介质表面高功率微波击穿中释气现象的数值模拟研究

建立了一个简单的高功率微波(HPM)介质表面击穿释气模型,并采用PIC(partiele-in-cell)-MCC(Monte Carlo collisions)方法,通过自行编写的介质表面击穿数值模拟程序对不同释气条件下的介质表面HPM击穿过程进行了数值模拟研究,得到了击穿过程中电子数量等的时间图像和不同释气速度下的击穿延迟时间.模拟结果表明,对于具有一定时间宽度的HPM脉冲,当介质表面气体脱附速度较小时,由于介质表面气体层形成太慢而不会发生击穿;只有当脱附速度大于一定值时,击穿才会发生且击穿延迟时间在一定范围内随着脱附速度的增加而缩短.最后,将数值模拟得到的介质表面HPM击穿数据,与单极性表面击穿的实验诊断图像进行了对比,两者的发展趋势符合很好. 关键词： 释气现象 介质表面击穿 高功率微波 数值模拟     

加压乙二醇/水混合液耐μs级高电压击穿实验研究

 采用同轴电极实验装置,在μs级充电时进行了加压乙二醇/水混合液正电极击穿实验,并对实验结果进行了分析和解释,得出结论如下：击穿场强随静压以1/8次幂的关系而增加;击穿场强系数随乙二醇浓度的增加而增加;加压和添加乙二醇对于提高水介质耐高电压击穿的能力具有可叠加性,加压比添加乙二醇更有效;在静压12×10⁵ Pa下乙二醇浓度80%的混合液击穿场强比常压下纯水击穿场强高112.2%。加压提高乙二醇/水混合液击穿场强的主要机制是加压增加了击穿延迟时间。     

薄SixOyNz膜击穿机理的研究

本文在研究极薄Si_xO_yN_x膜击穿特性的基础上,探讨了氮化SiO₂膜的击穿机构,讨论了氮化影响击穿性能的因素。实验结果与理论分析表明,氮化后的SiO₂膜击穿性能的改善主要决定于膜中及表界面的微观结构的改善及成分的改变。虽然,氮化引起介质膜带隙宽度的变窄将导致击穿电场的下降,但致密的材料结构、变得平整的表界面及陷阱的影响将大大推迟击穿的发生。实验结果表明,氮化SiO₂膜的本征型 关键词：     

百kV/cm场强下SF6气体开关纳秒脉冲击穿场强和时延经验公式

百kV/cm高场强纳秒脉冲条件下,采用J. C. Martin经验公式估算SF₆气体击穿场强时,估算值与实验结果差异显著。为了进一步指导高场强脉冲气体开关设计,为开关工作状态调节提供依据,借鉴经典击穿场强经验公式形式建立了百kV/cm场强下SF₆气体开关纳秒脉冲击穿场强和时延与实验参数之间的关系,基于实验数据拟合形成了修正系数的击穿场强和时延经验公式。研究表明,百kV/cm场强和纳秒脉冲条件下脉冲电压斜率对开关击穿特性有重要影响,击穿场强与击穿时延相互关联。百ns至μs脉冲与几十ns脉冲气体放电机理的区别引起放电过程中击穿时延组成发生变化,导致了经典击穿场强经验公式估算值与实验结果的显著差异。修正系数的击穿经验公式可为电磁脉冲模拟器输出开关提供更为精确的工程设计依据。     

不同气压下介质表面高功率微波击穿的数值模拟

介绍了用于模拟介质表面高功率微波击穿的粒子模拟-蒙特卡罗碰撞方法,并采用该方法模拟研究了氩气环境不同气压下的介质表面高功率微波击穿过程,获得了该击穿过程中粒子数量和电子平均能量的时间变化图像,并得到了击穿延迟时间。数值模拟结果发现:在低气压下,次级电子倍增的作用比较明显,但电子数量在次级电子倍增饱和后的增速较低,击穿延迟时间较长;随着气压的升高,次级电子倍增的影响逐渐变小,气体电离逐渐占主导地位,击穿延迟时间逐渐变短;在高气压下,由于介质表面吸收沉积电子而呈负电性,次级电子倍增消失,击穿延迟时间由气体碰撞电离来决定。     

加压水介质耐μs级高电压击穿实验研究

 采用水介质同轴电极实验装置,开展了μs级充电加压水介质击穿实验研究,并对实验结果进行了分析和讨论,结果表明：在水介质正电极击穿类型的实验中,常压下水介质击穿场强与Martin公式吻合。加压水介质击穿场强随静压的增加而增加,其场强增幅与Mirza定性理论场强增幅的相对差别在5%以内。根据实验结果推导出了更为准确的水介质击穿场强随静压变化的关系式。对水介质加压,将压缩电极表面气泡,减少气泡数目,从而可以提高水介质耐高电压击穿能力。     

开放空间重复频率微波脉冲击穿概率理论与实验研究

综合考虑有效初始电子产生理论、雪崩电子击穿理论等过程中的击穿延迟时间,探讨了开放空间微波脉冲的击穿延时概率分布,提出了重复频率微波脉冲击穿概率模型,定义了基于概率模型的微波脉冲击穿阈值。利用S波段微波准光学反射聚焦系统对一定气压大气击穿过程进行了模拟,监测击穿放电发光时刻作为击穿时间,分别在铯137放射源存在与否情况下开展了系列实验。研究结果表明,提高种子电子产生率相较于提高电离率是增大脉冲击穿概率更有效的方法;重复频率过程中,若存在累积效应,击穿延时概率分布曲线将左移并趋于稳定,击穿后的气体在短时间内容易再次击穿。     

Similarity law for a homogeneous discharge in the presence of a strong field and analogues of the Stoletov constant for the pulsed regime

It is demonstrated that the similarity relationships (breakdown curves), which establish a dependence of the field strength divided by the pressure on the product of the pressure and the delay time of the breakdown, are realized upon the uniform breakdown of the gas gap in the presence of both rectangular and triangular voltage pulses, which is interesting for the physics of gas and plasma discharges, and remain valid for strong fields. The breakdown criterion is described with a two-valued curve such that the effective multiplication of electrons in gas becomes possible in the presence of both weak and strong fields and at small products of the pressure and the pulse time. An analogue of the Stoletov effect, which corresponds to a maximum in the current with respect to pressure at a given voltage pulse, is demonstrated for the pulsed discharge. The analogues of the Stoletov constant are calculated for non-self-sustained pulsed discharges in various gases. The minimum delay time of the breakdown is also determined by these constants.     

Microwave breakdown in slots

The properties of microwave-induced breakdown of air in narrow metallic slots are investigated, both theoretically and experimentally, with emphasis on factors important for protection against transmission of incident high-power microwave radiation. The key factors investigated are breakdown power threshold, breakdown time, peak-leakage power, and total transmitted energy, as functions of incident pulse shape and power density. The theoretical investigation includes estimates of the electric field intensification in narrow slots and basic breakdown plasma modeling. New results important for application to the high-power microwave field, such as the influence of pulse shape on breakdown time and peak-leakage power, are presented. The experimental investigation comprises a set of slot breakdown experiments at atmospheric pressure, which are analyzed to extract key parameters, such as transmission cross section, breakdown time, peak leakage power, and transmitted energy. The experimental data is compared and shown to be in good agreement with results obtained in the theoretical investigation.     

液体介质快脉冲电压下击穿特性研究

 设计了液体介质快脉冲击穿试验装置和电压电流测量系统，研究了重复频率、电极形状及电极间距与介质击穿场强、击穿电压和击穿时延等击穿特性参数的关系，比较了变压器油、十二烷基苯、蓖麻油三种典型液体绝缘介质在直流及快脉冲电压作用下的绝缘性能。结果表明：短脉冲持续时间下液体绝缘材料有异常高的击穿场强；重复脉冲串作用下的击穿场强比单个脉冲下明显减小，重复频率2 kHz时击穿场强减小了约30％；电极头半径大小对击穿也有影响，半径R＝5 mm时，击穿电压最高；击穿时延随击穿场强减小而变长，在其他条件相同的情况下，测得击穿时延随机波动；蓖麻油的快脉冲电压绝缘性能最好，变压器油次之。     

空气和SF6气体击穿对微波传输的影响

通过喇叭有效口径渐变法进行了L波段、脉宽30 ns的高功率微波空气以及SF6气体击穿实验,给出了实验中得到的典型波形,分析了空气以及SF6气体击穿对微波传输的影响。实验表明:空气击穿产生等离子体对微波传输的影响主要表现为对微波功率的反射,使微波脉宽变窄,而SF6击穿则主要体现为对微波功率的吸收,使峰值功率降低。关键词: Abstract:Key words:     

三氯乙烯氧化硅膜推迟破坏性击穿的机理研究

本文对三氯乙烯(TCE)氧化推迟SiO₂膜的破坏性击穿及其机理进行了研究。结果表明,随着TCE流量的增大、处理时间的增加、温度的升高和氧分压的降低,SiO₂膜的击穿电流耐量增大。但过大的TCE流量和过长的处理时间,将使击穿特性变坏。结果还表明,击穿电流耐量的增大与膜内电子陷阱密度的增大有关。文中提出包括三种恶性循环在内的“低势垒点-电场增强”击穿模型,并考虑氧化气氛中的H₂O对击穿特性的影响,引入电子陷阱抑制低势垒点-电场增强的作用,分析T 关键词：     

Breakdown magnetic field in an inductively coupled plasma

The Paschen curve shows that the breakdown voltage over a gap is a non-linear function of the product of the gas pressure and the gap distance for plasmas which are generated inside an electric field driven source. The Paschen breakdown relationship does not depend on the applied frequency and covers secondary emission at the electrodes of the discharge. Adapting the Paschen curve, a breakdown curve for a time-dependent magnetic field, typical for inductively coupled plasmas which sources are without electrodes, is examined here. It is shown that in this case the magnetic field breakdown curve does depend on the applied frequency.     

重频纳秒高压脉冲下变压器油击穿特性的实验研究

介绍了重频纳秒高压脉冲下变压器油绝缘特性研究的现状和成果。进行了重频（1 Hz～1 kHz）纳秒高压脉冲下25#变压器油击穿特性的实验研究。实验发现相对于单次纳秒脉冲,重频脉冲下25#变压器油的击穿场强与频率相关,频率提高,击穿场强降低,但不是线性关系,在频率超过100 Hz时变压器油的击穿场强变化较小,在10~100 Hz时变压器油的击穿场强迅速下降。初步总结了重复频率、脉冲宽度和击穿场强的关系,对重频脉冲下变压器油的击穿机理进行了初步的探讨。     

强电磁脉冲(激光、微波)在高温离解氮气中的击穿效应

 通过对电子能量分布函数所满足的Boltzmann方程的求解，在理论上分析了强电磁脉冲(激光、微波)在高温氮气中的击穿效应。高温气体的一个主要特征是其中的部分气体分子会离解为原子，这一离解效应会对强电磁脉冲在气体中发生电离击穿的阈值产生影响。计算表明：随着温度的升高，氮分子的离解度增大，强电磁脉冲的击穿阈值下降；击穿阈值的下降幅度与电磁波的频率有关，对频率较高的红外激光，击穿阈值下降明显；而对微波，击穿阈值所受影响较小。     

Frequency breakdown in semiconductors

The effect of the frequency of the applied voltage on the breakdown of semiconductors is investigated. Unlike earlier observations, our experiment yields, in some cases, a breakdown voltage versus frequency curve which is similar in nature to the high-frequency breakdown characteristics in gas devices wherein the breakdown voltage shows a minimum at a certain frequency. A possible theoretical explanation for the above behaviour of semiconductor devices based on dielectric heating is given, which is in fair agreement with the observations.     

Over recovery in low pressure spark gaps-confirmation of pressurereduction in over recovery

The over recovery in sparkgaps (Nagesh, 1997, Nagesh et al., 1999) operating along the left-hand side of Paschens' characteristics is due to pressure reduction in the gap after the first pulse discharge. This pressure reduction leading to over recovery in low pressure spark gaps has been verified using a low pressure spark gap with two spark gaps placed one above the other in the same chamber. The breakdown voltage strength characteristics of the second gap has been determined for gap spacings of 3.5 mm to 10 mm, diffusion of plasma in the direction of vacuum pumping and opposite, at a pressure of 2.1 Pa for hydrogen gas. The vacuum pumping direction has a great influence on the breakdown strength characteristics of second gap after the first gap discharge. The breakdown voltage of the second gap can exceed its self breakdown voltage only 1) when the diffusion of plasma and vacuum pumping direction are same and 2) when the second gap spacing is greater than or equal to first gap spacing. Shorter gaps can always have breakdown voltage lower than or equal to their self breakdown voltage. The experimental setups, behavior of self breakdown voltages of second gap due to breakdown in the first gap, over recovery characteristics of spark gaps, the results, and discussions are presented here     

Counting of particles in aqueous solutions by laser-induced photoacoustic breakdown detection

Laser-induced photoacoustic breakdown detection is applied for the determination of particles in aqueous dispersion. Polystyrene (latex), alumina and thoriasol particles of different sizes are investigated for demonstration. Laser pulses at 500 nm with 28 ns pulse width (FWHM), generated by an excimer ( = 308 nm) pumped dye laser, are focused into aqueous particle dispersions to produce breakdown. The dye laser pulse energy is fixed at a value lower than the breakdown threshold of pure water to initiate a dielectric breakdown only when particles are present in a given focus volume. Focus volume parameters and particle size dependent breakdown thresholds are calculated and the results are compared with data from literature. Dependence of breakdown threshold values on the chemical composition of the particles is determined for polystyrene, alumina and thoriasol particles.     

Thickness dependent studies of dielectric breakdown in Langmuir thin molecular films

The usefulness of Langmuir thin molecular films for making devices has made it necessary to study their dielectric breakdown behaviour. Study of thickness dependence of the breakdown field in these films is important from the point of view of device applications as well as the understanding of breakdown phenomenon. In the present paper, thickness dependence of two breakdown events corresponding to ‘onset breakdown’ and ‘maximum breakdown’ voltages have been reported for the ‘build-up’ Langmuir films of barium palmitate, margarate and behenate in the thickness ranges (23–300 Å) and (370–2400 Å), respectively. These two events are of particular interest because the former determines the permissible operating voltage and the latter leads to the ‘practically’ important ultimate dielectric strength of the film. The Langmuir films have been chosen because of their accurately known and controllable uniform thickness, high dielectric strength and high structural perfection. The onset breakdown strength of all the substances is found to vary as d^-1 (d being film thickness) in the ultra-thin range which have been explained qualitatively in terms of boundary effects. The maximum breakdown strength is also found to be almost inversely proportional to the film thickness but the results remain inexplicable because the actual mechanism of destructive breakdown is not yet fully understood. The typical J-V characteristics in the ‘non-destructive’ phase have also been given.     

新型缓冲层分区电场调制横向双扩散超结功率器件

为了突破传统横向双扩散金属-氧化物-半导体器件(lateral double-diffused MOSFET)击穿电压与比导通电阻的极限关系,本文在缓冲层横向双扩散超结功率器件(super junction LDMOS-SJ LDMOS)结构基础上,提出了具有缓冲层分区新型SJ-LDMOS结构.新结构利用电场调制效应将分区缓冲层产生的电场峰引入超结(super junction)表面而优化了SJ-LDMOS的表面电场分布,缓解了横向LDMOS器件由于受纵向电场影响使横向电场分布不均匀、横向单位耐压量低的问题.利用仿真分析软件ISE分析表明,优化条件下,当缓冲层分区为3时,提出的缓冲层分区SJ-LDMOS表面电场最优,击穿电压达到饱和时较一般LDMOS结构提高了50%左右,较缓冲层SJ-LDMOS结构提高了32%左右,横向单位耐压量达到18.48 V/μm.击穿电压为382 V的缓冲层分区SJ-LDMOS,比导通电阻为25.6 mΩ·cm2,突破了一般LDMOS击穿电压为254 V时比导通电阻为71.8 mΩ·cm2的极限关系.