Hysteresis‐Free Hexagonal Boron Nitride Encapsulated 2D Semiconductor Transistors, NMOS and CMOS Inverters

Abstract

The next generation of semiconductors for electronics requires materials beyond silicon with increased functionality, performance, and scaling in integrated circuits. [1] Among nanomaterials, 2D semiconducting transition metal dichalcogenides (TMDCs) have becoming promising candidates due to their atomic thickness and nonzero bandgap. [2] As 2D metal-oxide-semiconductor field-effect transistors (MOSFETs) may be scaled down to atomic channel lengths due to the excellent electrostatic integrity and ability to suppress sourcedrain tunneling, [3] great strides and accomplishments have been achieved in TMDC-based electronics, such as the integration of 2D transistors into digital complementary metal-oxide semiconductor (CMOS) and flexible electronics. [4] However, the viability of 2D electronics remains under debate, as the electronic transport in 2D materials exhibits a large hysteresis (or the dependence of the system's state on its history). This is unavoidable and ubiquitous in 2D materials due to the large surface-to-volume ratio (i.e., surface effects are much more pronounced compared to 3D bulk solids). [5] For example, a 2D channel may have more than one possible conductivity at a given gate voltage, depending on how the gate voltage varied through the device history. This history dependence is the basis of 2D memory [6] but clearly undesirable for 2D FETs and related electronic devices that require consistent conductivities at given gate voltages. [7] While MoS 2 n-type metal-oxide semiconductor (NMOS) and MoS 2 -WSe 2 CMOS inverters also have been reported in the literature, [8] there have rarely been reports of hysteresis-free 2D circuitry, a necessary property in electronic reliability. [8c,9] Encapsulation with the van der Waals (vdWs) dielectric, hexagonal boron nitride (hBN), has proven to provide excellent protection of 2D semiconductors from environmental factors. By isolating the semiconductor from the ambient environment, device performance becomes highly stable even at elevated temperatures necessary for future device operation. [10] Using recently developed techniques for mechanically assembling vdWs heterostructures layer-by-layer and electrically edge-contacting graphite electrodes, [11] we fabricated hBN encapsulated high-performance 2D semiconductor transistors, NMOS and Graphene and subsequently discovered layered semiconducting transition metal dichalcogenides (TMDCs) exhibit numerous exotic physical properties and broad potential device applications. These 2D semiconducting TMDCs have become particularly interesting in next-generation electronic device applications due to their atomic thickness and nonzero bandgap. However, as there is no bulk volume, the 2D nature makes the electronic transport in these crystals highly sensitive to the environmental conditions, such as humidity, adsorbates, and trapped charges in neighboring dielectrics. Due to this environmental sensitivity, 2D-based circuits and devices suffer from a large and undesirable environment-induced hysteresis, which must ...

Building Functional Memories and Logic Circuits with 2D Boron Nitride

“…[ 216 ] For logical devices, 2D van der Waal heterostructures require hysteresis‐free static transfer characteristics by optimized heterostructure configuration. [ 217–219 ] The transistor‐based memories are activated by the injection of electrons rather than ion movements, allowing for high operating rate. The gate electrode allows simultaneous reading and writing process, which has potentials in parallel computing.…”

“…One was based on n‐type metal–oxide semiconductor (BN/graphite/MoS 2 /BN van der Waal heterostructures), and the other was complementary metal–oxide semiconductor (BN/graphite/WSe 2 /BN van der Waal heterostructures) inverters. [ 219 ] The graphite parallel strips were perpendicular to the TMDs channel layer. The top h‐BN encapsulation layer protected the environmentally sensitive n‐MoS 2 and p‐WSe 2 layers, which remained stable down to a few layers.…”

Theoretical approach to point defects in a single transition metal dichalcogenide monolayer: conductance and force calculations in MoS 2

“…But in a second time, the discovery of graphene has also shed light on a whole world of new bidimensional materials. For example, hexagonal boron nitride (hBN) as the graphene counterpart made of boron and nitrogen is widely used due to its widegap and its encapsulation properties [5,6]. Also we have seen the emergence of the great family of transition metal dichalcogenides (TMDC), made of a transition metal layer sandwiched in between two chalcogen atom layers, and presenting several different properties [7][8][9][10].…”

Seamless Fabrication and Threshold Engineering in Monolayer MoS2 Dual‐Gated Transistors via Hydrogen Silsesquioxane

“…However, monolayer semiconducting TMDCs offer a finite bandgap but suffer from relatively low carrier mobility . While the mobility is not important for aggressively scaled devices operating near the ballistic limit, multiple mobility enhancement strategies do exist for TMDCs, which include sandwiching the TMDC layer between layers of insulating hexagonal boron nitride (h‐BN) or a high‐ k dielectric material to protect it from scattering by charged impurities in the SiO 2 . The bandgaps of monolayer TMDCs are rather large, in the range of ≈1.5–2.0 eV, which poses a significant challenge for making low resistance contacts .…”