A facile process to achieve hysteresis-free and fully stabilized graphene field-effect transistors.

The operation of chemical vapor-deposited (CVD) graphene field-effect transistors (GFETs) is highly sensitive to environmental factors such as the substrate, polymer residues, ambient condition, and other species adsorbed on the graphene surface due to their high defect density. As a result, CVD GFETs often exhibit a large hysteresis and time-dependent instability. These problems become a major roadblock in the systematic study of graphene devices. We report a facile process to alleviate these problems, which can be used to fabricate stable high performance CVD GFETs with symmetrical current-voltage (I-V) characteristics and an effective carrier mobility over 6000 cm(2) V(-1) s(-1). This process combined a few steps of processes in sequence including pre-annealing in a vacuum, depositing a passivation layer, and the final annealing in a vacuum, and eliminated ∼50% of charging sources primarily originating from water reduction reactions.

Quantitatively estimating defects in graphene devices using discharge current analysis method.

Defects of graphene are the most important concern for the successful applications of graphene since they affect device performance significantly. However, once the graphene is integrated in the device structures, the quality of graphene and surrounding environment could only be assessed using indirect information such as hysteresis, mobility and drive current. Here we develop a discharge current analysis method to measure the quality of graphene integrated in a field effect transistor structure by analyzing the discharge current and examine its validity using various device structures. The density of charging sites affecting the performance of graphene field effect transistor obtained using the discharge current analysis method was on the order of 10(14)/cm(2), which closely correlates with the intensity ratio of the D to G bands in Raman spectroscopy. The graphene FETs fabricated on poly(ethylene naphthalate) (PEN) are found to have a lower density of charging sites than those on SiO2/Si substrate, mainly due to reduced interfacial interaction between the graphene and the PEN. This method can be an indispensable means to improve the stability of devices using a graphene as it provides an accurate and quantitative way to define the quality of graphene after the device fabrication.

Characteristics of a pressure sensitive touch sensor using a piezoelectric PVDF-TrFE/MoS2 stack.

A new touch sensor device has been demonstrated with molybdenum disulfide (MoS2) field effect transistors stacked with a piezoelectric polymer, polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE). The performance of two device stack structures, metal/PVDF-TrFE/MoS2 (MPM) and metal/PVDF-TrFE/Al2O3/MoS2 (MPAM), were compared as a function of the thickness of PVDF-TrFE and Al2O3. The sensitivity of the touch sensor has been improved by two orders of magnitude by reducing the charge scattering and enhancing the passivation effects using a thin Al2O3 interfacial layer. Reliable switching behavior has been demonstrated up to 120 touch press cycles.

Intrinsic photocurrent characteristics of graphene photodetectors passivated with Al2O3.

The intrinsic photo-response of chemical vapor deposited (CVD) graphene photodetectors were investigated after eliminating the influence of photodesorption using an atomic layer deposited (ALD) Al2O3 passivation layer. A general model describing the intrinsic photocurrent generation in a graphene is developed using the relationship between the device dimensions and the level of intrinsic photocurrent under UV illumination.

Ferroelectric polymer-gated graphene memory with high speed conductivity modulation.

The feasibility of a high speed ferroelectric graphene memory device using a ferroelectric polymer (PVDF-TrFE)/graphene stack has been demonstrated. The conductivity of this metal-ferroelectric-graphene (MFG) device could be modulated up to 775% with a very fast programming speed down to 10 ns. Also, programmed states were maintained up to 1000 s with endurance over 1000 cycles. In addition to demonstrating a single memory device, the array-level integration and cell write/read functionality of a 4 × 4 MFG array adopting a graphene bit line has also been confirmed to show the feasibility of MFG memory.

Effects of multi-layer graphene capping on Cu interconnects.

The benefits of multi-layer graphene (MLG) capping on Cu interconnects have been experimentally demonstrated. The resistance of MLG capped Cu wires improved by 2-7% compared to Cu wires. The breakdown current density increased by 18%, suggesting that the MLG can act as an excellent capping material for Cu interconnects, improving the reliability characteristics. With a proper process optimization, MLG capped Cu interconnects could become a promising technology for high density back end-of-line interconnects.

Fabrication of 380 nm ultra violet light emitting diodes on nano-patterned n-type GaN substrate.

380 nm ultraviolet (UV) light emitting diodes (LEDs) were grown on patterned n-type GaN substrate (PNS) with silicon dioxide (SiO2) nano pattern to improve the light output efficiency. Wet etched self assembled indium tin oxide (ITO) nano clusters serves as dry etching mask for converting the SiO2 layer grown on n-GaN template into SiO2 nano patterns by inductively coupled plasma etching. Three different diameter of ITO such as 200, 250 and 300 nm were used for SiO2 nano pattern fabrication. PNS is obtained by n-GaN regrowth on SiO2 nano patterns and UV LEDs were grown on PNS template by MOCVD. Enhanced light output intensity was observed by employing SiO2 nano patterns on n-GaN. Among different PNS UV LEDs, LED grown on PNS with 300 nm ITO diameter showed enhancement in light output intensity by 2.1 times compared to the reference LED without PNS.

Characteristics of CVD graphene nanoribbon formed by a ZnO nanowire hardmask.

A graphene nanoribbon (GNR) is an important basic structure to open a bandgap in graphene. The GNR processes reported in the literature are complex, time-consuming, and expensive; moreover, the device yield is relatively low. In this paper, a simple new process to fabricate a long and straight graphene nanoribbon with a high yield has been proposed. This process utilizes CVD graphene substrate and a ZnO nanowire as the hardmask for patterning. 8 µm long and 50-100 nm wide GNRs were successfully demonstrated in high density without any trimming, and ∼ 10% device yield was realized with a top-down patterning process. After passivating the surfaces of the GNRs using a low temperature atomic layer deposition (ALD) of Al(2)O(3), high performance GNR MOSFETs with symmetric drain-current-gate-voltage (I(d)-V(g)) curves were demonstrated and a field effect mobility up to ∼ 1200 cm(2) V(-1) s(-1) was achieved at V(d) = 10 mV.

Induction of apoptosis in a human lymphoma cell line by hydrophobic peptide fraction separated from anchovy sauce.

Peptide fractions showing anticancer activity were isolated from anchovy sauce, and their abilities to induce apoptosis in a human lymphoma cell (U937) were determined by biochemical and flow cytometric methods. The butanol extract (fraction Aob) from the desalted hydrophobic peptide fraction (Ao) separated from anchovy sauce by HP-20 adsorption chromatography was found to possess strong antiproliferative activity against U937 by inducing apoptosis. Treatment of U937 with Aob resulted in sub-G1 peak representing apoptosis in the cell cycle analysis, and apoptotic DNA fragmentation. Antiproliferative activity of the peptide fraction further purified successively by silica gel chromatography, TLC, and reversed-phase HPLC increased proportionally with the purification fold. The peptide fraction having antiproliferative activity was found to be composed of Ala and Phe, and its molecular weight was estimated to be 440.9 Da.

Peptides from anchovy sauce induce apoptosis in a human lymphoma cell (U937) through the increase of caspase-3 and -8 activities.

Various biological activities of peptides have been found. In this study, the induction of apoptosis in a human lymphoma cell line (U937) by peptide fraction separated from anchovy sauce was studied using biochemical and flow cytometric methods. After U937 was treated with a hydrophobic peptide fraction of the anchovy sauce, a sub-G1 peak, which represents apoptosis, was found in the cell cycle analysis. The apoptosis in the peptide-treated U937 cell was also confirmed by apoptotic DNA fragmentation. Furthermore, an increase of caspase-3 and -8 activities was observed. Our results suggest that the peptide fraction separated from the anchovy sauce may have cancer chemopreventive effects through the induction of apoptosis in cancer cells.