## 1 Introduction  
Decreasing the critical metal-oxide-semiconductor field effect transistor (MOSFET) dimensions up to the nanometer-scale induces the increasing of the defect influence on carrier mobility, subthreshold swing, and threshold voltage. It also stimulates both instability and degradation of the transistor in active mode. Depending on certain conditions and the type of measurements, the instability may be responsible for bias temperature instability (BTI), random telegraph noise (RTN), and a hysteresis of characteristics [1]. Especially amongst these effects, a single interface or oxide defect on the drain current can be noticed. These single charged traps can induce instability in the operation of the transistor [2], generate RTN in the MOSFET and affect both stability and reliability of MOSFET-based circuits [3; 4]. On the other hand, RTN can be used as a tool for analyzing and exploring the defect behavior of the oxide-semiconductor interface of the MOSFET [5; 6].  
Therefore, it is very important to investigate a single interface or the influence of an oxide charged trap on the characteristics of the MOSFET. One of the reliable simulation methods for studying such defects is the so-called atomistic approach [7]. However, this technique requires a magnificent effort in computation (in terms of time and memory), particularly while simulating integrated circuits on a MOSFET basis. Therefore, the development of a simple physical model of the single-trapped charge useable in commercial widely used Technology Computer Added Design (TCAD) programs is an important task from the point of view of significantly reducing the computational time required for these types of simulation studies. The model should properly describe the processes related to the trapped charge influence on the charge transfer processes in these devices. The TCAD Sentaurus provides the opportunity of simulating the charge trapping in the oxide layer or at the interface in MOSFET (model of traps and fixed charges). However, to fully describe the trapped charge, a clear specification of both the boundary conditions and the density of charge is required. In the literature, usually, the single trapped charge is modeled as simple cell with appropriate boundary conditions [2, 8]. However, there is no experimental research work indicating clear criteria for defining appropriate and specific sizes of the cell describing the single trapped charge. The sizes presented in various works differ by several orders of magnitude. Besides, to the best of our knowledge, no research has been carried out addressing the dependency and correlation between the single charge effect, the size and shape of the charged area. Therefore, in this work, the effect of a simple cell model is compared with other proposed models of single trapped charge with appropriate (i.e., using suitable) boundary conditions. The single trapped charge effect/ dependency on the size of the charged area are estimated. One of the important effects of the single trapped charge is generation of the Random Telegraph Noise. Therefore, the RTN amplitude dependency on the size and shape of the charged area is considered.  
The influence of a single trapped charge on the noise characteristics has been widely investigated for the planar MOSFETs [9, 10, 11, 12] and FinFETs [13, 14], while very few works were devoted to investigating the RTN amplitude in the relatively new Junctionless FinFET [15, 16]. Thus, the influence of both shape and size of the single trapped charge to noise characteristics of nanometer Junctionless FinFET is closely studied in this paper.