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1.
负微分迁移率和碰撞电离对GaAs光导开关非线性特性的影响 总被引:2,自引:2,他引:0
对GaAs光导开关非线性工作时,负微分迁移率和碰撞电离的作用进行了数值分析,给出了考虑和未考虑碰撞电离作用时的外电路电流输出波形,以及载流子和电场的空间分布和随时间演变的情况.计算表明GaAs材料的负微分迁移率引起的微分负阻,会导致阴极附近电场的动态增强,使得阴极附近的电场达到本征碰撞电离发生的阈值电场,从而引发本征碰撞电离的发生.分析结果表明,碰撞电离可以极大地延长电流输出的时间,但仅考虑负微分迁移率特性的本征碰撞电离过程不足以完全解释观察到的所有非线性现象,必须进一步考虑其它高电场效应. 相似文献
2.
Fani E. Asimakopoulou Ioannis F. Gonos Ioannis A. Stathopulos 《Journal of Electrostatics》2012,70(5):457-461
In this paper the results of the research being carried out on the impulse characteristics of soils and more specifically the ionization voltage gradient are presented. The determination of the soil ionization voltage and the respective gradient using a universally accepted method is yet to be established. Aiming at meeting this need, the present paper critically presents these methods and records the ionization gradient values for soil types, which have derived from different experimental approaches. The comprehensive study of these methods is intended to serve as a guide for researchers studying the nonlinear phenomena developed in the soil. 相似文献
3.
A novel design method for high Q piezoelectric resonators was presented and proposed using the 3-D equations of linear piezoelectricity with quasi-electrostatic
approximation which include losses attributed to mechanical damping in solid and resistance in current conduction. There is
currently no finite element sofware for estimating the Q of a resonator without apriori assumptions of the resonator impedance or damping. There is a necessity for better and more
realistic modeling of resonators and filters due to miniaturization and the rapid advances in frequency ranges in telecommunication.
We presented new three-dimensional finite element models of quartz and barium titanate resonators with mechanical damping
and resistance in current conduction. Lee, Liu and Ballato’s 3-D equations of linear piezoelectricity with quasi-electrostatic
approximation which include losses attributed to mechanical damping in solid and resistance in current conduction were formulated
in a weak form and implemented in COMSOL. The resulting finite element model could predict the Q and other electrical parameters for any piezoelectric resonator without apriori assumptions of damping or resistance. Forced
and free vibration analyses were performed and the results for the Q and other electrical parameters were obtained. Comparisons of the Q and other electrical parameters obtained from the free vibration analysis with their corresponding values from the forced
vibration analysis were found to be in excellent agreement. Hence, the frequency spectra obtained from the free vibration
analysis could be used for designing high Q resonators. Results for quartz thickness shear AT-cut and SC-cut resonators and thickness stretch poled barium titanate resonators
were presented. An unexpected benefit of the model was the prediction of resonator Q with energy losses via the mounting supports. 相似文献
4.
通过气体放电产生更高浓度的低温等离子体要求具有纳秒上升沿和纳秒脉宽的高重频快脉冲,而目前被广泛使用的MOSFET和IGBT都无法满足这些参数要求,而双极结型晶体管(BJT)的集电极与发射极之间的雪崩击穿过程具有快导通、快恢复、高稳定性等优点,适合作为小型Marx发生器的自击穿开关。文中对用多种型号的BJT进行击穿特性比较测试实验,发现可以通过改变BJT的门极和发射极的并联电阻来调节其雪崩击穿电压,实现一定范围的工作电压。雪崩击穿恢复特性实验表明,当击穿电流衰减到低于维持电流时,BJT就会开始恢复绝缘而关断,通过改变电路中的参数以控制击穿电流的变化就可以控制BJT的雪崩击穿导通时间(即导通脉宽)。将这些结论应用到实际电路中,可获得上升沿5 ns、脉宽为10 ns、幅值2 kV、重复频率高达100 kHz的纳秒快脉冲,可用于激发高浓度低温等离子体。 相似文献
5.
基于超短激光脉冲与气体作用通过光场离化电流产生太赫兹(THz)辐射的模型, 研究了用双色激光脉冲的方法产生强THz辐射的优化参数条件. 数值计算表明, 导致THz辐射产生的离化电流主要是由一阶电离过程产生的, 高阶离化对该电流产生的贡献很小. 通过调节基频光与倍频光的配比、相位差都能增大离化电流, 从而可以提高THz辐射振幅. 将激光波长拓展到中红外波段, 也有利于提高离化电流. 此外,改变作用气体的种类也能改变离化电流. 在激光和密度参数相等的情况下, 在氦气中可以产生高于氮气中2倍左右的离化电流. 相似文献
6.
对多元ZnO压敏陶瓷电阻片进行了多达14000次的大电流冲击老化试验, 通过显微结构、电气性能及介电特性的测量对其缺陷结构进行了表征, 并研究了缺陷结构与大电流冲击老化之间的关系. 试验表明多次大电流冲击老化导致试样的电气性能明显下降, 发现ZnO压敏陶瓷的几何效应不仅受控于晶粒还与晶界密切相关. 另外, 通过介电谱分析观察到ZnO压敏陶瓷存在四种缺陷弛豫过程, 低温-60 ℃下的两个缺陷弛豫峰激活能约为0.24 eV和0.35 eV, 认为它们分别对应着本征的锌填隙缺陷L(Zni··)和氧空位缺陷L(VO·)并且不受冲击老化的影响. 高温80℃以上两个松弛峰的活化能约为0.71 eV和0.84 eV, 认为它们分别对应着非本征的晶间相电子陷阱L(ingr)和晶界处界面态陷阱L(gb). 发现大电流冲击后, 仅界面态陷阱激活能从0.84 eV降低到0.76 eV, 认为界面态陷阱主要控制着ZnO压敏陶瓷的电气性能和稳定性. 相似文献
7.
Thermal stability and data retention of resistive random access memory with HfO_x/ZnO double layers 下载免费PDF全文
As an industry accepted storage scheme, hafnium oxide(HfO_x) based resistive random access memory(RRAM)should further improve its thermal stability and data retention for practical applications. We therefore fabricated RRAMs with HfO_x/ZnO double-layer as the storage medium to study their thermal stability as well as data retention. The HfO_x/ZnO double-layer is capable of reversible bipolar switching under ultralow switching current( 3 μA) with a Schottky emission dominant conduction for the high resistance state and a Poole–Frenkel emission governed conduction for the low resistance state. Compared with a drastically increased switching current at 120℃ for the single HfO_x layer RRAM, the HfO_x/ZnO double-layer exhibits excellent thermal stability and maintains neglectful fluctuations in switching current at high temperatures(up to 180℃), which might be attributed to the increased Schottky barrier height to suppress current at high temperatures. Additionally, the HfO_x/ZnO double-layer exhibits 10-year data retention @85℃ that is helpful for the practical applications in RRAMs. 相似文献
8.
Lin Chen Jing Ren Fan Guo LiangJi Zhou Ye Li An He Wei Jiang 《中国科学:物理学 力学 天文学(英文版)》2014,57(3):442-446
To understand the formation process of vacuum gap in coaxial microsecond conduction time plasma opening switch (POS), we have made measurements of the line-integrated plasma density during switch operation using a time-resolved sensitive He-Ne interferometer. The conduction current and conduction time in experiments are about 120 kA and 1 μs, respectively. As a result, more than 85% of conduction current has been transferred to an inductive load with rise time of 130 ns. The radial dependence of the density is measured by changing the radial location of the line-of-sight for shots with the same nominal POS parameters. During the conduction phase, the line-integrated plasma density in POS increases at all radial locations over the gun-only case by further ionization of material injected from the guns. The current conduction is observed to cause a radial redistribution of the switch plasma. A vacuum gap forms rapidly in the plasma at 5.5 mm from the center conductor, which is consistent with the location where magnetic pressure is the largest, allowing current to be transferred from the POS to the load. 相似文献
9.
Resistive switching characteristic and uniformity of low-power HfO_x-based resistive random access memory with the BN insertion layer 下载免费PDF全文
In this letter,the Ta/HfO_x/BN/TiN resistive switching devices are fabricated and they exhibit low power consumption and high uniformity each.The reset current is reduced for the HfO_x/BN bilayer device compared with that for the Ta/HfO_x/TiN structure.Furthermore,the reset current decreases with increasing BN thickness.The HfO_x layer is a dominating switching layer,while the low-permittivity and high-resistivity BN layer acts as a barrier of electrons injection into TiN electrode.The current conduction mechanism of low resistance state in the HfO_x/BN bilayer device is space-chargelimited current(SCLC),while it is Ohmic conduction in the HfO_x device. 相似文献
10.
会切磁场等离子体推力器是一种利用磁镜约束等离子体产生推力的新型推力器,具有寿命长、推力大范围连续可调等优点,在无拖曳控制领域具有较大的应用前景.分别采用Xe,Kr和Ar三种不同工质,开展了会切磁场等离子体推力器实验.首先,对所用的推力器进行了简要的原理和设计介绍;然后,对三种工质的点火电压分别进行了测试,发现Xe是最容易点火成功的,Kr和Ar点火难度较大.在阳极电流、推力、效率和比冲等性能方面,三种工质在同等条件下也存在明显的区别.分析发现,三者的工质利用率高低导致了性能上的差别,通过提升通流密度能够大幅提升Kr和Ar的工质利用率.在羽流结构方面,法拉第测量结果表明三者都存在明显的空心羽流,且离子电流密度峰值出现的角度随着原子量的减小而逐渐减小. 相似文献
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12.
Mosca R. Ferro P. Besagni T. Calestani D. Chiarella F. Licci F. 《Applied Physics A: Materials Science & Processing》2011,104(4):1181-1187
Impedance spectroscopy measurements show that complex conductivity of thermally ablated CH3NH3SnCl3 films is strongly enhanced when humidity increases. Coplanar two-electrode test devices are modeled through an equivalent
circuit comprising one resistance and two constant phase elements. It is shown that the influence of ambient humidity is mainly
resistive. The dynamic responses of the devices to humidification/dehumidification cycles point out that the a.c. current
varies by more than three orders of magnitude when humidity is varied between dry air and 80% relative humidity. The rise
times are few hundred seconds while fall times are as short as few tens of seconds. This observation suggests that impedance
variations are determined by mechanisms involving loosely bound water molecules physisorbed at the surface of the hybrid film.
The results obtained are discussed in terms of protonic conduction. 相似文献
13.
Nakamura H. Okamura T. Shioda S. 《IEEE transactions on plasma science. IEEE Nuclear and Plasma Sciences Society》1998,26(1):69-78
Isentropic efficiency of the nonequilibrium MHD power generator was studied by a shock tube driven disk generator. Cesium seeded helium was used as a working gas. From the measurements of Faraday current density distribution, it was possible to estimate the general tendency of Joule dissipation in the generator. The Joule dissipation did not decrease due to the occurrence of nonuniformity of the plasma when external load resistance was low, although it decreased with the decrease in the load resistance when the load resistance was high. The electrical efficiency increased with the increase in applied magnetic flux density. This fact is thought to be caused by high Hall parameter and the stabilization of the plasma due to high degree of seed ionization 相似文献
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高气压下的微型电热推进器(MPT)中的放电等离子体存在多负辉区结构,其负辉区有融合趋势。对矩形微放电等离子体推进器(RMPT)的负辉区融合过程进行了二维模拟分析,在方法上采用了非平衡态的自洽流体模型,并考虑了离子电流加热和三体碰撞过程。结果显示:矩形微放电等离子体推进器(RMPT)在低电流条件下存在两个稳定的负辉区,当超过某一电流阈值条件后,两个负辉区会在腔体中心重合。分析了这一过程的成因,认为其融合过程本质上是空心阴极的导通过程,其融合与否与鞘层电压有关。 相似文献
17.
An improved model for soil ionization around grounding system and its application to stratified soil
《Journal of Electrostatics》2004,60(2-4):203-209
An improved model for taking into account the effect of the soil ionization around grounding system under lightning strike is proposed in this paper. In this model, the soil ionization region is assumed to retain 7% of its pre-ionization resistivity, which is consistent with the experimental results on soil ionization found in literature (Trans. SA Inst. Electr. Eng. (1988) 63; AIEE Trans. 61 (1942) 349; Proc. IEE 121(2) (1974) 123) and our own laboratory experiments (Time domain modelling of the response of grounding systems subjected to lightning currents, Licenciate Thesis, Uppsala University, 2003). Compared with modelling the soil ionization as an increase in the size of the ground conductor, the model presented here will not overestimate the beneficial influence of the soil ionization in reducing the ground potential rise, especially in high resistivity soil. The model is also applied to study the transient behaviour of grounding conductors in stratified soil under lightning strike including soil ionization. It shows that making the grounding conductor to penetrate the lower resistivity soil layer could help to decrease the ground potential rise at the injection point several times. 相似文献
18.
Piero Cotti 《Zeitschrift für Physik B Condensed Matter》1964,3(1):40-74
The electronic charge transport in thin indium films of high purity is investigated (direct current, eddy current and magnetoresistance in a magnetic field perpendicular to the surface) at low temperatures where surface scattering of the electrons becomes important. A method is described which allows the determination of the mean free path (corresponding to a Sommerfeld-model for the conduction electrons) for a single specimen by measuring both the direct current conductivity and the decay time of eddy currents. For a multivalent metal like indium, with a Fermi surface extending over different Brillouin zones, the “mean free path” evaluated in this way can no longer be regarded as the mean value of the electronic free path calculated over the whole Fermi surface. It is shown, that for indium the ?mean free path” evaluated from our size effect investigations will mainly correspond to the electrons of the second zone, and that the electrons of the third zone only neglectingly contribute to the electronic charge transport. 相似文献
19.
We report on the results of investigation of properties of ultrahard Ti–Si–N coatings deposited by pulsed high-current magnetron reactive sputtering (discharge pulse voltage is 300–900 V, discharge pulse current is up to 200 A, pulse duration is 10–100 μs, and pulse repetition rate is 20–2000 Hz). It is shown that for a short sputtering pulse (25 μs) and a high discharge current (160 A), the films exhibit high hardness (66 GPa), wear resistance, better adhesion, and a lower sliding friction coefficient. The reason is an enhancement of ion bombardment of the growing coating due to higher plasma density in the substrate region (1013 cm–3) and a manifold increase in the degree of ionization of the plasma with increasing peak discharge current (mainly due to the material being sputtered). 相似文献
20.
The electron transport in hydrogenated amorphous carbon films a-C: H with copper nanocluster inclusions has been investigated. The conditions of cluster formation are derived. It is theoretically demonstrated that the energy band structure of the matrix substantially affects the conditions of cluster formation. The electron transport depends on the cluster structure. It is found that, below the percolation threshold (the case of isolated clusters), the transport current is governed by two components depending on the electric field strength. At low field strengths, the current is caused by electrons in the conduction band of amorphous carbon, which are thermally excited from copper clusters. At high field strengths, the transport current is provided by tunneling electrons from the Fermi level of copper clusters to the conduction band of a-C: H. The difference between the mobility edge of the conduction band of amorphous carbon and the Fermi level in copper clusters is determined from the temperature dependence of the resistance and proves to be equal to 0.48 eV. The temperature dependences of the resistance at low field strengths exhibit a fine structure. It is revealed that, above the percolation threshold, the electrical resistance of clusters is considerably contributed by the residual resistance, which is supposedly associated with the electron scattering by cluster surfaces. The temperature effect on the electron transport is examined using the spin-wave scattering technique at a frequency of 4.0 GHz. It is found that the spin wave in the yttrium iron garnet (YIG) film is predominantly affected by thermally excited electrons located above the mobility edge in the conduction band of a-C: H. 相似文献