Influence of the metal electrode on the characteristics of thermal Ta2O5 capacitors

The effect of various electrodes (Al, W, TiN) deposited by evaporation (Al) and sputtering (W, TiN) on the electrical characteristics of thermal thin film (15-35 nm) Ta₂O₅ capacitors has been investigated. The absolute level of leakage currents, breakdown fields, mechanism of conductivity, dielectric constant values are discussed in the terms of possible reactions between Ta₂O₅ and electrode material as well as electrode deposition process-induced defects acting as electrically active centers. The dielectric constant values are in the range 12-26 in dependence on both Ta₂O₅ thickness and gate material. The results show that during deposition of TiN and Al a reaction that worsens the properties of Ta₂O₅ occurs while there is not an indication for detectable reduction of Ta₂O₅ when top electrode is W, and the leakage current is 5-7 orders of magnitude lower as compared to Al and TiN-electroded capacitors. The high level of leakage current for TiN and Al gate capacitors are related to the radiation defects generated in Ta₂O₅ during sputtering of TiN, and damaged interface at the electrode due to a reaction between Al and Ta₂O₅, respectively. It is demonstrated that the quality of the top electrode affects the electrical characteristics of the capacitors and the sputtered W is found to be the best. The sputtered W gate provides Ta₂O₅ capacitors with a good quality: the current density <7 × 10⁻¹⁰ A/cm² at 1 V (0.7 MV/cm, 15 nm thick Ta₂O₅). W deposition is not accompanied by an introduction of a detectable damage leading to a change of the properties of the initial as-grown Ta₂O₅ as in the case of TiN electrode. Damage introduced during TiN sputtering is responsible for current deterioration (high leakage current) and poor breakdown characteristics. It is concluded that the sputtered W top electrode is a good candidate as a top electrode of storage capacitors in dynamic random access memories giving a stable contact with Ta₂O₅, but sputtering technique is less suitable (favorable) for deposition of TiN as a metal electrode due to the introduction of radiation defects causing both deterioration of leakage current and poor breakdown characteristics.     

Hf-doped Ta2O5 stacks under constant voltage stress

The stress-induced leakage current in Hf-doped Ta₂O₅ layers (7; 10 nm) under constant voltage stress at gate injection was investigated in order to assess the mechanisms of conduction, the traps involved and the effect of Hf doping. The amount of Hf is found to affect the conduction mechanisms, the temperature dependence of the leakage current and the current response to the stress. A significant leakage current increase is observed only when the stress voltage and/or stress time exceed the corresponding threshold values, where the charge trapping at the pre-existing traps dominates below and defect generation above these threshold values. The energy levels of the traps responsible for the current transport are estimated. The stress effect on dominant conduction mechanisms appears quite weak, and the nature of the traps controlling the current transport before and after the stress seems to be nearly identical. The results indicate that the constant voltage stress affects the pre-existing traps in Hf-doped Ta₂O₅ and modifies their parameters, but there is no evidence for stress-induced generation of traps with completely new nature different from oxygen-vacancy related defects.     

Influence of oxidation temperature on the microstructure and electrical properties of Ta2O5 on Si

The effect of the oxidation temperature (673-873 K) on the microstructural and electrical properties of thermal Ta₂O₅ thin films on Si has been studied. Auger electron spectroscopy and X-ray photoelectron spectroscopy results revealed that the films are non-stoichiometric in the depth; an interfacial transition layer between tantalum oxide and Si substrate, containing presumably SiO₂ was detected. It has been found by X-ray diffraction that the amorphous state of Ta₂O₅ depends on both the oxidation temperature and the thickness of the films—the combination of high oxidation temperature (>823 K) and thickness smaller than 50 nm is critical for the appearance of a crystal phase. The Ta₂O₅ layers crystallize to the monoclinic phase and the temperature of the phase transition is between 773 and 823 K for the thinner layers (<50 nm) and very close to 873 K for the thicker ones. The electrical characterization (current/voltage; capacitance/voltage) reveals that the optimal oxidation temperature for achieving the highest dielectric constant (∼32) and the lowest leakage current (10⁻⁸ A/cm² at 1 MV/cm applied field) is 873 K. The results imply that the poor oxidation related defects are rather the dominant factor in the leakage current than the crystallization effects.     

基于MIS电容器的Al2O3与In0.74Al0.26As的界面特性

采用In_0.74Al_0.26As/In_0.74Ga_0.26As/In_xAl_1-xAs异质结构多层半导体作为半导体层,制备了金属-绝缘体-半导体（MIS）电容器。其中,SiN_x和SiN_x/Al₂O₃分别作为MIS电容器的绝缘层。高分辨率透射电子显微镜和X射线光电子能谱的测试结果表明,与通过电感耦合等离子体化学气相沉积生长的SiN_x相比,通过原子层沉积生长的Al2_O3可以有效地抑制Al₂O₃和In_0.74Al_0.26As界面的In₂O₃的含量。根据MIS电容器的电容-电压测量结果,计算得到SiN_x/Al₂O₃/In...     

用于GaAs射频集成电路的不同厚度氧化铝MIM 电容的研究

本文研究了不同厚度的氧化铝对MIM电容直流和射频特性的影响。在1MHz下,对于20nm氧化铝MIM电容,其拥有3850 pF/mm₂的高电容密度和可接受的681 ppm/V₂的VCC-α电压系数。1MHz时突出的74 ppm/V₂VCC-α电压系数,8.2GHz谐振频率以及2GHz时41的Q值可以从100nm氧化铝MIM电容获得。采用GaAs工艺以及原子层淀积制造的高性能ALD氧化铝MIM电容很有可能成为GaAs射频集成电路很有前景的候选器件。     

Comparative study of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors with Al2O3 and HfO2 gate oxide

AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs) with Al₂O₃ gate oxide which was deposited by atomic layer deposition (ALD) were fabricated and their performance was then compared with that of AlGaN/GaN MOSHFETs with HfO₂ gate oxide. The capacitance (C)-voltage (V) curve of the Al₂O₃/GaN MOS diodes showed a lower hysteresis and lower interface state density than the C-V curve of the HfO₂/GaN diodes, indicating better quality of the Al₂O₃/GaN interface. The saturation of drain current in the I_D-V_GS relation of the Al₂O₃ AlGaN/GaN MOSHFETs was not as pronounced as that of the HfO₂ AlGaN/GaN MOSHFETs. The gate leakage current of the Al₂O₃ MOSHFET was five to eight orders of magnitude smaller than that of the HfO₂ MOSHFETs.     

Excellent performance of gas sensor based on In2O3-Fe2O3 nanotubes

In₂O₃-Fe₂O₃ nanotubes are synthesized by an electrospinning method. The as-synthesized materials are characterized by scanning electron microscope and X-ray powder diffraction. The gas sensing results show that In₂O₃-Fe₂O₃ nanotubes exhibit excellent sensing properties to acetone and formaldehyde at different operating temperatures. The responses of gas sensors based on In₂O₃-Fe₂O₃ nanotubes to 100 ppm acetone and 100 ppm formaldehyde are 25 (240℃) and 15 (260℃), and the response/recovery times are 3/7 s and 4/7 s, respectively. The responses of In₂O₃-Fe₂O₃ nanotubes to 1 ppm acetone (240℃) and formaldehyde (260℃) are 3.5 and 1.8, respectively. Moreover, the gas sensor based on In₂O₃-Fe₂O₃ nanotubes also possesses an excellent selectivity to acetone and formaldehyde.     

Co3O4/Fe2O3异质结复合材料的制备及其紫外光光电探测性能

分别采用旋涂法和水热法在FTO衬底上制备Co₃O₄种子层和Co₃O₄薄膜,再在Co₃O₄薄膜上水热生长Fe₂O₃纳米棒,获得了高质量的Co₃O₄/Fe₂O₃异质结复合材料。通过改变Fe₂O₃前驱体溶液浓度来改变异质结复合材料中Fe₂O₃组分的含量。结果表明,Fe₂O₃纳米棒覆盖在呈网状结构的Co₃O₄薄膜上,随着Fe₂O₃前驱体溶液浓度即Fe₂O₃组分含量的增加,Co₃O₄/Fe₂O₃异质结复合材料对紫外光的响应逐渐增强,当Fe₂O₃前驱体溶液浓度为0.015mol/L时,异质结复合材料有着很好的光电稳定性,并表现出较高的响应率(12.5mA/W)和探测率(4.4×10¹⁰Jones)。     

Electroluminescence of SrAl2O4:Eu phosphor

The SrAl₂O₄:Eu²⁺ phosphor powders have been synthesized by sol-gel process. Electroluminescent (EL) properties of the SrAl₂O₄:Eu²⁺ phosphor were investigated using a convenient thick film device. Green light emitting at a peak of 508 nm was obtained when driven by sine alternating current (AC). The color coordinate of the emission was x=0.148 and y=0.635. Luminance-voltage and afterglow characteristics of the SrAl₂O₄:Eu²⁺ EL devices were studied. The results show that SrAl₂O₄:Eu²⁺ can be used as green phosphor for EL displays.     

High-k HfO2-Ta2O5 mixed layers: Electrical characteristics and mechanisms of conductivity

Electrical properties of mixed HfO₂-Ta₂O₅ films (10;15 nm) deposited by rf sputtering on Si have been studied from the view point of their applications as high-k layers, by standard capacitance-voltage and temperature dependent current-voltage characteristics. The effect of HfO₂ addition to the Ta₂O₅ is thickness dependent and the thicker layers exhibit advantages over the pure Ta₂O₅ (higher dielectric constant, enhanced charge storage density and improved interface quality). The process of HfO₂ and Ta₂O₅ mixing introduces negative oxide charge, tends to creates shallow bulk traps and modifies the dominant conduction mechanisms in the stack capacitors as compared to the Ta₂O₅-based one (a contribution of tunneling processes through traps located below the conduction band of mixed layers to the leakage current in the HfO₂-Ta₂O₅ stacks is observed). The traps involved in both Poole-Frenkel and tunneling processes are identified.     

Temperature dependence of the dielectric properties of polymer composite based RF capacitors

The temperature dependence of the dielectric properties of high Q polymer-based composites was discussed in terms of microstructural differences with various filler contents. Liquid coatable high Q polymer-based composites with 3-4× improvement in dielectric constant and precisely controlled temperature coefficient of capacitance (TCC) were developed with Ta₂O₅ as the inorganic filler. The base polymer showed a negative TCC of −250 ppm/°C from room temperature to 125 °C. Measurement of TCC with samples containing Ta₂O₅ greater than 30 vol.% showed TCC of ±50 ppm/°C with moderate capacitance density, whereas no detectable improvement in the TCC was observed in samples having 20 vol.% Ta₂O₅. The electron micrographs of this low filler content sample gave a clear indication of clustering, i.e. particle agglomeration. The homogeneity of the particle distribution was more pronounced in the sample with 40 vol.% Ta₂O₅.     

Nanostructure effect of V2O5 buffer layer on performance of polymer-fullerene devices

Nanostructure of solar cell materials is often essential for the device performance. V₂O₅ nanobelt structure is synthesized with a solution process and further used as an anode buffer layer in polymer solar cells, resulting insignificantly improved power conversion efficiency (PCE of 2.71%) much higher than that of devices without the buffer layer (PCE of 0.14%) or with V₂O₅ powder as the buffer layer (1.08%). X-ray diffraction (XRD) results indicate that the V₂O₅ nanobelt structure has better phase separation while providing higher surface area for the P3HT:PCBM active layer to enhance photocurrent. The measured impedance spectrums show that the V₂O₅ nanobelt structure has faster charge transport than the powder material. This work clearly demonstrates that V₂O₅ nanobelt has great potential as a substitute of the conventionally used PEDOT-PSS buffer layer for high performance devices.     

Fabrication of Ge-MOS capacitors with high quality interface by ultra-thin SiO2/GeO2 bi-layer passivation combined with the subsequent SiO2-depositions using magnetron sputtering

Ge-MOS capacitors were fabricated by a novel method of ultra-thin SiO₂/GeO₂ bi-layer passivation (BLP) for Ge surface combined with the subsequent SiO₂-depositions using magnetron sputtering. For the Ge-MOS capacitors fabricated by BLP with O₂, to decrease oxygen content in the subsequent SiO₂ deposition is helpful for improving interface quality. By optimizing process parameters of the Ge surface thermal cleaning, the BLP, and the subsequent SiO₂ deposition, interface states density of 4 × 10¹¹ cm⁻² eV⁻¹ at around mid-gap was achieved, which is approximately three times smaller than that of non-passavited Ge-MOS capacitors. On the contrary, for the Ge-MOS capacitors fabricated by BLP without O₂, interface quality could be improved by an increase in oxygen contents during the subsequent SiO₂ deposition, but the interface quality was worse compared with BLP with O₂.     

具有界面依赖光致发光的双层WS2/Ga2O3异质结的能带工程(英文)

利用垂直WS₂/Ga₂O₃异质结构中异质界面诱导了反常的光致发光(PL)发射。垂直堆栈的WS₂/Ga₂O₃异质界面使其形成了II型能带结构,导致与Ga₂O₃层接触的底层WS₂的PL强度下降。而异质界面的强耦合作用也影响了双层WS₂中的同质层间相互作用,使得上层WS₂出现反常的PL增强。这种堆栈新型二维异质结构为定制目标能带结构并控制其光子和电子行为提供一种新的手段。     

Low temperature sintering properties of Y-doped BaTiO3 ceramics by BaB2O4 sintering aid

The sintering process of semiconducting Y-doped BaTiO₃ ceramics added with BaB₂O₄ as low temperature sintering aid were investigated. When the low temperature sintering aid BaB₂O₄ added Y-doped BaTiO₃ ceramics prepared by Sol-Gel method, the sintering temperature of BaTiO₃-based ceramics would be greatly decreased, and also widen sintering range. Y-doped BaTiO₃ ceramics with BaB₂O₄ addition can be obtained at 1050 °C. Ceramics samples with room temperature resistivity 60-80 Ω cm, ratio of the maximum resistivity to minimum resistance (Rmax/Rmin) 10⁴ and temperature coefficient of resistivity (α) 10%/°C were obtained.     

Investigation of 4H-SiC MOS capacitors annealed in diluted N2O at different temperatures

Thermally grown oxide on 4H-SiC has been post-annealed in diluted N₂O (10% N₂O in N₂) at different temperatures from 900 to 1100 °C. The quality of the nitrided oxide and the SiO₂/4H-SiC interface was investigated by AC conductance and high frequency C-V measurements based on Al/SiO₂/4H-SiC metal-insulator-semiconductor (MOS) structure. It is found that N₂O annealing at 1000 °C produces the lowest interface state density, though the difference is not so significant when compared to the other samples annealed at 900 and 1100 °C. These results can be explained by the high temperature dynamic decomposition process of N₂O. By fitting the AC conductance data, it is found that higher temperature nitridation increases the capture cross-section of the interface traps.     

BaSi2O5荧光粉中Eu2+的制备，电子结构和荧光性质

绿色发射磷光剂BaSi2O5：Eu2+是由常见的固体反应合成。在CASTEP代码中,BaSi2O5可视为存在3.2eV直能隙的媒介带隙半导体。正如预期所料的,BaSi2O5光学带隙的计算值比对应的实验值低。200-400nm宽光谱范围可以有效地激活活化的Eu2 的BaSi2O5磷光剂,当最大半宽为95nm时,500nm处有一个发射峰。浓度和发射强度的研究表明Eu2 的最优浓度是0.05mol,当Eu2 容量超过临界值时,会出现浓度淬灭。最优条件的BaSi2O5的外量子效率：在315nm、350nm和365nm的激发下,Eu2 分别是96.1%、70.2%和62.1%。样品优越的光学性能表明绿色发射磷光剂可替代白光LED。     

共沉淀法制备Y2O2SO4:Eu3+荧光粉及其光致发光研究

采用商业Y(NO3)3·6H2O、Eu(NO3)3·6H2O、(NH4)2SO4和NaOH为实验原料,通过共沉淀法制备了Y2O2SO4:Eu3+荧光粉。利用热分析(DTA-TG-DTG)、傅里叶变换红外(FT-IR)光谱、X射线衍射(XRD)、扫描电子显微镜(SEM)和光致发光(PL)光谱等手段对合成的粉体进行了表征。结果表明,当(NH4)2SO4引入到反应体系中时,前驱体具有非晶态结构,且在空气气氛中800℃煅烧2h能转化为单相的Y2O2SO4粉体,该Y2O2SO4粉体呈准球形,粒径范围分布在0.5~1.0μm之间,团聚较严重。PL光谱分析表明,在270nm紫外光激发下,Y2O2SO4:Eu3+荧光粉呈红光发射,主发射峰位于620nm,归属于Eu3+的5D0→7F2跃迁。Eu3+的猝灭浓度是5 mol%,其对应的荧光寿命为1.22 ms。另外,当(NH4)2SO4未引入到反应体系中时,采用类似的方法合成了Y2O3:Eu3+荧光粉,并对Y2O2SO4:Eu3+和Y2O3:Eu3+荧光粉的PL性能进行了比较。     

Analysis of interface trap density of metal-oxide-semiconductor devices with Pr2O3 gate dielectric using conductance method

In this study, the interface trap density of metal-oxide-semiconductor (MOS) devices with Pr₂O₃ gate dielectric deposited on Si is determined by using a conductance method. In order to determine the exact value of the interface trap density, the series resistance is estimated directly from the impedance spectra of the MOS devices. Subsequently, the dispersion characteristics are numerically analyzed on the basis of a statistical model. Lastly, the process-dependent interface trap density of Pr₂O₃ is evaluated. It is concluded that high-pressure annealing and a superior quality interfacial SiO₂ layer are of crucial importance for achieving a sufficiently low interface trap density.     

Influence of temperature on the etching rate of SiO2 in CF4 + O2 plasma

The plasmochemical etching of SiO₂ in CF₄ + O₂ plasma is considered. During the experiment SiO₂ films are etched in CF₄ + O₂ plasma at temperatures of 300 and 350 K. The dependences of plasmochemical etching rates of SiO₂ on O₂ content in the feed are measured. The experimental measurements are compared with theoretical calculations. The obtained theoretical results are used to predict the real dimensions of etched trenches. It is found that decrease in temperature reduces lateral undercutting due to decreased desorption of formed SiF₄ molecules from the sidewalls.