Papers by Keyword: 2D Simulation

Abstract: We evaluate and compare the static and dynamic performances of four different 4H-SiC power MOSFETs (Conventional DMOS and UMOS, Superjunction (SJ) DMOS and UMOS FETs) from 0.6 to 10kV. The static on-state performance is determined by analytically calculating the specific on-resistance (R_ON,sp), while the dynamic switching performance is determined by extracting the specific gate charge (Q_G,sp) and switching energy loss per cycle (E_sw,cycle) using 2D device simulations. It has been found that the SJ UMOS FET exhibits at least a 31% (up to 53% at 0.6kV) reduction in the R_ON,sp · Q_G,sp Figure-of-Merit (FoM) compared to the SJ DMOS FET within the breakdown voltage rating range studied.

Abstract: We determine the effective critical breakdown field for 4H-SiC superjunction (SJ) devices and compare it to their conventional counterparts. Also, we investigate its dependence on SJ device structural parameters, such as drift layer thickness (t) and pillar width (W). In 4H-SiC SJ devices, the effective critical breakdown field was found to be around 30% lower than that of conventional devices owing to their longer ionization paths. In particular, the effective critical electric field varies as ξ_cr α t^-1/10 and ξ_cr α t^-1/6 for 4H-SiC SJ and conventional devices respectively but independent of pillar width and doping concentration for high aspect ratio devices (t/W > 10).

Abstract: The microstructure evolution during the directional solidification of Al-Cu alloy is simulated using a phase field model. The transformation from liquid to solid phase is a non-equilibrium process with three regions (liquid, solid and interface) involved. Phase field model is defined for each of the three regions. The evolution of each phase is calculated by a set of phase field equations, whereas the solute in those regions is calculated by a concentration equation. In this work, the phase field model which is generally valid for most kinds of transitions between phases, it is applied to the directional solidification problem. Numerical results for the morphological evolution of columnar dendrite in Al-Cu alloy are in agreement with experimental observations found in the literature. The growth velocity of the dendrite tip and the concentration profile in the solid, interface and liquid region were calculated.

Abstract: Recently polycrystalline silicon (pc-Si) thin film transistors (TFT’s) have emerged as the devices of choice for many applications. The TFTs made of a thin un-doped polycrystalline silicon film deposited on a glass substrate by the Low Pressure Chemical Vapor Deposition technique LPCVD have limits in the technological process to the temperature < 600°C. The benefit of pc-Si is to make devices with large grain size. Unfortunately, according to the conditions during deposition, the pc-Si layers can consist of a random superposition of grains of different sizes, where grains boundaries parallels and perpendiculars appear. In this paper, the transfer characteristics IDS-VGS are simulated by solving a set of two-dimensional (2D) drift-diffusion equations together with the usual density of states (DOS: exponential band tails and Gaussian distribution of dangling bonds) localized at the grains boundaries. The impact of thickness of the active layer on the distribution of the electrostatic potential and the effect of density of intergranular traps states on the TFT’s transfer characteristics IDS-VGS have been also investigated.

Abstract: To preview of the final appearance of tufted carpet, this paper devises a solution to simulate the color appearance of tufted carpet. The simulation adopts color blocks to represent a single loop pile in carpet surface, through resizing color block size to simulate the extrusion between loop piles. The solution starts from traversing the control pattern to get the pile height level information. Base on the current and surrounded loop piles height level to infer the size and start point of color block for current loop pile. According to patterns’ information to generate the color appearance simulation for loop pile tufted carpet. Base on the proposed simulation, devise the frame work and control logic for simulation software, and developed the simulation software with C++. Simulation test is carried out, the result shows the method can effectively generate carpet color appearance simulation for tufted carpet comprising of multicolor yarns.

Abstract: This paper proposed a new 2D method to simulate the microstructure for normal grain growth of polycrystalline materials. In this method, the sample was discretized into geometry points and a straightforward geometric construction was implemented to estimate whether the current point was located at the interior of a certain grown grain. The ceramics material was assumed isotropic; furthermore, the single-phase and two-phase systems without pores were discussed respectively. So each grain core would grow up at the same velocity in all directions until it met another growing core in single-phase systems, while in two-phase systems, there would be two sorts of cores with different growing velocities. The ratio of these different velocities was the key factor of the sample microstructures after sintering. The simulation results and the analysis showed that the proposed method agree well with the experimental observation.

Abstract: A method is presented to measure lattice and grain boundary diffusion coefficients using secondary ion mass spectroscopy and 2-dimensional diffusion simulations. SIMS is used to measure concentration profiles of implanted species before and after annealing. The as-implanted concentration profile is used as the initial condition for 2-dimensional diffusion simulations using the finite element method. The geometry of the simulation is based on the microstructure of the sample observed by transmission electron microscopy. Both lattice and grain boundary diffusion are simulated. The final 2-dimensional concentration distribution is projected on the depth axis to obtain a simulated depth profile. The diffusion coefficients are adjusted to fit the profiles measured after annealing. We find that this method allows to determine simultaneously and independently the lattice and grain boundary diffusion coefficients from the same profiles. This method is used to measure the diffusion coefficients of As in polycrystalline Ni2Si thin films. The simulations are found to fit the measured profiles with accuracy. The coefficients are measured between 550 and 700°C. An activation energy ratio Qgb/Qv is found greater than one. This result is corroborated by existing data in silicides and is compared to results in other materials for discussion.