基于功率MOSFET的慢升快降型高压脉冲信号源

利用MOSFET（金属氧化物半导体场效应晶体管）导通过程中某一时段输出电流和门电压成比例的特点来获得前沿缓慢而后沿陡降的高压脉冲信号,通过栅极电阻降低脉冲前沿的上升速度;通过低驱动内阻对栅极电容电荷的快速泄放提高脉冲后沿的下降速度。在50Ω负载下脉冲的最大幅度为800V,下降沿约为15ns。     

金属氧化物半导体控制晶闸管的di/dt优化

金属氧化物半导体控制晶闸管(MCT)相比于绝缘栅双极型晶体管(IGBT)具有高电流密度、低导通压降和快速开启等优势,在高压脉冲功率领域具有广阔的应用前景.作为脉冲功率开关,MCT开启过程对输出脉冲信号质量有很大影响.采用理论分析并结合仿真优化重点研究了MCT开启瞬态特性.通过对MCT开启过程进行详细地理论分析推导,给出了MCT开启过程中阳极电流和上升时间的表达式.结合Sentaurus TCAD仿真优化,将MCT开启过程中电流上升速率(di/dt)由40 kA/s提升至80 kA/s,极大地改善了器件开启瞬态特性.最后,总结提出了提高器件开启瞬间di/dt的设计途径.     

Probed determination of turn-on spread of large area thyristors

Thyristors (SCR's) were specially constructed to permit the direct observation of the lateral spread of turn-on within the device. The effects on the spread of turn-on of the load current, basewidths, temperature, anode-cathode voltage, gate control pulse, and a large inhomogeneity were observed. The spreading velocity of the on-state and the load current are related approximately by the expressionV^{n} propto Iat high load currents. The spreading velocity is higher in devices with narrower basewidths and increases with temperature. Neither the anode-cathode voltage before turn-on nor the gate control pulse affect the spreading velocity of the on-state. Measurements on end gate devices and center gate linear devices show that triggering at the center enables an equivalent area of the SCR to turn on in less time than occurs when triggering at the end. A large gap in the emitter layer will delay the spread of the on-state but will not necessarily stop the spreading.     

用于ESD防护的PDSOI NMOS器件高温特性

研究了基于0.18μm部分耗尽型绝缘体上硅(PDSOI)工艺的静电放电(ESD)防护NMOS器件的高温特性。借助传输线脉冲(TLP)测试系统对该ESD防护器件在30~195℃内的ESD防护特性进行了测试。讨论了温度对ESD特征参数的影响,发现随着温度升高,该ESD防护器件的一次击穿电压和维持电压均降低约11%,失效电流也降低近9.1%,并通过对器件体电阻、源-体结开启电压、沟道电流、寄生双极结型晶体管(BJT)的增益以及电流热效应的分析,解释了ESD特征参数发生上述变化的原因。研究结果为应用于高温电路的ESD防护器件的设计与开发提供了有效参考。     

Filamentary thermal instabilities in IMPATT diodes

The unstable growth of thermal filaments in a diode with a fixed bias current is calculated on the basis of a model which includes thermal conduction in the plane of the junction, as well as perpendicular to it. The growth time of the instability is shown to be longer than the thermal relaxation time by the ratio of the space-charge resistance to the differential negative resistance. Analytic results are obtained for small temperature disturbances which are initially Guassian functions of the transverse coordinate. If A is the area of the junction, the negative differential resistance must be of the order of the space-charge resistance multiplied by 16W²/π²A (whereWis the thickness of the active region) or the filament can dissipate itself by diffusing outward and spreading over the entire junction area before the temperature rise becomes very large. The voltage fluctuation relaxes to its equilibrium value in the thermal relaxation time, which is independent of the differential resistance. Pulsing a diode will tend to prevent an instability from becoming destructive, provided the off-time is long enough to cool the heated filaments which develop during the pulse transmission.     

Switching behaviour of MISS diodes

A physical picture of the switching behaviour of MISS diodes is presented considering three phases of the turn-on process: a capacitive current rise time, an inversion charge delay time and a feedback regeneration time. Approximate calculations are derived based on the outlined physical picture and compared to the experimental results obtained in pulse experiments with polysilicon MISS diodes. A dynamic current-voltage characteristic is also presented which differs from the known static one.     

Time-dependent carrier flow in a transistor structure under nonisothermal conditions

A time-dependent temperature-dependent two-dimensional model has been developed to illustrate the internal behavior of bipolar transistors. Electrothermal interactions within the device are calculated in an attempt to better understand thermal instability modes. Numerically computed results are presented showing the electrical and thermal effects in the transistor operating in the switching mode during turn-on along a resistive load line. Plots of current density, electrostatic potential, and temperature versus time illustrate the combined effects of electrical rise time, thermal delay time, electrothermal interaction, current crowding, current spreading, conductivity modulation, and base pushout in bipolar transistors.     

关于雪崩结开启电压和关断电压差别的研究

本文详细研究了雪崩结导通电压和关断电压的差别。 当结特征尺度在微米量级时,这个差别将不能忽略, 这个结果与现有报道不一致,并且对对器件参数的正确表征有较大影响。 实验发现当结面积变小时, 这个差别将增大。 本文对该现象进行了分析, 给出了理论解释,认为这个现象是由于结导通的阈值增益随着结面积的减小而增加的缘故。在雪崩渐近电流公式中, 所谓的“击穿电压”实际上应该是雪崩结关断电压。 修正了传统的关于雪崩渐近电流和盖革模式雪崩光电二极管的增益公式。     

晶闸管的瞬态热阻抗及其结温温升的研究

系统地阐述了晶闸管的瞬态热阻抗 ,针对晶闸管承受不同的功率脉冲 ,利用不同的计算方法计算瞬态热阻抗值 ,从而确定结温温升 ,并比较了它们的原理、精度及其应用范围。特别是利用了一种新的瞬态热阻抗计算模型 ,当晶闸管承受持续时间极短且周期、占空比均变化的任意波形功率脉冲时 ,它能够比较精确地分析晶闸管的热特性 ,计算半导体结的最大温升     

A high-current and high-temperature 6H-SiC thyristor

A 6H-SiC thyristor has been fabricated and characterized. A forward breakover voltage close to 100 V and a pulse switched current density of 5200 A/cm² have been demonstrated. The thyristor is shown to operate under pulse gate triggering for turn-on and turn-off, with a rise time of 43 ns and a fall time of less than 100 ns. The forward breakover voltage is found to decrease by only 4% when the operating temperature is increased from room temperature to 300°C. It is found that anode ohmic contact resistance dominates the device forward drop at high current densities     

Calculation of the homogeneous degradation of injection laser parameters from initial degradation rates

The change of operating parameters above threshold of (Ga, Al)As injection lasers with aging time was calculated assuming a uniform mode of degradation mechanism with temperature-dependent degradation rates. In the calculation, the degradation rate for the threshold current was assumed to be temperature dependent, but not explicitly dependent on aging time and pumping current. Optical output power was kept constant during aging. The calculated time variation of laser parameters predicts a runaway after an initial slow rise. The mathematical model thus provides the means to correlate time-to-failure data with initial degradation rates and permits the evaluation of the influence of various laser parameters on lifetime. A selected group of laser diodes were aged at 80 °C under the conditions specified by the model. Degradation rates for the threshold current varied between4 times 10^{-5}and5 times 10^{-4}h^-1. These would extrapolate to lifetimes in excess of 10 000 h at the elevated temperature for half of the diodes in reasonable agreement with experimental values obtained by others.     

基于脉冲式U-I 特性的高功率型LED 热学特性测试

热学特性是影响功率型LED光学和电学特性的主要因素之一,设计了一套基于脉冲式U-I特性的功率型LED热学特性测试系统,可以测试在不同结温下LED工作电流与正向电压的关系,从而获得LED的热学特性参数。该系统通过产生窄脉冲电流来驱动LED,对其峰值时的电压电流进行采样,同时控制和采集LED的热沉温度,从而获得不同温度下LED的U-I特性曲线。与其他U-I测试系统相比,文中采用了窄脉冲(1 s)工作电流,LED器件PN结区处于发热与散热的交替过程,不会造成大的热积累,大大提高了测量精度。实验中,对某功率型LED进行了测试,获得了该器件的电压、电流和结温特性曲线,并利用B样条建立该器件的U-I-T模型,进而实现了对其结温的实时在线检测。     

Single-shot thermal energy mapping of semiconductor devices with the nanosecond resolution using holographic interferometry

A novel two-dimensional backside optical imaging method for thermal energy mapping inside semiconductor devices is presented. The method is based on holographic interferometry from the device backside and uses the thermo-optical effect. An image of the local thermal energy is obtained with 5-ns time resolution using a single stress pulse. The technique allows a unique recording of the internal device behavior. The method is demonstrated analyzing the nonrepetitive thermal and current flow dynamics in smart power electrostatic discharge (ESD) protection devices. A spreading of the current during the stress pulse is observed and explained by the effect of the negative temperature dependence of the impact ionization coefficient.     

Uniform turn-on in four-layer diodes

The turn-on characteristics of 200-volt four-layer diodes have been investigated as a function of the rate of rise of the applied voltage close to the breakover point. A fast rate of rise of the order of kv/µsec allows bringing the voltage up to, or higher than, the designed avalanche voltage of the center junction, even if localized spots having a lower breakdown voltage are present. Such spots, possibly due to crystalline defects, surface conditions and statistical or accidental variations of impurity concentration, may lead to localized turn-on and possible burn out. There is experimental evidence that a fast rate of rise results in uniform turn-on and allows current densities up to 55,000 a/cm²without damaging the device.     

A fast CAD model of plasma spread in thyristors using aseminumerical time-domain approach

This paper presents a fast CAD model to calculate plasma-spreading velocity in large area thyristors. The model is based on the two-dimensional two-transistor circuit model of a thyristor. At first, a simplified numerical solution of the semiconductor equations is developed to obtain the current amplification factor and the base transit time of each transistor of the thyristor model as a function of the emitter current density. The turn-on recurrence relations governing the evolution of the anode current at different lateral points are then derived by the transit function method. The time constant of the anode current rise and the plasma spreading velocity are calculated as functions of the anode current density. The results of simulation are in close agreement with the corresponding measured values of plasma spreading velocity by the electrical probes method. This agreement confirms the validity of our model over a large scale of anode current densities     

氮化镓基LED结温测量方法研究

分别研究了脉冲电流法、微小电流法和光学成像法测量氮化镓基LED结温的基本原理,并对比了不同方法的结果可靠性。结果表明:在大脉冲电流下,串联电阻效应不可忽略,脉冲电流法得到的平均结温偏低;微小电流法能够减小加热电流和测试电流的切换时间和串联电阻效应,提高测量准确性;光学成像法基于发光强度与结温的依赖关系,能够获得器件温度的空间分布,有助于制备高性能的LED。     

Study of the fast transient behaviour of peltier junctions

A method has been developed for measuring the temperature of a thermojunction after the passage of fast transient current pulses (30 msec to several seconds duration).

Using the model of a thermocouple whose branches are of infinite extent, it is shown theoretically that for rectangular current pulses the temperature of the cold junction is a function only of a parameter meter ζ = I√τ (I = pulse current, τ = pulse duration). The lowest temperature occurs for one particular value ζ_min of this parameter, and this temperature cannot be reduced further by any particular choice of the individual values of I and τ. In connexion with these rectangular pulses, various forms of the temperature dependence of the Seebeck coefficient are examined. For the case of logarithmic dependence, a method is developed which makes possible the determination of the temperature distribution along the couple from a measurement of the Seebeck potential as a function of time and allows the influence of the Thomson effect to be estimated.

It is further shown that, when a second rectangular current pulse is superimposed on to the first current pulse, the temperature drop due to the combined pulses may be at most twice that caused by a single pulse.

Finally it is proved, with the aid of a variational method, that the lowest transient temperature drops of the junction may be obtained with pulses for which the current is a continuous function of the time, of the form

where Θ is the time and t the time of observation.

If the pulse terminates at time t₁ and if t → t₁ then Z(Θ)_ex → ∞. Provided the current were allowed to rise indefinitely, the transient temperature would approach absolute zero if the process were not counteracted by changes in the Seebeck coefficient and the electrical and thermal conductivity which all have been assumed to be constant in this calculation.

The above results are also true for “real” thermocouples provided the length of the branches is where κ is the (average) diffusivity of the thermoelectric substances.

These calculations were essentially confirmed by experiments. With the rising current pulses, the accuracy of measurement is limited by the time resolution of the measuring circuit and by the fact that the temperature dependence of the Seebeck coefficient in this region is not known accurately. However, it is almost certain that we have observed transient temperatures well below 100°K.     

DC Current-Induced Rollover of Illumination Efficiency of GaN-Based Power LEDs

Pulse drive currents were utilized to investigate dc current-induced rollover of illumination efficiency of GaN-based power light-emitting diodes (LEDs). By using the pulse drive currents, we can separate the effects that junction temperature and current injection have on dc current-induced rollover of illumination efficiency of GaN-based power LEDs. Comparing the measurement results obtained from pulse and dc drive currents, we verified that junction temperature and current injection were the major causes of dc current-induced rollover of illumination efficiency of power LEDs.     

A four-terminal P-N-P-N switching device

A four-terminal germanium p-n-p-n switching transistor is described. In an appropriate circuit the device has useful switching gain for both the turn-on and turn-off operations. A pulse of one polarity turns the switch on, and a pulse of the opposite polarity turns it off. In the absence of triggers, the state is maintained. Equivalence to a pair of complementary conventional transistors in a direct-connected, common-base emitter-follower regenerative circuit is shown. The collector junction is common to both transistor sections so that saturation is simultaneous. Saturation current is kept small in one section, and the switch is turned off by withdrawing the small saturation current. Expressions are derived for switching gain, and requirements on device parameters are obtained. Common-emitter gain for one transistor section must exceed the ratio of load current to off-trigger current. Device structure is described. A combination of alloy, diffusion, and post-alloy diffusion techniques is used for fabrication. One transistor section with a thin base has high common-emitter gain, and the other has moderate gain. Switching performance data are given. A load current of 20 ma at 20 volts is switched with 2-ma pulses. Trigger pulse durations of the order of the switching time are required. Switching times of about 100 nsec are obtained.     

矩形截面Nd:GGG热容激光器热分析

为了研究长方体型Nd:GGG热容激光晶体的热效应,通过对激光晶体工作特点的分析,采用半解析各向异性热分析方法,建立了符合实际工作状态热模型,对长方体型Nd:GGG热容激光晶体进行了热分析,得到了激光晶体抽运阶段和冷却阶段晶体内部温度场计算公式,定量分析了晶体宽度和厚度对温度场的影响。结果表明,当使用输出功率为8100W、脉冲频率500Hz、脉冲宽度0.2ms的LD抽运晶体4s时,抽运面中心最高温升为169.1℃;停止抽运120s时,晶体最高温升下降到0.97%。所得结果为热容激光器的优化设计提供了理论依据。