New dielectric material system of Nd(Mg1/2Ti1/2)O3–CaTiO3 at microwave frequency

The microwave dielectric properties of (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ (0.1  x  1.0) ceramics prepared by the conventional solid state method have been investigated. The system forms a solid solution throughout the entire compositional range. The dielectric constant decreases from 152 to 27 as x varies from 0.1 to 1.0. In the (1 − x)CaTiO₃–xNd(Mg_1/2Ti_1/2)O₃ system, the microwave dielectric properties can be effectively controlled by varying the x value. At 1400 °C, 0.1CaTiO₃–0.9Nd(Mg_1/2Ti_1/2)O₃ has a dielectric constant (ε_r) of 42, a Q × f value of 35 000 GHz and a temperature coefficient of resonant frequency (τ_f) of −10 ppm/°C. As the content of Nd(Mg_1/2Ti_1/2)O₃ increases, the highest Q × f value of 43 000 GHz for x = 0.9 is achieved at the sintering temperature 1500 °C.     

Water-soluble poly(3,4-ethylenedioxythiophene)/nano-crystalline TiO2 heterojunction solar cells

Nanocrystalline titanium dioxide (TiO₂) thin films were prepared by the sol-gel method and were then used to fabricate an indium-tin oxide (ITO)/nano-crystalline TiO₂/poly(3,4-ethylenedioxythiophene) (PEDOT)/Au device. The junction thus obtained shows a rectifying behavior. Their current-voltage (I-V) characteristics in dark indicate that a heterojunction at the nano-crystalline TiO₂/PEDOT interface has been created. The measured open-circuit voltage (V_oc) and short-circuit current (I_sc) for the device under illumination with 50 mW/cm² light intensity under AM 1.5 conditions (device dimension was 1 cm²) are V_oc=0.39 V, I_sc=54.9 μA/cm², the filling factor (FF)=0.429 and the energy conversion efficiency (η)=0.03%.     

Controllable nanostructures on La0.7Sr0.3MnO3 thin film surfaces formed by scanning tunneling microscopy

Nanoscale structuring on La_0.7Sr_0.3MnO₃ (LSMO) thin film surfaces has been performed by scanning tunneling microscopy (STM) under ambient conditions. From line etching experiments we found that the line-depth increases in a stepwise fashion with increasing bias voltage. It also increases with decreasing scan speed and increasing scan repetition. We observed that the line-depth is an integral multiple of the LSMO out-of-plane lattice constant about 0.4 nm. Lateral structure with minimum feature size of 1 nm is possible to obtain. In addition, a four-level inverse-pyramid structure has been created on LSMO thin film surfaces. Our work shows the feasibility of using STM to fabricate controllable and complex nanostructures in LSMO thin film.     

Electrical properties of Pb(Zr,Ti)O3 films prepared on ITO glass

Pb(Zr,Ti)O₃ thin films were successfully prepared on a Pt bottom electrode with indium tin oxide coated glass substrates using RF magnetron sputtering. Use of the indium tin oxide coated glass substrate reduced the fatigue characteristics and provided for excellent crystallization of the Pb(Zr,Ti)O₃ thin films. The polarization versus fatigue characteristics showed 10% degradation after 10⁹ cycles. These results indicate that Pt/indium tin oxide double electrodes can be improved both in terms of fatigue and ferroelectric properties through the use of Pb(Zr,Ti)O₃ thin films on glass substrates, resulting in better performance than metal electrodes.     

Effects of surface passivation during atomic layer deposition of Al2O3 on In0.53Ga0.47As substrates

In this work we investigate the effect of different III-V surface passivation strategies during atomic layer deposition of Al₂O₃. X-ray photoelectron spectroscopy indicates that bare As-decapped and sulfur passivated In_0.53Ga_0.47As present residual oxides on the surface just before the beginning of the Al₂O₃ deposition while the insertion of a Ge interface passivation layer results in an almost oxide free Ge/III-V interface. The study of the initial growth regimes, by means of in situ spectroscopic ellipsometry, shows that the growth of Al₂O₃ on Ge leads to an enhanced initial growth accompanied by the formation of Ge-O-Al species thus affecting the final electrical properties of the stack. Alternatively, deposition on decapped and S-passivated In_0.53Ga_0.47As results in a more controlled growth process. The sulfur passivation leads to a better electrical response of the capacitor that can be associated to a lower oxide/semiconductor interface trap density.     

Influence of equilibrium charge reservoir formation on photo generated charge transport in TiO2/organic devices

Charge transport measurements have been performed using the photo induced charge extraction by linearly increasing voltage (photo-CELIV) technique on indium tin oxide/titanium dioxide/poly(3-hexylthiophene):[6,6]-phenyl C61 butyric acid methyl ester/copper (ITO/TiO₂/P3HT:PCBM/Cu) devices. By adjusting the offset voltage such that holes are accumulated at the ITO/TiO₂ contact we obtain space charge limited current (SCLC) extraction in the dark. Using photo-generation the current response is limited by SCLC extraction at low carrier concentrations but becomes purely recombination limited at high photo-generated carrier concentration. A 1-D drift diffusion model has been developed to simulate our results and we show that the hole blocking ITO/TiO₂ contact is responsible for the SCLC behavior. The highly reduced recombination of charges seen in P3HT:PCBM devices is necessary to obtain the large extraction current transients that are seen in the experimental measurements. By comparing the simulated dark CELIV and photo-CELIV we show that photo-generated extraction is more sensitive towards changes in the surface recombination velocity.     

xPb（Y1／2Nb1／2）O3—（1—x）Pb（Zr1／2Ti1／2）O3铁电陶瓷性能研究

系统地研究了xPb(Y1/2Nb1/2)O3-(1-x)Pb(Zr1/2Ti/2)O3三元系铁电陶瓷材料,测量并计算了不同组分时的压电常数(d33)、介电常数(εT33/ε0)、机电耦合系数(kp、k31)、以及弹性柔顺系数(sK11、sE12、sK33),对0.07Pb(Y1/2Nb1/2)O3-0.93Pb(Z[1/2Ti1/2)O3材料,D33为327×10-12C/N,介电常数εT33/ε0为1350,机电耦合系数kp大于0.6,弹性常数SE11和SE33均大于17×10-12m2/N.实现发现,当x大于0.55时,xPb(Y1/2Nb1/2)O3-(1-x)Pb(Zr1/2T11/2)O3不再是铁电材料.     

Mixtures of iron and anatase TiO2 by mechanical alloying

Fe-doped TiO₂ powders were obtained by mechanical alloying. The starting materials were anatase TiO₂ and metallic iron (α-Fe) or hematite (α-Fe₂O₃). The influence of different milling conditions such as: ball to powder weight ratio, milling time, rotation velocity of supporting disc, and dopant concentration on the structural and magnetic properties were investigated. All experiments were performed in atmospheric conditions. The milled powders were characterized by X-ray diffraction (XRD) using Rietveld refinement and room temperature Mössbauer spectrometry. The XRD patterns of all samples show the coexistence of both anatase and rutile phases and also the high-pressure srilankite phase. Mössbauer spectra reveal the presence of Fe²⁺ and Fe³⁺ states in Fe-doped TiO₂ as well as α-Fe or α-Fe₂O₃ in samples obtained from metallic iron or hematite, respectively. The Fe³⁺ contribution could be attributed to Fe incorporated in the TiO₂ structure and the Fe²⁺ can be probably assigned to surface ferrous ions in the TiO₂.     

The microwave properties of Li doped 0.7(Ba,Sr)TiO3-0.3MgO thick film interdigital capacitors on the alumina substrates

The crystalline and electrical properties of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick film interdigital capacitors have been investigated. Screen printing method was employed to fabricate Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films on the alumina substrates. (Ba,Sr)TiO₃ materials have high dielectric permittivity (>500 @ 1 MHz) and low loss tangent (0.01 @ 1 MHz) in the epitaxial thin film form. To improve dielectric properties and reduce sintering temperature, MgO and Li were added, respectively. 10 μm thick films were screen printed on the alumina substrates and then interdigital capacitors with seven fingers of 200 μm finger gap were patterned with Ag electrode. Current-voltage characteristics were analyzed with elevated temperature range. Up to 50 °C, the thick films showed positive temperature coefficient of resistivity (dρ/dT) of 6.11 × 10⁸ Ω cm/°C, then film showed negative temperature coefficient of resistivity (dρ/dT) of −1.74 × 10⁸ Ω cm/°C. From the microwave measurement, the relative dielectric permittivity of Li doped 0.7(Ba,Sr)TiO₃-0.3MgO thick films interdigital capacitors were between 313 at 1 GHz and 265 at 7 GHz.     

Novel three-layer TiO2 nanoparticle stacking architecture for efficient dye-sensitized solar cells

In this work, we report a novel three-layer TiO₂ nanoparticle photoelectrode for dye-sensitized solar cells (DSSCs). In such a DSSC, a very thin front scattering layer (∼1 μm thick) composed of small nanoparticles (∼20 nm) and larger scattering nanoparticles (>100 nm) is inserted in front of the typical small-nanoparticle absorption layer and the large-nanoparticle back-scattering/reflection layer. Such a very thin front scattering layer having mixture of small/large nanoparticles provides a larger haze (i.e., stronger scattering) and yet still retains a high integrated transmittance. With effectively scattering portion of the incident light into larger oblique angles and therefore increasing optical paths and absorption, DSSC efficiencies are enhanced by 15.2%, compared to the conventional two-layer DSSCs.     

Tailoring the surface morphology of TiO2 nanotube arrays connected with nanowires by anodization

Different surface morphologies of TiO₂ nanotube arrays were formed by anodization of Ti foils in various water-containing electrolytes at various voltages. Field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to investigate the morphology of TiO₂ nanowires. The results show that the morphology of TiO₂ nanowires is apparently influenced by viscosity of electrolytes and voltage. In this case, we introduce a detailed formation mechanism of nanowires that shows a strong relationship between the formation of TiO₂ nanowires and TiF₆²⁻ concentration. It was also found that TiO₂ nanowires are polycrystalline with anatase phase after annealing at 450 °C for 3 h.     

Effects of annealing schedule on orientations of Bi3.2Nd0.8Ti3O12 ferroelectric films prepared by metalorganic solution deposition

Fatigue-free Bi_3.2Nd_0.8Ti₃O₁₂ ferroelectric thin films were successfully prepared on p-Si(1 1 1) substrate using metalorganic solution deposition process. The orientation and formation of thin film under different annealing schedules were studied using XRD and AFM. XRD analysis indicated that (2 0 0)-oriented films with degree of orientation of I₍₂₀₀₎/I₍₁₁₇₎ = 2.097 and 0.466 were obtained by preannealing the film at 400 °C for 10 min followed by rapid thermal annealing at 700 °C for 3 min, 10 min and 20 min, respectively, (0 0 8)-oriented film with degree of orientation of I₍₀₀₈₎/I₍₁₁₇₎ = 1.706 were obtained by rapid thermal annealing the film at 700 °C for 3 min without preannealing, and (0 0 8)-oriented film with degree of orientation of I₍₀₀₈₎/I₍₁₁₇₎ = 0.719 were obtained by preheating the film from room temperature to 700 °C at 20 °C/min followed by annealing for 10 min. The a-axis and c-axis orientation decreased as increase in annealing time due to effects of (1 1 1)-oriented substrate. AFM analysis further indicated that preannealing at 400 °C for 10 min followed by rapid thermal annealing at 700 °C for 3 min resulted in formation of platelike crystallite parallel to substrate surface, however rapid thermal annealing at 700 °C for 3 min without preannealing resulted in columnar crystallite perpendicular to substrate surface.     

Ba(Zn_(1/3)Nb_(2/3))O_3微波介质陶瓷的研究进展

3G移动通信事业的迅速发展对应用于基站的微波介质谐振器陶瓷材料的Q值提出了更高的要求。Ba(Zn1/3Nb2/3)O3微波介质陶瓷材料因为具有很高的Q值、接近于零的τf和适宜的εr而备受关注。介绍了Ba(Zn1/3Nb2/3)O3系列微波介质陶瓷的结构和性能、改性研究、纳米化制备工艺及Ba(Zn1/3Nb2/3)O3-Ba(Co1/3Nb2/3)O3复合技术,以期对该领域其他研究者有所帮助。     

Influence of La substitution on the electrical properties of metal-ferroelectric (BiFeO3)-insulator (CeO2)-semiconductor nonvolatile memory structures

Metal-multiferroic (La-substituted BiFeO₃)-insulator (CeO₂)-semiconductor (MFIS) capacitors has been fabricated. The crystalline phase and amount of La³⁺ substitution at Bi-site were investigated by XRD and XPS in the postannealing temperature range from 500 to 700 °C, respectively. The microstructure and interfacial layer between CeO₂ and Si substrate were characterized by HRTEM. The memory windows as functions of insulator film thickness and DC power for La were measured. The maximum memory window is about 1.9 V under ±6 V applied voltage. The ferroelectric polarization increases with increasing substitution amount. The morphologies of La-substituted BiFeO₃ films were also studied by AFM.     

Study of thick film Ni(1−x)CoxMn2O4,(0?x?1) using overlay technique on thick film microstrip ring resonator

The effect of thick film Ni_(1−x)Co_xMn₂O₄ in-touch overlay on the X band resonance characteristics of thick film microstrip ring resonator is studied. The thick film overlay decreases the resonance frequency and increases the peak output. From the frequency shift the dielectric constant of the thick film Ni_(1−x)Co_xMn₂O₄ has been calculated. For the first time Ag thick film microstrip ring resonator has been used to study thick film Ni_(1−x)Co_xMn₂O₄ in the X band.     

Improvement on low-temperature deposited HfO2 film and interfacial layer by high-pressure oxygen treatment

In this study, high-pressure oxygen (O₂ and O₂ + UV light) technologies were employed to effectively improve the properties of low-temperature-deposited metal oxide dielectric films and interfacial layer. In this work, 13 nm HfO₂ thin films were deposited by sputtering method at room temperature. Then, the oxygen treatments with a high-pressure of 1500 psi at 150 °C were performed to replace the conventional high temperature annealing. According to the XPS analyses, integration area of the absorption peaks of O-Hf and O-Hf-Si bonding energies apparently raise and the quantity of oxygen in deposited thin films also increases from XPS measurement. In addition, the leakage current density of standard HfO₂ film after O₂ and O₂ + UV light treatments can be improved from 3.12 × 10⁻⁶ A/cm² to 6.27 × 10⁻⁷ and 1.3 × 10⁻⁸ A/cm² at |Vg| = 3 V. The proposed low-temperature and high pressure O₂ or O₂ + UV light treatment for improving high-k dielectric films is applicable for the future flexible electronics.     

Epitaxy of BaTiO3 thin film on Si(0 0 1) using a SrTiO3 buffer layer for non-volatile memory application

In this study we report the epitaxial growth of BaTiO₃ films on Si(0 0 1) substrate buffered by 5 nm-thick SrTiO₃ layer using both MBE and PLD techniques. The BaTiO₃ films demonstrate single crystalline, (0 0 1)-oriented texture and atomically flat surface on SrTiO₃/Si template. The electrical characterizations of the BaTiO₃ films using MFIS structures show that samples grown by MBE with limited oxygen pressure during the growth exhibit typical dielectric behavior despite post deposition annealing process employed. A ferroelectric BaTiO₃ layer is obtained using PLD method, which permits much higher oxygen pressure. The C-V curve shows a memory window of 0.75 V which thus enable BaTiO₃ possibly being applied to the non-volatile memory application.     

Anodic bonding of glass-ceramics to stainless steel coated with intermediate SiO2 layer

The anodic bonding between glass-ceramics and stainless steel (No. 430#) which was coated with SiO₂ layer were investigated. The SiO₂ layers with thickness comprised between 150 and 250 nm were coated on stainless steel surfaces by sol-gel method, the bonding process was achieved at 350 °C and 800 V for 45 min under atmosphere. The micro-topography and the compositions of the bonding interfaces were investigated by XRD, SEM and EDS. The results indicated SiO₂ layers could help the formation of the bonding with glass-ceramics to stainless steel, lithium iron oxide (LiFeO₂) was observed on the surface of glass-ceramics after bonding, and the bonding strength increased with increasing bonding temperature or voltage.     

Fabrication and electrical characteristics of ultrathin (HfO2)x(SiO2)1−x films by surface sol-gel method and reaction-anneal treatment

Hafnium oxide (HfO₂) films were deposited on Si substrates with a pre-grown oxide layer using hafnium chloride (HfCl₄) source by surface sol-gel process, then ultrathin (HfO₂)_x(SiO₂)_1−x films were fabricated due to the reaction of SiO₂ layer with HfO₂ under the appropriate reaction-anneal treatment. The observation of high-resolution transmission electron microscopy indicates that the ultrathin films show amorphous nature. X-ray photoelectron spectroscopy analyses reveal that surface sol-gel derived ultrathin films are Hf-Si-O alloy instead of HfO₂ and pre-grown SiO₂ layer, and the composition was Hf_0.52Si_0.48O₂ under 500 °C reaction-anneal. The lowest equivalent oxide thickness (EOT) value of 0.9 nm of film annealed at 500 °C has been obtained with small flatband voltage of −0.31 V. The experimental results indicate that a simple and feasible solution route to fabricate (HfO₂)_x(SiO₂)_1−x composite films has been developed by means of combination of surface sol-gel and reaction-anneal treatment.