Transport models and advanced numerical simulation of silicon-germanium heterojunction bipolar transistors

Applications in the emerging high-frequency markets for millimeter wave applications more and more use SiGe components for cost reasons. To support the technology effort, a reliable TCAD platform is required. The main issue in the simulation of scaled devices is related to the limitations of the physical models used to describe charge carrier transport. Inherent approximations in the HD formalism are discussed over different technology nodes, providing for the first time a complete survey of HD models capability and restrictions with scaling for simulation of SiGe HBTs. Moreover, a complete set of models for transport parameters of SiGe HBTs is reported, including low-field mobility, energy relaxation time, saturation velocity, high-field mobility and effective density of state. Implementation in a commercial device simulator is drawn and findings are compared with simulation results obtained using a standard set of models and with trustworthy results (i.e. MC and SHE simulation results and experimental data), validating proposed models and clarifying their reliability and accuracy over different technologies. Finally, electrical breakdown phenomena in SiGe HBTs are analyzed: a novel complete model for multiplication factor is reported and validated by experimental results; new M model provides an exhaustive accuracy over a wide range of collector voltages

Natural Biocides to Prevent the Microbial Growth On Cultural Heritage

Many historic, cultural and artistic objects and buildings are made of stone. Like all materials, stone is subject to inexorable deterioration. Along with chemical and physical weathering factors, microbial growth plays an important role in this process. Stones type and local climatic differences have a great impact on the biodeterioration process and their outcomes. Microbial metabolism results in deteriorating agents such as organic and inorganic acid, chelating agents, enzymes and extracellular polymeric substances (EPS) causing e.g. biocorrosion and biomineralization; furthermore phototropic and heterotropic microorganism (ex. Firmicutes and fungi) are able to penetrate into stone mineral [1,2,3]. In addition to structural damage, rock biofilms cause aesthetic damage. In general the biocides used to prevent the growth of microbes are mostly based by using chemical methods, but they show a restricted efficiency and can cause discolorations and severe damages to the cultural heritage and ,also, they affect higher organisms including humans. Recently, the biotechnology and the applied microbiology (the use of antagonistic organisms or their metabolites products against the biodeteriorating agents) offers a wide range of new procedures for the cleaning and conservation of the artistic substrata [4-9]. The case of the study regards two historical bridges: the “San Vito Bridge” located in Potenza and “Della Vecchia Bridge” located in Campomaggiore, a little village near Potenza. The bacteria isolated belong to a wide variety of phylogenetic group being closely related to species of 10 genera within the Proteobacteria, the Firmicutes and the Actinobacteria; the number of fungi was slightly lower than those of bacteria. The fungi isolated on two bridges belong to Aspergillus, Penicillium and Stemphylium genera. In this work secondary metabolites of Burkholderia gladioli pv. agaricicola (Bga) ICMP 11096 strain and glycoalkaloids derived from Solanacee extracts, were used against bacteria and fungi isolated. Results show that all secondary metabolites inhibited in vitro and in vivo the growth of these colonising confirming that the application of biopesticides will be is a promising alternative to synthetic pesticides over traditional technologies. In fact, the use of these natural substances consents a more homogeneous removal of the surface deposits without compromising the substrata structure and the preservation of patina noble ; in addition, bio-cleaning has proven to be more selective than chemicals

Influence of scaling and emitter layout on the thermal behavior of toward-THz SiGe:C HBTs

An extensive on-wafer experimental campaign is carried out to determine the thermal resistance dependence on scaling and emitter geometry in state-of-the-art toward-THz silicon–germanium bipolar transistors designed and fabricated within the framework of the European DOTFIVE project. The extraction is performed through a robust procedure, which—differently from classic approaches—exploits an accurately calibrated thermometer relating base-emitter voltage to junction temperature. Experimental data are then used to assess the accuracy of scalable thermal resistance laws for advanced transistor models; it was found that at least four parameters are needed to ensure a favorable agreement over wide ranges of emitter widths and length

Experimental DC extraction of the base resistance of bipolar transistors: Application to SiGe:C HBTs

This paper presents an improved variant of a dc method to experimentally evaluate the base resistance of a bipolar transistor. The technique relies on a device model associated with a simple parameter optimization methodology, and is suited for modern technologies wherein self-heating and impact-ionization effects play a relevant role. The approach is successfully applied to state-of-the-art SiGe:C heterojunction bipolar transistors for high-frequency applications, although it can in principle be exploited for any bipolar device. The accuracy of the method is verified by numerical and experimental procedure