Charge storage and its dynamics in porous polytetrafluoroethylene (PTFE) film electrets

The outstanding space charge storage stability of porous polytetrafluoroethylene (PTFE) film electrets is studied by isothermal surface potential decay measurements and open-circuit thermally stimulated discharge (TSD) experiments after corona charging at room and elevated temperatures, or corona charging at RT and then aging at different temperatures. Charge storage properties of porous PTFE, nonporous PTFE (Teflon/spl reg/ PTFE) and nonporous FEP (Teflon/spl reg/ FEP) electrets are compared. The results show that porous PTFE has the best charge storage stability of organic materials for both negative and positive charges, especially at high temperatures. The structure of porous PTFE, investigated by a scanning electron microscope (SEM), is important for understanding the electret properties of this material. Charge dynamics, including the influence of environmental humidity and temperature on charge stability and shift of mean charge depth, and the kinetics of detrapped charges for the porous PTFE film electrets were also investigated by means of isothermal surface potential decay measurements and analysis of the TSD current spectra in combination with the heat pulse technique. It is found that from about RT to 200/spl deg/C slow retrapping plays a dominant role; from about 200/spl deg/C to 300/spl deg/C fast retrapping controls the transport.     

Electric charge transport and trapping in dielectrics deduced from isothermal and nonisothermal measurements

By sequential use of the isothermal charging, the isothermal discharging, the final thermally stimulated discharge current and the final isothermal discharging current techniques, the charge dynamics in highly insulating materials may be investigated. The method is demonstrated for polyethylene terephthalate. The injected charge for a field of 20 MV m/sup -/1 and polarization temperatures up to 110/spl deg/C is almost totally trapped in the material and is released during the heating of the sample at 180/spl deg/C for a sufficiently long time. A significant current at high temperatures, about 90/spl deg/C above the poling temperature, was observed proving that it originates from charge detrapping. The final thermally stimulated discharge current peaks shift to higher temperature when the polarization temperature increases, and are characterized by activation energies in the range from 1.03 to 1.56 eV. They allowed the identification of the glass transition around 114/spl deg/C. The relaxation time of the trapped charge, at 180/spl deg/C, was determined to be about 3780 s, explaining the very good stability of trapped charge.     

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.     

Long-wavelength quantum-dot lasers on GaAs substrates: from media to device concepts

Recent progress in semiconductor quantum-dot (QD) lasers approaches qualitatively new levels, when dramatic progress in the development of the active medium already motivates search for new concepts in device and system designs. QDs, which represent coherent inclusions of narrower bandgap semiconductor in a wider gap semiconductor matrix, offer a possibility to extend the wavelength range of heterostructure lasers on GaAs substrates to 1.3 /spl mu/m and beyond and create devices with dramatically improved performance, as compared to commercial lasers on InP substrates. Low-threshold current density (100 A/cm/sup 2/), very high characteristic temperature (170 K up to 65/spl deg/C), and high differential efficiency (85%) are realized in the same device. The possibility to stack QDs (e.g., tenfold) without an increase in the threshold current density and any degradation of the other device parameters allow realization of high modal gain devices suitable for applications in 1.3-/spl mu/m short-cavity transmitters and vertical-cavity surface-emitting lasers (VCSELs). The 1.3-/spl mu/m QD GaAs VCSELs operating at 1.2-mW continuous-wave output power at 25/spl deg/C are realized, and long operation lifetime is manifested. Evolution of GaAs-based 1.3-/spl mu/m lasers offers a unique opportunity for telecom devices and systems. Single-epitaxy VCSEL vertical integration with intracavity electrooptic modulators for lasing wavelength adjustment and/or ultrahigh-frequency wavelength modulation is possible. Arrays of wavelength-tunable VCSELs and wavelength-tunable resonant-cavity photodetectors may result in a new generation of "intelligent" cost-efficient systems for ultrafast data links in telecom.     

Improved thermal, structural and electrical properties of epoxy for use at high voltages

In this paper, the epoxy elasticity factors were investigated by thermomechanical analysis (TMA), dynamic mechanical thermal analysis (DMTA), thermogravimetric analysis (TGA) and field emission scanning electron microscope (FESEM) to improve toughness and reduce brittleness of existing epoxy resin. Dumbbell shaped specimens were made and tested at rates of 0, 20 and 35 parts per hundred resins (phr). TMA and DMTA temperatures ranged from -20 to 200 /spl deg/C and TGA ranged from 0 to 600 /spl deg/C. The glass transition temperature (Tg) of elastic epoxy was measured by thermal analysis. Also investigated were the thermal expansion coefficient (/spl alpha/), the high-temperature characteristics, modulus and the loss factor (Tan /spl delta/). We analyzed the structure using FESEM and have found elastomer particles (elastic-factors) in the elastic epoxy matrix. We have made elastic epoxy by adding elastomer particles to existing epoxy. Generally, the toughness of elastic epoxy can be improved by changing the structure of existing epoxy of poor impact-strength. In addition, we measured the permittivity and Tan /spl delta/ for investigation of the electrical properties of elastic epoxy. The permittivity and Tan /spl delta/ depend on the elastomer composition. Namely, the permittivity and Tan /spl delta/ increase according to the elastomer contents. For experimental analysis results, 20 phr was considered an excellent specimen.     

Development of a silicone modified unsaturated polyester varnish for rated electrical insulation application

We report on the development of a silicone modified unsaturated polyester (SUP) using a novel combination of well known principles and rigorous calculation and control of mole fraction to produce what we believe the first SUP varnish which can be used in all insulation systems including those requiring application in vacuum (solvent free, single component). Silicone modified polyesters are available but not in solvent free and unsaturated varnish form and their chemistry is different. We believe that the nature of the chemical structure generated by the manufacturing protocol is critical to the properties of the cured SUP varnish. The properties of SUP are consistently better than those of unsaturated polyesters (UP) with respect to chemical resistance as defined by ASTM tests to moisture, acids, bases, toluene, transformer oil and silicone oil. IEC comparative tracking resistance was 300 drops vs 160-240 for UPs. Results of electrical properties vs temperature tests and heat deflection temperature suggested application to high voltage electric motors and other high temperature uses. Heat aging stability of bond strength of SUP treated helical coils was tested for tensile strength (ts) (using Stecker) and for flexural strength (fs) to determine the temperature index (TI) of the varnish alone. The end point was taken to be 14 kgf (50% loss for both ts and fs). Also, motorettes insulated with materials of high temperature class were treated with SUP for TI evaluation. The TI on a motorette was sufficient (208/spl deg/C) to suggest application at 200/spl deg/C rating level (20,000 h level). The TIs of helical and Stecker coils were 194 and 193/spl deg/C, respectively. The literature values of TIs of UPs on motorettes with similar insulating materials never exceeded 180/spl deg/C. These properties are consistently better than the properties of conventional unsaturated polyester.     

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.     

Treeing in mechanically prestressed electrical insulation

The technique of prestressing electrical insulation by the inclusion of fibers in tension during the curing process has been used to establish a region of balancing compressive stress adjacent to the fibers and through which growing electrical trees have to pass. It has been known for many years that compressive stress has a retarding effect on tree growth (and tensile stress has an accelerating effect). The compressive stress, therefore, set up due to prestressing decelerates tree growth and long treeing times have been observed. Room temperature cured epoxy resin readily demonstrates the prestressing phenomenon but, as a result of its relatively low glass transition temperature, it is unable to sustain the prestress at temperatures in excess of 40 /spl deg/C. Post curing at 100 /spl deg/C raises the glass transition temperature and although a greater initial fiber tension is required to produce the same degree of prestress, the prestress is subsequently sustainable at temperatures up to and beyond 80 /spl deg/C. This has been demonstrated by the determination of the remnant stress in the cast-in fibers using Raman spectroscopy and by the enhanced treeing times observed in high temperature cured samples.     

Design of a cylindrical high-voltage high-temperature vacuum insulator

A design for a high temperature, HV insulator is presented. This design exploits the temperature dependent thermal and electrical properties of alumina and a unique structural insulator design to increase the high voltage hold-off characteristics of the insulator, reduces thermal flux through the insulator, and alleviate stresses caused by mismatch between insulator and electrode thermal expansion coefficients. The designed insulators insulate graphite electrodes at temperatures approaching 1000/spl deg/C and potentials up to 50 kV. In this paper, the general methodology of designing these insulators is explored, and some limited performance data is presented.     

Fluorescent lamp model with power and temperature dependence for high-frequency electronic ballasts

The electrical behavior of a fluorescent lamp operating at high frequency can be characterized by a resistance. The lamp equivalent resistance varies with the operating power and ambient temperature. On this basis, an electrical circuit model of the fluorescent lamp for high-frequency steady-state operation is developed. A test system is set up to emulate the dimming operation of fluorescent lamps in a temperature range from -15/spl deg/C to 55/spl deg/C. For a given lamp, the voltage equation can be obtained from few test data. Then, the equations for the arc current and the equivalent resistance can be derived. These lamp equations can be used for predicting the operating characteristics of the dimmable ballast-lamp circuits with considerations on the temperature effects. The verification of the proposed lamp model is illustrated by implementation examples.     

Temperature stability of ZnO thin film SAW device on fused quartz

Surface acoustic wave (SAW) filters for low-frequency (38-65 MHz) applications have been developed using a radio frequency (RF)-magnetron-sputtered ZnO film on fused-quartz substrates. SAW propagation characteristics such as electromechanical coupling coefficient (K/sup 2/), SAW phase velocity (v), insertion loss, and temperature coefficient of delay (TCD) have been measured. The intergidital transducer (IDT)/ZnO/fused-quartz device structure yields almost zero TCD (1 ppm/spl middot//spl deg/C/sup -1/) with 0.316 /spl lambda/ thick ZnO layer (for the device operating at 60 MHz). Alternately, an overlayer of positive TCD material (ZnO itself) has also been deposited on the IDT/ZnO(<0.316 /spl lambda/)/fused-quartz device at a low substrate temperature to reduce the TCD. A modified layered structure consisting of ZnO/IDT/ZnO/fused quartz yields almost zero TCD (-3 ppm/spl middot//spl deg/C/sup -1/) with a 5.3-/spl mu/m-thick ZnO overlayer and a 8.1-/spl mu/m-thick (0.183 /spl lambda/) ZnO bottom layer. Experimentally obtained SAW propagation characteristics have been compared with the theoretical results.     

Charge storage in corona-charged polypropylene films analyzed by LIPP and TSC methods

Negatively corona-charged 50-/spl mu/m-thick polypropylene (PP) film is measured using laser-induced pressure pulse (LIPP) and thermally stimulated current (TSC) in order to study the charge storage mechanism in the PP film. The LIPP can reveal the space-charge distribution in the depth direction of the PP films and the TSC can be used to measure the energetic depth of the charge trap. The LIPP shows that negative charge is deposited on the charged surface of the sample. Almost all surface charges are removed by soaking the sample in ethanol. However, about 5% of the surface charge is injected into the sample up to a depth of about 7 /spl mu/m from the surface. The injected charge is not removed by the dip-in-ethanol method because the ethanol does not penetrate into the sample. The injection of the surface charge increases with corona-charging temperature. Besides the negative charge injection, the injection of positive charge from the opposite surface is also observed when the sample is charged at higher than 60/spl deg/C. In addition, negative bulk charge is formed when the sample is charged at higher than 80/spl deg/C. The LIPP profile is compared with the TSC spectrum. It is shown that the space charge observed using LIPP disappears when the temperature of the sample exceeds 80/spl deg/C. However, TSC is observed at even higher than 80/spl deg/C. This indicates that the TSC is observed even after the disappearance of the space charge measured using LIPP.     

Environmental factors affecting DC resistance to tracking of polyethylene

This paper discusses the environmental factors affecting DC resistance to tracking of polyethylene. The voltage, as determined under the conditions specified in the following, which will cause failure with the application of 50 drops of electrolyte, is used as a measure of the susceptibility of the material to tracking, it is called the CTI (contaminant tracking index). A tracking test was set up to investigate dc and ac tracking resistance of epoxy resin, phenolic resin and polycarbonate by IEC 112. The test solution was with 0.1 % ammonium chloride NH/sub 4/Cl in deionized water, giving a resistivity of approximately 4/spl Omega/m at 23/spl deg/C. A droplet was applied at intervals to keep up the discharge between the two electrodes. Epoxy and phenolic resins are tracking type materials.     

Impact of self-heating effect on long-term reliability and performance degradation in CMOS circuits

As the technology feature size is reduced, the thermal management of high-performance very large scale integrations (VLSIs) becomes an important design issue. The self-heating effect and nonuniform power distribution in VLSIs lead to performance and long-term reliability degradation. In this paper, we analyze the self-heating effect in high-performance sub-0.18-/spl mu/m bulk and silicon-on-insulator (SOI) CMOS circuits using fast transient quasi-dc thermal simulations. The impact of the self-heating effect and technology scaling on the metallization lifetime and the gate oxide time-to-breakdown (TBD) reduction are also investigated. Based on simulation results, an optimized clock-driver design is proposed. The proposed layout reduces the hot-spot temperature by 15/spl deg/C and by 7/spl deg/C in 0.09-/spl mu/m SOI and bulk CMOS technologies, respectively.     

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.     

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.     

Stress-induced electromigration backflow effect in copper interconnects

The electromigration threshold in copper interconnect is reported in this paper. The critical product (jL)/sub c/ is first determined for copper oxide interconnects with temperature ranging from 250/spl deg/C to 350/spl deg/C from package-level experiments. It is shown that the product does not significantly change in this temperature range. Then, (jL)/sub c/ was extracted for copper low-k dielectric (k=2.8) interconnects at 350/spl deg/C. A larger value than that for oxide dielectric was found. Finally, a correlation between the n values from Black's model and with jL conditions was established for both dielectrics.     

聚苯并咪唑的研究进展

介绍了聚苯并咪唑的合成,论述了聚苯并咪唑纤维、复合材料、质子交换膜的研究状况及应用成果,展望了聚苯并咪唑的发展动向。     

Low-temperature deposition of hafnium silicate gate dielectrics

The physical and electrical properties of hafnium silicate (HfSi/sub x/O/sub y/) films produced by low-temperature processing conditions (/spl les/150/spl deg/C) suitable for flexible display applications were studied using sputter deposition and ultra-violet generated ozone treatments. Films with no detectable low-/spl kappa/ interfacial layer were produced. Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy were used to determine the composition, chemical bonding environment, thickness, and film interface. The electrical behavior of the as-deposited and annealed hafnium silicate films were determined by current-voltage (I--V) and capacitance-voltage (C--V) measurements.     

Thermomechanical analysis of gold-based SiC die-attach assembly

The thermomechanical stresses due to mismatch of the coefficients of thermal expansion (CTE) of the base material (SiC) and the packaging has a significant impact on the stresses in MEMS pressure sensors used in high-temperature applications, to 600/spl deg/C. The pressure sensor studied essentially consists of a SiC die attached to an AlN substrate using a gold die attach. Characterization of the stress distribution within the die attach, die and substrate along with the fatigue resistance of the die attach at 600/spl deg/C is essential to estimating the reliability of the packaging structure. A parametric study has been performed using nonlinear finite element analysis to optimize the die-attach thermomechanical performance at high temperatures. This study includes the effects of varying porosity levels and varying reference temperatures (stress-free temperature). This study also provides information about the mechanical deformations of the pressure sensor due to the thermomechanical load, which must be compensated, for the effective performance of the pressure sensor. The outcome of the study provides guidelines to optimize the design of the pressure sensor.