Investigation of the power dissipation during IGBT turn-off using a new physics-based IGBT compact model

New compact models of the IGBTs (both non-punch through IGBT (NPTIGBT) and punch-through IGBT (PTIGBT)) are presented in this paper. The models are implemented in the SABER circuit simulator and used for a study of IGBT anode current and voltage characteristics during a device turn-off (clamped inductive load circuit with gate controlled turn-off), since these parts of the transient characteristics essentially predict the power dissipation (V×I) inside the device. It is shown that PTIGBTs are faster than NPTIGBTs, this becoming more apparent at higher clamp voltages.     

An investigation of the impact of a Ti barrier metal on the thermal stress field in passivated aluminium lines and vias in VLSI systems using finite element modelling approach

The impact of a thin titanium barrier layer on the residual thermal stress in passivated aluminium lines and vias during the manufacture of multilevel structures is investigated using an advanced finite element approach. It is confirmed that the titanium significantly improves the reliability of the aluminium metallization, since, though the residual stress may be higher, the resulting plastic deformation is still lower.     

Feedback supported isolation structure for blocking of minority leakage carriers in power integrated circuits

A combination of two conventional junction isolation structures is used to produce a device, which significantly improves the blocking of minority carriers injected into the substrate of a power IC due to switching of an inductive load. Simulation results show that the connection scheme employed greatly enhances the efficiency of the structures. A substrate current reduction of up to four orders of magnitude compared to conventional junction isolation structures is achieved. The significance of doping profiles in the p-sinker region is evaluated.     

Yogoslav politics, “ethnic cleansing” and co-authorship in science

Scientific outputs from Serbia, Croatia and Slovenia, and the patterns of co-authorship between them and five western countries and with each other have been determined from theScience Citation Index. They reflect accurately the political situation underlying the recent break-up of the former Yugoslavia, and long-term international alliances and friendships, but also take account of geographical proximity, which assists scientific co-operation. There is no evidence of changes in the ethnic composition of Serbian and Croatian scientists overall, as revealed by the names of their researchers before and after the civil war. However some changes appear to have taken place in Serbia outwith Belgrade, which are consistent with the reports of the expulsion of Croats living in Vojvodina.     

Highly effective junction isolation structures for PICs based on standard CMOS Process

This paper presents novel and highly effective junction isolation structures for power integrated circuits. The negative feedback-activated junction isolation is presented and it is proven to be very effective in blocking substrate current from reaching the logic circuitry (orders of magnitude more effective than standard junction isolation techniques). Additionally, in an attempt to further improve the blocking capabilities of junction isolations the use of multiple or combined structures is investigated whilst keeping the surface area used for isolation device in the same range as for the single structures. All isolation structures presented here are based on a 0.6-/spl mu/m CMOS technology.     

Load current observer based feed-forward DC bus voltage control for active rectifiers

In this paper, load current observer based feedforward control of DC bus voltage for a three-phase active rectifier is presented. The paper focuses on: (1) design of conventional proportional-integral (PI) current controller with fastest possible response, (2) the digital current control loop time-delay compensation, (3) design of dc-link-load current observer for identifying the dc load current without using actual current sensors and (4) the feedforward control of dc bus voltage based on the designed current controller and dc link load current observer. A prototype is developed based on the proposed control scheme and expected results have been achieved.     

A fast power loss calculation method for long real time thermal simulation of IGBT modules for a three‐phase inverter system

A fast power losses calculation method for long real time thermal simulation of IGBT module for a three‐phase inverter system is presented in this paper. The speed‐up is obtained by simplifying the representation of the three‐phase inverter at the system modelling stage. This allows the inverter system to be simulated predicting the effective voltages and currents whilst using large time‐step. An average power losses is calculated during each clock period, using a pre‐defined look‐up table, which stores the switching and on‐state losses generated by either direct measurement or automatically based upon compact models for the semiconductor devices. This simulation methodology brings together accurate models of the electrical systems performance, state of the art‐device compact models and a realistic simulation of the thermal performance in a usable period of CPU time and is suitable for a long real time thermal simulation of inverter power devices with arbitrary load. Thermal simulation results show that with the same IGBT characteristics applied, the proposed model can give the almost same thermal performance compared to the full physically based device modelling approach. Copyright © 2006 John Wiley & Sons, Ltd.     

Rare earth and transition metal based entropy stabilised perovskite type oxides

Multicomponent oxides with perovskite type of structure containing up to 10 different cations in equiatomic amounts have been synthesised for the first time. Out of eleven systems synthesised, only six systems crystallised as single phase perovskite type compounds with random and homogenous cation distribution on the respective sites. The formation of phase pure 10-cationic system, (Gd_0.2La_0.2Nd_0.2Sm_0.2Y_0.2)(Co_0.2Cr_0.2Fe_0.2Mn_0.2Ni_0.2)O₃, in contrast to the multiphase mixtures observed in five of the lower entropy systems (containing 6 cations) indicates a possible role of entropy in the stabilisation of a single phase crystal structure. The entropy driven structural stabilisation effect is further supported by the reversible phase transformation, from single phase to multiple phase upon cyclic heat treatment, observed in the (Gd_0.2La_0.2Nd_0.2Sm_0.2Y_0.2)MnO₃ system. This type of entropic signature has been observed in rocksalt based high entropy oxide systems. However, it has not been reported before for perovskite based compounds, as shown in this study.     

Functional synthesis for linear arithmetic and sets

Synthesis of program fragments from specifications can make programs easier to write and easier to reason about. To integrate synthesis into programming languages, synthesis algorithms should behave in a predictable way—they should succeed for a well-defined class of specifications. To guarantee correctness and applicability to software (and not just hardware), these algorithms should also support unbounded data types, such as numbers and data structures. To obtain appropriate synthesis algorithms, we propose to generalize decision procedures into predictable and complete synthesis procedures. Such procedures are guaranteed to find the code that satisfies the specification if such code exists. Moreover, we identify conditions under which synthesis will statically decide whether the solution is guaranteed to exist and whether it is unique. We demonstrate our approach by starting from a quantifier elimination decision procedure for Boolean algebra of set with Presburger arithmetic and transforming it into a synthesis procedure. Our procedure also works in the presence of parametric coefficients. We establish results on the size and the efficiency of the synthesized code. We show that such procedures are useful as a language extension with implicit value definitions, and we show how to extend a compiler to support such definitions. Our constructs provide the benefits of synthesis to programmers, without requiring them to learn new concepts, give up a deterministic execution model, or provide code skeletons.     

Implication of food safety measures on microbiological quality of raw and pasteurized milk

The effects of implementing food safety measures including pre-requisite programs (PRPs) and/or Hazard Analysis Critical Control Points (HACCP) on the microbiological quality of raw and pasteurized milk during four years was investigated in one of the biggest diary plant in Serbia. On the dairy farm, the measures included training of farmers, investments in the infrastructure of gathering points for the collection of raw milk and transportation, improvement of hygiene and decrease of the number of small farmers. As a result of these measures, the contribution of raw milk with of lower total plate count (TPC) in total raw milk quantity decreased over time.As a result of HACCP system implementation in the dairy plant, TPC of pasteurized milk decreased from 3.32 ± 0.48 till 3.11 ± 0.30 log CFU/ml. Eight months after HACCP system was implemented, a significant decrease in TPC from 3.11 ± 0.30 till 2.18 ± 0.54 log CFU/ml in pasteurized milk which could be related to the additional investments covering pasteurisation unit and automated cleaning and disinfection system. The research confirmed constrains of a solely HACCP system without adequate PRPs.Food safety improvements through PRPs and HACCP both on farm level and in the dairy plant present a basis for the production of dairy products.