Display device including polarizing unit with portions having different transmittances

A display device includes a display panel having a display surface, and a polarizing unit on the display surface of the display panel, the polarizing unit including a linear polarizer that includes at least two portions having different transmittances from each other.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to, and the benefit of, Korean Patent Application No. 10-2015-0077247, filed on Jun. 1, 2015, with the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Embodiments of the present invention relate to a display device including a polarizing unit, and to a method of manufacturing the display device.

2. Description of the Related Art

An organic light emitting diode (“OLED”) display device is a self-emission-type display device that may display an image by using an OLED that emits light. Because of the omission of a separate light source, contrary to a liquid crystal display (“LCD”) device, the OLED display device may have a relatively small thickness and a relatively light weight. Further, by virtue of its excellent characteristics, such as low power consumption, high luminance, high response speed, and the like, the OLED display device has drawn attention as a display device of the next generation.

The OLED display device generally includes electrodes of the OLED and various metal wirings, and such electrodes and metal wirings may reflect externally incident light (i.e., ambient light originating outside of the display device). Due to the reflection of the externally incident light, the OLED display device experiences difficulty in representing a black color in a relatively bright environment, and exhibits a relatively low contrast ratio.

To mitigate the abovementioned issues, a polarizing unit for reducing or preventing reflection of the external light is located on the OLED. However, due to the polarizing unit, an amount of light emitted from the OLED may decrease, and thus a greater amount of current may be required for light emission in the OLED display device. Accordingly, degradation of the OLED may be accelerated due to the increased current therethrough, which may cause image sticking (i.e., burn-in, or “ghosting”). In particular, the image sticking phenomenon may be aggravated at a position in which the same image, such as broadcasters logo, time, subtitles, etc., is displayed for a certain period of time.

It is to be understood that this background section is intended to provide useful background for understanding the technology, and as such, the technology background section may include ideas, concepts, or recognitions that were not part of what was known or appreciated by those skilled in the pertinent art prior to a corresponding effective filing date of subject matter disclosed herein.

SUMMARY

Aspects of embodiments of the present invention are directed to a display device capable of slackening or reducing degradation speed of an OLED.

According to an exemplary embodiment of the present invention, a display device includes a display panel having a display surface, and a polarizing unit on the display surface of the display panel, the polarizing unit including a linear polarizer that includes at least two portions having different transmittances from each other.

The at least two portions of the linear polarizer may include a first portion having a first transmittance, and a second portion having a second transmittance that is higher than the first transmittance.

The first portion may correspond to a center portion of the display panel, and the second portion may correspond to at least one corner portion of the display panel.

The first portion may corresponds to a center portion of the display panel, and the second portion may corresponds to at least one edge portion of the display panel.

The linear polarizer may include a polyvinyl alcohol-based (“PVA-based”) resin, and a dichroic dye dyed to the PVA-based resin.

The PVA-based resin may include a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer.

The dichroic dye may include iodine.

The polarizing unit may include an adhesive layer on the display panel, and

a phase retardation layer on the adhesive layer.

The display panel may include a first substrate, a first electrode on the first substrate, an organic light emitting layer on the first electrode, and a second electrode on the organic light emitting layer.

The display device may further include a thin film encapsulation layer on the second electrode, the thin film encapsulation layer including at least one organic layer alternately stacked with at least one inorganic layer.

According to an exemplary embodiment of the present invention, a method of manufacturing a display device includes forming an adhesive layer on a display surface of a display panel, forming a phase retardation layer on the adhesive layer for imparting a phase difference, forming a linear polarizer including at least two portions having different transmittances, and forming a protection layer on the linear polarizer.

The forming of the linear polarizer may include uniaxially elongating a PVA-based resin film, dyeing the PVA-based resin film by adhering a dichroic dye thereto, and selectively detaching the dichroic dye adhered to the PVA-based resin film to form the at least two portions of the linear polarizer.

The dichroic dye may include iodine.

The selectively detaching the dichroic dye may include using visible light, ultraviolet (UV) ray, or laser.

The selectively detaching the dichroic dye may form a first portion having a first transmittance, and a second portion having a second transmittance that is higher than the first transmittance.

The first portion may correspond to a center portion of the display panel, and the second portion may correspond to at least one corner portion of the display panel.

The first portion may correspond to a center portion of the display panel, and the second portion may correspond to at least one edge portion of the display panel.

DETAILED DESCRIPTION

The display device according to an exemplary embodiment is described as including an organic light emitting diode (“OLED”) display panel, but the present invention is not limited thereto. The display device according to the present invention may also be applied to a liquid crystal display panel, a plasma display panel, and an electrophoretic display panel.

FIG. 1is an exploded perspective view illustrating a display device according to an exemplary embodiment, andFIG. 2is an exploded perspective view illustrating a display device according to another exemplary embodiment.

In reference toFIGS. 1 and 2, the display device according to exemplary embodiments includes a display panel100having a display surface DS, and a polarizing unit400on the display surface DS of the display panel100.

The display panel100includes a substrate having a quadrangular planar shape, a plurality of OLEDs on the substrate in a matrix form, and a thin film transistor (“TFT”) for driving the OLED. The configuration of the display panel100will be described further below.

Meanwhile, the OLED is degraded as time elapses, due to properties of a material forming an organic light emitting layer of the OLED, and due to the fact that the degradation speed/rate of the OLED is proportional to the time of light emission by the OLED. Accordingly, when the same image, such as broadcasters logo, time, subtitles, etc., is continuously displayed at the same position on the display panel100, the degradation of the OLED at that position may be accelerated, thereby causing image sticking. The predetermined position may include, for example, at least one corner portion and/or at least one edge portion of the display panel100.

The polarizing unit400is on the display surface DS of the display panel100, and may have an area corresponding to the display panel100. The polarizing unit400may include two or more portions that have different transmittances. For example, the polarizing unit400may include a first portion401having a first transmittance, and may also include a second portion402having a second transmittance that is higher than the first transmittance.

According to one embodiment, the first portion401of the polarizing unit400may correspond to a center portion of the display panel100, and the second portion402of the polarizing unit400may correspond to at least one corner portion of the display panel100(refer toFIG. 1). However, the present invention is not limited thereto, and in alternative exemplary embodiments, the first portion401may correspond to the center portion of the display panel100, and the second portion402may correspond to at least one edge portion of the display panel100(refer toFIG. 2). That is, a portion of the polarizing unit400, which corresponds to a portion of the display panel100that has a higher probability of causing image sticking, has a transmittance that is higher than the transmittance of other portions of the polarizing unit400. For example, the first portion401of the polarizing unit400may have a transmittance of less than about 50%, and the second portion402of the polarizing unit400may have a transmittance of about 50% or more.

FIG. 3is an exploded perspective view illustrating a polarizing unit400according to an exemplary embodiment.

In reference toFIG. 3, the polarizing unit400according to the present embodiment includes an adhesive layer410on a display panel, a phase retardation layer420on the adhesive layer410, a linear polarizer430on the phase retardation layer420, and a passivation layer440on the linear polarizer430.

The adhesive layer410is configured to attach the polarizing unit400to the display panel, and may include, for example, at least one of an acryl-based adhesive, a vinyl ester-based adhesive, a silicon-based adhesive, and a urethane-based adhesive. The adhesive layer410may have a thickness in a range of about 50 nm to about 500 nm. When the thickenss of the adhesive layer410is less than 50 nm, the adhesive layer410might not provide sufficient adhesion. On the contrary, when the thickenss of the adhesive layer410is more than about 500 nm, the polarizing unit400may be too thick.

The polarizing unit400may further include a release layer on another surface of the adhesive layer410. The release layer may protect the adhesive layer410, and may be removed to expose the adhesive layer410prior to attaching the polarizing unit400to the display panel.

The phase retardation layer420is on the adhesive layer410, and retards the phase of light. The phase retardation layer420may convert linearly-polarized light into circularly-polarized light, or may convert circularly-polarized light into linearly-polarized light.

For example, external light incident to the polarizing unit400may be linearly polarized by the linear polarizer430, or may be circularly polarized by the phase retardation layer420. The external light, which is circularly-polarized, may be reflected within the display panel as reflected light. During the process of reflection, the phase and the polarization axis of the circularly-polarized external light may be shifted. The reflected light having the shifted phase might not be transmitted through the polarizing unit400, thus reducing or preventing reflection of the external light by virtue of the polarizing unit400.

A phase difference plate having a film form may be used as the phase retardation layer420. The phase difference plate may be formed by elongation of a film. For example, the phase difference plate may be formed by elongating a film formed of a polymer such as polycarbonate, polyvinyl alcohol, polystyrene, polymethyl methacrylate, polypropylene, polyolefin, polyarylate or polyamide. Further, a photocurable liquid crystal may be used to form the phase difference plate. For example, a liquid crystal may be aligned on a polymer-based film, and then a liquid crystal pattern may be formed thereon to thereby form the phase difference plate. The phase difference plate formed through such a manner may be a quarter wave plate QWP or a half wave plate HWP based on an alignment layer and based on alignment of the liquid crystal material.

According to the present embodiment, the quarter wave plate QWP may be used as the phase retardation plate420. However, the present embodiment is not limited thereto, and thus the half wave plate HWP may be used as the phase retardation plate420, or the quarter wave plate QWP and the half wave plate HWP may be used together.

The linear polarizer430is on the phase retardation layer420, and is configured to linearly polarize external light incident to the polarizing unit400. The linear polarizer430may use a film that is formed by oriented-adhering a dichroic dye onto a polyvinyl alcohol (“PVA”)-based resin. Examples of the PVA-based resin may include a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer. The linear polarizer430may include at least two portions having different transmittances, and may include a first portion431having a first transmittance, and may also include a second portion432having a second transmittance that is higher than the first transmittance.

The first portion431of the linear polarizer430may correspond to a center portion of the display panel, and the second portion432of the linear polarizer430may correspond to at least one corner portion of the display panel. However, the present invention is not limited thereto, and in alternative exemplary embodiments, the first portion431of the linear polarizer430may correspond to the center portion of the display panel, and the second portion432of the linear polarizer430may correspond to at least one edge portion of the display panel. That is, a portion of the linear polarizer430corresponding to the portion that has a higher probability of causing image sticking has a transmittance that is higher than the transmittance of other portions of the linear polarizer430. For example, the first portion431of the linear polarizer430may have a transmittance of less than about 50%, and the second portion432of the linear polarizer430may have a transmittance of about 50% or more.

The linear polarizer430may include a PVA-based resin and a dichroic dye dyed to the PVA-based resin. The PVA-based resin may be one of a homopolymer of vinyl acetate, or a copolymer of vinyl acetate and another monomer, and the dichroic dye may be iodine, although the present invention is not limited thereto. In alternative exemplary embodiments, another dichroic dye known in the pertinent art may be utilized. The linear polarizer430may be formed through the following processes, for example: a process of uniaxially elongating a PVA-based resin film; a process of dyeing the PVA-based resin film with a dichroic dye to be adhered thereto; or a process of selectively detaching the dichroic dye adhered to the PVA-based resin film so as to form at least two portions having different transmittances.

When iodine is used as the dichroic dye, the PVA-based resin film is immersed in an aqueous solution containing iodine and/or potassium iodine and dyed. The dichroic dye adhered to the PVA-based resin film may be detached using one of visible light, ultraviolet (UV) ray, and laser. In this case, a mask may be used so as to selectively detach the dichroic dye.

The thickness of the linear polarizer430may vary based on a product to which the linear polarizer430is to be applied. For example, the linear polarizer430may have a thickness in a range of about 5 micrometers (μm) to about 40 μm. The linear polarizer430may use a commercially available product.

The protection layer440is on the linear polarizer430, and is configured to protect the linear polarizer430. A tri-acetyl cellulose (“TAC”) film, which has excellent mechanical strength, may be used as the protection layer440. Further, a surface of the protection layer440may be treated to have anti-glare properties and/or anti-reflective properties.

FIG. 4is an enlarged view illustrating a portion of a display device100according to an exemplary embodiment, andFIG. 5is a cross-sectional view taken along the line I-II ofFIG. 4.

The display panel100according to the present embodiment will be described with reference toFIGS. 4 and 5. The display panel100according to the present embodiment includes a switching TFT10on a first substrate110, a driving TFT20, a capacitor30, and an OLED40.

The first substrate110may include, or may be formed of, an insulating material selected from the group consisting of glass, quartz, ceramic, and plastic.

A buffer layer120is on the first substrate110, and may serve to reduce or effectively prevent infiltration of undesirable elements, and may also serve to planarize a surface of the first substrate110, and may include various materials that may be suitable to perform such functions. For example, the buffer layer120may include at least one of silicon nitrides (SiNx), silicon oxides (SiOx), and silicon oxynitride (SiOxNy). However, the buffer layer120is not invariably necessary, and may be omitted in other embodiments of the present invention.

A switching semiconductor layer131and a driving semiconductor layer132are formed on the buffer layer120. The switching semiconductor layer131and the driving semiconductor layer132may include, or may be formed of, the following, for example: a polycrystalline silicon layer; an amorphous silicon layer; an oxide semiconductor such as indium-gallium-zinc oxide (IGZO); and/or indium-zinc-tin oxide (IZTO).

For example, when the driving semiconductor layer132is formed of a polycrystalline silicon layer, the driving semiconductor layer132may include a channel region135that is not doped with impurities, and may include a source region136and a drain region137that are respectively doped with p-type materials, and that are located at respective sides of the channel region135. The ions used for doping may be p-type impurities, such as boron (B), and in particular, diborane (B2H6) may be used. Such impurities may vary based on the type of the thin film transistor.

Although a p-type metal oxide semiconductor (PMOS) TFT using p-type impurities is described as the driving TFT20in the present embodiment, the type of the driving TFT20is not limited thereto. Accordingly, the driving TFT20may also use one of an n-type metal oxide semiconductor (NMOS) TFT, and a complementary metal oxide semiconductor (CMOS) TFT.

A gate insulating layer140is on the switching semiconductor layer131and on the driving semiconductor layer132. The gate insulating layer140may be formed of, for example, one or more of the following: tetraethyl orthosilicate (TEOS); silicon nitride (SiNx); and/or silicon oxide (SiO2). For example, the gate insulating layer140may have a double-layer structure in which a silicon nitride (SiNx) layer having a thickness of about 40 nm, and a tetraethyl orthosilicate (TEOS) layer having a thickness of about 80 nm, are sequentially stacked.

A gate wiring including gate electrodes152and155is formed on the gate insulating layer140. The gate wiring may further include a gate line151, a first capacitor plate158, and other wiring(s). The gate electrodes152and155respectively overlap at least respective portions of the switching semiconductor layer131and the driving semiconductor layer132(e.g., the channel region135of the driving semiconductor layer132). The gate electrodes152and155may block impurities from being doped in the channel region135during the formation of the switching semiconductor layer131and the driving semiconductor layer132when the impurities are doped in the source region136and the drain region137of the switching semiconductor layer131and the driving semiconductor layer132.

The gate electrodes152and155and the first capacitor plate158may be formed on the same layer (e.g., on the gate insulating layer140), and may be formed of substantially the same metal. The gate electrodes152and155and the first capacitor plate158may be formed of one or more of the following: molybdenum (Mo); chromium (Cr); and/or tungsten (W).

An insulating interlayer160is on the gate insulating layer140to cover the gate electrodes152and155. The insulating interlayer160may be formed of one or more of the following: silicon nitride (SiNx); silicon oxide (SiO2); and/or tetraethyl orthosilicate (TEOS), as in the gate insulating layer140. However, it should be noted that the present invention is not limited thereto.

A data wiring including source electrodes173and176and drain electrodes174and177is on the insulating interlayer160. The data wiring may further include a data line171, a common power line172, a second capacitor plate178, and other wiring(s). The source electrodes173and176may be respectively connected to the source regions (e.g., source region136) of the semiconductor layers131and132, and the drain electrodes174and177may be respectively connected to the drain regions (e.g., drain region137) of the semiconductor layers131and132, through respective contact holes formed in the gate insulating layer140and in the insulating interlayer160.

A planarization layer180covers the data line171, the common power line172, the source electrodes173and176, the drain electrodes174and177, and the second capacitor plate178, which are formed over the insulating interlayer160. The planarization layer180may remove a step difference, and may planarize a surface of the insulating interlayer160to enhance the light emission efficiency of the OLED40to be formed on the planarization layer180. The planarization layer180may be formed of one or more of the following: a polyacrylate resin; an epoxy resin; a phenolic resin; a polyamide resin; a polyimide resin; an unsaturated polyester resin; a polyphenylenether resin; a polyphenylenesulfide resin; and/or benzocyclobutene (BCB).

As such, the switching TFT10may include the switching semiconductor layer131, the gate electrode152(e.g., a switching gate electrode), the source electrode173(e.g., a switching source electrode), and the drain electrode174(e.g., a switching drain electrode). The driving TFT20may include the driving semiconductor layer132, the gate electrode155(e.g., a driving gate electrode), the source electrode176(e.g., a driving source electrode), and the drain electrode177(e.g., a driving drain electrode). The configuration(s) of the switching TFT10and the driving TFT20is not limited to the aforementioned description, and is susceptible to various modifications known in the art, and may be easily applicable by those skilled in the art. In addition, the capacitor30includes the first capacitor plate158and the second capacitor plate178, which oppose each other while having the insulating interlayer160therebetween.

In the present embodiment, the insulating interlayer160may be a dielectric material, and capacitance of the capacitor30may be determined by an amount of electric charge accumulated in the capacitor30, and by the voltage across the first and second capacitor plates158and178.

The switching TFT10may be used as a switching element for selecting a pixel to emit light. The switching gate electrode152is connected to the gate line151. The switching source electrode173is connected to the data line171. The switching drain electrode174is spaced from the switching source electrode173, and is connected to the first capacitor plate158.

The driving TFT20applies a driving power to a first electrode210, and the driving power allows the OLED40within the selected pixel to emit light. The driving gate electrode155is connected to the first capacitor plate158. The driving source electrode176and the second capacitor plate178are connected to the common power line172. The driving drain electrode177is connected to the first electrode210of the OLED40through a contact hole (e.g., a contact hole181in the planarization layer180).

Due to such a configuration, the switching TFT10may be operated by a gate voltage applied to the gate line151to thereby transmit a data voltage applied to the data line171to the driving TFT20. A voltage equivalent to a difference between a common voltage applied from the common power line172to the driving TFT20, and the data voltage transmitted from the switching TFT10, may be stored in the capacitor30. A current corresponding to the voltage stored in the capacitor30may flow into the OLED40through the driving TFT20, such that the OLED40may emit light.

The OLED40includes the first electrode210, an organic light emitting layer230on the first electrode210, and a second electrode240on the organic light emitting layer230.

At least one first electrode210may be formed in each pixel region. The first electrode210of the OLED40is formed on the planarization layer180, and is connected to the drain electrode177through a contact hole181formed in the planarization layer180.

A pixel defining layer220defining the pixel region by exposing at least a portion of the first electrode210is formed on the planarization layer180. The pixel defining layer220may be formed of a resin such as a polyacrylate resin or a polyimide resin.

The organic light emitting layer230is formed on the first electrode210within the pixel region, and the second electrode240is formed on the pixel defining layer220and the organic light emitting layer230. The organic light emitting layer230may be formed of one of a low molecular weight organic material, and a high molecular weight organic material. At least one of a hole injection layer (HIL) and a hole transporting layer (HTL) may further be interposed between the first electrode210and the organic light emitting layer230, and at least one of an electron transporting layer (ETL) and an electron injection layer (EIL) may further be interposed between the organic light emitting layer230and the second electrode240.

The first electrode210and the second electrode240may include one of a transmissive electrode, a transflective electrode, and a reflective electrode. The transmissive electrode may be formed of transparent conductive oxide (TCO), which may include at least one of indium-tin oxide (ITO), indium-zinc oxide (IZO), antimony-tin oxide (ATO), aluminum-zinc oxide (AZO), zinc oxide (ZnO), and/or a compound thereof.

The transflective electrode and/or the reflective electrode may be formed of magnesium (Mg), silver (Ag), gold (Au), calcium (Ca), lithium (Li), chromium (Cr), aluminum (Al), copper (Cu), and/or an alloy thereof. In the present embodiment, whether the electrode is transflective or reflective may be determined based on the thickness of the electrode. In general, the transflective electrode may have a thickness of about 200 nm or less, and the reflective electrode may have a thickness of about 300 nm or greater. As the thickness of the transflective electrode decreases, the light transmittance thereof increases, and the resistance thereof increases. Further, as the thickness of the transflective electrode increases, the light transmittance thereof decreases. In addition, the transflective and reflective electrodes may have a multilayer structure including a metal layer formed of a metal or a metal alloy, and a transparent conductive oxide (TCO) layer stacked on the metal layer.

A capping layer250is formed on the second electrode240to protect the OLED40prior to forming a thin film encapsulation layer300, and to prevent damage to the OLED40during the formation of the thin film encapsulation layer300. The capping layer250may have a single layer, or may have two or more layers, and may serve to block moisture or oxygen. Alternatively, the capping layer250may be omitted, and an organic layer320of the thin film encapsulation layer300may be formed in lieu of the capping layer250.

The thin film encapsulation layer300is formed on the capping layer250, and may include at least one inorganic layer310and at least one organic layer320. Further, the thin film encapsulation layer300may have a structure in which the inorganic layer310and the organic layer320are alternately stacked. In this regard, one of the inorganic layers310may be positioned in the lowermost portion of the thin film encapsulation layer300. The thin film encapsulation layer300may have a thickness of about 10 μm or less. The numbers of the inorganic layers310and the organic layers320are not limited to the example illustrated inFIG. 5.

The inorganic layer310may include at least one of aluminum oxide and silicon oxide. The organic layer320may include at least one of epoxy, acrylate, and urethane acrylate. The inorganic layer310may suppress infiltration of moisture and oxygen toward the flexible display panel100, and the organic layer320may alleviate stress within the inorganic layer310and/or may fill minute cracks, pin holes, and the like formed in the inorganic layer310.

As set forth above, in a display device according to one or more exemplary embodiments, a polarizing unit has increased transmittance at a corresponding position, such that a rate of degradation of an OLED at a corresponding position may be slackened. Further, image sticking phenomenon caused by degradation of the OLED may be significantly reduced.

From the foregoing, it will be appreciated that various embodiments in accordance with the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope and spirit of the present teachings. Accordingly, the various embodiments disclosed herein are not intended to be limiting of the true scope and spirit of the present teachings. Various features of the above described and other embodiments can be mixed and matched in any manner, to produce further embodiments consistent with the invention as set forth in the following claims and their equivalents.