Organic light emitting diode (OLED) display

An organic light emitting diode (OLED) display device that includes: a first substrate having a first area and a second area adjacent to the first area; an organic light emitting diode (OLED) disposed on the first area of the first substrate; a second substrate facing the first substrate such that the OLED is interposed between the first substrate and the second substrate so as to expose the second area of the first substrate; and a sealant disposed between the first substrate and the second substrate to attach and seal the first substrate to the second substrate, wherein the sealant surrounds the OLED by a predetermined distance and having a first width of one portion closer to the second area that is larger than a second width of an other portion which is farther from the second area.

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 earlier filed in the Korean Intellectual Property Office on the 14 Jul. 2010 and there duly assigned Serial No. 10-2010-0068077.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The described technology relates generally to an organic light emitting diode display, and more particularly, to an organic light emitting diode display including frit as a sealant.

2. Description of the Related Art

An organic light emitting diode (OLED) display has attracted public attention as a display device displaying an image. The OLED display is a self emitting display device that does not require an additional light source to emit light. Since the OLED display does not need the additional light source, which is used in a liquid crystal display, it is possible to reduce a thickness and a weight of the OLED display. Furthermore, the OLED display shows high-quality characteristics including lower power consumption, high luminance, and high response speed.

In general, the OLED display includes a first substrate, an OLED positioned on the first substrate, a second substrate facing the first substrate with the OLED interposed therebetween, and a sealant such as frit which attaches and seals the first substrate and the second substrate to each other. However, in a case where at least one of the first substrate and the second substrate is made of a fragile material such as glass, and the like, when a physical impact, or in other words an impact force, is applied to the OLED display from the outside or an external source, at least one of the first substrate, the second substrate, and the frit may be damaged.

SUMMARY OF THE INVENTION

Aspects of the present invention provide an organic light emitting diode (OLED) display having advantages of an improved impact-resistance.

According to an aspect of the present invention, there is provided an organic light emitting diode display (OLED) that includes: a first substrate having a first area and a second area adjacent to the first area; an organic light emitting diode (OLED) disposed on the first area of the first substrate; a second substrate facing the first substrate such that the OLED is interposed between the first substrate and the second substrate so as to expose the second area of the first substrate; and a sealant disposed between the first substrate and the second substrate to attach and seal the first substrate to the second substrate, wherein the sealant surrounds the OLED by a predetermined distance, and wherein the sealant has a first width of one portion closer to the second area that is larger than a second width of an other portion which is farther from the second area.

According to another aspect of the present invention, the sealant may be formed of a frit material.

According to another aspect of the present invention, the first width of the one portion of the sealant may be 1.1 to 3 times larger than the second width of the other portion.

According to another aspect of the present invention, the first width of the one portion of the sealant may be 1.5 times larger than the second width of the other portion.

According to another aspect of the present invention, the second width of the other portion of the sealant may be 450 μm, and the first width of the one portion of the sealant may be in the range of 550 μm to 950 μm.

According to another aspect of the present invention, the other portion of the sealant may be bent and extended from the one portion, and the bent portion between the other portion and the one portion of the sealant may be curved.

According to aspects of the present invention, there is provided an organic light emitting diode display having improved impact-resistance.

DETAILED DESCRIPTION OF THE INVENTION

Accordingly, the drawings and description are to be regarded as illustrative in nature and not restrictive. Like reference numerals designate like elements throughout the specification. In addition, the size and thickness of each component shown in the drawings are arbitrarily shown for understanding and ease of description, but the present invention is not limited thereto. In the drawings, the thickness of layers, films, panels, regions, etc., are exaggerated for clarity. In the drawings, for understanding and ease of description, the thicknesses of some layers and areas are exaggerated. It will be understood that when an element such as a layer, film, region, or substrate is referred to as being “on” another element, it can be directly on the other element or intervening elements may also be present. Further, in the specification, unless explicitly described to the contrary, the word “comprise” and variations such as “comprises” or “comprising”, will be understood to imply the inclusion of stated elements but not the exclusion of any other elements. Further, throughout the specification, “on” implies being positioned above or below a target element and does not imply being necessarily positioned on the top on the basis of a gravity direction.

Furthermore, in the accompanying drawings, although an active matrix (AM) type OLED display having a 2Tr-1 Cap structure, which is provided with two thin film transistors (TFTs) and one storage capacitor in one pixel is shown, exemplary embodiments are not limited thereto. Accordingly, the OLED display may be provided with three or more thin film transistors and two or more storage capacitors in one pixel and may be configured to have various structures with additional wires. Herein, the pixel represents a minimum unit displaying an image and the OLED display displays the image by means of a plurality of pixels.

Hereinafter, referring toFIGS. 1 to 5, an organic light emitting diode (OLED) display, according to an exemplary embodiment, will be described.FIG. 1is a plan view of an OLED display according to an exemplary embodiment.FIG. 2is a cross-sectional view taken along line II-II ofFIG. 1. As shown inFIGS. 1 and 2, the OLED display includes a first substrate100, a second substrate200, a wire part300, an organic light emitting diode (OLED)400, and a sealant500.

The first substrate100and the second substrate200are insulating substrates and may be formed of glass, polymer, stainless steel, or other similar materials. At least one of the first substrate100and the second substrate200is made of a light transmissive material. The wire part300and the OLED400are disposed on the first substrate100. The second substrate200faces the first substrate100. The wire part300and the OLED400are interposed between the first substrate100and the second substrate200. The first substrate100and the second substrate200are attached and sealed to each other by the sealant500with the OLED400interposed therebetween. The first substrate100and the second substrate200protect the wire part300and the OLED400from external interference.

Furthermore, the first substrate100includes a first area A1and a second area A2adjacent to the first area A1. The first area A1is between the first substrate100and the second substrate200and is covered in part by with the sealant500. The OLED400is positioned in the part of the first area A1that is covered by the sealant500.

The second area A2is adjacent to the first area A1and is positioned on an end of the second substrate200so as to be exposed to an outside. That is, the second substrate200faces the first substrate100with the OLED400interposed between the first substrate100and the second substrate200so as to expose the second area A2. A driving unit110, on which a circuit chip and the like is mounted, is disposed in the second area A2. The driving unit110drives the OLED400by transferring a signal to the wire part300.

The wire part300includes first and second thin film transistors10and20(shown inFIG. 3) and drives the OLED400by transferring a signal to the OLED400. The OLED400emits light depending on the signal received from the wiring part300. The OLED400is disposed on the wire part300. The OLED400is disposed on the first substrate100in the first area A1and receives the signal from the wire part300in order to display an image by using the received signal.

Hereinafter, referring toFIGS. 3 and 4, an internal structure of the OLED display according to the embodiment ofFIG. 1will be described in detail.FIG. 3is a layout view illustrating a structure of a pixel of an organic light emitting diode (OLED) display according to an exemplary embodiment.FIG. 4is a cross-sectional view taken along line IV-IV ofFIG. 3.

The detailed structures of the wire part300and the OLED400are shown inFIGS. 3 and 4, however, aspects of the present invention are not limited to the structures shown inFIGS. 3 and 4. The wire part300and the OLED400may be formed in various structures within the scope which can be easily modified by one of ordinary skill in the art. For example, although the OLED display is illustrated as an active matrix (AM) type OLED display having a 2Tr-1Cap structure, which is provided with two thin film transistors (TFTs) and one storage capacitor in one pixel, aspects of the present invention are not limited thereto. Therefore, the OLED display may vary with respect to a number of thin film transistors, a number of storage capacitors, and a number of wires. Additionally, a pixel represents a minimum unit displaying an image and the OLED display displays the image through the pixels.

As shown inFIGS. 3 and 4, the OLED display includes a switching thin film transistor10, a driving thin film transistor20, a storage capacitor80, and an organic light emitting diode (OLED)400formed in each pixel. In the present embodiment, the wire part300includes the switching thin film transistor10, the driving thin film transistor20, and the storage capacitor80. In addition, the wire part300further includes a gate line151disposed in one direction of the first substrate100, and a data line171and a common power supply line172crossing and insulated from the gate line151. Although a boundary of one pixel may be defined by the gate line151, the data line171, and the common power supply line172, aspects of the present invention are not limited thereto.

The OLED400includes a first electrode710, an organic emission layer720formed on the first electrode710, and a second electrode730formed on the organic emission layer720. The first electrode710, the organic emission layer720, and the second electrode730constitute the OLED400. In the present embodiment, the first electrode710is an anode which is a hole injection electrode and the second electrode730is a cathode which is an electron injection electrode. However, aspects of the present invention are not limited thereto, and the first electrode710may be the cathode and the second electrode730may be the anode according to a driving method of the OLED display. Holes and electrons are injected into the organic light emitting layer720from the first electrode710and the second electrode730, respectively. When excitons generated by combining the injected holes and the injected electrons fall from an excited state to a ground state, the organic emission layer720emits light. Furthermore, at least one of the first electrode710and the second electrode730is made of a transparent or translucent conductive material such as indium tin oxide (ITO) and indium zinc oxide (IZO).

In the OLED display according to the present exemplary embodiment, the OLED400emits light toward at least one of the first substrate100and the second substrate200. That is, according to aspects of the present invention, the OLED display may be a top emission type, a bottom emission type, or a double-sided emission type.

The storage capacitor80includes a pair of storage plates158and178and an interlayer insulating layer161is interposed between the storage plates158and178. An interlayer insulating layer161becomes a dielectric and a storage capacity of the storage capacitor80is determined by electric charges stored in the storage capacitor80and voltage between the storage plates158and178.

The switching thin film transistor10includes a switching semiconductor layer131, a switching gate electrode152, a switching source electrode173, and a switching drain electrode174. The driving thin film transistor20includes a driving semiconductor layer132, a driving gate electrode155, a driving source electrode176, and a driving drain electrode177. The switching thin film transistor10is used as a switching element that selects a desired 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 disposed away from the switching source electrode173and is connected to any one storage plate158.

The driving thin film transistor20applies driving power to the first electrode710so that the organic emission layer720in a selected pixel emits light. The driving gate electrode155is connected to the storage plate158which is connected with the switching drain electrode174. Each of the driving source electrode176and the other storage plate178is connected to a common power supply line172. The driving drain electrode177is connected to the first electrode710of the OLED400through a contact hole (not shown).

In the structure of the present embodiment, the switching thin film transistor10is operated by a gate voltage applied to the gate line151in order to transmit data voltage applied to the data line171to the driving thin film transistor20. A voltage equivalent to a difference between a common voltage applied to the driving thin film transistor20from the common power supply line172and the data voltage transmitted from the switching thin film transistor10is stored in the storage capacitor80. Also, a current corresponding to a voltage stored in the storage capacitor80flows to the OLED400through the driving thin film transistor20to allow the OLED400to emit light.

Referring back toFIGS. 1 and 2, the sealant500is positioned between the first substrate100and the second substrate200and surrounds the OLED400at predetermined intervals. The sealant500is disposed on edges of the first substrate100and the second substrate200to attach and seal the first substrate100and the second substrate200to each other. The sealant500includes a frit material. The frit material is cured by a curing member such as a laser or other similar devices and processes. The sealant500includes a first part510and a second part520. The first part510is closer to the second area A2than the second part520and the second part520of the sealant500is bent and extended from the first part510. A bent part between the first part510and the second part520of the sealant500has a curved shape.

The bent part between the first part510and the second part520of the sealant500has the curved shape, consequently, when an impact is applied to the OLED display, a maximum principal stress applied to the first part510of the sealant500is easily transitioned to the second part520. As a result, the maximum principal stress applied to the first part510of the sealant500decreases.

A first width W1of the first part510is larger than a second width W2of the second part520. The first width W1of the first part510is 1.1 to 3 times larger than the second width W2of the second part520and, for example, may be 1.5 times larger than the second width W2of the second part520. Furthermore, when the second width W2of the second part520of the sealant500is 450 um, the first width W1of the first part510of the sealant500may be in the range of 550 μm to 950 μm. However, it is understood that values of the first width W1of the first part510and the second width W2of the second part520of the sealant500can be other values in other aspects. As such, the first width W1of the first part510is larger than the second width W2of the second part520, such that the impact-resistance of an OLED display can be improved and a slim OLED display can be implemented.

Hereinafter, referring toFIGS. 5 to 10, in the OLED display according to the present exemplary embodiment, the reason why the first width W1of the first part510of the sealant500is larger than the second width W2of the second part520of the sealant500according to aspects of the present invention will be described in detail.

First, a frit material is used as a sealant500to provide a high-temperature melting adhesive using glass powder as a main raw material. However, the frit material is fragile. Therefore, the OLED display has a decreased mechanical strength (or in other words, a decreased structural strength) and, thus, is more vulnerable than a liquid crystal display in which both substrates are attached to each other by a sealant such as epoxy or another flexible material. In particular, when the OLED display drops from a height the structural strength of the OLED display is most vulnerable.

When a broken part of the dropped OLED display is observed, a probability that a breakage source is the frit material of the sealant500is 80% or more. In order to improve the structural strength of the OLED display by suppressing damage to the sealant500, an overall width of the sealant500may be increased. However, it is not preferable to increase an overall width of the sealant500when attempting to maximize a space occupied by an effective pixel where the OLED is positioned in the OLED display. In other words, a size and a thickness of the OLED display may increase when increasing an overall width of the sealant500. Thus, the following experiment is performed in order to provide an OLED display with improved impact-resistance and a slim thickness.

FIGS. 5 to 9are diagrams for describing a test in which an organic light emitting diode (OLED) display is provided according to an exemplary embodiment.FIG. 10is a graph describing a test in which an organic light emitting diode (OLED) display is provided according to the exemplary embodiment ofFIGS. 5 to 9.

First, a 3.1 inch cubic panel, which is an organic light emitting diode (OLED) display having a size shown inFIG. 5, is provided. In this panel, a width of the sealant500is set as 450 μm. The sealant500is glass frit attaching the first substrate100and the second substrate200, which are made of glass, to each other. Hereinafter, the OLED display will be referred to as the panel and the sealant500will be referred to as the glass frit.

When a drop test is performed on such a panel, the panel is inserted into a drop jig simulating a mobile device such as a cellular phone, as shown inFIG. 6. The panel drops from a predetermined height to a bottom without just throwing the panel to the bottom. In the present test, the weight of the drop jig is approximately 73 g and a panel having a weight of 8.26 g is added thereto. In the drop test, the panel and the drop jig drops to an iron-plate bottom disposed at 1.5 m or more below an initial start point of the dropping of the panel and the drop jig.

When this drop test is simulated by using ABAQUS, which is a structure, electricity, and heat analysis tool sold by SIMULIA of Dassault Systems, the glass frit around the second area A2of the first substrate100is damaged as shown inFIG. 7. More specifically, a portion of the end of the glass frit where the glass frit and the first substrate100contact each other, which is adjacent to the OLED is damaged. The portion where the glass frit and the first substrate contact each other is the maximum stress point of the glass frit shown inFIG. 7. In regards to the cause of the damage, the glass frit is damaged not by an impact generated when the panel first collides with the bottom. Rather, the glass frit is damaged by a transforming of the panel while the drop jig is bent in a W shape, as shown inFIG. 8, which happens at a time of tens of microseconds after the panel collides with the bottom.

When such a case as described above is determined on the basis of a simple beam theory, the second area A2of the first substrate100is larger than the second substrate200, such that the second area A2protrudes outwardly from an end of the second substrate200. Therefore, when viewed from the panel attached by the glass frit, a thickness of only the second area A2of the first substrate100may be regarded to be decreased. Therefore, when a bending moment, which is external force, is applied to the panel, an area having the smaller thickness is further bent and a larger stress is generated at this area. However, the glass fit is damaged because the ultimate strength of the glass frit is lower than that of the glass forming the first substrate100and the second substrate200. On the basis of the above noted causes, the following improvement measures are considered, including decreasing the maximum principal stress generated in the glass frit adjacent to the second area A2of the first substrate100.

In order to achieve the improvement measures, a width of the glass frit corresponding to a short side of the panel is increased, as shown inFIG. 9. At this time, the thickness of the glass frit is 4 μm. As shown inFIG. 9, two short-side glass frits are provided in the panel. When a width of the top short-side glass frit (shown as glass frit-top inFIG. 9) increases, panel adhesion strength increases as the adhesion area of the glass frit increases. However, the maximum principal stress generated in the panel cannot be reduced by the transformation of the glass frit generated while the part corresponding to the second area A2of the first substrate100is bent when the panel is transformed by dropping. Accordingly, in order to increase the width of the glass frit, a width of the bottom glass frit (shown as glass frit-bottom inFIG. 9), which is close to the second area A2of the first substrate100, should be increased.

Results acquired at the time of increasing the width of the upper short-side glass frit and the width of the bottom short-side glass frit are verified through simulation and are shown in a graph ofFIG. 10. In the graph shown inFIG. 10, an x axis represents the width of the bottom short-side glass frit [bottom frit width (μm)] and a y axis represents the maximum principal stress [Max. (S.Max.Principal) (MPa)] applied to the bottom short-side glass frit.

As shown inFIG. 10, the width of the top short-side glass frit is set as 450 μm to 750 μm [REF(T450), VAR1(T550), VAR1(650), VART(750)], the width of the bottom short-side glass frit is set as 450 μm to 950 μm, and a width of a long-side glass frit at the side (shown as glass frit-side inFIG. 9) is set as 450 μm. In such a case, when a width of the bottom short-side glass frit is approximately twice as large as the width of the long-side glass frit at the side, regardless of the size of the width of the top short-side glass frit, the maximum principal stress applied to the bottom short-side glass frit is decreased by approximately 50% as compared to when the bottom short-side glass frit has a witch of 450 μm. Meanwhile, the change in the width of the top short-side glass frit does not cause the maximum principal stress applied to the bottom short-side glass frit from being reduced.

That is, when the first width W1and the second width W2are varied as described above, the maximum principal stress applied to the first part510of the sealant500is reduced. The first width W1and the second width W2may be varied in the following manner. The first width W1of the first part510is set to be 1.1 to 3 times larger than the second width W2of the second part520. Also, the width of the side long-side glass frit or the first width W1of the first part510is in the range of 550 μm to 950 μm while the second width W2of the second part520is 450 μm. However, aspects of the present invention are not limited to the above widths of the first width W1and the second width W2, and other suitable widths of the first width W1and the second width W2may be used.

In the OLED display according to the present exemplary embodiment, the maximum principal stress applied to the first part510of the sealant500is reduced when the impact is applied to the OLED display. Thus, an impact-resistance of the OLED display is improved. In particular, since only the first width W1of the first part510of the sealant500is larger than the second width W2of the second part520, the impact-resistance of the OLED display is improved and a slim OLED display may be obtained.

Furthermore, in the OLED display according to the present exemplary embodiment, the bent part between the first part510and the second part520of the sealant500has the curved shape. Thus, when an impact is applied to the OLED display, the maximum principal stress applied to the first part510of the sealant500is easily transitioned to the second part520. As a result, the maximum principal stress applied to the first part510of the sealant500decreases, thereby improving the impact resistance of the OLED display. While described in terms of a sealant made of a frit material, it is understood that aspects of the invention could be used with other fragile and/or non-fragile sealant materials.