Organic light emitting diode display

An organic light emitting diode (OLED) display includes: a first substrate; an organic light emitting diode that is positioned on the first substrate and that emits light; a second substrate that is opposite to the first substrate with the organic light emitting diode interposed therebetween; a sealant that is positioned between the first substrate and the second substrate to cohere and seal the first substrate and the second substrate; and a refractive index change portion that is positioned on the second substrate to be opposite to the organic light emitting diode and that has a refractive index that sequentially reduces from the second substrate to the organic light emitting diode.

CLAIM OF PRIORITY

This application makes reference to, incorporates the same herein, and claims all benefits accruing under 35 U.S.C. §119 from an application entitled ORGANIC LIGHT EMITTING DIODE DISPLAY earlier filed in the Korean Intellectual Property Office on Nov. 26, 2009 and there duly assigned Ser. No. 10-2009-0115322.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to an organic light emitting diode (OLED) display. More particularly, to an OLED display that reflects light, that is emitted from an organic light emitting diode, more effectively with improved visibility.

2. Description of the Related Art

A display device is a device that displays an image, and currently, an OLED display is in the spotlight.

The OLED display has self luminous characteristics and does not require a separate light source, unlike a liquid crystal display device, and thus can have reduced thickness and weight. Further, the OLED display has high quality characteristics such as low power consumption, high luminance, and a high reaction speed.

In general, several metal wires that are included in the OLED display reflect light that is injected from the outside. When the OLED display is used at a bright place, due to such external light reflection, the OLED display is not good with regard to expression of a black color and contrast, and thus there is a problem that visibility is deteriorated.

Further, because the OLED display includes a plurality of thin films and substrates, due to interference of light by a refractive index difference thereof, there is a problem that a Newton's ring phenomenon, which is a pattern of an undesired concentric circle shape, occurs.

SUMMARY OF THE INVENTION

The described technology has been made in an effort to provide an OLED display having advantages of suppressing occurrence of a Newton's ring phenomenon while improving visibility.

An exemplary embodiment provides an OLED display including: a first substrate; an organic light emitting diode that is positioned on the first substrate and that emits light; a second substrate that is opposite to the first substrate with the organic light emitting diode interposed therebetween; a sealant that is positioned between the first substrate and the second substrate to cohere and seal the first substrate and the second substrate; and a refractive index change portion that is positioned on the second substrate to be opposite to the organic light emitting diode and that has a refractive index that is sequentially reduced from the second substrate to the organic light emitting diode.

The refractive index change portion may include a moth eye (or motheye) layer that is positioned on the second substrate.

The refractive index change portion may further include an air layer that is formed between the moth eye layer and the organic light emitting diode.

The moth eye layer may have a larger refractive index than that of the air layer.

The moth eye layer may include a plurality of protruding portions that are separated from each other by a uniform gap and that are tapered in a direction of the organic light emitting diode.

The moth eye layer may be formed in the second substrate, and the second substrate and the moth eye layer may be integrally formed.

The OLED display may further include an optical layer that is positioned between the second substrate and the moth eye layer.

The optical layer may include a polarizing film.

The optical layer may include a plurality of color filters that are separated from each other at separation space on the second substrate, and a black matrix that is positioned at the separation space.

The moth eye layer may be formed in the optical layer, and may be integrally formed with the optical layer.

According to the present invention, by suppressing occurrence of a Newton's ring phenomenon while improving visibility, an OLED display in which display quality is improved is provided.

DETAILED DESCRIPTION OF THE INVENTION

Further, like reference numerals designate like elements in several exemplary embodiments and are representatively described in the first exemplary embodiment and elements different from those of the first exemplary embodiment will be described in other exemplary embodiments.

The drawings and description are to be regarded as illustrative in nature and not restrictive.

Further, the size and thickness of each of elements that are displayed in the drawings are described for better understanding and ease of description, and the present invention is not limited by the described size and thickness.

In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, for better understanding and ease of description, thicknesses of some layers and areas are excessively displayed. When it is said that any part, such as a layer, film, region, or plate, is positioned on another part, it means the part is directly on the other part or above the other part with at least one intermediate part. In contrast, if any part is said to be positioned directly on another part, it means that there is no intermediate part between the two parts.

Further, in the accompanying drawings, an active matrix (AM) OLED display of a 2Tr-1Cap structure having two thin film transistors (TFT) and one capacitor in one pixel is described, but the present invention is not limited thereto. Therefore, the OLED display may have three or more TFTS and two or more capacitors in one pixel, and may have various structures as a separate wire is further formed. Here, a pixel is a minimum unit that displays an image, and the OLED display displays an image through a plurality of pixels.

Hereinafter, an OLED display101according to a first exemplary embodiment will be described with reference toFIGS. 1 to 5.

FIG. 1is a cross-sectional view illustrating an OLED display according to a first exemplary embodiment.

As shown inFIG. 1, the OLED display101according to the first exemplary embodiment includes a first substrate100, a second substrate200, a sealant300, a wire portion400, an organic light emitting diode500, and a refractive index change portion600.

The first substrate100and the second substrate200are insulation substrates including glass, polymer, or stainless steel, and at least one of the first substrate100and the second substrate200is made of a light transmitting material. The wire portion400and the organic light emitting diode500are positioned on the first substrate100, and the second substrate200is opposite to the first substrate100with the wire portion400and the organic light emitting diode500interposed therebetween. The first substrate100and the second substrate200are cohered and sealed by the sealant300with the organic light emitting diode500interposed therebetween, and the first substrate100and the second substrate200protect the wire portion400and the organic light emitting diode500from external interference.

The second substrate200includes a central portion corresponding to the organic light emitting diode500and an outer edge portion corresponding to the sealant300. The central portion of the second substrate200is bent in a direction of the organic light emitting diode500by a differential pressure between outer space and inner space that are formed by the first substrate100, the second substrate200, and the sealant300, and as the central portion of the second substrate200is bent in a direction of the organic light emitting diode500, the outer edge portion of the second substrate200is bent with a steeper slope than that of the central portion from a portion that is supported by the sealant300to the central portion.

In the outer edge portion of the second substrate200, a Newton's ring phenomenon occurs due to offsetting, reinforcement, and interference by a plurality of lights such as light that is emitted from the organic light emitting diode500, light that is radiated from the outside to inner space, and light that is reflected by the first substrate100, the second substrate200, and the organic light emitting diode500, and the Newton's ring phenomenon is minimized by the refractive index change portion600to be described later, and a detailed description thereof will be described later together with that of the refractive index change portion600.

The sealant300is positioned between the first substrate100and the second substrate200, and is disposed along the edge of the first substrate100and the second substrate200to cohere and seal the first substrate100and the second substrate200. The sealant300includes frit, etc., and is cured by a curing means such as a laser, etc. The sealant300encloses the organic light emitting diode500at a predetermined gap from the second substrate200. A differential pressure of substantially1atmosphere is formed between the outer space and the inner space of the OLED display101that are formed by the sealant300, the first substrate100, and the second substrate200, and by the differential pressure, the sealant300sustains a state that is pressurized by the first substrate100and the second substrate200.

The wire portion400includes first and second TFTS10and20(shown inFIG. 2), and transfers a signal to the organic light emitting diode500to drive the organic light emitting diode500. The organic light emitting diode500emits light according to a signal that is received from the wire portion400.

The organic light emitting diode500is positioned on the wire portion400.

The organic light emitting diode500is positioned at a display area on the first substrate100and is formed using microelectromechanical systems (MEMS) technology such as photolithography. The organic light emitting diode500receives a signal from the wire portion400and displays an image by the received signal.

Hereinafter, an internal structure of the OLED display101according to the first exemplary embodiment will be described in detail with reference toFIGS. 2 and 3.

FIG. 2is a layout view illustrating a structure of a pixel of the OLED display according to the first exemplary embodiment.FIG. 3is a cross-sectional view of the pixel taken along line III-III ofFIG. 2.

As shown inFIGS. 2 and 3, the OLED display101includes a switching TFT10, a driving TFT20, a capacitor80, and an organic light emitting diode500that are each formed in each pixel. Here, a configuration including the switching TFT10, the driving TFT20, and the capacitor80is referred to as a wire portion400. The wire portion400further includes a gate line151that is disposed in one direction of the first substrate100, and a data line171and a common power source line172that are insulated from and intersect the gate line151. Here, a pixel is defined by the gate line151, the data line171, and the common power source line172as the boundary, but a pixel is not always limited thereto.

The organic light emitting diode500includes a first electrode710, an organic emission layer720that is formed on the first electrode710, and a second electrode730that is formed on the organic emission layer720. Here, the first electrode710is an anode, which is a hole injection electrode, and the second electrode730is a cathode, which is an electron injection electrode. However, the first exemplary embodiment is not always limited thereto, and the first electrode710may become a cathode and the second electrode730may become an anode according to a driving method of the OLED display101. Holes and electrons are injected into the organic emission layer720from the first electrode710and the second electrode730, respectively, and when exitons that are formed by coupling of holes and electrons that are injected into the organic emission layer720drop from an exited state to a ground state, the organic emission layer720emits light. Further, the first electrode710of the OLED display101according to the first exemplary embodiment is made of a light reflecting material such as aluminum (Al), and the second electrode730is made of a light transmitting material including transparent or semitransparent indium tin oxide (ITO) or indium zinc oxide (IZO), but the present invention is not limited thereto, and at least one of the first electrode710and the second electrode730can be transparent or semitransparent or can be made of a conductive material.

Further, in the OLED display101according to the first exemplary embodiment, the organic light emitting diode500emits light in a direction of the second substrate200, but the present invention is not limited thereto, and light that is emitted from the organic light emitting diode500can be emitted in a direction of at least one of the first substrate100and the second substrate200. That is, the OLED display101according to the first exemplary embodiment is a front light emitting type, but an OLED display according to another exemplary embodiments may be a rear light emitting type or a both side light emitting type.

The capacitor80includes a pair of capacitor plates158and178that are disposed with an interlayer insulating layer161interposed therebetween. Here, the interlayer insulating layer161is a dielectric material, and the capacity of the capacitor80is determined by charges that are stored in the capacitor80and a voltage between both capacitor plates158and178.

The switching TFT10includes a switching semiconductor layer131, a switching gate electrode152, a switching source electrode173, and a switching drain electrode174. The driving TFT20includes a driving semiconductor layer132(having a source region, a channel region and a drain region), a driving gate electrode155, a driving source electrode176, and a driving drain electrode177.

The switching TFT10is used as a switch that selects 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 separated from the switching source electrode173and is connected to one capacitor plate158.

The driving TFT20applies a driving power source for allowing light emitting of the organic emission layer720of the organic light emitting diode500within the selected pixel to the first electrode710. The driving gate electrode155is connected to the capacitor plate158that is connected to the switching drain electrode174. The driving source electrode176and the other capacitor plate178are each connected to the common power source line172. The driving drain electrode177is connected to the first electrode710of the organic light emitting diode500through a contact hole.

By such a structure, the switching TFT10operates by a gate voltage that is applied to the gate line151and thus performs a function of transferring a data voltage, that is applied to the data line171, to the driving TFT20. A voltage corresponding to a difference between a common voltage, that is applied from the common power source line172to the first driving TFT20, and a data voltage, that is transferred from the switching TFT10, is stored in the capacitor80, and a current corresponding to the voltage that is stored in the capacitor80flows to the organic light emitting diode500through the driving TFT20, whereby the organic light emitting diode500emits light. The refractive index change portion600is positioned opposite to the organic light emitting diode500.

The refractive index change portion600is positioned on the second substrate200to be opposite to the organic light emitting diode500. The refractive index change portion600has a refractive index that is sequentially reduced from the second substrate200to the organic light emitting diode500. In more detail, the refractive index change portion600includes a moth eye layer610that is separated from the organic light emitting diode500and an air layer620that is formed between the moth eye layer610and the organic light emitting diode500, and the refractive index change portion600has a refractive index that is sequentially reduced from the second substrate200to the organic light emitting diode500due to a refractive index difference between the moth eye layer610and the air layer620.

Hereinafter, the refractive index change portion600having a refractive index that is sequentially reduced from the second substrate200to the organic light emitting diode500due to the moth eye layer610and the air layer620that are included in the refractive index change portion600will be described in detail with reference toFIGS. 4,5(a) and5(b).

FIG. 4is a picture illustrating a portion of a moth eye layer that is included in the OLED display according to the first exemplary embodiment.FIGS. 5(a) and5(b) are diagrams illustrating a refractive index change portion that is included in the OLED display according to the first exemplary embodiment.

As shown inFIG. 4, the moth eye layer610of the refractive index change portion600includes a plurality of protruding portions611that are opposite to the organic light emitting diode500to protrude in a direction of the organic light emitting diode500and that are separated from each other by a uniform gap. The protruding portion611is tapered in a direction of the organic light emitting diode500.

As shown inFIG. 5(a), the moth eye layer610of the refractive index change portion600has a refractive index (e.g., a refractive index of 1.1 to 2.5) that is larger than the air layer620having a refractive index of 1, and the tapered protruding portion611of the moth eye layer610is exposed to the air layer620that is positioned between the moth eye layer610and the organic light emitting diode500. At a refractive index change area ‘A’ the protruding portions611are positioned separated from each other by a uniform gap and having a larger refractive index than that of the air layer620having a refractive index of 1 and enclosing the plurality of protruding portions611. The protruding portion611protrudes in a tapered state toward a first direction in which the organic light emitting diode500is positioned, the refractive index sequentially reduces toward the first direction from the refractive index change area A, as shown inFIG. 5(b). That is, the refractive index change portion600has a refractive index that sequentially reduces from the second substrate200to the organic light emitting diode500.

In this way, as the refractive index change portion600has a refractive index that sequentially reduces from the second substrate200to the organic light emitting diode500due to the protruding portion611of the moth eye layer610and the air layer620that encloses the protruding portion611, light that is radiated to the refractive index change portion600is repeatedly refracted and scattered at an interface of the protruding portion611of the moth eye layer610and the air layer620that encloses the protruding portion611. That is, as a plurality of lights such as light that is emitted from the organic light emitting diode500, light that is radiated from the outside to internal space, and light that is reflected by the first substrate100, the second substrate200, and the organic light emitting diode500are repeatedly refracted and scattered while passing through the refractive index change portion600including the moth eye layer610, occurrence of a Newton's ring phenomenon that may occur by offsetting, reinforcement, and interference of light is minimized in the OLED display101according to the first exemplary embodiment.

Particularly, because the moth eye layer610of the refractive index change portion600is directly opposite to the organic light emitting diode500, light that is reflected by the organic light emitting diode500is first repeatedly refracted and scattered by the refractive index change portion600including the moth eye layer610and the air layer620, whereby occurrence of a visibility failure phenomenon by undesired interference of light such as a Newton's ring phenomenon is suppressed.

Further, even if a plurality of metal wires such as the first electrode710and the second electrode720that are included in the organic light emitting diode500reflect light that is injected from the outside, light that is reflected by the organic light emitting diode500is repeatedly refracted and scattered while passing through the refractive index change portion600, whereby deterioration of visibility of a display device due to reflection is suppressed.

An experiment for checking that the OLED display101according to the first exemplary embodiment includes the refractive index change portion600, and thus occurrence of a Newton's ring phenomenon is minimized was performed, and this will be described hereinafter in detail with reference toFIGS. 6 and 7.

Hereinafter, a comparative example and an experimental example will be described with reference toFIGS. 6 and 7.

FIG. 6is a graph illustrating a comparative example of the present invention.FIG. 7is a graph illustrating an experimental example of the present invention.

The comparative example that is shown inFIG. 6does not include the refractive index change portion600according to the first exemplary embodiment, and the experimental example that is shown inFIG. 7includes the refractive index change portion600according to the first exemplary embodiment.

FIG. 6illustrates a comparative example, and is a graph measuring a change of luminance at an air layer620that is formed between the first substrate100and the second substrate200, i.e., at different thicknesses between the second substrate200and the organic light emitting diode500.

As shown inFIG. 6, in the comparative example, a length of peak to valley of luminance that is measured when the thickness of the air layer620is about 5000 nm is a first length L1.

FIG. 7is an experimental example, and is a graph measuring a change of luminance at the air layer620that is formed between the first substrate100and the second substrate200, i.e., at different thicknesses between the second substrate200and the organic light emitting diode500.

As shown inFIG. 7, in the experimental example, a length of peak to valley of measured luminance when the thickness of the air layer620is about 5000 nm is a second length L2that is smaller than the first length L1of the comparative example, and the second length L2that is measured in the experimental example is about 60% of the first length L1that is measured in the comparative example.

A length of peak to valley of luminance indicates occurrence intensity of a Newton's ring phenomenon, and in such an experiment, the OLED display101according to the first exemplary embodiment includes the refractive index change portion600, whereby occurrence of a Newton's ring phenomenon was minimized, compared with the comparative example that does not include the refractive index change portion600.

As described above, the OLED display101according to the first exemplary embodiment includes the refractive index change portion600, whereby occurrence of a Newton's ring phenomenon is minimized and deterioration of visibility is suppressed and thus the entire display quality is improved.

Hereinafter, an OLED display102according to the second exemplary embodiment will be described with reference toFIG. 8.

FIG. 8is a cross-sectional view illustrating a main portion of an OLED display according to a second exemplary embodiment.

As shown inFIG. 8, a refractive index change portion602according to the second exemplary embodiment includes a moth eye layer610and an air layer620.

The moth eye layer610is formed in a surface of a second substrate200that is opposite to the organic light emitting diode500. The moth eye layer610is formed in a surface of the second substrate200using an MEMS process such as a photolithography process. That is, the moth eye layer610is integrally formed with the second substrate200.

In this way, in the OLED display102according to the second exemplary embodiment, as the moth eye layer610that is included in the refractive index change portion602is formed in the second substrate200, the second substrate200and the moth eye layer610are integrally formed, and thus the entire OLED display102according to the second exemplary embodiment can be formed in a smaller thickness than that of the OLED display101according to the first exemplary embodiment.

Further, the OLED display102according to the second exemplary embodiment includes a refractive index change portion602, whereby occurrence of a Newton's ring phenomenon is minimized and deterioration of visibility is suppressed and thus the entire display quality is improved.

Hereinafter, an OLED display103according to a third exemplary embodiment will be described with reference toFIGS. 9 and 10.

FIG. 9is a cross-sectional view illustrating an OLED display according to a third exemplary embodiment.FIG. 10is a cross-sectional view illustrating a main portion of the OLED display according to the third exemplary embodiment.

As shown inFIGS. 9 and 10, the OLED display103according to the third exemplary embodiment includes a first optical layer800that is positioned between a second substrate200and a refractive index change portion603having the moth eye layer610and an air layer620.

The first optical layer800includes an optical film, such as a polarizing film and a phase difference film, and as the first optical layer800includes an optical film, the first optical layer800suppresses external light reflection by light that is radiated from the outside to the inside of the OLED display103and that is reflected again to the outside.

In this way, the OLED display103according to the third exemplary embodiment includes the first optical layer800that is positioned between the refractive index change portion603and the second substrate200, whereby external light reflection is suppressed.

Further, the OLED display103according to the third exemplary embodiment includes the refractive index change portion603, so occurrence of a Newton's ring phenomenon is minimized and deterioration of visibility is suppressed.

That is, the OLED display103according to the third exemplary embodiment includes the first optical layer800and the refractive index change portion603, whereby the entire display quality is improved.

In another exemplary embodiment, the first optical layer800can be positioned at an external surface of the second substrate200.

Hereinafter, an OLED display104according to the fourth exemplary embodiment will be described with reference toFIG. 11.

FIG. 11is a cross-sectional view illustrating a main portion of an OLED display according to a fourth exemplary embodiment.

As shown inFIG. 11, the OLED display104according to the fourth exemplary embodiment includes a first optical layer800that is positioned between a second substrate200and the organic light emitting diode500.

The first optical layer800includes an optical film such as a polarizing film and a phase difference film, and as the first optical layer800includes an optical film, the first optical layer800suppresses external light reflection of light that is radiated from the outside to the inside of the OLED display104and that is reflected again to the outside.

Further, the moth eye layer610is formed in a surface of the first optical layer800that is opposite to the organic light emitting diode500. The moth eye layer610is formed in a surface of the first optical layer800using an MEMS process such as a photolithography process. That is, the moth eye layer610is integrally formed with the first optical layer800.

In this way, in the OLED display104according to the fourth exemplary embodiment, as the moth eye layer610that is included in a refractive index change portion604is formed in the first optical layer800, the first optical layer800and the moth eye layer610are integrally formed, whereby the entire OLED display104according to the fourth exemplary embodiment can be formed in a smaller thickness than that of the OLED display103of the third exemplary embodiment.

Further, the OLED display104according to the fourth exemplary embodiment includes the refractive index change portion604, whereby occurrence of a Newton's ring phenomenon is minimized and deterioration of visibility is suppressed.

That is, as the OLED display104according to the fourth exemplary embodiment includes the first optical layer800and the refractive index change portion604, the entire display quality is improved.

Hereinafter, an OLED display105according to a fifth exemplary embodiment will be described with reference toFIG. 12.

FIG. 12is a cross-sectional view illustrating a main portion of the OLED display according to the fifth exemplary embodiment.

As shown inFIG. 12, the OLED display105according to the fifth exemplary embodiment includes a second optical layer900that is positioned between a second substrate200and a refractive index change portion605having the moth eye layer610and an air layer620.

The second optical layer900includes a plurality of color filters910that correspond to each organic emission layer720and that are separated from each other with a separation space interposed therebetween on the second substrate200, and a black matrix920that is positioned at separation spaces between the separated color filters910. The color filter910improves a color reproduction rate of light that is emitted from the organic emission layer720, and the black matrix920intercepts a wire of the organic light emitting diode500from being viewed from the outside, thereby improving the entire contrast ratio of the OLED display105.

In this way, the OLED display105according to the fifth exemplary embodiment includes the second optical layer900having the color filter910and the black matrix920, thereby improving the contrast ratio while improving the color reproduction rate.

Further, the OLED display105according to the fifth exemplary embodiment includes the refractive index change portion605, thereby minimizing occurrence of a Newton's ring phenomenon and suppressing deterioration of visibility.

That is, the OLED display105according to the fifth exemplary embodiment includes the second optical layer900and the refractive index change portion605, thereby improving the entire display quality.

In another exemplary embodiment, the second optical layer900can be positioned at an external surface of the second substrate200.

Hereinafter, an OLED display106according to a sixth exemplary embodiment will be described with reference toFIG. 13.

FIG. 13is a cross-sectional view illustrating a main portion of the OLED display according to the sixth exemplary embodiment.

As shown inFIG. 13, the OLED display106according to the sixth exemplary embodiment includes a second optical layer900that is positioned between a second substrate200and the organic light emitting diode500.

The second optical layer900includes a plurality of color filters910that correspond to each organic emission layer720and that are separated from each other with a separation space interposed therebetween on the second substrate200, and a black matrix920that is positioned at the separation spaces between the separated color filters910. The color filter910improves the color reproduction rate of light that is emitted from the organic emission layer720, and the black matrix920intercepts a wire of the organic light emitting diode500from being viewed from the outside, thereby improving the entire contrast ratio of the OLED display106.

Further, the moth eye layer610is formed in a surface of the second optical layer900that is opposite to the organic light emitting diode500. The moth eye layer610is formed in a surface of the second optical layer900using an MEMS process such as a photolithography process. That is, the moth eye layer610is integrally formed with the second optical layer900.

In this way, in the OLED display106according to the sixth exemplary embodiment, as the moth eye layer610that is included in the refractive index change portion606is formed in the second optical layer900, the second optical layer900and the moth eye layer610are integrally formed, and thus the entire OLED display106according to the sixth exemplary embodiment can be formed in a smaller thickness than that of the OLED display105of the fifth exemplary embodiment.

Further, the OLED display106according to the sixth exemplary embodiment includes the refractive index change portion606, whereby occurrence of a Newton's ring phenomenon is minimized and deterioration of visibility is suppressed.

That is, the OLED display106according to the sixth exemplary embodiment includes the second optical layer900and the refractive index change portion606, thereby improving the entire display quality.