A single-layer MoS 2 achieves excellent gate controllability within the nanoscale channel length of a fieldeffect transistor (FET) owing to an ultra-short screening length. However, multilayer MoS 2 (ML-MoS 2 ) is more vulnerable to short channel effects (SCEs) owing to its thickness and long screening length. We eliminated the SCEs in an ML-MoS 2 FET (thickness of 4−13 nm) at a channel length of sub-30 nm using a Schottky barrier (SB) variable graphene/ML-MoS 2 heterojunction. Although the band modulation in the ML-MoS 2 channel worsens with a decrease in the channel length, which is similar to the SCEs occurring in conventional FETs, the variable Fermi level (E F ) of a graphene electrode along the gate voltage allows control of the SB at the graphene/MoS 2 junction and backs up the current modulation through a variable SB. Electrical measurements and a theoretical band simulation demonstrate the efficient SB modulation of our graphene nanogap (GrNG) ML-MoS 2 FET with three distinct carrier transports along V gs : a thermionic emission at a low SB, Fowler−Nordheim tunneling at a moderate SB, and direct tunneling at a high SB. Our GrNG FET shows an extremely high on−off current ratio of ∼10 8 , which is approximately threeorders of magnitude better than a previously reported metal nanogap (MeNG) FET and a self-aligned metal/graphene nanogap FET with a similar MoS 2 thickness. Our GrNG FET also exhibits a 100,000-times higher on−off ratio, 100-times lower subthreshold swing, and 10-times lower drain induced barrier.

Graphene has attracted a great deal of interest for applications in bio-sensing devices because of its ultra-thin structure, which enables strong electrostatic coupling with target molecules, and its excellent electrical mobility promising for ultra-fast sensing speeds. However, thickly stacked receptors on the graphene's surface interrupts electrostatic coupling between graphene and charged biomolecules, which can reduce the sensitivity of graphene biosensors. Here, we report a highly sensitive graphene biosensor by the monomolecular self-assembly of designed peptide protein receptors. The graphene channel was non-covalently functionalized using peptide protein receptors via the π-π interaction along the graphene's Bravais lattice, allowing ultra-thin monomolecular self-assembly through the graphene lattice. In thickness dependent characterization, a graphene sensor with a monomolecular receptor (thickness less than 3 nm) showed five times higher sensitivity and three times higher voltage shifts than graphene sensors with thick receptor stacks (thicknesses greater than 20 nm), which is attributed to excellent gate coupling between graphene and streptavidin via an ultrathin receptor insulator. In addition to having a fast-inherent response time (less than 0.6 s) based on fast binding speed between biotin and streptavidin, our graphene biosensor is a promising platform for highly sensitive real-time monitoring of biomolecules with high spatiotemporal resolution.

The chemical solution process of MoS2 on high‐k oxide films has been systematically investigated. The source solution used in this work is made of (NH4)2MoS4 powder dissolved in N‐methyl‐2‐pyrrolidone. We have spin‐coated the solution on various kinds of dielectric oxide films and shown that the coating properties strongly depend on the kind of dielectric, which can be understood by surface energy analysis, following this, the growth of high quality of MoS2 film is confirmed by Raman scattering spectroscopy and X‐ray diffraction. It is demonstrated that the MoS2 film can be grown on Nb doped ZrO2 using a solution with a two‐step annealing process, where the first annealing is performed at 450 °C in H2/Ar (5:95) atmosphere for 20 min and the second annealing at 1000 °C in Ar atmosphere with S vapor for 20 min. In addition, conformal growth of a MoS2 layered structure on the curved surface of the oxide film is confirmed by transmission electron microscope observations. A further conclusion is that the thickness of MoS2 can be controlled by the concentration of a source solution and that two‐layer MoS2 is obtained when the concentration of source solution is 0.00625 mol kg−1. The measured Hall mobility of the solution‐derived MoS2 film, annealed at 1000 °C is approximately 25 cm2 V−1s−1.

In this work, we fabricated metal-ferroelectric-semiconductor (MFS) diodes with polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE) (51/49) thin films for application to one transistor-type (1T-type) ferroelectric random access memories (FeRAMs). The thin films, with various thicknesses, were prepared on a silicon substrate by using a spin-coating method. The β-phase crystallinity and the grain size of the PVDF-TrFE increased as the film-thickness increased. Typical ferroelectric hysteresis loops were obtained from the capacitance-voltage (C-V) curves. These loops might be considered to be due to the ferroelectric nature of the PVDF-TrFE films. The values of the memory window width for 50-nm-, 150-nm-, and 350-nm-thick PVDF-TrFE films were about 1.4, 2.0, and 3.5 V for a bias sweeping from −5 V to 5 V, respectively. The values of the leakage current density, at a sweeping range of ±5 V, were about 2.7 × 10 −5 A/cm 2 , 1.1 × 10 −5 A/cm 2 , and 5.6×10 −6 A/cm 2 for 50-nm-, 150-nm-, and 350-nm-thick films, respectively. These results are useful and promising for realizing 1T-type FeRAMs operating at a low voltage.

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