Design Rules for High Performance Tunnel Transistors From 2-D Materials

Abstract

Tunneling field-effect transistors (TFETs) based on 2D materials are promising steep sub-threshold swing (SS) devices due to their tight gate control. There are two major methods to create the tunnel junction in these 2D TFETs: electrical and chemical doping. In this work, design guidelines for both electrically and chemically doped 2D TFETs are provided using full band atomistic quantum transport simulations in conjunction with analytic modeling. Moreover, several 2D TFETs' performance boosters such as strain, source doping, and equivalent oxide thickness (EOT) are studied. Later on, these performance boosters are analyzed within a novel figureof-merit plot (i.e. constant ON-current plot). II. INTRODUCTIONTransistor scaling has driven device designs toward thinner channels for better gate control over the channel. 2D materials can provide a shortcut to the ultimate channel thickness scaling: an atomically thin channel. A tight gate control is important in FETs to obtain a 1-to-1 band movement in the channel potential with respect to the gate voltage. The tight gate control is even more crucial for the performance of tunnel FETs (TFETs) [1], [2] since the scaling length and accordingly tunneling distance decreases with a better gate control [3], [4], [6]- [11]. The exponential dependence of the tunneling current on the tunneling distance emphasizes the role of a thin channel and tight gate control in TFETs.Some 2D materials, such as graphene or silicene suffer from the lack of a bandgap (E g ) and are not suitable for transistor applications. On the other hand, 2D materials such as transition metal dichacogenides (TMD: MoS 2 , WSe 2 , MoTe 2 , etc.) exhibit a sizable direct bandgap in their monolayer configuration. Among those, monolayer WTe 2 shows particular promise for high performance TFET applications [4] due to its rather small effective mass and an expected bandgap of about 0.75eV [15]. Note that a bandgap of about (1.1 − 1.5)qV DD provides the best performance in TFETs, where V DD is the supply voltage [12], which means that for a V DD of about 0.5V an E g range of 0.55-0.75eV is expected to provide best performance. Unfortunately, however, experiments indicate that the WTe 2 2H phase may not be stable [16].

Understanding contact gating in Schottky barrier transistors from 2D channels

“…For such a comparison in the case of back-gated Schottky barrier transistors with 2D channels, a 2D material which exhibits a prominent Schottky barrier current branch as well as a thermal branch observable above the measurement noise floor, needs to be chosen. WSe2, which is an important member of the family of two-dimensional transition metal dichalcogenides (TMDs) 18,24,[40][41][42][43][44][45] is known to satisfy these requirements 18, 46 . In order to fabricate back-gated WSe2 SB-FETs, flakes of WSe2 were micro-mechanically exfoliated on top of substrates with 90nm SiO2 thermally grown on highly doped silicon. Flakes of various thicknesses were identified by means of optical contrast after proper calibration and atomic force microscopy (AFM) in tapping mode.…”

Monolayer MoSe₂-Based Tunneling Field Effect Transistor for Ultrasensitive Strain Sensing

“…To this end, it is important to first evaluate the impact of strain on electrical characteristics of MoSe2 based TFETs. The impact of the strain on the transfer characteristics of WSe2 TFET has been briefly presented in past, without much explanation about the physics behind the strain dependence of the device performance [25]. Herein, we demonstrate that the uniaxial strain impacts the band gap as well as the effective mass of the charge carrier, resulting in the strain dependent performance of MoSe2 TFET.…”

Recent Advances in Low‐Dimensional Heterojunction‐Based Tunnel Field Effect Transistors

“…[7,133,137] The engineering is realized through a low-k dielectric sandwich by two high-k ones (Figure 9b). Similarly, it can also be improved by multidielectrics.…”

“…Besides, additional defects such as the Stone–Wales defects are also easy to be induced during the doping process . In comparisons, the electrostatic doping can overcome all these technology issues well . Besides, the p‐ and n‐type doping switching, threshold variation immunity, and bandgap dopant state elimination can also be achieved …”