1/f noise in large-area Hg<Subscript>1−x</Subscript>Cd<Subscript>x</Subscript>Te photodiodes

The 1/f noise in photovoltaic (PV) molecular-beam epitaxy (MBE)-grown Hg_1−xCd_xTe double-layer planar heterostructure (DLPH) large-area detectors is a critical noise component with the potential to limit sensitivity of the cross-track infrared sounder (CrIS) instrument. Therefore, an understanding of the origins and mechanisms of noise currents in these PV detectors is of great importance. Excess low-frequency noise has been measured on a number of 1000-μm-diameter active-area detectors of varying “quality” (i.e., having a wide range of I-V characteristics at 78 K). The 1/f noise was measured as a function of cut-off wavelength under illuminated conditions. For short-wave infrared (SWIR) detectors at 98 K, minimal 1/f noise was measured when the total current was dominated by diffusion with white noise spectral density in the mid-10⁻¹⁵A/Hz^1/2 range. For SWIR detectors dominated by other than diffusion current, the ratio, α, of the noise current in unit bandwidth i_n(f = 1 Hz, V_d = −60 mV, and Δf = 1 Hz) to dark current I_d(V_d = −60 mV) was α_SW-d = i_n/I_d ∼ 1 × 10⁻³. The SWIR detectors measured at 0 mV under illuminated conditions had median α_SW-P = i_n/I_ph ∼ 7 × 10⁻⁶. For mid-wave infrared (MWIR) detectors, α_MW-d = i_n/I_d ∼ 2 × 10⁻⁴, due to tunneling current contributions to the 1/f noise. Measurements on forty-nine 1000-μm-diameter MWIR detectors under illuminated conditions at 98 K and −60 mV bias resulted in α_MW-P = i_n/I_ph = 4.16 ± 1.69 × 10⁻⁶. A significant point to note is that the photo-induced noise spectra are nearly identical at 0 mV and 100 mV reverse bias, with a noise-current-to-photocurrent ratio, α_MW-P, in the mid 10⁻⁶ range. For long-wave infrared (LWIR) detectors measured at 78 K, the ratio, α_LW-d = i_n/I_d ∼ 6 × 10⁻⁶, for the best performers. The majority of the LWIR detectors exhibited α_LW-d on the order of 2 × 10⁻⁵. The photo-induced 1/f noise had α_LW-P = i_n/I_ph ∼ 5 × 10⁻⁶. The value of the noise-current-to-dark-current ratio, α appears to increase with increasing bandgap. It is not clear if this is due to different current mechanisms impacting 1/f noise performance. Measurements on detectors of different bandgaps are needed at temperatures where diffusion current is the dominant current. Excess low-frequency noise measurements made as a function of detector reverse bias indicate 1/f noise may result primarily from the dominant current mechanism at each particular bias. The 1/f noise was not a direct function of the applied bias.     

从PZT体系看无铅压电陶瓷的可能应用

总结了主要以(Bi0.5Na0.5)TiO3和NaNbO3为基的无铅压电陶瓷的性能，以Pb(Ti，Zr)TiO3基二元系、三元系压电陶瓷的性能与应用为参考，分析了无铅压电陶瓷可能的器件应用。此外，还对拓宽无铅压电陶瓷应用需要改进的性能提出了建议。     

Mechanical properties of polyethylene mixtures crystallized under high pressure

The mechanical properties of a medium molecular weight polyethylene (MMW‐PE) and an ultrahigh molecular weight PE (UHMW‐PE) binary mixture with different weight fractions crystallized from the melt at 0.1 and 450 MPa were studied. The tensile modulus, yield stress, and strain were obtained as a function of the weight fractions in the PE mixtures at 25 and 85°C. The tensile modulus in the sample crystallized at 0.1 MPa decreased from 1.5 GPa of pure MMW‐PE to about 0.4 GPa of pure UHMW‐PE with the UHMW‐PE content but it did not decrease with the UHMW‐PE in the sample crystallized at 450 MPa in testing at 25°C. A decreasing rate of the storage modulus E′ of UHMW‐PE in a dynamic measurement for the sample crystallized at 0.1 MPa with the temperature is larger than that of the sample crystallized at 450 MPa. These experimental facts are interpreted in relation to the molecular motion and crystallinity of the sample. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1962–1968, 2003     

抗真菌蛋白Rs-AFP2基因定点突变及其对大肠杆菌中表达的影响

为了研究遗传密码子对表达调控的影响,利用PCR重叠延伸法,对萝卜抗真菌蛋白Rs-AFP2基因编码序列区的部分核苷酸进行沉默突变,构建突变体Rs-AFPm.序列分析表明,PCR产物全长240bp,有一个阅读框,编码的蛋白由29个氨基酸的信号肽和51个氨基酸的抗真菌蛋白组成.突变体与突变前的Rs-AFP2基因相比,在编码区第3号氨基酸Lys相差一个碱基(TTG→TTA),第5号氨基酸Gln相差一个碱基(CAG→CAA),第6号稀有密码子Arg相差两个碱基(CAG→CGA).重新合成引物,将切除信号肽的Rs-AFP2基因和Rs-AFPm基因与原核表达载体pET-21b(+)分别重组到大肠杆菌BL21菌株.IPTG诱导后,二者均得到了表达.软件分析显示,突变前pETAFPo表达产物占全菌蛋白的3%,突变后pETAFPm的表达产物占全菌蛋白含量的8%;表达蛋白主要以包涵体的形式存在,包涵体经超声波破碎后,蛋白质复性,抑菌结果表明,pETAFPm表达产物的抑菌半径大于pETAFP2表达产物的抑菌半径.这些都说明改造后的Rs-AFPm基因与Rs-AFP2基因相比,已有效地提高表达量.     

基于ISP1581的USB2.0键盘数码管控制设备的固件编程

基于ISPl581的USB2．0键盘数码管控制设备的设计严格遵循USB2．0协议，体现了USB即插即用、易扩展、低干扰的特点，实现了主机和设备之间简单、快速、可靠的连接和通信。文章介绍了基于ISP1581的USB2．0键盘数码管控制设备的硬件、软件的设计方法。     

基于扩展分形和CFAR特征融合的SAR图像目标识别

研究了多信息融合技术在SAR图像目标识别中的应用。将扩展分形特征(Extended Fractal)与双参数恒虚警特征(Double Parameter CFAR)形成的多信息进行融合处理。运用Dempster-Shafer证据理论，在决策层对SAR图像中的像素进行识别分类。实验结果表明通过融合对像素分类的准确性明显好于单特征的检测结果，减少了虚警概率，提高了系统的识别能力。     

整合式有线电视的视频点播配置方法

提出一种视频点播系统传送数据的结构,结合单播与群播两种数据传送的方法,通过动态改变群播与单播的频道分配比例,让大部分的使用者无需等待即可开始观看影片,进而减少整体使用者的等待时间.     

CMP系统技术与市场

概述了CMP系统技术的发展历史、发展趋势以及在IC生产中的重要性,介绍了国外CMP设备主要制造厂家的设备型号和性能及CMP设备市场分布和需求,阐述了CMP系统技术的基础研究、关键技术和国内研究概况。     

基于光子带隙(PBG)结构的小型K波段谐振式带通滤波器

提出了一种新的基于光子带隙结构的K波段谐振式带通滤波器，给出了近似设计公式，并在半导体衬底上，采用微电子的工艺实现了这种结构。这种滤波器设计方法简单，体积小，整个长度接近谐振频率上的导波波长，加工方便，便于与其他电路集成，带内损耗小，阻带范围宽，带外抑制高。另外，本文的理论分析和实验结果均基于半导体衬底，可以直接应用于微波集成电路中。理论模拟与实际测量值基本吻合。     

Segmented polymer networks containing amino‐dendrimers

Polymer networks in which poly(propylene imine) dendrimers (Astramol?) are connected to each other by linear polytetrahydrofuran (polyTHF) segments, were prepared by two methods. The first method was a one‐step procedure in which bifunctionally living polyTHF, obtained by initiation of the THF polymerization with trifluoromethane sulfonic anhydride (triflic anhydride), was reacted with an amino‐dendrimer. This reaction was very fast but did not allow formation of the end products. The second method was a two‐step procedure. In a first step, living polyTHF, prepared with acryloyloxybutyl triflate as initiator, was grafted on an amino‐dendrimer, to form a star‐like, acrylate‐terminated polyTHF multi‐macromonomer with the dendrimer as core. In a second step, networks were obtained by Michael addition between the acrylate end‐groups and unreacted amino‐groups of the dendrimer. This cross‐linking reaction occurred spontaneously upon heating of the solution of the multi‐macromonomer with gelation times varying from a few minutes to a few hours, depending on the temperature and the composition of the prepolymers. With this method it was possible to prepare networks in the form of coatings or films. © 2003 Society of Chemical Industry