Optimisation of trench isolated bipolar transistors on SOI substrates by 3D electro-thermal simulations

This paper provides a comprehensive analysis of thermal resistance of trench isolated bipolar transistors on SOI substrates based on 3D electro-thermal simulations calibrated to experimental data. The impact of emitter length, width, spacing and number of emitter fingers on thermal resistance is analysed in detail. The results are used to design and optimise transistors with minimum thermal resistance and minimum transistor area. (c) 2007 Elsevier Ltd. All rights reserved.

Design, Manufacture and Performance of Germanium Bipolar Transistors

Germanium NPN bipolar transistors have been manufactured using phosphorus and boron ion implantation processes. Implantation and subsequent activation processes have been investigated for both dopants. Full activation of phosphorus implants has been achieved with RTA schedules at 535?C without significant junction diffusion. However, boron implant activation was limited and diffusion from a polysilicon source was not practical for base contact formation. Transistors with good output characteristics were achieved with an Early voltage of 55V and common emitter current gain of 30. Both Silvaco process and device simulation tools have been successfully adapted to model the Ge BJT(bipolar junction transistor) performance.

SiGe HBTs on Bonded SOI Incorporating Buried Silicide Layers

The performance of silicon bipolar transistors has been significantly improved by the use of ultra narrow base layers of SiGe. To further improve device performance by minimising parasitic resistance and capacitance the authors produced an unique silicon-on-insulator (SOI) substrate incorporating a buried tungsten disilicide layer. This structure forms the basis of a recent submission by Zarlink Semiconductors ( Silvaco, DeMontfort & Queen�s) to DTI for high voltage devices for automotive applications. The Queen�s part of the original EPSRC project was rated as tending to outstanding.

Improved Thermal Performance of SOI Using Compound Buried Layer

The buried oxide (BOX) layer in silicon on insulator (SOI) was replaced by a compound buried layer (CBL) containing layers of SiO2, polycrystalline silicon (polysilicon), and SiO2. The undoped polysilicon in the CBL acted as a dielectric with a higher thermal conductivity than SiO2. CBL provides a reduced thermal resistance with the same equivalent oxide thickness as a standard SiO2 buried layer. Thermal resistance was further reduced by lateral heat flow through the polysilicon. Reduction in thermal resistance by up to 68% was observed, dependent on polysilicon thickness. CBL SOI substrates were designed and manufactured to achieve a 40% reduction in thermal resistance compared with an 1.0-μm SiO2 BOX. Power bipolar transistors with an active silicon layer thickness of 13.5 μm manufactured on CBL SOI substrates showed a 5%-17% reduction in thermal resistance compared with the standard SOI. This reduction was dependent on transistor layout geometry. Between 65% and 90% of the heat flow from these power transistors is laterally through the thick active silicon layer. Analysis confirmed that CBL SOI provided a 40% reduction in the vertical path thermal resistance. Devices employing thinner active silicon layers will achieve the greater benefit from reduction in vertical path thermal resistance offered by CBL SOI.

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.

In situ diagnostics and prognostics of solder fatigue in IGBT modules for electric vehicle drives

This paper proposes an in situ diagnostic and prognostic (D&P) technology to monitor the health condition of insulated gate bipolar transistors (IGBTs) used in EVs with a focus on the IGBTs' solder layer fatigue. IGBTs' thermal impedance and the junction temperature can be used as health indicators for through-life condition monitoring (CM) where the terminal characteristics are measured and the devices' internal temperature-sensitive parameters are employed as temperature sensors to estimate the junction temperature. An auxiliary power supply unit, which can be converted from the battery's 12-V dc supply, provides power to the in situ test circuits and CM data can be stored in the on-board data-logger for further offline analysis. The proposed method is experimentally validated on the developed test circuitry and also compared with finite-element thermoelectrical simulation. The test results from thermal cycling are also compared with acoustic microscope and thermal images. The developed circuitry is proved to be effective to detect solder fatigue while each IGBT in the converter can be examined sequentially during red-light stopping or services. The D&P circuitry can utilize existing on-board hardware and be embedded in the IGBT's gate drive unit.

Normal levels of prepulse inhibition in the euthymic phase of bipolar disorder.

BACKGROUND:Deficits in prepulse inhibition (PPI) of the acoustic startle response have been suggested as a potentially useful endophenotype for schizophrenia spectrum disorders and may explain certain symptoms and cognitive deficits observed in the psychoses. PPI deficits have also been found in mania, but it remains to be confirmed whether this dysfunction is present in the euthymic phase of bipolar disorder.METHOD: Twenty-three adult patients with DSM-IV bipolar disorder were compared to 20 controls on tests of acoustic startle reactivity and PPI of the startle response. Sociodemographic and treatment variables were recorded and symptom scores assessed using the Hamilton Depression Inventory and the Young Mania Rating Scale.RESULTS:Overall, the patient and control groups demonstrated similar levels of startle reactivity and PPI, although there was a trend for the inter-stimulus interval to differentially affect levels of PPI in the two groups.CONCLUSIONS: In contrast to bipolar patients experiencing a manic episode, general levels of PPI were normal in this euthymic sample. Further studies are required to confirm this finding and to determine the mechanisms by which this potential disruption/normalization occurs. It is suggested that an examination of PPI in a high-risk group is required to fully discount dysfunctional PPI as a potentially useful endophenotype for bipolar disorder.

Effects of trauma on bipolar disorder: the mediational role of interpersonal difficulties and alcohol dependence

Objectives: This study examined: (i) the prevalence of trauma in a bipolar disorder (BD) sample, and (ii) how trauma histories mediated by interpersonal difficulties and alcohol dependence impact on the severity of BD. The prevalence of posttraumatic stress disorder (PTSD) and its relationship to outcomes in BD were also examined.

Methods: Sixty participants were recruited from a geographically well-defined mental health service in Northern Ireland. Self-reported trauma histories, PTSD, interpersonal difficulties and alcohol dependence and were examined in relation to illness severity.

Results: A high prevalence of trauma was found. Trauma predicted the frequency of hospital admissions (R-2 = 0.08), quality of life (R-2 = 0.23) and inter-episode depressive symptoms (R-2 = 0.13). Interpersonal difficulties, but not alcohol dependence, appeared to play an important role in mediating these adverse effects. While only 8% of the sample met criteria for active PTSD, this comorbid disorder was associated with BD severity.

Conclusions: This study indicates that awareness of trauma is important in understanding individual differences in bipolar presentations. The theoretical and clinical implications of evidence that trauma is related to more adverse outcomes in BD are discussed. The finding that interpersonal difficulties mediate the relationship between trauma and BD severity is novel. The need for adjunctive evidence-based treatments targeting interpersonal difficulties is considered.

Parameter sensitivity for optimal design of 65 nm node SOI transistors

Mixed-mode simulation, where device simulation is embedded directly within a circuit simulator, is used for the first time to provide scaling guidelines to achieve optimal digital circuit performance for double gate SOI MOSFETs. This significant advance overcomes the lack of availability of SPICE model parameters. The sensitivity of the gate delay and on-off current ratio to each of the key geometric and technological parameters of the transistor is quantified. The impact of the source-drain doping profile on circuit performance is comprehensively investigated.

Gender influences the detection of spatial working memory deficits in bipolar disorder.

Objective: Despite evidence that gender may influence neurocognitive functioning, few studies have examined its effects in bipolar disorder (BD) a priori. The aim of this study was to examine how gender influences executive-type functions, which are potentially useful as endophenotypes for BD. Methods: The performance of 26 euthymic patients(12 males, 14 females) with DSM-IV BD (20 BD type I and six BD type II) was compared to that of 26 controls (12 males, 14 females) on tests of executive function. Controls were matched to patients on an individual basis for sex, age and premorbid IQ. Tests assessed spatial working memory (SWM), planning, attentional set-shifting and verbal fluency. Results: Overall, patients showed deficits in SWM strategy (p < 0.001) and made more SWM errors relative to controls (p < 0.001). These deficits were more apparent in male-only comparisons (both p < 0.001) than in female-only comparisons (both p < 0.05). When examined in isolation, male controls were significantly better at performing the SWM task than female controls (both p < 0.05). This pattern was not observed in the patient cohort: male patients had poorer strategy scores than female patients (p < 0.05), but made a similar number of SWM errors. Conclusions: These findings provide evidence that gender can influence the detection of SWM deficits in the euthymic phase of BD, as the sex-related disequilibrium in SWM identified in healthy controls was disrupted in BD. © 2008 The Authors Journal compilation © 2008 Blackwell Munksgaard.