JP5135076B2 - Liquid crystal display - Google Patents

Description

  The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device in which a thin film transistor provided in each pixel is a so-called top gate type.

  Since the liquid crystal display device is configured such that each pixel of the liquid crystal display panel can control the light transmittance, the liquid crystal display panel is usually provided with a backlight on the back surface of the liquid crystal display panel.

  A liquid crystal display device called an active matrix type includes a thin film transistor in each pixel. Accordingly, the thin film transistors of the pixels arranged in the row direction are turned on by supplying scanning signals to the gate signal lines, and the pixels arranged in the column direction are selected in accordance with the selection. A video signal is supplied to each pixel selected through the thin film transistor from a drain signal line commonly connected to the pixel.

  The thin film transistor is a so-called top gate type in which the gate electrode is formed above the semiconductor layer by forming the semiconductor layer, the gate insulating film, and the gate electrode in this order on the substrate on which the thin film transistor is formed. Things are known. In this case, a substrate in which a thin film transistor substrate (sometimes referred to as a TFT substrate) of a liquid crystal display panel is arranged so as to face the backlight side is known.

Such a liquid crystal display device is disclosed in, for example, Patent Document 1 below.
JP 2007-219370 A

  However, the liquid crystal display device disclosed in Patent Document 1 has a configuration in which light from the backlight is irradiated to the semiconductor layer of the thin film transistor through the TFT substrate.

  For this reason, in the liquid crystal display device having such a configuration, when the luminance of the backlight is improved in order to realize a high luminance display, there is a disadvantage that a leak current is generated in the semiconductor layer of the thin film transistor. If this is left as it is, the display quality is prevented from being improved.

  In this case, various means for avoiding light irradiation to the semiconductor layer of the thin film transistor can be envisaged, but all of them increase the number of manufacturing steps and complicate the configuration.

  An object of the present invention is to provide a liquid crystal display device that can suppress the occurrence of leakage current in a semiconductor layer of a thin film transistor and can realize a high-luminance display despite its simple configuration.

  In the present invention, the counter electrode of each pixel is made of, for example, a transparent conductive film made of ITO (Indium Tin Oxide), and includes a metal layer that supplies a reference signal (a signal serving as a reference for the video signal) to each of the counter electrodes. In this configuration, the thin film transistor is prevented from being irradiated with light from the backlight by the counter voltage signal line.

  The configuration of the present invention can be as follows, for example.

(1) The liquid crystal display device of the present invention is, for example, disposed on the second substrate side of the liquid crystal display panel including a first substrate and a second substrate that are disposed to face each other with a liquid crystal interposed therebetween. A liquid crystal display device comprising a backlight,
A thin film transistor that is turned on by a scanning signal from a gate signal line to each pixel on the liquid crystal side of the first substrate, and a pixel electrode of a transparent conductive material to which a video signal from a drain signal line is supplied through the turned on thin film transistor A transparent conductive material counter electrode to which a reference signal is supplied to the video signal through the counter electrode signal line of the metal layer is formed;
The thin film transistor is configured such that its gate electrode is formed above the semiconductor layer and positioned below the counter electrode signal line via an insulating film,
The semiconductor layer excluding at least a region where an electrode is formed is disposed so as to overlap the counter electrode signal line.

(2) In the liquid crystal display device of the present invention, for example, in (1), the counter electrode signal line is formed so as to be directly overlapped with the counter electrode.

(3) In the liquid crystal display device of the present invention, for example, in (1), the counter electrode is formed on the pixel electrode above the pixel electrode via an interlayer insulating film,
The pixel electrode is composed of a planar electrode, and the counter electrode is composed of a plurality of parallel linear electrodes.

(4) In the liquid crystal display device of the present invention, for example, in (1), the pixel electrode is formed on the counter electrode so as to overlap the counter electrode via an interlayer insulating film,
The counter electrode is composed of a planar electrode, and the pixel electrode is composed of a plurality of parallel linear electrodes.

(5) The liquid crystal display device of the present invention includes, for example, a color filter in each pixel on the liquid crystal side of the second substrate.

  The above-described configuration is merely an example, and the present invention can be modified as appropriate without departing from the technical idea. In addition, the configuration of the present invention other than the configuration described above will be clarified from the entire description of the present specification or the drawings.

  According to the liquid crystal display device having such a configuration, although the configuration is simple, the generation of a leakage current in the semiconductor layer of the thin film transistor can be suppressed, and a high-luminance display can be realized.

  Other effects of the present invention will become apparent from the description of the entire specification.

  Embodiments of the present invention will be described with reference to the drawings. In each drawing and each example, the same or similar components are denoted by the same reference numerals and description thereof is omitted.

<Example 1>
(overall structure)
FIG. 2 is a block diagram showing the entire liquid crystal display device of the present invention. In FIG. 2, there is first a liquid crystal display panel PNL. The liquid crystal display panel PNL includes a transparent substrate SUB1 and a substrate SUB2 that are opposed to each other with a liquid crystal (not shown) interposed therebetween. The liquid crystal is interposed between the substrates SUB1 and SUB2 by a sealing material (not shown) that also serves to fix the substrate SUB1 to the substrate SUB1. In the liquid crystal display panel PNL, a large number of pixels (not shown) arranged in a matrix are formed on the liquid crystal side surfaces of the substrates SUB1 and SUB2, and the light transmittance of the liquid crystal can be controlled independently in each pixel. It has become. The configuration of this pixel will be described later.

  Here, the substrate SUB1 of the liquid crystal display panel PNL is arranged on the viewer (not shown) side, and the backlight BL is arranged on the back surface of the liquid crystal display panel PNL, that is, on the substrate SUB2 side. It has become.

  The backlight BL is composed of, for example, a light guide plate CLB arranged in parallel with the liquid crystal display panel PNL and a light source LS arranged on a side wall surface on one side of the light guide plate CLB. Light from the light source LS enters the light guide plate CLB through the side wall surface of the light guide plate CLB and repeats total reflection, and then is emitted from a surface parallel to the liquid crystal display panel PNL. The emitted light L is emitted from the liquid crystal display panel PNL. These pixels can be transmitted. The backlight BL is not necessarily limited to such a configuration, and may be a backlight called a direct type, for example.

  The substrate SUB1 of the liquid crystal display panel PNL is called a so-called TFT substrate, and a circuit (equivalent circuit) shown in FIG. 3 is formed on the surface on the liquid crystal side. FIG. 3 is an equivalent circuit, but is drawn corresponding to the actual pixel arrangement, and its xy plane corresponds to the liquid crystal side surface of the substrate SUB1.

  In FIG. 3, there is a gate signal line GL extending in the x direction and juxtaposed in the y direction, and there is a drain signal line DL extending in the y direction and juxtaposed in the x direction. A region surrounded by a pair of adjacent gate signal lines GL and a pair of adjacent drain signal lines DL constitutes a region of the pixel PIX.

  Each pixel PIX includes a thin film transistor TFT which is turned on by a scanning signal (voltage) from the gate signal line GL, a pixel electrode PX to which a video signal (voltage) from the drain signal line DL is supplied through the turned on thin film transistor TFT, A counter electrode CT is provided to which a reference signal (voltage) serving as a reference for the video signal is supplied. The reference signal is supplied to the counter electrode CT through a counter voltage signal line CL arranged in parallel with the gate signal line GL. An electric field corresponding to the voltage difference is generated between the pixel electrode PX and the counter electrode CT, and the liquid crystal molecules are caused to behave by this electric field.

  The circuit configured as described above selects each pixel by turning on the thin film transistor TFT of each pixel arranged in the x direction by supplying a scanning signal to the gate signal line GL. It is driven to supply a video signal from the drain signal line DL commonly connected to the pixels arranged in the direction to the pixel electrode PX of each pixel selected through the thin film transistor TFT. .

  The substrate SUB2 of the liquid crystal display panel PNL is called a counter substrate, and a black matrix, a color filter, and the like are formed on the surface on the liquid crystal side.

(Pixel configuration)
FIG. 1 is a plan view of the pixel PIX formed on the liquid crystal side surface of the substrate SUB1 of the liquid crystal display panel PNL, and is a configuration diagram corresponding to the dotted frame portion of FIG. 4 shows a cross-sectional view taken along line IV-IV in FIG. 1 together with the substrate SUB2, and FIG. 5 shows a cross-sectional view taken along line VV in FIG. 1 together with the substrate SUB2.

  First, a base layer GW (see FIGS. 3 and 4) made of, for example, a silicon nitride film is formed on the liquid crystal side surface of the substrate SUB1 (see FIGS. 3 and 4). The base layer GW prevents impurities from entering the semiconductor layer PS described later from the substrate SUB1.

  A semiconductor layer PS is formed in the formation region of the thin film transistor TFT on the upper surface of the base layer GW. The semiconductor layer PS is made of, for example, polysilicon (p-Si), and one end thereof is positioned as a part of a formation region of a drain signal line DL described later and the other end is positioned as a part of a formation region of a pixel electrode PX described later. It is like that. Although not shown, the semiconductor layer PS is formed by doping a channel region, a drain region, and a source region with a necessary conductivity type impurity.

  An insulating film GI (see FIGS. 3 and 4) is formed on the surface of the substrate SUB1 so as to cover the semiconductor layer PS. This insulating film GI functions as a gate insulating film in the formation region of the thin film transistor TFT.

  A gate signal line GL that runs in the x direction in FIG. 1 is formed on the upper surface of the insulating film GI. A protrusion is formed on the gate signal line GL so as to cross almost the center of the semiconductor layer PS, and this protrusion functions as the gate electrode GT of the thin film transistor TFT.

  On the surface of the substrate SUB1, an interlayer insulating film IN1 (see FIGS. 3 and 4) is formed so as to cover the gate signal line GL. This is for interlayer insulation between the gate signal line GL and a drain signal line DL described later.

  A drain signal line DL that runs in the y direction in the figure is formed on the upper surface of the interlayer insulating film IN1. The drain signal line DL is connected to one end of the semiconductor layer PS through a through hole TH1 formed in the interlayer insulating film IN1 and the insulating film GI. A connection portion of the drain signal line DL to the semiconductor layer PS functions as, for example, the drain electrode DT of the thin film transistor TFT.

  Note that the source electrode and the drain electrode of the thin film transistor TFT are switched by application of a bias. In this specification, for convenience, the side connected to the drain signal line DL is connected to the drain electrode and the pixel electrode PX. Is referred to as a source electrode.

  Further, the other end of the semiconductor layer PS is formed with the source electrode ST that is formed simultaneously with the formation of the drain signal line DL and connected through the through hole TH2 formed in the interlayer insulating film IN1 and the insulating film GI. Yes. The source electrode ST is an electrode that is electrically connected to the pixel electrode PX in a different layer, and the connection portion is formed to have a relatively wide area.

  A protective film PAS (see FIGS. 3 and 4) is formed on the surface of the substrate SUB1 so as to cover the drain signal line DL and the source electrode ST. This protective film PAS is provided in order to avoid direct contact with the liquid crystal of the thin film transistor TFT, and is composed of, for example, a sequentially laminated body of an inorganic insulating film and an organic insulating film. The organic insulating film is used for the purpose of flattening the surface, for example.

  On the surface of the protective film PAS, a pixel electrode PX made of, for example, a transparent conductive film of ITO (Indium Tin Oxide) is formed. The pixel electrode PX is formed so as to be electrically separated from the pixel electrode PX in another adjacent pixel region, and thus is a planar electrode formed in a region excluding a slight periphery of the pixel region. Yes. The pixel electrode PX is electrically connected to the source electrode ST through a through hole TH3 formed in the protective film PAS in a portion adjacent to the thin film transistor TFT.

  An interlayer insulating film IN2 is formed on the surface of the substrate SUB1 so as to cover the pixel electrode PX, and a counter electrode CT is formed on the upper surface of the interlayer insulating film IN2 so as to overlap the pixel electrode PX. . The counter electrode CT is made of, for example, a transparent conductive film made of ITO (Indium Tin Oxide), and is composed of a plurality of (two in the figure) linear electrode groups arranged in parallel. In FIG. 1, the counter electrode CT is formed so as to be connected to a counter electrode of another pixel adjacent in the x direction. However, the present invention is not limited to this, and may be configured to be connected to a counter electrode of another pixel adjacent in the y direction. Further, it may be formed separately from the counter electrode CT of another adjacent pixel.

  A counter voltage signal line CL is formed adjacent to the gate signal line GL and parallel to the gate signal line GL. The counter voltage signal line CL is formed of a metal layer made of, for example, Al or Cr, and is formed to directly overlap the counter electrode CT, for example. Thereby, the reference signal is supplied to the counter electrode CT of each pixel from the outside of the display region through the counter voltage signal line CL. The counter electrode CT made of a transparent conductive film such as ITO is made of a material having a relatively large electrical resistance, and the counter voltage signal line CL made of a metal layer is superimposed on the counter electrode CT as described above. As a result, the overall electric resistance of the counter electrode CT can be reduced.

  Furthermore, the counter voltage signal line CL is formed wide so that, for example, the side on the gate signal line GL side overlaps the side on the counter voltage signal line CL side of the gate signal line GL. The counter voltage signal line CL is configured to cover the thin film transistor TFT.

  Here, the thin film transistor TFT covered by the counter voltage signal line CL may be covered including the drain electrode DT and the source electrode ST, but at least the drain electrode DT, the source electrode ST, and the gate electrode GT. It suffices if the portion of the semiconductor layer PS excluding the formed region can be covered. The drain electrode DT, the source electrode ST, and the gate electrode GT are composed of metal layers, which can function as a light shielding film, and the semiconductor layer PS excluding the region where these electrodes are formed is shielded by the counter voltage signal line CL. is there.

  In this case, as shown in FIG. 4, the emitted light L from the backlight BL is irradiated from the substrate SUB2 side, but this emitted light L is transmitted by the counter voltage signal line CL. The formation region of the thin film transistor TFT is prevented from being irradiated. For this reason, it is possible to avoid the occurrence of a leak current in the semiconductor layer PS of the thin film transistor TFT, and it is possible to eliminate the concern that the image quality deteriorates. Therefore, display with high luminance can be achieved by improving the luminance of the backlight BL.

  In this case, as will be described later, a color filter CF is formed on the substrate SUB2 side, and the light from the backlight BL is reduced by the color filter CF, so that the luminance of the backlight BL is improved accordingly. be able to.

  An alignment film (not shown) is formed on the surface of the substrate SUB1 so as to cover the counter electrode CT and the counter voltage signal line CL. The alignment film is a film that is in direct contact with the liquid crystal LC, and determines the initial alignment direction of the molecules of the liquid crystal LC.

  4 and 5, a black matrix (light-shielding film) BM is formed on the surface of the substrate SUB2 on the liquid crystal side. The black matrix BM is formed to run in the y direction so as to cover the drain signal line DL, for example. A color filter CF is formed in a pixel region between the black matrixes BM on the substrate SUB2, and the color filter CF is given any one of red, green, and blue. Further, a planarization film OC is formed on the surface of the substrate SUB2 so as to cover the black matrix BM and the color filter CF, and an alignment film (not shown) is formed on the upper surface of the planarization film OC.

<Example 2>
FIG. 6 is a block diagram showing another embodiment of the liquid crystal display device of the present invention and corresponds to FIG.

  In the case of FIG. 4, the pixel electrode PX is formed on the protective film PAS covering the thin film transistor TFT, and is superimposed on the pixel electrode PX via the interlayer insulating film IN2 on the pixel electrode PX. Is formed.

  On the other hand, in the case of FIG. 6, the counter electrode CT is formed on the protective film PAS covering the thin film transistor TFT, and is superimposed on the counter electrode CT via the interlayer insulating film IN2 on the counter electrode CT. Thus, the pixel electrode PX is formed. In this case, the counter electrode CT is configured as a planar electrode that may be electrically connected to the counter electrode CT of another adjacent pixel. The pixel electrode PX is formed of an electrode that is electrically separated from the pixel electrode PX of another adjacent pixel, and includes a plurality of linear electrode groups arranged in parallel.

  In the same manner as shown in FIG. 1, the counter voltage CT is formed by directly overlapping the counter voltage signal line CL made of a metal layer so as to cover the lower layer thin film transistor TFT. Similarly, the light from the backlight BL is shielded by the counter voltage signal line CL so that the thin film transistor TFT is not irradiated.

  In the second embodiment, the pixel electrode PX must be electrically connected to the source electrode ST of the thin film transistor TFT below the counter electrode CT formed in a planar shape through the through hole TH4. The counter electrode CT is formed with a hole HL that positions the through hole TH4 therebetween, thereby avoiding a short circuit between the counter electrode CT and the pixel electrode PX.

  Further, in each of the above-described embodiments, the counter voltage signal line CL is disposed so as to partially overlap the gate signal line GL, but it is not necessarily required to overlap.

It is a top view which shows one Example of the pixel of the liquid crystal display device of this invention. It is a block diagram which shows one Example of schematic structure of the liquid crystal display device of this invention. It is a figure which shows the equivalent circuit of the pixel of the liquid crystal display device of this invention. It is a figure which shows the cross section in the IV-IV line of FIG. It is a figure which shows the cross section in the VV line | wire of FIG. It is sectional drawing which shows the other Example of the pixel of the liquid crystal display device of this invention.

Explanation of symbols

PNL: Liquid crystal display panel, SUB1, SUB2 ... Substrate, BL ... Backlight, CLB ... Light guide plate, LS ... Light source, GL ... Gate signal line, DL ... Drain signal line, TFT ... Thin film transistor, PX: Pixel electrode, CT: Counter electrode, CL: Counter voltage signal line, PIX: Pixel, PS: Semiconductor layer, GT: Gate electrode, DT: Drain electrode, ST: Source electrode, GI ... Insulating film, IN1, IN2 ... Interlayer insulating film, PAS ... Protective film, BM ... Black matrix, CF ... Color film, OC ... Flattening film, TH1-TH4 ... Through hole, HL ... Hole.

Claims (5)

A liquid crystal display device comprising a first substrate and a second substrate disposed opposite to each other with a liquid crystal interposed therebetween, and a backlight disposed on the second substrate side of the liquid crystal display panel,
A thin film transistor that is turned on by a scanning signal from a gate signal line to each pixel on the liquid crystal side of the first substrate, and a pixel electrode of a transparent conductive material to which a video signal from a drain signal line is supplied through the turned on thin film transistor A transparent conductive material counter electrode to which a reference signal is supplied to the video signal through the counter electrode signal line of the metal layer is formed;
The thin film transistor is configured such that its gate electrode is formed above the semiconductor layer and positioned below the counter electrode signal line via an insulating film,
A liquid crystal display device, wherein the semiconductor layer excluding at least a region where an electrode is formed is disposed so as to overlap the counter electrode signal line. The liquid crystal display device according to claim 1, wherein the counter electrode signal line is formed so as to be directly overlapped with the counter electrode. The counter electrode is formed on the pixel electrode overlying the pixel electrode via an interlayer insulating film,
2. The liquid crystal display device according to claim 1, wherein the pixel electrode is composed of a planar electrode, and the counter electrode is composed of a plurality of parallel linear electrodes. The pixel electrode is formed on the counter electrode overlying the counter electrode via an interlayer insulating film,
2. The liquid crystal display device according to claim 1, wherein the counter electrode is composed of a planar electrode, and the pixel electrode is composed of a plurality of parallel linear electrodes.   The liquid crystal display device according to claim 1, wherein each pixel on the liquid crystal side of the second substrate is provided with a color filter.

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