高能电子辐射下聚四氟乙烯深层充电特性

介质深层充放电现象是诱发航天器异常故障的重要因素之一.分析了高能电子辐射下介质内部电荷沉积、能量沉积特性和电导特性,考虑了真空与介质界面电荷对电场分布的影响,建立了介质二维深层充电的物理模型,并基于有限元方法实现了数值计算.计算了高能电子辐射下聚四氟乙烯的深层充电特性.结果表明:真空环境下,介质的表面存在较弱的反向电场,随着介质深度增大,电场减小至零,随后逐渐增大,最大值出现在靠近接地附近,但在接地点,电场存在小幅降低.分析了不同辐射时间下(1 h,1 d,10 d和30 d),介质内部最大电位和最大电场的时空演变特性.随着辐射时间的增加,最大电位由-128V增加至-7.9×104V,最大电场由2.83×105V·m-1增加至1.76×108V·m-1.讨论了入射电子束流密度对最大电场的影响,典型空间电子环境(1×10-10A·m-2)下,电子辐照10 d时,介质内部最大电场为2.95×106V·m-1.而恶劣空间电子环境(2×10-8A·m-2)下,电子辐射42 h,介质内部最大电场即达到108V·m-1,超过材料击穿阈值(约为108V·m-1),极易发生放电现象.该物理模型和数值方法可以作为航天器复杂部件多维电场仿真的研究基础.     

Materials,technologies, and circuit concepts for nanocrossbar-based bipolar RRAM

The paper reports on the characterization of bipolar resistive switching materials and their integration into nanocrossbar structures, as well as on different memory operation schemes in terms of memory density and the challenging problem of sneak paths. TiO₂, WO₃, GeSe, SiO₂ and MSQ thin films were integrated into nanojunctions of 100×100 nm². The variation between inert Pt and Cu or Ag top electrodes leads to valence change (VCM) switching or electrochemical metallization (ECM) switching and has significant impact on the resistive properties. All materials showed promising characteristics with switching speeds down to 10 ns, multilevel switching, good endurance and retention. Nanoimprint lithography was found to be a suitable tool for processing crossbar arrays down to a feature size of 50 nm and 3D stacking was demonstrated. The inherent occurrence of current sneak paths in passive crossbar arrays can be circumvented by the implementation of complementary resistive switching (CRS) cells. The comparison with other operation schemes shows that the CRS concept dramatically increases the addressable memory size to about 10¹⁰ bit.     

基于交叉结构的分子电子器件及其逻辑电路的研究进展

随着大规模集成电路的特征尺寸进入到纳米级，传统的硅基集成电路技术面临挑战，新材料及新结构的研究成为热点，纳电子学分支之一的分子电子器件正在蓬勃发展一场效应晶体管（FET）和交叉结构是目前主要的分子电子器件的结构，而交叉结构有利于集成受到广泛关注。文章概述了基于交叉结构的分子纳米器件工作原理、工艺流程，并着重介绍了逻辑功能的实现方法及其研究进展，最后，总结了交叉结构的前景及所面临的困难。     

Low specific contact resistivity to graphene achieved by AuGe/Ni/Au and annealing process

Low metal-graphene contact resistance is important in making high-performance graphene devices.In this work,we demonstrate a lower specific contact resistivity of Au_(0.88)Ge_(0.12)/Ni/Au-graphene contact compared with Ti/Au and Ti/Pt/Au contacts.The rapid thermal annealing process was optimized to improve AuGe/Ni/Au contact resistance.Results reveal that both pre- and post-annealing processes are effective for reducing the contact resistance.The specific contact resistivity decreases from 2.5 × 10~(-4) to 7.8 × 10~(-5) Ω·cm~2 by pre-annealing at 300 ℃ for one hour,and continues to decrease to9.5 × 10~(-7) H·cm~2 after post-annealing at 490 ℃ for 60 seconds.These approaches provide reliable means of lowering contact resistance.     

Robustness of the unidirectional stripe order in the kagome superconductor CsV3Sb5

V-based kagome materials AV₃Sb₅ (A=K, Rb, Cs) have attracted much attention due to their novel properties such as unconventional superconductivity, giant anomalous Hall effect, charge density wave (CDW) and pair density wave. Except for the 2a₀×2a₀ CDW (charge density wave with in-plane 2×2 superlattice modulation) in AV₃Sb₅, an additional 1×4 (4a₀) unidirectional stripe order has been observed at the Sb surface of RbV₃Sb₅ and CsV₃Sb₅. However, the stability and electronic nature of the 4a₀ stripe order remain controversial and unclear. Here, by using low-temperature scanning tunneling microscopy/spectroscopy (STM/S), we systematically study the 4a₀ stripe order on the Sb-terminated surface of CsV₃Sb₅. We find that the 4a₀ stripe order is visible in a large energy range. The STM images with positive and negative bias show contrast inversion, which is the hallmark for the Peierls-type CDW. In addition, below the critical temperature about 60 K, the 4a₀ stripe order keeps unaffected against the topmost Cs atoms, point defects, step edges and magnetic field up to 8 T. Our results provide experimental evidences on the existence of unidirectional CDW in CsV₃Sb₅.     

Etching mask optimization of InAs/GaSb superlattice mid-wavelength infared 640×512 focal plane array

In this paper we focused on the mask technology of inductively coupled plasma(ICP) etching for the mesa fabrication of infrared focal plane arrays(FPA).By using the SiO_2 mask,the mesa has higher graphics transfer accuracy and creates less micro-ripples in sidewalls.Comparing the IV characterization of detectors by using two different masks,the detector using the SiO_2 hard mask has the R_0A of 9.7×10~6 Ω·cm~2,while the detector using the photoresist mask has the R_0A of3.2 × 10~2 Ω·cm~2 in 77 K.After that we focused on the method of removing the remaining SiO_2 after mesa etching.The dry ICP etching and chemical buffer oxide etcher(BOE) based on HF and NH4 F are used in this part.Detectors using BOE only have closer R_0A to that using the combining method,but it leads to gaps on mesas because of the corrosion on AlSb layer by BOE.We finally choose the combining method and fabricated the 640×512 FPA.The FPA with cutoff wavelength of 4.8 μm has the average R_0A of 6.13 × 10~9 Ω·cm~2 and the average detectivity of 4.51 × 10~9 cm·Hz~(1/2).W~(-1)at 77 K.The FPA has good uniformity with the bad dots rate of 1.21%and the noise equivalent temperature difference(NEDT) of 22.9 mK operating at 77 K.     

Crystal growth,spectral properties and Judd–Ofelt analysis of Pr: CaF_2-YF_3

The 0.6 at.% Pr~(3+)-doped CaF_2-YF_3 crystal was successfully grown by the temperature gradient technique(TGT).X-ray diffraction analysis showed that the grown crystal still had cubic structure. The absorption spectrum, emission spectrum, Judd–Ofelt analysis and fluorescence decay curve at room temperature were discussed. The fluorescence lifetime of Pr: CaF_2-YF_3 crystal was 45.46 μs, and the σem ·τ of ~3P_0→~3H_6 and ~3P_0→~3F_2 transitions were calculated to be 80.92 × 10~(-20) cm~2·μs and 388.7 × 10~(-20) cm~2·μs, respectively. The FWHMs are 20.1 nm and 6.8 nm, which are higher than those of Pr: LiYF_4, Pr:LiLuF_4, Pr: LiGdF_4 and Pr: BaY_2F_8 crystals. The results show that the Pr: CaF_2-YF_3 crystal is expected to achieve 605 nm orange light and 642 nm red light laser operation.     

退火对AlGaInP/GaInP多量子阱 LED外延片性能的影响

采用LP-MOCVD技术在n-GaAs衬底上生长了AlGaInP/GaInP多量子阱红光LED外延片.研究表明退火对外延片性能有重要影响.与未退火样品相比,460℃退火15min,外延片p型GaP层的空穴浓度由5.6×10¹⁸cm^-3增大到6.5×10¹⁸cm^-3,p型AlGaInP层的空穴浓度由6.0×10¹⁷cm^-3增大到1.1×10¹⁸cm^-3.但退火温度为780℃时,p型GaP层和p型AlGaInP层的空穴浓度分别下降至8×10¹⁷cm^-3和1.7×10¹⁷cm^-3,且Mg原子在AlGaInP系材料中的扩散加剧,导致未掺杂AlGaInP/GaInP多量子阱呈现p型电导.在460～700℃退火范围内,并没有使AlGaInP/GaInP多量子阱的发光性能发生明显变化.但退火温度为780℃时,AlGaInP/GaInP多量子阱的发光强度是退火前的2倍.     

Switching of GaAs(001) termination by action of molecular iodine

This paper presents experimental results of an ultrahigh vacuum study of 4 × 2/c(8 × 2) → 2 × 4/c(2 × 8) structural transition on GaAs(001) caused by the thermal removal of the saturated iodine monolayer formed at GaAs(001)-4 × 2/c(8 × 2). It has been found out that the original c(8 × 2) low energy electron diffraction pattern transforms into 4 × 1 at 0.6 ML of iodine coverage and then keeps up to its saturation at 1.0 ML. We have determined that GaI is the only chemical product of the iodine action, its double peak was observed in the thermal desorption spectra at T = 150–370°C. The explanation of surface processes underlying 4 × 2/c(8 × 2) → 2 × 4/c(2 × 8) phase transition is presented below.     

Evaluation of threading dislocation density of strained Ge epitaxial layer by high resolution x-ray diffraction

The analysis of threading dislocation density(TDD)in Ge-on-Si layer is critical for developing lasers,light emitting diodes(LEDs),photodetectors(PDs),modulators,waveguides,metal oxide semiconductor field effect transistors(MOS-FETs),and also the integration of Si-based monolithic photonics.The TDD of Ge epitaxial layer is analyzed by etching or transmission electron microscope(TEM).However,high-resolution x-ray diffraction(HR-XRD)rocking curve provides an optional method to analyze the TDD in Ge layer.The theory model of TDD measurement from rocking curves was first used in zinc-blende semiconductors.In this paper,this method is extended to the case of strained Ge-on-Si layers.The HR-XRD 2θ/ωscan is measured and Ge(004)single crystal rocking curve is utilized to calculate the TDD in strained Ge epitaxial layer.The rocking curve full width at half maximum(FWHM)broadening by incident beam divergence of the instrument,crystal size,and curvature of the crystal specimen is subtracted.The TDDs of samples A and B are calculated to be 1.41×10~8cm~(-2)and 6.47×10~8cm~(-2),respectively.In addition,we believe the TDDs calculated by this method to be the averaged dislocation density in the Ge epitaxial layer.     

1×4光子晶体波导分束器的特性

在完整的二维光子晶体中引入线缺陷,形成了光子晶体波导,光子晶体波导分束器是集成化光学电路的重要组成元件。我们设计了一种线缺陷1×4光子晶体分束器,并且用有限时域差分法研究了它的特性。研究表明,输出端的透射传输特性与入射光的波长和分支的几何形状有关,并且入射波分别相等地流入四个输出端口。为了减少1×4分束器在三个Y型分支区的反射,可以通过调节在分支区的可调介质柱的半径R,使每个输出端口具有很高的透射率。     

不同覆盖度下丙硫醇在Au(111)面吸附的理论研究

采用基于密度泛函理论的第一性原理方法研究了丙烷硫醇 (C₃H₇SH)在Au(111)面五种覆盖度(1/16, 2/16, 3/16, 4/16, 1/3) 下的未解离和解离吸附的结构、能量和吸附性质. 发现丙烷硫醇的倾斜角和吸附能均受覆盖度影响, 计算结果显示丙烷硫醇的倾斜角随着覆盖度的增大减小了6°–10°, 吸附能随覆盖度的增大减小了0.21 eV. 特别针对饱和覆盖度, 研究了三种可能的表面结构: (2√3×2√3 ight)R30°, 2√3×3和(3×3). 发现S–H键未解离时三种表面结构的吸附构型和吸附能基本一致; S–H键解离后, (2√3×2√3 ight)R30°和2√3×3结构的吸附能比以(3×3)结构的吸附能约高0.05–0.07 eV, 说明C₃H₇S在Au(111)面吸附时, 倾向于形成(2√3×2√3 ight)R30°和2√3×3结构. 此外, 采用DFT-D2方法对饱和覆盖度下C₃H₇SH分子在Au(111)面的吸附进行了范德华修正, 结果显示分子间相互作用使吸附物和Au表面的距离减小, 该相互作用对吸附能的修正值为0.53 eV, 修正后结果与实验结果接近. 关键词： 第一性原理 覆盖度 表面结构 范德华力     

A novel circuit design for complementary resistive switch-based stateful logic operations

Recently, it has been demonstrated that memristors can be utilized as logic operations and memory elements. In this paper, we present a novel circuit design for complementary resistive switch(CRS)-based stateful logic operations. The proposed circuit can automatically write the destructive CRS cells back to the original states. In addition, the circuit can be used in massive passive crossbar arrays which can reduce sneak path current greatly. Moreover, the steps for CRS logic operations using our proposed circuit are reduced compared with previous circuit designs. We validate the effectiveness of our scheme through Hspice simulations on the logic circuits.     

Effect of Mo doping on phase change performance of Sb2Te3

Mo, as a dopant, is doped into SbTe to improve its thermal stability. It is shown in this paper that the Mo-doped Sb₂Te₃ (Mo_0.26Sb₂Te₃, MST) material possesses phase change memory (PCM) applications. MST has better thermal stability than Sb₂Te₃(ST) and will crystallize only when the annealing temperature is higher than 250 ℃. With the good thermal stability, MST-based PCM cells have a fast crystallization time of 6 ns. Furthermore, endurance up to 4×10⁵ cycles with a resistance ratio of more than one order of magnitude makes MST a promising candidate for PCM applications.     

Enhanced laser-induced plasma channels in air

Plasma is a significant medium in high-energy density physics since it can hardly be damaged. For some applications such as plasma based backward Raman amplification(BRA), uniform high-density and large-scale plasma channels are required. In the previous experiment, the plasma transverse diameter and density are 50–200 μm and 1–2 × 10~(19)cm~(-3),here we enhance them to 0.8 mm and 8 × 10~(19)cm~(-3), respectively. Moreover, the gradient plasma is investigated in our experiment. A proper plasma gradient can be obtained with suitable pulse energy and delay. The experimental results are useful for plasma physics and nonlinear optics.     

4×288 readouts and FPAs properties

Analysis of four types 4×288 designed and manufactured readouts is presented. All the readouts have the direct injection input circuit with the circuits incorporated that allows testing procedure of readouts without the photodiodes attached to readout circuits. TDI registers have three delay elements between neighbouring inputs. Some characteristics of 4×288 FPAs with mercury-cadmium-telluride (MCT) arrays are presented too. Analysis have shown that in spite of different constructions of four readout types, different numbers of outputs and external service, rather similar parameters of FPAs have been obtained. Detectivity values measured for all 4×288 FPAs at operation temperature T ≈ 78 K with skimming mode included and background temperature T_b ≈295 K were in the range D*_λ ≅ (1.2−1.7)×10¹¹ cmHz^1/2/W.     

Linear HgCdTe IR FPA 288×4 with bidirectional scanning

The long wavelength (8–12 μm) IR FPA 288×4 based on a hybrid assembly of n⁺-p diode photosensitive arrays (PA) of HgCdTe (MCT) MBE-grown structures and time delay integration (TDI) readout integrated circuits (ROIC) with bidirectional scanning have been developed, fabricated, and investigated. The p-type MCT structures were obtained by thermal annealing of as-grown n-type material in inert atmosphere. The MCT photosensitive layer with the composition 0.20–0.23 of mole fraction of CdTe was surrounded by the wide gap layers to decrease the recombination rate and surface leakage current. The diode arrays were fabricated by planar implantation of boron ions into p-MCT. The typical dark currents were about 4–7 nA at the reverse bias voltage of 150 mV. The differential resistance R was up to R₀ = 1.6×10⁷ Ω zero bias voltage, which corresponded to R₀A ～70 Ω ·cm² and to the maximal value R_max = 2.1 × 10⁸ Ω. The bidirectional TDI deselecting ROIC was developed and fabricated by 1.0-μm CMOS technology with two metallic and two polysilicon layers. The IR FPAs were free of defect channels and have the average values of responsivity S_λ = 2.27×10⁸ V/W, the detectivity D_λ ^* = 2.13 × 10¹¹ cm × Hz^1/2 × W^t1, and the noise equivalent temperature difference NETD = 9 mK.     

Low voltage program-erasable Pd-Al_2O_3-Si capacitors with Ru nanocrystals for nonvolatile memory application

Pd-Al2O3-Si capacitors with Ru nanocrystals are fabricated and electrically characterized for nonvolatile memory application.While keeping the entire insulator Al2O3thickness fixed,the memory window has a strong dependence on the tunneling layer thickness under low operating voltages,whereas it has weak dependence under high operating voltages.As for the optimal configuration comprised of 6-nm tunneling layer and 22-nm blocking layer,the resulting memory window increases from 1.5 V to 5.3 V with bias pulse increasing from 10 5s to 10 2s under±7 V.A ten-year memory window as large as 5.2 V is extrapolated at room temperature after±8 V/1 ms programming/erasing pulses.     

Ultrafast structural dynamics using time-resolved x-ray diffraction driven by relativistic laser pulses

Based on a femtosecond laser plasma-induced hard x-ray source with a high laser pulse energy( 100 mJ) at 10 Hz repetition rate,we present a time-resolved x-ray diffraction system on an ultrafast time scale.The laser intensity is at relativistic regime(2 × 10~(19) W/cm~2),which is essential for effectively generating K_α source in high-Z metal material.The produced copper K_α radiation yield reaches to 2.5 × 10~8 photons/sr/shot.The multilayer mirrors are optimized for monochromatizating and two-dimensional beam shaping of K_α emission.Our experiment exhibits its ability of monitoring the transient structural changes in a thin film SrCoO_(2.5) crystal.It is demonstrated that this facility is a powerful tool to perform dynamic studies on samples and adaptable to the specific needs for different particular applications with high flexibility.