Abstract
Two-dimensional molybdenum disulfide (MoS2) has substantial potential as a semiconducting material for devices. However, it is commonly prepared by mechanical exfoliation, which limits flake size to only a few micrometers, which is not sufficient for processes such as photolithography and circuit patterning. Chemical vapor deposition (CVD) has thus become a mainstream fabrication technique to achieve large-area MoS2. However, reports of conventional photolithographic patterning of large-area 2D MoS2-based devices with high mobilities and low switching voltages are rare. Here we fabricate CVD-grown large-area MoS2 field-effect transistors (FETs) by photolithography and demonstrate their potential as switching and driving FETs for pixels in analog organic light-emitting diode (OLED) displays. We spin-coat an ultrathin hydrophobic polystyrene layer on an Al2O3 dielectric, so that the uniformity of threshold voltage (Vth) of the FETs might be improved. Our MoS2 FETs show a high linear mobility of approximately 10 cm2 V−1 s−1, due to a large grain size around 60 μm, and a high ON/OFF current ratio of 108. Dynamic switching of blue and green OLED pixels is shown at ~5 V, demonstrating their application potential.
Highlights
Since 2D MoS2 obtained by mechanical exfoliation limits the length scale only to a few micrometers, researchers have studied on how to fabricate such 2D MoS2 in a large scale,[15,16,17,18,19,20] which would open the gate toward more practical applications enabling conventional photolithographic device/circuit patterning
For the Chemical vapor deposition (CVD) growth, we used a single precursor source consisting of MoS2 powder at a high growth temperature ~800 °C with a temperature of 900 °C for the powder precursor,[33] instead of the combination of MoO3 and S, which is more often reportedly used.[15,16,17]
To assess the quality of the MoS2 monolayer films,[37,38,39] we plot in Fig. 1e the full width at half maximum (FWHM) of the E12g and A1g Raman peaks for the material grown on the various thicknesses of SiO2
Summary
Molybdenum disulfide (MoS2), a two-dimensional (2D) transition metal dichalcogenide (TMD) semiconductor has attracted much attention from many researchers owing to its interesting physical properties and potentials for future nanoscale electronics.[1,2,3,4] Like graphene, those 2D semiconductors are formed by mechanical exfoliation using scotch tapes in general, while it displays high ON/OFF current ratio and good subthreshold swing in a field-effect transistor (FET) form with n-type conduction unlike graphene, which shows no bandgap.[5,6,7,8,9,10,11,12,13,14] Since 2D MoS2 obtained by mechanical exfoliation limits the length scale only to a few micrometers, researchers have studied on how to fabricate such 2D MoS2 in a large scale,[15,16,17,18,19,20] which would open the gate toward more practical applications enabling conventional photolithographic device/circuit patterning. Many of success on largescale MoS2 monolayer sheets have been reported.[21,22,23] Yet, reports on conventional photolithographic patterning for large-scale 2D MoS2-based devices with decently high mobilities are still rare,[24,25,26] to the best of our limited knowledge. We have fabricated CVD-grown large-scale MoS2 FETs with patterned bottom gate and investigated their applications toward analog OLED pixel as low voltage switching and high current driving FETs. In particular, we successfully spincoated an ultrathin hydrophobic polystyrene (PS) polymer layer on Al2O3 dielectric before the CVD MoS2 monolayer was transferred onto the gate-patterned Al2O3 on glass, so that the uniformity of threshold voltage (Vth) of FETs might be improved. Dynamic/static switchings of blue and green OLED pixels were nicely demonstrated using the CVD monolayer MoS2 FETs
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