Showing papers on "Thin-film transistor published in 2010"

Material characteristics and applications of transparent amorphous oxide semiconductors

Abstract: Transparent amorphous oxide semiconductors have unique electron transport properties, such as large electron mobility (10–50 cm2/Vs) and the absence of a Hall voltage sign anomaly, that are not seen in conventional amorphous semiconductors. This class of materials has been attracting much attention as a channel layer in thin-film transistors (TFTs) utilizing the above features along with the processing advantage that thin films can be deposited at low temperatures by conventional sputtering methods. The primary driving force for this trend is a rapidly emerging demand for backplane TFTs that can drive the next generation of flat-panel displays. This article reviews the recent advances in fundamental science of these materials and their TFT applications. Emphasis is placed on the view that high ionicity in chemical bonding and large spherical spread of unoccupied metal s orbitals in p-block metal oxides lead to the realization of electronic structures that are advantageous for n-channel TFT applications. Amorphous oxide semiconductors are compared with conventional hydrogenated amorphous silicon, which is used widely as the channel material for backplane TFTs in current liquid-crystal displays.

Role of gallium doping in dramatically lowering amorphous-oxide processing temperatures for solution-derived indium zinc oxide thin-film transistors

Abstract: [*] Prof. T. J. Marks, Dr. A. Facchetti, Dr. S. Jeong, Y.-G. Ha Department of Chemistry and the Materials Research Center Northwestern University 2145 Sheridan Road, Evanston, IL 60208 (USA) E-mail: t-marks@northwestern.edu; a-facchetti@northwestern.edu Prof. J. Moon Department of Materials Science and Engineering Yonsei University 134 Shinchon-dong, Seodaemun-gu, Seoul 120-749 (Korea) [+] Present address: Korea Research Institute of Chemical Technology, 19 Sinseongno, Yuseong, Daejeon 305-600 (Korea)

Organic semiconductor growth and morphology considerations for organic thin-film transistors.

Abstract: Analogous to conventional inorganic semiconductors, the performance of organic semiconductors is directly related to their molecular packing, crystallinity, growth mode, and purity. In order to achieve the best possible performance, it is critical to understand how organic semiconductors nucleate and grow. Clever use of surface and dielectric modification chemistry can allow one to control the growth and morphology, which greatly influence the electrical properties of the organic transistor. In this Review, the nucleation and growth of organic semiconductors on dielectric surfaces is addressed. The first part of the Review concentrates on small-molecule organic semiconductors. The role of deposition conditions on film formation is described. The modification of the dielectric interface using polymers or self-assembled mono-layers and their effect on organic-semiconductor growth and performance is also discussed. The goal of this Review is primarily to discuss the thin-film formation of organic semiconducting species. The patterning of single crystals is discussed, while their nucleation and growth has been described elsewhere (see the Review by Liu et. al).([¹]) The second part of the Review focuses on polymeric semiconductors. The dependence of physico-chemical properties, such as chain length (i.e., molecular weight) of the constituting macromolecule, and the influence of small molecular species on, e.g., melting temperature, as well as routes to induce order in such macromolecules, are described.

A low-bandgap diketopyrrolopyrrole-benzothiadiazole-based copolymer for high-mobility ambipolar organic thin-film transistors.

Abstract: A new, solution-processable, low-bandgap, diketopyrrolopyrrole- benzothiadiazole-based, donor-acceptor polymer semiconductor (PDPP-TBT) is reported. This polymer exhibits ambipolar charge transport when used as a single component active semiconductor in OTFTs with balanced hole and electron mobilities of 0.35 cm2 V-1s-1 and 0.40 cm 2 V-1s-1, respectively. This polymer has the potential for ambipolar transistor-based complementary circuits in printed electronics.

Ultrathin compound semiconductor on insulator layers for high-performance nanoscale transistors

Abstract: Compound semiconductor materials such as gallium arsenide and indium arsenide have outstanding electronic properties, but are costly to process and cannot, on their own, compete with silicon when it comes to low-cost fabrication. But as the relentless miniaturization of silicon electronics is reaching its limits, an alternative route of enhanced device performance is becoming more attractive: the integration of compound semiconductors within silicon. Ali Javey and colleagues now present a promising new concept to integrate ultrathin layers of single-crystal indium arsenide on silicon-based substrates with an epitaxial transfer method, a technique borrowed from large-area optoelectronics. With this technique, involving the use of an elastomeric stamp to lift off indium arsenide nanowires and transfer them to a silicon-based substrate, the authors fabricate thin film transistors with excellent device performance. A potential route to enhancing the performance of electronic devices is to integrate compound semiconductors, which have superior electronic properties, within silicon, which is cheap to process. These authors present a promising new concept to integrate ultrathin layers of single-crystal indium arsenide on silicon-based substrates with an epitaxial transfer method borrowed from large-area optoelectronics. With this technique, the authors fabricate thin-film transistors with excellent device performance. Over the past several years, the inherent scaling limitations of silicon (Si) electron devices have fuelled the exploration of alternative semiconductors, with high carrier mobility, to further enhance device performance1,2,3,4,5,6,7,8. In particular, compound semiconductors heterogeneously integrated on Si substrates have been actively studied7,9,10: such devices combine the high mobility of III–V semiconductors and the well established, low-cost processing of Si technology. This integration, however, presents significant challenges. Conventionally, heteroepitaxial growth of complex multilayers on Si has been explored9,11,12,13—but besides complexity, high defect densities and junction leakage currents present limitations in this approach. Motivated by this challenge, here we use an epitaxial transfer method for the integration of ultrathin layers of single-crystal InAs on Si/SiO2 substrates. As a parallel with silicon-on-insulator (SOI) technology14, we use ‘XOI’ to represent our compound semiconductor-on-insulator platform. Through experiments and simulation, the electrical properties of InAs XOI transistors are explored, elucidating the critical role of quantum confinement in the transport properties of ultrathin XOI layers. Importantly, a high-quality InAs/dielectric interface is obtained by the use of a novel thermally grown interfacial InAsO x layer (~1 nm thick). The fabricated field-effect transistors exhibit a peak transconductance of ~1.6 mS µm−1 at a drain–source voltage of 0.5 V, with an on/off current ratio of greater than 10,000.

Printed, sub-3V digital circuits on plastic from aqueous carbon nanotube inks.

Abstract: Printing electronic components on plastic foils with functional liquid inks is an attractive approach for achieving flexible and low-cost circuitry for applications such as bendable displays and large-area sensors. The challenges for printed electronics, however, include characteristically slow switching frequencies and associated high supply voltages, which together impede widespread application. Combining printable high-capacitance dielectrics with printable high-mobility semiconductors could potentially solve these problems. Here we demonstrate fast, flexible digital circuits based on semiconducting carbon nanotube (CNT) networks and high-capacitance ion gel gate dielectrics, which were patterned by jet printing of liquid inks. Ion gel-gated CNT thin-film transistors (TFTs) with 50 μm channel lengths display ambipolar transport with electron and hole mobilities >20 cm2/V·s; these devices form the basis of printed inverters, NAND gates, and ring oscillators on both polyimide and SiO2 substrates. Five-st...

Flexible organic transistor memory devices.

Abstract: The flexible nonvolatile organic memory devices were developed on the plastic substrates based on the organic thin-film transistors embedding self-assembled gold nanoparticles (Au(NP)). The organic memory devices exhibited good programmable memory characteristics with respect to the program/erase operations, resulting in controllable and reliable threshold voltage shifts. Additionally, the endurance, data retention, and bending cyclic measurements confirmed that the flexible memory devices exhibited good electrical reliability as well as mechanical stability. The memory devices were composed of the solution-processed organic dielectric layers/metallic nanoparticles and the low-temperature processed organic transistors. Therefore, this approach could potentially be applied to advanced flexible/plastic electronic devices as well as integrated organic device circuits.

Use of a 1H-Benzoimidazole Derivative as an n-Type Dopant and To Enable Air-Stable Solution-Processed n-Channel Organic Thin-Film Transistors

Abstract: We present here the development of a new solution-processable n-type dopant, N-DMBI. Our experimental results demonstrated that a well-known n-channel semiconductor, [6,6]-phenyl C(61) butyric acid methyl ester (PCBM), can be effectively doped with N-DMBI by solution processing; the film conductivity is significantly increased by n-type doping. We utilized this n-type doping for the first time to improve the air-stability of n-channel organic thin-film transistors, in which the doping can compensate for the electron traps. Our successful demonstration of n-type doping using N-DMBI opens up new opportunities for the development of air-stable n-channel semiconductors. It is also potentially useful for application on solution-processed organic light-emitting diodes and organic photovoltaics.

Photon-accelerated negative bias instability involving subgap states creation in amorphous In–Ga–Zn–O thin film transistor

Abstract: We investigated the visible photon accelerated negative bias instability (NBI) in amorphous In–Ga–Zn–O (a-IGZO) thin film transistor (TFT). As reported in previous works, the rigid shift in transfer curves with insignificant changes in field-effect mobility and subthreshold swing was observed. On the other hand, there is substantial change in capacitance-voltage characteristics caused by created subgap states. The suggested nature of created states is the ionized oxygen vacancy (VO2+) by the combination of visible light and negative bias. The generated VO2+ states enhance the NBI under illumination as increased deep hole trapping centers. Furthermore, the photoexcitation of VO to stable VO2+ yields excess free carriers in conduction band. The increased carrier density also enhances the negative shift in turn-on voltage of a-IGZO TFT.

Transparent p-type SnOx thin film transistors produced by reactive rf magnetron sputtering followed by low temperature annealing

Abstract: P-type thin-film transistors (TFTs) using room temperature sputtered SnOx (x<2) as a transparent oxide semiconductor have been produced. The SnOx films show p-type conduction presenting a polycrystalline structure composed with a mixture of tetragonal β-Sn and α-SnOx phases, after annealing at 200 °C. These films exhibit a hole carrier concentration in the range of ≈1016–1018 cm−3; electrical resistivity between 101–102 Ω cm; Hall mobility around 4.8 cm2/V s; optical band gap of 2.8 eV; and average transmittance ≈85% (400 to 2000 nm). The bottom gate p-type SnOx TFTs present a field-effect mobility above 1 cm2/V s and an ON/OFF modulation ratio of 103.

High-Performance a-IGZO TFT With $\hbox{ZrO}_{2}$ Gate Dielectric Fabricated at Room Temperature

Abstract: We have investigated the high-performance oxide thin-film transistor (TFT) with an amorphous indium gallium zinc oxide (a-IGZO) channel and ZrO2 gate dielectrics. The a-IGZO TFT is fully fabricated at room temperature without any thermal treatments. ZrO2 is one of the most promising high-k materials. The a-IGZO TFT (channel W/L = 240/30 ?m) with ZrO2 shows high performance such as high on current of 2.11 mA and high field effect mobility of 28 cm2/(V·s) at the gate voltage 10 V. The threshold voltage and the subthreshold swing are 3.2 V and 0.56 V/decade, respectively. Note that the high-performance a-IGZO TFT is higher than ever shown in previous researches.

High-performance solution-processed amorphous zinc-indium-tin oxide thin-film transistors.

Abstract: Films of the high-performance solution-processed amorphous oxide semiconductor a-ZnIn4Sn4O15, grown from 2-methoxyethanol/ethanolamine solutions, were used to fabricate thin-film transistors (TFTs) in combination with an organic self-assembled nanodielectric as the gate insulator. This structurally dense-packed semiconductor composition with minimal Zn2+ incorporation strongly suppresses transistor off-currents without significant mobility degradation, and affords field-effect electron mobilities of ∼90 cm2 V−1 s−1 (104 cm2 V−1 s−1 maximum obtained for patterned ZITO films), with Ion/Ioff ratio ∼105, a subthreshhold swing of ∼0.2 V/dec, and operating voltage <2 V for patterned devices with W/L = 50. The microstructural and electronic properties of ZITO semiconductor film compositions in the range Zn9−2xInxSnxO9+1.5x (x = 1−4) and ZnIn8−xSnxO13+0.5x (x = 1−7) were systematically investigated to elucidate those factors which yield optimum mobility, Ion/Ioff, and threshold voltage parameters. It is shown tha...

Flexible low-voltage organic transistors and circuits based on a high-mobility organic semiconductor with good air stability.

Abstract: Flexible transistors and circuits based on dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT), a conjugated semiconductor with a large ionization potential (5.4 eV), are reported. The transistors have a mobility of 0.6 cm(2) V-1 s(-1) and the ring oscillators have a stage delay of 18 mu s. Due to the excellent stability of the semiconductor, the devices and circuits maintain 50% of their initial performance for a period of 8 months in ambient air.

High and Balanced Hole and Electron Mobilities from Ambipolar Thin-Film Transistors Based on Nitrogen-Containing Oligoacences

Abstract: We demonstrate a strategy for designing high-performance, ambipolar, acene-based field-effect transistor (FET) materials, which is based on the replacement of C−H moieties by nitrogen atoms in oligoacenes. By using this strategy, two organic semiconductors, 6,13-bis(triisopropylsilylethynyl)anthradipyridine (1) and 8,9,10,11-tetrafluoro-6,13-bis(triisopropylsilylethynyl)-1-azapentacene (3), were synthesized and their FET characteristics studied. Both materials exhibit high and balanced hole and electron mobilities, 1 having μh and μe of 0.11 and 0.15 cm2/V·s and 3 having μh and μe of 0.08 and 0.09 cm2/V·s, respectively. The successful demonstration of high and balanced ambipolar FET properties from nitrogen-containing oligoacenes opens up new opportunities for designing high-performance ambipolar organic semiconductors.

Sputtering formation of p-type SnO thin-film transistors on glass toward oxide complimentary circuits

Abstract: Thin film transistors (TFTs) using polycrystalline tin oxides (SnO–SnO2) channels were formed on glass by a conventional sputtering method and subsequent annealing treatments. SnO-channel TFTs showed p-type operation with on/off current ratios of ∼102 and field-effect mobilities of 0.24 cm2 V−1 s−1. Incorporation of excess oxygen to SnO channel layers did not generate holes but did electrons, which in turn led to n-type operation. This result is explained by transformation to a local SnO2-like structure and finally to SnO2. We propose a simple method to fabricate complimentary circuits by simultaneous selective formation of p- and n-channel TFTs.

Instabilities in Amorphous Oxide Semiconductor Thin-Film Transistors

Abstract: Thin-film transistors (TFTs) fabricated using amorphous oxide semiconductors (AOS) exhibit good electron mobility (5 to >; 50 cm2/V · s), they are transparent, and they can be processed at low temperatures. These new materials show a great promise for high-performance large-area electronics applications such as flexible electronics, transparent electronics, and analog current drivers for organic light-emitting diode displays. Before any of these applications can be commercialized, however, a strong understanding of the stability and reliability of AOS TFTs is needed. The purpose of this paper is to provide a comprehensive review and summary of the recently emerging work on the stability and reliability of AOS TFTs with respect to illumination, bias stress, ambient effects, surface passivation, mechanical stress, and defects, as well as to point out areas for future work. An overview of the TFT operation and expected reliability concerns as well as a brief summary of the instabilities in the well-known Si3N4/a-Si:H system is also included.

Light induced instabilities in amorphous indium–gallium–zinc–oxide thin-film transistors

Abstract: The effect of exposure to ultraviolet radiation on the characteristics of amorphous indium–gallium–zinc–oxide thin-film transistors (TFTs) fabricated by sputtering is investigated. After illumination with 1.5 mW cm−2 of 365 nm radiation, in the absence of any bias stress, a persistent negative shift in the characteristics is observed in the dark. The magnitude of the shift increases with exposure time, saturating after about 10 min. Under these conditions the subthreshold exhibits a rigid shift of around 3.6 V and 7.5 V for TFTs with an active layer thickness of 20 nm and 50 nm, respectively. The shift in the dark increases (decreases) when a negative (positive) bias stress is applied under illumination. The instability behavior caused by exposure to light, in the absence of any bias stress, can be explained on the basis of ionization of neutral oxygen vacancies.

Thin-film transistors based on p-type Cu2O thin films produced at room temperature

Abstract: Copper oxide (Cu2O) thin films were used to produce bottom gate p-type transparent thin-film transistors (TFTs). Cu2O was deposited by reactive rf magnetron sputtering at room temperature and the films exhibit a polycrystalline structure with a strongest orientation along (111) plane. The TFTs exhibit improved electrical performance such as a field-effect mobility of 3.9 cm2/V s and an on/off ratio of 2×102.

Glass Substrates for Liquid Crystal Displays

Abstract: We present a brief history of substrate glasses developed by Corning Incorporated (Corning) for use in Active matrix liquid crystal display (AMLCD) displays. The most basic attributes required of AMLCD substrates include thermal and mechanical stability, precise geometry control, a surface that is basically perfectly smooth, and no inclusions large enough to block a pixel in the final display. In addition, the glasses used as substrate materials must be essentially alkali-free so that they do not interact chemically or electronically with thin-film transistors (TFT). Thin, precision sheet was first made at Corning via the slot-draw process, but was eventually moved to the fusion-draw process; neither process was originally intended for this application. Alkali-free glasses were originally developed for electronic applications and lamp envelopes, and considerable research was required to invent compositions that were compatible with the high-viscosity fusion-draw process. Examples of the technical challenges presented by the evolving industry requirements are provided, including eliminating arsenic from the substrate glass and reducing the dimensional change during high-temperature processing of polysilicon-based TFT.

Influence of positive bias stress on N2O plasma improved InGaZnO thin film transistor

Abstract: A post-treatment using N2O-plasma is applied to enhance the electrical characteristics of amorphous indium gallium zinc oxide thin film transistors. Improvements in the field-effect mobility and the subthreshold swing demonstrate that interface states were passivated after N2O-plasma treatment, and a better stability under positive gate-bias stress was obtained in addition. The degradation of mobility, resulted from bias stress, reduces from 6.1% (untreated devices) to 2.6% (N2O-plasma treated devices). Nevertheless, a strange hump characteristic occurs in transfer curve during bias stress, inferring that a parasitic transistor had been caused by the gate-induced electrical field.

Fully Flexible Solution-Deposited ZnO Thin-Film Transistors

Abstract: Electronic systems on fl exible substrates posses the advantage of mechanical fl exibility in actual use, but also provide more rugged rollable devices and may therefore result in lower manufacturing costs associated with continuous roll-to-roll fabrication. To realize these advantages of fl exible electronics, lowtemperature solution processing is strongly desirable. In this regard, organic semiconductor materials have been extensively researched. [ 1 ] Organic semiconductor polymers are soluble in a variety of solvents, and small molecules can be derivatized to soluble precursors. Organic transistors can also be fabricated by solution processing near room temperature, [ 2 ] compatible with temperature-sensitive plastic substrates. [ 3–5 ] Despite successful demonstrations of fl exible organic electronics, however, they are generally sensitive to operating conditions and are unstable during long-term operation. [ 6 ]

Effect of Zr addition on ZnSnO thin-film transistors using a solution process

Abstract: Thin-film transistors (TFTs) with a ZrZnSnO (ZZTO) channel layer were fabricated using a solution process. As-prepared ZnSnO (ZTO) TFTs had a large off-current. However, as the content of Zr ions increased in ZTO, the threshold voltage shifted, and the off-current in the TFTs decreased. Because Zr has a lower standard electrode potential, it is more readily oxidized than Sn or Zn. Thus, Zr acted as an effective carrier suppressor in the ZTO system and a ZZTO TFT with a high mobility of a 4.02 cm2 V−1 s−1 and a large on/off ratio of over 106 was achieved.

Three-terminal field effect devices utilizing thin film vanadium oxide as the channel layer

Abstract: Electrostatic control of the metal-insulator transition (MIT) in an oxide semiconductor could potentially impact the emerging field of oxide electronics. Vanadium dioxide (VO2) is of particular interest due to the fact that the MIT happens in the vicinity of room temperature and it is considered to exhibit the Mott transition. We present a detailed account of our experimental investigation into three-terminal field effect transistor-like devices using thin film VO2 as the channel layer. The gate is separated from the channel through an insulating gate oxide layer, enabling true probing of the field effect with minimal or no interference from large leakage currents flowing directly from the electrode. The influence of the fabrication of multiple components of the device, including the gate oxide deposition, on the VO2 film characteristics is discussed. Further, we discuss the effect of the gate voltage on the device response, point out some of the unusual characteristics including temporal dependence. A re...

Comparative Study on Light-Induced Bias Stress Instability of IGZO Transistors With $\hbox{SiN}_{x}$ and $ \hbox{SiO}_{2}$ Gate Dielectrics

Abstract: This letter examines the effect of the gate dielectric material on the light-induced bias-temperature instability of an In-Ga-Zn-O (IGZO) thin-film transistor (TFT) After applying positive and negative bias stresses, the SiNx-gated TFT exhibited inferior stability to the SiO2-gated TFT, which was explained by the charge trapping mechanism However, light illumination under a negative bias stress accelerated the negative displacement of the threshold voltage (Vth) of the SiNx-gated IGZO TFT compared to that of the SiO2-gated TFT This was attributed to the injection of photocreated hole carriers into the underlying gate dielectric bulk region as well as the hole trapping at the gate/channel interface

Thin film transistor and method of producing thin film transistor

Abstract: The invention provides a thin film transistor comprising an active layer, the active layer comprising an IGZO-based oxide material, the IGZO-based oxide material being represented by a composition formula of In 2-x Ga x ZnO 4-δ , where 0.75

Transistor and display device

Abstract: It is an object to manufacture a highly reliable display device using a thin film transistor having favorable electric characteristics and high reliability as a switching element. In a bottom gate thin film transistor including an amorphous oxide semiconductor, an oxide conductive layer having a crystal region is formed between an oxide semiconductor layer which has been dehydrated or dehydrogenated by heat treatment and each of a source electrode layer and a drain electrode layer which are formed using a metal material. Accordingly, contact resistance between the oxide semiconductor layer and each of the source electrode layer and the drain electrode layer can be reduced; thus, a thin film transistor having favorable electric characteristics and a highly reliable display device using the thin film transistor can be provided.

Organic n-Channel Field-Effect Transistors Based on Arylenediimide-Thiophene Derivatives

Abstract: The synthesis, structural, electrochemical, and thin film electrical and electronic structural properties of a series of arylene diimide-oligothiophene n-type semiconductors are reported. This family of compounds allows analysis of the effects on thin film transistor performance of the following: (i) oligothiophene backbone catenation; (ii) naphthalenediimide vs perylenediimide core interchange; (iii) phenylene group introduction in the oligothiophene backbone. Electrochemical experiments indicate similar redox energetics for all members of this series, while thin film transistor measurements reveal markedly different charge transport performances. The highest electron mobility of 0.35 cm2 V−1 s−1 is recorded for films of benzo[lmn]thieno[3′,4′:4,5]imidazo[2,1-b][3,8]phenanthroline-1,3,6(2H)-trione, 2-octyl (NDI-1T). Solution-processed field effect transistors were also fabricated and surprisingly exhibit electrical performances surpassing that of the vapor-deposited films in the case of isoquino[6′,5′,4′...

Extraction of Subgap Density of States in Amorphous InGaZnO Thin-Film Transistors by Using Multifrequency Capacitance–Voltage Characteristics

Abstract: An extraction technique for subgap density of states (DOS) in an n-channel amorphous InGaZnO thin-film transistor (TFT) by using multifrequency capacitance-voltage (C -V) characteristics is proposed and verified by comparing the measured I- V characteristics with the technology computer-aided design simulation results incorporating the extracted DOS as parameters. It takes on the superposition of exponential tail states and exponential deep states with characteristic parameters for N TA = 1.1 × 1017 cm-3 · eV-1, N DA = 4 × 1015 cm-3 · eV-1, kT TA = 0.09 eV, and kT DA = 0.4 eV. The proposed technique allows obtaining the frequency-independent C-V curve, which is very useful for oxide semiconductor TFT modeling and characterization, and considers the nonlinear relation between the energy level of DOS and the gate voltage V GS. In addition, it is a simple, fast, and accurate extraction method for DOS in amorphous InGaZnO TFTs without optical illumination, temperature dependence, and numerical iteration.