Impact of strained silicon on the device performance of a bipolar charge plasma transistor

In this manuscript we analyze a unique approach to improve the performance of the bipolar charge plasma transistor(BCPT) by introducing a strained Si/SiGe1-x layer as the active device region. For charge plasma realization different metal work-function electrodes are used to induce n+ and p+ regions on undoped strained silicon-on-insulator(sSOI or SiGe) to realize emitter, base, and collector regions of the BCPT. Here,by using a calibrated 2-D TCAD simulation the impact of a Si mole fraction x(in SiGe) on device performance metrics is investigated. The analysis demonstrates the band gap lowering with decreasing Si content or effective strain on the Si layer, and its subsequent advantages. This work reports a significant improvement in current gain, cutoff frequency, and lower collector breakdown voltage(BVCEO) for the proposed structure over the conventional device. The effect of varying temperature on the strained Si layer and its implications on the device performance is also investigated. The analysis demonstrates a fair device-level understanding and exhibits the immense potential of the SiGematerial as the device layer. In addition to this, using extensive 2-D mixed-mode TCAD simulation, a considerable improvement in switching transient times are also observed compared to its conventional counterpart.

Simulation of Bipolar Charge Transport in Graphene by Using a Discontinuous Galerkin Method

Charge transport in suspended monolayer graphene is simulated by a numerical deterministic approach,based on a discontinuous Galerkin(DG)method,for solving the semiclassical Boltzmann equation for electrons.Both the conduction and valence bands are included and the interband scatterings are taken into account.The use of a Direct Simulation Monte Carlo(DSMC)approach,which properly describes the interband scatterings,is computationally very expensive because the va-lence band is very populated and a huge number of particles is needed.Also the choice of simulating holes instead of electrons does not overcome the problem because there is a certain degree of ambiguity in the generation and recombination terms of electron-hole pairs.Often,direct solutions of the Boltzmann equations with a DSMC neglect the interband scatterings on the basis of physical arguments.The DG approach does not suffer from the previous drawbacks and requires a reasonable computing effort.In the present paper the importance of the interband scatterings is accurately evaluated for several values of the Fermi energy,addressing the issue related to the validity of neglecting the generation-recombination terms.It is found out that the inclusion of the interband scatterings produces huge variations in the average values,as the current,with zero Fermi energy while,as expected,the effect of the interband scattering becomes negligible by increasing the absolute value of the Fermi energy.

兼具高电流增益和高击穿性能的电荷等离子体双极晶体管

为了兼顾高电流增益β和发射极开路集电结的高击穿电压V_(CBO)与基极开路集电极-发射极间的高击穿电压V_(CEO),有效提升电荷等离子体双极晶体管(bipolar charge plasma transistor,BCPT)的高压大电流处理能力,利用SILVACO TCAD建立了npn型BCPT的器件模型。考虑到双极晶体管的击穿电压主要取决于集电区掺杂浓度,首先研究了集电极金属对BCPT性能的影响。分析表明,BCPT集电区的电子浓度强烈依赖于电极金属的功函数,当采用功函数较大的铝(Al)作为集电极金属时,由于减小了金属-半导体接触的功函数差,降低了集电区中诱导产生的电子等离子体浓度,从而有效降低了集电结空间电荷区峰值电场强度,减小了峰值电子温度以及峰值电子碰撞电离率,因此,达到改善击穿电压V_(CBO)和V_(CEO)的目的。然而,集电区电子浓度的减小会引起基区Kirk效应,增大基区复合,降低β。为此,进一步提出了一种采用衬底偏压结构的BCPT,通过在发射区和基区下方引入正衬底偏压,调制发射区和基区有效载流子浓度,达到提高发射结注入效率、增大β的目的。结果表明:与仅采用锆(Zr)作为集电极金属的BCPT相比,该器件的峰值电流增益改善了21.69%,击穿电压V_(CBO)和V_(CEO)分别改善了12.78%和56.41%,从而有效扩展了BCPT的高功率应用范围。

Temperature dependence of the P-hit single event transient pulse width in a three-transistor inverter chain

A comparison of the temperature dependence of the P-hit single event transient （SET） in a two-transistor （2T） inverter with that in a three-transistor （3T） inverter is carried out based on a three-dimensional numerical simulation. Due to the significantly distinct mechanisms of the single event change collection in the 2T and the 3T inverters, the temperature plays different roles in the SET production and propagation. The SET pulse will be significantly broadened in the 2T inverter chain while will be compressed in the 3T inverter chain as temperature increases. The investigation provides a new insight into the SET mitigation under the extreme environment, where both the high temperature and the single event effects should be considered. The 3T inverter layout structure （or similar layout structures） will be a better solution for spaceborne integrated circuit design for extreme environments.

Charge transfer and bipolar charging of particles in a bubbling fluidized bed

Particle-particle and particle-wall collisions in gas-solid fluidized beds lead to charge accumulation on particles.This work evaluated the effect of fluidization time on charge transfer and bipolar charging(charge separation)and their influence on hydrodynamic structures in a fluidized bed.Experiments were performed with glass beads and polyethylene particles in a glass column.The pressure fluctuations and net electrostatic charge of particles were measured during fluidization.Wavelet and short-time Fourier transforms were used to analyze pressure fluctuations.The results revealed that bipolar charging is the dominant tribocharging mechanism in a bed of glass beads.Bipolar charging in a bed of particles with a narrow size distribution does not affect either hydrodynamic structures or the transition velocity to the turbulent regime.A large difference between the work functions of the wall and particle in the bed of polyethylene particles leads to high charge transfer.Formation of a stagnant particle layer on the wall eventually causes the energy of macro-structures to increase to its maximum.At longer fluidization times,the macro-structural energy decreases and bubbles shrink until the electrostatic charge reaches the equilibrium level.These results well describe the effect of fluidization time on hydrodynamic structures.

Direct Simulation of Charge Transport in Graphene Nanoribbons

Graphene nanoribbons are considered as one of the most promising ways to design electron devices where the active area is made of graphene.In fact,graphene nanoribbons present a gap between the valence and the conduction bands as in standard semiconductors such as Si or GaAs,at variancewith large area graphenewhich is gapless,a feature that hampers a good performance of graphene field effect transistors.To use graphene nanoribbons as a semiconductor,an accurate analysis of their electron properties is needed.Here,electron transport in graphene nanoribbons is investigated by solving the semiclassical Boltzmann equation with a discontinuous Galerkin method.All the electron-phonon scattering mechanisms are included.The adopted energy band structure is that devised in[1]while according to[2]the edge effects are described as an additional scattering stemming from the Berry-Mondragon model which is valid in presence of edge disorder.With this approach a spacial 1D transport problem has been solved,even if it remains two dimensional in the wavevector space.A degradation of charge velocities,and consequently of the mobilities,is found by reducing the nanoribbon width due mainly to the edge scattering.