A compact model for III–V nanowire electrostatics including band non-parabolicity

The III–V materials have a highly non-parabolic band structure that significantly affects the MOS transistor electrostatics. The compact models used to simulate circuits involving III–V MOS transistors must account for this band structure non-parabolicity for accurate results. In this work, we propose a modification to the energy dispersion relation to include the band structure non-parabolicity in a way suitable for compact models. Unlike the available non-parabolic energy dispersion relation, the one proposed here is simple and includes the non-parabolicity in both confinement and transport directions. The proposed dispersion relation is then used to model the electrostatics of III–V nanowire transistors. The proposed model is scalable to a higher number of sub-bands and computationally efficient for circuit simulators. The model is also validated with the data from a 2D Poisson–Schrödinger solver for a wide range of nanowire dimensions, III–V channel materials, and found to be in excellent agreement with the simulation data

Large amplitude oscillatory shear of pseudoplastic and elastoviscoplastic materials

We explore the utility of strain-controlled large amplitude oscillatory shear (LAOS) deformation for identifying and characterizing apparent yield stress responses in elastoviscoplastic materials. Our approach emphasizes the visual representation of the LAOS stress response within the framework of Lissajous curves with strain, strain-rate, and stress as the coordinate axes, in conjunction with quantitative analysis of the corresponding limit cycle behavior. This approach enables us to explore how the material properties characterizing the yielding response depend on both strain amplitude and frequency of deformation. Canonical constitutive models (including the purely viscous Carreau model and the elastic Bingham model) are used to illustrate the characteristic features of pseudoplastic and elastoplastic material responses under large amplitude oscillatory shear. A new parameter, the perfect plastic dissipation ratio, is introduced for uniquely identifying plastic behavior. Experimental results are presented for two complex fluids, a pseudoplastic shear-thinning xanthan gum solution and an elastoviscoplastic invert-emulsion drilling fluid. The LAOS test protocols and the associated material measures provide a rheological fingerprint of the yielding behavior of a complex fluid that can be compactly represented within the domain of a Pipkin diagram defined by the amplitude and timescale of deformation.National Science Foundation (U.S.) (Graduate Research Fellowship)United States. Defense Advanced Research Projects Agency (DARPA) (Chemical Robots program