A subthermionic tunnel field-effect transistor with an atomically thin channel

Abstract

The fast growth of information technology has been sustained by continuous scaling down of the silicon-based metal-oxide field-effect transistor. However, such technology faces two major challenges to further scaling. First, the device electrostatics (the ability of the transistor's gate electrode to control its channel potential) are degraded when the channel length is decreased, using conventional bulk materials such as silicon as the channel. Recently, two-dimensional semiconducting materials have emerged as promising candidates to replace silicon, as they can maintain excellent device electrostatics even at much reduced channel lengths. The second, more severe, challenge is that the supply voltage can no longer be scaled down by the same factor as the transistor dimensions because of the fundamental thermionic limitation of the steepness of turn-on characteristics, or subthreshold swing. To enable scaling to continue without a power penalty, a different transistor mechanism is required to obtain subthermionic subthreshold swing, such as band-to-band tunnelling. Here we demonstrate band-to-band tunnel field-effect transistors (tunnel-FETs), based on a two-dimensional semiconductor, that exhibit steep turn-on; subthreshold swing is a minimum of 3.9 millivolts per decade and an average of 31.1 millivolts per decade for four decades of drain current at room temperature. By using highly doped germanium as the source and atomically thin molybdenum disulfide as the channel, a vertical heterostructure is built with excellent electrostatics, a strain-free heterointerface, a low tunnelling barrier, and a large tunnelling area. Our atomically thin and layered semiconducting-channel tunnel-FET (ATLAS-TFET) is the only planar architecture tunnel-FET to achieve subthermionic subthreshold swing over four decades of drain current, as recommended in ref. 17, and is also the only tunnel-FET (in any architecture) to achieve this at a low power-supply voltage of 0.1 volts. Our device is at present the thinnest-channel subthermionic transistor, and has the potential to open up new avenues for ultra-dense and low-power integrated circuits, as well as for ultra-sensitive biosensors and gas sensors.

Independent Band Modulation in 2D van der Waals Heterostructures via a Novel Device Architecture

“…In order to suppress the series resistance, recently, another self‐align method is proposed to fabricate short‐channel vdWs heterostructure device 38. It is also inefficient to modulate the band offset unless a more complicated architecture is used (e.g., dual‐gate structure24) or the gate‐control capability is drastically enhanced (e.g., by applying a thin, high‐k dielectric24 or ionic electrolyte34, 39). Moreover, in a vertically stacked 2DLM heterostructure, the energy‐band offset is mainly determined by the potential drop across the vdWs gap at the interface within the overlap region, and is difficult to be modulated directly by gate electrical field due to the screening effect associated with this vertically stacked structure.…”

Characteristics of Interlayer Tunneling Field-Effect Transistors Computed by a “DFT-Bardeen” Method

“…The Phos-Phos device shows a relatively large current, with I60 = 1.50×10 4 µA/µm and ION = 9.39×10 4 µA/µm. We emphasize that our theory ignores any modifications to the band structure of such a device due to interactions between the electrodes, and indeed these have been shown to be large for the case of Phos-Phos tunneling devices by Constantinescu et al 7 Those authors argued that a tunnel barrier consisting of one or few layers of h-BN is desirable in order to reduce the interactions between the Phos electrodes.…”

“…1 In recent years, two-dimensional (2D) layered materials have been studied both theoretically and experimentally for such devices. [2][3][4][5][6][7] We focus in this work on vertical, interlayer devices in which the tunneling occurs between 2D layers (rather than within a layer). Such devices consist of two electrodes (source and drain), surrounded by one or two gates, as pictured in Fig.…”

Magnitude of the current in 2D interlayer tunneling devices

“…11,12,13 A number of experimental efforts to produce such devices have been made, although the quality of the results considerably lag those in the G/h-BN/G system. 14,15,16 Nevertheless, it is important to consider the TMD-based devices, since they offer a wider range of operating modes with potential application in electronic circuits and systems. 17 Specifically, the TMD-based interlayer tunneling devices can be utilized for 2D-2D tunneling, just as for G/h-BN/G, and sharp resonant peaks exhibiting NDR are expected (though not yet experimentally observed).…”