Recently, for overcoming the fundamental limits of conventional silicon technology, multivalued logic (MVL) circuits based on two-dimensional (2D) materials have received significant attention for reducing the power consumption and the complexity of integrated circuits. Compared with the conventional silicon complementary metal oxide semiconductor technology, new functional heterostructures comprising 2D materials can be readily implemented, owing to their unique inherent electrical properties. Furthermore, their process integration does not pose issues of lattice mismatch at junction interfaces. This facilitates the realization of new functional logic gate circuit configurations. However, the reported three-valued NOT gates (ternary inverters) based on 2D materials require stringent operating conditions and complex fabrication processes to obtain three distinct logic states. Herein, a general structure of MVL devices based on a simple series connection of 2D materials with partial surface functionalization is demonstrated. By arranging three 2D materials exhibiting p-type, ambipolar, and n-type conductivities, ternary inverter circuits can be established based on the complementary driving between 2D heterotransistors. This ternary inverter circuit can be further improved for quaternary inverter circuits by controlling the charge neutral point of partial ambipolar 2D materials using surface functionalization, which is an effective and nondestructive doping method for 2D materials.
Keywords: 2D heterostructure; multiple-valued logic; negative differential transconductance; quaternary inverter; surface functionalization.