Ambipolar Charge Transport in Two-Dimensional WS₂ Metal–Insulator–Semiconductor and Metal–Insulator–Semiconductor Field-Effect Transistors

Abstract

Two-dimensional (2D) materials with ambipolar transport characteristics have attracted considerable attention as post-complementary metal−oxide semiconductor (CMOS) materials. These materials allow for electron-or hole-dominant conduction to be achieved in a single channel of the field-effect transistors (FETs) without an extrinsic doping. In this study, all-2D metal−insulator−semiconductor (MIS)-based devices, which were composed of all-2D graphene, hexagonal boron nitride, and WS 2 , exhibited ambipolar and symmetrical transport characteristics with a low surface state density (D it, min ≈ 7 × 10 11 cm −2 •eV −1 ). Hole-or electron-dominant inversion under the influence of electrostatic doping was obtained in a WS 2 -based 2D capacitor up to a frequency range of 1 MHz. n-and p-channel conductions with enhancement-mode operations were selectively realized in a single MISFET, which presented a current on/off ratio of >10 6 and high field-effect mobility (μ e = 58−67 cm 2 /V•s and μ h = 19−30 cm 2 /V•s). Furthermore, a monolithic CMOS-like logic inverter, which employed a single WS 2 flake, exhibited a high gain of 78. These results can be used to reduce the footprints of the device architectures and simplify the device fabrication processes of nextgeneration CMOS integrated circuits.

Thermal stability of monolayer WS2 in BEOL conditions

“…Indeed, some examples of WS2-based devices fabricated in typical CMOS BEOL conditions have already been reported: Yang and co-workers [34] have demonstrated a WS2-based alloptical modulator fully integrated with typical CMOS Si3N4 waveguides to modulate a 532 nm pump light source. Moreover, a fully CMOS-compatible graphene-hBN-WS2 metal-insulator-semiconductor transistor showing ambipolar behaviour has also been recently reported [35]. These early results confirm that the optimization of WS2-Si chips can be boosted by employing already-optimized CMOS BEOL fabrication steps, rather than implementing a completely new protocol.…”

“…Similarly to graphene, TMDs can be monolithically integrated with well-established CMOS BEOL [28]. Indeed, TMDs-Si chips have already been reported for a number of applications [29,[31][32][33][34][35]. This compatibility gives to TMDs a great advantage in terms of process optimization and cost reductions with respect to other "beyond-CMOS" candidates, such as III-V semiconductors or Ge, in which indirect integration with Si chips is much more challenging [36].…”

Ambipolar 2D Semiconductors and Emerging Device Applications

“…Through the above circuit structure engineering, many efforts were made to fabricate CMOS-like circuits with ambipolar 2D semiconductors. [267] Using graphene as the channel material and 300 nm thick SiO 2 as dielectric, Traversi et al demonstrated an inverter but the operating voltage was a little high (10 V) and the voltage gain was very low (only 0.044). [268] Li et al further improved the circuits with aluminum film as top gate, where the natural passivation layer between the graphene and aluminum served as dielectric.…”

Reconfigurable Multifunctional Ambipolar Polymer‐Blend Transistors with Improved Switching‐Off Capability

“…Complementary metal-oxide semiconductors (CMOS) logic circuits lay the foundation of modern electronics, where both p-type (hole transport) and n-type (electron transport) conjugated-polymers, in which both holes and electrons are allowed to transport, [18][19][20][21][22][23][24][25] are employed to fabricate ambipolar transistors with multiple operations to simplify the fabrication process of CMOS-like logics and miniaturize the integrated circuits. [19] Moreover, ambipolar transistors are more favorable for building reconfigurable electronics and endowing the circuits with multi-functionalities.…”