This patent application is assigned to
The following quote was obtained by the news editors from the background information supplied by the inventors: "In active-matrix displays such as liquid crystal displays or organic electro luminescence (EL) displays, thin film transistors (TFTs) are used in pixel circuits.
"For example, a thin film transistor includes a substrate, a gate electrode on the substrate, a gate insulating film over the gate electrode, a semiconductor layer on the gate insulating film, a source electrode and a drain electrode which are electrically connected to the semiconductor layer.
"Although silicon is often used for semiconductor layers of thin film transistors, organic thin film transistors whose semiconductor layers are made of organic materials have been in development in recent years. For example, Patent Literature 1 (PTL 1) discloses a conventional organic thin film transistor (PTL 1)."
In addition to the background information obtained for this patent application, VerticalNews journalists also obtained the inventors' summary information for this patent application: "Technical Problem
"In recent years, as display screens have been becoming larger, lines in pixel circuits have been also becoming longer. Since longer line increases line resistance and current losses in lines, the resistance reduction of lines is desirable. Lines are often patterned together with a gate electrode and a source electrode (drain electrode) in a thin film transistor at the same time. Therefore, resistance reduction of the lines requires the resistance reduction of the gate electrode and others.
"Here, as one way to lower line resistance, thickening of a line, i.e., thickening of the gate electrode and the source electrode (drain electrode) can be considered. On the other hand, to improve the characteristics of a thin film transistor, preferably a gate insulating film should be thinned.
"However, when the thickened gate electrode is coated with the thin gate insulating film, the coatability of the gate insulating film with respect to the gate electrode deteriorates, thus degrading the voltage endurance characteristics of the gate insulating film.
"One non-limiting and exemplary embodiment provides (i) a thin film transistor having a gate insulating film with improved voltage endurance characteristics, (ii) an organic EL light emitting device having the thin film transistor, and (iii) a method of fabricating the thin film transistor.
"Solution to Problem
"In one general aspect, the techniques disclosed here feature a thin film transistor including: a gate electrode above a substrate; a gate insulating layer covering the gate electrode; a semiconductor layer above the gate insulating layer; and a source electrode and a drain electrode which are above the gate insulating layer, and electrically connected to the semiconductor layer, in which the gate insulating layer includes a first area and a second area, the first area being above the gate electrode, the second area being different from an area above the gate electrode, and made of a same substance as the first area, the first area has a higher density than a density of the second area, and the gate insulating layer has a flat surface at an area above which an area where the semiconductor layer and at least one of the source electrode and the drain electrode are contiguous is located.
"In one general aspect, the techniques disclosed here feature a method of fabricating a thin film transistor including: (a) forming a gate electrode above a substrate; (b) forming a gate insulating layer to cover the gate electrode; © forming a source electrode and a drain electrode above the gate insulating layer so as to sandwich an area above the gate electrode; and (d) forming a semiconductor layer to be electrically connected to the source electrode and the drain electrode, in which step (b) includes: applying an insulating material to cover the gate electrode; heating the insulating material in a state where the insulating material applied to the area above the gate electrode protrudes over the insulating material applied to an area different from the area above the gate electrode; and after the heating of the insulating material, pressing a surface of the insulating material with a press member.
"Additional benefits and advantages of the disclosed embodiments will be apparent from the Specification and Drawings. The benefits and/or advantages may be individually obtained by the non-limiting embodiment and features of the Specification and Drawings, which need not all be provided in order to obtain one or more of such benefits and/or advantages.
"According to the exemplary embodiment, not only the voltage endurance characteristics of the gate insulating film can be improved, but also high relative permittivity of the gate insulating layer on the gate electrode can improve TFT characteristics.
BRIEF DESCRIPTION OF DRAWINGS
"These and other advantages and features will become apparent from the following description thereof taken in conjunction with the accompanying Drawings, by way of non-limiting examples of embodiments disclosed herein.
"FIG. 1 is a cross-sectional view of a thin film transistor according to the embodiment.
"FIGS. 2(a)-(e) are cross-sectional views for explaining each step in a method of fabricating a thin film transistor according to the embodiment.
"FIGS. 3(a)-(d) are cross-sectional views for explaining each step in a method of fabricating a thin film transistor according to the embodiment.
"FIG. 4 is a cross-sectional view illustrating a configuration of an organic EL light emitting device according to the embodiment.
"FIGS. 5(a)-(b) illustrate configurations of a thin film transistor according to a modification of the embodiment.
"FIG. 6A illustrates conditions of a gate insulating layer before and after being pressed in a thin film transistor according to the embodiment.
"FIG. 6B illustrates the relationship between the film reduction rate of a gate insulating layer in a thin film transistor according to the embodiment and the relative permittivity of the gate insulating layer after being pressed."
URL and more information on this patent application, see: UKEDA, Takaaki;
Keywords for this news article include: Electronics, Semiconductor,
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