JPH11274510A - Thin film transistor and liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain polarization of a flattened film or an interlayer insulating film of a thin film transistor, stabilize a threshold voltage, and obtain uniform brightness display in a plane, by specifying relative permittivity of the flattened film. SOLUTION: An interlayer film 12 is formed in which an SiO2 film 9, an SiN film 10 and an SiO2 film 11 are laminated in order on the whole surface of a gate insulating film 3, an active layer 4 and a stopper 8. Metal is applied in a contact hole, which is formed in the interlayer insulating film 12 corresponding to a drain 6, thereby forming a drain electrode 13. A flattened film 15 is formed on the whole surface. A contact hole is formed at a position in the flattened film 15 which corresponds to a source 5, and a display electrode 16 serving as a source electrode 14 being in contact with the source 5 is formed. In this case, relative permittivity of the flattened film 15 is made at most 5, preferably, at most 4. As a result, polarization generated by water content in liquid crystal or water content permeating from a gap of seal adhesive agent can be restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor (TFT) having a flattening film.
FT ”. ) And a liquid crystal display (Liquid Crystal Display,
Hereinafter, it is referred to as “LCD”. ).

[0002]

2. Description of the Related Art In recent years, active matrix type LCDs have been developed.
TFTs using a polycrystalline silicon film as an active layer as a driving driver element or a pixel driving element have been developed. Hereinafter, a conventional LCD will be described.

FIG. 3 is a plan view of a conventional TFT, and FIG.
1 shows a cross-sectional view of an LCD using a TFT. As shown in FIG. 4, a gate electrode 2 made of a high melting point metal such as chromium (Cr) and molybdenum (Mo), a gate insulating film 3, and a polycrystal are formed on an insulating substrate 1 made of quartz glass, non-alkali glass, or the like. An active layer 4 made of a silicon film is formed in order.

The active layer 4 is provided with a channel 7 on the gate electrode 2 and on both sides of the channel 7 a source 6 and a drain 5 formed by ion implantation using the stopper 8 on the channel 7 as a mask. ing. Then, the entire surface of the gate insulating film 3, the active layer 4 and the stopper 8 is covered with SiO 2
An interlayer film 12 is formed by stacking a film 9, a SiN film 10, and a SiO2 film 11 in this order, and a contact hole provided corresponding to the drain 6 is filled with a metal such as Al to form a drain electrode 13. Further, a flattening film 15 made of, for example, an organic resin and flattening the surface is formed on the entire surface. Then, a contact hole is formed at a position corresponding to the source 5 of the flattening film 15, and a transparent electrode 16 made of ITO (Indium Thin Oxide) contacting the drain 5 through the contact hole is formed on the flattening film 15. Form.

[0005] The insulating substrate 1 provided with the TFT thus formed and the opposing substrate 17 provided with electrodes (not shown) opposed to the substrate 1 are adhered around the periphery thereof with a sealing adhesive 18 to form the substrate. The gap is filled with the liquid crystal 19.

[0006]

However, in such a conventional TFT structure, impurities or impurity ions from the sealing adhesive generated during curing, or moisture or impurity ions in the liquid crystal 19 in contact with the flattening film 15, Alternatively, moisture that enters from the outside through the portion 20 where the seal portion has peeled off and floats, or moisture in the air that adheres when the flattening film 15 comes into contact with the air adheres to the surface of the flattening film and takes charge, Flattening film 15 or interlayer film 1
Polarization occurs above and below each of the two films.

Therefore, there is a disadvantage that a back channel is formed in the TFT, and the threshold voltage of the TFT changes. In addition, when an insulating film having a large relative dielectric constant is provided on the channel, a change in the electric field above the channel due to the gate is large, so that there is a disadvantage that the threshold voltage changes.

As a result, even when this TFT is used for an LCD, if the threshold voltage of the TFT changes in a direction to increase, the ON current of the TFT decreases, and a bright spot defect in which the pixel always shines occurs. If the threshold voltage changes in a decreasing direction, the off-current increases, which causes a dark spot defect in which the pixel does not shine sufficiently. As a result, a good display cannot be obtained, and the threshold voltage varies in each TFT. There is a disadvantage that it is not possible to obtain a display with uniform brightness within the display.

In view of the above, the present invention has been made in view of the above-mentioned conventional drawbacks, and has a TFT with a stable threshold voltage and a bright spot by suppressing polarization of a flattening film or an interlayer film on the TFT. It is an object of the present invention to provide an LCD that can reduce defects such as defects and obtain a display with uniform brightness in a plane.

[0010]

A TFT according to the present invention comprises a gate electrode, a gate insulating film, a polycrystalline silicon film having a channel, a stopper insulating film, an interlayer film comprising a plurality of layers, and an organic film on an insulating substrate. A TFT having a planarization film made of a material in order, wherein the relative dielectric constant of the planarization film is 5 or less.

Further, a gate electrode, a gate insulating film, a polycrystalline silicon film having a channel, a stopper insulating film, an interlayer film composed of a plurality of layers, and a planarizing film composed of an organic material are sequentially provided on an insulating substrate. In the TFT, the relative dielectric constant of the layer closest to the channel or the stopper insulating film in the interlayer film is 5 or less and the thickness is 4000 Å or more.

Further, a gate electrode, a gate insulating film, a polycrystalline silicon film having a channel, a stopper insulating film, an interlayer film having a plurality of layers, and a planarizing film made of an organic material are sequentially provided on the insulating substrate. In the TFT, a relative dielectric constant of a layer closest to a channel among the interlayer films and the stopper insulating film is 5 or less, and a total thickness is 4000 Å or more.

Further, the present invention is a liquid crystal display device having the above-mentioned TFT.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a TFT according to the present invention will be described with reference to the drawings. FIG. 1 is a sectional view taken along the line AA in FIG. As shown in FIG. 1, Cr and M are formed on an insulating substrate 1 made of quartz glass, non-alkali glass or the like.
A gate electrode 2 made of a high melting point metal such as o, a gate insulating film 3 made of a SiN film and a SiO2 film, and an active layer 4 made of a polycrystalline silicon film are formed in this order.

The active layer 4 is provided with a channel 7 above the gate electrode 2, and a source 5 and a drain 6 formed by ion implantation on both sides of the channel 7. On the channel 7, SiO functioning as a mask covering the channel 7 so that ions do not enter the channel 7 during ion implantation for forming the source 5 and the drain 6.
A stopper 8 made of two films is provided.

Then, an interlayer film 12 is formed on the entire surface of the gate insulating film 3, the active layer 4, and the stopper 8 in the order of the SiO2 film 9, the SiN film 10, and the SiO2 film 11. Further, a metal such as Al is filled in a contact hole provided in the interlayer film 12 corresponding to the drain 6 to form a drain electrode 13. Then, a flattening film 15 made of an organic resin is formed on the entire surface. The flattening film 15 is formed using an organic substance, for example, an acrylic resin. A contact hole is formed at a position corresponding to the source 5 of the flattening film 15, and a display electrode 16 made of a transparent conductive material such as ITO and in contact with the source 5 and also serving as the source electrode 14 is formed.

At this time, by reducing the relative dielectric constant of the above-described flattening film 15 of the TFT, it is possible to suppress the polarization generated by the moisture in the liquid crystal or the moisture entering from the gap of the seal adhesive. In particular, by using a substance having a relative permittivity of 5 or less, preferably 4 or less, polarization can be hardly generated, and thus generation of a back channel can be suppressed. Further, a change in an electric field due to a gate on a channel can be reduced.

Therefore, it is possible to obtain a TFT having a stable threshold voltage, and it is possible to reduce a variation in luminance in a plane of a liquid crystal display panel using the TFT. Further, as shown in FIG. 2, an LCD using the above-mentioned TFT has an insulating substrate 1 having the above-mentioned TFT.
And an opposing substrate 17 opposing the substrate 1, the periphery of which is bonded with a sealing adhesive, and a liquid crystal 19 is filled in a gap formed by the substrates 1 and 17.

By reducing the relative dielectric constant of the stopper 8, it is possible to suppress the polarization generated by the moisture in the liquid crystal or the moisture that has entered through the gap of the sealant. In addition, the occurrence of polarization can be suppressed by increasing the thickness of the stopper. In particular, when the stopper has a relative dielectric constant of 5 or less, preferably 4 or less, and has a thickness of 4000 Å or more, the effect of suppressing the occurrence of polarization is obtained. By doing so, the generation of the back channel can be suppressed.

Further, the relative dielectric constant of the film which is one of the films constituting the interlayer film 12, that is, the SiO2 film 9 which is the layer closest to the active layer in the present embodiment is reduced and the thickness thereof is increased. The occurrence of polarization can be suppressed. As in the case of the stopper, in particular, by using an interlayer film having a relative dielectric constant of 5 or less, preferably 4 or less and a thickness of 4000 Å or more, polarization can be suppressed and the generation of a back channel can be suppressed.

Further, in this embodiment, when the total film thickness of the SiO2 film 9 and the stopper 8 in the interlayer film 12 is large and the relative dielectric constant thereof is small, the polarization can be suppressed. That is, even if the total thickness of the SiO 2 film 9 and the stopper 8 in the interlayer film 12 is 4000 Å or more and the relative dielectric constant is 5 or less, preferably 4 or less, polarization can be suppressed and the back channel Generation can be suppressed.

In the present embodiment, the TFT in the display area of the LCD has been described. However, the present invention is not limited to this, and the driving around the display area for supplying a scanning signal or a video signal to the display area is performed. TFT in circuit
Application is also possible. In such a case as well, the threshold voltage of the TFT does not change as in the case of the TFT in the display area, and each signal can be stably supplied to the display area, so that good display can be obtained.

Further, in the present embodiment, the so-called double gate structure in which the TFT has two gates has been described. However, the same effect can be obtained with a so-called single gate structure having one gate.

[0024]

According to the present invention, polarization can be prevented above and below the interlayer film and the flattening film, so that a TFT having a stable threshold voltage can be obtained, and defects such as bright spots can be reduced to reduce in-plane defects. Thus, it is possible to obtain an LCD capable of obtaining a display with uniform brightness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a TFT showing an embodiment of the present invention.

FIG. 2 is a sectional view of an LCD showing an embodiment of the present invention.

FIG. 3 is a plan view of a conventional TFT.

FIG. 4 is a cross-sectional view of a conventional LCD.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Insulating substrate 2 Gate electrode 4 Active layer 5 Source 6 Drain 7 Channel 8 Stopper 12 Interlayer film 15 Flattening film 16 Display electrode

Claims (6)

[Claims] 1. A gate electrode, a gate insulating film, a polycrystalline silicon film having a channel, a stopper insulating film, an interlayer film composed of a plurality of layers, and a planarizing film composed of an organic material are sequentially provided on an insulating substrate. A thin film transistor, wherein the relative permittivity of the flattening film is 5 or less. 2. An insulating substrate comprising a gate electrode, a gate insulating film, a polycrystalline silicon film provided with a channel, a stopper insulating film, an interlayer film composed of a plurality of layers, and a planarization film composed of an organic material. A thin film transistor, wherein a film of the interlayer film closest to the channel or the thickness of the stopper insulating film is 4000 angstroms or more. 3. The thin film transistor according to claim 2, wherein a film of the interlayer film closest to the channel or a relative permittivity of the stopper insulating film is 5 or less. 4. A gate electrode, a gate insulating film, a polycrystalline silicon film having a channel, a stopper insulating film, an interlayer film composed of a plurality of layers, and a planarizing film composed of an organic material are sequentially provided on an insulating substrate. A thin film transistor, wherein a total thickness of a film of the interlayer film closest to a channel and the thickness of the stopper insulating film is 4000 Å or more. 5. The thin film transistor according to claim 4, wherein a relative dielectric constant of a film of said interlayer film closest to said channel and said stopper insulating film is 5 or less. 6. A liquid crystal display device comprising the thin film transistor according to claim 1.