Emulation of synaptic functions with low voltage organic memtransistor for hardware oriented neuromorphic computing.

Here, various synaptic functions and neural network simulation based pattern-recognition using novel, solution-processed organic memtransistors (memTs) with an unconventional redox-gating mechanism are demonstrated. Our synaptic memT device using conjugated polymer thin-film and redox-active solid electrolyte as the gate dielectric can be routinely operated at gate voltages (VGS) below - 1.5 V, subthreshold-swings (S) smaller than 120 mV/dec, and ON/OFF current ratio larger than 108. Large hysteresis in transfer curves depicts the signature of non-volatile resistive switching (RS) property with ON/OFF ratio as high as 105. In addition, our memT device also shows many synaptic functions, including the availability of many conducting-states (> 500) that are used for efficient pattern recognition using the simplest neural network simulation model with training and test accuracy higher than 90%. Overall, the presented approach opens a new and promising way to fabricate high-performance artificial synapses and their arrays for the implementation of hardware-oriented neural network.

Electroforming-free nonvolatile resistive switching of redox-exfoliated MoS2nanoflakes loaded polystyrene thin film with synaptic functionality.

Here, we report robust and highly reproducible nonvolatile resistive switching (RS) devices with artificial synaptic functionalities utilizing redox-exfoliated few-layered 2H-MoS2nanoflakes. Advantageous polar solvent compatibility of 2D MoS2from this method were utilized to fabricate thin film devices very easily and cost-effectively using polystyrene as matrix. Prominent RS property of polystyrene thin film devices with varying MoS2concentrations strongly favors electroforming-free operation. The conduction band position of 2D MoS2nanosheet in combination with the work functions of chosen electrodes looks alleviating to switch the current from low to high at a suitable positive bias voltage. We further confirmed the mechanism of charge transport through fitting the results with theoretical models, say injection-dominated Schottky emission model for low-conducting states and space-charge-limited current mechanism for the high-conducting state. Interestingly, a relatively high current On/Off ratio 102was recorded during the pump-probe testing to show resistive random-access memory (ReRAM) application. Finally, artificial synaptic functionalities- the building blocks of neuromorphic computing architectures is also illustrated by considering the robust RS property and ReRAM application.

Ultra-thin anodized aluminium dielectric films: the effect of citric acid concentration and low-voltage electronic applications.

Anodically oxidized, ultra-thin (d < 10 nm) aluminium films emerge as the dielectric of choice for low-cost thin film capacitors (TFCs), thin film transistors (TFTs), and bio- and chemical sensors. In this work, the dielectric properties of ultra-thin aluminium oxide films grown by anodization in aqueous solutions of citric acid (CA) have been studied. It is observed that the electrolyte strength variation from 0.1 mM to 1000 mM has virtually no influence on the chemical composition, surface morphology and the dielectric properties of the fabricated alumina films. The anodized films are very smooth having RMS area roughness around ∼5 Å. This was further improved after deposition of n-octadecyltrichlorosilane (OTS) self-assembled monolayer (SAM) to ∼4 Å. Also, the XRD and elemental analysis using EDS and XPS unambiguously confirms that the obtained oxide films are amorphous, stoichiometric Al2O3 without any carbon contamination. The fabricated Al/Al2O3/Al MIM capacitors show almost ideal capacitor characteristics from 10 Hz to 100 kHz. It has been found that the OTS coating does not only improve the capacitor frequency response further but also reduces the leakage current through the dielectric layer by passivating reactive dangling bonds on the oxide surface. As a result of the favourable properties of the anodized Al2O3/OTS films, high-performance, low threshold voltage organic thin film transistors (OTFTs) operating below 1 V are successfully demonstrated.

One-Volt, Solution-Processed Organic Transistors with Self-Assembled Monolayer-Ta2O5 Gate Dielectrics.

Low-voltage, solution-processed organic thin-film transistors (OTFTs) have tremendous potential to be key components in low-cost, flexible and large-area electronics. However, for these devices to operate at low voltage, robust and high capacitance gate dielectrics are urgently needed. Herein, the fabrication of OTFTs that operate at 1 V is reported. These devices comprise a solution-processed, self-assembled monolayer (SAM) modified tantalum pentoxide (Ta2O5) as the gate dielectric. The morphology and dielectric properties of the anodized Ta2O5 films with and without n-octadecyltrichlorosilane (OTS) SAM treatment have been studied. The thickness of the Ta2O5 film was optimized by varying the anodization voltage. The results show that organic TFTs gated with OTS-modified tantalum pentoxide anodized at 3 V (d ~7 nm) exhibit the best performance. The devices operate at 1 V with a saturation field-effect mobility larger than 0.2 cm2 V-1 s-1, threshold voltage -0.55 V, subthreshold swing 120 mV/dec, and current on/off ratio in excess of 5 × 103. As a result, the demonstrated OTFTs display a promising performance for applications in low-voltage, portable electronics.

Microwave assisted robust aqueous synthesis of Mn2+-doped CdSe QDs with enhanced electronic properties.

A robust doping strategy of Mn2+ ions in CdSe QDs has been developed in aqueous medium with mild microwave irradiation using the short-chain capping ligand 3-MPA. The concentration of the dopant is varied stoichiometrically in order to measure its effect on the conductivity of QD solids for further potential applications in the future. The synthesis parameters of CdSe QDs have been optimized to produce a uniform size among various samples to decouple the doping dependent conductivity from their bandgap. Doping yield is measured extensively by several studies like EDS, ICP-AES, and XPS. The layer-by-layer electrostatic assembly method has been exploited to fabricate thin film devices. I-V characteristics reveal that the electrical conductivity of 2% Mn2+-doped CdSe QD devices is enhanced on the order of ∼104 compared to its undoped counterpart. The "auto-ionization" of Mn2+ dopants in CdSe QDs due to the quantum confinement effect is one reason for this jump in conductivity as described in the Poole-Frenkel effect. STM measurements of the monolayer QD device shows its resistive switching properties. Importantly, the threshold voltage of switching decreased with the increase of doping concentration. All these results confirm the efficiency of Mn2+ doping in zinc-blende CdSe QDs in aqueous medium, by avoiding the "self-purification" effect of CdSe QDs, and their further application as a potential candidate for future memristor devices.