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Silicon and Metal Oxide Thin Film Transistors: Materials, Process Technology, Device Physics, and Reliability

A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Thin Films and Interfaces".

Deadline for manuscript submissions: closed (30 September 2020) | Viewed by 17970

Special Issue Editor

Prof. Dr. Mamoru Furuta

E-Mail Website1 Website2
Guest Editor
Environmental Science and Engineering, Kochi University of Technology, Kami 782-8502, Japan
Interests: oxide semiconductors; thin-film transistor (TFT); flexible devices; flat-panel displays
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The flat panel display (FPD) market is expected to further expand at a higher growth rate in upcoming years, due to the demand for high-resolution, compact, lightweight, and flexible displays. The thin film transistor (TFT) is a key component for controlling picture quality of FPDs.

TFT is a type of field-effect-transistor (FET), which is commonly used for large-area electronics. These transistors are produced by depositing different types of thin films, such as active semiconductors, dielectrics and metals, over a non-conducting substrate. The significant advantage of the TFT is a low fabrication temperature. The main application of TFTs is in active-matrix liquid-crystal displays (AM-LCDs) or organic light emitting diode (AM-OLED) displays, in which each pixel is controlled by one or several TFTs. In addition to AM-LCDs and OLED displays, TFTs are also used in X-ray imaging devices, various sensors (e.g., fingerprint, bio-medical, pH, temperature sensors), and radio-frequency identification (RFID) chips.

The present interest in TFT materials and their applications can be traced back to the mid-1970s with the invention of hydrogenated amorphous silicon (a-Si:H). Because the low mobility of a-Si:H makes it a weak candidate for high-resolution displays, high-mobility TFTs are an attractive alternative. Poly-Si is one such candidate for high-mobility TFTs, consisting of small quasi single crystals separated by grain boundaries. Thus, for poly-Si TFTs, various crystallization techniques have been proposed to enlarge and control their grain size and crystalline orientation. In recent years, metal oxide TFTs have attracted considerable attention for use in next-generation high-definition and large-area FPDs due to their mobility, large-area uniformity, and compatibility with low-temperature processes. However, the reliability, especially for light-instability, need to be addressed for practical applications. Very recently, hetero-integration of Si and metal oxide becomes more integrated into LSI technology. For a successful hetero-integration process, device structure and process technology have to be explored more deeply.

Nevertheless, the future of TFT technology is dependent on the success of high-resolution flexible displays with integrated circuits and sensors. For that reason, it was felt that a special issue covering up-to-date research efforts would be valuable for those exploring TFT technologies.

It is my honor and pleasure to invite you to submit a manuscript for this Special Issue. Full papers, communications, and reviews are welcome.

Prof. Mamoru Furuta
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • Poly-Si
  • Metal oxide
  • Device Physics
  • Reliability
  • Hetero integration

Published Papers (5 papers)

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Research

12 pages, 3131 KiB  
Article
Quantum Confinement Effect in Amorphous In–Ga–Zn–O Heterojunction Channels for Thin-Film Transistors
by Daichi Koretomo, Shuhei Hamada, Yusaku Magari and Mamoru Furuta
Materials 2020, 13(8), 1935; https://doi.org/10.3390/ma13081935 - 20 Apr 2020
Cited by 16 | Viewed by 3410
Abstract
Electrical and carrier transport properties in In–Ga–Zn–O thin-film transistors (IGZO TFTs) with a heterojunction channel were investigated. For the heterojunction IGZO channel, a high-In composition IGZO layer (IGZO-high-In) was deposited on a typical compositions IGZO layer (IGZO-111). From the optical properties and photoelectron [...] Read more.
Electrical and carrier transport properties in In–Ga–Zn–O thin-film transistors (IGZO TFTs) with a heterojunction channel were investigated. For the heterojunction IGZO channel, a high-In composition IGZO layer (IGZO-high-In) was deposited on a typical compositions IGZO layer (IGZO-111). From the optical properties and photoelectron yield spectroscopy measurements, the heterojunction channel was expected to have the type–II energy band diagram which possesses a conduction band offset (ΔEc) of ~0.4 eV. A depth profile of background charge density indicated that a steep ΔEc is formed even in the amorphous IGZO heterojunction interface deposited by sputtering. A field effect mobility (μFE) of bottom gate structured IGZO TFTs with the heterojunction channel (hetero-IGZO TFTs) improved to ~20 cm2 V−1 s−1, although a channel/gate insulator interface was formed by an IGZO−111 (μFE = ~12 cm2 V−1 s−1). Device simulation analysis revealed that the improvement of μFE in the hetero-IGZO TFTs was originated by a quantum confinement effect for electrons at the heterojunction interface owing to a formation of steep ΔEc. Thus, we believe that heterojunction IGZO channel is an effective method to improve electrical properties of the TFTs. Full article
(This article belongs to the Special Issue Silicon and Metal Oxide Thin Film Transistors: Materials, Process Technology, Device Physics, and Reliability)
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9 pages, 2614 KiB  
Article
Amorphous Tin Oxide Applied to Solution Processed Thin-Film Transistors
by Christophe Avis, YounGoo Kim and Jin Jang
Materials 2019, 12(20), 3341; https://doi.org/10.3390/ma12203341 - 14 Oct 2019
Cited by 16 | Viewed by 4245
Abstract
The limited choice of materials for large area electronics limits the expansion of applications. Polycrystalline silicon (poly-Si) and indium gallium zinc oxide (IGZO) lead to thin-film transistors (TFTs) with high field-effect mobilities (>10 cm2/Vs) and high current ON/OFF ratios (IOn [...] Read more.
The limited choice of materials for large area electronics limits the expansion of applications. Polycrystalline silicon (poly-Si) and indium gallium zinc oxide (IGZO) lead to thin-film transistors (TFTs) with high field-effect mobilities (>10 cm2/Vs) and high current ON/OFF ratios (IOn/IOff > ~107). But they both require vacuum processing that needs high investments and maintenance costs. Also, IGZO is prone to the scarcity and price of Ga and In. Other oxide semiconductors require the use of at least two cations (commonly chosen among Ga, Sn, Zn, and In) in order to obtain the amorphous phase. To solve these problems, we demonstrated an amorphous oxide material made using one earth-abundant metal: amorphous tin oxide (a-SnOx). Through XPS, AFM, optical analysis, and Hall effect, we determined that a-SnOx is a transparent n-type oxide semiconductor, where the SnO2 phase is predominant over the SnO phase. Used as the active material in TFTs having a bottom-gate, top-contact structure, a high field-effect mobility of ~100 cm2/Vs and an IOn/IOff ratio of ~108 were achieved. The stability under 1 h of negative positive gate bias stress revealed a Vth shift smaller than 1 V. Full article
(This article belongs to the Special Issue Silicon and Metal Oxide Thin Film Transistors: Materials, Process Technology, Device Physics, and Reliability)
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8 pages, 2875 KiB  
Article
Memristive Characteristic of an Amorphous Ga-Sn-O Thin-Film Device with Double Layers of Different Oxygen Density
by Ayata Kurasaki, Ryo Tanaka, Sumio Sugisaki, Tokiyoshi Matsuda, Daichi Koretomo, Yusaku Magari, Mamoru Furuta and Mutsumi Kimura
Materials 2019, 12(19), 3236; https://doi.org/10.3390/ma12193236 - 02 Oct 2019
Cited by 9 | Viewed by 2142
Abstract
We have found a memristive characteristic of an amorphous Ga-Sn-O (α-GTO) thin-film device with double layers of different oxygen density. The double layers are deposited using radio frequency (RF) magnetron sputtering, whose gas for the lower layer contains less oxygen, whereas that for [...] Read more.
We have found a memristive characteristic of an amorphous Ga-Sn-O (α-GTO) thin-film device with double layers of different oxygen density. The double layers are deposited using radio frequency (RF) magnetron sputtering, whose gas for the lower layer contains less oxygen, whereas that for the upper layer contains more oxygen, and it is assumed that the former contains more oxygen vacancies, whereas the latter contains fewer vacancies. The characteristic is explained by drift of oxygen and is stable without forming operation because additional structures such as filament are unnecessary. The fabrication is easy because the double layers are successively deposited simply by changing the oxygen ratio in the chamber. Full article
(This article belongs to the Special Issue Silicon and Metal Oxide Thin Film Transistors: Materials, Process Technology, Device Physics, and Reliability)
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9 pages, 2091 KiB  
Article
Colossal Permittivity and Low Dielectric Loss of Thermal Oxidation Single-Crystalline Si Wafers
by Yalong Sun, Di Wu, Kai Liu and Fengang Zheng
Materials 2019, 12(7), 1102; https://doi.org/10.3390/ma12071102 - 03 Apr 2019
Cited by 13 | Viewed by 4793
Abstract
In this work, thin SiO2 insulating layers were generated on the top and bottom surfaces of single-crystalline silicon plates (n type) by thermal oxidation to obtain an insulator/semiconductor/insulator (ISI) multilayer structure. X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) pictures implied [...] Read more.
In this work, thin SiO2 insulating layers were generated on the top and bottom surfaces of single-crystalline silicon plates (n type) by thermal oxidation to obtain an insulator/semiconductor/insulator (ISI) multilayer structure. X-ray diffraction (XRD) pattern and scanning electron microscope (SEM) pictures implied that all of the synthesized SiO2 layers were amorphous. By controlling the thermal oxidation times, we obtained SiO2 layers with various thicknesses. The dielectric properties of silicon plates with different thicknesses of SiO2 layers (different thermal oxidation times) were measured. The dielectric properties of all of the single-crystalline silicon plates improved greatly after thermal oxidation. The dielectric constant of the silicon plates with SiO2 layers was approximately 104, which was approximately three orders more than that of the intrinsic single-crystalline silicon plate (11.9). Furthermore, both high permittivity and low dielectric loss (0.02) were simultaneously achieved in the single-crystalline silicon plates after thermal oxidation (ISI structure). Full article
(This article belongs to the Special Issue Silicon and Metal Oxide Thin Film Transistors: Materials, Process Technology, Device Physics, and Reliability)
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10 pages, 4131 KiB  
Article
Temperature-Dependent Domain Dynamics and Electrical Properties of Nd-doped Bi4Ti2.99Mn0.01O12 Thin Films in Fatigue Process
by Wanli Zhang, Yanhu Mao, Shaoan Yan, Yongguang Xiao, Minghua Tang, Gang Li, Qiangxiang Peng and Zheng Li
Materials 2018, 11(12), 2418; https://doi.org/10.3390/ma11122418 - 29 Nov 2018
Cited by 2 | Viewed by 2702
Abstract
Bi4Ti2.99Mn0.01O12 (BTM) thin films with different ratio of neodymium (Nd) doping were prepared on Pt(111)/Ti/SiO2/Si(100) substrates through a sol-gel method. The effects of Nd doping on domain dynamics and temperature-dependent fatigue behaviors of BTM [...] Read more.
Bi4Ti2.99Mn0.01O12 (BTM) thin films with different ratio of neodymium (Nd) doping were prepared on Pt(111)/Ti/SiO2/Si(100) substrates through a sol-gel method. The effects of Nd doping on domain dynamics and temperature-dependent fatigue behaviors of BTM thin films were systematically studied. The polarization fatigues of BTM (not doped) and Bi3.5Nd0.5Ti2.99Mn0.01O12 (BNTM05) thin films first get better with the increasing temperature (T) from 300 to 350 K and then become worse from 350 to 400 K, while Bi3.15Nd0.85Ti2.99Mn0.01O12 (BNTM85) thin films show enhanced fatigue endurance from 300 to 400 K. It can be shown that the long-range diffusion of oxygen vacancies in BTM thin film happens more easily through the impedance spectra analysis with T from 300 to 475 K, which can be verified by a lower activation energies (0.13–0.14 eV) compared to those of BNTM05 and BNTM85 (0.17–0.21 eV). Using a temperature-dependent piezoresponse force microscopy (PFM), we have found more responsive domain fragments in Nd-substituted films. The microscopic domain evolution from 298 to 448 K was done to further explain that the domain wall unpinning effect has been enhanced with increasing T. The correlation between microscopic domain dynamics and macroscopic electrical properties clearly demonstrates the effects of charged domain wall in Nd-doped BTM thin films during the fatigue tests. Full article
(This article belongs to the Special Issue Silicon and Metal Oxide Thin Film Transistors: Materials, Process Technology, Device Physics, and Reliability)
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