KR20140084622A - Flexible display device - Google Patents

Abstract

A flexible display device according to an embodiment of the present invention comprises a substrate made of a flexible material; a device layer including multiple light emitting structures formed on the substrate to correspond to multiple pixel areas; and a protection layer formed on the device layer to cover the light emitting structures, wherein the cross section of one among the substrate, the device layer, and the protection layer is a neutral axis where stress is zero in a bending state. When the neutral axis is bent with a certain bending radius, the device layer is deformed at a first strain rate based on the bending radius of the neutral axis and a distance between a first axis corresponding to the upper surface of the device layer and the neutral axis and the protection layer is deformed at a second strain rate based on the bending radius of the neutral axis and a distance between a second axis corresponding to the upper surface of the protection layer and the neutral axis.

Description

[0001] FLEXIBLE DISPLAY DEVICE [0002]

The present invention relates to a flexible display device capable of improving lifetime and reliability.

As the era of informationization becomes full-scale, the display field for visually displaying electrical information signals is rapidly developing. Accordingly, studies are being continued to develop performance such as thinning, lightening, and low power consumption for various various flat display devices.

Typical examples of such flat panel display devices include a liquid crystal display device (LCD), a plasma display panel (PDP), a field emission display (FED) An electroluminescence display device (ELD), an electro-wetting display device (EWD), and an organic light emitting display device (OLED). Such flat panel display devices commonly include flat panel display panels for realizing images. A flat panel display panel is a structure in which a pair of substrates sandwiching a unique light emitting material or a polarizing material are face-to-face bonded.

2. Description of the Related Art In recent years, a flat panel display device, including a flexible substrate such as plastic, can be realized as a flexible display device capable of maintaining display performance even when bent like paper.

Since such a flexible display device can be applied to a wider range than existing display devices having no flexibility, research and development for commercializing a flexible display device has been continued.

On the other hand, since the flexible display device has a property of being easily bent by a load, the shape can be easily changed. Due to this shape deformation or repeated shape deformation, stress is applied to the thin film in the flexible display device, so that the thin film can be destroyed. Thus, there is a problem that the lifetime and the reliability of the flexible display device are lowered.

The present invention aims at providing a flexible display device capable of improving lifetime and reliability by designing a thin film in consideration of stress due to deformation of a shape.

According to an aspect of the present invention, there is provided a flexible display device comprising: a substrate provided with a flexible material; An element layer including a plurality of light emitting structures formed corresponding to a plurality of pixel regions on the substrate; And a protective layer formed on the element layer so as to cover the plurality of light emitting structures. Here, the cross section of any one of the substrate, the element layer and the protective layer is a neutral axis where the stress is zero in a bending state, and when the neutral axis is bent at an arbitrary bending radius, Layer is deformed to a first strain based on a bending radius of the neutral axis and a separation distance between a first axis corresponding to an upper surface of the element layer and the neutral axis and the protective layer has a bending radius of the neutral axis, And a second strain rate based on a distance between the second axis corresponding to the upper surface of the protective layer and the neutral axis.

The distance between the first axis and the neutral axis is set such that the distance between the first axis and the neutral axis is less than the first critical strain that causes the first strain to break the element layer when the neutral axis is bent at a bending radius greater than a predetermined reference radius, The critical strain and the first threshold distance based on the reference radius.

The distance between the second axis and the neutral axis is preferably less than a second critical distance corresponding to the second critical strain and the reference radius so that the second strain is less than a second critical strain, to be.

The flexible display device according to an embodiment of the present invention can measure the distance between the axis corresponding to each layer and the neutral axis based on the reference radius of the neutral axis and the critical strain of each layer when a maximum stress is generated for each layer It is possible to prevent the layer from being broken by the stress generated by the deformed shape deformation.

Therefore, the lifetime and reliability of the flexible display device can be improved.

1 is a cross-sectional view illustrating a flexible display device according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view showing one example of a light emitting structure of the element layers of FIG. 1. FIG.
Fig. 3 is a cross-sectional view showing a state in which the flexible display device of Fig. 1 is bent at a first bending radius; Fig.
Fig. 4 is a cross-sectional view showing a state in which the flexible display device of Fig. 1 is bent at a second bending radius; Fig.
5 is an example of the critical strain of the first and second axes.
6 to 8 are cross-sectional views showing other examples of the flexible display device according to an embodiment of the present invention.

Hereinafter, a flexible display device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

1 is a cross-sectional view illustrating a flexible display device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing one example of a light emitting structure of the element layers of FIG. 1. FIG. Fig. 3 is a cross-sectional view showing a state in which the flexible display device of Fig. 1 is bent at a first bending radius, and Fig. 4 is a cross-sectional view showing a state where the flexible display device of Fig. 1 is bent at a second bending radius.

1, the flexible display device 100 according to one embodiment of the present invention includes a substrate 110 formed of a soft material, a plurality of light emitting structures corresponding to a plurality of pixel regions on a substrate 110, And a protective layer 130 formed on the device layer 120. The protective layer 130 is formed on the device layer 120,

The substrate 110 is made of a flexible material such as stainless steel and plastic.

The element layer 120 includes a plurality of light emitting structures corresponding to a plurality of pixel regions. At this time, the light emitting structure is not limited within the range applicable to the flexible display device. For example, the light emitting structure may be any one of an E-paper device, an electro wetting device, and an organic light emitting display device.

2, the element layer 120 includes a driving switch element DTr corresponding to each pixel region and an organic electroluminescent element E (organic electroluminescent element) corresponding to each pixel region, ).

A semiconductor layer 121 is formed on the substrate 110. The semiconductor layer 121 includes an active region 121a constituting a channel and a source region 121b formed by doping impurities on both sides of the active region 121a 121b and a drain region 121c.

The first interlayer insulating film 122a is sequentially formed on the entire surface of the substrate 110 so as to cover the semiconductor layer 121. [

The gate electrode 123 is formed on the first interlayer insulating film 122a so as to at least partially overlap with the active region 121a.

The second interlayer insulating film 122b is formed so as to be laminated on the entire surface of the first interlayer insulating film 122a so as to cover the gate electrode 123. [

The source electrode 124a is formed on the second interlayer insulating film 122b so as to at least partially overlap with the source region 121b and is connected to the source region 121b through the contact hole passing through the first and second interlayer insulating films 122a and 122b 121b. Similarly, the drain electrode 124b is formed on the second interlayer insulating film 122b so as to overlap at least part of the drain region 121c and through the contact hole passing through the first and second interlayer insulating films 122a and 122b Drain region 121c.

Thereby, the driving switch element DTr including the semiconductor layer 121, the gate electrode 123, the source electrode 124a, and the drain electrode 124b is provided.

The third interlayer insulating film 122c is formed on the entire surface of the second interlayer insulating film 122b so as to cover the source electrode 124a and the drain electrode 124b.

The bank 125 is formed on the third interlayer insulating film 122c as a partition corresponding to the outline of each of the plurality of pixel regions.

The organic light emitting device E is formed on the third interlayer insulating film 122c in correspondence with each of the plurality of pixel regions and includes first and second electrodes 126a and 126b facing each other and an organic layer 126c. At this time, the first electrode 126a is connected to the drain electrode 124b through the contact hole passing through the third interlayer insulating film 122c.

1 will be described again.

The protective layer 130 is formed to protect the element layer 120 from external physical and electrical impacts, and is formed of a single layer or a plurality of layers including AlO _x .

On the other hand, the cross section of any one of the flexible display device 100 including the substrate 110, the element layer 120 and the protective layer 130 is a surface where the stress becomes zero in a bending state, NA: neutral axis).

At this time, the neutral axis NA controls the substrate 110, the element layer 120, and the protective layer 130 by adjusting the thickness and material of each of the substrate 110, the element layer 120, and the protective layer 130, Layer 130 may be any one of the cross-sections. 1, the neutral axis NA may be a cross-section of the element layer 120. In one embodiment,

3, in the case of the flexible display device 101 to which the first load F1 in the upward direction is applied, the neutral axis NA has a first bending radius (R = 1) corresponding to the first load F1, r1, and the length of the neutral axis NA is not deformed, so that the strain of the neutral axis NA is maintained at zero. That is, stress along the neutral axis NA substantially does not occur in accordance with the first load F1.

However, the first axis A1 corresponding to the upper surface of the element layer 120 and the second axis A2 corresponding to the upper surface of the protective layer 130 are curved convexly outside the neutral axis NA. Thus, the first and second axes A1 and A2 are deformed to be longer by being bent by the first load F1. Therefore, a tensile stress due to the first load F1 is generated in the first and second axes A1 and A2, and the element layer 120 and the protective layer 130 corresponding to the first and second axes A1 and A2.

Specifically, the first axis A1 corresponding to the upper surface of the element layer 120 is spaced apart from the neutral axis NA by the first distance Y1 from the outside of the neutral axis NA. Therefore, the first axis A1 is a bending radius (= r1 + Y1) that is larger than the bending radius R of the neutral axis NA, i.e., the first bending radius R = r1 by the first separation distance Y1 It bends convexly.

The first axis A1 and the element layer 120 including the first axis A1 are deformed by the first load F1 changing the bending radius R of the neutral axis NA to the first bending radius r1, And is deformed to a first strain based on the radius r1 and the first spacing distance Y1.

Similarly, the second axis A2 corresponding to the upper surface of the protective layer 130 is spaced apart from the neutral axis NA by the second distance Y2 from the outside of the neutral axis NA. Therefore, the second axis A2 is a bending radius (= r1 + Y2) that is larger than the bending radius R of the neutral axis NA, i.e., the first bending radius R = r1 by the second separation distance Y2 It bends convexly.

The second shaft A2 and the corresponding protective layer 130 are moved in the first direction F1 by the first load F1 which varies the bending radius R of the neutral axis NA to the first bending radius r1, And is deformed to a second strain based on the bending radius r1 and the second spacing distance Y2.

In addition, since the second axis A2 is farther from the neutral axis NA than the first axis A1, the second axis A2 is deformed to a greater strain than the first axis A1 even under the same load. That is, since the second spacing distance Y2 is larger than the first spacing distance Y1, the second strain rate is larger than the first strain rate.

Unlike the first and second axes A1 and A2, the third and fourth axes A3 and A4 corresponding to the upper and lower surfaces of the substrate 110 are curved convexly from the inside of the neutral axis NA. That is, the third and fourth axes A3 and A4 are deformed to be shorter by being bent by the first load F1. Therefore, the first and second axes A3 and A4 and the substrate 110 including the third and fourth axes A3 and A4 generate compressive stress in accordance with the first load F1.

At this time, as in the first and second strains, the strain of the third axis A3 is determined by the first load F1 that varies the bending radius R of the neutral axis NA to the first bending radius r1, The first bending radius r1 and the fourth bending radius r2 are determined based on the first bending radius R = r1 and the separation distance between the third axis A3 and the neutral axis NA, A4) and the neutral axis NA.

Alternatively, as shown in Fig. 4, in the case of the flexible display device 102 to which the second load F2 in the downward direction is applied, the neutral axis NA corresponds to the second bending radius corresponding to the second load F2 R = r2), and the length is not deformed, so that the strain of the neutral axis NA is kept at zero.

However, the first axis A1 corresponding to the upper surface of the element layer 120 and the second axis A2 corresponding to the upper surface of the protective layer 130 are concavely bent inside the neutral axis NA. Thus, the first and second axes A1 and A2 are deformed to be shorter by being bent by the second load F2. Therefore, a compressive stress is generated in the element layer 120 and the protective layer 130 corresponding to the first and second axes A1 and A2 and the second load F2.

Specifically, the first axis A1 corresponding to the upper surface of the element layer 120 is spaced apart from the neutral axis NA by a first distance Y1 from the inside of the neutral axis NA. Thus, the first axis A1 is concavely bent with a bending radius (= r2-Y1) smaller than the neutral layer NA by the first separation distance Y1.

Therefore, by the second load F2 which varies the bending radius R of the neutral axis NA to the second bending radius r2, the first axis A1 and the corresponding element layer 120 are arranged in the second The first strain? -2A1 based on the bending radius r2 and the first spacing distance Y1.

Similarly, the second axis A2 corresponding to the upper surface of the protective layer 130 is spaced apart from the neutral axis NA by a second distance Y2 from the inside of the neutral axis NA. Thus, the second axis A2 is concavely curved at a bending radius r2-Y2 that is smaller than the neutral axis NA by a second spacing distance Y2.

Therefore, by the second load F2 that varies the bending radius R of the neutral axis NA to the second bending radius r2, the second axis A2 and the corresponding protective layer 130 are arranged in the second The second strain? -2 based on the bending radius r2 and the second spacing distance Y2.

Unlike the first and second axes A1 and A2, the third and fourth axes A3 and A4 corresponding to the upper and lower surfaces of the substrate 110 are concavely curved outside the neutral axis NA. That is, the third and fourth axes A3 and A4 are deformed to be longer by being bent by the second load F2, so that the third and fourth axes A3 and A4 and the substrate 110 including the third and fourth axes A3 and A4, Tensile stress is generated according to the second load F2.

As described above, the strain rate of each axis due to the load applied to the flexible display device 100 is based on the bending radius of the neutral axis NA corresponding to the load and the separation distance between each axis and the neutral axis NA. This can be expressed by the following equation (1).

As shown in Equation 1, the strain rate? _Ai of each axis may be a ratio between the bending radius R of the neutral axis NA corresponding to the load and the separation distance Yi between each axis and the neutral axis NA .

According to this formula (1), as the bending radius R of the neutral axis NA corresponding to the load becomes smaller, or as the separation distance Yi between each axis and the neutral axis NA becomes larger, the strain? ) Is larger.

However, the strain rate of each axis can not be increased to infinity. That is, the strain rate of each axis is limited to within a critical strain based on the strength of the material. That is, the strain rate of the shaft can be increased only up to the critical strain that destroys the material of the shaft.

In addition, in designing the flexible display device 100, the bending radius R of the neutral axis NA is limited to be equal to or larger than the reference radius. That is, the reference radius represents the minimum value among the bending radii R of the neutral axis NA. For reference, the maximum value of the bending radius R of the neutral axis NA is infinity (∞), which corresponds to the case where the neutral axis NA is flat.

This reference radius may be selected based on the strength of the substrate 110 material, such that the substrate 110 is not fractured. Alternatively, the reference radius may be arbitrarily selected according to the standard value of the product or the designer's intention.

As the critical strain of each axis Ai and the reference radius of the neutral axis NA are set in this way, the first and second axes A1 and A1 are formed so that the element layer 120 and the protective layer 130 are not broken accordingly. , A2) need to be adjusted.

That is, due to the load that varies the bending radius R of the neutral axis NA by the reference radius, the first axis A1 and the element layer 120 including the first axis A1 are less than the first critical strain that destroys the element layer 120 It should be deformed to the first strain.

Therefore, the first separation distance Y1 between the first axis A1 and the neutral axis NA is equal to or larger than 0 and falls within a range less than the first critical distance Y1 _max , as shown in the following equation (2) , The first critical distance Y1 _max is based on the first critical strain epsilon A1 _max and the reference radius _Rmin .

Similarly, the second axis A1 and the protective layer 130 including the second axis A1 are deformed by the load that varies the bending radius R of the neutral axis NA by the reference radius, and the second critical strain Lt; RTI ID = 0.0 > strain. ≪ / RTI >

Therefore, as shown in Equation 3 below, and the second axis (A2) and the neutral axis (NA) and the second distance (Y2) is greater than or equal to zero between the second critical distance corresponding to the range less than (Y2 _max), and wherein , And the second critical distance Y2 _max is based on the second critical strain epsilon A2 _max and the reference radius _Rmin .

On the other hand, as mentioned above, the critical strain of each axis is predetermined based on the strength of each axis material.

5 is an example of the critical strain of the first and second axes.

5, the abscissa axis represents the separation distance between each of the first and second axes A1 and A2 and the neutral axis NA, and the ordinate axis represents the bending radius of the neutral axis NA. Each graph shows the critical strain according to the separation distance and the bending radius.

5, the critical strain of the first axis A1 is represented by the slope of the red graph, that is, approximately 0.0005, and the critical strain of the second axis A2 is represented by the slope of the blue graph, .

Assuming here that the reference radius _Rmin is 1 mm, the first critical distance Y1max is 5 占 퐉 and the second critical distance Y2max is 10 占 퐉, as indicated by the dotted line in Fig.

Substituting this into equations (2) and (3), the first separation distance Y1, which is the distance that the first axis A1 is spaced from the neutral axis NA, is in the range of 0 占 퐉 to less than 5 占 퐉, The second spacing distance Y2, which is a distance apart from the neutral axis NA, is in the range of 0 占 퐉 to less than 10 占 퐉.

Since the second separation distance Y2 corresponds to the sum of the first separation distance Y1 and the thickness of the protection layer 130, the thickness of the protection layer 130 may be equal to the thickness of the first separation distance Y2 (Y2-Y1) obtained by subtracting the separation distance Y1. Therefore, the thickness of the protective layer 130 corresponds to a range of more than 0 mu m and less than 5 mu m.

1 shows a state in which the neutral axis NA of the flexible display device 100 is perpendicular to the third axis A3 corresponding to the cross section in the element layer 120, that is, the upper surface of the substrate 110, And the first axis A1 corresponding to the first axis A1. 1, however, according to one embodiment of the present invention, the neutral axis NA may not be a cross-section in the element layer 120. [

6 to 8 are cross-sectional views showing other examples of the flexible display device according to an embodiment of the present invention.

6, the neutral axis NA of the flexible display device 100 'may substantially coincide with the first axis A1 corresponding to the top surface of the element layer 120. In other words, At this time, the first separation distance Y1 becomes zero.

7, the neutral axis NA of the flexible display device 100 '' is defined by a first axis A1 corresponding to an end face in the passivation layer 130, that is, the top face of the element layer 120, And the second axis A2 corresponding to the upper surface of the protective layer 130. [

8, the neutral axis NA of the flexible display device 100 '' 'has a fourth axis A4 corresponding to the end surface in the substrate 110, that is, the lower surface of the substrate 110, And may be positioned between the third axis A3 corresponding to the upper surface of the substrate 110. [

As described above, in the flexible display device according to the embodiment of the present invention, on the basis of the reference radius of the neutral axis and the critical strain of each layer, which is the case where the stress due to warped shape deformation reaches a maximum, To adjust the separation distance. As a result, even when the shape deformation due to the load is repeated one or more times, the layer can be prevented from being broken, so that the lifetime and reliability of the flexible display device can be improved.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the invention. Will be clear to those who have knowledge of.

100, 100 ', 100 ", 100 "': Flexible display device
110: substrate 120: element layer
130: protective layer NA: neutral axis
A1: a first axis corresponding to the upper surface of the element layer
A2: a second axis corresponding to the upper surface of the protective layer
A3, A4: third and fourth axes corresponding to the upper and lower surfaces of the substrate
Y1: First separation distance between the first axis and the neutral axis
Y2: second separation distance between the second axis and the neutral axis

Claims (6)

In the flexible display device,
A substrate provided with a flexible material;
An element layer including a plurality of light emitting structures formed corresponding to a plurality of pixel regions on the substrate; And
And a protective layer formed on the element layer so as to cover the plurality of light emitting structures,
A cross section of any one of the substrate, the device layer and the protective layer is a neutral axis in which a stress is zero in a bending state,
When the neutral axis is bent with an arbitrary bending radius,
Wherein the element layer is deformed to a first strain based on a bending radius of the neutral axis and a distance between a first axis corresponding to an upper surface of the element layer and the neutral axis,
Wherein the protective layer is deformed to a second strain based on a bending radius of the neutral axis and a distance between a second axis corresponding to an upper surface of the protective layer and the neutral axis,
Wherein when the neutral axis is bent at a predetermined reference radius, the first strain is less than a first critical strain,
Wherein the distance between the first axis and the neutral axis is less than the first critical distance based on the first critical strain and the reference radius. The method according to claim 1,
And the second strain is less than a second critical strain that destroys the protective layer,
Wherein the distance between the second axis and the neutral axis is less than a second critical distance corresponding to the second critical strain and the reference radius. 3. The method of claim 2,
Wherein the thickness of the protective layer is less than a value obtained by subtracting the first critical distance from the second critical distance. The method of claim 3,
The protective layer may be a single layer or multiple layers including AlO _x ,
The reference radius is 1 mm,
Wherein the first critical strain is 0.005 mu m and the second critical strain is 0.01 mu m,
Wherein the first critical distance is 5 占 퐉 and the second critical distance is 10 占 퐉. 5. The method of claim 4,
Wherein the thickness of the protective layer is more than 0 占 퐉 and less than 5 占 퐉. 6. The method according to any one of claims 1 to 5,
Wherein the first axis substantially coincides with the neutral axis.

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