Reproducible Performance Improvements to Monolayer MoS₂ Transistors through Exposed Material Forming Gas Annealing

Abstract

Metal-mediated exfoliation has been demonstrated as a promising approach for obtaining largearea flakes of 2D materials to fabricate prototypical nanoelectronics. However, several processing challenges related to organic contamination at the interfaces of the 2D material and the gate oxide must be overcome to realize robust devices with high yield. Here, we demonstrate an optimized process to realize high-performance field-effect transistor (FET) arrays from largearea (» 5000 μm 2 ) monolayer MoS2 with a yield of 85 %. A central element of this process is an exposed material forming gas anneal (EM-FGA) that results in uniform FET performance metrics (i.e., field-effect mobilities, threshold voltages, and contact performance). Complementary analytical measurements show that the EM-FGA process reduces deleterious channel doping effects by decreasing organic contamination, while also reducing the prevalence of insulating molybdenum oxide, effectively improving the MoS2-gate oxide interface. The uniform FET performance metrics and high device yield achieved by applying the EM-FGA technique on large-area 2D material flakes will help advance the fabrication of complex 2D nanoelectronics devices and demonstrates the need for improved engineering of the 2D materialgate oxide interface.

Can Metals Other than Au be Used for Large Area Exfoliation of MoS2 Monolayers?

“…The ML flake dimensions, determined optically, had an average lateral dimension of 47.13 ± 3.23 µm, although some flakes are hundreds of microns in size (see Figure S1a, Supporting Information). Despite Pd/MoS 2 having been predicted to have 5× less strain [ 24,27 ] than Au/MoS 2 , Pd exfoliation yields results comparable or better than Au reported in literature, [ 10,30,31 ] suggesting that strain may not be the leading cause in the successful metal exfoliation of large‐area ML MoS 2 . If uniform strain was the determining factor in exfoliation, then we would not be able to use Pd to exfoliate large‐area ML MoS 2 as Pd/MoS 2 has negligible predicted strain.…”

Rapid, quantitative therapeutic screening for Alzheimer's enzymes enabled by optimal signal transduction with transistors

“…A detailed description of the device fabrication process and monolayer characterization for dual-gate 2D field-effect transistors (dg2DFETs) was provided in our previous work. 8,13,20 Briefly, monolayer MoS2 was first transferred onto an oxidized Si substrate (SiO2 with a thickness of 70 nm) by using a gold-mediated exfoliation technique. 21 The thickness of the transferred material was confirmed with Raman spectroscopy.…”

“…21 The thickness of the transferred material was confirmed with Raman spectroscopy. 13 Optical lithography was used to first pattern the source (S) and drain (D) contacts followed by electronbeam metal deposition (80 nm Au on 2 nm Ti) and lift-off in acetone. A second optical lithography step was then used to define and etch a 5 μm ´ 5 μm channel for each FET.…”

“…The devices were then annealed under forming gas (5 % H2, 95 % Ar) for 24 hours to minimize organic contamination and improve the contact resistance. 13 This was immediately followed by the atomic layer deposition (ALD) of a 20 nm top-gate (TG) Al2O3 dielectric. Finally, another optical lithography step was used to pattern the top-gate metal, followed by electron-beam metal deposition (100 nm Au on 10 nm Ti) and lift-off in acetone.…”

“…More recently, the emergence of 2D semi-conducting materials has resulted in new FET-based chemical sensors, 11,12 and novel device geometries such as dual-gate FETs, which provide »100-fold higher sensitivity than silicon devices, while simultaneously improving the signal-to-noise ratio (SNR) of the measurements. 8,13 The sensitivity and resolution of pH measurements are important metrics of device function and are used, in particular, to validate the performance of new FET structures and designs. 8,14,15 Traditional ion sensitive field-effect transistors (ISFET) technology has been optimized to return a pH sensitivity that approaches the Nernst value of 59.5 mV when the solution pH changes by 1 at room temperature.…”