光电导开关面临的问题及发展趋势

光电导开关具有传统高功率脉冲器件不具备的优良性能,在产生高功率脉冲领域有很大发展潜力。使用光导开关能直接从直流电源产生电磁脉冲。根据各种应用对光导开关性能指标的不同要求,将其归纳为大功率脉冲应用与超短电磁脉冲应用两类。阐述了光电导开关在理论、实用化方面遇到的问题以及目前学术界、业界对其解决的方法。对各种解决方法做出评价并展望光导开关未来发展趋势。     

Investigation of oxide charge trapping and detrapping in a MOSFETby using a GIDL current technique

We proposed a new measurement technique to investigate oxide charge trapping and detrapping in a hot carrier stressed n-MOSFET by measuring a GIDL current transient. This measurement technique is based on the concept that in a MOSFET the Si surface field and thus GIDL current vary with oxide trapped charge. By monitoring the temporal evolution of GIDL current, the oxide charge trapping/detrapping characteristics can be obtained. An analytical model accounting for the time-dependence of an oxide charge detrapping induced GIDL current transient was derived. A specially designed measurement consisting of oxide trap creation, oxide trap filling with electrons or holes and oxide charge detrapping was performed. Two hot carrier stress methods, channel hot electron injection and band-to-band tunneling induced hot hole injection, were employed in this work. Both electron detrapping and hole detrapping induced GIDL current transients mere observed in the same device. The time-dependence of the transients indicates that oxide charge detrapping is mainly achieved via field enhanced tunneling. In addition, we used this technique to characterize oxide trap growth in the two hot carrier stress conditions. The result reveals that the hot hole stress is about 10⁴ times more efficient in trap generation than the hot electron stress in terms of injected charge     

Time-Domain Electromagnetic Fields Radiating Along the Horizontal Interface Between Vertically Uniaxial Half-Space Media

At the horizontal interface between vertically uniaxial half-space media, the propagation of electromagnetic fields is theoretically investigated for an interfacial impulse current source of infinitesimal size. For the electric field, the problem divides into the horizontal source and horizontal receiver (HH), vertical source and vertical receiver (VV), horizontal source and vertical receiver (HV), and vertical source and horizontal receiver (VH) cases. Employing the interface scheme of the Cagniard-style analysis, the solutions of the HH and VV cases are obtained in exact explicit forms. The solutions of the HV and VH cases cannot be expressed in integral-free forms, but the impulse components implicit in the integral solutions can be analytically extracted without the aid of the frequency-domain asymptotic techniques. Investigation is also made of the magnetic field and of the variation of waveforms when the receiver is taken a little off the interface. The uniaxial case is a generalization of the isotropic case, affording richer information of the wave physics     

Characterization of various stress-induced oxide traps in MOSFET'sby using a subthreshold transient current technique

An oxide trap characterization technique by measuring a subthreshold current transient is developed. This technique consists of two alternating phases, an oxide charge detrapping phase and a subthreshold current measurement phase. An analytical model relating a subthreshold current transient to oxide charge tunnel detrapping is derived. By taking advantage of a large difference between interface trap and oxide trap time-constants, this transient technique allows the characterization of oxide traps separately in the presence of interface traps. Oxide traps created by three different stress methods, channel Fowler-Nordheim (F-N) stress, hot electron stress and hot hole stress, are characterized. By varying the gate bias in the detrapping phase and the drain bias in the measurement phase, the field dependence of oxide charge detrapping and the spatial distribution of oxide traps in the channel direction can be obtained. Our results show that 1) the subthreshold current transient follows a power-law time-dependence at a small charge detrapping field, 2) while the hot hole stress generated oxide traps have a largest density, their spatial distribution in the channel is narrowest as compared to the other two stresses, and 3) the hot hole stress created oxide charges exhibit a shortest effective detrapping time-constant     

Kinetics of trapping,detrapping, and trap generation

The trapping and detrapping of charge in the oxides have been studied for two decades. While there has been a lot of progress in understanding the mechanisms responsible for charge trapping and detrapping in these oxides, it is still not fully understood. For example, even under low field injection conditions first order trapping kinetics do not accurately model the observed data. Under high field injection the situation is exacerbated by the generation of additional trapping sites during the injection process, which is also not completely understood. The paper presents a review of the kinetics of trapping and detrapping and describes various models that have been proposed to explain experimentally observed trapping-detrapping behavior.     

A multiple-scale analysis of grating-assisted couplers

Optical directional couplers with longitudinal periodic perturbations or gratings are analyzed by a multiple-scale solution to the coupled-mode equations. The use of two length scales in the analysis becomes the key to obtaining globally valid analytic solutions, which are shown to be in excellent agreement with the exact numerical solutions. Because of the nonorthogonality of the coupled modes in the structure, two different coupling lengths, a maximum power transfer length and a zero crosstalk length, are predicted for the power exchange. The spectral properties of the coupler are also studied through a generalized multiple scale method     

Efficient transient analysis of nonlinearly loaded low-loss multiconductor interconnects

The combined time- and frequency-domain analysis of nonlinearly loaded low-loss interconnects is addressed. We show that a variety of interconnects commonly employed in different technological applications are characterized by transfer functions, whose impulse responses have a fast initial-time structure (due to the skin effect) and a slow long-time part (due to ohmic losses). The dependence of the impulse response structure on the line parameters is discussed, along with the exact analytical solutions valid for the skin effect and ohmic losses, separately. A piecewise linear approximation of the transient functions with nonuniform sampling is proposed as an effective method to obtain high accuracy at low computational costs. Various numerical examples are used to validate the effectiveness of the proposed representation, and to show that a matched characterization of the line must be adopted in order to avoid numerical artifacts.     

应用改进的G/G展开法求ZS方程的精确解

应用改进的G/G展开法构造出Zhiber-Shabat(ZS)方程的20组精确解,这些解的类型主要包含双曲函数通解、三角函数通解和有理函数通解三种形式。对解的性质进行了相应分析,当对双曲函数通解中的参数取特殊值时,可以得到孤立波解。当对三角函数通解中的参数取特殊值时,可以得到对应的周期波函解。实践证明,应用改进的G/G'展开法能够得到方程一些新的精确解,扩大了解的范围。     

Rise and fall time calculations of junction transistors

Expressions for rise and fall time calculations of junction transistors are derived based on the charge controlled model. In solving the differential equation of the charge controlled model, a new approach is taken and exact solutions are obtained. Comparison of the experimental results of the rise and fall time measurements with the theoretical prediction, using the measured transistor parameters, shows very good agreement.     

A Novel Bias Temperature Instability Characterization Methodology for High-$k$nMOSFETs

The power law dependence of the threshold voltage shift$(Delta V_ th)$on stress time for high-$k$nMOSFETs is studied using a single-pulse$I_d - V_g$technique. The power law exponent value is found to be strongly affected by fast transient charge detrapping during the stress interruption time, which may result in an inaccurate lifetime prediction. A new analysis method that eliminates the impact of the stress interruption time is proposed to evaluate bias temperature instability in n-type high-$k$devices.     

A fast measurement technique of MOSFETI/sub d/-V/sub g/ characteristics

In this letter, we developed an improved ultrafast measurement method for threshold voltage V/sub th/ measurement of MOSFETs. We demonstrate I/sub d/--V/sub g/ curve measurement within 1 /spl mu/s to extract the threshold voltage of MOSFET. Errors arising from MOSFET parasitics and measurement setup are analyzed quantitatatively. The ultrafast V/sub th/ measurement is highly needed in the investigation of gate dielectric charge trapping effect when traps with short detrapping time constants are present. Application in charge trapping measurement on HfO/sub 2/ gate dielectric is demonstrated.     

时变源作用下介观LC电路系统量子态的演化

采用代数动力学规范变换方法,求出含时变电压源的介观LC电路量子态随时间演化算符的精确解,研究含时变电压源的介观LC电路量子态的相干特性.结果表明,电路中电容器储电量q的几率是一个运动的Gauss波包,导出波包中心电量与外电源的一般关系.研究了输入电压源为单矩形脉冲电压的特例.     

Closed-Form Expressions of the Axial Step and Impulse Responses of a Parabolic Reflector Antenna

Electromagnetic pulses radiated by parabolic antennas and similar structures are needed in many applications like air and ground penetrating radar or high power microwaves (HPM) weapons. In this paper, an approach based on Skulkin and Turchin's work and on physical optics approximation in the time domain is developed to determine the radiated fields. Closed-form time-domain expressions of the electromagnetic step and impulse responses, along the axis of a classical parabolic reflector antenna, are derived. A closed-form expression of the impulse response duration is also given. The obtained E-field and H-field formula are valid along the axis, both near and far from the reflector. Using these closed-form expressions, the radiated fields are computed by means of a convolution product of the primary source excitation and the impulse response. Numerical results have been obtained in the case of a causal sine and a generalized Gaussian impulse excitations to illustrate some specific transients effects which occur with such an antenna     

Passive Microwave Planar Circuitsfor Arbitrary UWB Pulse Shaping

We propose and demonstrate a new technique for generating customized pulse-shapes intended for use in ultrawideband (UWB) applications. The technique employs tailored microstrip lines that have been designed using an exact analytical series solution of the synthesis problem derived from the coupled mode theory. This solution permits the synthesis of waveguides and transmission lines with arbitrary impulse responses limited only by the principles of causality, passivity and stability. Time-domain measurements are performed demonstrating the generation of two pulse-shapes using microstrip circuits and satisfying pre-established UWB mask requirements.     

A Diffraction Transfer Function Approach to the Calculation of the Transient Field of Acoustic Radiators

A computationally-efficient approach to the calculation of the transient field of an acoustic radiator was developed. With this approach, a planar or curved source, radiating either continuous or pulsed waves, is divided into a finite number of shifted and/or rotated versions of an incremental source such that the Fraunhofer approximation holds at each field point. The acoustic field from the incremental source is given by a 2-D spatial Fourier transform. The diffraction transfer function of the entire source can be expressed as a sum of Fraunhofer diffraction pattern of the incremental sources with the appropriate coordinate transformations for the particular geometry of the radiator. For a given spectrum of radiator velocity, the transient field can be computed directly in the frequency domain using the diffraction transfer function. To determine the accuracy of the proposed approach, the impulse response was derived using the inverse Fourier transform. The results obtained agree well with published data obtained using the impulse response approach. The computational efficiency of the proposed method compares favorably to those of the point source method and the impulse response approach.     

Modeling of oxide-charge generation during hot-carrier degradationof PMOSFET's

Oxide-charge generation determines the lifetime for hot-carrier degradation of PMOSFET's. We present a model for the generation of oxide charge and its influences on transistor characteristics. Our model explains the logarithmic time dependence for the generation of oxide charge that is observed systematically for many PMOSFET types. This model is in accordance with an empirical prediction method for PMOSFET degradation that has been published earlier. Furthermore, a relation between the injected charge and the amount of degradation is presented. The paper ends with some applications     

Minority carrier generation time and surface generation velocity determination from Q-t measurements

The time variation of the charge stored in an MOS capacitor during the transient period following the application of a step voltage is related to the minority-carrier generation mechanisms both in the bulk and in the surface. Therefore, the minority-carrier generation time and surface generation velocity can be determined by measuring the charge as a function of time. The method has been shown to be applicable to samples with both uniform and nonuniform doping concentrations. This technique does not require that the amplitude of the step voltage be kept small. Values of lifetime and surface generation velocity obtained by this technique are shown to agree well with those obtained by theC-ttechnique.     

Hot carrier effects in n-MOSFETs with SiO2/HfO2/HfSiO gate stack and TaN metal gate

Charge trapping and trap generation in field-effect transistors with SiO₂/HfO₂/HfSiO gate stack and TaN metal gate electrode are investigated under uniform and non-uniform charge injection along the channel. Compared to constant voltage stress (CVS), hot carrier stress (HCS) exhibits more severe degradation in transconductance and subthreshold swing. By applying a detrapping bias, it is demonstrated that charge trapping induced degradation is reversible during CVS, while the damage is permanent for hot carrier injection case.     

Characterization of interface trap dynamics responsible for hysteresis in organic thin-film transistors

In this paper, the current hysteresis of organic thin film transistors (OTFTs) formed by TIPS-Pentacene has been demonstrated by bi-directional gate-voltage scan and explained using the trapping and detrapping mechanism. The trapping and detrapping rates have been further verified by the gate-voltage sampling method and the channel charge pumping method. The validity of the methods to characterize interface states of OTFTs that lead to the hysteresis is justified. The two independent methods consistently reveal that the hole trapping and release rates at the interface between the channel of the OTFTs to the gate dielectric are asymmetric.     

All-Optically Controlled Memristor for Optoelectronic Neuromorphic Computing

Neuromorphic computing (NC) is a new generation of artificial intelligence. Memristors are promising candidates for NC owing to the feasibility of their ultrahigh-density 3D integration and their ultralow energy consumption. Compared to traditional electrical memristors, the emerging optoelectronic memristors are more attractive owing to their ability to combine the advantages of both photonics and electronics. However, the inability to reversibly tune the memconductance with light has severely restricted the development of optoelectronic NC. Here, an all-optically controlled (AOC) analog memristor is realized, with memconductance that is reversibly tunable over a continuous range by varying only the wavelength of the controlling light. The device is based on the relatively mature semiconductor material InGaZnO and a memconductance tuning mechanism of light-induced electron trapping and detrapping. It is found that the light-induced multiple memconductance states are nonvolatile. Furthermore, spike-timing-dependent plasticity learning can be mimicked in this AOC memristor, indicating its potential applications in AOC spiking neural networks for highly efficient optoelectronic NC.