Effects of drop size and temperature on forward and backward scattering of microwaves by raindrops

An explanation is given for the peak sensitivity around 9?11 GHz to drop-size distribution and temperature of microwave attenuation due to a rain-filled medium. The sensitivity of radar reflectivity, differential radar reflectivity and differential radar cross-section to drop-size and temperature are also given. It is shown that at frequencies in excess of about 25 GHz the vertical radar cross-section of water drops can be greater than the horizontal.     

Microwave thermal emission of rain

The effective medium temperature necessary for the conversion of microwave thermal emission to slant-path attenuation has been calculated for 11.8 GHz for a homogeneous slab of rain. The first results from calculations on a cylindrical model of rain at 11.8 GHz are also presented. The influence of ground reflectivity coefficient is investigated.     

Effects of barrier layer and processing conditions on thin film Cu microstructure

The crystallographic texture and grain size of sputtered Cu films were characterized as a function of deposition temperature, barrier layer material, and vacuum conditions. For Cu deposited in a HV chamber, (111) Cu texture was found to weaken with increasing deposition temperatures on W, amorphous C and Ta barrier layers, each deposited at 30°C. Conversely, under identical Cu deposition conditions, texture was found to strengthen with increasing deposition temperature on Ta deposited at 100°C. Median Cu grain size varied parabolically with deposition temperature on all barrier layers and was slightly higher on the 100°C Ta at a given Cu deposition temperature, relative to the other underlayers. For depositions in an UHV chamber, Cu texture was found to strengthen with increasing Cu deposition temperature, independent of Ta deposition temperature. Median Cu grain size, however, was still higher on 100°C Ta than on 30°C Ta. The observed differences between the two different chambers suggest that the trend of weak texture at elevated deposition temperatures may be related to contamination. Characterization of the Ta underlayers revealed that the strengthened texture of Cu films deposited on 100°C Ta is likely related to textural inheritance.     

Reliability studies of MOCVD TiSiN and EnCoRe Ta(N)/Ta

Passivated single damascene copper SiO₂ damascene lines were evaluated in combination with TiSiN and Ta(N)/Ta diffusion barriers. Leakage current, breakdown and time-dependent dielectric breakdown properties were investigated on a wafer level basis for temperatures ranging between room temperature and 150 °C. It is found that the leakage performance of the wafers with a TiSiN barrier is better at room temperature, but at 150 °C the performance levels out with Ta(N)/Ta. Time-dependent dielectric breakdown measurements at 150 °C show that the lifetime of the interconnect is higher with the selected Ta(N)/Ta barrier than for TiSiN.     

Fermi-level pinning induced thermal instability in the effective work function of TaN in TaN/SiO/sub 2/ gate stack

In this letter, we demonstrate for the first time that the Fermi-level pinning caused by the formation of Ta(N)-Si bonds at the TaN/SiO/sub 2/ interface is responsible for the thermal instability of the effective work function of TaN in TaN/SiO/sub 2/ devices after high temperature rapid thermal annealing (RTA). Because of weak charge transfer between Hf and Ta(N) and hence negligible pinning effect at the TaN/HfO/sub 2/ interface, the effective work function of TaN is significantly more thermally stable on HfO/sub 2/ than on SiO/sub 2/ dielectric during RTA. This finding provides a guideline for the work function tuning and the integration of metal gate with high-/spl kappa/ dielectric for advanced CMOS devices.     

Refractive index and temperature dependent displacements of resonant peaks of long period grating inscribed in hydrogen loaded SMF-28 fiber

In this paper, the effects of refractive index (RI) of surrounding medium and ambient temperature on the transmission characteristics of a long period grating (LPG) are experimentally analyzed. The spectral behavior of LPG is investigated when the ambient index is higher or lower than that of the cladding material. The results show that the refractive index sensitivity of lower order attenuation bands is very low compared with that of the highest order attenuation band. But in the case of temperature, the lower order attenuation bands of the LPG can also exhibit good sensitivity like the higher-order bands.     

A simple expression for estimating attenuation by fog at millimeter wavelengths

At millimeter wavelengths, fog attenuation is a function of the fog density, extent, index of refraction of the fog medium, and wavelength. The attenuation is usually determined by first estimating the index of refraction of water for the wavelength and temperature of interest and then calculating the attenuation using the Rayleigh approximation. In this communication fog attenuation is computed for a large set of wavelengths and indices of refraction. A regression analysis of the attenuation is then conducted as a function of wavelength and temperature. It is shown that an almost perfect fit can be obtained with a four-term regression on wavelength and temperature for the ranges of 3 mm <lambda < 3cm and-8degC< T < 25degC, respectively 5666. This expression produces a normalized fog attenuation; the total attenuation is easily computed by multiplying the normalized attenuation by the fog density and extent. If fog density data are not available, a formula for estimating the density from fog visibility is given.     

Choice of standard medium temperature for tropical and equatorialclimates: Comparison between radiometric and satellite beaconattenuation data on two 12 GHz links in Brazil

Results are presented for two years of satellite beacon and radiometric attenuation measurements on two 12 GHz Earth-space links located in Rio de Janeiro, south-eastern Brazil and Belem, northern Brazil. Results suggest that the choice of 285 K for the standard medium temperature, to be used in the calculation of attenuation from radiometric measurements of sky temperature, may underestimate the conditions for tropical and equatorial environments     

Prediction and Measurement of Electron Density and Collision Frequency in a Weakly Ionised Pine Fire

Pine litter flame is a weakly ionised medium. Electron-neutral collisions are a dominant form of particle interaction in the flame. Assuming flame electrons to be in thermal equilibrium with neutrals and average electron-neutral collision frequency to be much higher than the plasma frequency, the propagation of microwaves through the flame is predicted to suffer signal intensity loss. A controlled fire burner was constructed where various natural vegetation species could be used as fuel. The burner was equipped with thermocouples and used as a cavity for microwaves with a laboratory quality network analyzer to measure wave attenuation. Electron density and collision frequency were then calculated from the measured attenuation. The parameters are important for numerical prediction of electromagnetic wave propagation in wildfire environments. A controlled pine litter fire with a maximum flame temperature of 1080 K was set in the burner and microwaves (8–10.5 GHz) were caused to propagate through the flame. A microwave signal loss of 1.6–5.8 dB was measured within the frequency range. Based on the measured attenuation, electron density and electron-neutral collision frequency in pine fire were calculated to range from 0.51–1.35?×?10¹⁶ m^?3 and 3.43–5.97?×?10¹⁰ s^?1 respectively.     

Deposition of thin refractory MIS structures on InP

In the present investigation, we report on significant increases in the refractory-InP Schottky barrier by process modification of the metal-semiconductor interface. Refractory-InP MIS structures were investigated as pos-sible gate metallizations. These structures consisted of Ta/Ta₂}O₅}/InP and TiW/TiO₂} /InP. A thin layer of Ta (100å) was electron beam vapor aeposited followed by the in situ formation of Ta₂}O₅} at 300?C and an oxygen overpressure. The remainder of the Ta film was deposited at 90?C substrate temperature. The TiW/TiO₂} system was formed by sputter deposition of Ti (100A?), in situ oxidation to form TiO₂} followed by deposition of TiW (88 wt % W, 12 wt % Ti). Effective barrier height for the TiW/TiO /InP structure was measured to be 0.65 eV and for the Ta/Ta₂}O₂} /InP, 0.5 eV. Leakage current at-5V was less than 3 A/cm²} for both refractory-InP MIS structures. The TiW/TiO₂} /InP structure was stable up to 400-450°C, while the Ta/Ta₂ O₅/InP system degraded to 0.2 eV at 300-350?C.     

弥散介质条件下辐射测温方法（特邀）

在航空航天、冶金铸造等各种工业现场高温热试验过程中,需要在高浓度弥散介质遮蔽物件表面的条件下,快速、准确地获取试验件表面的高温温度。传统的辐射测温方法包括波段辐射法、亮度法、比色测温法、多波长测温法等,是实现高温测量的一种主要测量方法。弥散介质由于介质粒子的作用会产生各种光谱散射、吸收和发射效应,给高温的准确测量带来了很大的干扰,导致测量结果产生偏差,必须要改进经典辐射测温方法。论述了弥散介质条件下几种主要的辐射测温方法,包括试验数据反推法、热辐射计算法、多通道分裂窗法、信息复原计算法、神经网络计算法等,分析了各种方法的优点和不足,总结了弥散介质条件下辐射测温方法面临的挑战和发展趋势。     

参量变化对长程表面等离子体波特性的影响

为了掌握长程表面等离子体波的共振角度、共振峰半峰全宽以及衰减峰深度等重要特性,采用棱镜耦合激发介质-金属薄膜-介质对称结构中的长程表面等离子体波,研究了金属膜材料、厚度、介质折射率及介质厚度等参量变化时对长程表面等离子体波特性的影响。结果表明,实验中激发的长程表面等离子体波的衰减峰半峰全宽比传统的窄1~2个数量级;当介质膜厚度为500nm和1300nm时,激发的表面等离子体波的衰减深度只有薄膜厚度为700nm和1000nm时的1/2左右;随着介质膜厚度的增加,半峰全宽减小,金属膜越薄,衰减深度越深,衰减峰的半峰全宽值越小;介质膜折射率的改变对于半峰全宽的影响不明显;金属膜参量的变化将改变共振峰的位置。该研究为长程表面等离子体波的激发及应用于传感领域提供了有效依据,有利于其在波导和生物传感等方面的应用。     

The use of thermopower and DC electrical conductivity measurements to determine the dynamic resistance and Fermi surface distortion of a thin film of gold

The dynamic resistance of an evaporated thin film of gold is calculated from the effective resistance (from thermopower measurements) and the ohmic resistance (from two-terminal measurements). The dynamic resistance is positive over the temperature range 323-493?K. A positive thermopower at room temperature indicates that the Fermi surface is considerably distorted along the <111> direction, Thermal expansion is identified to occur between 323-393?K and 414-443?K and thermal compression between 393-413?K and 443-493?K     

颗粒包覆法制备BZT-CT复合陶瓷

采用预合成的方法,分别用得到的单斜类锆钙钛矿相Bi2(Zn1/3Ta2/3)2O7(β-BZT)和钙钛矿相CaTiO3(CT)的粉末作为正负温度系数组元,用sol-gel法制备的ZnO-B2O3-SiO2玻璃,包覆两组元颗粒以阻止其相互反应,从而制备复相零温度系数微波陶瓷。结果表明:预合成及颗粒包覆法可抑制两相固溶反应,有效降低复相陶瓷的烧结温度,调节温度系数。特别是900℃烧结的w(CT)为4%的样品,其εr约为47,αε为2.8×10–6℃–1。     

Study of Ta-barrier and pore sealing dielectric layer interaction for enhanced barrier performance of Cu/ultralow /spl kappa/(/spl kappa/<2.2) interconnects

For Cu/ultralow /spl kappa/ application, understanding of interfacial interaction between Ta and pore-sealing layer over porous dielectric is very important in order to achieve a good barrier performance. However, characterizing the effect of pore-sealing layer on barrier performance poses a big challenge. Most studies monitored degradation of the electrical performance of the Ta barrier after integration process with little discussions on interfacial interaction. In this letter, the interaction at the interface between Ta and pore-sealing layer deposited over porous SiLK (/spl kappa//spl sim/2.2) film is investigated. The barrier performance is improved significantly by nitrogen incorporation during liner growth. This methodology is very effective for improving metal barrier and pore-sealing performance for Cu/ultralow /spl kappa/ interconnects.     

单晶钽裂纹尖端的位错原位观察

本文利用原创双金属片技术,在透射电子显微镜中实现了对小尺寸单晶钽(Ta)拉伸变形的原位实验观察.由于裂纹尖端的塑性区具有与材料整体塑性变形类似的特征,因此本实验针对裂纹尖端处的位错行为进行了研究.实验发现随着裂纹的扩展,有大量呈弯曲或钩状的位错不断形核,并朝着位错弯曲的部分滑移.在进一步的拉伸应力作用下,位错的长直部分不断长大并使这些位错在裂纹尖端堆积.对裂纹尖端的原位高分辨图像观察,发现在单晶钽中有大量伯氏矢量b=1/2〈111〉型位错的形核和逃逸现象.因此,证明这些混合位错对BCC单晶钽的塑性变形有一定贡献,并首次给出了纳米尺度材料中位错堆积的实验证据.     

Low-OH-absorption fluoride glass infra-red optical fibres

Ultralow losses of 10?2 to 10?3 dB/km have been predicted in fluoride glass optical fibres between 2 and 4.5 ?m. At 2.9 ?m, in the central part of this spectral region, the OH? ion presents its fundamental stretching vibration which gives rise to a strong and broad absorption. The attenuation at 2.9 ?m in a step-index fluorozirconate glass fibre has been brought down to 58 dB/km, by reducing the OH? concentration in the glass. It is the lowest attenuation yet reported at this wavelength in any optical fibre.     

Sem,auger spectroscopy and ion backscattering techniques applied to analyses of Au/refractory metallizations

The concurrent application of the SEM, AES, X-ray diffractometry and Rutherford Backscattering (RBS) techniques to Au/refractory metallizations is analyzed with respect to the study of thin film interdiffusion, intermetallic formation, microcracking and oxidation phenomena. The SEM in the backscatter electron image mode was used for resolution of intermetallic compounds and interdiffusion products, while AES and RBS analyses were used to obtain depth-composition profiles. The metallizations studied were Ta/Pt/Ta/Au and W/Au. The combination of Ta/Pt/Ta and Ti/Pt have been shown to be effective barriers to gold-silicon interdiffusion. Defects in the tungsten barrier were found to result in silicon migration to the front surface and gold migration toward the substrate at temperatures between 550°C-700°C . The diffusion constants for Au-Ta and Au-Pt interdiffusion have been determined from the AES data.     

Study on ta diffusion barrier in Al/Si system

The property of Ta as a diffusion barrier is studied for Al/Ta/Si structure. Interfacial reactions of Al(180 nm)/Ta(130 nm)/Si and Al(180 nm)/Ta(24 nm)/Si, in the temperature range 450∼600°C for 30 min, have been investigated. In Al/Ta(130 nm)/Si system, which is Ta-excess case, Al₃Ta is formed at 500°C. At 575°C, TaSi₂ is formed at the interface of Ta Si. At 600°C, after Al₃Ta decomposes at the interface of Al₃Ta TaSi₂, free Ta is bonded to TaSi₂ with the supply of Si from Si substrate and free Al diffuses through TaSi₂, resulting in Al spiking. In Al/Ta(24 nm)/Si system, which is Al-excess case, Al₃Ta is formed at 500°C. At the same temperature of 500°C, after Al₃Ta decomposes at the interface of Al₃Ta/Si, free Ta reacts with Si to form TaSi₂ and free Al diffuses to Si substrate, resulting in Al spiking. The results of interfacial reactions can be understood from the calculated Al-Si-Ta ternary phase diagram. It can be concluded that the reaction at Al/Ta should be suppressed to improve the performance of Ta diffusion barrier in Al/Si system.     

Propagation characteristics of superconducting microstrip lines

The modified spectral-domain approach is applied to study the propagation characteristics of high temperature superconducting microstrip lines whose signal strip and ground plane are of arbitrary thickness. In this study, numerical results for effective dielectric constant, attenuation constant, and strip current distribution are presented to discuss the effects due to frequency, temperature, strip thickness, and substrate loss tangent. In particular, the conductor and dielectric attenuation constants of superconducting microstrip line are depicted separately to discuss the mechanism of the line losses. A comparison with published theoretical and experimental results is also included to check the accuracy of the new approach's results