An improved methodology for determining temperature dependentmoduli of underfill encapsulants

Finite element analyses (FEAs) have been widely used to preventively predict the reliability issues of flip-chip (FC) packages. The validity of the simulation results strongly depends on the inputs of the involved material properties. For FC packages Young's modulus-temperature relationship is a critical material property in predicting of the package reliability during -55°C to 125°C thermal cycling. Traditional tensile tests can obtain the modulus at selected temperatures, but are tedious, expensive, and unable to accurately predict the Young's modulus-temperature relationship within a wide temperature range. Thus, this paper is targeted to provide a simple but relatively accurate methodology to obtain the Young's modulus-temperature relationship. In this paper, three commercial silica filled underfill materials were studied. A simple specimen (based on ASTM D638M) preparation method was established using a Teflon mold. A dynamic-mechanical analyzer (DMA) was used to obtain the stress-strain relationship under controlled force mode, storage and loss modulus under multi-frequency mode, and stress relaxation under stress relaxation mode. A simple viscoelastic model was used and an empirical methodology for obtaining Young's modulus-temperature relationship was established     

涂覆层参数对FBG温度灵敏度的影响

分析了涂覆层的物理参数对光纤光栅（FBG）温度灵敏度的影响,数值分析结果表明,大涂覆厚度、高弹性模量、高泊松比、高线膨胀系数有助于提高FBG的温度灵敏度。FBG温度灵敏度的饱和值主要取决于涂覆层的弹性模量和泊松比,因此不能单纯依靠选取大弹性模量或泊松比的涂覆来提高温度灵敏度,还须综合考虑弹性模量和泊松比对温度灵敏度的影响,以确定两参数的最佳值。     

EMC材料特性参数对QFN器件热应力的影响

利用动态机械分析仪测定环氧模塑封（EMC）材料随温度变化的杨氏模量;使用热机械分析仪测定EMC随温度变化的尺寸变化量,并拟合得到热膨胀系数。在实验数据的基础上,变动EMC的橡胶态杨氏模量、玻璃态杨氏模量、玻璃转化温度以及热膨胀系数,并使用有限元软件MSC Marc分别模拟其热应力,以此来分析材料特性参数对热应力的影响。结果表明：QFN器件的最大热应力出现在芯片、粘结剂和EMC的连接处;减小橡胶态或玻璃态的杨氏模量可以有效地减小热应力;增大玻璃转化温度或热膨胀系数,QFN器件的热应力都会有所增加。     

Doubly coated optical fibres with a low sensitivity to temperatureand microbending

In order to prevent microbending losses in optical fibers over a wide temperature range, a new buffer coating and a new top coating have been developed. The buffer coating has a low Young's modulus over a wide temperature range, whereas the top coating has a modulus which is high compared with the modulus of the coatings that are generally used. The application of these coatings results in fibers with a very low microbending sensitivity. However, at low temperatures added optical loss is observed which correlates with a change in the radial stress state of the buffer coating from compression to tension. It is demonstrated by model calculations as well as by experiments that these optical losses can be avoided if the thickness of the buffer layer does not exceed a critical value. The new coatings are shown to provide a good protection of the fiber from mechanical damage     

Kinetics of Diffusion-Induced Recrystallization in the Cu(Ni) System at Low Temperatures

During annealing at temperatures around 800 K, Ni can quickly penetrate into Cu due to diffusion-induced recrystallization (DIR). To examine this penetration rate, the kinetics of DIR in the Cu(Ni) system was experimentally determined in the present study. Experiments were conducted using polycrystalline Cu/Ni/Cu diffusion couples which were prepared by a diffusion bonding technique. The diffusion couples were isothermally annealed at temperatures of T = 723 K to 823 K for various times up to t = 144 h. During annealing, a region alloyed with Ni is formed in Cu from the Cu/Ni interface due to DIR. The concentration of Ni on the Ni-rich side in the DIR region remains almost constant independent of the annealing time, but gradually increases with increasing annealing temperature. However, the mean thickness of the DIR region increased with increasing annealing time. The growth rate of the DIR region is a monotonically increasing function of the annealing temperature. The experimental findings of the kinetics study were quantitatively analyzed using a mathematical model. The analysis indicates that the growth of the DIR region is controlled by the interface reaction at the moving boundary of the DIR region as well as the boundary diffusion along the grain boundaries across the DIR region.     

Influence of optical properties of the SOI structure on the wafer temperature during rapid thermal annealing

Optical characteristics are compared theoretically, and temperature differences of the Si wafer with the B-doped SOI structure and substrate wafer are evaluated during rapid thermal annealing. It is shown that under identical annealing conditions and temperatures above 800 K, the difference in their temperatures can reach ∼30 K. We studied the dependence of the total emissivity and temperature of the wafer with the SOI structure on the concentration of the doping impurity in the Si layer. The method of the quantitative analysis of variations of the wafer temperature under invariable annealing conditions depending on the variations of emissivity of its surfaces is suggested.     

Ferromagnetism in Co- and Mn-doped ZnO

Bulk single crystals of Sn-doped ZnO were implanted with Co or Mn at doses designed to produce transition metal concentrations of 3–5 at.% in the near-surface (2000 Å) region. The implantation was performed at 350 °C to promote dynamic annealing of ion-induced damage. Following annealing at 700 °C, temperature-dependent magnetization measurements showed ordering temperatures of 300 K for Co- and 250 K for Mn-implanted ZnO. Clear hysteresis loops were obtained at these temperatures. The coercive fields were 100 Oe for all measurement temperatures. X-ray diffraction showed no detectable second phases in the Mn-implanted material. One plausible origin for the ferromagnetism in this case is a carrier-induced mechanism. By sharp contrast, the Co-implanted material showed evidence for the presence of Co precipitates with hexagonal symmetry, which is the cause of the room temperature ferromagnetism. Our results are consistent with the stabilization of ferromagnetic states by electron doping in transition metal-doped ZnO predicted by Sato and Katayama–Yoshida [Jpn. J. Appl. Phys. 40 (2001) L334]. This work shows the excellent promise of Mn-doped ZnO for potential room temperature spintronic applications.     

Co-Implantation and autocompensation in close contact rapid thermal annealing of Si-implanted GaAs:Cr

Close contact rapid thermal annealing of semi-insulating GaAs:Cr implanted with Si, Si + Al, and Si + P has been studied using variable temperature Hall effect measurements and low temperature (4.2K) photoluminescence (PL) spectroscopy. Isochronal (10 sec) and isothermal (1000° C) anneals indicate that As is lost from the surface during close contact annealing at high anneal temperatures and long anneal times. Samples which were implanted with Si alone show maximum activation at an annealing temperature of 900° C, above which activation efficiency decreases. Low temperature Hall and PL measurements indicate that this reduced activation is due to increasing auto-compensation of Si donors by Si acceptors at higher anneal temperatures. However, co-implantation of column V elements can increase the activation of Si implants by reducing Si occupancy of As sites and increasing Si occupancy of Ga sites, and therebyoffset the effects of As loss from the surface. For samples implanted with Si + P, activation increases continuously up to a maximum at an anneal temperature of 1050° C, and both low temperature Hall and PL measurements indicate that autocompensation does not increase in this case as the anneal temperature increases. In contrast, samples implanted with Si + Al show very low activation and very high compensation at all anneal temperatures, as expected. The use of column V co-implants in conjunction with close contact RTA can produce excellent donor activation of Si implanted GaAs.     

Preparation and characterization of new window material CdS thin films at low substrate temperature (<300 K) with vacuum deposition

Low-temperature vacuum deposition instead of the commonly used vacuum deposition at high substrate temperatures has been applied to prepare new window material CdS thin films. The structural, optical and electrical properties of vacuum-evaporated CdS thin films were investigated as a function of substrate temperature (100–300 K) and the post-deposition annealing temperature (at 473, 573 and 673 K). It was determined that films deposited at all substrate temperatures were polycrystalline in nature with hexagonal structure and a strong (0 0 2) texture. The AFM and SEM studies showed that the microstructures of the as-deposited films agreed with the expectations from structure zone model. X-ray diffraction studies showed that the crystallinity of the CdS films was improved on annealing. Optical spectroscopy results of the films indicated that the optical band gap value increased from 2.40 to 2.42 eV with decreased substrate temperature. Increasing the annealing temperature sharpened the band edge. The dark resistivity increased from 4.5×10³ to 7.3×10³ Ω cm and the carrier concentration decreased from 4.7×10¹⁷ to 3.5×10¹⁵ cm⁻³ as the substrate temperature decreased from 300 to 100 K.     

Exfoliation and blistering of Cd<Subscript>0.96</Subscript>Zn<Subscript>0.04</Subscript>Te substrates by ion implantation

As part of a series of wafer bonding experiments, the exfoliation/blistering of ion-implanted Cd_0.96Zn_0.04Te substrates was investigated as a function of postimplantation annealing conditions. (211) Cd_0.96Zn_0.04Te samples were implanted either with hydrogen (5×10¹⁶ cm⁻²; 40–200 keV) or co-implanted with boron (1×10¹⁵ cm⁻²; 147 keV) and hydrogen (1–5×10¹⁶ cm⁻²; 40 keV) at intended implant temperatures of 253 K or 77 K. Silicon reference samples were simultaneously co-implanted. The change in the implant profile after annealing at low temperatures (<300°C) was monitored using high-resolution x-ray diffraction, atomic force microscopy (AFM), and optical microscopy. The samples implanted at the higher temperature did not show any evidence of blistering after annealing, although there was evidence of sample heating above 253 K during the implant. The samples implanted at 77 K blistered at temperatures ranging from 150°C to 300°C, depending on the hydrogen implant dose and the presence of the boron co-implant. The production of blisters under different implant and annealing conditions is consistent with nucleation of subsurface defects at lower temperature, followed by blistering/exfoliation at higher temperature. The surface roughness remained comparable to that of the as-implanted sample after the lower temperature anneal sequence, so this defect nucleation step is consistent with a wafer bond annealing step prior to exfoliation. Higher temperature anneals lead to exfoliation of all samples implanted at 77 K, although the blistering temperature (150–300°C) was a strong function of the implant conditions. The exfoliated layer thickness was 330 nm, in good agreement with the projected range. The “optimum” conditions based on our experimental data showed that implanting CdZnTe with H⁺ at 77 K and a dose of 5×10¹⁶/cm² is compatible with developing high interfacial energy at the bonded interface during a low-temperature (150°C) anneal followed by layer exfoliation at higher (300°C) temperature.     

Annealing behavior of radiation damage in JFET-input operational amplifiers

The elevated and room temperature annealing behavior of radiation damage in JFET-input operational amplifiers (op-amps) were investigated. High-and low-dose-rate irradiation results show that one of the JFET-input op-amps studied in this paper exhibits enhanced low-dose-rate sensitivity and the other shows time-dependent effect. The offset voltage of both op-amps increases during long-term annealing at room temperature. However, the offset voltage decreases at elevated temperature. The dramatic difference in annealing behavior at room and elevated temperatures indicates the migration behavior of radiation-induced species at elevated and room temperatures. This provides useful information to understand the degradation and annealing mechanisms in JFET-input op-amps under total ionizing radiation. Moreover, the annealing of oxide trapped charges should be taken into consideration, when using elevated temperature methods to evaluate low-dose-rate damage.     

JFET输入运算放大器辐射损伤的退火行为

The elevated and room temperature annealing behavior of radiation damage in JFET-input operational amplifiers （op-amps） were investigated. High- and low-dose-rate irradiation results show that one of the JFET-input op-amps studied in this paper exhibits enhanced low-dose-rate sensitivity and the other shows time-dependent effect. The offset voltage of both op-amps increases during long-term annealing at room temperature. However, the offset voltage decreases at elevated temperature. The dramatic difference in annealing behavior at room and elevated temperatures indicates the migration behavior of radiation-induced species at elevated and room temperatures. This provides useful information to understand the degradation and annealing mechanisms in JFET-input op-amps under total ionizing radiation. Moreover, the annealing of oxide trapped charges should be taken into consideration, when using elevated temperature methods to evaluate low-dose-rate damage.     

Material effects on phase sensitivity in polarimetric optical fibersensors

The material effect on the phase sensitivity in polarimetric fiber sensors is considered using inhomogeneous stress analysis. It is found that both the Young's modulus and the Poisson's ratio of the stress-producing regions have a significant effect on the phase sensitivity. For the pressure, temperature, and strain sensors considered, it is found that the phase sensitivity has a strong linear dependence on the transverse optoelastic coefficient and a lesser nonlinear dependence on the Young's modulus of the core material. It is only possible to null the phase sensitivity to a particular measurand by adjusting the material coefficients in the stress-producing region but not in the core region     

Effect of the annealing temperature on erbium ion electroluminescence in Si:(Er,O) diodes with (111) substrate orientation

The influence of the temperature of secondary annealing, stimulating the formation of optically and electrically active centers, on the erbium ion electroluminescence (EL) at λ≈1.54 μm in (111) Si:(Er,O) diodes has been studied. The diodes were fabricated by the implantation of 2.0 and 1.6 MeV erbium ions at doses of 3×10¹⁴ cm⁻² and oxygen ions (0.28 and 0.22 MeV, 3×10¹⁵ cm⁻²). At room temperature, the EL intensity in the breakdown mode grows with the annealing temperature increasing from 700 to 950°C. At annealing temperatures of 975–1100°C, no erbium EL is observed in the breakdown mode owing to the formation of microplasmas. The intensity of the injection EL at 80 K decreases with the annealing temperature increasing from 700 to 1100°C. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 35, No. 10, 2001, pp. 1224–1227. Original Russian Text Copyright ? 2001 by Sobolev, Emel’yanov, Nikolaev.     

Optical fibre jacketed with high-modulus low-linear-expansion-coefficient polymer

A high Young's modulus, low-linear-expansion-coefficient-polymer loose-jacket optical fibre has been developed using orientated polyoxymethylene (POM), which exhibits Young's moduli 20 to 40 GPa and linear expansion coefficients ? 10?6°C?1. The highly orientated POM loose-jacket fibre has no microbending losses in a temperature range ?60 to 80°C.     

Behaviour of erbium implanted in InP

Erbium impurities were implanted in indium phosphide. The 2 K, 77 K and 300 K photoluminescence spectra show, after annealing at high temperature, the main erbium emission centered at 1.536μm. The variation of this Er-peak luminescence is studied as a function of the implanted dose, the annealing temperature and the annealing duration.     

Effect of temperature rise and hydrostatic pressure on microbending loss and refractive index change in double-coated optical fiber

This paper presents an analysis of the effect of temperature rise and hydrostatic pressure on microbending loss, refractive index change, and stress components of a double-coated optical fiber by considering coating material parameters such as Young's modulus and the Poisson ratio.

It is shown that, when temperature rises, the microbending loss and refractive index changes would decrease with increase of thickness of primary coating layer and will increase after passing through a minima. Increase of thickness of secondary coating layer causes the microbending loss and refractive index changes to decrease.

We have shown that the temperature rise affecting the fiber makes the microbending loss and refractive index decrease, linearly. At a particular temperature, the microbending loss takes negative values, due to tensile pressure applied on the fiber.

The increase of Young's modulus and the Poisson ratio of primary coating would lower the microbending loss and refractive index change whereas in the secondary coating layer, the condition reverses.     

Formation and annealing of radiation defects in tin-doped <Emphasis Type="Italic">p</Emphasis>-type germanium crystals

The effect of tin on the formation and annealing of radiation defects in p-type germanium crystals irradiated with 6-MeV electrons at a temperature of 80 K is studied. It is shown that acceptor complexes SnV with a hole ionization enthalpy of 0.16 eV are dominant in irradiated Ge:(Sn, Ga) crystals after their heating to a temperature of 300 K. These complexes disappeared as a result of the annealing of irradiated crystals in the temperature range 30–75°C. Annealing of irradiated crystals at temperatures in the range 110–150°C brings about the formation of deep-level centers with a donor level at E _v + 0.29 eV; this center is presumably related to a complex consisting of a tin atom and an interstitial gallium atom.     

Attenuation and dispersion for high-Tc superconductingmicrostrip lines

The attenuation and dispersion of microstrip lines of the high-T_c superconductor YBa₂Cu₃O₇ (YBCO) on yttria-stabilized zirconia substrates as a function of frequency and temperature are calculated. The effect on pulse propagation of superconducting and model dispersion in addition to the attenuation is demonstrated. At 60 K, microstrip lines of YBCO are significantly less attenuating at frequencies below 500 GHz than microstrip lines of copper at the same temperature. This advantage is particularly significant at the higher attenuations that result as the substrate thickness is made smaller for miniaturization or to improve the microstrip line bandwidth. The application of YBCO for microstrip lines appears to be most useful at frequencies above 100 GHz and dielectric thicknesses less than 100 μm, where the attenuation of cooled copper is prohibitively large. Cooled to temperatures below 20 K, YBCO may make possible a new generation of extremely high bandwidth (~5 THz), small-feature-size (~5 μm) circuits and devices     

Comparison of NMOS and PMOS hot carrier effects from 300 to 77 K

Since hot carrier effects can pose a potential limit to device scaling, hot-carrier-induced device degradation has been one of the major concerns in modern device technology. Currently, there is a great interest in pursuing low-temperature operation of MOS devices since it offers many advantages compared to room temperature operation. Also, low-temperature operation is often required for space applications. However, low-temperature operation exacerbates hot carrier reliability of MOS devices. Even though hot carrier effects are significantly worse at low temperature, most of the studies on hot-carrier-induced device degradation were done at room temperature and little has been done at low temperature. In this work, hot-carrier-induced device degradation is characterized from 77 K to room temperature for both NMOS and PMOS devices with the emphasis on low-temperature behavior of hot carrier degradation. For NMOS devices, the worst case bias condition for hot carrier effects is found to be a function of temperature. It is also determined that one of the primary reasons for the great reduction on hot carrier device lifetime at low temperature is that a given amount of damage simply induces a greater reduction on device performance at low temperature. For PMOS devices, the initial damage appears similar for both room temperature and 77 K; however, subsequent annealing indicates that the damage mechanism at 77 K differs markedly from that at 300 K. Hot carrier stressing on PMOS devices at low temperature appears to induce hole generation and substantial interface state creation upon annealing unlike 300 K stressed devices. This finding may have serious reliability implications for PMOS devices operated at cryogenic temperatures