Origins of thermally stimulated current in polyethersulfone

In order to understand the dominant carrier species in electrical conduction in polyethersulfone (PES), thermally stimulated current (TSC) measurements were carried out under various conditions. It was found that PES has two TSC peaks in the temperature range from 20 to 220°C, consisting of an α peak at ~210°C and a β peak whose peak temperature moves towards a higher temperature with an increasing poling temperature. Even when the sample was not poled, PES shows a spontaneous current with its peak at ~210°C. Both the spontaneous current peak and the α peak were found to disappear when the sample had been heated to 230°C, keeping the external circuit closed. From such similarity of appearance and disappearance between the two peaks, it is concluded that they have the same origin. From the change in the spatial distribution of space charges inside the sample measured simultaneously with the TSC measurements, positive charges, probably due to K⁺ ions, existed nonuniformly in the sample from the beginning, and are thought to be responsible for the two peaks. From a similar study, the β peak is considered to be due to polarization of ionic space charges during the poling process     

Ionic behavior of dc conduction in polyetheretherketone

The conduction process in polyetheretherketone (PEEK) is discussed mainly from the results of dc conduction, thermal pulse current (TPC), thermally stimulated current (TSC), and pulsed electroacoustic (PEA) measurements. It was found that dc conduction currents in PEEK are consistent with the values predicted by a theory based on the conventional thermally activated ionic hopping process. The ionic hopping distance was calculated to change from 2.5 to 3.9 nm when the temperature crosses the glass transition temperature. The results of TPC and PEA measurements show the existence of heterocharges in the vicinity of both electrodes. In TSC spectra, a peak appears at a temperature of ~5 to 20°C above the biasing temperature. The peak position approaches to the constant temperature of 155°C when the biasing temperature is >150°C. The peak height is maximum when the biasing temperature is 150°C. It is considered that this peak is related to the glass transition and caused by the depolarization of ionic space charge. From these results, it is concluded that ionic carriers which may come from byproducts of synthesis play an important role in the dc conduction process in PEEK     

Charge storage in double layers of thermally grown silicon dioxideand APCVD silicon nitride

Experimental results on charge storage and discharge in double layers of silicon dioxide and silicon nitride will be reported and discussed. SiO₂ with a thickness of 300 nm was thermally grown on silicon wafers, while cover layers of Si₃N₄ with thicknesses of 50, 100, and 150 nm were deposited chemically at atmospheric pressure. The samples were charged by the point-to-grid corona method. At room temperature, the measured surface potential V was stable during a period of almost three years. Isothermal measurements under different environmental conditions showed an improved charge retention compared to a single layer grown silicon dioxide. After ~3 h at 300°C, the observed voltage drop was <10% for the double layers and ~60% for bare SiO₂. Similar results were obtained under a humid condition of 95%RH and 60°C. Besides, thermally stimulated current (TSC) was measured in setup with a temperature ramp of 200°C/h. For the double layers, a current peak with a maximum temperature at ~500°C was observed. The measured current in the range of 300 to 400°C, the location of current maxima observed in thermally grown silicon dioxide or APCVD silicon nitride, was negligible. In addition to improved electret properties the internal stress in the investigated double layers can be adjusted by a proper thickness ratio of oxide layer to nitride layer. Therefore double layers of silicon dioxide and nitride seem to be promising materials for integrated sensors and actuators based on the electret effect     

Investigations on charge storage and transport in plasma-depositedinorganic electrets

The storage and transport of charges in plasma deposited inorganic electrets with low mechanical stress were investigated under different conditions. Silicon dioxide, nitride and oxynitride were chemically deposited on Si substrates by means of a radio frequency (13.56 MHz) plasma system. The samples were negatively charged by the constant voltage corona method. The surface potential was observed during aging at room temperature, at elevated temperatures of 200, 250 and 300°C and at a relative humidity of 95% at 60°C. The thermal activation process was examined by thermally stimulated discharge (TSC) measurements. Silicon oxynitride possessed the highest charge stability during the different experiments, correlating with the current maximum located at ~400°C. The charge transport in silicon dioxide, with a current maximum located at ~330°C, was described by a theoretical model which considered the drift and the partial retrapping of free charges in the bulk. Despite treatment with hexamethyldisilazane, it was not possible to stabilize the surface potential of silicon nitride samples even at room temperature     

Correlation of piezoelectric effect and TSC in stretchedpolystyrene-acrylonitrile films

The piezoelectric coefficient d₃₁ of stretched SAN (polystyrene-co-acrylonitrile) films has been measured under different poling and stretching conditions. The maximum average value of d₃₁ has been found to be 3.85 pC/N for 2.5× stretched films, corona poled at field E_P≃50 MV/m, and poling temperature T_P=85°C. The TSC (thermally stimulated current) experiments were performed to obtain the contribution of the polarization to the piezoelectric activity. The shrinkage effect and the TSC results are correlated to elucidate the molecular relaxation processes. The elastic modulus, crystallinity and polarization parameters are correlated to the piezoelectricity. The contributions of the dimensional and the local field effects to the piezoelectric activity in SAN are discussed     

The stability of ferroelectric polarization of PVDF uponirradiation

Polymeric actuator and sensor materials suffer from a low thermal and temporal stability. We report on an attempt to slow down the underlying structural relaxation in polyvinylidenefluoride (PVDF) films by irradiation with electrons of 1.5 MeV. This treatment yielded a dose-dependent crosslinking of the macromolecular chains. It caused a considerable rise of the ferroelectric remanent and saturation polarization, and the material became a harder ferroelectric. These changes were almost completely and irreversibly lost upon subsequent annealing. Electron spin resonance (ESR) measurements revealed that a large number of radicals and trapped electrons remained after irradiation (~1 per crystallite), and that the electric conductivity increased from 0.11 pS/m in the un-irradiated but poled sample to 1.1 pS/m at 450 kGy. The increase in conductivity with dose is caused completely by a corresponding increase of the product μn of the charge carrier mobility μ and the number density n. Based on a discussion of depolarization effects, we conclude that the change in ferroelectric behavior upon irradiation is caused mainly by the activity of those charges which are implanted or created by irradiation, and that the majority of them are annihilated by thermal treatment. However, the reduction of polarization with time, or at elevated temperature, is considerably slowed down due to the existence of crosslinks     

Charge trapping and conduction in pure and iodine-dopedbiaxially-oriented polypropylene

Study of charge trapping and conduction in pure and iodine doped biaxially oriented polypropylene (BOPP) is presented. Structural and chemical modifications induced by iodine were investigated using X-ray, optical and infrared methods. Optical spectra of doped BOPP show absorption at 290 nm from charge transfer complexes. X-ray examination revealed a decrease in crystallinity and crystallite size after doping. The effect of iodine on charge trapping was determined by thermally stimulated current technique. Deep traps (120°C peak) at crystalline-amorphous interfaces are destroyed by iodine, which provides new traps (68°C peak) with activation energy 0.9 eV. Pressure dependence of conductivity indicates ionic conduction in pure samples and electronic conduction in doped samples. Steady state currents in 0.5%wt iodine doped BOPP were measured for fields 1 to 5×10⁵ V cm^-1 and at elevated temperatures 22 to 50°C. Iodine enhances conductivity by ~700× in pure BOPP and the steady state conductivity shows a good fit of the 3-D Poole-Frenkel theory to the experiment. It is proposed that trapped electrons (arising due to donor-acceptor action) thermally released through PF lowering, predominantly contribute to the conduction     

Polarization and electric field distribution in thermally poledPVDF and FEP

In the present paper, heat wave (LIMM) and pressure step (PPS) measurements of the spatial polarization and electric field distributions in nonuniformly thermally poled α-PVDF and Teflon FEP films are reported. The spatial distributions obtained by the two methods are compared over the entire thickness range, and a satisfactory agreement is found. For PVDF the results of both methods are in accordance with literature data for similarly poled specimens of similar material, the so-called `thermal profile', a polarization peak near the anode. Furthermore, in the LIMM experiments we found a small peak near the cathode, which can be explained by a positive compensation charge layer extending ≈2 μm in depth. For the first time, LIMM spectra of FEP are published. The space charge distribution in the FEP sample is nearly homogeneous inside the sample. Near the anode side an accumulation of negative charges appear. Near both surfaces a positive compensation charge was found with a thickness of ~1 μm. It is demonstrated that by means of our deconvolution the spatial distribution can be determined simultaneously with two thermal parameters, the diffusivity of the sample material and the heat transfer coefficient between sample and sample holder     

Increase in capacitance and tan δ between conductors onprinted circuit board at low frequency due to ionic migration

An endurance test for a printed circuit board to ionic migration was carried out for 2000 h in a chamber controlled at 85°C and 85%RH. The capacitance C and tan δ between the conductors on the board were measured to find their correlation with ionic migration in the board. The measurement frequency of C and tan δ ranged from 1 to 1000 Hz. The configuration of the test circuit was designed according to IPC-SM-840. The material of the insulating board was fiberglass-reinforced epoxy resin. The distance between the Cu conductors was 0.165 mm, and 70 V dc was applied continuously. In the low frequency region (<30 Hz), C and tan δ gradually increase after ~800 h voltage application. During the gradual increase, steeply transient increases in C and tan δ are detected at about the same time when a deposit was seen to have formed on the board between the conductors, although no significant decrease in insulating resistance between the conductors is observed. It was confirmed that the deposit could be detected early from the steep increases in C and tan δ in the low frequency region. In the high frequency region (>30 Hz), on the other hand, gradual slight increases are observed from ~1100 h after voltage application, but no steep increases. The dependence of C and tan δ on frequency at the measurement is due to the low mobility of Cu ions in the water film on the insulating board     

0.78- and 0.98-μm ridge-waveguide lasers buried with AlGaAsconfinement layer selectively grown by chloride-assisted MOCVD

The 0.78- and 0.98-μm buried-ridge AlGaAs laser diodes (LD's) with a high Al-content AlGaAs confinement layer selectively grown by using a Cl-assisted MOCVD are demonstrated. By employing the AlGaAs confinement layer, the threshold current and the slope efficiency of the 0.78-μm LD are improved by ~40%, compared to those of the conventional loss-guided LD with the GaAs confinement layer. In addition, the stable fundamental mode up to 150 mW and the small astigmatic distance less than 1 μm are obtained. The 0.78-μm LD also shows the excellent high-power and high-temperature characteristic such as 100 mW CW operation at 100°C and the reliable 2,000-hour operation under the condition of 60°C and 55 mW. In the 0.98-μm LD, the narrow beam with the low aspect ratio of 1.86 and the stable fundamental transverse mode over 200 mW are exhibited. As a result, the 0.98-μm LD realizes the high fiber-coupled-power of 148 mW. Moreover, the high-power and high-temperature operation of 150 mW at 90°C is obtained. In the preliminary aging test, the LD's have been stably operating for over 900 hours under the condition of 50°C and 100 mW     

硅橡胶热刺激电流试验参数的研究

为研究硅橡胶的耐电蚀性能,利用TSC系统测试了硅橡胶合成绝缘子在不同试验参数下的TSC特性。试验结果表明,极化电压、极化温度和极化时间等均对硅橡胶的TSC特性有一定影响,主要体现在低温区曲线形状的变化及最大幅值的出现;计算所得陷阱电荷量随极化电压、极化温度的变化呈现出倒“V”字型,随极化时间的增加呈现饱和趋势。理论分析表明,入陷电荷量及其与硅橡胶内部荷电粒子的相互作用因外加试验条件的改变而不同,因此所得TSC曲线也不同;结合计算所得陷阱电荷量,为后续试验确定了合适的TSC试验参数。     

Surface potential of ferroelectric domain investigated by kelvin force microscopy

We have investigated the surface potential of poled area by varying the poled size and the sign of applied voltage on 100 nm thick Pb(Zr_0.25Ti_0.75)O₃ films grown by chemical solution deposition using Kelvin force microscopy (KFM). In the negative poled area, as the poled size increases from 300 to 4800 nm, the domain size and the KFM contrast increased in a linear way. However, in the positive poled area, the KFM contrast increased at first and then didn’t increase because of Coulomb repulsion. In two opposite poled areas, the values of the KFM contrast differed because of the internal field near the ferroelectric/electrode interface. These results imply that the surface overcharge of poled area in ferroelectric materials should be increased and the ferroelectric/electrode interface should be improved for the ultra high-density memory device.     

Dielectric phase angle of gall stones as a function of density

This paper presents the dielectric phase angle of different types of gall stones at a fixed frequency of 150 kHz and at room temperature, 28°C. The average value of this parameter for soft, mixed and hard type of gallstones are found to be -83.21, -85.31 and -86.89° respectively. This was found to increase as the density of the specimen increased     

The application of recurrence plot in DC tracking test of gamma-ray irradiated polycarbonate

Irradiation effects on tracking resistance of polymer insulation materials should be investigated due to the increasing usage in radiation-prone environments. This paper presents a study on dc tracking resistance of gamma-ray irradiated polycarbonate mixed with polyethylene by use of IEC 60112 method. The samples were irradiated in air up to 100 kGy and 1000 kGy with a dosage rate of 10 kGy/h using a /sup 60/Co gamma source. Because the data of tracking resistance obtained from the tracking test has a wide variation, discharge current in the test is considered as a main factor to estimate the tracking resistance. A recurrence plot analysis of discharge current has been made to evaluate the tracking resistance more consistently. Obtained results showed that after gamma-ray irradiation, the tracking resistance was improved compared with that of the unirradiated sample. The tracking resistance showed an increasing tendency from 0 kGy to 100 kGy but a decreasing tendency from 100 kGy to 1000 kGy. There was a threshold value for the tracking resistance around 100 kGy, which was related to the reaction of cross-linking and degradation. The topological structures of the recurrence plots with the irradiated samples were different from that of the unirradiated one. There were bigger white space segments, which indicated that there were high amplitude transients in the discharge currents of unirradiated sample. The recurrence point density increased from 100 kGy to 1000 kGy, which suggested that the discharge process of the total dose at 1000 kGy was more intensive than that at 100 kGy. The irradiation effects on the tracking resistance can be visually identified by the recurrence plot.     

Hottest spot temperatures in ventilated dry type transformers

The hottest spot temperature allowance to be used for the different insulation system temperature classes is a major unknown facing IEEE Working Groups developing standards and loading guides for ventilated dry type transformers. In 1944, the hottest spot temperature allowance for ventilated dry type transformers was established as 30°C for 80°C average winding temperature rise. Since 1944, insulation temperature classes have increased to 220°C but IEEE standards continue to use a constant 30°C hottest spot temperature allowance. IEC standards use a variable hottest spot temperature allowance from 5 to 30°C. Six full size test windings were manufactured with imbedded thermocouples and 133 test runs performed to obtain temperature rise data. The test data indicated that the hottest spot temperature allowance used in IEEE standards for ventilated dry type transformers above 500 kVA is too low. This is due to the large thermal gradient from the bottom to the top of the windings caused by natural convection air flow through the cooling ducts. A constant ratio of hottest spot winding temperature rise to average winding temperature rise should be used in product standards for all insulation temperature classes. A ratio of 1.5 is suggested for ventilated dry type transformers above 500 kVA. This would increase the hottest spot temperature allowance from 30°C to 60°C and decrease the permissible average winding temperature rise from 150°C to 120°C for the 220°C insulation temperature class     

2150t/h切圆燃烧锅炉低氧燃烧的试验研究

为了给锅炉低氧燃烧优化提供依据,在2 150 t/h四角切圆燃烧锅炉上进行了燃烧试验,以研究降低炉内氧量对锅炉燃烧的影响。结果表明：稳定工况下,炉膛温度随氧量变化存在一个峰值点,在峰值点两侧,降低氧量对燃烧和锅炉运行参数的影响不同;NO_x排放在炉膛温度峰值点附近存在一个峰值点,在深度降低氧量时存在一个谷值点,仅当氧量位于峰谷值中间区域时,降低氧量能够降低NO_x排放;降低氧量将加大稳定工况的旋流指数和降负荷过程中旋流指数的变化幅度,易引起蒸汽温度偏差大、超温等问题;当降低氧量未使锅炉不完全燃烧热损失明显增加时,会加大变负荷过程炉温、NO_x排放波动幅度,反之,变负荷时风量改变对燃煤放热量的影响,会使负荷变化对炉膛温度、NO_x排放影响降至很小。     

Silicon-based inorganic electrets for application in micromachineddevices

Layers of SiO₂ and Si₃N₄ have good mechanical properties for application in micro-machined electret capacitor microphones. These materials are investigated as single or double layers in terms of chargeability and long-term charge stability. The main emphasis is put on the miniaturization of electret layers. The lateral dimensions of the electrets are reduced to 2 mm and the charge decay characteristics under different environmental conditions are described. According to the experimental data, multilayer samples of silicon dioxide and nitride possess good chargeability and higher charge stability compared to the well investigated single layers. Typically, the double layers loose ~10% of their surface potential when annealed for 200 min at 300°C and show a peak of the thermally stimulated current at 430°C. It can also be shown that the miniaturization of samples does not necessarily cause a faster charge decay     

Modulation and free-space link characteristics of monolithicallyintegrated vertical-cavity lasers and photodetectors with microlenses

We present temperature, modulation, and free-space link characteristics of monolithically integrated vertical-cavity lasers (VCLs) and resonant photodetectors. The devices have been integrated using a novel structure that makes it possible to fabricate devices with through-the-substrate emission and detection. Taking advantage of the substrate emitting/detecting architecture, we monolithically integrate microlenses on the substrate side of the devices and flip-chip bond arrays without via processes or substrate removal. Low-threshold high-efficiency VCLs exhibit maximum small-signal modulation bandwidths, which are limited by parasitics, of ~9.5 GHz at 20°C and ~8.4 GHz at 70°C. The VCLs have the lowest reported bias currents required to reach bandwidths of up to ~8 GHz. A free-space optical link is demonstrated with flip-chip-bonded arrays of microlensed, monolithically integrated VCLs and detectors. The link is found to be tolerant to temperature differences of ±75°C between the VCL and detector, with error free (BER<10^-12) data transmission demonstrated in each case     

Temperature effects on torque production and efficiency of PMmotors using NdFeB magnets

Recent developments in high energy magnets have created widespread interest in the area of permanent magnet (PM) motors. The use of PM synchronous motors or brushless motors to replace conventional DC or induction type motors has not been as speedy as anticipated earlier. This paper deals with the temperature effects of PM motors using neodymium magnets on the torque production capability and on the efficiency of the motor. When PM motors are designed to operate in a wide temperature range, the reversible demagnetization of the neodymium magnets with temperature and the increase in winding resistance with temperature influence the maximum torque capability at rated speed and efficiency of the PM motor. The maximum torque at rated speed is limited due to the fixed DC link voltage of the inverter feeding the motor. In this paper, it is shown that over an operating range of -40°C to 150°C the maximum torque capability and efficiency of the motor can vary over a wide range. It is also shown that for certain designs, a near flat maximum torque versus temperature characteristic may be obtained. The major factors influencing these variations are identified. The discussion in this paper is concentrated on PM motors with a trapezoidal back EMF waveform. The idea could be extended to sinusoidal back EMF motors and to PM DC motors     

High-temperature operation of 1.3-μm tapered-active-stripe laserfor direct coupling to single-mode fiber

High-temperature operation of 1.3-μm wavelength multiquantum-well (MQW) lasers with an active stripe horizontally tapered over whole cavity, for direct coupling to single-mode fibers (SMFs), are reported. The lasers have reduced the output-beam divergence in a simple structure which does not contain an additional spot-size transformer. To improve high-temperature characteristics, we have investigated the influence of the thickness of separate-confinement-heterostructure layers and the number of quantum wells (QWs) on the threshold current and the output-beam divergence at high temperature. As a result, the fabricated lasers show low-threshold current (~18 mA) and high-slope efficiency (~0.4 mW/mA) with narrow output-beam divergence (~12°) at 85°C. Moreover, we have obtained maximum coupling efficiency of -4.7 dB in a direct coupling to a SMF, and the reliability of longer than 10⁵ h (MTTF) by a lifetime test of over 2000 h at 85°C