High-performance Ambipolar Dual-gate Transistors Based on Transition Metal Dichalcogenides for Logic Applications

Two-dimensional materials possess distinctive electrical and physical properties, providing great opportunities towards the next-generation semiconductor devices. Compared with unipolar transistors, ambipolar devices that allows both the electron and hole transport provide more flexibility in circuit applications. The potential of the ambipolar device can be maximized in a dual-gate structure, where one of the gates can tune the ambipolar transistor from p-type to n-type, or vise versa. The major benefit of these transistors is that due to the two independent gate inputs, the number of transistors needed in a circuit can be reduced. Previously, ambipolar dual-gate transistors based on low-dimensional materials such as graphene, carbon nanotube and transition metal dichalcogenides (TMD), and their application in logic gates, are demonstrated [1][2]. But the problem exists, for example, in the unsymmetric n- and p-branch transport, lack of ability to form logic gates that can be cascaded, inequivalent gate control and so on. Till now, a well-designed ambipolar transistor that can be used in cascadable, standard, non-pass-transistor logic circuits is never developed.<br/>In this work we designed and fabricated high-performance ambipolar dual-gate transistors based on TMDs and demonstrated their applications in logic circuits. Through the hBN sandwiched structure, the well-engineered contacts for both electron and hole injection, and the control of threshold voltages, for the first time, the transistors have achieved simultaneously the correct logic input and output, low contact resistance, high on-off ratio, well-balanced p- and n-branch transport, and low hysteresis. We then connected the devices and formed logic gates such as XOR, NAND, etc. All gate stages are connected between a Vdd and Vss, to prevent the problems brought by other pass transistor logics. We found that the logic input and output of these gates are stable, and they can work in the same operation voltages ranges, which means these logic gates can be cascaded. The total number of transistors are reduced, comparing with the traditional CMOS technology. Then the ability of forming more complicated logic circuits is demonstrated through a full adder. This work shows the potential of 2D material based transistors, and paves the way of using 2D based ambipolar transistors in practical application of logic circuits.<br/>References:<br/>[1] Pan, Chen, et al. Nature Electronics 3.7 (2020): 383-390.<br/>[2] Resta, Giovanni V, et al. <i>ACS nano</i> 12.7 (2018): 7039-7047.