Multiscale contact resistance and device modelling

In order to effectively understand and improve device functionality it is important to have a theoretical support for the experimental measurements. The complexity of the PETMEM device requires a full multiscale modelling approach, which goes from atomic scale simulations to finite elements modelling, and includes the development of effective analytical models. In order to evaluate the contact resistance between metal and piezoresist, an atomistic model is used which allows us to investigate the fundamental charge transport behaviour across the metal/piezoresist interface, and its dependence on strain. We use density functional theory (DFT) combined with the non-equilibrium Green’s function technique to this aim, as implemented in the Smeagol electron transport code [A. R. Rocha et al., Phys. Rev. B. 73, 085414 (2006); I. Rungger and S. Sanvito, Phys. Rev. B 78, 035407 (2008)]. Methodological and software developments are required to properly treat the SmS/metal interface, which allow to appropriately describe the strong correlations and strong spin-orbit interaction in the SmS. A thermodynamically consistent analytical model of charge transport within a layered material whose resistance varies from layer to layer is required to effectively model the whole device, and the results of the atomistic model will eventually inform the parameters used in the analytical model.

 

Finite elements (FE) simulations are the ideal tool to predict and characterize device performance of the entire PETMEM device stack. These allow us to explore the sensitivity of the device to some of the key geometric parameters of the structure (as shown in figure below), so that such simulations provide guidance on device design for experimental realization. The results of these simulations will therefore inform design decisions made during fabrication.

Bringing FE setup close to experimental realization and investigating the effect of variation in device parameters.
Bringing FE setup close to experimental realization and investigating the effect of variation in device parameters.