High-Temperature Capacitor Materials Based on Modified BaTiO<Subscript>3</Subscript>

High-temperature capacitor materials sintered at 1120°C were prepared in a BaTiO₃ (BT)-Na_0.5Bi_0.5TiO₃ (NBT)-Nb₂O₅-ZnO-CaZrO₃ system. The Curie temperature of BaTiO₃ was increased by NBT doping, and a secondary phase occurred when adding ≥5 mol% NBT. The effects of Nb₂O₅, ZnO, and CaZrO₃ on the dielectric properties and the microstructure of BT ceramics doped with 1 mol% NBT were analyzed. The overall dielectric constant decreased when the Nb₂O₅ content increased, and increased when the ZnO content increased. The dielectric constant peak at the Curie temperature was effectively depressed, and a broad secondary dielectric constant peak appeared at 60°C when the ZnO concentration was ≥4.5 mol%. Significant grain growth was observed by scanning electron microscope (SEM) analysis as the amount of ZnO increased. The high-temperature capacitor specification (−55°C to +175°C, ΔC/C _25°C less than ±15%) is met when 7 mol% to 8 mol% CaZrO₃ is added.     

Characterization of physical and electrical properties of BaTiO<Subscript>3</Subscript> films deposited on p-Si by modified polymeric precursors

Highly uniform BaTiO₃ (BTO) films with thickness well below 100 nm were deposited on p-Si by spin coating using a modified polymeric precursor method. The polymeric precursor gel was redissolved into glacial acetic acid to improve the wetting property of the spinning solution to the Si substrates (2.5-in. diameter). The morphology, composition, thickness, and refractive index of the films were investigated using x-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and ellipsometry. The films are found to be polycrystalline. They exhibit uniformity over the whole wafer in regard to thickness, composition, and absence of surface features. The capacitors constructed with the BTO films on Si were further investigated by electrical characterizations. Current-voltage (I-V) measurements reveal a leakage current due to a Poole-Frenkel mechanism. The energy gap is evaluated to be 3.95 eV. A metal-insulator-semiconductor (MIS) behavior is observed through capacitance-conductance-voltage (C-G-V) measurements. The interface state density (D_it) at the BTO/p-Si interface is estimated to be of the order of 10¹² eV⁻¹ cm⁻².     

CaTiO_3掺杂对BST铁电电容器陶瓷性能的影响

采用固相法制备了CaTiO3掺杂的(Ba0.65Sr0.35)TiO3(BST)陶瓷,研究了CaTiO3掺杂量对BST电容器陶瓷介电性能和微观结构的影响。结果表明:随着CaTiO3掺杂量的增加,BST陶瓷的相对介电常数(εr)先增大然后减小然后增大,介质损耗(tanδ)和交流耐压强度(Eb)先增大然后减小。当CaTiO3掺杂量为摩尔分数10%时,BST陶瓷的综合介电性能较好:εr为4480,tanδ为0.022,Eb为5.8×103V/mm(AC),容温特性符合Y5U特性。     

埋容电路用高介电常数热塑性聚酰亚胺的性能研究

通过填料预分散法和原位聚合法合成了一种BaTiO3填充的热塑性聚酰亚胺树脂。考察不同填充量的填料对热塑性聚酰亚胺的力学性能,热性能和电性能的影响。结果发现:随着BaTiO3添加量的增大,TPI的介电常数和介电损耗都增大,力学性能急剧下降,尤其是柔韧性急剧降低;玻璃化转变温度不变,热分解温度相应增加,热膨胀系数减小,吸潮率降低,TPI与铜箔之间的粘接力减少。     

Effect of the polymer matrices on the dielectric behavior of a percolative high-k polymer composite for embedded capacitor applications

High dielectric constant (high-k) polymer composites are of great interest for embedded capacitor applications. Previously, we demonstrated that epoxy—aluminum composites are promising for embedded capacitor applications, because they have a high dielectric constant and a low dielectric loss due to the core—shell structure of the self-passivated aluminum particles. In this work, to further understand the dielectric behavior of aluminum composites, lower-loss polymers such as silicone, polyimide, polynorbornene, and benzocyclobutene were explored as matrices for the aluminum composites. It is found that the polymer matrices can significantly change the dielectric properties of the aluminum composites. A polymer matrix with a lower dielectric constant generally results in a lower dielectric constant of its aluminum composites. In this regard, polymer—aluminum composites have a similar dielectric characteristic as polymer—ceramic composites. Thermomechanical properties of aluminum composites were characterized by a thermomechanical analyzer.     

High electric-field-induced strain beahvior of single-crystal Pb(Mg<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>-xPbTiO<Subscript>3</Subscript> multilayer piezoelectric actuators

Two 10-mm-long multilayer prototype actuators were fabricated by a stack method using 55 pieces of 5 mm×5 mm×0.15 mm Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMNT) single crystals and PZT-5A ceramics, respectively. The strain values for PMNT multilayer piezoelectric actuators are twice those of PZT-5A multilayer actuators, and 20.8-μm displacements can be achieved at the same E-field of 15 kV/cm. Although thermal and electrical history markedly impact dielectric and piezoelectric performance of PMNT crystals, the PMNT multilayer actuator can still achieve large displacements with approximately linear behavior below 60°C. Broad stable dynamic displacement characteristic and fast displacement response make the new-type actuators promising candidates for the application in new-generation high-performance solid-state actuators.     

Pressure dependence of intersubband transitions in HgTe/Hg<Subscript>0.3</Subscript>Cd<Subscript>0.7</Subscript>Te superlattices

The optical absorption coefficient of HgTe/Hg_0.3Cd_0.7Te superlattices (SLs) and its pressure dependence has been investigated at hydrostatic pressures up to 30 kbar at room temperature. The corresponding intersubband transition energies result from a comparison of experimental and theoretical absorption coefficients. The latter is based on the band structure, which is calculated using Kane’s four-band (8×8 k · p) model together with the envelope function approximation. The experimental linear pressure coefficients of the H1 — E1 and H1 — L1 intersubband transitions are in good agreement with the theoretical values, e.g., 7.15±0.3 meV/kbar and 6.2±0.3 meV/kbar compared to 7.4 and 6.4 meV/kbar, respectively. this is in stark contrast to the pressure dependence of ≤1 meV/kbar of the photoluminescence (PL) peaks of a similar SL reported in the literature. Consequently, we conclude that the reported PL peaks are not due to intersubband transitions and that the k · p model correctly reproduces the electronic band structure and its pressure dependence of HgTe/Hg_1−xCd_xTe SLs.     

热处理对(Ba,Cd)TiO3纳米粉体制备的影响

从Ba（CH3COO）2-CA（NO3）2-Ti（OC4H9）-H2O-CH3COOH--CH3CH2OH体系,采用溶液．溶胶-凝胶法研究多层陶瓷电容器用（Ba1-xCAx）TiO3（x=0．05）（BCT）超细粉体的制备。利用热重差热分析仪（TG--DSC）研究BCT前驱体干凝胶加热过程中各阶段的反应历程。借助X射线衍射（XRD）、比表面积测定仪研究了热处理温度对BCT粉体的物相组成、晶粒尺寸、比表面积等的影响。得到晶相单一、颗粒尺寸在35-40nrn左右、比表面积为12．9m^2／g的BCT超细粉体。     

Crystallization behavior and ferroelectric properties of PbTiO<Subscript>3</Subscript>/Ba<Subscript>0.85</Subscript>Sr<Subscript>0.15</Subscript>TiO<Subscript>3</Subscript>/PbTiO<Subscript>3</Subscript> sandwich thin film on Pt/Ti/SiO<Subscript>2</Subscript>/Si substrates

A PbTiO₃/Ba_0.85Sr_0.15TiO₃/PbTiO₃ (PT/BST15/PT) sandwich thin film has been prepared on Pt/Ti/SiO₂/Si substrates by an improved sol-gel technique. It is found that such films under rapid thermal annealing at 700°C crystallize more favorably with the addition of a PbTiO₃ layer. They possess a pure, perovskite-phase structure with a random orientation. The polarization-electric field (P-E) hysteresis loop and current-voltage (I-V) characteristic curves reveal that a PT/BST15/PT film exhibits good ferroelectricity at room temperature. However, no sharp peak, only a weak maximum, is observed in the curves of the dielectric constant versus temperature. The dielectric constant, loss tangent, leakage current density at 20 kV/cm, remnant polarization, and coercive field of the PT/BST15/PT film are 438, 0.025, 1.3 × 10⁻⁶ Acm⁻², 2.46 μCcm⁻², and 41 kVcm⁻¹, respectively, at 25°C and 10 kHz. The PT/BST15/PT film is a candidate material for high sensitivity elements for uncooled, infrared, focal plane arrays (UFPAs) to be used at near ambient temperature.     

苯并噁嗪/钛酸钡复合材料介电性能的研究

通过共混法制备了苯并噁嗪/钛酸钡复合材料,探讨了钛酸钡粒径和填充量对复合材料介电性的影响。当?(BaTiO3)=50%时,复合材料介电常数εr达54、介质损耗tanδ为0.027、体积电阻率ρv大于1011?·m、击穿电压Vb大于8×103V/mm的高εr低tanδ绝缘材料。并将其应用于制备内嵌式电容器用玻璃布复合层压板。     

Fabrication and Characterization of Pb(Zr<Subscript>0.53</Subscript>,Ti<Subscript>0.47</Subscript>)O<Subscript>3</Subscript>-Pb(Nb<Subscript>1/3</Subscript>,Zn<Subscript>2/3</Subscript>)O<Subscript>3</Subscript> Thin Films on Cantilever Stacks

0.9Pb(Zr_0.53,Ti_0.47)O₃-0.1Pb(Zn_1/3,Nb_2/3)O₃ (PZT–PZN) thin films and integrated cantilevers have been fabricated. The PZT–PZN films were deposited on SiO₂/Si or SiO₂/Si₃N₄/SiO₂/poly-Si/Si membranes capped with a sol–gel-derived ZrO₂ buffer layer. It is found that the membrane layer stack, lead content, existence of a template layer of PbTiO₃ (PT), and ramp rate during film crystallization are critical for obtaining large-grained, single-phase PZT–PZN films on the ZrO₂ surface. By controlling these parameters, the electrical properties of the PZT–PZN films, their microstructure, and phase purity were significantly improved. PZT–PZN films with a dielectric constant of 700 to 920 were obtained, depending on the underlying stack structure.     

Temperature dependence of the band gap of the single-crystal compounds In<Subscript>2</Subscript>S<Subscript>3</Subscript> and AgIn<Subscript>5</Subscript>S<Subscript>8</Subscript>

For the single-crystal compounds In₂S₃ and AgIn₅S₈ produced by chemical gas-transport reactions and the Bridgman method (vertical version), the transmission spectra in the region of the fundamental absorption edge are studied in the temperature range from 20 to 300 K. From the recorded spectra, the band gaps of the In₂S₃ and AgIn₅S₈ single crystals are determined and the temperature dependences of the band gaps are constructed. It is established that, as the temperature is lowered, the band gap increases for both of the compounds. Calculation of the temperature dependences is performed. It is shown that the calculated and experimental values are in agreement with each other.     

The Effect of Hydrogen on the Fracture Properties of 0.8(Na<Subscript>1/2</Subscript>Bi<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript>-0.2(K<Subscript>1/2</Subscript>Bi<Subscript>1/2</Subscript>)TiO<Subscript>3</Subscript> Ferroelectric Ceramics

The effect of hydrogen on the fracture properties of lead-free ferroelectric ceramics has been studied. For hydrogen precharged samples, the fracture toughness decreased linearly with both increasing hydrogen concentration and the logarithm of dwell time of indenting. Hydrogen-induced delayed propagation of unloaded indentation cracks can occur, and the threshold stress intensity factor of hydrogen-induced cracking induced by residual stress decreases linearly with increasing hydrogen concentration.     

Effect of Proton Irradiation on Interface State Density in Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/GaN and Sc<Subscript>2</Subscript>O<Subscript>3</Subscript>/MgO/GaN Diodes

Proton irradiation of Sc₂O₃/GaN and Sc₂O₃/MgO/GaN metal-oxide semiconductor diodes was performed at two energies, 10 MeV and 40 MeV, and total fluences of 5 × 10⁹ cm⁻², corresponding to 10 years in low-earth orbit. The proton damage causes a decrease in forward breakdown voltage and a flat-band voltage shift in the capacitance-voltage characteristics, indicating a change in fixed oxide charge and damage to the dielectric. The interface state densities after irradiation increased from 5.9 × 10¹¹ cm⁻² to 1.03 × 10¹² cm⁻² in Sc₂O₃/GaN diodes and from 2.33 × 10¹¹ to 5.3 × 10¹¹ cm⁻² in Sc₂O₃/MgO/GaN diodes. Postannealing at 400°C in forming gas recovered most of the original characteristics but did increase the interfacial roughness.     

Influence of dual-frequency plasma-enhanced chemical-vapor deposition Si<Subscript>3</Subscript>N<Subscript>4</Subscript> passivation on the electrical characteristics of AlGaN/GaN heterostructure field-effect transistors

The influence of dielectric stress on the direct current (DC) electrical characteristics of AlGaN/GaN heterostructure field-effect transistors (HFETs) has been investigated. Dual-frequency plasma deposition was used to vary the amount of stress induced by a passivating dielectric on the surface of the devices. Initial data suggested a strong influence from the induced dielectric stress, but the low-frequency, radio-frequency (RF) excitation of the plasma deposition process was found to induce a severe nonreversible damage to the exposed AlGaN surface through N ion bombardment. The consequence is a drastic reduction of the sheet carrier concentration and mobility of the two-dimensional electron gas (2DEG). Subsequently, an alternative damage-free technique using a helium precursor was used to obtain compressive films. Based on the results, uniform dielectric stress has a minimal impact on the polarization charges within the AlGaN barrier.     

Thermal expansion of CuIn<Subscript>5</Subscript>S<Subscript>8</Subscript> single crystals and the temperature dependence of their band gap

Single crystals of the CuIn₅S₈ ternary compound are grown by planar crystallization of the melt (the vertical Bridgman method). The composition and structure of the crystals are established. The specific expansion is measured by the dilatometric technique, and the coefficients of thermal expansion are calculated. From the data, the Debye temperatures (Θ_D) and the root-mean-square dynamic displacements of atoms \(\left( {\sqrt {\bar u^2 } } \right)\) in the CuIn₅S₈ compound are calculated. From the transmittance spectra recorded in the region of the fundamental absorption edge in the temperature range 20 to 300 K, the band gap is determined and its temperature dependence is constructed.     

A comparative study on the electronic and optical properties of Sb<Subscript>2</Subscript>Se<Subscript>3</Subscript> thin film

The thin film of Sb₂Se₃ was deposited by thermal evaporation method and the film was annealed in N₂ flow in a three zone furnace at a temperature of 290°С for 30 min. The structural properties were characterized by scanning electron microscopy (SEM), transmission electron microscopy (ТЕМ), X-ray diffraction (XRD) and Raman spectroscopy, respectively. It is seen that the as-deposited film is amorphous and the annealed film is polycrystalline in nature. The surface of Sb₂Se₃ film is oxidized with a thickness of 1.15 nm investigated by X-ray photolecetron spectroscopy (XPS) measurement. Spectroscopic ellipsometry (SE) and UV–vis spectroscopy measurements were carried out to study the optical properties of Sb₂Se₃ film. In addition, the first principles calculations were applied to study the electronic and optical properties of Sb₂Se₃. From the theoretical calculation it is seen that Sb₂Se₃ is intrinsically an indirect band gap semiconductor. Importantly, the experimental band gap is in good agreement with the theoretical band gap. Furthermore, the experimental values of n, k, ε₁, and ε₂ are much closer to the theoretical results. However, the obtained large dielectric constants and refractive index values suggest that exciton binding energy in Sb₂Se₃ should be relatively small and an antireflective coating is recommended to enhance the light absorption of Sb₂Se₃ for thin film solar cells application.     

Time and temperature dependence on rapid thermal annealing of molecular beam epitaxy grown Ga<Subscript>0.8</Subscript>In<Subscript>0.2</Subscript>N<Subscript>0.01</Subscript>As<Subscript>0.99</Subscript> quantum wells analyzed using photoluminescence

GaInNAs has received a great deal of attention among the scientific community, owing to its ability to be grown pseudomorphically on GaAs substrates and, thus, to extend the possibility of using GaAs based materials for technologically important wavelengths such as 1.3 μm. Annealing was found to be a very useful tool in improving the optical characteristics of as-grown GaInNAs films. This work presents a systematic statistical analysis of two annealing parameters, time and temperature, for Ga_0.8In_0.2N_0.01As_0.99 quantum wells. Annealing, in general, has resulted in decreasing the emission wavelength by at most 0.08 μm, narrowing the peaks by at most ∼25 meV and increasing the intensity by at most 90 times. However, from the statistical analysis, it is observed that the temperature is the dominant factor among time and temperature in recovering the optical properties.     

Effect of Vacancy Distribution on the Thermal Conductivity of Ga<Subscript>2</Subscript>Te<Subscript>3</Subscript> and Ga<Subscript>2</Subscript>Se<Subscript>3</Subscript>

Our group has focused attention on Ga₂Te₃ as a natural nanostructured thermoelectric material. Ga₂Te₃ has basically a zincblende structure, but one-third of the Ga sites are structural vacancies due to the valence mismatch between Ga and Te. It has been confirmed that (1) vacancies in Ga₂Te₃ exist as two-dimensional (2D) vacancy planes, and (2) Ga₂Te₃ exhibits an unexpectedly low thermal conductivity (κ), most likely due to highly effective phonon scattering by the 2D vacancy planes. However, the effect of the size and periodicity of the 2D vacancy planes on κ has been unclear. In addition, it has also been unclear whether only the 2D vacancy planes reduce κ or if point-type vacancies can also reduce κ. In the present study, we tried to prepare Ga₂Te₃ and Ga₂Se₃ with various vacancy distributions by controlling annealing conditions. The atomic structures of the samples were characterized by means of transmission electron microscopy, and κ was evaluated from the thermal diffusivity measured by the laser flash method. The effects of vacancy distributions on κ of Ga₂Te₃ and Ga₂Se₃ are discussed.     

Microstructure and Characteristics of Thin-Film La<Subscript>0.8</Subscript>Sr<Subscript>0.2</Subscript>Co<Subscript>0.5</Subscript>Ni<Subscript>0.5</Subscript>O<Subscript>3</Subscript>/ZnO:Al Heterocontact CO Sensors Prepared by RF Magnetron Sputtering

Highly sensitive CO gas sensors based on heterocontacts of ZnO:Al on La_0.8Sr_0.2Co_0.5Ni_0.5O₃ (LSCNO) were fabricated successfully. La_0.8Sr_0.2Co_0.5Ni_0.5O₃ thin films were coated on (100) silicon wafers by a sol-gel method including the Pechini process followed by a spin-coating procedure. Then, ZnO:Al films prepared by radiofrequency (RF) magnetron sputtering at various oxygen partial pressures and deposited on as-deposited La_0.8Sr_0.2Co_0.5Ni_0.5O₃ films were investigated. The results revealed that the CO sensing ability of the film prepared with the ratio of O₂/Ar = 5/5 (ratio of volume flow rate) was the worst, owing to the highest (002) plane orientation in the ZnO:Al film. In contrast, the ZnO:Al film prepared with O₂/Ar = 3/7 exhibited better CO sensitivity. Furthermore, all two-layer samples showed higher CO sensitivities than single-layer samples. The CO sensitivity of ZnO:Al/La_0.8Sr_0.2Co_0.5Ni_0.5O₃ thin film was 45% for 500 ppm CO at a sensing temperature of 200°C.