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.     

New TIT capacitor with ZrO2/Al2O3/ZrO2 dielectrics for 60 nm and below DRAMs

New ZrO₂/Al₂O₃/ZrO₂ (ZAZ) dielectric film was successfully developed for DRAM capacitor dielectrics of 60 nm and below technologies. ZAZ dielectric film grown by ALD has a mixture structure of crystalline phase ZrO₂ and amorphous phase Al₂O₃ in order to optimize dielectric properties. ZAZ TIT capacitor showed small Tox.eq of 8.5 Å and a low leakage current density of 0.35 fA/cell, which meet leakage current criteria of 0.5 fA/cell for mass production. ZAZ TIT capacitor showed a smaller cap leak fail bit than HAH capacitor and stable leakage current up to 550 °C anneal. TDDB (time dependent dielectric breakdown) behavior reliably satisfied the 10-year lifetime criteria within operation voltage range.     

Investigation of Ta2O5/SiO2/4H-SiC MIS capacitors

Tantalum pentoxide (Ta₂O₅) deposited by pulsed DC magnetron sputtering technique as the gate dielectric for 4H-SiC based metal-insulator-semiconductor (MIS) structure has been investigated. A rectifying current-voltage characteristic was observed, with the injection of current occurred when a positive DC bias was applied to the gate electrode with respect to the n type 4H-SiC substrate. This undesirable behavior is attributed to the relatively small band gap of Ta₂O₅ of around 4.3 eV, resulting in a small band offset between the 4H-SiC and Ta₂O₅. To overcome this problem, a thin thermal silicon oxide layer was introduced between Ta₂O₅ and 4H-SiC. This has substantially reduced the leakage current through the MIS structure. Further improvement was obtained by annealing the Ta₂O₅ at 900 °C in oxygen. The annealing has also reduced the effective charge in the dielectric film, as deduced from high frequency C-V measurements of the Ta₂O₅/SiO₂/4H-SiC capacitors.     

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.     

用溶胶-凝胶法制备的Cu2Bi2Cr2O8薄膜 及其光学和铁磁性能研究

以硝酸铜Cu(NO₃)₂·3H₂O、硝酸铬Cr(NO₃)₃·9H₂O、硝酸铋Bi(NO₃)₃·3H₂O和乙二醇为原料,利用溶胶-凝胶工艺在石英衬底上制备了纳米Cu₂Bi₂Cr₂O₈薄膜。通过X射线衍射(X-Ray Diffraction, XRD)和拉曼测试对样品进行了表征。结果表明,Cu₂Bi₂Cr₂O₈薄膜具有良好的光学特性,其禁带宽度为1.49 eV;在磁性测试方面,Cu₂Bi₂Cr₂O₈薄膜呈现出了良好的铁磁性。     

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。     

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.     

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。     

SO2-4/Bi2O3固体超酸的制备及其可见光催化性能

采用水热法结合H2SO4浸泡处理成功合成了SO^2-₄/Bi₂O₃可见光催化材料, 并采用XRD、TG DTA和UV Vis等对合成产物的物相结构、热化学性能、光吸收性能以及可见光催化性能进行了研究, 对H2SO4浸泡工艺条件对产物的可见光催化性能的影响进行了探讨。研究表明, 水热合成产物为α-Bi₂O₃、Bi₂O₄和Bi₂O₂CO₃的混合物, 其中α-Bi₂O₃为主要成分;H₂SO₄浸泡处理并未改变产物的物相结构, 但经H₂SO₄浸泡处理后产物的光催化性能得到了显著的提高, 并且H₂SO₄浸泡工艺条件对产物的光催化活性有着重要的影响。在实验范围内, 在浓度为0.5mol·L^-1的H₂SO₄溶液中浸泡75min, 再经700℃热处理4h可制备出具有较佳光催化活性的产物, 经75min可见光的照射后对甲基橙溶液的光催化脱色率可达93.1%。     

不同深宽比GaAs衬底的Al22O3/HfO2复合薄膜材料原子层沉积及能谱分析

利用热原子层沉积（Atomic Layer Deposition, ALD）技术在不同深宽比GaAs衬底上进行了Al2₂O₃/HfO₂复合薄膜的沉积。通过对其表面和能谱进行分析发现,沉积温度对复合薄膜的摩尔比具有较大的影响。随着深宽比的增大,其沉积表面和沟槽内会出现残留物;随着ALD沉积温度的上升,其沉积表面和沟槽内的残留物减少,摩尔比趋向均匀。当深宽比为2.2并利用150 ℃的低沉积温度时,表面及底面基本无残留物。但当深宽比为4.25时,150 ℃沉积明显有大量残留物。只有当温度升高到300 ℃时,表面和沟槽里复合薄膜的残留物才被明显消除。ALD技术可以实现各种器件结构的全方位钝化,这是其他化学气相沉积法无法比拟的。     

氧化铟纳米管的制备及它的甲苯气敏特性研究

Abstract： The pristine In2O3 nanotubes were synthesized by electrospinning and subsequent calcination. Scanning electron microscope, X-ray powder diffraction and transmission electron micrograph were employed to analyze the morphology and crystal structure of the as-synthesized nanotubes. Gas-sensing properties of the as-synthesized In203 nanotubes were investigated by exposing the corresponding sensors to toluene, acetone, ethanol, formalde- hyde, ammonia and carbon monoxide at 340 ℃. The results show that the gas sensor possesses a good selectivity to toluene at 340 ℃. The response of the In2O3 nanotube gas sensor to 40 ppm is about 5.88. The response and recovery times are about 3 s and 17 s, respectively.     

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.     

Atomic-layer-deposited Al2O3 and HfO2 on GaN: A comparative study on interfaces and electrical characteristics

Al₂O₃, HfO₂, and composite HfO₂/Al₂O₃ films were deposited on n-type GaN using atomic layer deposition (ALD). The interfacial layer of GaON and HfON was observed between HfO₂ and GaN, whereas the absence of an interfacial layer at Al₂O₃/GaN was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The dielectric constants of Al₂O₃, HfO₂, and composite HfO₂/Al₂O₃ calculated from the C-V measurement are 9, 16.5, and 13.8, respectively. The Al₂O₃ employed as a template in the composite structure has suppressed the interfacial layer formation during the subsequent ALD-HfO₂ and effectively reduced the gate leakage current. While the dielectric constant of the composite HfO₂/Al₂O₃ film is lower than that of HfO₂, the composite structure provides sharp oxide/GaN interface without interfacial layer, leading to better electrical properties.     

Low-cost supercritical CO2/H2O2 treatment on ITO anodes of fluorescent organic light-emitting diodes

A simple and cost-effective approach is proposed as an alternative to conventional oxygen plasma treatment to modify surface property of Indium tin oxide (ITO) anode of a fluorescent organic light-emitting diode (OLED). This was achieved by treating the ITO anode in supercritical CO₂ (SCCO₂) fluids with hydrogen peroxide (H₂O₂). The SCCO₂/H₂O₂ treatment yielded an ITO work function of 5.35 eV after 15 min treatment at 85 °C and 4000 psi, which was significant higher than 4.8 eV of the as-cleaned ITO surface and was slightly less than 5.5 eV of the ITO surface treated by oxygen plasma. The highest work function achieved was 5.55 eV after 45 min SCCO₂/H₂O₂ treatment. The SCCO₂/H₂O₂ treatment can be used to tailor the ITO work function through changing the operation pressure of the treatment. In addition, the correlated dependence of OLED performance on the ITO anodes with and without the treatments was investigated. The maximum power efficiency of 1.94 lm/W was obtained at 17.3 mA/cm² for the device with 15 min SCCO₂/H₂O₂ treatment at 4000 psi. This power efficiency was 19.3% and 33.8% higher than those of the oxygen plasma treatment and as-clean, respectively. The improvement in device efficiency by the SCCO₂/H₂O₂ treatments can be attributed to enhanced hole injection and balance in charge carriers due to increased work function and surface energy of the ITO anodes.     

插层Al2O3对氧化铪基忆阻器的性能优化及多值特性研究

近年来,氧化铪基忆阻器因其优异的阻变性能及与CMOS工艺兼容等特点而被广泛研究。然而,氧化铪基忆阻器仍存在以下问题:1) 器件良率、可靠性、均一性不足；2) Set和Reset 过程中电流突变,导致多值特性较差。为实现氧化铪基忆阻器的性能优化及多值特性,文章在HfO₂表面生长一层1~5 nm Al₂O₃,构造Al₂O₃/HfO₂双介质层忆阻器,并对HfO₂和Al₂O₃的厚度进行优化,最终得到性能显著提升的Al₂O₃/HfO₂双介质层多值忆阻器。该器件呈现出保持性良好的10个不同电阻态(1×10⁴ s@85℃)。由于氧离子在Al₂O₃层的迁移率更低,限制了氧空位细丝生长速率及宽度,且Al₂O₃具有热增强作用,使氧空位分布更均匀,促使氧空位细丝生成/断裂过程由突变转为渐变。该工作为进一步实现氧化铪基忆阻器的性能优化及多值特性提供了参考。     

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.     

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.     

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。     

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.     

MOS devices with tetragonal ZrO2 as gate dielectric formed by annealing ZrO2/Ge/ZrO2 laminate

A Ge-stabilized tetragonal ZrO₂ (t-ZrO₂) film with permittivity (κ) of 36.2 was formed by depositing a ZrO₂/Ge/ZrO₂ laminate and a subsequent annealing at 600 °C, which is a more reliable approach to control the incorporated amount of Ge in ZrO₂. On Si substrates, with thin SiON as an interfacial layer, the SiON/t-ZrO₂ gate stack with equivalent oxide thickness (EOT) of 1.75 nm shows tiny amount of hysteresis and negligible frequency dispersion in capacitance-voltage (C-V) characteristics. By passivating leaky channels derived from grain boundaries with NH₃ plasma, good leakage current of 4.8 × 10⁻⁸ A/cm² at V_g = V_fb − 1 V is achieved and desirable reliability confirmed by positive bias temperature instability (PBTI) test is also obtained.