Abstract:Resistive switching effect in transition metal oxide (TMO) based material is often associated with the valence change mechanism (VCM). Typical modeling of valence change resistive switching memory consists of three closely related phenomena, i.e., conductive filament (CF) geometry evolution, conduction mechanism and temperature dynamic evolution. It is widely agreed that the electrochemical reduction-oxidation (redox) process and oxygen vacancies migration plays an essential role in the CF forming and rupture process. However, the conduction mechanism of resistive switching memory varies considerably depending on the material used in the dielectric layer and selection of electrodes. Among the popular observations are the Poole-Frenkel emission, Schottky emission, space-charge-limited conduction (SCLC), trap-assisted tunneling (TAT) and hopping conduction. In this article, we will conduct a survey on several published valence change resistive switching memories with a particular interest in the I-V characteristic and the corresponding conduction mechanism.

Electrochemical biosensors have shown great potential in the medical diagnosis field. The performance of electrochemical biosensors depends on the sensing materials used. ZnO nanostructures play important roles as the active sites where biological events occur, subsequently defining the sensitivity and stability of the device. ZnO nanostructures have been synthesized into four different dimensional formations, which are zero dimensional (nanoparticles and quantum dots), one dimensional (nanorods, nanotubes, nanofibers, and nanowires), two dimensional (nanosheets, nanoflakes, nanodiscs, and nanowalls) and three dimensional (hollow spheres and nanoflowers). The zero-dimensional nanostructures could be utilized for creating more active sites with a larger surface area. Meanwhile, one-dimensional nanostructures provide a direct and stable pathway for rapid electron transport. Two-dimensional nanostructures possess a unique polar surface for enhancing the immobilization process. Finally, three-dimensional nanostructures create extra surface area because of their geometric volume. The sensing performance of each of these morphologies toward the bio-analyte level makes ZnO nanostructures a suitable candidate to be applied as active sites in electrochemical biosensors for medical diagnostic purposes. This review highlights recent advances in various dimensions of ZnO nanostructures towards electrochemical biosensor applications.

Recent development of trilayer graphene nanoribbon Schottky-barrier field-effect transistors (FETs) will be governed by transistor electrostatics and quantum effects that impose scaling limits like those of Si metal-oxide-semiconductor field-effect transistors. The current–voltage characteristic of a Schottky-barrier FET has been studied as a function of physical parameters such as effective mass, graphene nanoribbon length, gate insulator thickness, and electrical parameters such as Schottky barrier height and applied bias voltage. In this paper, the scaling behaviors of a Schottky-barrier FET using trilayer graphene nanoribbon are studied and analytically modeled. A novel analytical method is also presented for describing a switch in a Schottky-contact double-gate trilayer graphene nanoribbon FET. In the proposed model, different stacking arrangements of trilayer graphene nanoribbon are assumed as metal and semiconductor contacts to form a Schottky transistor. Based on this assumption, an analytical model and numerical solution of the junction current–voltage are presented in which the applied bias voltage and channel length dependence characteristics are highlighted. The model is then compared with other types of transistors. The developed model can assist in comprehending experiments involving graphene nanoribbon Schottky-barrier FETs. It is demonstrated that the proposed structure exhibits negligible short-channel effects, an improved on-current, realistic threshold voltage, and opposite subthreshold slope and meets the International Technology Roadmap for Semiconductors near-term guidelines. Finally, the results showed that there is a fast transient between on-off states. In other words, the suggested model can be used as a high-speed switch where the value of subthreshold slope is small and thus leads to less power consumption.

An explicit charge-based solution for the drain current, terminal charges and intrinsic capacitance of a long-channel junctionless nanowire transistor (JNT) incorporating the importance of an interface trap density that affect the threshold voltage and the subthreshold slope is presented in this study. Initially, a continuous implicit solution of the unified charge-based control model (UCCM) is derived from the 1D Poisson equation by invoking the parabolic potential approximation. The the continuous solution of the mobile charge density at the source/drain is obtained by adding the decoupled UCCM expression for the depletion and complementary parts, where each part is explicitly solved using the Lambert function without having an additional smoothing function to unify the two limits. The omission of an additional smoothing function could lead to a shorter computation time. Secondly, by solving Pao-Sah’s dual integral, a continuous charge-based expression for the drain current is derived. The expressions for the terminal charge are then derived based on the decoupled drain current model that also becomes an input for computing all four independent capacitances of the JNT. The explicit continuous models show a good agreement with numerical simulation over practical terminal voltages, doping levels, and geometry effects. For a given maximum surface potential error of 5%, the model is accurate for a dopant-geometry ratio of 0.001 < qNDR2/4ϵSi < 0.3 and it is also independent of fitting parameters that may vary for different terminal biases or dopant geometries. The nonpiecewise models for drain current, terminal charges and intrinsic capacitance are significantly resolved by decoupling the mobile charge into depletion and complementary parts with no additional smoothing function to unify between operating regions, and omitting fitting parameters that have no physical meaning.

The ballistic saturation velocity in a nanoscale metal-oxide-semiconductor field effect transistor (MOSFET) is revealed to be limited to the Fermi velocity in a degenerately induced channel appropriate for the quasi-two-dimensional nature of the inverted channel. The saturation point drain velocity is shown to rise with the increasing drain voltage approaching the intrinsic Fermi velocity, giving the equivalent of channel-length modulation. Quantum confinement effect degrades the channel mobility to the confining gate electric field as well as increases the effective thickness of the gate oxide. When the theory developed is applied to an 80nm MOSFET, excellent agreement to the experimental data is obtained.