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Amorphous oxide and thin film transistor achieved

Foreign code F110003742
File No. E06015US1
Posted date Jul 4, 2011
Country United States of America
Application number 50411609
Gazette No. 20090278122
Date of filing Jul 16, 2009
Gazette Date Nov 12, 2009
International application number JP2005003273
International publication number WO2005088726
Date of international filing Feb 28, 2005
Date of international publication Sep 22, 2005
Priority data
  • P2004-071477 (Mar 12, 2004) JP
  • P2004-325938 (Nov 10, 2004) JP
  • 200510592431 (Feb 28, 2005) US
  • 2005JP03273 (Feb 28, 2005) WO
Title Amorphous oxide and thin film transistor achieved
Abstract The present invention relates to an amorphous oxide and a thin film transistor using the amorphous oxide.In particular, the present invention provides an amorphous oxide having an electron carrier concentration less than 1018/cm3, and a thin film transistor using such an amorphous oxide.In a thin film transistor having a source electrode 6, a drain electrode 5, a gate electrode 4, a gate insulating film 3, and a channel layer 2, an amorphous oxide having an electron carrier concentration less than 1018/cm3 is used in the channel layer 2.
Outline of related art and contending technology BACKGROUND ART
A thin film transistor (TFT) is a three-terminal element having a gate terminal, a source terminal, and a drain terminal.It is an active element in which a semiconductor thin film deposited on a substrate is used as a channel layer for transportation of electrons or holes and a voltage is applied to the gate terminal to control the current flowing in the channel layer and switch the current between the source terminal and the drain terminal.Currently, the most widely used TFTs are metal-insulator-semiconductor field effect transistors (MIS-FETs) in which the channel layer is composed of a polysilicon or amorphous silicon film.
Recently, development of TFTs in which ZnO-based transparent conductive oxide polycrystalline thin films are used as the channel layers has been actively pursued (Patent Document 1).These thin films can be formed at low temperatures and is transparent in visible light; thus, flexible, transparent TFTs can be formed on substrates such as plastic boards and films.
However, known ZnO rarely forms a stable amorphous phase at room temperature and mostly exhibits polycrystalline phase; therefore, the electron mobility cannot be increased because of the diffusion at the interfaces of polycrystalline grains.Moreover, ZnO tends to contain oxygen defects and a large number of carrier electrons, and it is thus difficult to decrease the electrical conductivity.Therefore, it has been difficult to increase the on/off ratio of the transistors.
Patent Document 2 discloses an amorphous oxide represented by ZnxMyInzO(x+3y/2+3z/2) (wherein M is at least one element selected from Al and Ga, the ratio x/y is in the range of 0.2 to 12, and the ratio z/y is in the range of 0.4 to 1.4).However, the electron carrier concentration of the amorphous oxide film obtained herein is 1018/cm3 or more.Although this is sufficient for regular transparent electrodes, the film cannot be easily applied to a channel layer of a TFT.This is because it has been found that a TFT having a channel layer composed of this amorphous oxide film does not exhibit a sufficient on/off ratio and is thus unsuitable for TFT of a normally off type.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-298062
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2000-044236
Scope of claims [claim1]
1. A transparent semi-insulating amorphous oxide thin film comprising In, Ga, Zn, and O, wherein the composition in a crystallized state is represented by InGaO3(ZnO)m (wherein m is a natural number less than 6), the electron mobility is more than 1 cm2/(V·sec) and the electron carrier concentration is less than 1016/cm3.
[claim2]
2. A transparent semi-insulating amorphous oxide thin film according to claim 1, wherein the transparent semi-insulating amorphous oxide thin film is a channel layer in a thin film transistor comprising the channel layer, a gate insulating film, a gate electrode, a source electrode, and a drain electrode.
[claim3]
3. A transparent semi-insulating amorphous oxide thin film according to claim 2, wherein the gate insulating film contains one or more selected from Al2O3, Y2O3, or HfO2.
[claim4]
4. A transparent semi-insulating amorphous oxide thin film according to claim 2, wherein the substrate is one of a glass plate, a plastic plate or a plastic film.
[claim5]
5. A transparent semi-insulating amorphous oxide thin film comprising In, Ga, Zn, Mg, and O, wherein the composition in a crystallized state is represented by InGaO3(Zn1-xMgxO)m (wherein m is a natural number less than 6, and 0.80≦x<0.85), the electron mobility is more than 1 cm2/(V·sec) and the electron carrier concentration is less than 1016/cm3.
[claim6]
6. A transparent semi-insulating amorphous oxide thin film according to claim 5, wherein the transparent semi-insulating amorphous oxide thin film is a channel layer in a thin film transistor comprising the channel layer, a gate insulating film, a gate electrode, a source electrode, and a drain electrode.
[claim7]
7. A transparent semi-insulating amorphous oxide thin film according to claim 6, wherein the gate insulating film contains one or more selected from Al2O3, Y2O3, or HfO2.
[claim8]
8. A transparent semi-insulating amorphous oxide thin film according to claim 6, wherein the substrate is one of a glass plate, a plastic plate or a plastic film.
  • Inventor, and Inventor/Applicant
  • HOSONO Hideo
  • HIRANO Masahiro
  • OTA Hiromichi
  • KAMIYA Toshio
  • NOMURA Kenji
  • CANON
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
  • TOKYO INSTITUTE OF TECHNOLOGY
IPC(International Patent Classification)
Reference ( R and D project ) ERATO HOSONO Transparent ElectroActive Materials AREA
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