Transient thermal response of amplifying gate thyristors

A computer-aided investigation of the transient thermal behaviour of amplifying gate thyristors (a.g.t.s.) has been performed by taking into consideration the nonlinear properties of silicon over a wide range of temperature excursions.     

Mutual and self-aging effects of power semiconductors on the thermal behaviour of DC-DC boost power converter

A shift from conventional to renewable resources has increased the importance of power exploitation via power converters. In this respect, estimating an accurate useful lifetime of power converters plays a major role for the manufacturers and users. This paper touches the issues related to the self and the mutual degradation effects of the power semiconductors such as IGBT and diode on each other in a conventional DC-DC boost converter. By IGBT and diode aging, junction-case thermal resistance, IGBT collector-emitter voltage and diode forward voltage have been increased leading to thermal operating point changes. These changes have a significant effect on the degradation and the useful lifetime of devices. It is shown that by either IGBT or diode aging due to the thermo-mechanical fatigue, an increase in the IGBT or diode junction temperature has been occurred. The results reveal the importance of mutual- and self-aging effects on the reliability assessment. An experimental validation has been also performed via a prototype setup of 200/400V 3000W DC-DC boost converter.     

Three-dimensional transient thermal simulation: application to delayed short circuit protection in power ICs

Thermal effects may represent a limiting factor in the development of integrated circuits. As the power dissipated by integrated circuits becomes more relevant, the need increases for accurate modeling of the stationary and transient thermal behavior of the die-package structure. An analytical solution of the three-dimensional transient thermal diffusion problem is presented for a two-layer structure, together with a simple computer program for the calculation of the solution. The program, implemented on a minicomputer, is proven to be fast and accurate. The simulation technique is then applied to the design of a new short-circuit protection of a 6A current booster.     

Consumer applications of power semiconductors

Power semiconductors--transistors, thyristors, and rectifiers --all have found widespread application in the three major consumer markets --automotive, entertainment, appliance. These devices have been developed to provide low-cost solutions to existing needs. In the mid-1950's, the germanium power transistor, as used in hybrid auto radio sets, was the sole power semiconductor represented in a consumer application. It was soon joined by rectifiers designed for power supply use in line operated television sets. Near the turn of the decade, the development of press-fit alternator rectifiers created a completely new consumer use. Today these devices in only slightly modified form are used for the original application as well as a host of allied uses. Recently, power thyristors expressly designed for appliance controls have opened up entirely new concepts in this market area. Upwards of 200 million [1] power semiconductors are used in consumer applications each year. As technology progresses, indications are that this market will more than double in the next few years as TRIAC [2], [3] and QUADRAC open new appliance markets, as high-voltage power transistors phase into television, and as alternator regulators switch to large area integrated circuitry. Whether the market is automotive, appliance, or entertainment, and whether the application is audio, phase control, or switching, the penetration of power semiconductors into consumer use has followed a history of applying advanced device technology directly to a market opportunity. The successes have always been the result of providing lower costs, a better way, or in adding value to the consumer product. This paper will discuss the features of consumer power devices and their applications that make them different from their predecessors.     

Transient thermal analysis of sapphire wafers subjected to thermal shocks

Rapid heating and cooling are commonly encountered events in integrated circuit processing, which produce thermal shocks and consequent thermal stresses in wafers. The present paper studies the heat transfer in sapphire wafers during a thermal shock as well as the dependence of the wafer temperature on various process parameters. A three-dimensional finite-element model of a single sapphire wafer was developed to analyze the transient heat conduction in conjunction with the heat radiation and heat convection on the wafer surfaces. A silicon wafer was also investigated, for comparison. It was found that the rapid thermal loading leads to a parabolic radial temperature distribution, which induces thermal stresses even if the wafer is not mechanically restrained. The study predicted that for sapphire wafers the maximum furnace temperature of 800 /spl deg/C should be held for two hours in order to get a uniform temperature throughout the wafer.     

Transient capacitance spectroscopy in heavily compensated semiconductors

We have developed the theory of the capacitance transient of a junction in the case where the usual approximation, namely that the defect concentration N_T is not negligible compared to the free carrier concentration, is not fulfilled. We show that the correct analysis of this transient by the so-called Deep Level Transient Spectroscopy technique must take into account the fact that, during the transient, the width of the space charge region varies. The validity of the expressions obtained for the shift of the signature (variation of the emission rate vs temperature) and for the concentration N_t is verified by comparison with experimental results obtained for electron induced defects in n-GaAs.     

Transient behavior of high-field domains in bulk semiconductors

A simple formula giving the growth rate of high-field domains in bulk semiconductors is derived. When the diffusion constant is small, it reduces to an extension of the equal-area law discussed by Butcher et al.     

碳纳米管提升了功率半导体器件的性能

Infineon Technologies AG公司(位于德国慕尼黑)的研究人员已制作成功首款采用碳纳米管的功率半导体器件,在此之前人们一直认为这种器件不适合于功率应用中所使用的高电压和高电流。采用常规化学汽相淀积工艺生产的这种纳米管过去曾被用来试制功率晶体管。被用作LED或电机控制开关的这种试制器件由大约300个并行排列的纳米管组成,它能够在2.5V电压条件下提供2mA的电流。虽然人们已经在研究实验室里采用纳米管来制作电脑芯片用的晶体管,但这种场合中的电压则低了大约1000倍。研究小组的实验结果表明:采用碳纳米管制作的功率晶体管的开关…     

Linear optical response of semiconductors

The linear optical constants of photovoltaic semiconductors, that is, their complex dielectric function, are required for the proper choice of materials and the design of photovoltaic devices. Our understanding of the linear dielectric function of semiconductors in the optical region is reviewed using germanium and GaAs as models. Experimental and theoretical results are compared. The discussion is extended to the influence of perturbations such as an applied strain or a finite temperature. Effects of a finite -vector (spatial dispersion), including birefrigence in cubic materials, are reviewed. Recent data involving stress-induced optical activity of GaAs are presented.     

An analysis of the thermal response of power chip packages

Since power densities in integrated circuits and power semiconductor devices are continuously increasing due to miniaturization of circuitry, the design of optimum heat spreaders and heat sinks for these applications requires rather sophisticated calculational methods. The chips and spreaders are usually rectangular in shape and although the problem is three-dimensional in nature, it is usually approximated by two-dimensional configurations. Steady-state and transient analytic solutions are presented for the axisymmetric, two-dimensional, and three-dimensional spreader geometries, which can be used to calculate the thermal resistance of the base alone. To determine the thermal resistance of the chip-base combination, the one-dimensional chip thermal resistance should be added to that of the base. These analytic solutions provide calculational means which are easier than the numerical methods. The exact analytic steady-state and transient solutions developed for the axisymmetric, two-dimensional, and three-dimensional configurations are in excellent agreement with the numerical calculations. The parametric calculations provide information on the important guidelines that a packaging engineer should bear in mind while designing and optimizing heat spreaders for power semiconductor applications. These points can be summarized as follows: 1) for a given chip area there exists an optimal base area, 2) increasing the base thickness initially decreases the thermal resistance and beyond a certain limit the latter increases with base thickness, and 3) the convective heat transfer coefficient strongly affects the thermal resistance and the usual assumption of an isothermal base is not always appropriate.     

Transient space-charge phenomena in semiconductors at high electric fields

The transient response of trap-free semiconductors subjected to a voltage step function and unipolar injection of charge is analyzed for the case that the velocity of the carriers is a non-linear function of the electric field. The method of characteristics is used to evaluate current, density and field profiles as functions of time. Numerical results are presented for the case of n-Si. These results show that there is a sharp bunching of charge accompanying the cusp. This bunching of charge is shown to be a consequence of the decreased differential mobility at high fields.These results are compared with the previously published results for a constant mobility case. A simple model is used to derive exactly the results for a saturated-velocity transient. It is shown that the numerical results for the actual case of non-linear velocity fit well between the results for these two limiting behaviors for the velocity-field curve.Effects of a finite rise-time in the voltage pulse are also studied. It is shown that a significant rise time can considerably reduce the sharpness of the current cusp.     

Photorefractive material response to short pulse illuminations

Photoconduction and hologram recording in a Bi12SiO20single crystal are studied from both theoretical and experimental points of view in the case of short pulse excitations. An approach taking into account two kinds of acceptor centers explains the charge transport processes in the case of both pulsed and continuous illuminations. A nanosecond temporal resolution allows us to access a time domain that is not normally considered, and on this time scale, the electron migration velocity is governed by the intrinsic mobility, which we have estimated to he greater than 3.2 cm²/V . s. Using this value, our theoretical developments explain the fast beam coupling phenomenon that we have experimentally observed.     

全新功率半导体技术助力数据中心节能

世界各地计算机数量众多,耗能量也相当庞大,而支撑互联网运作的数据中心就是一大耗能实例.在一个典型的数据中心设施中,其实只有不到一半的功耗是用在计算功能上的.所以数据中心运营商千方百计寻找机会来提高功率转换效率和分配效率,例如通过高压直流源的分配来减小转换级的数目.     

Optimum semiconductors for power field effect transistors

The optimization of semiconductor material properties for high voltage field effect transistors is discussed. The on-resistance of these devices is shown to be inversely proportional to the carrier mobility and inversely proportional to the cube of the energy band gap. Based upon this, the on-resistance of GaAs FETs is predicted to be at least twelve times smaller than that of present silicon FETs. Comparison of the projected GaAs FET power switching performance with competing silicon devices (MOSFETs, FCTs, GTOs, and bipolar transistors) indicates that the GaAs FET will have better switching efficiency at all operating frequencies for devices designed with breakdown voltages ranging from 200 to 1000 volts.     

Spectral response of photoconductivity in polycrystalline semiconductors

Photoconductivity in polycrystalline semiconductors can arise from the modulation, by the optical illumination, of the diffusion potentials at the grain boundaries, which in turn control the majority carrier current in these materials. The photogenerated carriers are captured by interface states at the grain boundaries through Shockley-Read-Hall processes, and under constant illumination this affects the steady-state charge at these boundaries so as to reduce the diffusion potentials from their dark values. The dependence of the diffusion potentials and of the photoconductivity upon position is calculated from the dependence of the optical absorption on wavelength. Finally, the average photoconductivity (expected from measurement) of polycrystalline semiconductor thin films is determined as a function of the intensity of the optical illumination, the grain size, the film thickness and the grain-boundary interface parameters.     

Theoretical investigation on thermal effect in organic semiconductors

Thermal effect on a neutral and a doped polymer chain is studied in the frame work of Su–Schrieffer–Heeger tight-binding model considering electronic Fermi–Dirac distribution as well as atomic square-random distribution. It is found that in a neutral polymer chain, the band gap is decreasing as the temperature increases. For a doped polymer chain, extra electrons will occupy high energy levels. The localization and stability of the electronic self-trapped state will decrease with temperature. We also show that at temperature high enough (⩾340 K in present parameters), a hot electron will get rid of the trap of the lattice and become extended over the whole polymer molecule. In addition, the effects of the quantity of charge carriers and the electron–phonon coupling at room temperature are also investigated.     

Molecular orientation and thermal stability of thin-film organic semiconductors

Molecular orientation in organic semiconductors plays a critical role in maximizing external quantum efficiencies of organic light-emitting diodes. It was generally believed that the molecular packing of organic semiconductors is either amorphous or liquid-crystal-like with a preferred molecular orientation distributed uniformly throughout the film. In this paper, however, we report that the orientation of organic molecules in physical-vapor deposited films varies drastically depending on thickness. The thermal stability of the molecular network, measured by its characteristic glass transition temperature, also varies as a function of the film thickness. Based on a two-layered film-structure model, we propose a simple function to quantify the molecular dipole orientation S parameter as a function of film thickness. This function describes well experimental data. In addition to contributing to external quantum efficiency, the molecular orientation parameter S is found to have a strong impact on disruptive change in material density after thermal anneal and glass transition.