A novel analytical approach to optimize the work functions of dual-material double-gate Tunneling-FETs

Abstract

In this paper, we have developed a novel technique for optimizing the work functions of a dual-material double-gate tunnel field effect transistor using analytical models. For this purpose, at first, the surface potential equation in the channel is obtained using a 2D solution of the Poissonʼs equation with suitable boundary conditions. The analytical models of the surface electric field and energy bands which are required for the optimization procedure are derived from the surface potential expression. Then, the optimum value of the work function for the material of the gate closer to the source is formulated in terms of device physical parameters including the work function of the other material of the gate. The formula is derived based on the fact that the optimal work function is the value which leads to the alignment of the channel conduction band and the valence band of the source in the OFF-state mode. Therefore the tunneling at this junction will be started for the positive values of the gate voltage. Next, the work function for the other material of the gate that is near to the drain is optimized through the proper goal function. This goal function is defined based on the value of the surface electric field in the ON and ambipolar states at source/channel and channel/drain interfaces respectively. Finally, the validation of the proposed method to select the optimal values of the work function for both gate materials has been confirmed by the TCAD simulation results.