Monthly Archives: January 2015

Improvement of negative-bias-illumination-stress stability in all-transparent double-gate InGaZnO thin-film transistors

Fully transparent amorphous-InGaZnO thin-film transistors (TFTs) with double-gate (DG) configuration were fabricated. Both top-gate and bottom-gate (BG) TFT fabricated with a single gate-stack structure were found to exhibit sound device characteristics with μsat of 17.0 and 18.1 cm2 V−1 s−1, respectively. Confirmed benefits of DG configuration include improved current drivability and threshold voltage tunability. Further, controlling the fixed voltage bias to the BG was observed to enhance device stability under negative-bias-illumination-stress conditions.

Improved Output characteristics of Organic Thin Film Transistors by using an Insulator/Protein Overlayer and their applications

J. Mater. Chem. C, 2015, Accepted ManuscriptDOI: 10.1039/C4TC02823F, PaperJinsung Choi, Hong Goo Jeon, O Eun Kwon, Ingon Bae, Jaewon Cho, Yunki Kim, Byoungchoo ParkWe herein present our study of the effect of an insulator/protein overlayer deposited onto semiconducting active layers in organic thin film transistors (OTFTs) with regard to their electrical performance. The...The content of this RSS Feed (c) The Royal Society of Chemistry

Simulation of Laterally Coupled InGaZnO<sub>4</sub>-Based Electric-Double-Layer Transistors for Synaptic Electronics

Artificial synapse is the key element for neuromorphic systems. Recently, synaptic transistors have been proposed and investigated, but physical understanding of such synaptic devices based on ion/electron electrostatic coupling effect remains unknown. Here, laterally coupled InGaZnO4 electric-double-layer synaptic transistors were numerically simulated. An ion drift-diffusion model is employed to describe the laterally capacitive coupling of the proton conducting electrolyte. Important synaptic behaviors, such as excitatory postsynaptic current and paired-pulse facilitation, are mimicked by the transient solution. InGaZnO4 synaptic device exhibits an extremely low-power consumption of $sim 0.2$ pJ/spike. Our simulation results are interesting for energy-efficient synaptic electronics and neuromorphic systems.

Energy-Efficient Artificial Synapses Based on Flexible IGZO Electric-Double-Layer Transistors

Flexible low-voltage indium-gallium-zinc-oxide (IGZO) electric-double-layer transistors are fabricated on polyethylene terephthalate substrates at room temperature and proposed for energy-efficient artificial synapse application. The IGZO channel conductance and the gate voltage pulse are regarded as synaptic weight and synaptic spike, respectively. The energy consumption of our IGZO synaptic transistor is estimated to be as low as $sim 0.23$ pJ/spike. Short-term synaptic plasticity and high-pass filtering behaviors are also mimicked in an individual IGZO synaptic transistor.

Photochemically Activated Flexible Metal-Oxide Transistors and Circuits Using Low Impurity Aqueous System

High mobility flexible metal-oxide thin-film transistors and circuits have been fabricated on an ultrathin plastic substrate using environmentally benign aqueous solution system and low-temperature photochemical activation process ( $sim 150$ °C). Results show that the indium-gallium–zinc oxide (IGZO) thin-film transistors (TFTs) fabricated from nitrate-based precursors in aqueous solution outperform the devices from acetate-based precursors in alcohol solution. Here, IGZO TFTs and seven-stage ring oscillators are demonstrated on a $3sim 5~mu $ m-thick polyimide substrates with an average mobility of $>6.9~mathrm{cm}^{2}$ /V-s, subthreshold slope of $sim 0.14$ V/decade, and oscillation frequency of $sim 340$ kHz corresponding to 210 ns of propagation delay per stage at a supply bias of 20 V.

$1/f$ Noise Expressions for Amorphous InGaZnO TFTs Considering Mobility Power-Law Parameter in Above-Threshold Regime

Analytical $1/f$ noise expressions are presented for amorphous InGaZnO thin-film transistors considering the well-known power-law parameter $alpha $ in the mobility equation. The drain current noise power spectral density (PSD) is derived from Ghibaudo’s carrier number fluctuation model. It is found that the parameter $alpha $ clarifies the relationship between the drain current noise PSD and the drain current. The relationship is verified by the available experimental data.

High-Speed Pseudo-CMOS Circuits Using Bulk Accumulation a-IGZO TFTs

We propose a way to achieve high-speed circuits with dual-gate (DG) bulk-accumulation back-channel-etched (BCE) amorphous indium-gallium–zinc-oxide (a-IGZO) thin-film transistors (TFTs) using the pseudo-CMOS structure. The DG BCE a-IGZO TFTs exhibit field-effect mobility ( $mu _{mathrm {mathbf {FE}}}$ ), threshold voltage ( $V_{mathrm {mathbf {th}}}$ ), and subthreshold swing of 30 ± 3 $mathrm{cm}^{mathrm {mathbf {2}}}$ /Vs, 2 ± 0.5 V, and 120 ± 30 mV/decade, respectively. For input voltage ( $V_{mathrm {mathbf {DD}}}$ ) of 20 V, seven-stage pseudo-CMOS ring oscillators implemented with the BCE bulk-accumulation a-IGZO TFTs show oscillation frequency of 6.51 MHz, which corresponds to a propagation delay time of 11 ns/stage and is faster than the 17 ns/stage delay of the fastest single-gate-driven ratioed coplanar a-IGZO TFT circuits.

Dual-Sweep Combinational Transconductance Technique for Separate Extraction of Parasitic Resistances in Amorphous Thin-Film Transistors

We report a dual-sweep combinational transconductance technique for separate extraction of parasitic source ( ${R}_{S}$ ) and drain ( $R_{D}$ ) resistances in thin-film transistors (TFTs) by combining forward and reverse transfer characteristics. In the proposed technique, gate bias-dependent total resistance [ $R_{rm TOT}$ ( $V_{rm GS}$ )] and degradation of the transcond- uctance due to the parasitic resistance at the source terminal during the dual-sweep characterization are employed. Applying the proposed technique to amorphous oxide semiconductor TFTs with various combinations of channel length ( ${L}$ ) and width ( $W$ ), we successfully separated $R_{S}$ and $R_{D}$ . A model for the $W$ - and $L$ -dependences of the extracted parasitic resistances is also provided.

Bethe–Salpeter calculation of optical-absorption spectra of In 2 O 3 and Ga 2 O 3

Transparent conducting oxides keep attracting strong scientific interest not only due to their promising potential for ‘transparent electronics’ applications but also due to their intriguing optical absorption characteristics. Materials such as In 2 O 3 and Ga 2 O 3 have complicated unit cells and, consequently, are interesting systems for studying the physics of excitons and anisotropy of optical absorption. Since currently no experimental data is available, for instance, for their dielectric functions across a large photon-energy range, we employ modern first-principles computational approaches based on many-body perturbation theory to provide theoretical-spectroscopy results. Using the Bethe–Salpeter framework, we compute dielectric functions and we compare to spectra computed without excitonic effects. We find that the electron–hole interaction strongly modifies the spectra and we discuss the anisotropy of optical absorption that we find ...

Towards environmental friendly solution-based ZTO/AlO x TFTs

Solution based deposition has been recently considered as a viable option for low-cost flexible electronics. In this context research efforts have been increasingly centred on the development of suitable solution-processed materials for oxide based transistors. Nevertheless, the majority of synthetic routes reported require the use of toxic organic solvents. In this work we report on a new environmental friendly solution combustion synthesis route, using ethanol as solvent, for the preparation of indium/gallium free amorphous zinc-tin oxide (ZTO) thin film transistors (TFTs) including AlO x gate dielectric. The decomposition of ZTO and AlO x precursor solutions, electrical characterization and stability of solution processed ZTO/AlO x TFTs under gate-bias stress, in both air and vacuum atmosphere, were investigated. The devices demonstrated low hysteresis ( ΔV = 0.23 V), close to zero turn on voltage, low threshold voltage ...