Guanggui Cheng

Synaptic behaviors mimicked in indium-zinc-oxide transistors gated by high-proton-conducting graphene oxide-based composite solid electrolytes

The large protonic conductivity of proton conductor films is of considerable significance for low-power transistor-based synapse applications. In this work, a 3-triethoxysilylpropylamine graphene-oxide (KH550–GO) solid electrolyte with a protonic conductivity of ∼4.2 × 10−3 S cm−1 is synthesized and proposed to be used as a gate dielectric material for protonic/electronic hybrid synaptic transistors. The microstructure and the electrochemical characteristics of the KH550–GO solid electrolyte are investigated. In addition, the protonic/electronic hybrid synaptic transistor gated by KH550–GO can exhibit excellent electrical performance. Finally, the paired-pulse facilitation, excitatory post-synaptic current, and spike-rate-dependent plasticity of biological synapses are mimicked by such a synaptic transistor, which is, therefore, a promising artificial synapse for synaptic electronics and neuromorphic systems.

Excitatory Post-Synaptic Potential Mimicked in Indium-Zinc-Oxide Synaptic Transistors Gated by Methyl Cellulose Solid Electrolyte

The excitatory postsynaptic potential (EPSP) of biological synapses is mimicked in indium-zinc-oxide synaptic transistors gated by methyl cellulose solid electrolyte. These synaptic transistors show excellent electrical performance at an operating voltage of 0.8 V, Ion/off ratio of 2.5 × 106, and mobility of 38.4 cm2/Vs. After this device is connected to a resistance of 4 MΩ in series, it exhibits excellent characteristics as an inverter. A threshold potential of 0.3 V is achieved by changing the gate pulse amplitude, width, or number, which is analogous to biological EPSP.

Experimental Investigation of Microstructure and Piezoresistive Properties of Phosphorus-Doped Hydrogenated Nanocrystalline Silicon Thin Films Prepared by PECVD

This paper presents an experimental investigation of microstructure and piezoresistive properties of phosphorus-doped hydrogenated nanocrystalline silicon (nc-Si:H) thin films. The phosphorus-doped nc-Si:H thin films (5% doping ratio of PH3 to SiH4) were deposited by plasma enhanced chemical vapor deposition (PECVD) technique. The microstructure and surface morphology of the deposited thin films was characterized and analyzed with Raman spectroscopy and atomic force microscopy (AFM), respectively. The piezoresistive properties of the deposited thin films were investigated with a designed four-point bending-based evaluation system. In addition, the influence of temperature on the piezoresistive properties of these thin films was evaluated with the temperature coefficient of resistance (TCR) measurements from room temperature up to 80°C. The experimental results show that phosphorus-doped nc-Si:H thin films prepared by PECVD technique are a two-phase material that constitutes of nanocrystalline silicon and amorphous silicon, and they present a granular structure composed of homogeneously scattered nanoclusters formed by nanocrystalline silicon grains (6nm). Moreover, phosphorus-doped nc-Si:H thin films exhibit negative GF at room temperature and show good thermal stability from room temperature up to 80°C, and the value of GF and TCR is about-31 and-509ppm/°C, respectively. These features could make phosphorus-doped nc-Si:H thin films act as a promising material for piezoresistive-based MEMS sensor.

Design and Evaluation of a High-Accuracy Measurement System for Sheet Resistance of Thin Films

Inspection and measurement for the sheet resistance and resistivity play a pivotal role in the semiconductor industry. In this study, a high-accuracy measurement system for sheet resistance of thin films was designed based on dual-measurement with four-point probe method. The measurement system was composed of a special switching circuit, a digital output module, Keithley 2400 SourceMeter, and a computer running LabVIEW. The special switching circuit designed based on the multiplexer played an important role in current probes and voltage probes automatic switching under the control of virtual instrumentation software LabVIEW and National instruments digital output module hardware NI 9401. Keithley 2400 SourceMeter controlled by LabVIEW was used for two-times high-precision voltage measurement. Van der Pauw correction factor were calculated based on the results of the two-times voltage measurement. Then the sheet resistance of thin films was calculated by LabVIEW softwares powerful computing. The experimental results show that the designed and developed system can meet the needs of fast on-line measurement of thin films sheet resistance with a wide range, and moreover, the accuracy of measurements and the level of automatization have been dramatically improved compared to the conventional measurement system.

Numerical Study on Thermal Boundary Resistance and Conductive Properties of Cu/Al Interface

In this paper, the thermal boundary resistance and conductive properties of Cu/Al interface are investigated by using first-principles calculations based on density functional theory (DFT) with considering the pressure influence. Based on the atomic model of Cu/Al interface the simulation results show that the lattice parameters for both Cu and Al are sensitive to pressure and density states of Cu/Al interface increase as pressure increases from 0 to 5 GPa. Although Cu and Al have the same atomic structure, the significant differences of the density of phonon states lead to the thermal resistance that exists at the Cu/Al interface. At the Cu/Al interface, Cu and Al atoms can diffuse into each other and form an alloy-like interfacial region. The change of the copper component in the alloy can considerably affect the conductive properties of Cu/Al interface.

Flow Properties of Fluids Confined in Parallel-Plate Nanochannels

Molecular dynamics simulations are carried out to explore the fluid flows in parallel-plate nanochannels. A “channel moving” pressure-driven model is utilized to study the planar Poiseuille flows. Considering the slip boundary conditions, relationships among the pressure gradient, mean flow velocity and the channel width are investigated to couple the atomistic regime to continuum. The results show that the mean flow velocity almost linearly increases with the increase of the pressure gradient. The slope of the linear relationship between the pressure gradient and the mean flow velocity is nonlinearly decreased with increasing the channel width. The results indicate that the approximate accuracy is reduced with decreasing the channel width while the pressure-driven flows confined in nanochannels are approximately described by the Navier-Stokes equations.

Synthesis and Investigation on the Mechanical Properties of the Polypyrrole Film Doped with P-Toluene Solfonate

In this paper, conducting polypyrrole (PPy) films doped with p-toluene solfonate (pTS) was electrochemically synthesized. The chemical groups of the sample were analysed by FT-IR, an in situ nanotribolab system together with the four-probe instrument were employed to investigate the mechanical and conductivity of the prepared films. The surface morphology was studied by scanning electron microscopy (SEM). It demonstrates that the dopant anion was doped into the PPy while the overoxidation did not occur during the polymerization. The conductivity of PPy film is stable, during indentation, different loads were applied and hardness, elastic modulus were obtained. SEM images showed that the film is uniform. The characteristic microstructure of polypyrrole, the cauliflower-like, is appeared and the film is compact and homogeneous.

Investigation of a Micromixer for the MTPV System

In this paper, a micromixer used in micro thermo photovoltaic system (MTPV system) is simulated and fabricated. The optimal structure parameters were investigated by computational fluent dynamical software (CFD)，during the simulation, three main parameters n,τ and δ were introduced to studied on the influence of the mixing intensity . The simulation results show that the number of the static elements added in the mixing channel n should be more than 4, the side-length of the static elements should be half of the channel’s width and the static elements should be equidistant and interlaced distribution.

FEM Simulation of a Twin-Island Structure Chip in Piezoresistive Pressure Sensor

In this paper a twin-island structure in piezoresistive pressure sensor based on MEMS technology has been presented, and a finite element mechanical model has been developed to simulate the static mechanical behavior of this twin-island structure sensor chip, especially the stress distributions in diaphragm of the sensor chip, which has a vital significance on piezoresistive pressure sensors’ sensitivity. The possible impacts of twin-island’s location and twin-island’s width on the stress distributions, as well as the maximum value of compressive stress and tensile stress, have been investigated based on numerical simulation with Finite Element Method (FEM). The simulation results show that twin-island’s location has great effect on the stress distributions in sensor chips’ diaphragms and the sensitivity of piezoresistive pressure sensors, compared with the twin-island’s width.

Effect of Volume Fraction of Nanoparticles to the Convective Heat Transfer of Nanofluids

A numerical study on the convective heat transfer characteristics of Cu-water nanofluid under the laminar flow condition was performed. The results show that the convective heat transfer coefficient increases with the increase of the volume fraction of the nanoparticles and the Reynolds number. There is a significant difference between the numerical simulation result and the result calculated from the Shah equation in the entrance region, but a small difference in full development areas. The numerical results agree well with that obtained from the Xuan equation when the Reynolds number and the volume fraction of the nanoparticles are small, but the errors between them increase as the increase of the Reynolds number and the volume fraction of nanoparticles.