Charge transport modelling in silicon ultra-scaled devices with native oxide (SINOXI)

在接近最终的硅技术缩放极限时，有源沟道和氧化物之间的界面严重影响电荷传输特性：它决定了波函数限制，从而决定了有源沟道的电子和介电特性;它通过界面粗糙度和介电无序引入弹性散射，并有助于屏蔽远程库仑散射。然而，在器件建模中适当地包含原生氧化物是一个公开的挑战。经验紧束缚方法，超尺度原子器件建模的一个非常流行的选择，不能很容易地解释在界面处的化学无序和通道的介电性质的尺寸效应。另一方面，完全从头算方法在计算上太昂贵，因此它们在全器件建模中的应用到目前为止仅限于概念证明。在所有的情况下，输运形式主义的非平衡绿色函数（NEGF）方法的框架内开发。该提案的目的是通过明确包括栅极氧化物和电子-声子相互作用，推进超尺寸硅基场效应晶体管的量子原子建模，以实现电流-电压（I-V）特性的定量准确预测。该项目的目标是双重的：技术和方法。技术上，由于氧化物界面的包含和不同散射机制的作用的阐明将在这种系统的设计和工程中是极其重要的。在方法上，为了实现这一目标，我们将进一步推进NEGF模拟方案，再加上基于密度泛函的紧束缚（DFTB）哈密顿量;在这样做的过程中，我们将尝试克服经验紧束缚方法的一些局限性，同时保持合理的计算成本。事实上，我们最近证明了NEGF-DFTB方法在计算上是可行的，并且可以准确描述硅-氧化物界面。方法学上的改进将具有足够的普遍性，可以与从头算方法相结合，并适用于不同的材料和技术。

In approaching the ultimate silicon technology scaling limits, the interface between the active channel and the oxide affects critically the charge transport properties: it determines the wave function confinement, thus the electronic and dielectric properties of the active channel; it introduc-es elastic scattering by means of interface roughness and dielectric disorder and it contributes to the screening of remote Coulomb scattering. Nevertheless a proper inclusion of native oxide in device modeling is an open challenge. The Empirical Tight Binding method, a very popular choice for ultra-scaled atomistic device modeling, cannot easily account for the chemical disorder at the interface and for size effects in dielectric properties of the channel. On the other hand, fully ab-initio methods are computationally too expensive and therefore their application in full device modeling is so far limited to proofs of concept. In all cases, the transport formalism is developed in the framework of Non Equilibrium Green Function (NEGF) method. The aim of this proposal is to advance the quantum atomistic modeling of ultra-scaled silicon based field effect transistors towards a quantitatively accurate prediction of current-voltage (I-V) characteristics by including explicitly the gate oxide and electron-phonon interactions. The goal of the project is dual: technological and methodological. Technological, as the inclusion of the oxide interface and the elucidation of the role of different scattering mechanism will be of utmost im-portance in the design and engineering of such systems. Methodological, as in order to achieve this goal we will further advance the NEGF simulation scheme coupled with a Density Functional based Tight Binding (DFTB) Hamiltonian; in doing so we will try overcome some of the limitations of Empirical Tight Binding methods maintaining at the same time a reasonable computational cost. In fact, we recently demonstrated that the NEGF-DFTB method is computationally feasible and allows for an accurate description of the silicon-oxide interface. The methodological improvements will be general enough to be combined with ab-initio methods and to be applied to different materi-als and technologies.