The impact on power semiconductor device operation due to local electric field alterations in the planar junction termination

In this paper, we present and discuss simulation and experimental results obtained from investigating the impact of local alterations of the electric field profile in the power device planar junction termination region. Such local modifications are due to possible various extrinsic causes (manufacturing, operational or environmental) and are shown to have a critical influence on the device voltage blocking capability and reliability. The results point towards junction termination sensitivity to locally modified fields especially under voltage switching conditions due to higher leakage current densities in the modified area compared to the rest of the JT region.     

Influence of the trench corner design on edge termination of UMOS power devices

In this article, the voltage blocking capability of UMOS power devices is experimentally demonstrated to be limited by the onset of a premature breakdown at the corners of the trench located at the device periphery. With the aid of numerical simulations performed in cylindrical co-ordinates, it is shown for the first time that a race-track shape of the trench gate fingers alleviates the electric fields at the trench corners and maximizes the UMOS voltage blocking capability. In addition, it is also shown that the breakdown voltage at the trench corners can be made to exceed the UMOS unit cell breakdown voltage by using a deep p diffusion around the trenches located at the device periphery.     

Probing carrier behavior in organic semiconductor device by electric field induced optical second harmonic generation measurement

Electric field induced optical second harmonic generation (EFISHG) measurement is capable of probing carrier motions in organic devices. By measuring nonlinear polarization induced in active layer of organic devices, the carrier motion is visualized. After summarizing the conventional SHG measurement as a tool for material characterization, we show that the EFISHG is a way for probing carrier motions, and thus extends the potentiality of the conventional SHG measurement. We employ the EFISHG measurement to probe carrier behaviors in double-layer metal-insulator–metal diodes, e.g., Au/TIPS-pentacene/PI/ITO diodes, and demonstrate how the time-resolved SHG measurement probes carrier motion in the diodes, in terms of the I–V and C–V characteristics. Results give an insightful picture on the carrier injection, and the succeeding carrier transport.     

Three-dimensional nanometric sub-surface imaging of a silicon flip-chip using the two-photon optical beam induced current method

Two- and three-dimensional sub-surface optical beam induced current imaging of a silicon flip-chip is described and is illustrated by results corresponding to 166 nm lateral resolution and an axial performance capable of localising feature depths to around 100 nm accuracy. The experimental results are compared with theoretically modelled performance based on analytic expressions for the system point spread functions valid for high numerical apertures, and are interpreted using numerical geometric ray tracing calculations. Examples of depth-resolved feature profiling are presented and include depth cross-sections through a matrix of tungsten vias and a depth-resolved image of part of a poly-silicon wire.     

A technique for optimizing the design of power semiconductor devices

A technique is described that provides a basis for predicting whether any device design change will improve or degrade the unavoidable trade-off that must be made between the conduction loss and the turn-off speed of fast-switching high-power thyristors. The technique makes use of a previously reported method by which, for a given design, this trade-off was determined for a wide range of carrier lifetimes. It is shown that by extending this technique, one can predict how other design variables affect this trade-off. The results show that for relatively slow devices the design can be changed to decrease the current gains to improve the turn-off time without significantly degrading the losses. On the other hand, for devices having fast turn-off times design changes can be made to increase the current gain to decrease the losses without a proportionate increase in the turn-off time. Physical explanations for these results are proposed.     

Study for the non-contact characterization of metallization ageing of power electronic semiconductor devices using the eddy current technique

The ageing of the metallization layers of power semiconductor dies may be the cause of failure of power semiconductor modules. Usual indicators of failure like on-state voltage drops make it difficult to highlight the deterioration of the metallization layer. In this study, we evaluate the relevance of the characterization of power device metallizations by means of the eddy current sensors. Experimental results show the ability to monitor the state and the evolution of the metallization ageing with such a technique.     

Electric current and electric field induced in the human body whenexposed to an incident electric field near the resonant frequency

The electric field and current density induced in the human body when this is exposed to electric fields near the resonant frequency, 53 MHz, are determined analytically. Since this frequency range includes an important amateur radio band of 50-60 MHz and exposure to electric fields at this frequency has been shown to be hazardous, the study has a specific motivation. A cylindrical model of the body is used to derive formulas for the total axial current and current density induced in the body subject to skin effect. Tabulations and graphical representations illuminate the results     

Extraction technique for characterization of electric field distribution and drain current in VDMOS power transistor

This paper presents a methodology for modeling the electric field distribution in the vertical direction of VDMOS power transistors, considering the effects of cell spacing and drain voltage. An accurate and consistent extraction technique is developed to extract the values of various important parameters based on non-linear and multivariable regression techniques for the first time. The generalized form of electric field distribution enables the physical modeling of drain current at the onset of quasi-saturation considering the effect of non-uniform electron distribution in the n-epi region. Results so obtained are in good agreement with PISCES simulation over wide range of device parameters. The proposed model will be highly suitable for CAD (Computer Aided Design) tools in HVIC applications.     

Flux method for the analysis of excess carrier transport in multilayer devices in the presence of electric field

The flux method of treating the one-dimensional steady-state transport problem of excess charge carriers, created by the generating sources, is analysed for multilayer devices in the presence of electric field. General analytical expressions for the forward (parallel to the electric field) and backward (antiparallel to the electric field) fluxes of excess carriers at any arbitrary boundary of the multilayer device are derived in terms of the reflection and transmission coefficients of the individual layers and boundaries. As an application of this general analysis, a simple example of a multilayer device consisting of only two layers is considered. The results are shown to reduce those obtained by other calculations in appropriate limiting cases.     

An analytical expression for the electric field in MSM structures

In this work the conformal mapping is used to determine an analytical expression for the electric field in MSM structures. The expression simplifies the analysis of optically generated carriers transport, i.e. the determination of the response of the MSN photodetectors. It can also be useful in the analysis of MSM electrooptical modulators operation.     

On the optical behavior of the electromagnetic field excited by a semi-infinite electric traveling-wave current

A closed-form solution for the spatial distribution of the electromagnetic field excited by an electric traveling-wave current source is presented. Incomplete Hankel and modified Bessel functions are employed to represent progressive and evanescent wave fields, respectively. It is shown that these fields are expressed in terms of spherical and cylindrical waves exhibiting optical character. Using the properties of the incomplete Hankel and modified Bessel functions, the spatial regions where the fields exist in optical sense are determined. It is shown that different shadow boundaries (SBs), featuring complex shapes, identify discontinuity surfaces for the geometrical optics (GO) field. Three surfaces, one being the well-know Keller's cone, are found to describe in the general case the SBs for both the progressive and the evanescent wave fields. It is demonstrated that these surfaces collapse to the Keller's cone surface in the limit of /spl beta//spl rarr//spl infin/.     

The investigation into charge degradation of MIS structures under strong electric field by a method of controlled current load

A new method for studying charge degradation of MIS structures by applying a controlled current load to the structure and taking the time dependence of the voltage is suggested. It allows designers (without switching the structure) to monitor changes in the charge state of MIS structures under the conditions when the capacitance is charged and the charge is injected into the insulator. Charge degradation of metal-PSG-passivated thermal silicon dioxide-insulator structures was studied. It was found that both the SiO₂ space charge and the density of fast surface states generated by tunnel electron injection from the SiO₂ electrode decrease once current load has disappeared.     

New analytical expressions for dark current calculations of highlydoped regions in semiconductor devices

We studied highly doped quasi-neutral regions of semiconductor devices with position dependent doping concentration in the absence of illumination. An important parameter of a highly doped region is its dark current. To clarify how the doping profile influences the dark current, simple analytical expressions are useful. To this end, we first transformed the transport equations to a simple dimensionless form. This enables us to write already existing analytical expressions in an elegant way. It is demonstrated how, from any analytical dark current expression, a direct counterpart can be derived. Next, we derived a dimensionless form for a nonlinear first-order differential equation for the effective recombination velocity. Starting from the analytical solution of this differential equation for uniformly doped regions and using linearization techniques, we obtained two new simple and accurate expressions for the dark current. The expressions are valid for general doping profiles with different minority carrier transparencies. The exact solution is included between both new approximate solutions. The new expressions are compared with previous approximate solutions     

A model for the electric field in lightly doped drain structures

A semi-quantitative model for the lateral channel electric field in LDD MOSFET's has been developed. This model is derived from a quasi-two-dimensional analysis under the assumption of a uniform doping profile. A field reduction factor and voltage improvement, indicating the effectiveness of an LDD design in reducing the peak channel field, are used to compare LDD structures with, without, and with partial gate/drain overlap. Approximate equations have been derived that show the dependencies of the field reduction factor on bias conditions and process parameters. Plots showing the trade-off between, and the process-dependencies of, the field reduction factor/voltage improvement and the series resistance are presented for the three cases. Structures with gate-drain overlap are found to provide greater field reduction than those without the overlap for the same series resistance introduced. This should be considered when comparing the double-diffused and spacer LDD structures. It is shown that gate-drain offset can cause the rise of channel field and substrate current at large gate voltages. This offset is also found to be responsible for nonsaturation of drain current. The model has also been compared with two-dimensional simulation results.     

A wide-band wattmeter for the measurement and analysis of power dissipation in semiconductor switching devices

A technique is presented for accurately measuring and displaying the magnitude and time function of the exchange and absorption of electrical energy in linear and nonlinear circuit elements such as semiconductor power switches. A novel electronic wattmeter with a wide-band (dc to 10 MHz) linear multiplier is used to observe the instantaneous product of the time-varying voltage and current in an arbitrary load. Experimental data show that the peaks of power dissipation during the turn-on and turn-off phases of a switching power transistor are much greater than the power dissipated during the time intervals of settled current flow. Furthermore, it is verified experimentally that the average power dissipation increases linearly with the transistor pulse-repetition frequency beyond a static (dc) value. The absence of such a frequency-dependent component of power dissipation in switches of resonant-current circuits is also confirmed.     

A simple method for evaluating the transient thermal response of semiconductor devices

In this paper, a simple experimental method for the transient thermal characterisation of semiconductor packages is presented. The method is based upon the assumption that in many cases, device temperature evolution can be accurately described by a few exponential terms, as will be shown to be the case when transient thermal response has widely separated time constants.The proposed method, begins with the experimental determination of transient thermal response followed by numerical extraction of the time constants and amplitudes for the significant exponential terms, and is applied to a number of commercial Smartpack^® modules in order to obtain a dynamic model that can be used in circuit and numerical simulators, in order to predict the dynamic thermal behaviour of the device under any working condition.     

Practical machine for electric arc splicing of optical fibres in the field

A portable machine is provided with a 7 cm × 5 cm daylight screen where a stereogram of the fibre ends is displayed. Easy adjustment is made without first cleaning the supports. The fibres are then polished, butted and welded automatically. Average losses of 0?06 dB arc obtained with graded-index fibres.     

Numerical method for the solution of the transient behavior of bipolar semiconductor devices

A numerical technique is presented which permits a computer solution of the complete set of time dependent partial differential equations governing bipolar semiconductor behavior. The scheme does not require any of the often made assumptions and approximations such as abrupt junctions, quasi-neutrality or restricted injection levels. The resulting solution describes device terminal properties and gives a detailed account of internal parameters as a function of time and distance.The present method is distinguished from others by the use of the technique of quasilinearization which converts the nonlinear boundary value problem into a linear form. The latter is solved iteratively, yielding highly stable and convergent solutions. The method uses the complete form of Poisson's equation and an implicit time advancement formulation to generate a stable time trajectory of the solution. The Scharfetter-Gummel spatial discretization scheme is used for greater accuracy.Computer and experimental results are given and compared for the transient behavior of a p⁺nn⁺ diode structure. Both forward and reverse transients are described.     

Impact of crosstalk induced beat noise on the size of semiconductor laser amplifier based optical space switch structures

The size limitation of a semiconductor laser amplifier (SLA) based optical matrix-vector multiplier (MVM) switch structure arising from amplifier noise and crosstalk is investigated theoretically and experimentally. Computer simulation reveals that the number of input/output channels in such a switch structure may be limited to less than 60/spl times/60 if the contrast ratio of each SLA is 20 dB or lower.