Browsing by Subject "Carrier mobility"
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Item Spatial dependence of electron concentration and effect of localized conductivity in n-type silicon wafers due to neutron damage(2021-08-05) Quiroz, Crystal Baker; Landsberger, Sheldon; Capolungo, Laurent; Pryor, Mitch; Charlton, William; Kulkarni, JaydeepImage sensors in radioactive environments are especially sensitive to radiation damage due to their internal circuitry and direct exposure to radiative particles. Displacement damage from neutron interactions creates non-uniformity in the crystal lattice of semiconductors that comprise the devices. Defects, dislocations, and dopant atoms create new electron traps within the bandgap of the semiconductor. This affects the microscopic and macroscopic properties of the material by decreasing carrier mobility and results in spatial nonhomogeneity of conductivity leading to a decrease in performance or failure of the device. An experimental campaign, along with a two part mathematical model, is proposed that investigates the spatial dependence of carrier concentration on conductivity in an n-type silicon wafer that is exposed to neutron damage. The model determines an expression for the concentration of free electrons that take into account the defects and dislocations in a system after neutron irradiation. This expression is then used to determine the local conductivity changes in the system, and then, the overall conductivity change of the material. This model is compared to electrical properties of n-type silicon (nSi) wafers and charged-coupled devices (CCD) before and after neutron irradiation. Three neutron sources were chosen based on their neutron spectra and similarities to neutron sources utilized at Los Alamos National Laboratory (LANL) and the University of Texas (UT) facilities. A 32 to 39% increase to resistance of nSi wafers was found with the TRIGA MARK II rotary specimen rack (RSR) neutron source, while a negligible difference was found with the TRIGA MARK II BP5 and PuBe sources. A decrease in resistance was found in CCD sensors after irradiation with the TRIGA RSR, with an increase in leakage current as a function of voltage. Comparisons with the mathematical model to experimental and published results indicate further investigations must be accomplished to achieve a more complete model.Item Stability analysis for SRAM cells with TSV induced stress in 3D ICs(2012-08) Zhang, Wen, 1990-; Pan, David Z.; Sun, NanThree-dimensional integrated circuits (3D-IC) have emerged as promising candidates to overcome the interconnect bottlenecks of nanometer scale designs while also helping to reduce wire delay and increase memory throughput. While this technology offers many potential advantages, it also produces large thermal mismatch stress in 3D-IC structures employing Through-Silicon-Via (TSV). The stress distribution in silicon and interconnect is affected by the via diameter and layout geometry. TSV-induced stress effects on electron/hole mobility and device performance will be studied for the widely used 6-transistor (6T) SRAM cell. Simulation results in this study show that static noise margin (SNM), Read Margin (RM) and write margin (WM) tend to increase with decreasing electron mobility or increasing hole mobility. Considering TSV-induced stress, we propose that for practical layouts of TSV-based 3D-IC, p-type substrates should be placed further away from TSVs or closer to the smaller TSVs if multiple TSVs exist.