Electrical properties of micrometric metallic dots obtained by porous polymeric membranes

We report on the fabrication of micrometric regular metallic arrays obtained by using, as a template, a polymeric membrane with regular pores. The membranes were prepared by embedding hydrophobized silica colloids into a polymer layer and subsequently removing them. We have investigated the electronic transport properties of the metallic arrays as a function of the applied electric field and temperature. Simple current voltage (IV) characteristics present a strong switching behavior with I_ON/I_OFF ratios up to 10⁴. Different temperature dependences of the resistance in the different ranges of the applied electric field have been observed. Finally, the performances of a field effect device (FET), with the conducting channel and insulating layer consisting of a Gold dot array and a STO substrate, respectively, have been investigated. The channel resistivity has been modified at least of two orders of magnitude and a mobility of about 2 cm²/V*s has been extracted by the analysis of the FET transfer curve.     

Electrical bistability of tris-(8-hydroxyquinoline) aluminum (Alq3)/ZnSe organic-inorganic bistable device

We present that the electrical bistability in organic-inorganic bistable devices based on tris-(8-hydroxyquinoline) aluminum (Alq₃) and zinc selenide (ZnSe) with the tri-layer structure of Alq₃/aluminum (Al)/ZnSe. The current-voltage characteristics of the bistable device exhibit two electrical states as low (OFF state) and high (ON state) conductivity with ON/OFF ratio about four orders of magnitude. The conduction mechanisms in both ON and OFF states were analyzed by theoretical model. In the OFF state, the conduction mechanisms can be explained by thermionic emission model, which the ON state can be described by ohmic conduction model. The retention times of both states are more than 8000 s, and the device can reproduce continuous write-read-erase-read switching cycles. Moreover, for the organic-inorganic bistable device was kept at one year in ambient condition without encapsulation. The device still exhibited the electrical bistable behavior. Consequently, the ZnSe layer may be led to improve the lifetime property of the bistable device which acted as a self-encapsulating layer.     

Electrical generation of pure spin current with oscillating spin-orbit interaction

We propose an electrical scheme for the generation of a pure spin current without a charge current in a two-terminal device, which consists of a scattering region of a two-dimensional electron gas (2DEG) with Rashba (R) and/or Dresselhaus (S) spin-orbit interaction (SOI) and two normal leads. The SOI is modulated by a time-dependent gate voltage to pump a spin current. Based on a tight-binding model and the Keldysh Green’s function technique, we obtain the analytical expression of the spin current. It is shown that a pure spin current can be pumped out, and its magnitude could be modulated by device parameters such as the oscillating frequency of the SOI, as well as the SOI strength. Moreover, the spin polarisation direction of the spin current could also be tuned by the strength ratio between RSOI and DSOI. Our proposal provides not only a fully electrical means to generate a pure spin current but also a way to control the spin polarisation direction of the generated spin current.     

Electrical properties and memory effect in the field effect transistor based on organic ferroelectric insulator and pentacene

We have fabricated a field effect transistor (FET) based on an organic ferroelectric insulator and molecular conductor, and investigated the electrical properties and memory effects on the PEN-FET. We have observed a drastic change in the drain current at around the coercive electric fieldE _c of the organic ferroelectric insulator in not only a FET (PEN-FET) based on a pentacene (PEN) film but also a FET (IPEN-FET) based on an iodine doped PEN film. The magnitude of the change of the drain current for the IPEN-FET is 200 times larger than that for the PEN-FET. It is expected from these results that the PEN-FET (especially the IPEN-FET) is an improvement in such devices, since it operates at a low gate electric field accompanied by the appearance of the spontaneous polarization in the organic ferroelectric insulator. In addition, we have found that the drain current for the PEN-FET does not return to the initial drain current ofE _G =0 V/cm for more than one week, even if the gate electric field is changed to 0 V/cm from 500 V/cm(>E _c ). From these results, it is suggested that the PEN-FET becomes a memory device.     

Thermoelectric effect in a serial two-quantum-dot

We study the thermoelectric effect in a serial-coupled two quantum dots (QDs) device in the Coulomb blockade regime. The electrical conductance, the thermal conductance, the thermopower, and the thermoelectrical figure of merit are calculated by using the Green's function method. It is found that the energy levels of the two dots are split into a series of molecular states, where the electrical and the thermal conductances show resonance peaks. These peaks in the electrical conductance are eliminated by the increase of the temperature, while those in the thermal conductance are enhanced because of the bipolar effect. In quite high temperature regime, the figure of merit has two huge peaks with maximums exceeding 20 in the vicinity of the electron-hole symmetry point. The magnitude of the figure of merit will be suppressed for unequal dots' levels, but is enhanced by the asymmetry of the dot-lead coupling strengths.     

Modulation of electronic properties with external fields in silicene-based nanostructures

This work reviews our recent works about the density functional theory(DFT) calculational aspects of electronic properties in silicene-based nanostructures with the modulation of external fields, such as electric field, strain, etc. For the two-dimensional(2D) silicene-based nonostructures, the magnetic moment of Fe-doped silicene shows a sharp jump at a threshold electric field, which indicates a good switching effect, implying potential applications as a magnetoelectric(ME) diode. With the electric field, the good controllability and sharp switching of the magnetism may offer a potential applications in the ME devices. For the one-dimensional(1D) nanostructures, the silicene nanoribbons with sawtooth edges(SSi NRs) are more stable than the zigzag silicene nanoribbons(ZSiNRs) and show spin-semiconducting features. Under external electric field or uniaxial compressive strain, the gapless spin-semiconductors are gained, which is significant in designing qubits for quantum computing in spintronics. The superlattice structures of silicene-based armchair nanoribbons(ASiSLs) is another example for 1D silicene nanostructures. The band structures of ASi SLs can be modulated by the size and strain of the superlattices. With the stain increased, the related energy gaps of ASi SLs will change, which are significantly different with that of the constituent nanoribbons. The results suggest potential applications in designing quantum wells.     

Recent progress on integrating two-dimensional materials with ferroelectrics for memory devices and photodetectors

Two-dimensional(2D) materials, such as graphene and Mo S2 related transition metal dichalcogenides(TMDC), have attracted much attention for their potential applications. Ferroelectrics, one of the special and traditional dielectric materials,possess a spontaneous electric polarization that can be reversed by the application of an external electric field. In recent years, a new type of device, combining 2D materials with ferroelectrics, has been fabricated. Many novel devices have been fabricated, such as low power consumption memory devices, highly sensitive photo-transistors, etc. using this technique of hybrid systems incorporating ferroelectrics and 2D materials. This paper reviews two types of devices based on field effect transistor(FET) structures with ferroelectric gate dielectric construction(termed Fe FET). One type of device is for logic applications, such as a graphene and TMDC Fe FET for fabricating memory units. Another device is for optoelectric applications, such as high performance phototransistors using a graphene p-n junction. Finally, we discuss the prospects for future applications of 2D material Fe FET.     

Reduced graphene oxide field-effect transistor with indium tin oxide extended gate for proton sensing

In this study, the reduced graphene oxide field-effect transistor (rGO FET) with indium tin oxide (ITO) extended gate electrode was demonstrated as a transducer for proton sensing application. In this structure, the proton sensing area of the ITO extended gate electrode is isolated from the active area of the rGO FET. The proton sensing properties based on the rGO FET transducer were analyzed. The rGO FET device with encapsulation by a tetratetracontane (TTC) layer showed good stability in electrolytic solutions. The device showed an ambipolar behavior with shifts in Dirac point as the pH of the electrolyte is varied. The pH sensitivity based on the Dirac point shift as a sensing parameter was about 43–50 mV/pH for a wide range of pH values from 2 to 12. The ITO extended gate rGO FET may be considered a potential transducer for sensing of H⁺ in electrolytes. Its sensing area can be modified further for various ions sensing applications.     

Optical Vector Network Analyzer with an Improved Dynamic Range Based on a Polarization Multiplexing Electro-Optic Modulator

We present a new method to achieve an optical vector network analyzer(OVNA) based on a polarization multiplexing electro-optic modulator(PM-EOM) without an optical bandpass filter. Optical single sideband(OSSB)modulated signals with a tunable optical carrier-sideband ratio(OCSR) are obtained at the output of the PMEOM. The OCSR can be flexibly tuned by controlling bias voltages of the PM-EOM. The dynamic range of the OVNA is expanded by taking the improvement of the OCSR into account. The transmission response of an optical device under test(ODUT) is measured based on one-to-one mapping from optical domain to electrical domain. By optimizing the OCSR of the OSSB modulated signals, the dynamic range of the OVNA can be effectively improved with 3.7 dB. An analytical model is derived to describe the transfer function of the ODUT.The magnitude and phase responses of a fiber Bragg grating are characterized with a large dynamic range.     

Electrical transport properties of graphene-covered-Cu wires grown by chemical vapor deposition

We investigated the field-effect transistor (FET) characteristics of 15-μm graphene-covered copper wires (G-wires). Unlike the previously reported graphene FET, carries initially showed p-type like FET characteristics in two-terminal transport measurements. Our results indicate that the electrical transport processes in a G-wire FET occur in both the heavily p-doped contact and the p-doped radial graphene channel, as a p-channel. The interfacial potential barrier between the contact electrode and the radial graphene channel is small, but there is a radial potential barrier that limits electrical transport through the copper core in chemical vapor deposition (CVD) grown samples. The p-type FET characteristics appeared clearly after the oxidation of the G-wires.     

Low noise field-effect transistor for integrated strain sensing in microelectromechanical systems at 77 K

We have fabricated a strain-sensing field-effect transistor (FET) from a GaAs/AlGaAs heterostructure containint a near surface two-dimensional electron gas. At 77 K the FET shows a typical transconductance of 30 μS and small signal drain-source resistance of 30 MO. The charge noise has a flat spectrum at high frequencies with magnitude 0.7eHz^−1/2and a 1/fnoise corner of approximately 1 kHz. The strain response, due to the piezoelectric effect, shows a noise limited strain sensitivity <4×10⁻⁹Hz^−1/2. Integrated strain sensing FETs offer advantages in small GaAs/AlGaAs microelectromechanical systems.     

Analytical capacitance model for 14 nm Fin FET considering dual-k spacer

The conformal mapping of an electric field has been employed to develop an accurate parasitic capacitance model for nanoscale fin field-effect transistor(Fin FET) device. Firstly, the structure of the dual-layer spacers and the gate parasitic capacitors are thoroughly analyzed. Then, the Cartesian coordinate is transferred into the elliptic coordinate and the equivalent fringe capacitance model can be built-up by some arithmetical operations. In order to validate our proposed model, the comparison of statistical analysis between the proposed calculation and the 3D-TCAD simulation has been carried out, and several different material combinations of the dual-k structure have been considered. The results show that the proposed analytical model can accurately calculate the fringe capacitance of the Fin FET device with dual-k spacers.     

介电力显微镜探测氧化锌纳米线表面吸附分子对电导率的影响

利用场效应晶体管器件和介电力显微镜来研究氧化锌纳米线表面吸附分子对其电导率的影响. 相比于空气中,ZnO纳米线场效应晶体管器件在氮气中电导率更高,介电力显微镜得的介电信号也是在氮气中更大. 影响ZnO纳米线电导率变化的主要原因是表面吸附分子数量的变化,而并不是电极与材料之间接触性质的变化.     

Electrical switching effect in a photochromic molecule between two graphene electrodes

We propose a single-molecule electrical switches consisting of a photochromic dimethyldihydropyrene/cyclophanediene molecule sandwiched between two graphene electrodes and investigate the electronic transport by using density-functional theory and nonequilibrium Green's function methods. The “open” and “closed” isomers of the photochromic molecule are shown to have electrical switching behavior and negative differential resistance effect. Moreover, it is also found that the switching ratio between two different conductive states depends on the ambient temperature, and the device behaves as a stable electrical switch around room temperature, which is in agreement with a recent experimental study of another photochromic molecule diarylethene reported by Jia et al. (2016) [17].     

Electrical current in nanoelectronic devices

In ultra-small electronic devices of the next generations the semiclassical model of electron motion in a periodical lattice between collisions turns out to be inadequate because the electron spread has magnitude order of the size of the ultra-small electronic device. In this Letter we consider the basic conceptual framework regarding how the length scale of the electrical device influences the transport behavior of the electrons between collisions and the electrical current. By taking into account the interference effects we obtain a very basic model for electrons transport, where the density current peak is given as function on the ratio between the thermal de Broglie wavelength and the lattice period. This result could be also useful in order to understand the basic effect of the insulator/metal transition.     

A scheme for electrical detection of single-electron spin resonance

We study a scheme for electrical detection of the spin resonance of a single-electron trapped near a field effect transistor (FET) conduction channel. In this scheme, the resonant Rabi oscillations of the trapped electron spin cause a modification of the average charge of a shallow trap, which can be detected through the change in the FET channel resistivity. We show that the dependence of the channel resistivity on the frequency of the rf field can have either peak or dip at the Larmor frequency of the electron spin in the trap.     

Electrical properties of an organic memristive system

We present a study on an organic resistive switching device based on the heterojunction of a thin conducting polyaniline (PANI) layer and a ions containing gel (or solution). We have studied the device, characterized by a non-linear and rectifying response to the applied voltage, as a function of some chemical and geometrical parameters such as solution pH, ions concentration and junction contact area, finding out their influence on the device electrical parameters such as the saturation current, the activation voltage, and the response time. The study leads us to develop a physical model of the device and control its response through the fabrication process predicting also interesting properties obtainable with a device miniaturization.     

光电耦合器件闪烁噪声模型

对电应力前后光电耦合器件的闪烁噪声（1/f噪声）进行了实验和理论研究.实验发现,应力前后1/f噪声幅值随偏置电流均有相同的变化规律：在低电流区,1/f噪声幅值与偏置电流成正比,在高电流区,1/f噪声幅值与偏置电流的平方成正比,且应力后1/f噪声幅值增大了约7倍.理论分析表明,小电流时该器件的1/f噪声为扩散1/f噪声,大电流时为复合1/f噪声,应力在器件有源区诱生的陷阱是1/f噪声增大的根本原因.基于载流子数涨落和迁移率涨落机制,建立了一个光电耦合器件1/f噪声的定量分析模型,实验结果和模型符合良好.     

Statistical emission of electrons from nanocrystalline silicon quantum dot memory nodes in a few-electron MOSFET memory device

Operation of a short and narrow channel metal-oxide-semiconductor field-effect transistor (MOSFET) memory device with a few nanocrystalline Si (nc-Si) dots in the active region has been investigated at 300 and 30 K. The discrete shift of the threshold voltage (V_th) in the current-voltage characteristics that arises from the screening effect of the charge stored in the nc-Si dot above the FET channel, suggests memory operation. It is found that the value of V_th changes with temperature whereas the magnitude of the shift in V_th is independent of temperature. The lifetime of the electrons stored in the floating node has also been investigated at different read voltages.     

The characterization of plasma-polymerized C60 thin films

Plasma-polymerized C₆₀ thin films were investigated in the form of a field effect transistor (FET) structure. In the FET device, the C₆₀ polymer acts as a p-type semiconductor, whereas C₆₀ is an n-type semiconductor. Its conduction mechanism can be described as due to variable range hopping. As a sensing device, the C₆₀ polymer can behave as a gas sensor for electrophoric gases and can also be operated as a photo-sensing device in air. Received: 21 April 2001 / Accepted: 23 July 2001 / Published online: 2 October 2001