Annealing time dependence at very high temperature of electricarc-induced long-period fibre gratings

Long-period fibre gratings fabricated with an electric arc have been annealed at high temperatures. The time dependence of transmitted spectra are reported and related to the evolution of internal stresses in the fibre     

Annealing studies of undoped Hg1−xMnx Te bulk crystals at high temperatures

The effect of high temperature annealing treatments in varying mercury atmospheres on Hg_1−xMn_xTe crystals with long wavelength infrared/very long wavelength infrared cut off wavelengths has been studied. The undoped Hg_1−xMn_xTe crystals were grown using the traveling heater method with a tellurium solvent zone, and composition was verified by infrared transmission measurements. The crystals were subjected to annealing temperatures of 500 and 550°C under mercury pressures varying from Hg-rich conditions to Te-rich conditions. The samples were either air cooled or water cooled to room temperature. Hall effect measurements were carried out at 77K at magnetic fields varying from 500 Gauss to 10 kGauss. The hole concentration in the annealed crystals was found to be roughly inversely proportional to the partial pressure of Hg indicating that the material is essentially intrinsic at the anneal temperature. A defect model and a relationship between the mass action constants for the native acceptor defects of HgMnTe are presented.     

Simultaneous measurement of temperature and strain based on arc-induced long-period fibre gratings

A study on arc-induced long-period fibre gratings (LPFGs) revealed that their strain sensitivity depends on the electric current of the arc discharge. Based on that property, a sensor scheme comprising two concatenated LPFGs was implemented for discrimination of temperature and strain effects. This sensor presented resolutions of /spl plusmn/0.1/spl deg/C//spl radic/Hz and /spl plusmn/35 /spl mu//spl epsiv///spl radic/Hz, respectively.     

Tuning and wavelength switching erbium-doped fiber ring lasers by controlled bending in arc-induced long-period fiber gratings

In this paper, we report a simple method for the production of an all-fiber, tunable and wavelength switchable erbium-doped fiber ring laser (EDFRL). We use the shift in resonance wavelength and notch-depth of arc-induced long-period fiber gratings (LPFGs) when it is subject to controlled bend to suppress some wavelength gain and promote lasing in a selective way in a fiber laser system. By changing the bending radius, the operating wavelength of the EDFRL can be tuned from 1526 to 1538 nm and then switched and tuned from 1568 to 1557 nm. The maximum separation measured between laser lines was ～42 nm. This is one of the highest laser separations reported in a wavelength switching operation of an EDFL using a single LPFG as wavelength selective filter.     

Behavior of analog MOS integrated circuits at high temperatures

Thermal effects on small-signal characteristics of MOS transistors are studied and parameters of MOS amplifiers operating at high temperatures are calculated. The predicted performance has been experimentally verified and high-temperature measurements of an operational amplifier and a switched-capacitor precision amplifier are presented.     

Evaluation of graded-channel SOI MOSFET operation at high temperatures

This paper presents a comparative analysis between graded-channel (GC) and conventional fully depleted SOI MOSFETs devices operating at high temperatures (up to 300 °C). The electrical characteristics such as threshold voltage and subthreshold slope were obtained experimentally and by two-dimensional numerical simulations. The results indicated that GC transistors present nearly the same behavior as the conventional SOI MOSFET devices with similar channel length. Experimental analysis of the g_m/I_DS ratio and Early voltage demonstrated that in GC devices the low-frequency open-loop gain is significantly improved in comparison to conventional SOI devices at room and at high-temperature due to the Early voltage increase. The multiplication factor and parasitic bipolar transistor gain obtained by two-dimensional numerical simulations allowed the analysis of the breakdown voltage, which was demonstrated to be improved in the GC as compared to conventional SOI transistors in thin silicon layer devices in the whole temperature range under analysis.     

高温条件下光声信号的激光外差测量

用激光外差法在温度500K下获得了本征GaAs的光声吸收测量。     

High-frequency measurements of AlGaN/GaN HEMTs at high temperatures

High-frequency measurements of the 1.3-μm-long gate AlGaN-GaN HEMTs have been performed at temperatures ranging from 23 to 187°C. The cutoff frequency f_T decreased with increasing temperature. It was 13.7 and 8.7 GHz at 23 and 187°C, respectively. The effective electron velocities υ_eff in the channel evaluated from the total delay time versus I_D-inverse relation were 1.2 and 0.8×10⁷ cm/s at 23 and 187°C, respectively     

Fibre loss increase due to hydrogen generated at high temperatures

The loss changes at 1.39 and 1.88 ?m are measured for various nylon-jacketed fibres at a high temperature of 200°C. The loss increase at 1.39 ?m is due to the Si-OH-bond formation, and that at 1.88 ?m is caused by the absorption of hydrogen molecules in the silica glass. It is found that the loss increase due to the OH-bond formation is in proportion to the time-integrated concentration of the generated hydrogen molecules.     

Operating limits for RF power amplifiers at high junction temperatures

LDMOS RF––power amplifier components usually operate under severe conditions challenging long-term reliability. These components are subjected to high power dissipation and consequently high junction temperatures. Failure mechanisms are highly temperature dependent and driven by coupled electro-thermo-mechanical fields as a function of stress time. In this work we have investigated the reliability of such a component. Power cycling was used to assess its reliability by introduction of temperature gradients and transient at elevated junction temperatures. The experimental lifetime acceleration conditions provided transient thermal constraints to the thermo-mechanical strength of the silicon die. Power dissipation has been adjusted to cover a broad temperature range (T_{j max}: 200–300 °C) in the peak of a single power cycle. Different failure modes have been observed and related to the different temperature ranges. The experimental results have been combined with thermo-mechanical FE-simulations in ANSYS, leading to the validation of simulation models and implementation in a larger simulation network. The power cycling approach as applied in this paper provided a useful addition to the steady state reliability information. In this way, clear information about margins for safe operation under dynamical conditions has been obtained. This information is needed to fully exploit the functional capability of the component and avoid over-specification in the final application. Overall, the LDMOS RF–PA component showed excellent reliability which makes it suitable for application in telecom devices.     

Doping of 3C-SiC by implantation of nitrogen at high temperatures

Doping profiles and electrical properties are investigated on SiC samples doped with single energy implants from nitrogen. The profiles are analyzed using Pearson distributions for different implantation energies and temperatures. Implantations are performed for temperatures up to 1200°C. Diffusion during high temperature implantation is investigated and the diffusion coefficients measured range from 1.09 × 10⁻¹⁵ to 1.53 × 10⁻¹⁴cm²/s depending on temperature. The activation energy for implantation enhanced diffusion is estimated to be 0.91 eV. A comparison is made with diffusion during annealing. The activated dopants from high temperature implantation are investigated by the Hall probe method, showing that activation and mobility increase with temperature.     

GKZ-A型石英与钨的高温扩散封接

石英玻璃广泛地应用于高功率的放电器件和电光源中.由于石英的膨胀系数比钨小很多,不能直接封接.过去主要采用多道过渡玻璃封接或钼箔封     

Electrical characteristics of CdTe:Pb single crystals at high temperatures

The electrical properties of CdTe:Pb single crystals at high temperatures (400–900°C) and under controlled Cd vapor pressure (0.001–3 atm) were investigated for the first time. The temperature and baric dependences of the conductivity and Hall coefficient were measured. Low (in comparison with undoped CdTe) electron concentration indicates an increase in the number of impurity point defects related to the Pb impurity. The results obtained are explained within the Kröger theory of quasi-chemical reactions of defect formation on the assumption that lead may exist in the isolated state (Pb _Cd ⁺ ) and as a component of (Pb _Cd ⁺ V _Cd ^2? )^? associates.     

Physical limits and lifetime limitations of semiconductor devices at high temperatures

In many applications of electronics, a growing demand for devices being capable of operating at increased temperatures is developing. In automotive and aerospace industry, the replacement of mechanical or hydraulic systems by electronics requires harsh environmental conditions. Furthermore, the oil-well business, military, industrial, chemical, and consumer electronics show increasing interest in higher operating temperatures.In this paper, the influence of temperature on semiconductor device characteristics is discussed with regard to physical limits for device operation. Different semiconductor materials are compared with respect to high temperature electronics, and an overview of the state-of-the-art of high-temperature devices is given. With standard silicon technology, high operation temperatures (200°C) can be reached with reduced performance, the use of SiC enables electronic devices for much higher temperatures (600°C). For practical use, device lifetime becomes the limiting factor at increased temperatures, especially chip metallisation systems and packaging technologies are critical factors for device lifetime in most cases.     

Infrared loss increase phenomenon of coated optical fibers at high temperatures

The loss increase phenomenon of coated optical fibers at high temperature has been studied. The wavelength dependent loss increase, observed for plastic-coated fibers at 200°C, is found to be irreversible. During heating, the absorption peak of second overtone of Ge-OH preferentially appeared. The dependence of the loss increase on temperature, heating time, and dopant is also examined. The loss increase level is strongly dependent on phosphorous concentration. The experimental results indicate that the loss increase is caused by chemical reactions between fiber constituent materials and hydrogen generated from coating materials. It is also confirmed that the heating test of secondary coated fiber is a practical, useful method to evaluate the hydroxyl loss increase of optical fibers.