An efficient way to reduce the power consumption of electronic devices is to lower the supply voltage, but this voltage is restricted by the thermionic limit of subthreshold swing (SS), 60 millivolts per decade, in field-effect transistors (FETs). We show that a graphene Dirac source (DS) with a much narrower electron density distribution around the Fermi level than that of conventional FETs can lower SS. A DS-FET with a carbon nanotube channel provided an average SS of 40 millivolts per decade over four decades of current at room temperature and high device current of up to 40 microamperes per micrometer at 60 millivolts per decade. When compared with state-of-the-art silicon 14-nanometer node FETs, a similar on-state current is realized but at a much lower supply voltage of 0.5 volts (versus 0.7 volts for silicon) and a much steeper SS below 35 millivolts per decade in the off-state.
An increase in power consumption necessitates a low-power circuit technology to extend Moore’s law. Low-power transistors, such as tunnel field-effect transistors (TFETs), negative-capacitance field-effect transistors (NC-FETs), and Dirac-source field-effect transistors (DS-FETs), have been realised to break the thermionic limit of the subthreshold swing (SS). However, a low-power rectifier, able to overcome the thermionic limit of an ideality factor (η) of 1 at room temperature, has not been proposed yet. In this study, we have realised a DS diode based on graphene/MoS2/graphite van der Waals heterostructures, which exhibits a steep-slope characteristic curve, by exploiting the linear density of states (DOSs) of graphene. For the developed DS diode, we obtained η < 1 for more than four decades of drain current (ηave_4dec < 1) with a minimum value of 0.8, and a rectifying ratio exceeding 108. The realisation of a DS diode represents an additional step towards the development of low-power electronic circuits.
The generation and manipulation of spin-polarized current are critical for spintronic devices. In this work, we propose a mechanism to generate and switch spin-polarized current by an electric field in multiferroic tunnel junctions (MFTJs), with symmetric interface terminations in an antiparallel magnetic state. In such devices, different spin tunneling barriers are realized by the magnetoelectric coupling effect, resulting in a spin-polarized current. By reversing the electric polarization of the ferroelectric layer, the spin polarization of current is efficiently switched for the exchange of spin tunneling barriers. By first-principles quantum transport calculations, we show that a highly spin-polarized current is obtained and manipulated by the electric field in hafnia-based MFTJs based on the proposed mechanism. We also demonstrate that four resistance states are realized in Co/HfO2/Co junctions with asymmetric interface terminations. This work provides a promising approach for realizing the electrical control of spin current for spintronic applications.
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