Demonstration, analysis, and device design considerations for independent DG MOSFETs

This paper describes a comprehensive study on the threshold voltage (V_th) controllability of four-terminal-driven double-gate (DG) MOSFETs (4T-XMOSFETs) with independently switched DGs. Two types of 4T-XMOSFETs (fin and vertical) are experimentally demonstrated and their V_th controllability is thoroughly investigated in relation to the initial V_th in the DG-mode based on comprehensible modeling of the devices. Based on the investigation and simulated predictions, device design guidelines for 4T-XMOSFETs are proposed. Decreasing the workfunction of the DGs and increasing the oxide thickness of the second gate (T_ox2) are preferable for improving the performance of the 4T-XMOSFET. The optimum workfunction of DGs for attaining low I_{off(stand-by)} and high I_on(active) under the limited V_g2 condition is also proposed.