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Mark Townsend

Bio: Mark Townsend is an academic researcher. The author has contributed to research in topics: Quantum tunnelling & Contact resistance. The author has an hindex of 3, co-authored 6 publications receiving 227 citations.

Papers
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Journal ArticleDOI
TL;DR: In this article, a two-dimensional simulation of electrical properties of the radio frequency (RF) sputter amorphous In-Ga-Zn-O (a-IGZO) thin-film transistors (TFTs) is presented.
Abstract: We reported on a two-dimensional simulation of electrical properties of the radio frequency (rf) sputter amorphous In–Ga–Zn–O (a-IGZO) thin-film transistors (TFTs). The a-IGZO TFT used in this work has the following performance: field-effect mobility (μeff) of ∼12 cm2/V s, threshold voltage (Vth) of ∼1.15 V, subthreshold swing (S) of ∼0.13 V/dec, and on/off ratio over 1010. To accurately simulate the measured transistor electrical properties, the density-of-states model is developed. The donorlike states are also proposed to be associated with the oxygen vacancy in a-IGZO. The experimental and calculated results show that the rf sputter a-IGZO TFT has a very sharp conduction band-tail slope distribution (Ea=13 meV) and Ti ohmic-like source/drain contacts with a specific contact resistance lower than 2.7×10−3 Ω cm2.

234 citations

Journal ArticleDOI
TL;DR: In this paper, a two-dimensional simulation methodology for organic heterojunction thin film devices was developed, including multilayer organic light emitting diodes, organic thin-film heter-junction field effect transistors, and stacked heterjunction organic complementary devices.
Abstract: A two-dimensional device simulation methodology for organic heterojunction thin film devices has been developed. Multilayer organic light emitting diodes, organic thin film heterojunction field effect transistors, and stacked heterojunction organic complementary devices were simulated. Heterojunction organic layer devices have been analyzed using a two-dimensional simulator with heterointerface models and organic material specific models. The stacked heterojunction organic double carrier device exhibits both horizontal and vertical carrier flow in the organic thin film. This unique dual-directional carrier flow shows efficient electron-hole recombination resulting in exciton generation in the organic heterojunction layers. Furthermore, the enhanced behavior of the generated excitons has been analyzed using a self-consistent exciton diffusion model. The vertical (thickness) diffusion of the excitons and the lateral (along heterointerface) diffusion (accompanied by exciton hopping) were simulated. The excit...

9 citations

Journal ArticleDOI
TL;DR: In this paper, the numerically efficient Buttiker-probe model is expanded to include electron-hole recombination and generation in the non-equilibrium Green's function (NEGF) framework.
Abstract: State-of-the-art industrial semiconductor device modeling is based on highly efficient Drift-Diffusion (DD) models that include some quantum corrections for nanodevices In contrast, latest academic quantum transport models are based on the non-equilibrium Green’s function (NEGF) method that covers all coherent and incoherent quantum effects consistently Carrier recombination and generation in optoelectronic nanodevices represent an immense numerical challenge when solved within NEGF In this work, the numerically efficient Buttiker-probe model is expanded to include electron–hole recombination and generation in the NEGF framework Benchmarks of the new multiple-particle Buttiker probe method against state-of-the-art quantum-corrected DD models show quantitative agreements except in cases of pronounced tunneling and interference effects

7 citations

Journal ArticleDOI
TL;DR: In this paper, the unidirectional current that is found to flow in the plate circuit when grounded and its relationship to the formation of a cathode spot on the mercury cathode are described.
Abstract: Experiments relating to mercury‐pool stroboscope tubes with external starting bands are described. Of particular interest is the unidirectional current that is found to flow in the plate circuit when grounded and its relationship to the formation of a cathode spot on the mercury cathode. Cathode‐ray oscillograms are exhibited showing the periodic nature of this current. The potential of a disconnected electrode is negative with respect to the cathode and has a value of several thousand volts. Curves of the volt‐ampere characteristics of an anode are given as a function of tube dimensions, gas pressure and other factors.

2 citations

Proceedings ArticleDOI
23 Sep 2020
TL;DR: Thanks to a combination of non-equilibrium Green’s functions and state-of-the-art band structure calculations, versatile, predictive, and fast simulations become accessible within the self-consistent Born approximation, optimized by a generalized low-rank projection.
Abstract: Ultra-scaled FET technology requires simulations at the atomic scale. We present the Victory Atomistic tool inherited from Nemo5. Thanks to a combination of non-equilibrium Green’s functions and state-of-the-art band structure calculations, versatile, predictive, and fast simulations become accessible within the self-consistent Born approximation, optimized by a generalized low-rank projection.

2 citations


Cited by
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Journal ArticleDOI
TL;DR: The recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed andp-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed.
Abstract: Transparent electronics is today one of the most advanced topics for a wide range of device applications. The key components are wide bandgap semiconductors, where oxides of different origins play an important role, not only as passive component but also as active component, similar to what is observed in conventional semiconductors like silicon. Transparent electronics has gained special attention during the last few years and is today established as one of the most promising technologies for leading the next generation of flat panel display due to its excellent electronic performance. In this paper the recent progress in n- and p-type oxide based thin-film transistors (TFT) is reviewed, with special emphasis on solution-processed and p-type, and the major milestones already achieved with this emerging and very promising technology are summarizeed. After a short introduction where the main advantages of these semiconductors are presented, as well as the industry expectations, the beautiful history of TFTs is revisited, including the main landmarks in the last 80 years, finishing by referring to some papers that have played an important role in shaping transparent electronics. Then, an overview is presented of state of the art n-type TFTs processed by physical vapour deposition methods, and finally one of the most exciting, promising, and low cost but powerful technologies is discussed: solution-processed oxide TFTs. Moreover, a more detailed focus analysis will be given concerning p-type oxide TFTs, mainly centred on two of the most promising semiconductor candidates: copper oxide and tin oxide. The most recent data related to the production of complementary metal oxide semiconductor (CMOS) devices based on n- and p-type oxide TFT is also be presented. The last topic of this review is devoted to some emerging applications, finalizing with the main conclusions. Related work that originated at CENIMAT|I3N during the last six years is included in more detail, which has led to the fabrication of high performance n- and p-type oxide transistors as well as the fabrication of CMOS devices with and on paper.

2,440 citations

Journal ArticleDOI
TL;DR: Most device issues, such as uniformity, long-term stability against bias stress and TFT performance, are solved for a-IGZO TFTs.

1,573 citations

Journal ArticleDOI
TL;DR: The formation of amorphous metal oxide semiconducting thin-films using a ‘sol–gel on chip’ hydrolysis approach from soluble metal alkoxide precursors affords unprecedented high field-effect mobilities, reproducible and stable turn-on voltages Von≈0 V and high operational stability at maximum process temperatures as low as 230 °C.
Abstract: A low-temperature, solution-based preparation of amorphous, metal oxide semiconducting thin-films is reported. This ‘sol–gel on chip’ hydrolysis approach yields thin-film transistors with high field-effect mobilities, reproducible and stable turn-on voltages and high operational stability.

895 citations

Patent
04 Nov 2009
TL;DR: In this paper, a gate insulating layer is treated with oxygen radical treatment on a surface of a gate, and a peak of the oxygen concentration at an interface between the gate and a semiconductor layer is observed.
Abstract: An object is to provide favorable interface characteristics of a thin film transistor including an oxide semiconductor layer without mixing of an impurity such as moisture. Another object is to provide a semiconductor device including a thin film transistor having excellent electric characteristics and high reliability, and a method by which a semiconductor device can be manufactured with high productivity. A main point is to perform oxygen radical treatment on a surface of a gate insulating layer. Accordingly, there is a peak of the oxygen concentration at an interface between the gate insulating layer and a semiconductor layer, and the oxygen concentration of the gate insulating layer has a concentration gradient. The oxygen concentration is increased toward the interface between the gate insulating layer and the semiconductor layer.

205 citations

Journal ArticleDOI
TL;DR: Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) invented only one decade ago are now being commercialized for active-matrix liquid crystal display (AMLCD) backplane applications.
Abstract: Amorphous oxide semiconductor (AOS) thin-film transistors (TFTs) invented only one decade ago are now being commercialized for active-matrix liquid crystal display (AMLCD) backplane applications. They also appear to be well positioned for other flat-panel display applications such as active-matrix organic light-emitting diode (AMOLED) applications, electrophoretic displays, and transparent displays. The objectives of this contribution are to overview AOS materials design; assess indium gallium zinc oxide (IGZO) TFTs for AMLCD and AMOLED applications; identify several technical topics meriting future scrutiny before they can be confidently relied upon as providing a solid scientific foundation for underpinning AOS TFT technology; and briefly speculate on the future of AOS TFTs for display and non-display applications.

152 citations