The Experts below are selected from a list of 93 Experts worldwide ranked by ideXlab platform
Seunghyup Yoo - One of the best experts on this subject based on the ideXlab platform.
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modeling the electrical characteristics of tips pentacene thin film transistors effect of contact barrier field dependent mobility and traps
Organic Electronics, 2008Co-Authors: Dipti Gupta, Namho Jeon, Seunghyup YooAbstract:Abstract The device characteristics of organic thin-film transistors (OTFT) fabricated using tris-isopropylsilylethynyl (TIPS)-pentacene are analyzed with the help of a two-dimensional physics-based numerical simulation. The model incorporates contact barrier at a metal–semiconductor Interface, field-dependent mobility, and trap distribution in TIPS-pentacene films and at Dielectric-Semiconductor Interface. The Poole–Frenkel type field-dependence of mobility is included in addition to the contact barrier height of 0.38 eV to describe the non-ideal behavior in the linear region of the output characteristics. An account of the transfer characteristics and its hysteresis behavior is completed in both below- and above- threshold region upon consideration of the presence of acceptor-like traps of an exponential distribution in TIPS-pentacene films and positive trapped charges at Dielectric-Semiconductor Interface. The obtained device parameters not only match the electrical characteristics but also give one an insight on the charge injection, transport, and trap properties of TIPS-pentacene from the perspectives of TFT operation.
Han Wang - One of the best experts on this subject based on the ideXlab platform.
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the role of solution processed high κ gate dielectrics in electrical performance of oxide thin film transistors
Journal of Materials Chemistry C, 2014Co-Authors: Han WangAbstract:We developed a simple and environmentally friendly spin-coating method for high-κ dielectrics (AlOx, ZrOx, YOx and TiOx). These materials were used as gate dielectrics for solution-processed nanocrystalline In2O3 or amorphous InZnO TFTs with a maximum processing temperature of 300 °C. The role of high-κ dielectrics in device performance was systematically studied. Among the high-κ dielectrics, the AlOx-based devices showed the best performance with mobilities of 21.7 cm2 V−1 s−1 in an In2O3 TFT and 11.6 cm2 V−1 s−1 in an InZnO TFT with the on/off current ratio exceeding 106. Furthermore, the devices exhibited ultra-low operating voltages (<3 V) and negligible hysteresis. A comprehensive study suggests that the high performance of the AlOx-based devices could be attributed to the smooth dielectric/semiconductor Interface and the low Interface trap density besides its good insulating properties. Therefore, the solution-processed AlOx can be used as a promising high-κ dielectric for low cost, low voltage, high-performance oxide electronic devices.
N S Sariciftci - One of the best experts on this subject based on the ideXlab platform.
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mobile ionic impurities in poly vinyl alcohol gate dielectric possible source of the hysteresis in organic field effect transistors
Advanced Materials, 2008Co-Authors: Martin Egginger, Mihai Irimiavladu, Reinhard Schwodiauer, Andreas Tanda, Irene Frischauf, Siegfried Bauer, N S SariciftciAbstract:Threshold voltage shifts in organic field effect transistors (OFETs) have been reported frequently. Cyclic sweeps of the gate voltage in OFETs reveal a hysteresis in the transfer characteristics (drain-source current versus gate-source voltage) thereby unfolding an electrical instability of the transistor element. On the one hand bistable transistors with a nonvolatile hysteresis in the transfer characteristics may be used in organic memory elements, whereas on the other hand hysteresis free transistors are desired in integrated organic circuits. Therefore understanding the causes of these electrical bior instabilities in organic field-effect devices is of primary interest. OFETs using charged electrets or ferroelectric-like gate dielectrics (e.g., see [7,8,12,14]) show a hysteresis which is normally attributed to the intrinsic properties of these materials. In polymer dielectrics without an intrinsic hysteresis such as poly(vinyl alcohol) (PVA), gate voltage induced hysteresis are often interpreted in terms of electrostatic screening of trapped charge carriers released under the influence of the electric field between the gate and the source/drain electrodes. Experimental results so far revealed a fairly complex picture of this “bias-stress” effect where the detailed mechanisms involved are not yet fully understood. Several publications report evidences of a charge trapping process in the organic semiconductor close to the semiconductor/dielectric Interface. Lindner et al. supposed that the origin of the hysteresis in organic devices is a combination of slow transport (polarons or mobile ions) with a reaction other than trap recharging, e.g., a direct polaron-bipolaron reaction or a complex formation reaction of polarons / bipolarons with counterions. Bias-stress experiments with pentacene on various inorganic dielectrics indicate a reversible structural change of the semiconductor. A substantial number of experiments demonstrate an influence of the gate dielectric material on the formation of hysteresis effects. Transistors with a polymer gate dielectric are more likely to show a pronounced hysteresis than transistors with an inorganic gate dielectric. It has been reported that hydroxyl groups in the form of silanols at the SiO2-dielectric/semiconductor Interface can work as electron traps which can be eliminated by a thin alkane interlayer. In many organic dielectrics hydroxyl groups are present in large numbers, either as integral part of the chemical structure and/or as impurities remaining from the process of synthesis. Such hydroxyl groups therefore were suspected of being responsible for the hysteresis effect in many OFET configurations. Lee et al. conclude that the increase of hydroxyl groups in polymer dielectrics equally increases electron trapping sites which in turn cause a large hysteresis in OFETs, but as they also discussed, the drain current as well as the gate leakage current increased with increasing hydroxyl density, which may be in contradiction with the proposed idea of immobilized carriers. Polymer dielectrics are often hosts for mobile ions. It has been demonstrated for example that mobile Na ions may diffuse from an underlying substrate into organic semiconductors, like pentacene or poly(3-hexylthiophene) under the influence of an applied voltage. Thereby they cause an increase of the current through the semiconductor and, additionally, a current-voltage hysteresis. The finding that mobile ions in semiconductors alter their electrical performance is not new. p-n junction devices, called flexodes, with a variable current-voltage (I–V) characteristics resulting from a reversible drift of Li ions were suggested in 1963. Two years later, small traces of mobile alkali ions in SiO2 gate dielectrics were reported to cause significant problems in semiconductor devices. In fact, the practical application of MOSFETs was delayed in the early 1960s because of severe gate bias instability problems caused by mobile ionic oxide charges like Na, C O M M U N IC A TI O N
Alex K Y Jen - One of the best experts on this subject based on the ideXlab platform.
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dielectric surface controlled low voltage organic transistors via n alkyl phosphonic acid self assembled monolayers on high k metal oxide
ACS Applied Materials & Interfaces, 2010Co-Authors: Orb Acton, Guy Ting, Patrick J Shamberger, F S Ohuchi, Alex K Y JenAbstract:In this paper, we report on n-alkyl phosphonic acid (PA) self-assembled monolayer (SAM)/hafnium oxide (HfO(2)) hybrid dielectrics utilizing the advantages of SAMs for control over the dielectric/semiconductor Interface with those of high-k metal oxides for low-voltage organic thin film transistors (OTFTs). By systematically varying the number of carbon atoms of the n-alkyl PA SAM from six to eighteen on HfO(2) with stable and low leakage current density, we observe how the structural nature of the SAM affects the thin-film crystal structure and morphology, and subsequent device performance of low-voltage pentacene based OTFTs. We find that two primary structural factors of the SAM play a critical role in optimizing the device electrical characteristics, namely, the order/disorder of the SAM and its physical thickness. High saturation-field-effect mobilities result at a balance between disordered SAMs to promote large pentacene grains and thick SAMs to aid in physically buffering the charge carriers in pentacene from the adverse effects of the underlying high-k oxide. Employing the appropriate n-alkyl PA SAM/HfO(2) hybrid dielectrics, pentacene-based OTFTs operate under -2.0 V with low hysteresis, on-off current ratios above 1 x 10(6), threshold voltages below -0.6 V, subthreshold slopes as low as 100 mV dec(-1), and field-effect mobilities as high as 1.8 cm(2) V(-1) s(-1).
Aivars J Lelis - One of the best experts on this subject based on the ideXlab platform.
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multi resonance frequency spin dependent charge pumping and spin dependent recombination applied to the 4h sic sio2 Interface
Journal of Applied Physics, 2017Co-Authors: Mark A Anders, P M Lenahan, Aivars J LelisAbstract:We report on a new electrically detected magnetic resonance (EDMR) approach involving spin dependent charge pumping (SDCP) and spin dependent recombination (SDR) at high (K band, about 16 GHz) and ultra-low (360 and 85 MHz) magnetic resonance frequencies to investigate the dielectric/semiconductor Interface in 4H-SiC metal-oxide-semiconductor field-effect transistors (MOSFETs). A comparison of SDCP and SDR allows for a comparison of deep level defects and defects with energy levels throughout most of the bandgap. Additionally, a comparison of high frequency and ultra-low frequency measurements allows for (1) the partial separation of spin-orbit coupling and hyperfine effects on magnetic resonance spectra, (2) the observation of otherwise forbidden half-field effects, which make EDMR, at least, in principle, quantitative, and (3) the observation of Breit-Rabi shifts in superhyperfine measurements. (Observation of the Breit-Rabi shift helps in both the assignment and the measurement of superhyperfine parame...