KR20170026720A - Liquid crystal display device - Google Patents

Abstract

The present invention relates to a display device which can improve charge mobility without changing a threshold voltage value. According to an embodiment of the present invention, the display device comprises: a substrate; a first gate electrode positioned on the substrate; a gate insulation film positioned on the first gate electrode; a semiconductor positioned on the gate insulation film and made of an oxide semiconductor material; an etching prevention film positioned on the semiconductor; a first and a second contact hole formed on the etching prevention film to expose the semiconductor; a source electrode positioned on the etching prevention film and connected to the semiconductor through the first contact hole; a drain electrode positioned on the etching prevention film and connected to the semiconductor through the second contact hole; a protective film positioned on the source electrode and the drain electrode; and a second gate electrode positioned on the protective film.

Description

[0001] LIQUID CRYSTAL DISPLAY DEVICE [0002]

The present invention relates to a display device, and more particularly, to a display device capable of improving charge mobility without changing a threshold voltage value.

In general, a thin film transistor (TFT) is used as a switching element for independently driving each pixel in a flat panel display device such as a liquid crystal display device or an organic light emitting display. A thin film transistor panel including a thin film transistor includes a thin film transistor, a pixel electrode connected to the thin film transistor, a gate line for transmitting a gate signal to the thin film transistor, and a data line for transmitting a data signal.

The thin film transistor includes a gate electrode connected to the gate line, a source electrode connected to the data line, a drain electrode connected to the pixel electrode, and a semiconductor positioned over the gate electrode between the source electrode and the drain electrode And transmits a data signal, which is transmitted through the data line, to the pixel electrode in accordance with the gate signal transmitted through the gate line.

At this time, the semiconductor of the thin film transistor may be formed of amorphous silicon, polycrystalline silicon, metal oxide, or the like.

In recent years, research on oxide semiconductors using metal oxides with lower cost and uniformity than polycrystalline silicon has been actively pursued with higher electron mobility and higher on / off ratio than amorphous silicon.

An object of the present invention is to provide a display device capable of improving charge mobility without changing a threshold voltage value when an oxide semiconductor material is used as a semiconductor of a thin film transistor.

According to another aspect of the present invention, there is provided a display device including a substrate, a first gate electrode disposed on the substrate, a gate insulating film disposed on the first gate electrode, A first contact hole and a second contact hole formed in the etch stop layer to expose the semiconductor; and a second contact hole located on the etch stop layer, A source electrode, a drain electrode connected to the semiconductor through the second contact hole, a protection film located on the source electrode and the drain electrode, and a second gate electrode located on the protection film, And a control unit.

The etch stopping layer may cover the upper surface and the side surface of the semiconductor.

The width of the second gate electrode may be narrower than the width of the etch stopping film.

A constant voltage may be applied to the second gate electrode.

A positive DC voltage may be applied to the second gate electrode.

A voltage of 0V or more and 40V or more may be applied to the second gate electrode.

The second gate electrode may receive a different signal from the first gate electrode.

The semiconductor may be made of ITZO or IGZO.

The second gate electrode may be made of ITO or IZO.

A display device according to an embodiment of the present invention includes a switching control signal generating unit for generating a switching control signal based on an input control signal from the outside, a data driver for outputting a data voltage, a plurality of pixels, And a plurality of switching elements for transmitting the data voltage to the data line in accordance with the switching control signal, wherein the switching element includes a first gate electrode, a second gate electrode, The first contact hole, the second contact hole, the source electrode, the drain electrode, the protective film, and the second gate electrode.

The display device according to an embodiment of the present invention as described above has the following effects.

The present invention can realize a thin film transistor having a high charge mobility without changing the threshold voltage value.

In addition, when such a thin film transistor is applied to a switching element of a demultiplexer of a high-resolution display device, the cost can be reduced and a decrease in transmittance can be prevented.

1 is a cross-sectional view of a display device according to an embodiment of the present invention.
2 is a graph showing a threshold voltage according to a voltage value applied to the second gate electrode.
3 is a graph showing charge mobility according to a voltage value applied to the second gate electrode.
4 is a cross-sectional view of a display device according to a comparative example.
5 is a block diagram of a display device according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

In the drawings, the thickness is enlarged to clearly represent the layers and regions. Like parts are designated with like reference numerals throughout the specification. It will be understood that when an element such as a layer, film, region, plate, or the like is referred to as being "on" another portion, it includes not only the element directly over another element, Conversely, when a part is "directly over" another part, it means that there is no other part in the middle.

First, a display device according to an embodiment of the present invention will be described with reference to FIG.

1 is a cross-sectional view of a display device according to an embodiment of the present invention.

As shown in FIG. 1, a first gate electrode 124 is formed on a substrate 110.

The substrate 110 may be made of transparent glass, plastic, or the like. The substrate 110 may be formed of a flat plate or a bent material.

The first gate electrode 124 may be formed of a metal material or alloy such as gold, silver, copper, nickel, aluminum, molybdenum, or the like. The first gate electrode 124 may be a single layer or may be a multi-layered structure. For example, a layer made of copper and a layer made of titanium may be stacked.

A gate insulating layer 140 is formed on the first gate electrode 124. The gate insulating layer 140 may be formed of an inorganic insulating material such as silicon nitride (SiNx), silicon oxide (SiOx), or the like. In addition, the gate insulating film 140 may be composed of a single film or a multi-film.

A semiconductor 154 is formed on the gate insulating film 140. The semiconductor 154 is positioned to overlap with the first gate electrode 124. The semiconductor 154 may be made of an oxide semiconductor material. For example, the semiconductor 154 may be formed of indium tin zinc oxide (ITZO), indium gallium zinc oxide (IGZO), or the like.

An etching prevention film 180a is formed on the semiconductor 154. [ An inorganic insulating material such as silicon nitride (SiNx), silicon oxide (SiOx), or the like.

The etch stopping film 180a covers the upper surface and the side surface of the semiconductor 154.

A first contact hole 181 and a second contact hole 183 are formed in the etch stopping film 180a. A part of the upper surface of the semiconductor 154 is exposed by the first contact hole 181 and the second contact hole 183. The etching prevention film 180a entirely covers the upper surface of the semiconductor 154 except for the portion where the first contact hole 181 and the second contact hole 183 are formed.

A source electrode 173 and a drain electrode 175 are formed on the etch stopping layer 180a. The source electrode 173 and the drain electrode 175 may be formed of a metal material or an alloy. The source electrode 173 and the drain electrode 175 may be formed of a single layer or a multi-layered structure. For example, a layer made of copper and a layer made of titanium may be stacked.

The source electrode 173 is connected to the semiconductor 154 through the first contact hole 181. The drain electrode 175 is connected to the semiconductor 154 through the second contact hole 183.

On the source electrode 173 and the drain electrode 175, a protective film 180b is formed. The passivation layer 180b may be formed of an inorganic insulating material such as silicon nitride (SiNx), silicon oxide (SiOx), or the like. However, the present invention is not limited thereto, and the protective layer 180b may be formed of an organic insulating material.

A second gate electrode 195 is formed on the passivation layer 180b. The second gate electrode 195 may be formed of a transparent metal oxide such as ITO (Indium Tin Oxide) or IZO (Indium Zinc Oxide).

The second gate electrode 195 overlaps with the semiconductor 154. In addition, an etching prevention film 180a is disposed between the semiconductor 154 and the second gate electrode 195. The width of the second gate electrode 195 is narrower than the width of the etch stopping film 180a.

The first gate electrode 124, the second gate electrode 195, the source electrode 173 and the drain electrode 175 together with the semiconductor 154 form a thin film transistor (TFT).

The display device according to an embodiment of the present invention may include a plurality of pixels and a driver for driving the pixels. Such a thin film transistor may be used as a switching element connected to each pixel or as a switching element located in a driving portion. Each pixel may include a pixel electrode and / or a common electrode, and the second gate electrode 195 may be located on the same layer as the pixel electrode or the common electrode, and may be formed of the same material.

The first gate electrode 124 and the second gate electrode 195 are not electrically connected. Different signals are applied to the first gate electrode 124 and the second gate electrode 195. A gate-on voltage and a gate-off voltage are periodically applied alternately to the first gate electrode 124, and a constant voltage is applied to the second gate electrode 195.

Hereinafter, the relationship between the voltage applied to the second gate electrode of the display device, the threshold voltage, and the charge mobility will be described with reference to FIGS. 2 and 3. FIG.

FIG. 2 is a graph showing a threshold voltage according to a voltage value applied to a second gate electrode, and FIG. 3 is a graph illustrating a charge mobility according to a voltage value applied to the second gate electrode.

As shown in FIG. 2, when a negative voltage is applied to the second gate electrode of the display device according to an exemplary embodiment of the present invention, the threshold voltage tends to decrease as the voltage increases. When a positive voltage is applied to the second gate electrode, the threshold voltage tends to be constant regardless of the voltage value. That is, when a positive voltage is applied to the second gate electrode, the threshold voltage does not decrease even if the voltage value increases.

As shown in FIG. 3, when negative voltage is applied to the second gate electrode of the display device according to an exemplary embodiment of the present invention, the charge mobility shows a low value, and the charge mobility I can confirm almost constant. And when the positive voltage is applied to the second gate electrode, the charge mobility tends to increase as the voltage value increases. That is, the higher the positive voltage is applied to the second gate electrode, the more the charge mobility increases.

Referring to the graphs of FIG. 2 and FIG. 3, a thin film transistor having a high charge mobility can be realized by applying a positive DC voltage to a second gate electrode of a display device according to an embodiment of the present invention without changing a threshold voltage .

Hereinafter, a comparative example will be described with reference to FIG.

4 is a cross-sectional view of a display device according to a comparative example.

In the display device according to the comparative example, the first gate electrode 124 is formed on the substrate 110, the gate insulating film 140 is formed on the first gate electrode 124, A semiconductor 154 made of a material is formed. An etch stopping film 180a is formed on the semiconductor 154 and the etch stopping film 180a is located only on the center of the semiconductor 154. [ A source electrode 173 and a drain electrode 175 are formed on the etch stopping film 180a and the semiconductor 154. A protective film 180b is formed on the source electrode 173 and the drain electrode 175. [ A second gate electrode 195 is formed on the passivation layer 180b.

In the comparative example, the etch stopping film 180a is located only in a partial region between the second gate electrode 195 and the semiconductor 154. On the other hand, in one embodiment of the present invention, the etch stopping layer 180a is entirely disposed between the second gate electrode 195 and the semiconductor 154. In the case of the display device according to the comparative example, as the voltage value is increased, the charge mobility increases as the positive voltage is applied to the second gate electrode, and thus the threshold voltage value tends to decrease. In contrast, when the positive voltage is applied to the second gate electrode 195, the charge mobility increases as the voltage value increases, and the threshold voltage value is prevented from being fluctuated by the etch stopping layer 180a. can do. This is because the region where the etch stopping layer 180a is formed is wider than that in the comparative example, so that the influence of the voltage applied to the second gate electrode 195 on the semiconductor 154 can be reduced.

Hereinafter, a display device according to an embodiment of the present invention will be described with reference to FIG. The overall structure of a display device to which the thin film transistor structure shown in FIG. 1 described above is applied will be described.

5 is a block diagram of a display device according to an embodiment of the present invention.

A display device according to an exemplary embodiment of the present invention includes a liquid crystal panel assembly 300 and a gate driver 400 connected to the data driver 500 and a gray voltage generator 800 connected to the data driver 500 And a signal controller 600 for controlling them.

The display panel unit 300 includes a plurality of display signal lines G ₁ -G _n and D ₁ -D _m and a plurality of pixels Px connected to the display signal lines G ₁ -G _n and D ₁ -D _m and arranged in the form of a matrix.

The display signal lines G ₁ -G _n and D ₁ -D _m include a plurality of gate lines G ₁ -G _n for transmitting gate signals (also referred to as "scan signals") and data signal lines or data And a line D ₁ -D _m . The gate lines G _{1 to} G _n extend in a substantially row direction, are substantially parallel to each other, and the data lines D _{1 to} D _m extend in a substantially column direction and are substantially parallel to each other.

Each pixel includes a switching element Q connected to the display signal lines G ₁ -G _n , D ₁ -D _m and a pixel circuit PX connected thereto.

The switching element Q is a three-terminal element, and its control terminal and input terminal are connected to gate lines G _{1 to} G _n and data lines D _{1 to} D _m, respectively, Respectively. At this time, the switching element Q may be formed of the thin film transistor described with reference to FIG.

The gradation voltage generator 800 generates one or two sets of gradation voltages related to the brightness of the pixel. If there are two sets, one of the two sets has a positive value for the common voltage (V _com ) and the other set has a negative value.

A gate driver 400, a gate a gate signal which is a combination of a gate-on voltage (V _on), and the gate-off voltage (V _off) from the outside is connected to a gate line (G ₁ -G _n) of the display panel unit 300 To the lines G ₁ -G _n . The gate driver 400 includes a plurality of stages arranged substantially in series as shift registers.

The data driver 500 is connected to the data lines D ₁ -D _m of the display panel unit 300 to select the gradation voltage from the gradation voltage generator 800 and apply it to the pixel as a data signal.

A demultiplexer DMX is formed between the data driver 500 and the data lines D _{1 to} D _m . The demultiplexer DMX includes a plurality of switching elements SW1 to SWm. At this time, the switching elements SW1-SWm may be formed of the thin film transistor described with reference to FIG.

In a high-resolution flat panel display device of 800 ppi or higher, it is desirable to include a demultiplexer (DMX) for cost reduction and prevention of transmittance degradation, and such demultiplexer (DMX) requires high charge mobility. Since the thin film transistor of the display device according to the embodiment of the present invention described above with reference to FIG. 1 has a high charge mobility, it is preferable that the switching element of the demultiplexer DMX is formed of such a thin film transistor.

The signal controller 600 controls the operations of the gate driver 400 and the data driver 500 and the switching control signal generator 650 controls the operation of the switching elements SW1 to SWm located in the demultiplexer DMX .

The display operation of such a display device will now be described in more detail.

The signal controller 600 receives an input control signal for controlling the display of the RGB video signals R, G, and B from an external graphic controller (not shown), for example, a vertical synchronization signal V _sync , (H _sync ), a main clock (MCLK), a data enable signal (DE), and the like. The signal controller 600 generates a gate control signal CONT1, a data control signal CONT2 and a switching control signal CONT3 on the basis of the input control signal and the input video signals R, G and B, R, G and B according to the operating conditions of the display panel unit 300 and then outputs the gate control signal CONT1 to the gate driver 400 and the video signal DAT processed with the data control signal CONT2, To the data driver 500.

The switching control signal generation unit 650 of the signal control unit 600 may turn on / off the switching elements SW1-SWm based on an input control signal CONTSW from a timing generator (not shown) And generates and outputs a switching control signal CONT3 for controlling the timing.

The gate control signal (CONT1) includes a gate-on voltage vertical synchronization start signal (STV) for instructing the start of output of the (V _on), the gate-on voltage gated clock signal that controls the output timing of the (V _on) (CPV) and the gate-on an output enable signal (OE), such as to limit the duration of a voltage (V _on).

The data control signal CONT2 includes a horizontal synchronization start signal STH for indicating the start of inputting the video data DAT and a load signal LOAD for applying the corresponding data voltage to the data lines D _{1 to} D _m , (HCLK).

The data driver 500 sequentially receives the video data DAT corresponding to the pixels of one row in accordance with the data control signal CONT2 from the signal controller 600 and receives the video data DAT from the gray voltage generator 800 By selecting the gradation voltage corresponding to each image data DAT, the image data DAT is converted to the corresponding data voltage and applied to the data lines D ₁ -D _m .

The gate driver 400 applies a gate-on voltage V _on to the gate lines G ₁ -G _n in accordance with the gate control signal CONT 1 from the signal controller 600 and applies the gate-on voltages G ₁ -G _n The switching element Q is turned on. The data voltages supplied to the data lines D _{1 to} D _m are applied to the corresponding pixels through the turned-on switching elements Q.

After one horizontal period (or "1H") (one cycle of the horizontal synchronizing signal H _sync , the data enable signal DE, and the gate clock CPV), the data driver 500 and the gate driver 400 The same operation is repeated for the pixels of the row. In this way, by applying the one frame (frame) every gate line gate-on voltage (V _on) in turn with respect to (G ₁ -G _n) during the data voltage is applied to all of the pixels.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, Of the right.

110: substrate 124: first gate electrode
154: semiconductor 173: source electrode
175: drain electrode 180a: etch stop film
180b: protective film 181: first contact hole
183: second contact hole 195: second gate electrode

Claims (10)

Board,
A first gate electrode located on the substrate,
A gate insulating film disposed on the first gate electrode,
A semiconductor layer formed on the gate insulating layer and made of an oxide semiconductor material,
An anti-etching film disposed on the semiconductor,
A first contact hole and a second contact hole formed in the etch stopping layer to expose the semiconductor,
A source electrode located on the etch stopping layer and connected to the semiconductor through the first contact hole,
A drain electrode located on the etch stop layer and connected to the semiconductor through the second contact hole,
A protective film disposed on the source electrode and the drain electrode, and
And a second gate electrode located on the protective film. The method according to claim 1,
Wherein the etch stopping film covers an upper surface and a side surface of the semiconductor. 3. The method of claim 2,
And the width of the second gate electrode is narrower than the width of the etch stopping film. The method according to claim 1,
And a constant voltage is applied to the second gate electrode. 5. The method of claim 4,
And a positive DC voltage is applied to the second gate electrode. 6. The method of claim 5,
And a voltage of 0V or more and 40V or more is applied to the second gate electrode. The method according to claim 1,
And the second gate electrode receives a different signal from the first gate electrode. The method according to claim 1,
Wherein the semiconductor is made of ITZO or IGZO. The method according to claim 1,
And the second gate electrode is made of ITO or IZO. The method according to claim 1,
A switching control signal generator for generating a switching control signal based on an input control signal from outside,
A data driver for outputting a data voltage,
A plurality of pixels,
A plurality of data lines for transmitting the data voltages to the pixels,
Further comprising a demultiplexer including a plurality of switching elements for transmitting the data voltage to the data line according to the switching control signal,
Wherein the switching element has a gate electrode, a gate electrode, a gate electrode, the gate electrode, the gate electrode, the gate insulating film, the semiconductor, the etch stopping film, the first contact hole, .

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