Characterization of the temperature sensitivity of gain and recombination mechanisms in 1.3-/spl mu/m AlGaInAs MQW lasers

The potential of 1.3-/spl mu/m AlGaInAs multiple quantum-well (MQW) laser diodes for uncooled operation in high-speed optical communication systems is experimentally evaluated by characterizing the temperature dependence of key parameters such as the threshold current, transparency current density, optical gain and carrier lifetime. Detailed measurements performed in the 20/spl deg/C-100/spl deg/C temperature range indicate a localized T/sub 0/ value of 68 K at 98/spl deg/C for a device with a 2.8 /spl mu/m ridge width and 700-/spl mu/m cavity length. The transparency current density is measured for temperatures from 20/spl deg/C to 60/spl deg/C and found to increase at a rate of 7.7 A/spl middot/cm/sup -2//spl middot/ /spl deg/C/sup -1/. Optical gain characterizations show that the peak modal gain at threshold is independent of temperature, whereas the differential gain decreases linearly with temperature at a rate of 3/spl times/10/sup -4/ A/sup -1//spl middot//spl deg/C/sup -1/. The differential carrier lifetime is determined from electrical impedance measurements and found to decrease with temperature. From the measured carrier lifetime we derive the monomolecular ( A), radiative (B), and nonradiative Auger (C) recombination coefficients and determine their temperature dependence in the 20/spl deg/C-80/spl deg/C range. Our study shows that A is temperature independent, B decreases with temperature, and C exhibits a less pronounced increase with temperature. The experimental observations are discussed and compared with theoretical predictions and measurements performed on other material systems.     

Power transistors fabricated using isotopically purified silicon (/sup 28/Si)

It is well known that isotopic purification of group IV elements can lead to substantial increases in thermal conductivity due to reduced scattering of the phonons. The magnitude of the increase in thermal conductivity depends on the level of isotopic purification, the chemical purity, as well as the test temperature. For isotopically pure silicon (/sup 28/Si) thermal conductivity improvements as high as sixfold at 20 K and 10%-60% at room temperature have been reported. Device heating during operation results in degradation of performance and reliability (electromigration, gate oxide wearout, thermal runaway). In this letter, we discuss the thermal performance of packaged RF LDMOS power transistors fabricated using /sup 28/Si. A novel technique allows the cost effective deployment of this material in integrated circuit manufacturing. A clear reduction of about 5/spl deg/C-7/spl deg/C in transistor average temperature and a corresponding 5%-10% decrease in overall packaged device thermal resistance is consistently measured by infrared microscopy in devices fabricated using /sup 28/Si over natural silicon.     

Al/sub 0.10/Ga/sub 0.90/As-GaAs microcoolers

GaAs-based microcoolers were fabricated and tested. An Al/sub 0.10/Ga/sub 0.90/As layer grown on GaAs, having a lower thermal conductivity and comparable electrical conductivity to that of the substrate, was employed in the microcooler structure to reduce the heat conduction back from the heat sink. Maximum cooling temperatures of 0.87 /spl deg/C and 2.3 /spl deg/C were obtained at ambient temperatures of 25 /spl deg/C and 100 /spl deg/C, respectively, from 60 /spl times/ 60 /spl mu/m microcoolers.     

SiC thin-film Fabry-Perot interferometer for fiber-optic temperature sensor

Polycrystalline SiC grown on single-crystal sapphire substrates have been investigated as thin-film Fabry-Perot interferometers for fiber-optic temperature measurements in harsh temperatures. SiC-based temperature sensors are compact in size, robust, and stable at high temperatures, making them one of the best choices for high temperature applications. SiC films with thickness of about 0.5-2.0 /spl mu/m were grown at 1100/spl deg/C by chemical vapor deposition (CVD) with trimethylsilane. The effect of operating temperature on the shifts in resonance minima, /spl Delta//spl lambda//sub m/, of the SiC/sapphire substrate has been measured in the visible-infrared wavelength range. A temperature sensitivity of 1.9/spl times/10/sup -5///spl deg/C is calculated using the minimum at /spl sim/700 nm. Using a white, broadband light source, a temperature accuracy of /spl plusmn/3.5/spl deg/C is obtained over the temperature range of 22/spl deg/C to 540/spl deg/C.     

A Stable Microwave Integrated Circuit X-Band Gunn Oscillator (Letters)

A stable microwave integrated circuit (MIC) X-band Gunn oscillator is described. Frequency stability is achieved by use of a modified Pound stabilizing system. An average short-term frequency stability of 2 x 10/sup -7/ at room temperature and a thermal stability of 9 x 10/sup -7/ / /spl deg/C between -15 and 30/spl deg/C have been obtained.     

Stability of amorphous-silicon TFTs deposited on clear plastic substrates at 250/spl deg/C to 280/spl deg/ C

Amorphous-silicon (a-Si) thin-film transistors (TFTs) were fabricated on a free-standing new clear plastic substrate with high glass transition temperature (T/sub g/) of >315/spl deg/ C and low coefficient of thermal expansion of <10 ppm/ /spl deg/ C. Maximum process temperatures on the substrates were 250/spl deg/C and 280/spl deg/C, close to the temperatures used in industrial a-Si TFT production on glass substrates. The first TFTs made at 280/spl deg/C have dc characteristics comparable to TFTs made on glass. The stability of the 250/spl deg/C TFTs on clear plastic is approaching that of TFTs made on glass at 300/spl deg/C-350/spl deg/C. TFT characteristics and stability depend only on process temperature and not on substrate type.     

Nanoscale Thermal Transport and Microrefrigerators on a Chip

In this paper we review recent advances in nanoscale thermal and thermoelectric transport with an emphasis on the impact on integrated circuit (IC) thermal management. We will first review thermal conductivity of low-dimensional solids. Experimental results have shown that phonon surface and interface scattering can lower thermal conductivity of silicon thin films and nanowires in the sub-100-nm range by a factor of two to five. Carbon nanotubes are promising candidates as thermal vias and thermal interface materials due to their inherently high thermal conductivities of thousands of W/mK and high mechanical strength. We then concentrate on the fundamental interaction between heat and electricity, i.e., thermoelectric effects, and how nanostructures are used to modify this interaction. We will review recent experimental and theoretical results on superlattice and quantum dot thermoelectrics as well as solid-state thermionic thin-film devices with embedded metallic nanoparticles. Heat and current spreading in the three-dimensional electrode configuration, allow removal of high-power hot spots in IC chips. Several III-V and silicon heterostructure integrated thermionic (HIT) microcoolers have been fabricated and characterized. They have achieved cooling up to 7 /spl deg/C at 100 /spl deg/C ambient temperature with devices on the order of 50 /spl mu/m in diameter. The cooling power density was also characterized using integrated thin-film heaters; values ranging from 100 to 680 W/cm/sup 2/ were measured. Response time on the order of 20-40 ms has been demonstrated. Calculations show that with an improvement in material properties, hot spots tens of micrometers in diameter with heat fluxes in excess of 1000 W/cm/sup 2/ could be cooled down by 20 /spl deg/C-30 /spl deg/C. Finally we will review some of the more exotic techniques such as thermotunneling and analyze their potential application to chip cooling.     

Low-noise silicon carbide X-ray sensor with wide operating temperature range

A silicon carbide (SiC) sensor is presented with high energy resolution in X-ray spectroscopy over a wide temperature range (27-100/spl deg/C). The sensor, consisting of a Schottky barrier diode on high resistivity epitaxial SiC, is characterised by an extremely low noise due to its ultra-low reverse current density even at high operating temperature (15 pA/cm/sup 2/ at 27/spl deg/C and 0.5 nA/cm/sup 2/ at 100/spl deg/C). Equivalent noise charges as low as 17 electrons rms at 27/spl deg/C and 47 electrons rms at 100/spl deg/C have been measured, allowing X-ray spectroscopy with an energy resolution as low as 315 eV and 797 eV FWHM, respectively.     

电子封装用低膨胀高导热SiCp／A1复合材料研究进展

随着微电子技术及半导体技术的快速发展,高封装密度对材料提出了更高的要求。SiCP／Al复合材料具有低膨胀系数、高导热率、低密度等优异的综合性能,受到了广泛的关注。作为电子封装材料,SiCP／Al复合材料已经在航空航天、光学、仪表等现代技术领域取得了实际的应用。文章介绍了SiC颗粒增强铝基复合材料的研究现状,详细阐述并比较了几种常用的制备方法,包括粉末冶金法、喷射沉积法、搅拌铸造法、无压渗透法、压力铸造法等,进一步分析了各种方法的优缺点,并在此基础上展望了未来研究和发展的方向。     

Low-threshold continuous-wave 1.5-/spl mu/m GaInNAsSb lasers grown on GaAs

We present the first continuous-wave (CW) edge-emitting lasers at 1.5 /spl mu/m grown on GaAs by molecular beam epitaxy (MBE). These single quantum well (QW) devices show dramatic improvement in all areas of device performance as compared to previous reports. CW output powers as high as 140 mW (both facets) were obtained from 20 /spl mu/m /spl times/ 2450 /spl mu/m ridge-waveguide lasers possessing a threshold current density of 1.06 kA/cm/sup 2/, external quantum efficiency of 31%, and characteristic temperature T/sub 0/ of 139 K from 10/spl deg/C-60/spl deg/C. The lasing wavelength shifted 0.58 nm/K, resulting in CW laser action at 1.52 /spl mu/m at 70/spl deg/C. This is the first report of CW GaAs-based laser operation beyond 1.5 /spl mu/m. Evidence of Auger recombination and intervalence band absorption was found over the range of operation and prevented CW operation above 70/spl deg/C. Maximum CW output power was limited by insufficient thermal heatsinking; however, devices with a highly reflective (HR) coating applied to one facet produced 707 mW of pulsed output power limited by the laser driver. Similar CW output powers are expected with more sophisticated packaging and further optimization of the gain region. It is expected that such lasers will find application in next-generation optical networks as pump lasers for Raman amplifiers or doped fiber amplifiers, and could displace InP-based lasers for applications from 1.2 to 1.6 /spl mu/m.     

High performance quantum dot lasers on GaAs substrates operating in 1.5 /spl mu/m range

Stacked InAs/InGaAs quantum dots are used as an active media of metamorphic InGaAs-InGaAlAs lasers grown on GaAs substrates by molecular beam epitaxy. High quantum efficiency (/spl eta//sub i/>60%) and low internal losses (/spl alpha/<3-4 cm/sup -1/) are realised. The transparency current density per single QD layer is estimated as /spl sim/70 A/cm/sup 2/ and the characteristic temperature is 60 K (20-85/spl deg/C). The emission wavelength exceeds 1.51 /spl mu/m at temperatures above 60/spl deg/C.     

High-T/sub 0/ strain-compensated InGaAsSb-AlGaAsSb quantum-well lasers emitting at 2.43 /spl mu/m

Strain-compensated InGaAsSb-AlGaAsSb quantum-well (QW) lasers emitting near 2.5 /spl mu/m have been grown by solid-source molecular beam epitaxy. The relatively high arsenic composition causing a tensile strain in the Al/sub 0.25/GaAs/sub 0.08/Sb barriers lowers the valence band edge and the hole energy level, leading to an increased hole confinement and improved laser performance. A 60% external differential efficiency in pulsed mode was achieved for 1000-/spl mu/m-long lasers emitting at 2.43 /spl mu/m. A characteristic temperature T/sub 0/ as high as 163 K and a lasing-wavelength temperature dependence of 1.02 nm//spl deg/C were obtained at room temperature. For 2000 /spl times/ 200 /spl mu/m/sup 2/ broad-area three-QW lasers without lateral current confinement, a low pulsed threshold of 275 A/cm/sup 2/ was measured.     

A Highly Stabilized MIC Gunn Oscillator Using a Dielectric Resonator

An X-band frequency-stabilized MIC Gunn oscillator of a very simple structure using a dielectric resonator is developed. It is studied how the oscillating characteristics can be controlled by circuit parameters, with special attention to the factors affecting the frequency stability with temperature. By optimizing these factors and by selecting the proper temperature coefficient of a newly developed dielectric resonator, the high frequency stability of less than /spl plusmn/100 MHz over the temperature range from -20 to 60/spl deg/C (2x10 /sup -7/ / /spl deg/C) was obtained.     

SiCp/Al复合材料在电子封装应用中的基础研究

采用挤压铸造方法,制备了高体积分数的SiC增强铝基复合材料。经扫描电镜分析,复合材料颗粒分布均匀,材料组织致密。通过改变铝合金成分与SiC含量,SiCp/Al复合材料材料热膨胀系数介于(6.9~9.7)106℃1之间可调,热导率大于120 W/(m·℃),材料的比强度、比模量高。对材料表面涂覆性能进行了可行性研究,得到了实用的Ni和Cu镀层。     

Preparation and Thermoelectric Characterization of SiC-B<Subscript>4</Subscript>C Composites

SiC-B₄C composites with various values of SiC-to-B₄C ratio and grain size were fabricated by pressureless sintering. This paper presents the results of current investigations of this composite material. This includes the parameters of manufacture (shrinkage, density, and open porosity), thermoelectric properties (electrical and thermal conductivity, and thermopower), and material characterization (x-ray diffraction, scanning electron microscopy, oxidation resistance, and thermal expansion). The results indicate high potential of this composite as an alternative material for thermoelectric applications at high temperatures. The Seebeck coefficient of the composite was higher than that of the single-component materials B₄C and SiC and reached 400 μV/K at 500°C.     

Measuring thermal and mechanical stresses on optical fiber in a DC module using fiber Bragg gratings

Fiber Bragg gratings (FBGs) can be used as sensors to monitor stress and test temperature during the processing and handling of optical fiber. As the FBG experiences a combination of mechanical and thermal loading, the return Bragg wavelength will shift proportionately to the magnitude of the load. This paper discusses the use of these sensors in quantifying induced stress on fiber during the packaging of a dispersion-compensating module (DCM) and the ensuing environmental exposure. There are two potential fiber-failure modes for fiber wound in DCMs, namely microbend-induced attenuation and fiber failure from fatigue. The ability to quantify fiber stress provides a useful feedback tool in the design phase of these modules that can aid in reducing the risk of mechanical and optical failure modes. A practical characterization process was developed to decouple thermal and stress effects on FBGs based on results from current literature and from this study. Uncoated Bragg sensors were found to respond linearly between -40 to 80/spl deg/C. Gratings with a protective polymer recoat departed from the linear behavior of the uncoated gratings below -5/spl deg/C. It was determined that the recoat material places less than 25 MPa (3.6 klbf/in/sup 2/) of axial compression on the fiber at -40/spl deg/C. Four gratings with different Bragg wavelengths were spliced into 10 km of fiber and wound into a DCM. The wind-induced stress on all four gratings quickly relaxed. The module was then thermal cycled between -40 and +75/spl deg/C. The overall stress on each grating was acceptably low for reliability purposes. The maximum stress of 17 MPa (2.5 klbf/in/sup 2/) was observed at the lowest temperature.     

电子封装用AlSiC复合材料热导率影响因素探讨

采用模压成型和真空压力浸渗工艺制备了高体积分数SiC增强Al基复合材料(AlSiC)。物相和显微结构研究结果表明,此种方法制备的AlSiC复合材料,组织致密且大小两种粒径的SiC颗粒均匀分布于Al基质中,界面结合强度高;SiC增强颗粒与Al基质界面反应控制良好,未出现Al4C3等脆性相。在此基础上,研究了基体金属、粘结剂用量、粗细SiC颗粒比例对复合材料热导率的影响。结果表明,以1A90高纯铝为基体的复合材料的热导率高于以6061铝合金为基体的复合材料的热导率;粘结剂用量减少时,复合材料热导率提高;当SiC体积分数一定时,AlSiC复合材料的热导率随增强体中粗颗粒SiC比例增大而增大。     

Highly reliable non-conductive adhesives for flip chip CSP applications

Non-conductive adhesives (NCA), widely used in display packaging and fine pitch flip chip packaging technology, have been recommended as one of the most suitable interconnection materials for flip-chip chip size packages (CSPs) due to the advantages such as easier processing, good electrical performance, lower cost, and low temperature processing. Flip chip assembly using modified NCA materials with material property optimization such as CTEs and modulus by loading optimized content of nonconductive fillers for the good electrical, mechanical and reliability characteristics, can enable wide application of NCA materials for fine pitch first level interconnection in the flip chip CSP applications. In this paper, we have developed film type NCA materials for flip chip assembly on organic substrates. NCAs are generally mixture of epoxy polymer resin without any fillers, and have high CTE values un-like conventional underfill materials used to enhance thermal cycling reliability of solder flip chip assembly on organic boards. In order to reduce thermal and mechanical stress and strain induced by CTE mismatch between a chip and organic substrate, the CTE of NCAs was optimized by filler content. The flip chip CSP assembly using modified NCA showed high reliability in various environmental tests, such as thermal cycling test (-55/spl deg/C/+160/spl deg/C, 1000 cycle), high temperature humidity test (85/spl deg/C/85%RH, 1000 h) and high temperature storage test (125/spl deg/C, dry condition). The material properties of NCA such as the curing profile, the thermal expansion, the storage modulus and adhesion were also investigated as a function of filler content.     

Thermally stable Ge/Ag/Ni Ohmic contact for InAlAs/InGaAs/InP HEMTs

Excellent annealed ohmic contacts based on Ge/Ag/Ni metallization have been realized in a temperature range between 385 and 500/spl deg/C, with a minimum contact resistance of 0.06 /spl Omega//spl middot/mm and a specific contact resistivity of 2.62 /spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ obtained at an annealing temperature of 425/spl deg/C for 60 s in a rapid thermal annealing (RTA) system. Thermal storage tests at temperatures of 215 and 250/spl deg/C in a nitrogen ambient showed that the Ge/Ag/Ni based ohmic contacts with an overlay of Ti/Pt/Au had far superior thermal stabilities than the conventional annealed AuGe/Ni ohmic contacts for InAlAs/InGaAs high electron mobility transistors (HEMTs). During the storage test at 215/spl deg/C, the ohmic contacts showed no degradation after 200 h. At 250/spl deg/C, the contact resistance value of the Ge/Ag/Ni ohmic contact increased only to a value of 0.1 /spl Omega//spl middot/mm over a 250-h period. Depletion-mode HEMTs (D-HEMTs) with a gate length of 0.2 /spl mu/m fabricated using Ge/Ag/Ni ohmic contacts with an overlay of Ti/Pt/Au demonstrated excellent dc and RF characteristics.     

As/sup +/-implanted AlGaAs oxide-confined VCSEL with enhanced oxidation rate and high performance uniformity

We report the utilization of an As/sup +/-implanted AlGaAs region and regrowth method to enhance and control the wet thermal oxidation rate for 850-nm oxide-confined vertical-cavity surface-emitting laser (VCSEL). The oxidation rate of the As/sup +/-implanted device showed a four-fold increase over the nonimplanted one at the As/sup +/ dosage of 1/spl times/10/sup 16/ cm/sup -3/ and the oxidation temperature of 400/spl deg/C. 50 side-by-side As/sup +/-implanted oxide-confined VCSELs fabricated using the method achieved very uniform performance with a deviation in threshold current of /spl Delta/I/sub th//spl sim/0.2 mA and slope-efficiency of /spl Delta/S.E./spl sim/3%.