Multiphysics Nanodevice Modeling

Figure 1 (Top) Schematic of feedback controlled carbon-nanotube based NEMS switch; (Bottom) Equivalent Circuit of NEMS switch.

This project focuses on the exploration of numerical simulation of nanoscale electronic device, such as carbon nanotube (CNT) and nanowire-based nanoelectromechanical systems (NEMS) shown in Figure 1. Electromechanical static and dynamic finite element methods are used to simulate the performance of nanoscale electronic devices using the commercial FEM code, ABAQUS. The models are based on equations governing the electrostatic and mechanical device response. We have used first order approximations leading to the following equations:







 

In the static FEM model, user-defined subroutines are employed to account for van der Waals and electrostatic interactions between a carbon nanotube and the bottom electrode. The static FEM model predicts important device parameters, such as pull-in voltage, which agree well with analytically derived solutions.

 

To analyze the dynamic behavior of the CNT-based devices and to explain the experimentally-observed failure modes, we employ both analytical and finite element methods. Based on the above analytical model, we develop subroutines within the ABAQUS/explicit solver to simulate the dynamic response of the nanodevice during pull-in. In this way, detailed information about stress distribution, wave propagation, current and temperature transients can be obtained. The simulations are then validated through comparisons with experiments, allowing for the development of failure maps. Figure 2 shows the stress distribution on the CNT during pull-in, an animation of a sudden temperature increase at the CNT tip during discharge (electrical breakdown when CNT getting close to the bottom electrode), and the evolution of the current through the CNT.

 

Figure 2 Simulation of electro-mechanical coupling in a NEMS switch. (Top) Evolution of stress on CNT during pull-in (unit = 1MPa) (inset shows cross-section shape changing during pull-in); (Middle) Animation showing sudden temperature increase at CNT tip during electrical discharge; (Bottom) Evolution of current through CNT (inset shows detail of discharge current peak within 5 picoseconds).

 

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