A touch pressure sensor using a graphene-Si Schottky junction barristor gated with the piezoelectric polymer poly(vinylidenefluoride-cotrifluoroethylene) has been demonstrated that combines a high on-off ratio (over 10(2)) and low leakage current characteristics. The performance of this device was optimized by presetting the initial Fermi level of graphene using a polymer doping process. Sensing current modulation ratios up to 312% were achieved under 3 MPa touch pressure. (C) 2019 The Japan Society of Applied Physics

The transition metal dichalcogenides (TMDCs) have been extensively investigated for various applications such as logic, memory and optical devices, and sensors. The pressing challenge in the research of TMDCs is the electrical performance limited by the high contact resistance. We report more than 5000 times reduction in the contact resistance of WS2 field-effect transistor (FET) with Ti contact (81 MΩ μm to 14.6 kΩ μm) by high-pressure hydrogen annealing. Schottky barrier height reduction appears to play a major role in the reduction of the contact resistance. This process can be used to reduce the contact resistance even further by combining with a doping technique for TMDCs and a contact metal optimization for TMDC FETs.

We have successfully demonstrated a graphene-ZnO:N Schottky barristor. The barrier height between graphene and ZnO:N could be modulated by a buried gate electrode in the range of 0.5-0.73 eV, and an on-off ratio of up to 107 was achieved. By using a nitrogen-doped ZnO film as a Schottky contact material, the stability problem of previously reported graphene barristors could be greatly alleviated and a facile route to build a top-down processed graphene barristor was realized with a very low heat cycle. This device will be instrumental when implementing logic functions in systems requiring high-performance logic devices fabricated with a low temperature fabrication process such as back-end integrated logic devices or flexible devices on soft substrates.

We demonstrate and explain the operation of PVDF-TrFE/graphene/ZnO:N barristor using electrostatic force microscopy (EFM) poling system. The device was successfully reconfigured using a ferroelectric polymer, PVDF-TrFE. 103 of device current modulation were achieved. And, it will be very useful for dynamically reconfigurable logic, memory and logic memory hybrid device applications.

High contact resistance and symmetrical conduction are serious challenges in practical applications of transition metal dichalcogenide (TMD) field-effect transistors (FETs). Unipolar behavior and reduced contact resistance are achieved for tungsten disulfide (WS2) FETs by using a TiO2 interfacial layer inserted between a metal layer and a WS2 layer. As a service to our authors and readers, this journal provides supporting information supplied by the authors. Such materials are peer reviewed and may be re-organized for online delivery, but are not copy-edited or typeset. Technical support issues arising from supporting information (other than missing files) should be addressed to the authors. Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.

Barium titanate nanocrystals (BT NCs) were prepared under solvothermal conditions at 200 °C for 24 h. The shape of the BT NCs was tuned from nanodot to nanocube upon changing the polarity of the alcohol solvent, varying the nanosize in the range of 14-22 nm. Oleic acid-passivated NCs showed good solubility in a nonpolar solvent. The effect of size and shape of the BT NCs on the ferroelectric properties was also studied. The maximum polarization value of 7.2 μC/cm(2) was obtained for the BT-5 NC thin film. Dielectric measurements of the films showed comparable dielectric constant values of BT NCs over 1-100 kHz without significant loss. Furthermore, the bottom gate In2O3 NC thin film transistors exhibited outstanding device performance with a field-effect mobility of 11.1 cm(2) V(-1) s(-1) at a low applied gate voltage with BT-5 NC/SiO2 as the gate dielectric. The low-density trapped state was observed at the interface between the In2O3 NC semiconductor and the BT-5 NCs/SiO2 dielectric film. Furthermore, compensation of the applied gate field by an electric dipole-induced dipole field within the BT-5 NC film was also observed.

The long-term stability and superior device reliability through the use of delicately designed metal contacts with two-dimensional (2D) atomic-scale semiconductors are considered one of the critical issues related to practical 2D-based electronic components. Here, we investigate the origin of the improved contact properties of alloyed 2D metal-semiconductor heterojunctions. 2D WSe2-based transistors with mixed transition layers containing van der Waals (M-vdW, NbSe2/WxNb1-xSe2/WSe2) junctions realize atomically sharp interfaces, exhibiting long hot-carrier lifetimes of approximately 75,296 s (78 times longer than that of metal-semiconductor, Pd/WSe2 junctions). Such dramatic lifetime enhancement in M-vdW-junctioned devices is attributed to the synergistic effects arising from the significant reduction in the number of defects and the Schottky barrier lowering at the interface. Formation of a controllable mixed-composition alloyed layer on the 2D active channel would be a breakthrough approach to maximize the electrical reliability of 2D nanomaterial-based electronic applications.

Two‐dimensional transition metal dichalcogenides (TMDCs) are potential candidate materials for future thin‐film field effect transistors (FETs). However, many aspects of this device must be optimized for practical applications. In addition, low‐frequency noise that limits the design window of electronic devices, in general, must be minimized for TMD‐based FETs. In this study, the low‐frequency noise characteristics of multilayer molybdenum disulphide (MoS2) FETs were investigated in detail, with two different contact structures: titanium (Ti) metal–MoS2 channel and Ti metal–TiO2 interlayer–MoS2 channel. The results showed that the noise level of the device with a TiO2 interlayer reduced by one order of magnitude compared with the device without the TiO2 interlayer. This substantial improvement in the noise characteristics could be explained using the carrier number of fluctuation model. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)

Material properties of PVDF-TrFE related to dipole alignment and crystallinity, such as surface potential, polarization direction, piezoelectric coefficient, and remnant polarization, have been systematically examined to explain the improvement in the piezoelectric properties of PVDF-TrFE formed at a high spin-coating speed. The correlations between the distribution of the dipole moment vector and the degree of crystallinity were studied as a function of strain rate using a computational molecular dynamic simulation.

Display Omitted The sensitivity of graphene based touch sensor has been improved by Al2O3 scaling.Al assisted Al2O3 deposition is an easy way to get smooth and thin dielectric.The piezoelectric induced charges were increased by enhancing the charge coupling.7 times higher sensitivity could be achieved. The sensitivity of touch sensor using piezoelectric polymer/graphene stack has been drastically improved by scaling the thickness of dielectric on the graphene. The piezoelectric effect induced charges in graphene channel were increased from 0.6195 to 4.314µC/cm2 at 1kg press weight, which by enhancing the charge coupling between the PVDF-TrFE and graphene channel through the Al2O3 scaling from 30nm to 5nm.

Achieving a low contact resistance for 2D materials is a critical challenge for device applications. In this work, the contact resistance of MoS 2 FETs has been drastically reduced by five times from the reference data using an optimized TiO 2 Fermi level de-pinning layer which reduced the effective Schottky barrier height to 0.1 eV. As a result, a very low contact resistance ~5.4 kΩ·μm was achieved without any doping technique.

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.

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.

Novel multi-bit memory using a graphene/PVDF-TrFE stack has been demonstrated.Two polarization generate four states of junction combinations in the graphene.The four states are maintained up to 1000 sec and 100 times endurance.Flexible or a low cost and medium density memory would be suitable applications. Novel multi-bit memory device using a graphene/a ferroelectric polymer stack has been successfully demonstrated. The dual top gate electrodes are used to change the Fermi level of graphene by polarizing PVDF-TrFE layer. Two different polarization states in the same graphene channel generate four states of junction combinations, resulting in four channel resistance values. Four different states are maintained up to 1000s and 100 cycles of endurance has been confirmed. This device can be utilized in high performance memory device with high bit density per memory cell since the response time of ferroelectric polymer is faster than 10ns.

Characteristics of new reconfigurable graphene device with Metal/ Ferroelectric (PVDF-TrFE)/Graphene (MFG) stack is presented. Key features include programming speed <; 100nsec, retention up to 1000sec, endurance upto 1000 cycles and more than 775% on/off ratio. While memory like functionalities are primarily presented in this paper, MFG device has many versatile applications such as reconfigurable interconnect resistor or logic device, pressure sensitive touch sensor and so on.