Operation of 1550-nm electroabsorption-Modulated laser at 40/spl deg/C for 10-gb/s, 40-km transmission

Semicooled operation at 40/spl deg/C of electroabsorptive modulator integrated laser (EML) for intermediate reach communication has been demonstrated. Reproducible operation at the elevated temperature was achieved through a device parameter optimized based on the temperature dependence of the dc characteristics of EML and a design of multi-quantum-well structure providing both relevant output power and high-frequency bandwidth at 40/spl deg/C. Good eye pattern and near zero chirp with the average power over 0 dBm are obtained at 40/spl deg/C, with an estimated lifetime over 20 years.     

Threshold voltage instabilities in high-/spl kappa/ gate dielectric stacks

Over recent years, there has been increasing research and development efforts to replace SiO/sub 2/ with high dielectric constant (high-/spl kappa/) materials such as HfO/sub 2/, HfSiO, and Al/sub 2/O/sub 3/. An important transistor reliability issue is the threshold voltage stability under prolonged stressing. In these materials, threshold voltage is observed to shift with stressing time and conditions, thereby giving rise to threshold voltage instabilities. In this paper, we review various causes of threshold voltage instability: charge trapping under positive bias stressing, positive charge creation under negative bias stressing (NBTI), hot-carrier stressing, de-trapping and transient charge trapping effects in high-/spl kappa/ gate dielectric stacks. Experimental and modeling studies for these threshold voltage instabilities are reviewed.     

Electrical characterization of benzocyclobutene polymers for electric micromachines

An approach using interdigitated capacitors for electrical characterization of CYCLOTENE, a spin-on low-k benzocyclobutene (BCB)-based polymer is introduced and the effect of moisture uptake is investigated. The dielectric constant of CYCLOTENE is extracted from capacitance measurements with a systematic error less than 0.1%, giving an average value of 2.49 with a standard deviation of 1.5%. The dielectric constant increases by 1.2% after a humidity stress of 85% RH at 85/spl deg/C. The I-V characteristics of CYCLOTENE show a dependency of breakdown strength and leakage current on the geometrical dimensions of the device under test. A breakdown strength of 225V//spl mu/m and 320 V//spl mu/m for 2-/spl mu/m and 3-/spl mu/m finger spacing, respectively, and a leakage current of a few to tens of pA are measured. The I-V characteristics degrade drastically after the humidity stress, showing a breakdown strength of 100 V//spl mu/m and 180 V//spl mu/m for 2-/spl mu/m and 3-/spl mu/m finger spacing, respectively, and a maximum increase in the leakage current as large as one order of magnitude. The maximum performance and long-term reliability of an electric micromachine are adversely affected by the degradation of the breakdown voltage and the leakage current after moisture absorption. It is expected, however, that the electrical efficiency is improved using BCB-based polymers with negligible dependency on moisture absorption.     

1.3-/spl mu/m-range GaInNAsSb-GaAs VCSELs

1.3-/spl mu/m-range GaInNAsSb vertical-cavity surface-emitting lasers (VCSELs) with the doped mirror were investigated. GaInNASb active layers that include a small amount of Sb can be easily grown in a two-dimensional manner as compared with GaInNAs due to the suppression of the formation of three-dimensional growth in MBE growth. The authors obtained the lowest J/sub th/ per well (150 A/cm/sup 2//well) for the edge-emission type lasers due to the high quality of GaInNAsSb quantum wells. Using this material for the active media, the authors accomplished the first continuous wave operation of 1.3-/spl mu/m-range GaInNAsSb VCSELs. For the reduction of the threshold voltage and the differential resistance, they used the doped mirror grown by metal-organic chemical vapor deposition (MOCVD). By three-step growth, they obtained 1.3-/spl mu/m GaInNAs-based VCSELs with the low threshold current density (3.6 kA/cm/sup 2/), the low threshold voltage (1.2 V), and the low differential resistance (60 /spl Omega/) simultaneously for the first time. The back-to-back transmission was carried out up to 5 Gb/s. Further, the uniform operation of 10-ch VCSEL array was demonstrated. The maximum output power of 1 mW was obtained at 20/spl deg/C by changing the reflectivity of the front distributed Bragg reflector mirror. GaInNAsSb VCSELs were demonstrated to be very promising material for realizing the 1.3-/spl mu/m signal light sources, and the usage of the doped mirror grown by MOCVD is the best way for 1.3-/spl mu/m VCSELs.     

Validity of constant voltage stress based reliability assessment of high-/spl kappa/ devices

Charge trapping in high-/spl kappa/ gate dielectrics affects the result of electrical characterization significantly. DC mobility degradation and device threshold voltage instability and C-V and I-V hysteresis are a few examples. The charging effects in high-/spl kappa/ gate dielectric also affect the validity of conventional reliability test methodologies developed for SiO/sub 2/ devices. In this paper, we review high-/spl kappa/ materials specific phenomena that can affect the validity of constant-voltage-stress-based reliability test methods to address the direction of future reliability study on high-/spl kappa/ devices.     

Single-mode 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP quantum well vertical cavity surface emitting lasers

The 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current varies from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% from 0.17 to 0.11 mW/mA as the temperature is raised from room temperature to 75/spl deg/C. The VCSELs continuously operate up to 105/spl deg/C with a slope efficiency of 0.023 mW/mA. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is estimated to be 10.7 GHz with modulation current efficiency factor of /spl sim/5.25GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C. We also accumulated life test data up to 1000 h at 70/spl deg/C/10 mA.     

1.3-/spl mu/m AlGaInAs strain compensated MQW-buried-heterostructure lasers for uncooled 10-gb/s operation

We have successfully fabricated 1.3-/spl mu/m AlGaInAs strain-compensated multiple-quantum-well (MQW) buried-heterostructure (BH) lasers by narrow-stripe selective metalorganic vapor-phase epitaxy. Based on the optimization of AlGaInAs strain compensated MQW and the Al-oxidation-free BH process, we obtained a low-threshold current of 12.5 mA and a relaxation frequency of more than 10 GHz at 85/spl deg/C for Fabry-Perot lasers. For distributed feedback lasers, we demonstrated a 10-Gb/s operation and transmission of over 16 Km for a single mode fiber at 100/spl deg/C. Furthermore, a record-low 25.8-mA/sub p-p/ modulation current for a 10-Gb/s modulation at 100/spl deg/C was demonstrated with shorter cavity and high grating-coupling coefficient. A median life of more than 1/spl times/10/sup 5/ h at 85/spl deg/C was estimated after an aging test of over 5000 h for these lasers. These superior characteristics at high temperatures were achieved by the combination of the high differential gain of AlGaInAs strain compensated MQW and the BH structure.     

Switching of capacitive currents and the correlation of restrike and pre-ignition behavior

The new IEC 62271-100 requires an extensive proof of the capability of capacitive switching for a breaker under test. For vacuum circuit breakers, dielectric properties are mainly determined by the condition and topology of the contact surfaces, which are modified by in-rush currents as well as load-breaking currents and other effects. A synthetic single-phase test device has been erected in order to simulate three-phase network conditions and to collect more data on the statistical properties of the relevant processes. The distribution of pre-ignition field strengths is evaluated for different contact strokes and surface conditions, when discharging a capacitor through the closing interrupter. On the other side, the probability of restrikes for a given switching condition defined by full contact gap d/sub 0/ and peak recovery voltage U/sub re//spl circ/ is measured and compared with the cumulative probability of pre-ignition just at the field strength E=U/sub re//spl circ//d/sub 0/. A correlation between pre-ignition and restrike probabilities suggests a breakdown mechanism being field-emission dominated. In addition a rather strong conditioning effect has been observed at smaller contact gaps smoothening the contact surfaces.     

The statistics of NBTI-induced V/sub T/ and /spl beta/ mismatch shifts in pMOSFETs

Negative bias temperature instability (NBTI) is a pFET degradation mechanism that can result in threshold voltage shifts up to 100 mV or more, even in very thin oxide devices. Since analog circuits that utilize matched pairs of devices, such as current mirrors and differential pairs, generally depend on V/sub T/ matching considerably better than this, NBTI-induced V/sub T/ mismatch shift may represent a serious reliability concern for CMOS analog applications. Furthermore, induced /spl beta/ mismatch shift (affecting drain current level at a fixed gate overdrive voltage) may also impact drain current and transconductance mismatch. In this paper, experimental results of the statistics and scaling properties of NBTI-induced V/sub T/ and /spl beta/ mismatch shifts in saturation, and models describing these results, are presented.     

Design consideration and performance of high-power and high-brightness InGaAs-InGaAsP-AlGaAs quantum-well diode lasers (/spl lambda/=0.98 /spl mu/m)

We conduct a theoretical analysis of the design, fabrication, and performance measurement of high-power and high-brightness strained quantum-well lasers emitting at 0.98 /spl mu/m. The material system of interest consists of an Al-free InGaAs-InGaAsP active region and AlGaAs cladding layers. Some key parameters of the laser structure are theoretically analyzed, and their effects on the laser performance are discussed. The laser material is grown by metal-organic chemical vapor deposition and demonstrates high quality with low-threshold current density, high internal quantum efficiency, and extremely low internal loss. High-performance broad-area multimode and ridge-waveguide single-mode laser devices are fabricated. For 100-/spl mu/m-wide stripe lasers having a cavity length of 800 /spl mu/m, a high slope efficiency of 1.08 W-A, a low vertical beam divergence of 34/spl deg/, a high output power of over 4.45 W, and a very high characteristic temperature coefficient of 250 K were achieved. Lifetime tests performed at 1.2-1.3 W (12-13 mW//spl mu/m) demonstrates reliable performance. For 4-/spl mu/m-wide ridge waveguide single-mode laser devices, a maximum output power of 394 mW and fundamental mode power up to 200 mW with slope efficiency of 0.91 mW//spl mu/m are obtained.     

The search for low-/spl epsiv/ and ultra-low-/spl epsiv/ dielectrics: how far can you get with polymers? Part 2: materials, structures, properties

The need for continuing miniaturization of the structures on microchips has always resulted in new challenges concerning materials properties. A large variety of polymers have been proposed for this application, as organic materials are among those with the lowest dielectric constants known. The chemical structures and selected properties of these polymers are discussed in this review. Polymides; heteroaromatic polymers; polyaryl ethers; fluoropolymers, polyarylenes, and other hydrocarbon polymers without any polar groups; films deposited from the gas phase by chemical vapor deposition (CVD); plasma-enhanced CVD (PECVD); and other techniques are included. Based on the properties described and the requirements for application as intermetal dielectric (IMD) material, conclusions regarding the possibilities for further developments are draw. This article focuses on the structure, synthesis, and properties of the polymers studied as ILD/IMD materials.     

Impact of high-/spl kappa/ dielectric HfO/sub 2/ on the mobility and device performance of sub-100-nm nMOSFETs

Scaling of Si MOSFETs beyond the 90-nm technology node requires performance boosters in order to satisfy the International Technology Roadmap for Semiconductors requirements for drive current in high-performance transistors. Amongst the preferred near term solutions are transport enhanced FETs utilizing strained Si (SSi) channels. Additionally, high-/spl kappa/ dielectrics are expected to replace SiO/sub 2/ around or after the 45-nm node to reduce the gate leakage current problem, facilitating further scaling. However, aside from the many technological issues such as trapped charge and partial crystallization of the dielectric, both of which are major issues limiting the reliability and device performance of devices employing high-/spl kappa/ gate stacks, a fundamental drawback of MOSFETs with high-/spl kappa/ dielectrics is the mobility degradation due to strong soft optical phonon scattering. In this work we study the impact of soft optical phonon scattering on the mobility and device performance of conventional and strained Si n-MOSFETs with high-/spl kappa/ dielectrics using a self-consistent Poisson Ensemble Monte Carlo device simulator, with effective gate lengths of 67 and 25-nm. Additionally we have also briefly investigated the effect (the percentage change) that a trapped charge within the gate oxide will have on the drive current for both a SiO/sub 2/ oxide and an equivalent oxide thickness of high-/spl kappa/ dielectric.     

Correlation between dielectric properties and sintering temperatures of polycrystalline CaCu/sub 3/Ti/sub 4/O/sub 12/

Dielectric properties of polycrystalline CaCu/sub 3/Ti/sub 4/O/sub 12/ (CCTO) pellets sintered in the temperature range 1000-1200/spl deg/C were evaluated with impedance spectroscopy at frequency range of 10/sup 2/ to 10/sup 7/ Hz from 90 K to 294 K. A correlation has been established between the pair values of low frequency limit dielectric constant and the total resistivity and the sintering temperature. For example, the sample sintered at 1100/spl deg/C demonstrates higher value of low frequency limit dielectric constant and lower value of total resistivity, while the sample sintered at 1000/spl deg/C demonstrates lower values of low frequency limit dielectric constant and higher value of total resistivity. This correlation has been successfully explained by relating with the difference in grain size and grain volume resistivities of these two polycrystalline CCTO samples. Further, it is suggested that donor doping of oxygen vacancies Vo' and Vo" may be the reason to cause the difference in the grain volume resistivities of these two samples.     

Measurement of the interface trap and dielectric charge density in high-/spl kappa/ gate stacks

We demonstrate an accurate measurement of the interface trap density and the stress-induced dielectric charge density in Si/high-/spl kappa/ gate dielectric stacks of metal-oxide-semiconductor field-effect transistors (MOSFETs) using the direct-current current-voltage (DCIV) technique. The capture cross section and density of the interface traps in the high-/spl kappa/ gate stack were found to be similar to those of the Si/SiO/sub 2/ interface. A constant-voltage stress of the p-channel MOSFET in inversion is shown to result in a negative dielectric charging and an increase in the interface trap density.     

Effects of manufacturing technology on electrical breakdown and morphology of thin films of low density polyethylene blended with polypropylene copolymer

Extruded films prepared from blends of low-density polyethylene (LDPE) and random copolymer of ethylene and propylene (EP) with the T-die method were studied with respect to electrical properties and morphology. Comparisons with data on blown films are made. These blends are of interest as improved LDPE for making XLPE for insulated power cable. In the high temperature region (90/spl deg/C), a specimen with a slightly higher EP content had higher impulse breakdown strength than that with a lower EP content, but no improvement of DC breakdown strength by blending could be found. The improvement of impulse breakdown strength (90/spl deg/C) is explained in terms of morphological changes by blending such as the orientation of chains in a film and the size of spherulites on the assumption of the thermal breakdown. In comparison, a T-die film had higher impulse breakdown strength than that of a blown film for the same composition. The impulse breakdown strength also increased with the use of the higher density LDPE. In the current versus electric field characteristics at 30/spl deg/C, the blend polymer with EP content of 5-10% showed a transition from LDPE behavior at low field region to EP behavior at high field region. However, no appreciable difference in current behavior among the specimens was observed at 90/spl deg/C, which suggests an incompatibility between the two materials that exists at 30/spl deg/C but not at 90/spl deg/C.     

Partial discharge inception characteristics under butt gap condition in liquid nitrogen/ PPLP/sup /spl reg// composite insulation system for high temperature superconducting cable

The partial discharge (PD) inception characteristics are studied in liquid nitrogen (LN/sub 2/)/polypropylene laminated paper (PPLP/sup /spl reg//) composite insulation system for high temperature superconducting (HTS) cable. Experimental results revealed that the magnitude of the initial PD increased as the PD inception electric field strength was increased, because the injected energy increased. Initial PD was generated at the first and third quadrant of applied AC voltage phase. The probability of initial PD at the positive and negative voltage phase was almost the same. The reason is because liquid nitrogen is a nonpolar molecule and we used symmetric electrode configuration with uniform electric field distribution. Finally, it was pointed out that PD inception electric field strength (PDIE) depended on the volume of the butt gap because of the increasing probability of weak points of electrical insulation, and PDIE linearly decreased with increasing stressed volume of the butt gap in the log-log scale.     

Modeling and measurements of the radiative characteristics of high-power /spl alpha/-DFB lasers

A new above-threshold model of /spl alpha/-DFB lasers is presented. It is based on a generalized beam-propagation method and takes into account spatial hole burning and self-heating effects. Up to moderate output powers, a good agreement between simulated and measured radiative characteristics is obtained. The theoretical model was used to design an optimized laser structure with a 4-mm-long cavity, which yielded a maximum output power of 3 W with a times-diffraction-limit factor of M/sup 2//spl ap/3.     

Special reliability features for Hf-based high-/spl kappa/ gate dielectrics

Several special reliability features for Hf-based high-/spl kappa/ gate dielectrics are highlighted, including: 1) trapping-induced threshold voltage (V/sub th/) shift is much more of a concern than TDDB in determining the operating lifetime; 2) n-channel MOSFETs (nMOSFETs) are more vulnerable than p-channel MOSFETs (pMOSFETs); and 3) MOSFETs with polySi gates are more vulnerable than those with metal gates. These will be discussed in the context of existing electron/hole traps and trap generation by high-field stress. A novel technique to probe traps in ultrathin gate dielectrics, inelastic electron tunneling spectroscopy (IETS), will be shown to be capable of revealing the energies and locations of traps in high-/spl kappa/ gate dielectrics.     

Phase modeling based on the /spl alpha/-factor in bulk semiconductor optical amplifiers

Different approaches based on the /spl alpha/-factor to model the phase of the optical fields in bulk semiconductor optical amplifiers are analyzed. Our time-domain numerical model is presented and it is calibrated by means of experimental characterizations of the device gain, of the amplified spontaneous emission spectra, and of the effective /spl alpha/-factor. We then compare the phase modulation at the SOA output for three cases. In the first one, the /spl alpha/-factor is always taken as constant. In the second case, the /spl alpha/-factor is set according to the SOA working point and then kept fixed. In the last case, we take into account the dependence of the /spl alpha/-factor on the carrier density and on the wavelength for every simulated time step. We shall identify when the first two approximations listed above deliver reliable results. In particular cases, the use of a constant value for the /spl alpha/-factor can lead to phase errors up to 50%.     

Comparative laboratory evaluation of TR-XLPE and XLPE cables with Super-smooth conductor shields

This paper provides data on four commercial tree retardant crosslinked polyethylene (TR-XLPE) and one cross-linked polyethylene (XLPE) insulated 15 kV cables supplied by three manufacturers. The cables have "super-smooth" conductor shields and "extra-clean" insulation and insulation shields. AC and impulse voltage breakdown and selected other characterization data are presented for cables that were aged immersed in room temperature water (15-30/spl deg/C) up to 24 months of a planned 48 months aging program. The five cables have high ac voltage breakdown strength, three of the TR-XLPE cables, actually increased in breakdown strength during aging. The one TR-XLPE cable that had the lowest ac voltage breakdown had vented trees at the insulation shield and high dissipation factor, which the other cables did not have. The impulse voltage breakdown strength of all cables decreased during aging; the cable with the lowest ac voltage breakdown also has the lowest impulse voltage breakdown. The dissimilar performance of the TR-XLPE cables and the excellent performance of the XLPE cable indicates evaluations at longer times are required to differentiate between modern TR-XLPE and XLPE insulated cables.