KR100684868B1 - A reflective-transmissive complex type TFT LCD and A Method of forming it - Google Patents

Abstract

The present invention relates to a reflective transmissive thin film transistor liquid crystal display device and a method for forming the same. The method includes forming liquid crystal layer thicknesses in a transmissive region and a reflective region for controlling the phase of polarization in each pixel portion constituting the screen of the liquid crystal display. In order to form differently, a transparent electrode pattern formed by stacking a transparent electrode of a pixel electrode and a metal such as chromium in a gate electrode or source / drain electrode forming step and forming a protective insulating film on the thin film transistor is first formed by patterning the transparent electrode pattern. Exposing the upper part and forming the reflective electrode, also exposing the transparent electrode pattern, and then removing the upper opaque metal layer from the transparent electrode pattern.

Therefore, in the reflection-transmission composite thin film transistor liquid crystal display, the polarization phase is adjusted for each transmission region and reflection region to obtain the maximum amount of emitted light, thereby increasing the overall screen brightness and contrast.

Description

A reflective-transmissive complex type TFT LCD and a method of forming it}

1 and 2 are a plan view and a side cross-sectional view of a pixel portion of a thin film transistor-side substrate in an example of a conventional reflection-transmission composite thin film transistor liquid crystal display device;

3 is a conceptual diagram illustrating a cross-sectional structure of a liquid crystal display panel and a phase change of light in a reflection area and a transmission area to explain a conventional problem.

4 is a plan view showing a pixel portion and a pad portion plane of a lower substrate in an embodiment of the present invention;

FIG. 5 is a cross-sectional view illustrating the lower substrate pixel section taken along the AA line of the embodiment of FIG. 4.

※ Explanation of symbols for main parts of drawing

10: substrate 11: gate pattern

13: gate insulating film 15: semiconductor layer

17: ohmic contact layer 19: source / drain electrode

21: transparent electrode pattern 23: organic insulating film

25: reflective film pattern 27: transmission region

31,33: polarizer 35,37: phase difference plate                 

39: liquid crystal layer 41: reflecting plate

51: transparent electrode layer 61: chromium layer

The present invention relates to a reflective transparent thin film transistor liquid crystal display device and a method for forming the same. More specifically, a reflective reflective thin film transistor liquid crystal display in which a separate reflective film and a transmissive film forming a pixel electrode are formed to occupy a predetermined area of a pixel. An apparatus and a method of forming the same.

A thin film transistor liquid crystal display device is a typical form of an active matrix liquid crystal display device, and an active nonlinear element called a transistor is used to control each pixel. In the thin film transistor liquid crystal display device, unlike the semiconductor device in which the transistor device is formed on the semiconductor substrate, the transistor is formed on the glass substrate. The thin film transistor liquid crystal display device can be divided into top gate type and bottom gate type depending on whether the gate is formed above or below the channel, and the semiconductor forming the channel is amorphous. Depending on whether it is made of silicon, it can be divided into amorphous silicon type and active silicon type.

In addition, according to the characteristics of the liquid crystal that does not emit light by itself, the liquid crystal display device including the thin film transistor liquid crystal display device is provided with an independent light source on the rear panel so that the image of the liquid crystal panel is recognized by the user while light passes through the liquid crystal panel. It can be divided into a transmissive type and a reflective type in which an image of the liquid crystal panel is recognized as a light source or external light installed on the front surface is reflected.

In the thin film transistor liquid crystal display device, the pixel electrode formed for each pixel is formed on a substantial portion of the pixel through the photolithography and etching process by stacking aluminum by sputtering mainly in the reflective liquid crystal display device. It is connected through and serves as a reflector.

The pixel electrode of the backlight or transmissive thin film transistor liquid crystal display device is formed of transparent indium tin oxide (ITO), indium zinc oxide (IZO), etc. because light passes through the pixel electrode and enters the user's eyes.

According to the current trend, many search for reflective thin film transistor liquid crystal display devices capable of realizing high quality images using external light while reducing power consumption even where a large screen high quality image is required such as a notebook computer. Reflective and transmissive, the reflection and transmissive composite liquid crystal display device has been introduced through Sharp company to ensure the appropriate visibility according to the use environment in spite of the change of ambient light. have.

1 and 2 are plan views and side cross-sectional views of respective pixel portions of a thin film transistor side substrate in one example of a reflection-transmission hybrid liquid crystal display device. In the reflection-transmission composite liquid crystal display, when the pixel electrode is formed in the electrode forming process of the conventional thin film transistor-side substrate 10, the transparent electrode pattern 21 is first formed as a transparent electrode layer, and the organic insulating layer 23 is formed thereon. ), And then a metal film such as aluminum or chromium, that is, a reflective film layer is formed by sputtering or the like, and then a desired reflective film pattern 25 is formed by using a mask process, that is, photolithography and etching. have. In this way, the pixel is divided into an external region in which no pixel electrode of a reflective layer or a transparent electrode layer remains, a transparent region in which only a transparent electrode remains, and a reflective region in which a reflective pattern 25 remains. .

In the panel of the conventional reflection-transmission composite thin film transistor liquid crystal display device, the liquid crystal layer thickness or the cell gap of the transmission region and the reflection region for each pixel only differs from the thickness of the reflection layer, and the liquid crystal is substantially in the two regions. The thickness of the layers is the same. However, considering the phase of light in a TN type liquid crystal cell adopted by almost all thin film transistor liquid crystal displays, it is impossible to obtain the maximum luminance simultaneously in both the transmission mode and the reflection mode when the liquid crystal layer thickness is the same. there is a problem.

FIG. 3 is a conceptual diagram illustrating a cross-sectional structure of a liquid crystal display panel and a phase change of light in the reflection region and the transmission region to explain this problem. Since light does not pass below the reflecting film 41 in the reflecting region, the backlight or the retarder under the reflecting point is meaningless and thus will be omitted. The polarizing plate 31 of the upper part of the panel (front side) is installed to pass only light components having a phase oscillating left and right on the drawing, and the lower (rear) polarizing plate 33 of the transmission region vibrates perpendicular to the drawing. It is installed to pass only the light component that it has. And inside the polarizing plate, the retardation plates 35 and 37 are provided so that the axial directions are perpendicular to each other. The liquid crystal layer 39 adjusts physical properties and thicknesses so that the phase change on the optical path corresponds to λ / 4. The liquid crystal layer thicknesses of both regions are substantially the same.

In both regions, no light exits from the panel when the voltage is applied to the panel upper and lower electrodes. In this case, since the liquid crystal layers are arranged in parallel without being twisted, the liquid crystal layers do not cause a phase change on the path of light. Therefore, the thickness of the liquid crystal layer does not matter. However, in order to maximize the amount of light emitted from the panel when the voltage is not applied to the upper and lower electrodes of the panel, the light exiting from the panel is counterclockwise on the drawing just before passing through the upper phase difference plate (λ / 4 plate). It should be in phase to rotate. On the other hand, the phase change of light passing through the liquid crystal layer, which is normally designed, is λ / 4, and the light emitted from the pixel electrode (for example, the light reflected from the reflective film in the reflective mode) is perpendicular to the drawing for the maximum output light amount. It must be in a vibrating phase.

However, as shown in FIG. 3, the polarizing plate 31, the retardation plate 35, the liquid crystal layer 39, the (-) retardation plate 37, and the polarizing plate 33 which are related to the polarization, the detection, and the phase change of light from the front surface. Considering the arrangement of the polarizing plate and the retardation plate in structure, in order to prevent natural light incident from the rear side in the transmissive region in the transmissive region from emitting light from the panel, the transparent electrode 43 is used. The passing light is in a phase that rotates clockwise. As a result, when the thickness of the liquid crystal layer is conventionally designed, if the phase change of light passing through is λ / 4, it vibrates perpendicularly to the drawing, not to rotate counterclockwise immediately before passing through the upper retardation plate. It has a phase and has a phase that rotates counterclockwise before passing through the polarizer, so that the amount of emitted light has a phase difference of λ / 4 with polarization passing through the polarizer without loss, so that the amount of light is reduced to half of the maximum value.

In particular, in view of the fact that the problem of brightness may be the biggest weakness in the reflective transmissive thin film transistor liquid crystal display device, a supplementary means capable of avoiding such a loss of light is very urgently required.

In the present invention, as described above, the conventional reflection-transmissive composite thin film transistor liquid crystal display device having the same thickness of the liquid crystal layer in the transmission region and the reflection region has a problem that the maximum luminance cannot be obtained in both the transmission region and the reflection region. An object of the present invention is to provide a novel reflective transmission composite thin film transistor liquid crystal display device and a method of forming the same.

According to an aspect of the present invention, there is provided a reflective transmissive composite thin film transistor liquid crystal display device including a glass substrate, a thin film transistor formed on the substrate, and a first substrate formed on the substrate and electrically connected to a drain region of the thin film transistor. An insulating film having a hole formed on the pixel electrode, the first pixel electrode and the thin film transistor, and having the hole formed to expose the first pixel electrode, and formed to expose the first pixel electrode on the insulating film and electrically connected to the drain. And a second pixel electrode.                     

In the present invention, the first pixel electrode will mainly be a transparent electrode pattern, and the second pixel electrode will be a reflective electrode.

In the reflective transmissive composite thin film transistor liquid crystal display device of the present invention, the insulating film is formed of an organic film thicker than that of the inorganic film in that it can increase the liquid crystal layer thickness difference for phase control between the transmissive area and the reflective area. The thickness of the organic layer is preferably such that the Δnd value of the liquid crystal layer having a corresponding thickness is 1/4, since the light is matched with the mode of the polarizing plate when the transmitted light exits through the polarizing plate to minimize the loss in the light intensity. Of course, even if the thickness is less than this can be as effective as the thickness. Δnd is obtained by multiplying the thickness of the material layer by the difference in refractive index along the axial direction of the material layer through which light passes.

In addition, the thin film transistor may be a bottom gate type or a top gate type, and in some cases, a semiconductor layer forming a source / drain region and a channel may be formed of polysilicon in addition to amorphous silicon.

The first pixel electrode is electrically connected to the drain electrode directly or indirectly. The second pixel electrode is also electrically connected to the drain electrode directly or indirectly.

In order to achieve the above object, a method of forming a reflective transmissive composite thin film transistor liquid crystal display device includes forming a thin film transistor, a data line, a gate line, and a first pixel electrode pattern on a glass substrate; Exposing the drain electrode and the first pixel electrode pattern of the thin film transistor, and stacking and patterning a second pixel electrode layer on the patterned insulating layer to expose the first pixel electrode while forming a second pixel electrode. It is provided with.

In the method of the present invention, the first pixel electrode pattern will mainly be a transparent electrode pattern, and the second pixel electrode will be a reflective electrode.

In the method of the present invention, when the first pixel electrode pattern is formed of a transparent electrode capped with a metal, exposing the first pixel electrode while forming the second pixel electrode followed by etching the second pixel electrode and the patterned insulating layer. The method may further include forming a first pixel electrode by etching and removing the capping metal of the first pixel electrode pattern. In this case, the transparent electrode pattern may be formed by simultaneously patterning the same material layer when forming the gate electrode or the source / drain electrode of the thin film transistor, wherein the gate electrode or the source / drain electrode is formed The material layer is formed by laminating ITO, IZO, and the like to form a transparent electrode. The capping metal may be chromium or the like which does not form an insulating oxide even when it is in contact with the indium oxide transparent electrode.

On the other hand, when there is a metal that does not cause a problem such as forming a non-conducting opaque film even when contacting the transparent electrode, and if the metal has a small difference in etching selectivity with the second pixel electrode, patterning the reflective plate for forming the second pixel electrode In addition, the capping metal may also be removed to expose the transparent electrode, thereby saving process steps, and in some cases, the metal itself may be used as the second pixel metal. Such metals include tungsten molybdenum (MoW).                     

Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

4 is a diagram illustrating a pixel portion and a pad portion plane of a lower substrate in an embodiment of the present invention. The reflective electrode and the transparent electrode pattern may be reversed. At the boundary between the reflective electrode and the transparent electrode, the two electrode layers are directly and indirectly contacted with each other via an intermediate metal to be electrically connected.

FIG. 5 is a cross-sectional view illustrating a lower substrate pixel portion obtained by cutting the embodiment plane of FIG. 4 along an AA line. As an example of a method of forming such a structure, first, a multilayer film made of a transparent electrode layer 51 and a chromium layer 61 is laminated and patterned on a glass substrate 10 to form a gate electrode, a gate line, a gate pad, and a transparent electrode pattern. To form. The transparent electrode layer 41 may be formed by sputtering ITO, IZO, or the like, and the chromium layer 51 may be formed by sputtering. The transparent electrode pattern is electrically separated from the gate pattern. The gate insulating film 13 is CVD laminated and patterned to cap the gate electrode and the gate line using a silicon nitride film or a silicon oxide film.

The amorphous silicon semiconductor layer 15 and the amorphous silicon ohmic contact layer 17 doped with impurities are stacked by CVD (Chemical Vapor Deposition) method, and the active region is left through patterning. The active region becomes a source / drain region and a channel region of the thin film transistor. A metal film, such as aluminum, is stacked and patterned by sputtering to form source / drain electrodes 19, data lines, and pads. The ohmic contact layer 17 is etched away using the source / drain electrodes 19 as an etch mask.

As described above, in the state in which the thin film transistor and the transparent electrode pattern are formed on the glass substrate 10, the organic insulating layer 13 is stacked and holes are formed to expose the drain electrode and the transparent electrode pattern. The organic insulating film 13 can be patterned only by a photolithography process using a photosensitive film, and the thickness of the organic film is such that the Δnd value of the liquid crystal layer having the corresponding thickness is 1/4 wavelength. At this time, most of the transparent electrode patterns are exposed. Next, a reflective layer is formed of metal such as aluminum and patterned to form the reflective electrode 25.

The reflective electrode 25 is in electrical contact with the drain electrode 19 and a portion of the transparent electrode pattern through the holes, and most of the region of the transparent electrode pattern is exposed. In this state, the chromium layer 61 on the transparent electrode layer 51 is removed by etching. The chromium layer 61 in a portion where the transparent electrode pattern and the reflective electrode are in contact with each other may be protected by an aluminum mask to prevent direct contact between the transparent electrode and the aluminum of the indium oxide-based transparent electrode forming the transparent electrode. The drain electrode and the transparent electrode pattern are indirectly connected through the reflective electrode.

In the above example, the transparent electrode pattern may not be formed like a gate electrode, but may be formed of the same layer as the source / drain electrode. In this case, it is preferable that the gate electrode or the like is formed of aluminum, and the source / drain electrode layer is formed by laminating a transparent electrode and chromium, and the reflective electrode is made of chromium or aluminum. In addition, the drain electrode and the transparent electrode pattern may be patterned to be connected.

Even when the organic insulating film is used, the curved surface of the insulating film may be formed without forming the upper surface of the insulating film to be flat to serve as a condensing lens. When other factors such as the alignment angle and the tilt angle of the alignment film on the inner surface of the substrate are not taken into consideration, the thickness of the liquid crystal layer in the transmissive region should be twice as large as the liquid crystal layer in the transmissive region. If it is formed at least thicker in the area, it is as effective. In addition, when the treatment of the alignment layer may be controlled differently in both regions, the thickness difference of the liquid crystal layer may vary.

In the example in which the positions of the transparent electrode and the reflective electrode are reversed, the transparent electrode is formed of a single layer such as ITO or IZO, and the gate electrode layer or source / drain electrode layer for forming the reflective electrode is formed of a multilayer film in which aluminum and chromium are sequentially stacked. Process steps may be performed.

According to the present invention, in the reflection type composite thin film transistor liquid crystal display device, the amount of emitted light in another region is increased while fixing the amount of emitted light in one region by controlling the phase of polarization by varying the thickness of the liquid crystal layer between the reflective and transmissive regions. It is possible to increase the overall screen brightness and contrast.

Claims (10)

Glass substrate, A thin film transistor formed on the substrate, A first pixel electrode formed on the substrate and electrically connected to the drain electrode of the thin film transistor; An insulating layer formed on the first pixel electrode and the thin film transistor and having a hole formed to expose the first pixel electrode; And a second pixel electrode formed on the insulating layer to expose the first pixel electrode and electrically connected to the drain electrode. The method of claim 1, The liquid crystal display of claim 1, wherein the first pixel electrode is a transparent electrode pattern and the second pixel electrode is a reflective electrode. The method of claim 2, And the insulating film is formed of an organic film and has a Δnd value of a liquid crystal layer having the same thickness so as to have a 1/4 wavelength. The method of claim 2 or 3, The first pixel electrode is formed by simultaneously patterning a material layer formed by stacking chromium or tungsten molybdenum (MoW) on a transparent electrode layer such as the gate electrode of the thin film transistor, and forming an upper layer of chromium or tungsten molybdenum on the first pixel electrode material layer. And a portion corresponding to the hole is opened. The method of claim 2 or 3, The insulating layer has a contact hole exposing the drain electrode, and the second pixel electrode is in contact with the drain electrode through the contact hole and in contact with the first pixel electrode through the hole. Type thin film transistor liquid crystal display device. In the method of forming a reflective transmissive thin film transistor liquid crystal display device, Forming a thin film transistor and a first pixel electrode pattern on the glass substrate; Stacking and patterning an insulating film on a substrate on which the thin film transistor and the first pixel electrode pattern are formed to expose the first pixel electrode; And stacking and patterning a second pixel electrode layer on the patterned insulating film to form a second pixel electrode, thereby exposing the first pixel electrode pattern. The method of claim 6, The first pixel electrode pattern is formed at the same time through patterning so as to be connected to each other by the same material layer as the drain electrode of the thin film transistor including the transparent electrode layer, And the second pixel electrode is formed of a reflective metal layer. The method of claim 7, wherein The first pixel electrode pattern is formed of a transparent electrode layer capped with a metal, And exposing the first pixel electrode while forming the second pixel electrode, followed by etching and removing the capping metal of the first pixel electrode using the second pixel electrode and the patterned insulating layer as an etch mask. A method of forming a reflective transmissive composite thin film transistor liquid crystal display device. The method of claim 8, The capping method of claim 1, wherein the capping layer comprises chromium as a metal, the reflective metal layer is aluminum, and the transparent metal layer is formed by using ITO or IZO. The method of claim 6, The first pixel electrode pattern is formed by patterning the tungsten molybdenum (MoW) layer, which is a capping layer, on the transparent electrode layer to be connected to the same material layer as the drain electrode of the thin film transistor. And the second pixel electrode is formed of an aluminum layer to expose the transparent electrode of the first pixel electrode pattern simultaneously when the second pixel electrode is closed.

Images