure and fast shot velocity have a secondary influence on the IHTC peak values. By curve fitting, it was found that the IHTC peak value (hmax) changes as a function of the IDST in a manner of hmax =eαTγDI. Such relationship between the IHTC peak value and the IDST can also be found when the casting alloy is ADC12, indicating that this phenomenon is a common characteristic in the HPDC process.