Momentum-dependent field-effect transistor

Abstract

The silicon-based field-effect transistor (FET) is approaching the physical limits for the prominent short-channel effects and the sequent leakage currents under the conventional paradigm. Here, we propose a momentum-dependent field-effect transistor (MD-FET) to address this issue, in which a monolayer 2D semiconductor is sandwiched by two cross 1D carbon nanotube electrodes. The MD-FET enables a perfect off state, as the elastic tunneling is forbidden by the momentum mismatch between the cross 1D contacts. It can also access a substantial on state, because the momentum mismatch can be compensated by the electron-phonon scattering in a 2D channel. The MD-FET with sub-1-nm channel thus exhibits high on/off ratios of ~10⁷, which breaks through the theoretical limit on the short-channel effect. The MD-FET opens up a previously unknown paradigm to further scale down transistors beyond silicon and inspires a promising solution for the post-Moore era.

Fig. 1.. Concept of momentum mismatch between contacts.

(A) Spherical Fermi surface of conventional 3D contacts. Inset: The fully overlapping Fermi sphere of drain and source. (B) Elastic tunneling between 3D contacts. (C) Dirac cones of 2D graphene contacts. The red curves represent the overlapped regimes between two pieces of graphene. (D) Elastic tunneling between 2D contacts. (E) Band structure of 1D metallic contacts. (F) Forbidden elastic tunneling between 1D contacts.

Fig. 2.. Schematic illustration and transport characteristics of MD-FET.

(A) Band structures of semimetallic CNTs according to the zone-folding approximation (red curves). (B) Momentum mismatch of two 90° cross semimetallic CNTs in momentum space. (C) Schematic illustration of MD-FETs with a sub–1-nm WS₂ channel. (D) Typical transfer characteristics of MD-FET and graphene-CNT VFET. (E) Typical output characteristics MD-FET. Inset: False color scanning electron microscopy (SEM) image of the MD-FET structure. Scale bar, 10 μm. The white dashed lines represent CNT contacts.

Fig. 3.. Temperature-dependent transistor characteristics.

(A) Schematic illustration of electron-phonon scattering within WS₂ including phonon absorption and phonon emission. (B) Output characteristics of MD-FET at various temperatures. V_g = 12 V to turn on the MD-FET. (C) I-T characteristics under various biases (0.02 to 0.1 V, with steps of 20 mV). (D) Phonon dispersion of monolayer WS₂ calculated by DFT. (E) Ratios of the currents due to phonon absorption and emission to the total current. The left axis for phonon absorption and the right for phonon emission. (F) Arrhenius plots of the planar FET at various V_g. Considering the longer channel, a V_d of 1 V is applied to ensure the similar on-state current with MD-FET. (G) Arrhenius plots of the MD-FET at various V_g under a V_d of 0.1 V. (H) The gate-dependent barrier height extracted by the thermionic emission. Inset: Schematic illustration of planar FET and MD-FET.

Fig. 4.. MD-FETs’ capability to enhance the switching performance for various 2D semiconductors.

(A) Typical I_ds-V_g curves of WS₂ MD-FET with V_d changes from 1 mV to 1 V. (B) Typical I_ds-V_g curves of MoS₂ MD-FET with V_d changes from 1 mV to 1 V. (C) Switching performance comparison with recent reports (, , , , , , –46). The red background regime represents the high switching performances of MD-FETs. Details and data can be found in table S2.