Special Issue "Thin Film Transistor"

A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Crystalline Materials".

Deadline for manuscript submissions: closed (28 February 2019)

Special Issue Editor

Guest Editor
Prof. Dr. Ray-Hua Horng

Department of Electronics Engineering, National Chiao Tung University, Hsinchu 300, Taiwan
Website | E-Mail
Interests: optoelectronic device; LEDs; solar cells; power devices; epilayer transfer; wafer bonding

Special Issue Information

Dear Colleagues,

Thin film transistors are a type of field effect transistor made by depositing thin films of an active semiconductor layer, as well as the dielectric layer. There exist a wide variety of applications, such as active-matrix liquid-crystal displays, activematrix organic light-emitting displays, photodetecting devices, and biosensors. Each individual LCD pixel is controlled by one to four transistors. The TFTs acts as an switches which allows the pixels to turn on and off very easily.The basis difference between LCD and TFT is that TFT is technology is used to produce LCDs. Solution processed organic semiconductors have offered potential applications due to their low cost, facile solution process, easy functionalization, mass production, low temperature, large area manufacture, and flexibility. However, conductive polymers have low conductivity and organic materials degrade in moisture, prohibiting suitable application of OTFTs in ambient condition. OTFT have higher on-off ratio, however, suffers from poor field-effect mobility as compared to inorganic semiconductor based thin film transistors.

Recently, new wide-band energy gap semiconductors can be grown by ALD, PLD, sputtering or MOCVD. They have a high potential to fabricate and apply to TFT. The inorganic semiconductors have good stability against environmental degradation over Organic counter parts whereas organic materials are usually flexible, transparent, and solution-processed at low temperatures, they are prone to degradation, when exposed to heat, moisture, and oxygen.

We invite researchers to submit papers that discuss the development of new functional and smart materials inorganic, as well as organic, semiconductor materials such as, ZnO, InZnO, GaO, AlGaO, AnGaO, AlN/GaN, conducting polymers, molecular semiconductors, perovskite based materials, carbon nanotubes, carbon naotubes/polymer composites and 2D materials (for example, grapheme, MoS2), etc., in potential applications for display drivers, radio frequency identification tags, e-paper, gas, chemical and biosensors, etc.

Prof. Dr. Ray-Hua Horng
Guest Editor

Manuscript Submission Information

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Keywords

  • Materials and Method: Synthesis of proposed semiconductor materials as well as dielectrics materials by low-temperature solution process and different thin film deposition techniques
  • Crystal growth of semiconductor materials and modeling
  • Controlling and optimizing the grain size, crystallinity and surface morphology modification of solution-processed organic semiconductors. Crystallization to improve the field-effect mobility as well as the on–off ratio for application of large-area electronics on flexible substrates
  • Understanding the physical parameter of thin film devices 
  • Material physical, structural and optical characterization such as SEM, HRTEM, BET, XRD, Raman, FTIR, UV-Vis, PL spectroscopy and optimization to improve the interfacial charge transfer
  • Morphology, band gaps (Eg), nanostructures, photoluminescence, and charge carrier transport will be implemented to investigate the morphology-structure-property relationship. A simulation model to predict charge trapping behavior, grain boundary effcets, defect states will be developed as well to complement the experimental results of devices
  • Study and charge trapping in high-k materials used as gate dielectric
  • A facile strategy will be developed to achieve nanostructured morphology variation which generates plasmonics effect
  • Organic thin film transistor for chemical and biological sensing
  • The reliability (failure modes by measuring the electrical properties) and stability (against the environment moisture) of Organic TFT devices with respect to time, bending (stress and strain) analysis for flexible devices. Demonstrate the resistivity of contact electrodes. Verify the local heating at the electrode/semiconductor interface under continued operation

Published Papers (6 papers)

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Research

Open AccessArticle Study on Correlation between Structural and Electronic Properties of Fluorinated Oligothiophenes Transistors by Controlling Film Thickness
Crystals 2019, 9(3), 144; https://doi.org/10.3390/cryst9030144
Received: 1 February 2019 / Revised: 5 March 2019 / Accepted: 7 March 2019 / Published: 12 March 2019
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Abstract
α,ω-diperfluorohexylquaterthiophene (DFH-4T) has been an attractive n-type material employed in the development of high-mobility organic field-effect transistors. This paper presents a systematic study of the relationship between DFH-4T transistor performance and film structure properties as controlled by deposited thickness. When the DFH-4T thickness [...] Read more.
α,ω-diperfluorohexylquaterthiophene (DFH-4T) has been an attractive n-type material employed in the development of high-mobility organic field-effect transistors. This paper presents a systematic study of the relationship between DFH-4T transistor performance and film structure properties as controlled by deposited thickness. When the DFH-4T thickness increases from 8 nm to 80 nm, the room-temperature field-effect mobility increases monotonically from 0.01 to 1 cm2·V−1·s−1, while the threshold voltage shows a different trend of first decrease then increase. The morphology of thin films revealed by atomic force microscopy shows a dramatic change from multilayered terrace to stacked rod like structures as the film thickness is increased. Yet the crystallite structure and the orientation of molecular constituent, as determined by X-ray diffraction and near-edge X-ray absorption fine structure respectively, do not differ much with respect to film thickness increase. Further analyses of low-temperature transport measurements with mobility-edge model demonstrate that the electronic states of DFH-4T transistors are mainly determined by the film continuity and crystallinity of the bottom multilayered terrace. Moreover, the capacitance-voltage measurements of DFH-4T metal-insulator-semiconductor diodes demonstrate a morphological dependence of charge injection from top contacts, which well explains the variation of threshold voltage with thickness. The overall study provides a deeper understanding of microstructural and molecular growth of DFH-4T film and clarify the structural effects on charge transport and injection for implementation of high-mobility top-contact transistors. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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Open AccessArticle Critical Evaluation of Organic Thin-Film Transistor Models
Crystals 2019, 9(2), 85; https://doi.org/10.3390/cryst9020085
Received: 20 December 2018 / Revised: 23 January 2019 / Accepted: 2 February 2019 / Published: 6 February 2019
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Abstract
The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters [...] Read more.
The thin-film transistor (TFT) is a popular tool for determining the charge-carrier mobility in semiconductors, as the mobility (and other transistor parameters, such as the contact resistances) can be conveniently extracted from its measured current-voltage characteristics. However, the accuracy of the extracted parameters is quite limited, because their values depend on the extraction technique and on the validity of the underlying transistor model. We propose here a new approach for validating to what extent a chosen transistor model is able to predict correctly the transistor operation. In the two-step fitting approach we have developed, we analyze the measured current-voltage characteristics of a series of TFTs with different channel lengths. In the first step, the transistor parameters are extracted from each individual transistor by fitting the output and transfer characteristics to the transistor model. In the second step, we check whether the channel-length dependence of the extracted parameters is consistent with the underlying model. We present results obtained from organic TFTs fabricated in two different laboratories using two different device architectures, three different organic semiconductors and five different materials combinations for the source and drain contacts. For each set of TFTs, our approach reveals that the state-of-the-art transistor models fail to reproduce correctly the channel-length-dependence of the transistor parameters. Our approach suggests that conventional transistor models require improvements in terms of the charge-carrier-density dependence of the mobility and/or in terms of the consideration of uncompensated charges in the carrier-accumulation channel. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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Open AccessArticle Role of Hydrogen in Active Layer of Oxide-Semiconductor-Based Thin Film Transistors
Crystals 2019, 9(2), 75; https://doi.org/10.3390/cryst9020075
Received: 26 December 2018 / Revised: 24 January 2019 / Accepted: 30 January 2019 / Published: 31 January 2019
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Abstract
Hydrogen in oxide systems plays a very important role in determining the major physical characteristics of such systems. In this study, we investigated the effect of hydrogen in oxide host systems for various oxygen environments that acted as amorphous oxide semiconductors. The oxygen [...] Read more.
Hydrogen in oxide systems plays a very important role in determining the major physical characteristics of such systems. In this study, we investigated the effect of hydrogen in oxide host systems for various oxygen environments that acted as amorphous oxide semiconductors. The oxygen environment in the sample was controlled by the oxygen gas partial pressure in the radio-frequency-sputtering process. It was confirmed that the hydrogen introduced by the passivation layer not only acted as a “killer” of oxygen deficiencies but also as the “creator” of the defects depending on the density of oxide states. Even if hydrogen is not injected, its role can change owing to unintentionally injected hydrogen, which leads to conflicting results. We discuss herein the correlation with hydrogen in the oxide semiconductor with excess or lack of oxygen through device simulation and elemental analysis. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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Open AccessArticle Surface Treatments on the Characteristics of Metal–Oxide Semiconductor Capacitors
Crystals 2019, 9(1), 1; https://doi.org/10.3390/cryst9010001
Received: 29 November 2018 / Revised: 16 December 2018 / Accepted: 17 December 2018 / Published: 20 December 2018
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Abstract
The properties of metal-oxide semiconductor (MOS) capacitors with different chemical treatments have been examined in this study. A MOS capacitor consists of an Al2O3/n-GaN/AlN buffer/Si substrate. Four chemical treatments, containing organic solvents, oxygen plasma and BCl3 plasma, dilute [...] Read more.
The properties of metal-oxide semiconductor (MOS) capacitors with different chemical treatments have been examined in this study. A MOS capacitor consists of an Al2O3/n-GaN/AlN buffer/Si substrate. Four chemical treatments, containing organic solvents, oxygen plasma and BCl3 plasma, dilute acidic and alkali solvents, and hydrofluoric acid, were used to reduce the metal ions, native oxides, and organic contaminants. The n-GaN surface was treated with these chemical treatments before Al2O3 was grown on the treated n-GaN surface to reduce the interface state trap density (Dit). The value of Dit was calculated using the capacitance–voltage curve at 1 MHz. The Dit of a u-GaN surface was modified using various solutions, which further influenced the contact properties of GaN. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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Open AccessArticle Optical Detection of Green Emission for Non-Uniformity Film in Flat Panel Displays
Crystals 2018, 8(11), 421; https://doi.org/10.3390/cryst8110421
Received: 9 September 2018 / Revised: 31 October 2018 / Accepted: 5 November 2018 / Published: 8 November 2018
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Abstract
Among colours, the green colour has the most sensitivity in human vision so that green colour defects on displays can be effortlessly perceived by a photopic eye with the most intensity in the wavelength 555 nm of the spectrum. With the market moving [...] Read more.
Among colours, the green colour has the most sensitivity in human vision so that green colour defects on displays can be effortlessly perceived by a photopic eye with the most intensity in the wavelength 555 nm of the spectrum. With the market moving forward to high resolution, displays can have resolutions of 10 million pixels. Therefore, the method of detecting the appearance of the panel using ultra-high resolutions in TFT-LCD is important. The machine vision associated with transmission chromaticity spectrometer that quantises the defects are explored, such as blackening and whitening. The result shows the significant phenomena to recognize the non-uniformity of film-related chromatic variation. In contrast, the quantitative assessment illustrates that the just noticeable difference (JND) of chromaticity CIE xyY at 0.001 is the measuring sensitivity for the chromatic variables (x, y), whereas JND is a perceptible threshold for a colour difference metric. Moreover, an optical device associated with a 198Hg discharge lamp calibrates the spectrometer accuracy. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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Open AccessArticle Effectiveness of Light Source on Detecting Thin Film Transistor
Crystals 2018, 8(10), 394; https://doi.org/10.3390/cryst8100394
Received: 9 September 2018 / Revised: 17 October 2018 / Accepted: 19 October 2018 / Published: 21 October 2018
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Abstract
Light sources tend to affect images captured in any automatic optical inspection (AOI) system. In this study, the effectiveness of metal-halide lamps, quartz-halogen lamps, and LEDs as the light sources in AOI systems for the detection of the third and fourth layers electrodes [...] Read more.
Light sources tend to affect images captured in any automatic optical inspection (AOI) system. In this study, the effectiveness of metal-halide lamps, quartz-halogen lamps, and LEDs as the light sources in AOI systems for the detection of the third and fourth layers electrodes of thin-film-transistor liquid crystal displays (TFT-LCDs) is examined experimentally. The results show that the performance of LEDs is generally comparable or better than that of metal-halide and quartz-halogen lamps. The best optical performance is by the blue LED due to its spectrum compatibility with the time-delay-integration charged-coupled device (TDI CCD) sensor and its better spatial resolution. The images revealed by the blue LED are sharper and more distinctive. Since current LEDs are more energy efficient and environmentally friendly, using LEDs as the light source for AOI is very beneficial. As the blue LED performs the best, it should be adopted for AOI using TDI CCD sensors. Full article
(This article belongs to the Special Issue Thin Film Transistor)
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