Dielectric pocket Ge-source Double Gate Junctionless MOSFET with improved OFF-current and subthreshold characteristics

The concept of Dielectric Pocket (DP) in Ge-source Double Gate Junctionless MOSFET (DG JLMOSFET) is proposed to suppress the Short Channel Effects (SCEs) and provide better O_FF current characteristics. The use of Dielectric Pocket at the source and drain ends suppress the entrance of lateral electric field and diffusion of carriers from source/drain into channel and improves I_ON/I_OFF current ratio for optimum performance of the device. This results in significant reduction in SCEs and O_FF current. The switching speed of Ge-source DG JLMoSFET is investigated for different length and thickness of Dielectric Pocket. It is seeing that the Switching speed improves as the length and thickness of Dielectric Pocket is increased. On comparison with conventional MOSFET (without Dielectric Pocket), it is observed that the proposed structure gives better performance. Thus DP Ge-source DG JLMOSFET is useful in the design of Low Power VLSI circuits.

I. Introduction

The scaling down of MOSFET devices in integrated circuits into nanoscale regime increases the Short Channel Effects (SCEs) [1]–[3]. Leakage current occurs because of SCEs dissipates more power in the device and reduces switching speed of MOSFET device [4], [5]. SCEs cannot be reduced in convention MOSFET. Hence, Multigate technologies are used like Surrounded gate MOSFET, Double Gate MOSFET and FinFET. Multigate MOSFET have better gate controllability on channel region. Due to these technologies channel length can be reduced without causing power loss in the devices [6]. The challenges of Ultra sharp doping between source and drain region which occurs in multigate MOSFET can be overcome by using a Junctionless transistors (JLTs) and high mobility materials which resulting better scalability [4]–[6]. A short channel Junctionless transistor needed large gate work function to work in OFF-state [7]. Good thermal stabilization and good adhesion is obtained by gate metals with large work function [8]. However, transistor Off-state leakage limit the MOSFET energy efficiency [9]. Therefore, a MOSFET with lower off current is designed that provide better subthreshold swing (SS) and On state current. In this paper, we have modelled a Dielectric Pocket double gate Junctionless MOSFET using Ge-Source with High-K spacer. However, current in the MOSFET depends on electrons and holes mobility. Hence, use of Germanium as source material generate the highest ON/OFF current ratio at low operation gate voltage (Vgs) [10]–[12]. because Germanium has low band gap (0.732eV) and high mobility (3800 cm2/V/s) which gives better transfer characteristics of MOSFET. The use of Germanium has more leakage in comparison to silicon. Hence, to overcome this problem high-k dielectric material HfO₂ is used as spacer which enhance analog and RF performances [11]. Pocket implantation is done to protect the electric field penetration from source to drain region. Therefore, the dielectric pocket (DP) MOSFET is used because of it's superior capability of suppressing the Short Channel Effects and provide better subthreshold transfer characteristics over the conventional DG (without DP) [13]. Ge-source MOSFET with DP gives better results in comparison with Ge-source MOSFET (without DP). Reduction of charge sharing between source and drain by using DP at the side wall of source and drain decrease the SCEs and leakage current [13], [14]. The scope of this paper involves the study of various parameters such as ON current , OFF current I, subthreshold swing (SS) and threshold voltage using transfer characteristics of Dielectric Pocket Ge-source DG JL MOSFET. And simulations have been done using Sentaurus TCAD [15].