Multiobjective design optimization of IGBT power modules considering power cycling and thermal cycling

Insulated-gate bipolar transistor (IGBT) power modules find widespread use in numerous power conversion applications where their reliability is of significant concern. Standard IGBT modules are fabricated for general-purpose applications while little has been designed for bespoke applications. However, conventional design of IGBTs can be improved by the multiobjective optimization technique. This paper proposes a novel design method to consider die-attachment solder failures induced by short power cycling and baseplate solder fatigue induced by the thermal cycling which are among major failure mechanisms of IGBTs. Thermal resistance is calculated analytically and the plastic work design is obtained with a high-fidelity finite-element model, which has been validated experimentally. The objective of minimizing the plastic work and constrain functions is formulated by the surrogate model. The nondominated sorting genetic algorithm-II is used to search for the Pareto-optimal solutions and the best design. The result of this combination generates an effective approach to optimize the physical structure of power electronic modules, taking account of historical environmental and operational conditions in the field.

Production and Productive Reason

This article explores two rival understandings of production and what it means to be a rational productive subject. Against ‘technicist’ models of productive reason, it defends a ‘phronetic’ model on both normative and pragmatic grounds. The discussion begins with a description of the general principles underpinning technicist theories of workplace organisation, principles which continue to inform work design approaches to this day. The technicist model is thereafter criticised on three counts: that it represents a specific managerial agenda which privileges sectional interests; that it is suspect morally for a number of reasons; and that despite its aspiration of arriving at ‘one best method’, it represents but one way of organising work processes. The phronetic model is then set out using the notion of ‘practices’ as a guide. This notion is important in providing a view of production in which technical reason is subsumed under a broader practical reason incorporating individual experience and judgement. Against the charge that this view is merely an instance of nostalgic craft romanticism having little relevance to present industrial realities, there are recognisable contemporary instances of phronetic production, one of the most interesting being Volvo’s innovations in automotive assembly systems.

Outcome measurement and service evaluation - a note on research design.

The purpose of this research note is to demonstrate how an individualised quality of life instrument could be adapted to provide a more accurate estimate of the impact of a social service on a person’s quality of life. An increase in quality of life between the start and end of a service is often taken as an indication that the service impacted positively on quality of life. The modifications to the quality of life instrument suggested in this paper show that this assumption is not always accurate and should be questioned directly.

Mental Health Social Work and the Troubles in Northern Ireland: A Study of Practitioner Experiences

• Summary: During the last decade increasing attention has been paid to the impact of the Troubles1 on social work in Northern Ireland. In this paper, the authors describe the first survey used to test some of the assumptions which exist in the literature. An 87-item questionnaire was applied to a range of social work staff currently working in, or associated with, mental health settings. One hundred and one questionnaires were returned: it is estimated that this represented over 70 per cent of mental health social workers in Northern Ireland. • Findings: The design of the questionnaire elicited both qualitative and quantitative data. The findings reveal a workforce with complex religious and national identities and many of the respondents have experienced relatively high levels of Troubles-related incidents whilst carrying out their duties in a variety of organizational and geographical settings. High proportions of respondents received minimal agency support and training to equip them to deal with Troubles-related problems faced by them during this period. • Applications: The authors conclude that the profession and employing agencies should pay greater attention to past and present effects of the Troubles on social work practice and develop appropriate strategies for supporting, training and resourcing staff in this neglected area.

Source/drain extension region engineering in nanoscale double gate SOI MOSFETs: Novel design methodology for low-voltage analog applications

The present paper proposes for the first time, a novel design methodology based on the optimization of source/drain extension (SDE) regions to significantly improve the trade-off between intrinsic voltage gain (A(vo)) and cut-off frequency (f(T)) in nanoscale double gate (DG) devices. Our results show that an optimally designed 25 nm gate length SDE region engineered DG MOSFET operating at drain current of 10 mu A/mu m, exhibits up to 65% improvement in intrinsic voltage gain and 85% in cut-off frequency over devices designed with abrupt SIDE regions. The influence of spacer width, lateral source/drain doping gradient and symmetric as well as asymmetrically designed SDE regions on key analog figures of merit (FOM) such as transconductance (g(m)), transconductance-to-current ratio (g(m)/I-ds), Early voltage (V-EA), output conductance (g(ds)) and gate capacitances are examined in detail. The present work provides new opportunities for realizing future low-voltage/low-power analog circuits with nanoscale SDE engineered DG MOSFETs. (C) 2007 Elsevier B.V. All rights reserved.

Engineering source/drain extension regions in nanoscale double gate (DG) SOI MOSFETs: Analytical model and design considerations

In this paper, we propose for the first time, an analytical model for short channel effects in nanoscale source/drain extension region engineered double gate (DG) SOI MOSFETs. The impact of (i) lateral source/drain doping gradient (d), (ii) spacer width (s), (iii) spacer to doping gradient ratio (s/d) and (iv) silicon film thickness (T-si), on short channel effects - threshold voltage (V-th) and subthreshold slope (S), on-current (I-on), off-current (I-on) and I-on/I-off is extensively analysed by using the analytical model and 2D device simulations. The results of the analytical model confirm well with simulated data over the entire range of spacer widths, doping gradients and effective channel lengths. Results show that lateral source/drain doping gradient along with spacer width can not only effectively control short channel effects, thus presenting low off-current, but can also be optimised to achieve high values of on-currents. The present work provides valuable design insights in the performance of nanoscale DG Sol devices with optimal source/drain engineering and serves as a tool to optimise important device and technological parameters for 65 nm technology node and below. (c) 2006 Elsevier Ltd. All rights reserved.

'Research Training and Professional Social Work Education: Developing Research-Minded Practice' Social Work Education, .

The movement towards developing practice more firmly grounded on empirical research has, arguably, been one of the most significant international trends in social work during the past decade. However, in the UK the implications of this trend for pedagogical practices and the design of educational programmes have still to be fully explored. This paper reports on the findings of a repeated cross-sectional survey of MSW students in Queen's University Belfast which focused on their perceptions of the value of research training to professional practice. The study, conducted over a four year period, explored students' awareness of the relationship between research and practice and their readiness to engage with research training. The findings suggested that the majority of students perceived research training as a valuable component of professional development. However, the study also found a level of scepticism among students about its practical utility along with some resistance towards actively embracing a research agenda. The paper evaluates the significance of these findings for developing research and evidence-based practice as integral components of the new degrees in social work in the UK and for social work education programmes in other countries aiming to develop research-minded practice.

Design and Evaluation of a "Pharmacists in Schools" Community Outreach Programme: A Pilot Study.

Aims: To design, evaluate and pilot a novel programme that would allow school children to become “pharmacists for the day”,encouraging them to recognise the importance of science, to contribute to the Department of Health‟s Building the Community Partnership strategy and University Outreach to the community and to provide undergraduate pharmacy students with teaching experience and an opportunity to build their CV.

Methods: Concept and formulation development, branding work,schools visits,questionnaires and semi-structured interviews.

Results: Suitable formulations were developed and prepared by school children on visits to their schools. The children seemed to enjoy the experience and their teachers gave both positive and constructive feedback. Pharmacy undergraduate students felt they had gained valuable experience that will benefit their future careers.

Conclusion: The Pharmacists in Schools outreach programme has now been successfully piloted and launched and will now be fully implemented in 20 schools in the local community.

Sensing Spaces:A Body-oriented Architectural Design Education

The contemporary dominance of visuality has turned our understanding of space into a mode of unidirectional experience that externalizes other sensual capacities of the body while perceiving the built environment. This affects not only architectural practice but also architectural education when an introduction to the concept of space is often challenging, especially for the students who have limited spatial and sensual training. Considering that an architectural work is not perceived as a series of retinal pictures but as a repeated multi-sensory experience, the problem definitions in the design studio need to be disengaged from the dominance of a ‘focused vision’ and be re-constructed in a holistic manner. A method to address this approach is to enable the students to refer to their own sensual experiences of the built environment as a part of their design processes. This paper focuses on a particular approach to the second year architectural design teaching which has been followed in the Department of Architecture at Izmir University of Economics for the last three years. The very first architectural project of the studio and the program, entitled ‘Sensing Spaces’, is conducted as a multi-staged design process including ‘sense games, analyses of organs and their interpretations into space’. The objectives of this four-week project are to explore the sense of space through the design of a three-dimensional assembly, to create an awareness of the significance of the senses in the design process and to experiment with re-interpreted forms of bodily parts. Hence, the students are encouraged to explore architectural space through their ‘tactile, olfactory, auditory, gustative and visual stimuli’. In this paper, based on a series of examples, architectural space is examined beyond its boundaries of structure, form and function, and spatial design is considered as an activity of re-constructing the built environment through the awareness of bodily senses.

Non Classical Design in MOSFETs for Improving OTA gain-bandwidth trade off

In this paper, gain-bandwidth (GB) trade-off associated with analog device/circuit design due to conflicting requirements for enhancing gain and cutoff frequency is examined. It is demonstrated that the use of a nonclassical source/drain (S/D) profile (also known as underlap channel) can alleviate the GB trade-off associated with analog design. Operational transconductance amplifier (OTA) with 60 nm underlap S/D MOSFETs achieve 15 dB higher open loop voltage gain along with three times higher cutoff frequency as compared to OTA with classical nonunderlap S/D regions. Underlap design provides a methodology for scaling analog devices into the sub-100 nm regime and is advantageous for high temperature applications with OTA, preserving functionality up to 540 K. Advantages of underlap architecture over graded channel (GC) or laterally asymmetric channel (LAC) design in terms of GB behavior are demonstrated. Impact of transistor structural parameters on the performance of OTA is also analyzed. Results show that underlap OTAs designed with spacer-to-straggle ratio of 3.2 and operated below a bias current of 80 microamps demonstrate optimum performance. The present work provides new opportunities for realizing future ultra wide band OTA design with underlap DG MOSFETs in silicon-on-insulator (SOI) technology. Index Terms—Analog/RF, double gate, gain-bandwidth product, .

Design of quantum-dot cellular automata circuits using cut-set retiming

As a potential alternative to CMOS technology, QCA provides an interesting paradigm in both communication and computation. However, QCAs unique four-phase clocking scheme and timing constraints present serious timing issues for interconnection and feedback. In this work, a cut-set retiming design procedure is proposed to resolve these QCA timing issues. The proposed design procedure can accommodate QCAs unique characteristics by performing delay-transfer and time-scaling to reallocate the existing delays so as to achieve efficient clocking zone assignment. Cut-set retiming makes it possible to effectively design relatively complex QCA circuits that include feedback. It utilizes the similar characteristics of synchronization, deep pipelines and local interconnections common to both QCA and systolic architectures. As a case study, a systolic Montgomery modular multiplier is designed to illustrate the procedure. Furthermore, a nonsystolic architecture, an S27 benchmark circuit, is designed and compared with previous designs. The comparison shows that the cut-set retiming method achieves a more efficient design, with a reduction of 22%, 44%, and 46% in terms of cell count, area, and latency, respectively.

Work-place social capital and smoking cessation: The Finnish Public Sector Study

AIMS:
To examine whether high social capital at work is associated with an increased likelihood of smoking cessation in baseline smokers.
DESIGN:
Prospective cohort study.
SETTING:
Finland.
PARTICIPANTS:
A total of 4853 employees who reported to be smokers in the baseline survey in 2000-2002 (response rate 68%) and responded to a follow-up survey on smoking status in 2004-2005 (response rate 77%).
MEASUREMENTS:
Work-place social capital was assessed using a validated and psychometrically tested eight-item measure. Control variables included sex, age, socio-economic position, marital status, place of work, heavy drinking, physical activity, body mass index and physician-diagnosed depression.
FINDINGS:
In multi-level logistic regression models adjusted for all the covariates, the odds for being a non-smoker at follow-up were 1.26 [95% confidence interval (CI)=1.03-1.55] times higher for baseline smokers who reported high individual-level social capital than for their counterparts with low social capital. In an analysis stratified by socio-economic position, a significant association between individual-level social capital and smoking cessation was observed in the high socio-economic group [odds ratio (OR) (95% CI)=1.63 (1.01-2.63)], but not in intermediate [(OR=1.10 (0.83-1.47)] or low socio-economic groups [(OR=1.28 (0.86-1.91)]. Work unit-level social capital was not associated with smoking cessation.
CONCLUSIONS:
If the observed associations are causal, these findings suggest that high perceived social capital at work may facilitate smoking cessation among smokers in higher-status jobs.

Building Clouds Drifting Walls:Year One Design Studio: A Critical Appraisal

This is a Booklet about a first year design studio in a school of architecture. It describes and reflects on changes that happened in the course over a three year period starting September 2000. The Studio is made up of students from mainstream architecture, and dual courses with landscape and engineering. The booklet is for those who are thinking of studying architecture. It might also be for those already learning and teaching architecture who want to see how other design studios work.