259 research outputs found
An Approach to Simultaneously Test Multiple Devices for High-Throughput Production of Thin-Film Electronics
New generation of thin-film transistors (TFTs), where the active material is amorphous oxide, conjugated polymer, or small molecules, have the advantage of flexibility, high form factor, and large scale manufacturability through low cost processing techniques, e.g., roll-to-roll printing, screen printing. During high-throughput production using these techniques, the probability of defects being present increases with the speed of manufacturing and area of devices. Therefore a high-throughput and low cost testing technique is absolute essential to maintain high quality of final product. We report a Simultaneous Multiple Device Testing (SMuDT) approach which is up to 10 times faster and cost effective than conventional testing methods. The SMuDT approach was validated using circuit simulation and demonstrated by testing large scale indium gallium zinc oxide (IGZO) TFTs. A method to ‘bin’ the tested devices using Figure of Merit was established.The authors acknowledge the support of this project provided by the EPSRC and Innovate UK through the AUTOFLEX Project (grant no. EP/L505201/1) and CIMLAE Project (EP/K03099X/1). AK and AJF would like to thank PragmatIC Printing Ltd. for wafer samples. Additional data related to this publication which is not of a commercially sensitive nature is available at the DSpace@Cambridge data repository (www.repository.cam.ac.uk).This is the final version of the article. It first appeared from IEEE via http://dx.doi.org/10.1109/JDT.2015.246229
Single-step fabrication of thin-film linear variable bandpass filters based on metal-insulator-metal geometry
A single-step fabrication method is presented for ultra-thin, linearly variable optical bandpass filters (LVBFs) based on a metal–insulator–metal arrangement using modified evaporation deposition techniques. This alternate process methodology offers reduced complexity and cost in comparison to conventional techniques for fabricating LVBFs. We are able to achieve linear variation of insulator thickness across a sample, by adjusting the geometrical parameters of a typical physical vapor deposition process. We demonstrate LVBFs with spectral selectivity from 400 to 850 nm based on Ag (25 nm) and MgF (75–250 nm). Maximum spectral transmittance is measured at ∼70% with a -factor of ∼20.Engineering and Physical Sciences Research Council (EPSRC) (EP/L015455/1); Cambridge Commonwealth, European and International Trust
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Analysis of amorphous indium-gallium-zinc-oxide thin-film transistor contact metal using Pilling-Bedworth theory and a variable capacitance diode model
It is widely reported that threshold voltage and on-state current of amorphous indium-gallium-zinc-oxide bottom-gate thin-film transistors are strongly influenced by the choice of source/drain contact metal. Electrical characterisation of thin-film transistors indicates that the electrical properties depend on the type and thickness of the metal(s) used. Electron transport mechanisms and possibilities for control of the defect state density are discussed. Pilling-Bedworth theory for metal oxidation explains the interaction between contact metal and amorphous indium-gallium-zinc-oxide, which leads to significant trap formation. Charge trapping within these states leads to variable capacitance diode-like behavior and is shown to explain the thin-film transistor operation.This work was supported by the Engineering and Physical Sciences Research CouncilThis is the author's accepted manuscript of the publication: http://dx.doi.org/10.1063/1.480199
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Effects of post-deposition vacuum annealing on film characteristics of p-type CuO and its impact on thin film transistor characteristics
Annealing of cuprous oxide (CuO) thin films in vacuum without phase conversion for subsequent inclusion as the channel layer in p-type thin film transistors (TFTs) has been demonstrated. This is based on a systematic study of vacuum annealing effects on the sputtered p-type CuO as well as the performance of TFTs on the basis of the crystallographic, optical, and electrical characteristics. It was previously believed that high-temperature annealing of CuO thin films would lead to phase conversion. In this work, it was observed that an increase in vacuum annealing temperature leads to an improvement in film crystallinity and a reduction in band tail states based on the X-ray diffraction patterns and a reduction in the Urbach tail, respectively. This gave rise to a considerable increase in the Hall mobility from 0.14 cm/V·s of an as-deposited film to 28 cm/V·s. It was also observed that intrinsic carrier density reduces significantly from 1.8 × 1016 to 1.7 × 10 cm as annealing temperature increases. It was found that the TFT performance enhanced significantly, resulting from the improvement in the film quality of the CuO active layer: enhancement in the field-effect mobility and the on/off current ratio, and a reduction in the off-state current. Finally, the bottom-gate staggered p-type TFTs using CuO annealed at 700 °C showed a field-effect mobility of ∼0.9 cm/V·s and an on/off current ratio of ∼3.4 × 102.This work was supported by the Engineering and Physical Sciences Research Council under Grant No. EP/M013650/1. G.R. acknowledges the support of the Cambridge Trusts
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The Origin of the High Off-State Current in p-Type Cuâ‚‚O Thin Film Transistors
There is a need for a good quality p-type accumulation-mode thin film transistor (TFT) using a metal oxide semiconducting channel. P-type cuprous oxide (Cuâ‚‚O) has been proposed as a suitable semiconductor, but such TFTs have suffered from unacceptably high off-state currents. This paper studies the main origin of this high off-state current. Capacitance-voltage (C-V) characteristics reveal the accumulation of minority carriers (electrons) in the off-state regime (i.e. for a positive gate voltage). The activation energy extracted from the temperature dependence of the drain current as a function of gate voltage shows an abrupt lowering of the activation energy and pinning of the Fermi energy in the off-state region, which is attributed to subgap states at 0.38 eV from the conduction band minimum. This suggests that an electron flow in the off-state causes the high off-state current in p-type Cuâ‚‚O TFTs and not an inability to deplete the channel of holes
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Air Stable Indium-Gallium-Zinc-Oxide Diodes with a 6.4 GHz Extrinsic Cutoff Frequency Fabricated Using Adhesion Lithography
High speed rectifiers that can be fabricated at low cost whilst still maintaining a high performance are of interest for wireless communication applications. In this letter amorphous indium gallium zinc oxide (a-IGZO) has been used with adhesion lithography (a technique to create asymmetric planar electrodes separated by a nanogap) to fabricate high performance Schottky diode rectifiers. The diode area and junction capacitance can be significantly reduced using this technique, improving device cut-off frequencies. Devices of different widths have been fabricated showing rectification ratios between 103-104. Capacitances measured for devices of various sizes were all on the order of 0.1 pF. By applying ac signals to the diode and measuring the output voltage across a load resistor a cut-off frequency was found. a IGZO diodes with an extrinsic cut-off frequency of 6.4 GHz at a 15 dBM input power have been realized. The devices also show good air stability with little change in current-voltage characteristics after 12 months
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