Flexible liquid crystal display device

A flexible liquid crystal display device includes a first flexible substrate having a display region and a non-display region at a periphery of the display region; an organic electroluminescent diode including a first electrode on the first flexible substrate, an organic emitting layer on the first electrode and a second electrode on the organic emitting layer, wherein each of the first electrode, the organic emitting layer and the second electrode covering an entire surface of the display region; a buffer layer on the organic electroluminescent diode; a gate line on the buffer layer; a data line over the buffer layer and crossing the gate line to define a pixel region at the display region; a thin film transistor connected to the gate and data lines; a pixel electrode connected to the thin film transistor; a second flexible substrate facing the first flexible substrate; a common electrode on the second flexible substrate; and a liquid crystal layer between the pixel and common electrodes.

The present application claims the benefit of Korean Patent Application No. 10-2008-0122371 filed in Korea on Dec. 4, 2008, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a liquid crystal display (LCD) device and more particularly to an LCD device having advantages in weight and thickness and being flexible.

2. Discussion of the Related Art

As the society has entered in earnest upon an information age, flat panel display devices, which have excellent capabilities of a thin profile, light weight and low power consumption, and so on, are introduced. For example, the flat panel display devices include an LCD device, a plasma display panel (PDP) device, a vacuum fluorescent display (VFD) device and an electroluminescent display (ELD) device.

Among these devices, LCD devices are widely used for notebook computers, monitors, TV, and so on instead of a cathode ray tube (CRT), because of their high contrast ratio and characteristics adequate to display moving images.

The LCD device uses optical anisotropy and polarization properties of liquid crystal molecules. The liquid crystal molecules have a definite alignment direction as a result of their thin and long shapes. The alignment direction of the liquid crystal molecules can be controlled by application of an electric field across the liquid crystal molecules. As the intensity or direction of the electric field is changed, the alignment of the liquid crystal molecules also changes. Since incident light is refracted based on the orientation of the liquid crystal molecules due to the optical anisotropy of the liquid crystal molecules, images can be displayed by controlling light transmissivity.

Since the LCD device including a thin film transistor (TFT) as a switching element, referred to as an active matrix LCD (AM-LCD) device, has excellent characteristics such as high resolution and display of moving images, the AM-LCD device has been widely used.

FIG. 1is a schematic cross-sectional view of the related art LCD device. InFIG. 1, the LCD device1includes first and second substrates5and10, a liquid crystal layer15and a backlight unit90. The first and second substrates5and10face each other, and the liquid crystal layer15is interposed between the first and second substrates5and10. The backlight unit90is disposed under the first substrate5. A combination of the first and second substrates5and10and the liquid crystal layer15may be called as a liquid crystal panel30. For example, each of the first and second substrates5and10may be formed of a transparent glass.

On the first substrates5, a pixel region P, which is defined by gate and data lines (not shown) crossing each other, and a switching region S, where a thin film transistor (TFT) T as a switching element is formed, are defined. The TFT T is disposed at a crossing portion of the gate and data lines. The TFT T includes a gate electrode25, a gate insulating layer45, a semiconductor layer40, a source electrode32and a drain electrode34. The semiconductor layer40may include an active layer of intrinsic amorphous silicon and an ohmic contact layer of impurity-doped amorphous silicon.

A passivation layer55is formed on the TFT T and includes a drain contact hole DCH exposing the drain electrode34. In addition, a pixel electrode70connected to the drain electrode34through the drain contact hole DCH is formed on the passivation layer55in each pixel region P. For example, the pixel electrode70may be formed of a transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO).

On the second substrate10, a black matrix12for shielding the gate and data lines and the TFT T on the first substrate is formed. A color filter layer16including red (R), green (G) and blue (B) sub-color filters16a,16band16cis formed on the black matrix12. The sub-color filters16a,16band16ccorrespond to each pixel region P. In addition, a common electrode75is formed on the color filter layer16. For example, the common electrode75may be formed of a transparent conductive material such as ITO and IZO. Although not shown, first and second alignment layers may be formed on the pixel electrode70and the common electrode75, respectively.

Liquid crystal molecules L in the liquid crystal layer15is driven by a vertical electric field induced between the pixel and common electrodes70and75such that light transmissivity is controlled. The light is provided from the backlight unit90. Color images are displayed due to the color filter layer16.

The backlight unit90includes one of a cold cathode fluorescent lamp (CCFL), a hot cathode fluorescent lamp (HCFL), an external electrode fluorescent lamp (EEFL) and a light emitting diode (LED) as a light source. The backlight unit90further includes members depending on a kind of the light source. For example, the backlight unit90may include a reflective sheet and an optical sheet.

Recently, a flexible substrate, for example, a plastic or a flexible metal substrate, is used for each of the first and second substrates5and10to obtain a flexible LCD device. Unfortunately, the backlight unit90is formed of rigid material, for example, a glass substrate, such that there is a limitation to provide a flexible LCD device.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a flexible LCD device that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.

An object of the present invention is to provide a flexible LCD device including a flexible organic electroluminescent diode as a light source.

An object of the present invention is to provide a thinner and lighter flexible LCD device.

To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described herein, a flexible liquid crystal display device includes a first flexible substrate having a display region and a non-display region at a periphery of the display region; an organic electroluminescent diode including a first electrode on the first flexible substrate, an organic emitting layer on the first electrode and a second electrode on the organic emitting layer, wherein each of the first electrode, the organic emitting layer and the second electrode covering an entire surface of the display region; a buffer layer on the organic electroluminescent diode; a gate line on the buffer layer; a data line over the buffer layer and crossing the gate line to define a pixel region at the display region; a thin film transistor connected to the gate and data lines; a pixel electrode connected to the thin film transistor; a second flexible substrate facing the first flexible substrate; a common electrode on the second flexible substrate; and a liquid crystal layer between the pixel and common electrodes.

In another aspect of the present invention, a flexible liquid crystal display device includes a first flexible substrate having a display region, pixel regions in the display region and a non-display region at a periphery of the display region; a driving element in each pixel region; an organic electroluminescent diode in each pixel region and including a first electrode connected to the driving element, an organic emitting layer on the first electrode and a second electrode on the organic emitting layer, wherein each of the first electrode and the organic emitting layer has an island shape, and the second electrode covering an entire surface of the display region; a buffer layer on the organic electroluminescent diode; a gate line on the buffer layer; a data line over the buffer layer and crossing the gate line to define a pixel region at the display region; a thin film transistor connected to the gate and data lines; a pixel electrode connected to the thin film transistor; a second flexible substrate facing the first flexible substrate; a common electrode on the second flexible substrate; and a liquid crystal layer between the pixel and common electrodes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 2is a cross-sectional view of a flexible LCD device according to a first embodiment of the present invention, andFIGS. 3A to 3Dare cross-sectional view for illustrating a fabricating process of a flexible LCD device according to the first embodiment of the present invention. InFIGS. 2 and 3Ato3D, an LCD device101includes TFT substrate105aand color filter substrate110aand a liquid crystal layer115. The TFT substrate105aand color filter substrate110aface each other, and the liquid crystal layer115is interposed between the TFT substrate105aand color filter substrate110a. Both the TFT substrate105aand color filter substrate110aare flexible. A combination of the TFT substrate105aand color filter substrate110aand the liquid crystal layer115may be called as a liquid crystal panel130. Liquid crystal molecules L are driven by a vertical electric field. Furthermore, liquid crystal molecules L can be driven by a horizontal electric field.

A display region AA for displaying images and a non-display region NAA at a periphery of the display region AA are defined on a first substrate105. On the first substrate105, an organic electroluminescent diode E as a light source, a buffer layer120and an array element A are formed. The organic electroluminescent diode E is passive matrix type. The passive matrix type organic electroluminescent diode E includes a first electrode180on an entire surface of the display region AA, an organic emitting layer182on the first electrode180and a second electrode184on the organic emitting layer182. The organic electroluminescent diode E is selectively turned on or off by a driving signal from an inverter (not shown). Namely, an operation of the organic electroluminescent diode E is controlled by the inverter. The first electrode180is formed of a first metallic material having a relatively low work function, while the second electrode184is formed of a second metallic material having a relatively high work function. For example, the first metallic material may include one of calcium (Ca), magnesium (Mg) and aluminum (Al), and the second metallic material may include one of ITO and IZO. Since the first electrode180is formed of the first metallic material having a low work function, a barrier between the first electrode180and the organic emitting layer182is decreased such that a high current density can be obtained.

The first electrode180is opaque and serves as a cathode, while the second electrode184is transparent and serves as an anode. Light, which is emitted by re-combination of electrons and holes in the organic emitting layer182, passes through the second electrode184. This may be called as a top emission type. The organic emitting layer182is formed of an organic material being capable of emitting a white light. Since the electroluminescent diode E is formed on an entire surface of the display region AA, a plane light source is provided onto an entire area of a second substrate110.

Although not shown inFIG. 2, ends of the electroluminescent diode E is covered with a sealing material pattern at edges of the non-display region NAA. The sealing material pattern may be formed of a transparent sealing material, for example, sealant, photo-acryl or polyimide.

The first substrate105is formed of one of plastic, metal or a metallic foil to be flexible. The first substrate105may be opaque. The second substrate110is formed of a plastic material which is flexible and transparent. For example, when each of the first and second substrates105and110is formed of a plastic material, a polymer, such as polyethyleneterephthalate (PET), polyethersulphone (PES), polyimide (PI) and polyehylenenaphthalate (PEN), is used. The plastic-based substrates105and110may have a multiple-stack layered structure to obtain improvement in a moisture absorption property or an anti-oxidization property. The metal or metallic foil for the first substrate105may be iron, iron alloy, Al or Al alloy.

The buffer layer120is formed on the electroluminescent diode E. The buffer layer120is formed of an inorganic insulating material, such as silicon oxide (SiO2) and silicon nitride (SiNx), or an organic insulating material, such as benzocyclobutene, photo-acryl and polyimide. The buffer layer120may have a double-layered structure of an inorganic insulating material and an organic insulating material.

The array element A is formed on the buffer layer120. The array element A includes a gate line (not shown) and a data line (not shown), a TFT T and a pixel electrode170. The gate and data lines cross each other to define a pixel region P in the display region AA. The TFT T is formed at a crossing portion of the gate and data lines. The TFT T is connected to the gate and data lines. The TFT T includes a gate electrode125, a gate insulating layer145, a semiconductor layer140, a source electrode132and a drain electrode134. The gate electrode125is connected to the gate line, and the source electrode132is connected to the data line. The semiconductor layer140may include a single layer of polycrystalline silicon. Alternatively, the semiconductor layer140may include double layers of an active layer of intrinsic amorphous silicon and an ohmic contact layer of impurity-doped amorphous silicon. The drain electrode134is spaced apart from the source electrode132.

A passivation layer155is formed on the TFT T and includes a drain contact hole DCH exposing the drain electrode134. In addition, a pixel electrode170connected to the drain electrode134through the drain contact hole DCH is formed on the passivation layer155in each pixel region P. For example, the pixel electrode170may be formed of a transparent conductive material such as indium-tin-oxide (ITO) and indium-zinc-oxide (IZO).

On the second substrate110, a black matrix112for shielding the gate and data lines and the TFT T on the first substrate is formed. A color filter layer116including red (R), green (G) and blue (B) sub-color filters116a,116band116cis formed on the black matrix112. The sub-color filters116a,116band116ccorrespond to each pixel region P. In addition, a common electrode175is formed on the color filter layer116. For example, the common electrode175may be formed of a transparent conductive material such as ITO and IZO. Although not shown, first and second alignment layers may be formed on the pixel electrode170and the common electrode175, respectively.

Since the electroluminescent diode E as a light source is on the first substrate105with the array element A, a backlight unit under a lower substrate is not required such that the LCD device has advantages in thickness and weight. In addition, since the LCD device101does not require a rigid backlight unit, the LCD device101is flexible. Moreover, since the electroluminescent diode E is a passive type, the electroluminescent diode E can be formed by a heat-evaporation depositing method such that a fabricating process for the electroluminescent diode E can be simplified. Furthermore, there is also an advantage on a fabricating process of the electroluminescent for a large size substrate. Since the electroluminescent diode E serves as a light source, the LCD device101does not require a reflective sheet and an optical sheet such that a thickness of the LCD device101is further reduced.

Referring toFIGS. 3A to 3DandFIGS. 4A and 4B, a fabricating process of a flexible LCD device according to the first embodiment of the present invention is illustrated.FIGS. 4A and 4Bare plan views for illustrating a fabricating process inFIGS. 3A and 3B.

InFIGS. 3A and 4A, the first electrode180is formed on an entire surface of the display region AA of the first substrate105by depositing one or two selected from a metallic material group having a relatively low work function. For example, the metallic material group may include powder type calcium (Ca), magnesium (Mg) and aluminum (Al). On the first substrate105, the display region AA and the non-display region NAA are defined. In the display region AA, the pixel region P, which is defined by crossing gate and data lines, and a switching region S(T) (ofFIG. 2), where the TFT T (ofFIG. 2) is formed, are defined. The first substrate105is formed of one of plastic, metal or a metallic foil to be flexible. For example, when the first substrate105is formed of a plastic material, a polymer, such as polyethyleneterephthalate (PET), polyethersulphone (PES), polyimide (PI) and polyehylenenaphthalate (PEN), is used. The plastic-based substrates105and110may have a multiple-stack layered structure to obtain improvement in a moisture absorption property or an anti-oxidization property. The metal or metallic foil for the first substrate105may be iron, iron alloy, Al or Al alloy.

Next, the organic emitting layer182is formed on the first electrode180and on the entire surface of the display region AA by depositing an organic material. The organic emitting layer182emits white light. The second electrode184is formed on the organic emitting layer182and the entire surface of the display region AA by depositing one of a transparent conductive material group. For example, the transparent conductive material group may include powder type ITO and IZO. A material of the second electrode184has a greater work function than that of the first electrode180. The first electrode180, the organic emitting layer182and the second electrode184have substantially the same shape as one another. The first electrode180, the organic emitting layer182and the second electrode184constitute the organic electroluminescent diode E. The first electrode180, the organic emitting layer182and the second electrode184are formed in a single process chamber by a heat-evaporation depositing method or a spin coating method.

InFIGS. 3B and 4B, a sealing material pattern135is formed on the first substrate105. The sealing material pattern135covers edges of the organic electroluminescent diode E to protect the organic electroluminescent diode E. Particularly, the sealing material pattern135covers a side surface of the organic emitting material layer182. The sealing material pattern135may be positioned at boundaries of the display region AA and the non-display region NAA. The sealing material pattern135may be formed of a transparent sealing material, for example, sealant, photo-acryl or polyimide.

InFIG. 3C, a buffer layer120is formed on the sealing material pattern135and the organic electroluminescent diode E. The buffer layer120may correspond to the entire surface of the display region AA. The buffer layer120is formed of an inorganic insulating material, such as silicon oxide (SiO2) and silicon nitride (SiNx), or an organic insulating material, such as benzocyclobutene, photo-acryl and polyimide. The buffer layer120may have a double-layered structure of an inorganic insulating material and an organic insulating material. Alternatively, a buffer sheet of plastic may be laminated over the organic electroluminescent diode E with an adhesive layer. The sealing material pattern135and the buffer layer120can obtain improvement for the organic electroluminescent diode E in a moisture absorption property or an anti-oxidization property.

Next, the array element A, which includes the gate and data lines, the TFT, the passivation layer and the pixel electrode, is formed on the buffer layer120. As mentioned above, the gate and data lines cross each other to define the pixel region P. The TFT is disposed at a crossing portion of the gate and data line and located in the switching region S(T). The passivation layer includes the drain contact hole exposing the drain electrode of the TFT, and the pixel electrode is connected to the drain electrode through the drain contact hole.

InFIG. 3D, the black matrix112having a lattice shape is formed on the second substrate110. The black matrix112corresponds to and shields the gate and data lines and the TFT on the first substrate105. The black matrix112has an opening corresponding to the pixel region P. The color filter layer116including red (R), green (G) and blue (B) sub-color filters116a,116band116cis formed in the opening of the black matrix112. Namely, each of the red (R), green (G) and blue (B) sub-color filters116a,116band116ccorresponds to the pixel region P. The common electrode175is formed on the color filter layer116by depositing a transparent conductive material, for example, ITO or IZO.

Next, a seal pattern190is formed in the non-display region NAA and on one of the first and second substrates105and110by coating a sealant. Then, the first and second substrates105and110are disposed to face each other and attached with irradiating UV light to harden the seal pattern190. Namely, a space between the first and second substrates105and110is sealed by the seal pattern190. Next, the liquid crystal layer115is injected into a space between the first and second substrates105and110. Alternatively, the liquid crystal layer115may be formed before a step of attaching the first and second substrates105and110.

FIG. 5is a cross-sectional view of a flexible LCD device according to a second embodiment of the present invention. In the second embodiment, the organic electroluminescent diode of an active matrix type serves as a light source. The explanation is focused on the organic electroluminescent diode.

InFIG. 5, an LCD device201includes TFT substrate205aand color filter substrate210aand a liquid crystal layer215. The TFT substrate205aand color filter substrate210aface each other, and the liquid crystal layer215is interposed between the TFT substrate205aand color filter substrate210a. A combination of the TFT substrate205aand color filter substrate210aand the liquid crystal layer215may be called as a liquid crystal panel230. Liquid crystal molecules L are driven by a vertical electric field. Furthermore, liquid crystal molecules L can be driven by a horizontal electric field.

In the second embodiment, an organic electroluminescent diode E of an active matrix type is used as a light source. The active matrix type organic electroluminescent diode E includes a first electrode280on the first substrate205, an organic emitting layer282on the first electrode280and a second electrode284on the organic emitting layer282. The first electrode280and the organic emitting layer282are disposed in each pixel region P, while the second electrode284is disposed in an entire area of the display region AA. Namely, the first electrode280in one pixel region P is separated from the first electrode280in adjacent pixel region P. Similarly, the organic emitting layer282in one pixel region P is separated from the organic emitting layer282in adjacent pixel region P. Each of the first electrode280and the organic emitting layer282has an island shape. Meanwhile, the second electrode284in one pixel region P is continuous from the second electrode284in adjacent pixel region P. The organic emitting layer282can be isolated due to a bank260at boundaries of the pixel region P. Other elements have the same structure as those in the first embodiment.

Since the electroluminescent diode E as a light source is on the first substrate205with the array element A, a backlight unit under a lower substrate is not required such that the LCD device has advantages in thickness and weight. In addition, since the LCD device201does not require a rigid backlight unit, the LCD device201is flexible. Moreover, since the electroluminescent diode E serves as a light source, the LCD device201does not require a reflective sheet and an optical sheet such that a thickness of the LCD device201is further reduced.

FIG. 6is a cross-sectional view of an organic electroluminescent diode for a flexible LCD device according to the second embodiment of the present invention. InFIG. 6, a scan line (not shown) and a driving data line (not shown) are formed in each pixel region P of the display region AA and on the first substrate205. A driving TFT Td is formed at a crossing portion of the scan line and the driving data line. The driving TFT Td includes a driving gate electrode225a, a driving gate insulating layer245a, a driving semiconductor layer240aand a driving source electrode232aand a driving drain electrode234a. For example, the driving semiconductor layer240aincludes a single layer of polycrystalline silicon. Alternatively, the driving semiconductor layer240aincludes two layers of an active layer and an ohmic contact layer. The active layer is formed of intrinsic amorphous silicon, the ohmic contact layer is formed of impurity-doped amorphous silicon.

In the non-display region, a scan pad252is formed on the first substrate205, and a data pad262is formed on the driving gate insulating layer245. The scan pad252is connected to the scan line, and the data pad262is connected to the data line.

A driving passivation layer255ais formed on driving TFT Td and the gate insulating layer245a. The driving passivation layer255aincludes first to third contact holes CH1, CH2and CH3. The first contact hole CH1through the driving passivation layer and the gate insulating layer245aexposes the scan pad252, and the second contact hole CH2exposes the data pad262. The third contact hole CH3exposes the driving drain electrode234a.

The first electrode280is formed on the driving passivation layer255a. The first electrode280is connected to the driving drain electrode234athrough the third contact hole CH3. The first electrode280in one pixel region P is separated from the first electrode280in adjacent pixel region P. A scan pad electrode254and a data pad electrode264are formed on the driving passivation layer255a. The scan pad electrode254is connected to the scan pad252through the first contact hole CH1, and the data pad electrode264is connected to the data pad262through the second contact hole CH2. InFIG. 6, each of the scan pad electrode254and the data pad electrode264is formed of a different material than the first electrode280. However, the scan pad electrode254and the data pad electrode264may be formed of the same material as the first electrode280.

A bank260is formed on the first electrode280and at boundaries of each pixel region P. Namely, the bank260has an opening corresponding to the pixel region P. The organic emitting layer282is formed on the first electrode280and in the opening of the bank260. As mentioned above, the organic emitting layer282in one pixel region P is separated from the organic emitting layer282in adjacent pixel region P. Namely, the organic emitting layer282has an island shape. In addition, the second electrode284is formed on the organic emitting layer282and an entire surface of the display region. The first electrode280, the organic emitting layer282and the second electrode284constitute the organic electroluminescent diode E. As mentioned above, the organic electroluminescent diode E serves as a light source so that light emitting from the organic emitting layer282is provided onto the liquid crystal layer215(ofFIG. 5). The first electrode280is formed of a first metallic material having a relatively low work function. For example, the first metallic material may include one of calcium (Ca), magnesium (Mg) and aluminum (Al). The second electrode284is formed of a second metallic material having a relatively high work function. For example, the second metallic material may include one of ITO and IZO. Since the first electrode280is formed of the first metallic material having a low work function, a barrier between the first electrode280and the organic emitting layer282is decreased such that a high current density can be obtained. The second electrode284is formed of a transparent conductive material, such as ITO and IZO, such that light is provided onto the liquid crystal layer215(ofFIG. 5) over the electroluminescent diode E. It may be called as a top emission type. The organic emitting layer282emits white light. In this embodiment, since the organic electroluminescent diode E is an active matrix type, light luminescence is controlled in each pixel region P.