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.     

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.     

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。     

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.     

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。     

采用ALD Al2O3作为栅介质的薄势垒增强型AlGaN/GaN MIS-HEMT

本文报道了高性能的增强型（E-mode）氮化镓（GaN）基金属-绝缘体-半导体高电子迁移率晶体管（MIS-HEMT）,该器件势垒层为5-nm厚的铝镓氮（Al0.3Ga0.7N）,并采用氮化硅（SiN）钝化来控制二维电子气（2DEG）密度。与SiN钝化不同,采用原子层淀积（ALD）技术生长的氧化铝（Al2O3）不会增强异质结中的2DEG密度。刻蚀栅区的SiN介质可以耗尽沟道电子,之后采用ALD Al2O3作为栅介质,可以实现MIS结构。栅长为1 μm的E-mode MIS-HEMT具有657mA/mm的最大饱和电流（IDS）、187mS/mm的最大跨导（gm）和1V的阈值电压（Vth）。与相应的E-mode HEMT对比,由于Al2O3栅介质的引入,使器件的性能得到了很大的提升。本文对于同时实现高的Vth和IDS提供了很好的方法。     

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.     

电子束辐照下的石墨烯上的原子层沉积Al2O3介质层

为了研究石墨烯与高k介质的结合,使用原子层沉积氧化铝在石墨衬底上。沉积前使用电子束辐照,观测到了氧化铝明显改善的形貌。归因于电子束辐照过程中的石墨层的无定形变化过程。     

一种具有高能量分辨率Al2O3钝化结区的PIN探测器

提出了一种Al₂O₃钝化结区的PIN探测器,与传统PIN探测器不同的是,在器件正面的pn结和背面的高低结处沉积了10 nm厚的Al₂O₃薄膜。经TCAD仿真结果表明,该探测器具有更低的漏电流和保护环处的电子电流密度,能对高能粒子射线入射产生良好的响应。设计了两种探测器的制备步骤并制备了器件,通过薄膜少子寿命的表征、器件的暗态I-V测试和²⁴¹Am元素能谱测试对其进行了评估。测试结果表明,与传统的PIN探测器相比,Al₂O₃钝化结区的PIN探测器的少子寿命提升至1 061μs,漏电流降低至5 nA,能量分辨率提升至521 eV,表现出更好的探测性能。     

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)。     

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.     

Effective passivation of defects in Ge-rich SiGe-on-insulator substrates by Al2O3 deposition and subsequent post-annealing

A method of Al₂O₃ deposition and subsequent post-deposition annealing (Al₂O₃-PDA) was proposed to passivate electrically active defects in Ge-rich SiGe-on-insulator (SGOI) substrates, which were fabricated using Ge condensation by dry oxidation. The effect of Al₂O₃-PDA on defect passivation was clarified by surface analysis and electrical evaluation. It was found that Al₂O₃-PDA could not only suppress the surface reaction during Al-PDA in our previous work [Yang H, Wang D, Nakashima H, Hirayama K, Kojima S, Ikeura S. Defect control by Al-deposition and the subsequent post-annealing for SiGe-on-insulator substrates with different Ge fractions. Thin Solid Films 2010; 518: 2342-5.], but could also effectively passivate p-type defects generated during Ge condensation. The concentration in the range of 10¹⁶-10¹⁸ cm⁻³ for defect-induced acceptors and holes in Ge-rich SGOI drastically decreased after Al₂O₃-PDA. As a result of defect passivation, the electrical characteristics of both back-gate p-channel and n-channel metal-oxide-semiconductor field-effect transistors fabricated on Ge-rich SGOI were greatly improved after Al₂O₃-PDA.     

原子层沉积氧化铝薄膜对多晶太阳能电池表面钝化的影响

A stack of Al2O3/SiNx dual layer was applied for the back side surface passivation of p-type multi-crystalline silicon solar cells, with laser-opened line metal contacts, forming a local aluminum back surface field （local Al-BSF） structure. A slight amount of Al2O3, wrapping around to the front side of the wafer during the thermal atomic layer deposition process, was found to have a negative influence on cell performance. The different process flow was found to lead to a different cell performance, because of the Al2O3 wrapping around the front surface. The best cell performance, with an absolute efficiency gain of about 0.6% compared with the normal full Al-BSF structure solar cell, was achieved when the Al2O3 layer was deposited after the front surface of the wafer had been covered by a SiNx layer. We discuss the possible reasons for this phenomenon, and propose three explanations as the Ag paste, being hindered from firing through the front passivation layer, degraded the SiNx passivation effect and the Al2O3 induced an inversion effect on the front surface. Characterization methods like internal quantum efficiency and contact resistance scanning were used to assist our understanding of the underlying mechanisms.     

掺入不同粒径Al2O3纳米颗粒的光致聚合物全息特性研究

在丙烯酰胺基光致聚合物材料中,分别掺入几种不同粒径的高分散性Al2O3纳米颗粒,用Ar+Kr+激光器647nm激光对其进行全息曝光,对其全息记录性能进行研究。结果表明,聚合物中掺入Al2O3纳米颗粒后,Al2O3纳米颗粒能够促进聚合物中光化反应的进行,同时用分散剂对Al2O3纳米颗粒的修饰,使Al2O3纳米颗粒的团簇效应降低,增加其单分散性。聚合物经曝光后,有效地形成由纳米颗粒与聚合物单体空间分布的折射率调制光栅,并且在聚合物中组成类"骨架"结构,有效地起到抑制材料的缩皱的作用,使材料的衍射效率和布拉格偏移等光学特性得到很大改善。此外,体系存在一个最优值,当掺入平均粒径约为10nm且同时控制浓度为1.02×10-3 mol/L的Al2O3纳米颗粒时,样品的衍射效率从52.6%提升到93.8%,缩皱率降低到0.8%,布拉格偏移降低到0.04°,极大地提高了材料的全息性能。     

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.     

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。     

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...     

Improved retention characteristic of charge-trapped flash device with sealing layer/Al2O3 or Al2O3/high-k stacked blocking layers

Although programming and erase speeds of charge trapping (CT) flash memory device are improved by using Al₂O₃ as blocking layer, its retention characteristic is still a main issue. CT flash memory device with Al₂O₃/high-k stacked blocking layer is proposed in this work to enhance data retention. Moreover, programming and erase speeds are slightly improved. In addition, sealing layer (SL), which is formed by an advanced clustered horizontal furnace between charge trapping layer and Al₂O₃ as one of the blocking layers is also studied. The retention characteristic is enhanced by SL approach due to lower gate leakage current with less defect. With the combination of SL and Al₂O₃/high-k stacked blocking layer approaches, retention property can be further improved.     

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.     

Resistive switching characteristics of Sm2O3 thin films for nonvolatile memory applications

This study investigates a sputtered Sm₂O₃ thin film to apply into a resistive random access memory device. The proposed device exhibits a stable resistance ratio of about 2.5 orders after 10⁴ cycling bias pulses and no degradation for retention characteristics monitored after an endurance test at 85 °C. The conduction mechanisms for low and high resistance states are dominated by ohmic behavior and trap-controlled space-charge limited current, respectively. The resistance switching is ascribed to the formation/rupture of conductive filaments.