D M S Sultan | American International University-Bangladesh (original) (raw)

Papers by D M S Sultan

Owing to their intrinsic (geometry dependent) radiation hardness, 3D pixel sensors are promising ... more Owing to their intrinsic (geometry dependent) radiation hardness, 3D pixel sensors are promising candidates for the innermost tracking layers of the forthcoming experiment upgrades at the “Phase 2” High-Luminosity LHC (HL-LHC). To this purpose, extreme radiation hardness up to the expected maximum fluence of 2×10^16 neq.cm^-2 must come along with several technological improvements in a new generation of 3D pixels, i.e., increased pixel granularity (50×50 or 25×100 µm^2 cell size), thinner active region (~100 µm), narrower columnar electrodes (~5µm diameter) with reduced inter-electrode spacing (~30 µm), and very slim edges (~100 µm). The fabrication of the first batch of these new 3D sensors was recently completed at FBK on Si-Si direct wafer bonded 6” substrates. Initial electrical test results, performed at wafer level on sensors and test structures, highlighted very promising performance, in good agreement with TCAD simulations: low leakage current (<1 pA/column), intrinsic breakdown voltage of more than 150 V, capacitance of about 50 fF/column, thus assessing the validity of the design approach. A large variety of pixel sensors compatible with both existing (e.g., ATLAS FEI4 and CMS PSI46) and future (e.g., RD53) read-out chips were fabricated, that were also electrically tested on wafer using a temporary metal layer patterned as strips shorting rows of pixels together. This allowed a statistically significant distribution of the relevant electrical quantities to be obtained, thus gaining insight into the impact of process-induced defects. A few 3D strip test structures were irradiated with X-rays, showing inter-strip resistance of at least several GΩ even after 50 Mrad(Si) dose, thus proving the p-spray robustness. We present the most important design and technological aspects, and results obtained from the initial investigations.

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We report on an experimental study aimed at gaining deeper insight into the leakage current and b... more We report on an experimental study aimed at gaining deeper insight into the leakage current and breakdown voltage of irradiated double-sided 3D silicon sensors from FBK, so as to improve both the design and the fabrication technology for use at future hadron colliders such as the High Luminosity LHC. Several 3D diode samples of different technologies and layout are considered, as well as several irradiations with different particle types. While the leakage current follows the expected linear trend with radiation fluence, the breakdown voltage is found to depend on both the bulk damage and the surface damage, and its values can vary significantly with sensor geometry and process details.

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Following 3D pixel sensor production for the ATLAS Insertable B-Layer, Fondazione Bruno Kessler (... more Following 3D pixel sensor production for the ATLAS Insertable B-Layer, Fondazione Bruno Kessler (FBK) fabrication facility has recently been upgraded to process 6-inch wafers. In 2014, a test batch was fabricated to check for possible issues relevant to this upgrade. While maintaining a double-sided fabrication technology, some process modifications have been investigated. We report here on the technology and the design of this batch, and present selected results from the electrical characterization of sensors and test structures. Notably, the breakdown voltage is shown to exceed 200 V before irradiation, much higher than in earlier productions, demonstrating robustness in terms of radiation hardness for forthcoming productions aimed at High Luminosity LHC upgrades.

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Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with m... more Temperature dependence of intersubband transitions in AlN/GaN multiple quantum wells grown with molecular beam epitaxy is investigated both by absorption studies at different temperatures and modeling of conduction-band electrons. For the absorption study, the sample is heated in increments up to 400◦C. The self-consistent Schr¨odinger-Poisson modeling includes temperature effects of the band-gap and the influence of thermal expansion on the piezoelectric field. We find that the intersubband absorption energy decreases only by ∼ 6 meV at 400◦C relative to its room temperature value.

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Aquafil S.p.A. has been one of the leading players in the production of Nylon 6. Over 60% of its ... more Aquafil S.p.A. has been one of the leading players in the production of Nylon 6. Over 60% of its total production is composed by the so called solution dyed industrial yarns. The fibers are colored through a mass pigmentation process by the addition of Color Master batch during the melt spinning. From the industrial point of view, the most important problem
for the Color Master batch production is to maximize the tinting strength of the color pigment. This have to be achieved by optimizing the fillers dispersion into the polymer bulk without using the dispersing additives, that can show detrimental effect during melt spinning. The dispersion degree of the pigments is the key point of the master batch production process and
it depends on the physical properties of pigment particles, on the process parameters involved during extrusion and on the pigment concentration in color master batch. During IPSP2014, the Aquafil team of students and researchers worked on the realization of two models, one empirical and one theoretical, that could reproduce and predict the tinting strength of the Color Master batches, starting from the production process parameters. At the end of the week, the two developed models were able to qualitatively reproduce the experimental results measured on a set of Monoconcentrated Color Master batches, which were realized for this purpose by Aquafil during the event. Moreover, both models suggest that a critical production parameter for the realization of masterbatches with optimized tinting strength is the temperature profile of the extruder barrels.

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