2D MoSe₂ Transistor with Polymer‐Brush/Channel Interface

Abstract

depletion mode in general, that is to say, threshold voltage (V th ) is located quite away from 0 V whether the channel is nor p-type. [1,11,13,18,[22][23][24] This means that practical switching is not easy without applying high voltages; distinct OFF state is sometimes desperate in any smart functional/electrical applications involving either driving or sensing. [13,22,25,26] Second, gate bias induced hysteresis of 2D TMD transistor is, in fact, quite a critical issue for realizing prototype sensor applications because consistent dynamic property of real circuits should be secured both in ON and OFF states. [27][28][29][30] Several reports disclose that the electrical stability of the devices is significantly improved by the interface and surface states of the FET devices. [28,29,[31][32][33][34][35][36] For a good candidate to minimize the interfacial defect states in FET, the hexagonal boron nitride (h-BN), dangling-bond free dielectric layer, has been proposed. [37] Although this approach has been encouraging, h-BN is still expensive and less practical due to its special growth processes for good crystalline quality control. Hence, alternatives to replace h-BN have been suggested: self-assembled monolayer and hydrophobic organic insulating materials. [32,38] We have here chosen an ultrathin organic layer for two n-type TMD FETs: (8.46 nm) polystyrene (PS)-brush poly mer layer which is tethered by chlorosilane end group onto the oxide dielectric. The two TMD devices are n-MoS 2 and n-MoSe 2 FETs as a current driver, to be integrated into low-voltage organic P(VDF-TrFE) piezoelectric sensor circuit with organic light-emitting diode (OLED) indicator. The polymer PS-brush allows a hydrophobic, covalently bonded, ultrathin, and adherent layer directly on hydrophilic SiO 2 or Al 2 O 3 layer, providing hydroxyl group-minimized interface between TMD and dielectric layer. [39][40][41] To the best of our limited knowledge, PSbrush has never been reported for the TMD-based FETs while it is very robust as a conventional organic solvent. It is regarded that a standard lithography and lift-off process can be allowed. As a result, our TMD FETs with PS-brush show minimum hysteresis, but still display depletion mode behavior (V th was still larger than 0 V). Fortunately, the V th of n-MoSe 2 FET appears closer to 0 V than that of n-MoS 2 FETs, and its mobility could increase up to ≈11 cm 2 V −1 s −1 with electron doping by atomic layer deposited (ALD) Al 2 O 3 top layer. [42] When our TMD FETs were integrated into piezoelectric touch sensor circuit which allows instantaneous switching between ≈+5 and −5 V, the Toward any practical applications of 2D transition metal dichalcogenide (TMD) transistors, two issues are often met. First, threshold voltage (V th ) of usual TMD 2D field effect transistors (FETs) is located quite away from 0 V, making the device already on and less practical. Second, a large hysteresis exists during transistor operation. Here, hysteresis-minimized n-TMD FETs are fabricated using polymer-brush/channel...

Monolayer MoS2 field-effect transistors patterned by photolithography for active matrix pixels in organic light-emitting diodes

“…The PS-brush solution (10 mg/mL) was spin-coated onto the Al 2 O 3 surface and then heated at 170°C for 48 h inside a vacuum oven, so that the ultrathin PS layer may be covalently bonded to the plasma-treated Al 2 O 3 surface. 49,50 As stated in the above transfer process, as-grown monolayer was transferred from SiO 2 /p + -Si substrate to patterned bottom gate substrate using PS transfer method (Supporting Information, Figure S4). 48 After transfer, CVD MoS 2 flakes were patterned by photolithography and O 2 plasma dry etching process.…”

Complementary Type Ferroelectric Memory Transistor Circuits with P‐ and N‐Channel MoTe2

“…The detail procedure of PS‐brush has been already reported elsewhere as also seen in Figure S3 (Supporting Information). [ 44 ] However, it should be noted that annealing process for PS‐brush at 170 °C was done for quite a short duration of 6 h in this study (in general, it is used to be taking more than 48 h). For the semiconducting channel, p‐type MoTe 2 nanosheet (HQ graphene) was exfoliated and transferred onto the PS‐brush/50 nm thick Al 2 O 3 dielectric using polydimethylsiloxane (PDMS), [ 52 ] followed by source/drain electrode (25/25 nm Ti/Au) patterning for the channel of 5 °C length (using conventional UV photolithography).…”

Low Voltage and Ferroelectric 2D Electron Devices Using Lead‐Free BaxSr1‐xTiO3 and MoS2 Channel

“…Besides, our BST surface appears very hydrophilic as analyzed by de‐ionized (DI) water contact angle measurement (≈20°). Hydrophilic dielectric surface would cause high density traps at the channel/dielectric interface . We thus applied an ultrathin PMMA‐brush layer on BST by spin coating, to improve the surface quality.…”

“…Hydrophilic dielectric surface would cause high density traps at the channel/dielectric interface. [18,44] We thus applied an ultrathin PMMA-brush layer on BST by spin coating, to improve the surface quality. As a result, it was observed in Figure 1c that the BST surface becomes much smoother (RMS roughness ≈1.97 nm) and more hydrophobic (DI water contact angle ≈60°).…”