Monthly Archives: April 2015

Black Nanostructured Nb2O5 with Improved Solar Absorption and Enhanced Photoelectrochemical Water Splitting

J. Mater. Chem. A, 2015, Accepted ManuscriptDOI: 10.1039/C5TA01544H, PaperHouLei Cui, Guilian Zhu, YiAn Xie, Wei Zhao, Chongyin Yang, Tianquan Lin, Hui Gu, Fu Qiang HuangBlack TiO2, with increased solar light absorption and enhanced photocatalytic and photoelectrochemical (PEC) performance, has attracted enormous attention, stimulating us to explore the blackening of other oxide semiconductors for enhanced...The content of this RSS Feed (c) The Royal Society of Chemistry

Properties of bottom and top channel interfaces in double-gate back-channel-etched amorphous indium-gallium-zinc oxide thin-film transistors

In this paper, the bottom and top channel interface properties are investigated in the back channel etch-type double-gate amorphous indium–gallium–zinc oxide (a-IGZO) thin-film transistors. The authors apply the subthreshold technique by depleting one channel, while sweeping the gate voltage of the opposite channel to separately characterize the bottom and top channel interfaces. The extracted surface energy distribution of the bottom and top channel interface trap densities is well fitted with an exponential distribution, and the top channel interface trap density is found to be around 2.5 times greater than that of the bottom channel interface at the conduction band edge. This is mainly attributed to the poor quality of the top gate SiOx insulator owing to the low plasma-enhanced chemical vapor deposition temperature or to the defect generation at the back surface of the a-IGZO caused by the plasma damage during the top gate SiOx insulator deposition. The electrons are shown to be more easily trapped at the top channel interface than at the bottom channel interface under high gate bias stresses in the fabricated back channel etch-type double-gate a-IGZO thin-film transistors.

Enhancement of Ru–Si–O/In–Ga–Zn–O MESFET Performance by Reducing Depletion Region Trap Density

In this letter, we investigated the effect of magnetron cathode current ( $I_{c})$ during reactive sputtering of In–Ga–Zn–O (a-IGZO) channel layer on properties of metal-semiconductor field-effect transistors with Ru–Si–O Schottky gate electrode. One can observe that as $I_{c}$ increased from 90 to 150 mA channel mobility ( $mu _{mathrm {ch_{_{}}}!})$ and subthreshold swing $(S)$ improved from $mu _{mathrm {ch_{_{}}!}} =7.5$ cm $^{2}$/$text{V}cdot text{s}$ and $S = 580$ V/dec to $mu _{mathrm {ch}} =8.8$ cm $^{2}$/$text{V}cdot text{s}$ and $S=420$ V/dec, respectively. This enhancement in transistors performance was attributed to the reduction of charge density in the depletion region of Ru–Si–O/In–Ga–Zn–O Schottky contacts, which we assigned to the densification of a-IGZO films fabricated at higher $I_{c}$ .

Metal-Semiconductor Field-Effect Transistors With In–Ga–Zn–O Channel Grown by Nonvacuum-Processed Mist Chemical Vapor Deposition

In-Ga–Zn–O (IGZO) thin films (TFs) were grown by cost-effective nonvacuum solution-processed mist chemical vapor deposition. High quality AgOx Schottky contacts (SCs) were fabricated on these IGZO TFs with rectification ratios and barrier heights as high as $7.9 times 10^{mathrm {mathbf {7}}}$ and 1 eV, respectively, combined with ideality factors as low as 1.32. These SCs were subsequently used as gate contacts in the production of metal–semiconductor field-effect transistors (MESFETs) with excellent switching and stability characteristics. For example, typical ( $W/L$ 785 $mu text{m}/5~mu text{m}$ ) MESFETs were capable of providing ON-currents up to 245 $mu text{A}$ , combined with a large ON/OFF ratio of $3.8 times 10^{mathrm {mathbf {7}}}$ . A mobility of 3.2 cm $^{mathrm {mathbf {2}}}$ /(V.s) and a low subthreshold swing of 356 mV/decade were achieved in the $W/L~524mu text{m}/10~mu text{m}$ transistors. Under positive bias stress, these MESFETs were highly stable, demonstrating the feasibility of using a combination of mist chemical vapor deposition grown IGZO and AgOx SCs to produce stable, low power consumption, and low-cost switching devices.

Influence of addition of indium and of post-annealing on structural, electrical and optical properties of gallium-doped zinc oxide thin films deposited by direct-current magnetron sputtering

Publication date: 29 May 2015 Source:Thin Solid Films, Volume 583 Author(s): Duy Phong Pham , Huu Truong Nguyen , Bach Thang Phan , Van Dung Hoang , Shinya Maenosono , Cao Vinh Tran In this study, both gallium-doped zinc oxide (GZO) and indium-added gallium-doped zinc oxide (IGZO) thin films were deposited on commercial glasses by magnetron dc-sputtering in argon atmosphere. The crystal structure, electrical conductivity and optical transmission of as-deposited as well as post-annealed thin films of both GZO and IGZO were investigated for comparison. A small amount of indium introduced into GZO thin films had improved their polycrystalline structure and increased their electrical conductivity by over 29%. All obtained GZO and IGZO thin films have strong [002] crystalline direction, a characteristic orientation of ZnO thin films. Although post-annealed in air at high temperatures up to 500°C, IGZO thin films still had very low sheet resistance of 6.6Ω/□. Furthermore, they had very high optical transmission of over 80% in both visible and near-infrared regions.

Indigo-based Polymer Bearing Thermocleavable Side Chains for N-Type Organic Thin Film Transistors

J. Mater. Chem. C, 2015, Accepted ManuscriptDOI: 10.1039/C5TC00512D, PaperChang Guo, Jesse Quinn, Bin Sun, Yuning LiA new n-type semiconducting polymer based on indigo having thermocleavable tert-butoxycarbonyl (t-Boc) groups was synthesized and used as an active layer in organic thin film transistors (OTFTs). Twisting of the...The content of this RSS Feed (c) The Royal Society of Chemistry

Comparison of composition and atomic structure of amorphous indium gallium zinc oxide thin film transistor before and after positive bias temperature stress by transmission electron microscopy

In this paper high resolution transmission electron microscopy analysis is performed on indium gallium zinc oxide thin film transistors to determine the crystal structure of the material. The relative elemental concentrations of indium, gallium, zinc and oxygen were quantified and analyzed using energy dispersive spectroscopy before and after subjection to positive gate bias temperature stress at 80 °C. Notable changes in the concentration of oxygen in the device channel were observed along with a reduced concentration of the elements indium, gallium and zinc after electrical stressing. We speculate this relative reduction in metal concentration could be attributed to the outdiffusion of metal ions from the channel region into the surrounding thermal oxide and the increase in the oxygen concentration in the stressed device is related to electric field assisted adsorption of oxygen from the ambient.

Solution-based 5,6,11,12-tetrachlorotetracene crystal growth for high-performance organic thin film transistors

Publication date: July 2015 Source:Organic Electronics, Volume 22 Author(s): Zhengran He , Nereo Lopez , Xiaoliu Chi , Dawen Li 5,6,11,12-Tetrachlorotetracene is a p-type semiconductor with high hole mobility due to its face-to-face molecular packing and improved electronic coupling. In this study, we demonstrate for the first time the solution processing of 5,6,11,12-tetrachlorotetracene with crystal alignment for the application of organic thin film transistors (OTFTs). Enhanced crystal orientation is achieved by confining the solvent evaporation in a restricted space, which introduces a capillary force and effectively aligns the 5,6,11,12-tetrachlorotetracene crystals. At the same time, a double solvent approach (chloroform/methanol) is utilized to tune the crystal size. The addition of polar hydroxyl groups from methanol weakens the interaction between the less polar 5,6,11,12-tetrachlorotetracene solutes and chloroform solvent, and leads to the formation of supramolecular aggregation. The aggregation acts as nucleation seeds for the crystallization of 5,6,11,12-tetrachlorotetracene semiconductor with enlarged crystal width. As a result, the 5,6,11,12-tetrachlorotetracene based OTFTs demonstrate a maximum hole mobility of 1.1cm2/Vs, which is the highest value ever reported from the solution-processed OTFTs based on 5,6,11,12-tetrachlorotetracene semiconductor. Graphical abstract

Self-aligned flexible organic thin-film transistors with gates patterned by nano-imprint lithography

Publication date: July 2015 Source:Organic Electronics, Volume 22 Author(s): H. Gold , A. Haase , A. Fian , C. Prietl , B. Striedinger , F. Zanella , N. Marjanović , R. Ferrini , J. Ring , K.-D. Lee , R. Jiawook , A. Drost , M. König , R. Müller , K. Myny , J. Genoe , U. Kleb , H. Hirshy , R. Prétôt , J. Kraxner , R. Schmied , B. Stadlober Many applications that rely on organic electronic circuits still suffer from the limited switching speed of their basic elements – the organic thin film transistor (OTFT). For a given set of materials the OTFT speed scales inversely with the square of the channel length, the parasitic gate overlap capacitance, and the contact resistance. For maximising speed we pattern transistor channels with lengths from 10μm down to the sub-micrometre regime by industrially scalable UV-nanoimprint lithography. The reduction of the overlap capacitance is achieved by minimising the source–drain to gate overlap lengths to values as low as 0.2μm by self-aligned electrode definition using substrate reverse side exposure. Pentacene based organic thin film transistors with an exceptionally low line edge roughness <20nm of the channels, a mobility of 0.1cm2/Vs, and an on–off ratio of 104, are fabricated on 4″×4″ flexible substrates in a carrier-free process scheme. The stability and spatial distribution of the transistor channel lengths are assessed in detail with standard deviations of L ranging from 185 to 28nm. Such high-performing self-aligned organic thin film transistors enabled a ring-oscillator circuit with an average stage delay below 4μs at an operation voltage of 7.5V. Graphical abstract

High-density plasma etching characteristics of indium–gallium–zinc oxide thin films in CF4/Ar plasma

Publication date: 29 May 2015 Source:Thin Solid Films, Volume 583 Author(s): Young-Hee Joo , Chang-Il Kim We investigated the etching process of indium–gallium–zinc oxide (IGZO) thin films in an inductively coupled plasma system. The dry etching characteristics of the IGZO thin films were studied by varying the CF4/Ar gas mixing ratio, RF power, DC-bias voltage, and process pressure. We determined the following optimized process conditions: an RF power of 700W, a DC-bias voltage of −150V, and a process pressure of 2Pa. A maximum etch rate of 25.63nm/min for the IGZO thin films was achieved in a plasma with CF4/Ar(=25:75), and the selectivity of IGZO to Al and TiN was found to be 1.3 and 0.7, respectively. We determined the ionic composition of the CF4/Ar plasma using optical emission spectroscopy. Analysis of chemical reactions at the IGZO thin film surfaces was performed using X-ray photoelectron spectroscopy.