Monthly Archives: September 2014

Large-grain SiGe-on-insulator with uniform Si concentration by segregation-free rapid-melting growth

Large-grain SiGe-crystal-on-insulator is essential for fabrication of devices such as advanced thin film transistors and/or photosensors. For these purposes, rapid-melting growth of amorphous SiGe stripes (7%–20% Si concentration) on insulating substrates is investigated over a wide range of cooling rates (from 2 to 17 °C/s). The growth features of SiGe change dynamically, depending on the cooling rate. A low cooling rate produces large crystals with laterally graded Si concentration profiles caused by significant Si segregation during solidification. In contrast, a high cooling rate suppresses the Si segregation, but small grains form because of high spontaneous nucleation under super-cooling conditions. By tuning of the cooling rate, moderate super-cooling conditions are obtained as a function of the Si concentration. This controls both the Si segregation and the spontaneous nucleation, and produces large SiGe crystals (∼400 μm length, 7%–20% Si concentration) with three-dimensionally uniform Si profiles.

Origin of High Photoconductive Gain in Fully Transparent Heterojunction Nanocrystalline Oxide Image Sensors and Interconnects

A technique for invisible image capture using a photosensor array based on transparent conducting oxide semiconductor thin-film transistors and transparent interconnection technologies is presented. A transparent conducting layer is employed for the sensor electrodes as well as interconnection in the array, providing about 80% transmittance at visible-light wavelengths. The phototransistor is a Hf–In–Zn–O/In–Zn–O heterostructure yielding a high quantum-efficiency in the visible range.

Electrical characteristics of GdTiO3 gate dielectric for amorphous InGaZnO thin-film transistors

Publication date: 31 October 2014 Source:Thin Solid Films, Volume 569 Author(s): Jim-Long Her , Tung-Ming Pan , Jiang-Hung Liu , Hong-Jun Wang , Ching-Hung Chen , Keiichi Koyama In this article, we studied the structural properties and electrical characteristics of GdTiO3 gate dielectric for amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistor (TFT) applications. The a-IGZO TFT device featuring the GdTiO3 gate dielectric exhibited better electrical characteristics, including a small threshold voltage of 0.14V, a large field-effect mobility of 32.3cm2/V-s, a high Ion/Ioff current ratio of 4.2×108, and a low subthreshold swing of 213mV/decade. Furthermore, the electrical instability of GdTiO3 a-IGZO TFTs was investigated under both positive gate-bias stress (PGBS) and negative gate-bias stress (NGBS) conditions. The electron charge trapping in the gate dielectric dominates the PGBS degradation, while the oxygen vacancies control the NGBS degradation.

The Impact of Orbital Hybridization on the Electronic Structure of Crystalline InGaZnO: A New Perspective on the Compositional Dependence

J. Mater. Chem. C, 2014, Accepted ManuscriptDOI: 10.1039/C4TC01529K, PaperYoungho Kang, Sanghyun Lee, Hasung Sim, Chang Hee Sohn, Wongoo Park, Seul Ji Song, Un Ki Kim, Cheol Seong Hwang, Seungwu Han, Deok-Yong ChoWe report an investigation of the electronic structure of crystalline InGaZnO (IGZO) using X-ray absorption spectroscopy (XAS) and ab-initio density functional theory calculations. The electronic properties of the conduction band...The content of this RSS Feed (c) The Royal Society of Chemistry

A unified physical model of Seebeck coefficient in amorphous oxide semiconductor thin-film transistors

A unified physical model for Seebeck coefficient was presented based on the multiple-trapping and release theory for amorphous oxide semiconductor thin-film transistors. According to the proposed model, the Seebeck coefficient is attributed to the Fermi-Dirac statistics combined with the energy dependent trap density of states and the gate-voltage dependence of the quasi-Fermi level. The simulation results show that the gate voltage, energy disorder, and temperature dependent Seebeck coefficient can be well described. The calculation also shows a good agreement with the experimental data in amorphous In-Ga-Zn-O thin-film transistor.

Charge-Trap Flash-Memory Oxide Transistors Enabled by Copper–Zirconia Composites

A solution-processed electrochemical charge-trap flash memory element is based on a solid solution of copper and zirconium oxides (Cu-ZrO2) as a charge-trapping layer. Because of the facile reduction of Cu2+ to Cu1+, Cu-ZrO2 thin films are especially effective in memory devices based on thin-film transistors when the devices are fabricated from combustion-processed metal–oxide semiconductors (In2O3 and an indium–gallium oxide).

A high-yield vacuum-evaporation-based R2R-compatible fabrication route for organic electronic circuits

Publication date: July 2014 Source:Organic Electronics, Volume 15, Issue 7 Author(s): Eifion R. Patchett , Aled Williams , Ziqian Ding , Gamal Abbas , Hazel E. Assender , John J. Morrison , Stephen G. Yeates , D. Martin Taylor Advances are described in a vacuum-evaporation-based approach for the roll-to-roll (R2R) production of organic thin film transistors (TFTs) and circuits. Results from 90-transistor arrays formed directly onto a plasma-polymerised diacrylate gate dielectric are compared with those formed on polystyrene-buffered diacrylate. The latter approach resulted in stable, reproducible transistors with yields in excess of 90%. The resulting TFTs had low turn-on voltage, on–off ratios ∼106 and mobility ∼1cm2/Vs in the linear regime, as expected for dinaphtho[2,3-b:2′,3′-f] thieno[3,2-b]thiophene the air stable small molecule used as the active semiconductor. We show that when device design is constrained by the generally poor registration ability of R2R processes, parasitic source–drain currents can lead to a >50% increase in the mobility extracted from the resulting TFTs, the increases being especially marked in low channel width devices. Batches of 27 saturated-load inverters were fabricated with 100% yield and their behaviour successfully reproduced using TFT parameters extracted with Silvaco’s UOTFT Model. 5- and 7-stage ring oscillator (RO) outputs ranged from ∼120Hz to >2kHz with rail voltages, VDD , increasing from −15V to −90V. From simulations an order of magnitude increase in frequency could be expected by reducing parasitic gate capacitances. During 8h of continuous operation at VDD =−60V, the frequency of a 7-stage RO remained almost constant at ∼1.4kHz albeit that the output signal amplitude decreased from ∼22V to ∼10V. Over the next 30days of intermittent operation further degradation in performance occurred although an unused RO showed no deterioration over the same period. Graphical abstract Highlights

Contact resistance improvement using interfacial silver nanoparticles in amorphous indium-zinc-oxide thin film transistors

We describe an approach to reduce the contact resistance at compositional conducting/semiconducting indium-zinc-oxide (IZO) homojunctions used for contacts in thin film transistors (TFTs). By introducing silver nanoparticles (Ag NPs) at the homojunction interface between the conducting IZO electrodes and the amorphous IZO channel, we reduce the specific contact resistance, obtained by transmission line model measurements, down to ∼10−2 Ω cm2, ∼3 orders of magnitude lower than either NP-free homojunction contacts or solid Ag metal contacts. The resulting back-gated TFTs with Ag NP contacts exhibit good field effect mobility of ∼27 cm2/V s and an on/off ratio >107. We attribute the improved contact resistance to electric field concentration by the Ag NPs.

Highly transparent bipolar resistive switching memory with In-Ga-Zn-O semiconducting electrode in In-Ga-Zn-O/Ga 2 O 3 /In-Ga-Zn-O structure

In this work, based on wide bandgap Ga2O3 films, we demonstrated a fully transparent bipolar resistive random access memory (RRAM) device with very high average transmittance of 91.7% in the visible region. The semiconducting In-Ga-Zn-O (IGZO) films were used as symmetric electrodes to reduce sneak current. Different I-V performance will introduce a change in the overall oxygen vacancy distribution by an opposite polarity of electroforming voltage. The temperature dependent of I-V characteristics will be fitted to the hopping conduction mechanism for both of the high-resistance states (HRS) and low-resistance states (LRS) with semiconducting nature. The activation energy and trap spacing of LRS were lower and shorter than that of HRS. A model of resistive switching mechanism related to correlated barrier hopping theory has been proposed for the fully transparent IGZO/Ga2O3/IGZO RRAM device.

The effect of the annealing temperature on the transition from conductor to semiconductor behavior in zinc tin oxide deposited atomic layer deposition

We investigated the electrical properties of zinc tin oxide (ZTO) films deposited via atomic layer deposition and compared them to ZnO and SnO2 films as a function of the annealing temperature. The ZTO and ZnO, except for SnO2, films exhibited an electrical transition from a metal to semiconductor characteristics when annealed above 300 °C. The X-ray photoelectron spectroscopy analyses indicate that the relative area of the oxygen vacancy-related peak decreased from 58% to 41% when annealing at temperatures above 400 °C. Thin film transistors incorporating ZTO active layers demonstrated a mobility of 13.2 cm2/V s and a negative bias instability of −0.2 V.