Verilog-A Device Models for Cryogenic Temperature Operation of Bulk Silicon CMOS Devices

Verilog-A based cryogenic bulk CMOS (complementary metal oxide semiconductor) compact models are built for state-of-the-art silicon CMOS processes. These models accurately predict device operation at cryogenic temperatures down to 4 K. The models are compatible with commercial circuit simulators. The models extend the standard BSIM4 [Berkeley Short-channel IGFET (insulated-gate field-effect transistor ) Model] type compact models by re-parameterizing existing equations, as well as adding new equations that capture the physics of device operation at cryogenic temperatures. These models will allow circuit designers to create optimized, reliable, and robust circuits operating at cryogenic temperatures

Random matrix ensemble with random two-body interactions in presence of a mean-field for spin one boson systems

For $m$ number of bosons, carrying spin ($S$=1) degree of freedom, in $\Omega$ number of single particle orbitals, each triply degenerate, we introduce and analyze embedded Gaussian orthogonal ensemble of random matrices generated by random two-body interactions that are spin (S) scalar [BEGOE(2)-$S1$]. The embedding algebra is $U(3) \supset G \supset G1 \otimes SO(3)$ with SO(3) generating spin $S$. A method for constructing the ensembles in fixed-($m$, $S$) space has been developed. Numerical calculations show that the form of the fixed-($m$, $S$) density of states is close to Gaussian and level fluctuations follow GOE. Propagation formulas for the fixed-($m$, $S$) space energy centroids and spectral variances are derived for a general one plus two-body Hamiltonian preserving spin. In addition to these, we also introduce two different pairing symmetry algebras in the space defined by BEGOE(2)-$S1$ and the structure of ground states is studied for each paring symmetry.Comment: 22 pages, 6 figure

Thermalization in one- plus two-body ensembles for dense interacting boson systems

Employing one plus two-body random matrix ensembles for bosons, temperature and entropy are calculated, using different definitions, as a function of the two-body interaction strength \lambda for a system with 10 bosons (m=10) in five single particle levels (N=5). It is found that in a region \lambda \sim \lambda_t, different definitions give essentially same values for temperature and entropy, thus defining a thermalization region. Also, (m,N) dependence of \lambda_t has been derived. It is seen that \lambda_t is much larger than the \lambda values where level fluctuations change from Poisson to GOE and strength functions change from Breit-Wigner to Gaussian.Comment: 7 pages, 4 figure

Global Properties of fp-Shell Interactions in Many-nucleon Systems

Spectral distribution theory, which can be used to compare microscopic interactions over a broad range of nuclei, is applied in an analysis of two modern effective interactions based on the realistic CD-Bonn potential for $0\hbar\Omega$ no-core shell model calculations in the fp shell, as well as in a comparison of these with the realistic shell-model GXPF1 interaction. In particular, we explore the ability of these interaction to account for the development of isovector pairing correlations and collective rotational motion in the fp shell. Our findings expose the similarities of these two-body interactions, especially as this relates to their pairing and rotational characteristics. Further, the GXPF1 interaction is used to determine the strength parameter of a quadrupole term that can be used to augment an isovector-pairing model interaction with Sp(4) dynamical symmetry, which in turn is shown to yield reasonable agreement with the low-lying energy spectra of $^{58}$Ni and $^{58}$Cu.Comment: 21 pages, 3 figures, accepted in Nuclear Physics

Buddhist Councils (Sangiti) and its Literature: A Review

There are two main philosophical sciences in India; atheistic (Charavka, Jain and Bauddha) and theist (Sankhya, Yoga, Nyaya, Vaishehika, Purva mimansa and Uttar mimansa). In India, abundant literatures of philosophical sciences are available except Buddhist literature and the reasons are unknown. Buddhist literatures were in Pali language which was a dialect of ancient India and to preserve the invaluable teaching of the Buddha, till dated six Councils (Shangiti) were convened out of which three councils were assembled in ancient India. It is said that the knowledge of history of Indian culture is incomplete without the knowledge of Pali literature. Ayurveda is a Darshanshashtra (Philosophy) as well as clinical science having the goal of Moksha. Every Darshanshashtra has its goal to achieve the Moksha. Aastika and Nastika darshanshashtras have their influence on Ayurveda. The purpose of this paper is to know about the Buddhist councils along with at least appellations of the Buddhist literature

Modeling and Characterization of 4H-SIC MOSFETs: High Field, High Temperature, and Transient Effects

We present detailed physics based numerical models for characterizing 4H-Silicon Carbide lateral MOSFETs and vertical power DMOSFETs for high temperature, high field, DC, AC and transient switching operating conditions. A complete 2-D Drift-Diffusion based device simulator has been developed specifically for SiC MOSFETs, to evaluate device performance in a variety of operating scenarios, and to extract relevant physical parameters. We have developed and implemented room and high temperature mobility models for bulk phonon and impurity scattering, surface phonon scattering, Coulomb scattering from interface traps, and surface roughness scattering. High temperature models for interface trap density of states and occupation probability of interface traps are also implemented. By rigorous comparison of simulated I-V characteristics to experimental data at high temperatures, physical parameters like interface trap density of states, surface step height, saturation velocity, etc. have been extracted. Insight into relative importance of scattering mechanisms influencing transport in SiC MOSFETs has been provided. We show that the strongest contribution to low current in SiC MOSFETs is from the loss of mobile inversion charge due to large amount of trapping at the interface, and due to very low surface mobility arising due to a rough SiC-SiO2 interface. We show that surface roughness scattering dominates at high gate biases and is the most important scattering mechanism in 4H-SiC MOSFETs. Switching characteristics of SiC lateral MOSFETs have been modeled and simulated using our custom device simulator. A comprehensive generation-recombination model for interaction between inversion layer electrons and interface traps has been developed. Using this model, we have modeled the time-dependent occupation of interface traps spread inside the SiC bandgap. We have measured the transient characteristics of these devices, and compare our simulation to experiment and have extracted capture cross-sections of interface traps. Using the coupled experiment and modeling approach, we are able to distinguish between fast interface traps and slow oxide traps, and explain how they contribute to threshold voltage instability. High power 4H-SiC DMOSFET operation in the ON and the OFF states has also been analyzed. We show that in current generation SiC DMOSFETs, the ON resistance is dominated by the channel resistance instead of the drift-layer resistance. This makes the design of SiC DMOSFETs far from ideal. OFF state blocking capability and breakdown due to impact ionization of the DMOSFETs are also modeled and simulated. We show that the 4H-SiC DMOSFETs have excellent leakage characteristics and can support extremely high OFF state drain voltages

Characterization of 4H-SiC MOSFETs Using First Principles Coulomb Scattering Mobility Modeling and Device Simulation

Detailed analysis of a 4H-SiC MOSFET has been carried out by numerically solving the steady state semiconductor Drift-Diffusion equations. Mobility models for bulk phonon scattering, surface phonon scattering, surface roughness scattering, Coulomb scattering by interface traps and oxide charges, and high field effects, have been developed and implemented. A first principles Coulomb scattering mobility model has been developed specifically to model the physics of the inversion layer in 4H-SiC MOSFETs. The Coulomb scattering model takes into account, scattering of mobile charges by occupied interface traps and fixed oxide charges, distribution of mobile charges in the inversion layer, and screening. Simulated IV curves have been compared to experimental data. Density of states for the interface traps have been extracted, and seem to be in agreement with experimental measurements. Simulations indicate that occupied interface traps in 4H-SiC MOSFETs are responsible for mobility degradation, low currents and high threshold voltages. Their effect diminishes at high temperatures due to reduction in trap occupancy, and at high gate voltages due to increased screening. At high gate voltages, surface roughness scattering plays the major role in mobility degradation in 4H-SiC MOSFETs