Structural and electrical properties of HfO2/Dy2O3 gate stacks on Ge substrates

In the present work we report on the structural and electrical properties of metal-oxide-semiconductor (MOS) devices with HfO₂/Dy₂O₃ gate stack dielectrics, deposited by molecular beam deposition on p-type germanium (Ge) substrates. Structural characterization by means of high-resolution Transmission Electron Microscopy (TEM) and X-ray diffraction measurements demonstrate the nanocrystalline nature of the films. Moreover, the interpretation of the X-ray reflectivity measurements reveals the spontaneous growth of an ultrathin germanium oxide interfacial layer which was also confirmed by TEM. Subsequent electrical characterization measurements on Pt/HfO₂/Dy₂O₃/p-Ge MOS diodes show that a combination of a thin Dy₂O₃ buffer layer with a thicker HfO₂ on top can give very good results, such as equivalent oxide thickness values as low as 1.9 nm, low density of interfacial defects (2-5 × 10¹² eV^− 1 cm^− 2) and leakage currents with typical current density values around 15 nA/cm² at V_g = V_FB − 1V.     

La2O3、Nd2O3、Y2O3对高岭石高温相变动力学的影响

利用综合热分析技术、X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)和扫描电镜(SEM)研究了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温条件下转变成莫来石过程的作用,并采用Kissinger方程、Ozawa方程以及JMA修正方程(Ⅰ)和(Ⅱ)分析了La_2O_3、Nd_2O_3、Y_2O_3对高岭石高温相变动力学的影响。结果表明:3种稀土氧化物的掺入对高岭石的相变动力学参数产生了影响,相变活化能和频率因子与未掺入稀土氧化物的高岭石相比有所降低,析晶方式则未发生变化,均属于体积晶化。对比掺入3种稀土氧化物的高岭石相变活化能和频率因子可以看出,Y_2O_3对于高岭石高温条件下相变的促进作用最为明显,相变活化能最低。稀土氧化物对于高岭石高温相变产物影响不大,主晶相为莫来石相,次晶相为方石英相,但稀土氧化物的掺入使得方石英相的结晶度明显提高。     

Varistor properties of ZnO-Pr6O11-CoO-Cr2O3-Y2O3-In2O3 ceramics

The varistor properties of the ZnO-Pr₆O₁₁-CoO-Cr₂O₃-Y₂O₃-In₂O₃ ceramics were investigated for different concentrations of In₂O₃. The increase of In₂O₃ concentration slightly increased the sintered density (5.60-5.63 g/cm³) and slightly decreased the average grain size (3.4-2.9 μm). The breakdown field increased from 6023 to 14822 V/cm with increasing concentration of In₂O₃. The nonlinear coefficient increased from 17.6 to 44.6 for up to 0.005 mol%, whereas the further doping caused it to decrease to 36.8. In₂O₃ acted as an acceptor due to the donor concentration, which decreases in the range of 1.02 × 10¹⁷ to 0.24 × 10¹⁷/cm³ with increasing concentration of In₂O₃.     

Preparation and luminescence properties of nanocrystalline La2O3:Eu phosphor

Powders La₂O₃ doped with 1 mol% Eu were prepared via a combustion route using different reducers (urea, glycine and citric acid). The structure and morphology were determined with XRD and HRTEM measurement. The main emission positions centered at 626 nm for ⁵D₀ → ⁷F₂ transition are observed. The variation of CT band with different reducers is observed. The intensity of ⁵D₀ → ⁷F₂ transition centered at 626 nm with respect to that of ⁵D₀ → ⁷F₁ transition is a function of the energy difference ΔE between the two CT band positions.     

微波和真空烧结制备La2O3掺杂Al2O3透明陶瓷

通过共沉淀法制备La2O3掺杂Al_2O_3纳米粉,粉体经压制后分别采用微波和真空烧结制备Al_2O_3透明陶瓷。结果表明:Al_2O_3粉末颗粒大小均匀,近似球形,为40~60nm;两种烧结方式制备的试样XRD图中均为α-Al_2O_3,未检测到其它相。La2O3掺杂量为1%时,随烧结温度升高,两种烧结方法得到的Al_2O_3陶瓷的相对密度和抗弯强度均呈上升趋势,且微波烧结陶瓷的相对密度和抗弯强度明显高于真空烧结。1500℃烧结时,随La2O3掺杂量的增加,Al_2O_3陶瓷的相对密度均先增大后减小,当La2O3掺杂量为1%时,Al_2O_3陶瓷的相对密度和抗弯强度均最大。微波烧结陶瓷的透光率明显高于真空烧结,且其断口晶粒比真空烧结明显细少。     

Pentacene thin-film transistors and inverters with plasma-enhanced atomic-layer-deposited Al2O3 gate dielectric

The performances of pentacene thin-film transistor with plasma-enhanced atomic-layer-deposited (PEALD) 150 nm thick Al₂O₃ dielectric are reported. Saturation mobility of 0.38 cm²/V s, threshold voltage of 1 V, subthreshold swing of 0.6 V/decade, and on/off current ratio of about 10⁸ have been obtained. Both depletion and enhancement mode inverter have been realized with the change of treatment method of hexamethyldisilazane on PEALD Al₂O₃ gate dielectric. Full swing depletion mode inverter has been demonstrated at input voltages ranging from 5 V to − 5 V at supply voltage of − 5 V.     

Microstructure and electrical properties of Al2O3-ZrO2 composite films for gate dielectric applications

Al₂O₃-ZrO₂ composite films were fabricated on Si by ultrahigh vacuum electron-beam coevaporation. The crystallization temperature, surface morphology, structural characteristics and electrical properties of the annealed films are investigated. Our results indicate that the amorphous and mixed structure is maintained up to an annealing temperature of 900 °C, which is much higher than that of pure ZrO₂ film, and the interfacial oxide layer thickness does not increase after annealing at 900 °C. However, a portion of the Al₂O₃-ZrO₂ film becomes polycrystalline after 1000 °C annealing and interfacial broadening is observed. Possible explanations are given to explain our observations. A dielectric constant of 20.1 is calculated from the 900 °C-annealed ZrO₂-Al₂O₃ film based on high-frequency capacitance-voltage measurements. This dielectric characteristic shows an equivalent oxide thickness (EOT) as low as 1.94 nm. An extremely low leakage current density of ∼2×10⁻⁷ A/cm² at a gate voltage of 1 V and low interface state density are also observed in the dielectric film.     

添加La2O3对粉煤灰合成Al2O3-SiC复合粉体的影响

以粉煤灰和活性炭为原料,通过碳热还原反应在Ar气氛下合成Al_2O_3-SiC粉体,探究了一条低成本合成Al_2O_3-SiC粉体的可行途径。研究了添加La_2O_3对合成过程的影响。采用XRD和SEM表征了材料的物相组成和显微形貌。结果表明:当粉煤灰与活性炭质量比为100∶44,在1 550℃下保温5h,添加6%(质量分数)的La_2O_3时,可合成性能良好的Al_2O_3-SiC粉体,颗粒分布均匀,平均粒径为0.5~1μm,较不添加La_2O_3合成温度降低约50℃。     

Structural and thermal characterization of La5Ca9Cu24O41 thin films grown by pulsed laser deposition on (1 1 0) SrTiO3 substrates

In the present study stoichiometric, b-axis oriented La₅Ca₉Cu₂₄O₄₁ thin films were grown by pulsed laser deposition on (1 1 0) SrTiO₃ substrates in the temperature range 600-750 °C. High resolution transmission electron microscopy was employed to investigate the growth mechanism and the epitaxial relationship between the SrTiO₃ substrates and the La₅Ca₉Cu₂₄O₄₁ films grown at 700 °C. The 3-ω method was used to measure the cross-plane thermal conductivity of La₅Ca₉Cu₂₄O₄₁ films in the temperature range 50-350 K. The observed glass-like behavior is attributed to atomic-scale defects, grain boundaries and an interfacial layer formed between film and substrate.     

Anomalous phase formation during annealing of La2O3 thin films deposited by ion beam assisted electron beam evaporation

The fifty seven nm thick La₂O₃ thin films were deposited on Si (100) substrates. After deposition, the amorphones thin films, were amorphous, were annealed at 750 and 900 °C for 1 h. It was found that their amorphous structure had been crystallized to hexagonal and cubic structures, respectively. The phase formation of the La₂O₃ thin films was anomalous at higher annealing temperatures. The theory of heterogeneous nucleation was used to interpret the anomalous phase formation of La₂O₃ films. To investigate the effects of the phase structure on these properties, Refractive indexes and dielectric constants of different structures of La₂O₃ films were measured.     

The effect of substitution of Bi2O3 for alkali oxides on thermal properties, structure and wetting behavior of the borosilicate glass

The effect of substitution of Bi₂O₃ for alkali oxides in the borosilicate sealing glass on thermal properties, structure and wetting behavior of the borosilicate glass was studied. The thermal expansion coefficient (TEC) decreased with the substitution, however, the TEC varied little while the alkali oxides were completely consumed. The variation in glass transition temperature (T_g) and the FTIR results of the glasses indicated significant effect of Bi₂O₃ substitution on the glass structure, which caused a progressive conversion of BO₃ to BO₄ unit in the glass. The appropriate amount of Bi₂O₃ obviously improved the wetting performance of the borosilicate glass on Al₂O₃ substrate due to the high polarizability of Bi³⁺ ion.     

Electrical properties of Ge metal-oxide-semiconductor capacitors with La2O3 gate dielectric annealed in different ambient

Ge metal-oxide-semiconductor capacitors with La₂O₃ as gate dielectric are fabricated by e-beam evaporation of La₂O₃ followed by post-deposition annealing in different gases (NH₃, N₂, NO, N₂O and O₂). Experimental results indicate that the NH₃, NO, N₂O and O₂ anneals give higher interface-state and oxide-charge densities, and thus larger gate leakage current, with the highest for the O₂ anneal due to the growth of an unstable GeO_x interlayer. On the other hand, the NH₃ annealing improves the k value of the dielectric, while the annealings in O₂-containing ambients (NO, N₂O and O₂) lead to the formation of a low-k GeO_x interlayer, thus decreasing the equivalent k value. Compared with the above four samples, the sample annealed in N₂ exhibits not only larger k value (18.3) and smaller capacitance equivalent thickness (2.14 nm), but also lower leakage current density (~ 10⁻³ Acm^− 2 at V_g = 1 V) and smaller interface-state density (4.5 × 10¹¹ eV^− 1 cm^− 2).     

Synthesis, structure and exchange bias in Cr2O3/CrO2/Cr2O5 particles

We report on the synthesis, structure and magnetic properties of a novel exchange bias system with Cr₂O₃/CrO₂/Cr₂O₅ interfaces. Chromium oxide particles with mixed chromium valences were prepared by sintering CrO₃ in air. X-ray diffraction patterns show that CrO₃ lost its oxygen gradually with increasing temperature and time through Cr₃O₈, Cr₂O₅, CrO₂, and finally Cr₂O₃ at temperatures above 760 K. X-ray photoelectron spectra indicate a low CrO₂ content and a binding energy of 579.3 eV for Cr 2p_3/2 photoelectrons in Cr₂O₅. Chromium dioxide was found to stably coexist with Cr₂O₃ and Cr₂O₅ in the particles. Magnetic measurements show hysteresis loop shifts in the sample, indicating an exchange bias induced by antiferromagnetic Cr₂O₃/Cr₂O₅ in ferromagnetic CrO₂. An exchange bias of 9 mT at 5 K and a coercivity of 26.3 mT were observed in the chromium oxide particles containing CrO₂.     

Y2O3添加量对Al2O3/ZrO2共晶陶瓷显微组织及力学性能的影响

为探索第三组元Y₂O₃添加对Al₂O₃/ZrO₂共晶陶瓷显微组织与机械性能的影响,本文利用低温度梯度的高温熔凝法制备了直径为20 mm的Al₂O₃/ZrO₂(Y₂O₃)共晶陶瓷块体,采用SEM、EDS及XRD技术对共晶陶瓷进行微结构分析,并利用维氏压痕法对其硬度和断裂韧性进行测试。SEM结果表明,凝固组织由群集的共晶团结构组成,随着Y₂O₃添加量的增加,共晶团形态由胞状转变为枝晶状,内部相间距在1~2 μm范围内变化。力学测试表明,Y₂O₃摩尔分数小于1.1%时,由于组织内部存在低硬度m-ZrO₂及微裂纹缺陷,故陶瓷硬度较低,约为(9.53±0.22 )GPa;当Y₂O₃摩尔分数为1.1%时,陶瓷硬度最大,约为(18.05±0.27)GPa;当Y₂O₃的摩尔分数大于1.1%时,由于共晶团边界区内气孔缺陷及粗大组织增多,引起陶瓷硬度值略有下降。低Y₂O₃摩尔分数添加时,陶瓷断裂韧性相对较高,约为(6.30±0.16)MPa·m^1/2,这与其内部存在大量微裂纹缺陷有关;随着Y₂O₃添加量的增加,陶瓷的微裂纹数量减少、边界区内缺陷增多,断裂韧性降低。     

Hysteresis-free HfO2 film grown by atomic layer deposition at low temperature

Hysteresis-free hafnium oxide films were fabricated by atomic layer deposition at 90 °C without any post-deposition annealing, and their structures and properties were compared with films deposited at 150 °C and 250 °C. The refractivity, bandgap, dielectric constant and leakage current density all increase with deposition temperature, while the growth rate and breakdown field decrease. All films are amorphous with roughly the same composition. Although the thin films deposited at the above-mentioned temperatures all show negligible hysteresis, only the 90 °C-deposited films remain hysteresis-free when the film thickness increases. The 90 °C-deposited films remain hysteresis-free after annealing at 300 °C. The hysteresis in films deposited at high temperatures increases with deposition temperature. Evidences show such hysteresis originates in the HfO₂ film instead of the interface. Based on a careful structure analysis, middle-range order is suggested to influence the trap density in the films. HfO₂ films deposited at low temperature with negligible hysteresis and excellent electrical properties have great potential for the fabrication and integration of devices based on non-silicon channel materials and in applications as tunneling and blocking layers in memory devices.     

Electrical conductivity of 5 mol.% Yb2O3 and 5 mol.% Gd2O3 co-doped Sm2Zr2O7

Sm₂Zr₂O₇ co-doped with and without 5 mol.% Yb₂O₃ and 5 mol.% Gd₂O₃ were prepared by a pressureless-sintering method at 1973 K for 10 h in air. The relative density, structure and electrical conductivity were investigated by the Archimedes method, X-ray diffraction, scanning electron microscopy and impedance spectra measurements. Both Sm₂Zr₂O₇ and (Sm_0.9Gd_0.05Yb_0.05)₂Zr₂O₇ ceramics exhibit a single phase of pyrochlore-type structure. The grain conductivity, grain-boundary conductivity and total conductivity obey the Arrhenius relation, respectively, and gradually increase with increasing temperature from 723 to 1173 K. (Sm_0.9Gd_0.05Yb_0.05)₂Zr₂O₇ ceramic is the oxide-ion conductor in an oxygen partial pressure range of 1.0 × 10⁻⁴ to 1.0 atm at all test temperature levels. The grain conductivity, grain-boundary conductivity and total conductivity of (Sm_0.9Gd_0.05Yb_0.05)₂Zr₂O₇ with dual Yb³⁺ + Gd³⁺ doping are higher than those of undoped Sm₂Zr₂O₇ at identical temperature levels.     

Variations of microstructures and electrical properties of Bi4Ti3O12/SrTiO3/(La0.5, Sr0.5)CoO3/MgO epitaxial thin films by annealing

Epitaxial thin films of a heterostructure with Bi₄Ti₃O₁₂(BIT)/SrTiO₃(ST) were successfully grown with a bottom electrode consisting of La_0.5Sr_0.5CoO₃(LSCO) on MgO(001) substrates using pulsed laser deposition. The grown BIT and ST (001) planes were parallel to the growth surface with the orientation relationship of BIT <110>//ST <010>. In the as-deposited film, the BIT (001) plane appeared to expand to relieve a lattice mismatch with the ST (001) plane. However, annealing for 20-40 min induced the BIT (001) plane to contract horizontally with its c-axis expanding, which was associated with a local perturbation in the layer stacking of the BIT structure. This structural distortion was reduced in the film annealed for 1 h, with restoration of the periodicity of the layer stacking. Correspondingly, the dielectric constant of the as-deposited film was increased from 292 to 411 by annealing for 1 h. In parallel, the film was paraelectric but became more ferroelectric, with the remanent polarization and the coercive field changing from 0.1 μC/cm² and 14 kV/cm to 1.7 μC/cm² and 69 kV/cm, respectively.     

Piezoelectric, ferroelectric and dielectric properties of La2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics

La₂O₃ (0–0.8 wt.%)-doped (Bi_0.5Na_0.5)_0.94Ba_0.06TiO₃ (abbreviated as BNBT6) lead-free piezoelectric ceramics were synthesized by conventional solid-state reaction. The influences of La₂O₃ on the microstructure, the dielectric, ferroelectric and piezoelectric properties of the composites were investigated. X-ray diffraction (XRD) patterns indicate that 0.2-0.8 wt.% of La₂O₃ has diffused into the lattice of BNBT6 ceramics. Consequently, a pure perovskite phase is formed. SEM images show that the microstructure of the ceramics is changed with the addition of a small amount of La₂O₃. The temperature dependence of the relative dielectric constant shows that Curie point decreases with the increase of La₂O₃. At room temperature, the ceramics doped with 0.6 wt.% La₂O₃ show superior performance with high piezoelectric constant (d₃₃ = 167 pC/N), high planar electromechanical coupling factor (k_p = 0.30), high mechanical quality factor (Q_m = 118), high relative dielectric constant (ε_r = 1470) and lower dissipation factor (tanδ = 0.056) at a frequency of 10 kHz.     

The study on electrical behavior of Gd2O3-WO3 complex ceramics at high temperature

Gd₂O₃-WO₃ complex ceramics are fabricated by the conventional solid-state reaction process. The electrical characteristics and dielectric properties of the samples were measured at various ambient temperatures in a low electric field (E < 150 V/mm). As the temperature increases, the dielectric constant and the loss tangent show an obvious change at about 50 °C and 330 °C. When the temperature is above 200 °C, the samples display stable nonlinear electrical properties characterized by semiconductivity, and the nonlinearity increases along with increasing temperature. XRD analysis reveals that Gd₂W₂O₉ is the main phase and Gd₂O₃ is the secondary phase. Based on the phase transition of tungsten trioxide, these electrical properties of Gd₂O₃-WO₃ complex ceramics can be simply explained.     

Thermo-optic properties of TiO2, Ta2O5 and Al2O3 thin films for integrated optics on silicon

The direct measurement of the thermo-optic coefficients of aluminium oxide, tantalum pentoxide and titanium dioxide thin films is presented. Using ellipsometry on monolithically integrated permutations of the layers of silicon, silicon dioxide and the material under test, allows the direct measurement of the overall thermo-optic coefficient accounting for thermally induced changes in the dielectric permittivity and density of the materials as well as the elasto-optic effect due to the non-matching thermal expansion coefficients of the different materials.