Gain measurements in 1.3 µm InGaAsP-InP double heterostructure lasers

The net gain per unit length (G) versus current (I) is measured at various temperatures for 1.3 μm InGaAsP-InP double heterostructure lasers.Gis found to vary linearly with the currentIat a given temperature. The gain bandwidth is found to decrease with decreasing temperature. The lasing photon energy decreases at 0.325 meV/K with increasing temperature. Also, the slopedG/dIat the lasing photon energies decreases with increasing temperature. This decrease is more rapid forT > sim210K. This faster decrease is consistent with the observed higher temperature dependence of threshold (low T0at high temperatures) of 1.3 μm InGaAsP lasers. A carrier loss mechanism, due to Auger recombination, also predicts thatdG/dIshould decrease much faster with increasing temperature at high temperatures. We also find that the slopedG/dIdecreases slowly with increasing temperature for a GaAs laser, which is consistent with the observed temperature dependence of threshold of these lasers.     

Electrical properties of high permittivity ZrO2 gate dielectrics on strained-Si

Deposition and electrical properties of high dielectric constant (high-k) ultrathin ZrO₂ films on tensilely strained silicon (strained-Si) substrate are reported. ZrO₂ thin films have been deposited using a microwave plasma enhanced chemical vapor deposition technique at a low temperature (150 °C). Metal insulator semiconductor (MIS) structures are used for high frequency capacitance–voltage (C–V), current–voltage (I–V), and conductance–voltage (G–V) characterization. Using MIS capacitor structures, the reliability and the leakage current characteristics have been studied both at room and high temperature. Schottky conduction mechanism is found to dominate the current conduction at a high temperature. Observed good electrical and reliability properties suggest the suitability of deposited ZrO₂ thin films as an alternative as gate dielectrics. Compatibility of ZrO₂ as a gate dielectric on strained-Si is shown.     

金属化光纤光栅高温失效及其光谱特性

光纤光栅(FBG)作为温度传感器在智能结构领域得到广泛关注,然而将其埋入金属基体的方法大多是焊接方法。由于焊接过程经历高温,对FBG传感特性将产生一定不良影响。为提高FBG在高温工况下的应用,采用化学镀结合电镀的方法,对FBG进行了镀铜、镀镍金属化试验。采用高温加热炉对金属化FBG进行了短时间高温失效试验,分析了300~900℃区间内金属化FBG的温度灵敏度、光谱特性以及功率衰减规律。结果表明:在300~800℃温度区间,镀铜、镀镍的FBG以及裸光栅的平均温度灵敏度分别为15.35 pm/℃、16.34 pm/℃、16.1 pm/℃;金属化FBG的失效温度约为900℃,与裸光栅相比提高了约100℃;获得了金属化FBG失效过程的光谱及反射峰功率衰减情况。     

Gate oxide integrity of thermal oxide grown on high temperatureformed Si0.3Ge0.7

We have investigated the gate oxide integrity of thermal oxides direct grown on high temperature formed Si_0.3Ge_0.7. Good oxide integrity is evidenced by the low interface-trap density of 5.9×10¹⁰ eV^-1 cm^-2, low oxide charge density of -5.6×10¹⁰ cm^-2, and the small stress-induced leakage current after -3.3 V stress for 10 000 s. The good gate oxide integrity is due to the high temperature formed and strain-relaxed Si_0.3Ge_0.7 that has a original smooth surface and stable after subsequent high temperature process     

Strain-insensitive and high temperature fiber sensor based on a Mach–Zehnder modal interferometer

In this paper, a strain insensitive high temperature fiber sensor based on the modal interferometer is proposed. It is composed of a piece of small-core photosensitive fiber (SCPSF) which is spliced between two pieces of single mode fiber (SMF). Compared to other high temperature fiber sensor based on the modal interferometer, the sensor owns the highest temperature sensitivity of 106.64 pm/°C from 200 °C to 1000 °C. The temperature to strain cross sensitivity of the sensor is low and only 0.00675 °C/με. The reasons for realizing the high temperature sensitivity is also discussed.     

Temperature effects on tungsten etching

The influence of the substrate temperature (from T_s = +20°C to T_s = −45°C) on the etching characteristics (etch rate and anisotropy) of tungsten material has been investigated using a surface-wave sustained magnetoplasma reactor operated with SF₆. By correlating the F-atom concentration and the ion current density to the etching characteristics, we found that ion-assisted etching becomes more important than spontaneous chemical etching as the substrate temperature and SF₆ gas pressure decrease, ensuring, in absence of external biasing, high etching anisotropy together with high microscopic uniformity for submicrometer features (0.2 to 1 μm). Our results reveal the competitive influence between substrate temperature (which inhibits spontaneous chemical reaction as it is lowered) and gas pressure (which favours spontaneous chemical reaction as it is increased). Obtaining high anisotropy requires, in the present case, a substrate temperature of T_s = −20°C for P = 0.5 mTorr and a temperature as low as T_s = −35°C for P = 1.5 mTorr.     

Temperature dependence of light-current characteristics of0.98-μm Al-free strained-quantum-well lasers

The decrease of the differential efficiency of 0.98-μm semiconductor lasers with temperature can make high power, high temperature applications difficult. We present an experimental and theoretical study of the temperature dependence of the internal quantum efficiency, internal loss and differential gain of 0.98-μm InGaAs/InGaAsP/InGaP strained quantum well lasers. In contrast to some earlier results, our measurements show the dominance of internal loss, attributed to free carrier absorption, in determining the temperature dependence of the differential efficiency, and show that leakage current is negligible below 120°C     

Layered Al2O3-TiO2 compositedielectric resonators

Aluminium oxide displays a very low tanδ at microwave frequencies. It also possesses a remarkably high thermal conductivity, ideal for heat dissipation in high power satellite filters. However, its temperature coefficient of the resonant frequency (τ_f) is approximately 60 ppm/K. It is shown that the application of a film of titanium oxide which has a T_f of opposite sign (45O ppm/K) produces a composite in which the τ_f can be tuned to be zero over a wide temperature range. The tanδ of the composite at zero T_f is 3.3×10⁵ (Q=30000) at room temperature and at 10 GHz     

High power and high efficiency operation of Al-freeInGaAs/GaInAsP/GaInP GRINSCH SQW lasers (λ≃0.98 μm)

High power and high quantum efficiency Al-free InGaAs/GaInAsP/GaInP GRINSCH SQW lasers emitting at 0.98 μm are reported. A CW output power as high as 580 mW and single lateral mode power up to 280 mW were achieved for the Al-free ridge waveguide lasers at room temperature. The lasers exhibited a high internal quantum efficiency of 99% and low internal waveguide loss of 3.2 cm^-1. A high characteristic temperature of 217 K and low threshold current density of 109 A/cm² were also obtained. The results are the best obtained for Al-free 0.98 μm pumping lasers     

High temperature performance and operation of HFETs

The high temperature performance of Al_0.75Ga_0.25 As/In_0.25Ga_0.75As/GaAs Complementary Heterojunction FETs (CHFETs) is reported between 25 and 500°C. Both experimental and modeled devices have shown acceptable digital characteristics to 400°C. Digital logic circuits have also been shown to operate at temperatures of over 400°C. This strongly suggests that GaAs based devices are capable of satisfying high temperature electronics requirements in the 125-400°C range. Two dimensional physically based modeling has been used to understand the high temperature operation of the HFETs. This work has shown that the devices suffer from gate limited drain leakage currents at elevated ambient temperatures. This off-state leakage current is higher than anticipated. Simulation has shown that, although forward gate leakage currents are reduced with the heterostructure device design, the reverse current is not     

Customized glass sealant for ceramic substrates for high temperature electronic application

This study investigates the ceramic to ceramic bonding, using composite glass frit as the binding layer that is able to tolerate a high temperature environment for ruggedized microelectronic applications. Shear strength measurements were carried out at both room and high temperature (i.e. 250 °C) to evaluate room and high temperature performance of the joints. The glass joints in both the Al₂O₃/glass/Al₂O₃ and AlN/glass/AlN systems maintained their integrity even when shear-tested at 250 °C. The results of the mechanical and microstructural characterizations demonstrate that Bi-based two phase glass frit bonding is an effective ceramic bonding method for harsh-environment electronic packaging.     

High temperature ohmic contacts to 3C–silicon carbide films

Currently, large-area 3C–SiC films are available from a number of sources and it is imperative that stable high temperature contacts be developed for high power devices on these films. By comparing the existing data in the literature, we demonstrate that the contact behavior on each of the different polytypes of SiC will vary significantly. In particular, we demonstrate this for 6H–SiC and 3C–SiC. The interface slope parameter, S, which is a measure of the Fermi-level pinning in each system varies between 0.4–0.5 on 6H–SiC, while it is 0.6 on 3C–SiC. This implies that the barrier heights of contacts to 3C–SiC will vary more significantly with the choice of metal than for 6H–SiC. Aluminum, nickel and tungsten were deposited on 3C–SiC films and their specific contact resistance measured using the circular TLM method. High temperature measurements (up to 400°C) were performed to determine the behavior of these contacts at operational temperatures. Aluminum was used primarily as a baseline for comparison since it melts at 660°C and cannot be used for very high temperature contacts. The specific contact resistance (ρ_c) for nickel at room temperature was 5×10⁻⁴ Ω cm², but increased with temperature to a value of 1.5×10⁻³ Ω cm² at 400°C. Tungsten had a higher room temperature ρ_c of 2×10⁻³ Ω cm², which remained relatively constant with increasing temperature up to 400°C. This is related to the fact that there is hardly any reaction between tungsten and silicon carbide even up to 900°C, whereas nickel almost completely reacts with SiC by that temperature. Contact resistance measurements were also performed on samples that were annealed at 500°C.     

Thermal stability investigations of AlGaN/GaN HEMTs with various high work function gate metal designs

The operation of high power RF transistor generates a huge amount of heat and thermal effect is a major consideration for improving the efficiency of power transistors. AlGaN/GaN high electron mobility transistors (HEMTs) on silicon substrates have been studied extensively because of their high thermal conductivity. This study comprehensively investigates the DC, low frequency noise, microwave and RF power performance of Al_0.27Ga_0.73N/GaN HEMTs on silicon substrates at temperatures from room temperature to 100 °C using high work function metals such as palladium (Pd) and iridium (Ir) gate metals. Although the conventional Ni gate exhibited a good metal work function with AlGaN, which is beneficial for increasing the Schottky barrier height of HEMTs, the diffusion of Ni metal toward the AlGaN and GaN layers influences the DC and RF stability of the device at high temperatures or over long-term operation. Pd and Ir exhibited less diffusion at high temperature than Ni, resulting in less degradation of device characteristics after high temperature operation.     

High-performance Si/SiGe n-type modulation-doped transistors

Enhancement-mode Si/SiGe n-type modulation-doped transistors with a 0.5-μm-length T-gate have been fabricated. Peak transconductances of 390 mS/mm at room temperature and 520 mS/mm at 77 K have been achieved. These high values are attributable to a combination of the high quality of the material used, having a room temperature mobility of 2600 cm²/V-s at an electron sheet concentration of 1.5×10¹² cm², and an optimized layer design that minimizes the parasitic series resistance and the gate-to-channel distance     

High current bond design rules based on bond pad degradation and fusing of the wire

In this paper design rules for maximum current handling capability of gold bond wires are derived based on two failure mechanisms: (1) fusing of the wire; and (2) degradation of the interface between gold bond balls and the aluminum bond pads under high current/high temperature stress. For determination of the fuse current as a function of the length an analytical model is used to calculate the temperature and power distribution in the wire as a function of the position. The current level at which the melt temperature of gold is reached is the fuse current. The degradation mechanism under high current stress (up to 2.5 A) was studied by in-situ monitoring of the gold bond ball–aluminum interconnect contact resistance under high current stress at various temperatures and stress currents. The cumulative failure distributions were used to fit a model for lifetime as a function of current and temperature that shows an order of magnitude difference in lifetime between positive and negative current stress. Finally, fuse current and the lifetime model result in data-driven high current design rules for bond pad and wire.     

高温高压油气井下光纤光栅传感器的应用研究

设计并研制了耐高温、高压、防腐蚀、抗氧化和具有温度补偿功能的双光纤光栅(FBG)传感器.采用高温恒弹合金作为FBG的基底材料和耐高温、高强度的粘接胶,将压力传感FBG和温度传感FBG与基底材料封装为一体,组成温度和压力双FBG传感器.实验室标定表明,压力检测范围为0~20MPa,温度检测范围为0~315℃;压力响应灵敏...     

Effect of post-PECVD photo-assisted anneal on multicrystallinesilicon solar cells

Silicon nitride (SiN_x) films deposited by plasma enhanced chemical vapor deposition (PECVD) contain large amount of atomic hydrogen which can be driven into bulk silicon by post-PECVD anneal. The objective of this paper is to understand and quantify the effects of the anneal on multicrystalline silicon (mc-Si) solar cells. Detailed cell analysis and model calculations are performed to assess the impact of the anneal on mc-Si cells. Simple n⁺-p-p⁺ solar cells with PECVD SiN_x/SiO₂ antireflection (AR) coating are annealed in the temperature range of 350°C to 700°C. The efficiency of the cells made on EFG silicon increases by 45% due to the AR coating and then additional 25% due to the anneal. A trade off between short and long wavelength response is found during the anneal. Low temperature anneal increases the short wavelength response, while high temperature anneal improves the long wavelength response at the expense of the short wavelength response. It is shown that the increase in short wavelength response is due to improved surface passivation, and the decrease in short wavelength response after high temperature anneals is the result of the increase in short wavelength absorption in the SiN_x film. Higher quality HEM silicon cells do not show appreciable increase in the long wavelength response at higher anneal temperatures. Thus post-PECVD low temperature anneal helps all mc-Si cells, but the effect of high temperature anneal is material specific. Cells made from materials which do not respond to hydrogenation can degrade at high temperature anneal     

Power cycling issues and challenges of SiC-MOSFET power modules in high temperature conditions

Silicon carbide (SiC) MOSFETs power modules are very attractive devices and are already available in the market. Nevertheless, despite technological progress, reliability remains an issue and reliability tests must be conducted to introduce more widely these devices into power systems. Because of trapping/de-trapping phenomena at the SiC/SiO₂ interface that lead to the shift of threshold voltage, test protocols based on silicon components cannot be used as is, especially in high temperature conditions. Using high temperature SiC MOSFET power modules, we highlight the main experimental difficulties to perform power cycling tests. These reversible physical mechanisms preclude the use of temperature sensitive parameters (TSEP) for junction temperature measurements, so we set up fiber optic temperature sensors for this purpose. Moreover, these degradation phenomena lead to difficulties in both controlling the test conditions and seeking for reliable aging indicator parameters. Finally, a power cycling test protocol at high temperature conditions is proposed for such devices.     

Thermal effects on the forward characteristics of silicon p-i-n diodes at high pulse currents

When applying high pulse currents, the resulting temperature increase in the base regions of p-i-n diodes and thyristors leads to notable changes in the forward characteristics. (I) Decrease of carrier mobility noticeably increases the voltage drop across the diode and tends to limit the current density. (II) When the temperatures are sufficiently high to supply high intrinsic carrier concentrations, the temperature coefficient of the resistivity becomes negative. This can lead to current localization and destruction of the diodes.

To study these effects, the temperature of the base regions was monitored during high pulse currents using thermal i.r. emission. Indication for current limit occurs above 200°C, when the diodes are heated from room temperature. The negative temperature coefficient of the resistivity occurs at temperatures at which the intrinsic carrier concentration has reached the same order of magnitude as the injected carrier density. Simple theoretical treatment yields reasonably good agreement with the experimental results.     

High temperature studies of electron-beam pumped argon-nitrogen laser characteristics

Gain and laser output power of an electron beam pumped Ar-N2mixture were measured over the temperature range 25 to 350°C. The gain is about 0.6 cm^-1at room temperature, and increases to almost 1 cm^-1at 250°C. The laser performance at elevated temperatures was determined using a specially designed high temperature resonator. The fluorescence yield and laser output are found to decrease monotonically with temperature.