Study of subthreshold behavior of FinFET

The study of subthreshold behavior of Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is critically important in the case of submicron devices for the successful design and implementation of digital circuits. Fin Field Effect Transistor (FinFET) is considered to be an alternate MOSFET structure in the deep sub-micron regime. A 3D Poisson equation solver is employed to study the subthreshold behavior of FinFET. Based on potential distribution inside the fin, the appropriate band bending and the subthreshold value called the S-factor is calculated. It is observed that the S-factor of the device increases as the channel width, T_fin increases. This is attributed to the fact that the change in the band bending is less than the change in the applied gate voltage. This is only a first order analysis; hence the device is simulated in a device simulator Taurus. It is observed that the S-factor increases exponentially for channel lengths L_g < 1.5T_fin. Further, for a constant L_g, the S factor is observed to increase as T_fin increases. An empirical relationship between S, L_g and T_fin is developed based on the simulation results, which can be used as a rule of thumb for determining the S-factor of devices.