Patent Description:
Display devices used in the monitor of a computer, a television (TV), a mobile phone, or the like may include an organic light-emitting display (OLED) that emits light by itself, or a liquid-crystal display (LCD) that requires a separate light source.

More and more applications are being found for such display devices, including computer monitors and televisions, as well as personal portable devices. Accordingly, research is ongoing to develop display devices having a larger display area with reduced volume and weight.

Recently, stretchable display devices are attracting attention as next generation display devices. These stretchable display devices may be fabricated by disposing display elements and lines on a flexible substrate made of a flexible material such as plastic, so that they can be expanded and contracted in a particular direction and can be changed into various shapes.

<CIT> describes a sensor array having several stretchable interconnects for electrically connecting electronic devices, which are supported for movement relative to one another by a flexible and/or stretchable substrate, wherein the electronic devices can comprise sensors, circuit elements, control elements, microprocessors or any other desired electronic device, as well as combinations of the foregoing. LEDs for emitting light, which may be reflected and detected by integrated photodiodes, are arranged in the devices to sense proximity. Further, other uses of such an array <NUM> are described, including, for example, flexible displays. In addition, the interconnects <NUM> comprise stretchable conductors connected between respective contact pads of two adjacent electronic devices for electrically coupling a contact of one device to a contact of another device. Piezoelectric sensors of the electronic devices sense changes in the spring tension of the stretchable interconnects.

<CIT>describes a flexible display screen including a flexible display panel and a deformable driver disposed on the back surface of the flexible display panel, wherein the deformable driver comprises a plurality of deformable units arranged in an array. The deformable unit includes four branches, which are arranged in a cross shape. The four branches are fixed to the back surface of the flexible display panel by a first fixing member and a second fixing member. The branch of the drive unit includes a piezoelectric material layer.

A display device capable of displaying an image even if it is bent or stretched may be referred to as a stretchable display device. A stretchable display device may have higher flexibility than existing typical display devices. Accordingly, the shape of a stretchable display device may be changed as a user desires, such as by bending or stretching. For example, if a user grasps an end of a stretchable display device and pulls it, the stretchable display device may be stretched by the user's force. Alternatively, when a user places a stretchable display device on an uneven wall, the stretchable display device may be transformed according to the contours of the surface of the wall. In addition, when the force exerted by the user is removed, the stretchable display device may return to its original shape.

Such a stretchable display device is implemented to have rigid regions and a flexible region. Display elements are disposed in the rigid regions to emit light, and the flexible region is stretched when an external force is applied to the stretchable display device.

As described above, when a stretchable display device is stretched, it may not be uniformly stretched over the entire region of the display device. Instead, only the flexible region may be substantially stretched. Therefore, the distance between the rigid regions may increase when the stretchable display device is stretched, and the distance between the light-emitting elements may also increase accordingly. As a result, the density of the light-emitting regions in the stretchable display device may be reduced, and image quality may deteriorate. Thus, the lattice pattern perceived by a user when the stretchable display device is stretched-that is, mura artifacts such as a stripe feature visually recognized by a user when the luminance drops in the regions between the light-emitting elements-becomes more serious. In addition, when the stretchable display device is stretched, the screen may sag along a stretched direction, and the ratio of the image displayed on the stretchable display device may be distorted.

In view of the above, the inventors of the present disclosure have recognized such particular issues of stretchable display devices and have devised a novel display device to improve the issues.

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

An object of the present disclosure is to provide a display device that may suppress the deterioration of image quality when the display device is stretched. According to an aspect of the present disclosure, the object may be achieved, for example, by having a particular structure disposing a plurality of light-emitting elements on the lower substrate.

Another object of the present disclosure is to provide a display device that may reduce mura artifacts such as a lattice pattern when the display device is stretched. According to an aspect of the present disclosure, the object may be achieved, for example, by having a particular structure disposing a plurality of light-emitting elements on a flexible region between the light-emitting elements.

Additional advantages and features of the disclosure will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the disclosure. The objectives and other advantages of the disclosure may be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

To achieve these and other advantages and in accordance with the purpose of the disclosure, as embodied and broadly described herein, a stretchable display device according to claim <NUM> is provided.

The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this application, illustrate embodiments of the disclosure and together with the description serve to explain various principles. In the drawings:.

Reference will now be made in detail to embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers may be used throughout the drawings to refer to the same or like parts.

Advantages and characteristics of the present disclosure and a method of achieving the advantages and characteristics will be clear by referring to example embodiments described below in detail together with the accompanying drawings.

The shapes, sizes, ratios, angles, numbers, and the like illustrated in the accompanying drawings for describing the example embodiments of the present disclosure are merely examples, and the present disclosure is not limited thereto. Further, in the following description of the present disclosure, a detailed explanation of known related technologies may be omitted to avoid unnecessarily obscuring the subject matter of the present disclosure. The terms such as "including," "having," and "consist of" used herein are generally intended to allow other components to be added unless the terms are used with the term "only". Any references to singular may include plural unless expressly stated otherwise.

Hereinafter, a display device according to example embodiments of the present disclosure will be described in detail with reference to accompanying drawings.

<FIG> is an exploded perspective view of a display device according to an embodiment. With reference to <FIG>, a stretchable display device <NUM> includes a lower substrate <NUM>, a plurality of island substrates <NUM>, a plurality of connection substrates CS, a chip-on-film (COF) <NUM>, a printed circuit board <NUM>, an upper substrate <NUM>, and a polarizing layer <NUM>. In <FIG>, a plurality of additional connection substrates is not shown for convenience of illustration.

The lower substrate <NUM> supports and protects a variety of elements of the stretchable display device <NUM>. The lower substrate <NUM> may be made of an insulating material that can be bent or stretched as a flexible substrate. For example, the lower substrate <NUM> may be made of an elastomer including a silicone rubber such as polydimethylsiloxane (PDMS) and a polyurethane (PU), and accordingly can have flexibility. It is, however, to be understood that the material of the lower substrate <NUM> is not limited thereto.

The lower substrate <NUM> is a flexible substrate and can be reversibly expanded and contracted. In addition, the elastic modulus may be several MPa to several hundred MPa, and the elongation at break may be <NUM>% or higher. The thickness of the lower substrate <NUM> may be, but is not limited to, <NUM> to <NUM>.

The lower substrate <NUM> includes a display area AA and a non-display area NA surrounding the display area AA. The display area AA is an area where an image is displayed in the stretchable display device <NUM>, and a plurality of light-emitting elements <NUM> and a variety of driving elements for driving the plurality of light-emitting elements <NUM> are disposed therein.

The non-display area AA is adjacent to and surrounds the display area AA. In the non-display area NA, no image is displayed, and lines, circuit parts, etc. may be formed. For example, a plurality of pads may be disposed in the non-display area NA. Each of the pads may be connected to light-emitting elements <NUM> in the display area AA or to driving elements for driving the light-emitting elements <NUM>.

A plurality of island substrates <NUM> is disposed on the lower substrate <NUM>. The island substrates <NUM> may be rigid boards, and are spaced apart from one another on the lower substrate <NUM>. The island substrates <NUM> are more rigid than the lower substrate <NUM>. In other words, the lower substrate <NUM> is more flexible than the island substrates <NUM>.

The island substrates <NUM>, which are rigid boards, may be made of a plastic material having flexibility, and may be made of, for example, polyimide (PI), polyacrylate, polyacetate, etc..

The modulus of the island substrates <NUM> is higher than the modulus of the lower substrate <NUM>. As used herein, the modulus may refer to a modulus of elasticity, which indicates a quantity that measures a substrate's resistance to being deformed elastically when a stress is applied to it. The higher the modulus, the higher the hardness. Accordingly, the island substrates <NUM> are rigid boards having rigidity as compared with the lower substrate <NUM>. The modulus of the island substrates <NUM> may be, but is not limited to, <NUM> times larger than the modulus of the lower substrate <NUM>.

The island substrates <NUM> having rigidity are arranged on the lower substrate <NUM>, and portions of the lower substrate <NUM> overlapping the island substrates <NUM> are defined as rigid regions due to the island substrates <NUM>. The other portions of the lower substrate <NUM> that do not overlap with the island substrates <NUM> are defined as a flexible region because there is only the lower substrate <NUM>. That is to say, the portions of the lower substrate <NUM> where the island substrates <NUM> are arranged are defined as rigid regions, while the other portions of the lower substrate <NUM> where the island substrates <NUM> are not arranged are defined as a flexible region. Because the island substrates <NUM> are spaced apart from one another, the rigid regions are also be spaced apart from one another. The flexible region surrounds the rigid regions.

In some embodiments, the portions of the lower substrate <NUM> in the rigid regions have a higher modulus than the portions in the flexible region. That is to say, the portions of the lower substrate <NUM> overlapping the island substrates <NUM> may be made of a material having a modulus similar to that of the island substrates <NUM>, whereas the portions not overlapping the island substrates <NUM> may be made of a material having a modulus lower than that of the island substrates <NUM>.

A plurality of connection substrates CS is disposed between the island substrates <NUM>. The connection substrates CS connect adjacent ones of the island substrates <NUM> with one another. The connection substrates CS may be formed integrally with the island substrates <NUM>, but the present disclosure is not limited thereto.

The connection substrates CS have a curved shape. For example, as shown in <FIG>, the connection substrates CS may have a sine wave shape. However, it is to be understood that the shape of the connection substrates CS is not limited thereto. For example, the connection substrates CS may be extended in a zigzag shape, or may have the shape of diamond borders having their vertices connected to one another. The number and shape of the connection substrates CS shown in <FIG> are illustrative, and the number and shape of the connection substrates CS may be variously altered and is not limited herein.

The chip-on-film (COF) <NUM> is a film in which a variety of elements are disposed on a base film <NUM> having flexibility. The COF <NUM> provides signals to a plurality of light-emitting elements <NUM> in the display area AA and a variety of driving elements for driving the light-emitting elements <NUM>. The COF <NUM> may be bonded to a plurality of pads arranged in the non-display area NA, and may provide the light-emitting elements <NUM> in the display area AA and a variety of driving elements for driving the light-emitting elements <NUM> with the supply voltage, data voltage, gate voltage, etc. through the pads. The COF <NUM> may include the base film <NUM> and a driver integrated circuit (IC) <NUM>, and a variety of other elements may be disposed thereon.

The base film <NUM> is a layer for supporting the driver IC <NUM> of the COF <NUM>. The base film <NUM> may be made of an insulating material, for example, an insulating material having flexibility.

The driver IC <NUM> is an element for processing data for displaying image and driving signals for processing the data. Although the driver IC <NUM> is mounted in the form of a COF in <FIG>, it is to be understood that the driver IC <NUM> may also be mounted in the form of a chip-on-glass (COG), a tape-carrier-package (TCP), etc..

A control unit such as an IC chip and circuitry may be mounted on the printed circuit board <NUM>. A memory, a processor, etc. may also be mounted on the printed circuit board <NUM>. The printed circuit board <NUM> transmits signals for driving the light-emitting elements <NUM> from the control unit to the display area AA. The printed circuit board <NUM> may be connected to the COF <NUM> to thereby be electrically connected to the light-emitting elements <NUM> in the display area AA and the driving elements for driving the light-emitting elements <NUM>.

The upper substrate <NUM> overlaps with the lower substrate <NUM> and protects a variety of elements of the stretchable display device <NUM>. The upper substrate <NUM> may be made of an insulating material that can be bent or stretched as a flexible substrate. For example, the upper substrate <NUM> is made of a flexible material, and may be made of the same material as the lower substrate <NUM>, but the present disclosure is not limited thereto.

The polarizing layer <NUM> is an element for suppressing reflection of external light in the stretchable display device <NUM>, and may be disposed on the upper substrate <NUM> to overlap with it. It is, however, to be understood that the present disclosure is not limited thereto. The polarizing layer <NUM> may be disposed under the upper substrate <NUM> or may be eliminated depending on the structure of the stretchable display device <NUM>.

Hereinafter, the stretchable display device <NUM> according to an inventive embodiment of the present disclosure will be described in more detail with reference to <FIG> and <FIG>.

<FIG> is an enlarged plan view of a stretchable display device according to an inventive embodiment when including the sub-pixel and the additional sub-pixel as shown in the schematic cross-sectional view of <FIG>.

With reference to <FIG> and <FIG>, the lower substrate <NUM> has a plurality of first areas A1 in which a plurality of island substrates <NUM> is disposed, a plurality of second areas A2 in which a plurality of connection lines <NUM> is disposed, and a plurality of third areas A3 in which a plurality of additional sub-pixels SPXA is defined, other than the plurality of first areas A1 and the plurality of second areas A2.

In the first areas A1 of the lower substrate <NUM>, the island substrates <NUM> are respectively disposed. The first areas A1 have rigidity. The first areas A1 are defined on the lower substrate <NUM> such that they are spaced apart from one another. For example, the first areas A1 may be arranged in a matrix on the lower substrate <NUM>, as shown in <FIG>. It is, however, to be understood that the present disclosure is not limited thereto.

With reference to <FIG>, a plurality of pixels PX each including a plurality of sub-pixels SPX is defined on the island substrates <NUM> of the first areas A1. In each of the sub-pixels SPX, a light-emitting element <NUM> and a variety of driving elements for driving the light-emitting element <NUM> are disposed. Each of the sub-pixels SPX is connected to a variety of lines. For example, each of the sub-pixels SPX is connected to a variety of lines such as a gate line, a data line, a high-voltage supply line, a low-voltage supply line, a reference voltage line, and/or a common line CL.

On the lower substrate <NUM>, the second areas A2 are defined such that they are adjacent to the first areas A1. Each of the second areas A2 is defined between two adjacent ones of the first areas A1. Accordingly, as shown in <FIG>, second areas A2 are defined on the upper side, the lower side, the left side, and the right side of each of the first areas A1. In the second areas A2, a plurality of connection lines <NUM> and a plurality of connection substrates CS are disposed. The second areas A2 have flexibility. The second areas A2 are defined on the lower substrate <NUM> such that they are spaced apart from one another. For example, the second areas A2 may be arranged in a matrix on the lower substrate <NUM>, as shown in <FIG>. It is, however, to be understood that the present disclosure is not limited thereto.

In the second areas A2 of the lower substrate <NUM>, the connection lines <NUM> and the connection substrates CS are disposed. The connection lines <NUM> are disposed on the connection substrates CS and electrically connect the pads on the island substrates <NUM> with one another. For example, the connection lines <NUM> may electrically connect the pads disposed on adjacent ones of the island substrates <NUM>. The connection lines <NUM> are disposed on the second areas A2 between the first areas A1 to electrically connect the island substrates <NUM> with one another.

For a typical display device, a variety of lines such as gate lines and data lines are extended between the sub-pixels SPX. A plurality of sub-pixels SPX is connected to a single signal line. Accordingly, in a typical display device, the lines such as the gate lines, the data lines, the high-voltage supply line and the reference voltage line are seamlessly extended from one side to the other side of the display device on the substrate.

In contrast, for the stretchable display device <NUM> according to the embodiment, a variety of lines made of a metal, such as the gate line, the data line, the high-voltage supply line, the low-voltage supply line, the reference voltage line and the common line CL are disposed only on the island substrates <NUM>. That is to say, in the stretchable display device <NUM> according to the embodiment, a variety of lines made of a metal are disposed only on the island substrates <NUM> but are not in contact with the lower substrate <NUM>. Accordingly, the variety of lines made of a metal may be patterned such that they are disposed only on the island substrates <NUM> and extend discontinuously.

In the stretchable display device <NUM> according to the embodiment the connection lines <NUM> may be disposed between every two adjacent ones of the islands substrates <NUM> in order to connect the discontinuous lines on the island substrates <NUM> with one another. For example, the connection lines <NUM> are connected to the pads on the two adjacent island substrates <NUM>. A variety of lines such as the gate lines, the data lines, the high-voltage supply lines, the low-voltage supply lines, the reference voltage line and the common line CL on two adjacent island substrates <NUM> may be electrically connected to one another by the connection lines <NUM>.

For example, a gate line may be disposed on the island substrates <NUM> disposed adjacent to each other in the x-axis direction, and gate pads GP may be disposed at both ends of the gate line. The gate pads GP on the island substrates <NUM> disposed adjacent to each other in the x-axis direction may be connected to each other by the connection lines <NUM> serving the gate lines. Accordingly, a gate line disposed on an island substrate <NUM> in the first area A1 and a connection line <NUM> disposed in the second area A2 may serve as a single gate line. In addition, each of the lines that may be included in the stretchable display device <NUM> such as the data lines, the high-voltage supply line, the low-voltage supply line, the reference voltage line and the common lines CL may also serve as a single line by each of the connection lines <NUM>.

The connection lines <NUM> are disposed on connection substrates CS. As described above with reference to <FIG>, the connection substrates CS have a curved shape. Accordingly, the connection lines <NUM> disposed on the connection substrates CS may have a curved shape, like the connection substrates CS.

The connection lines <NUM> are made of a conductive material. The connection lines <NUM> may be made of the same material as the various conductive elements disposed on the island substrates <NUM>. For example, the connection lines <NUM> may be made of, but are not limited to, a metal material. In addition, the connection lines <NUM> may include a base polymer and conductive particles dispersed in the base polymer.

With reference to <FIG>, the connection lines <NUM> include first connection lines <NUM> and second connection lines <NUM>.

The first connection lines <NUM> are extended in the x-axis direction. Each of the first connection lines <NUM> may connect the pads on two island substrates <NUM> adjacent to each other in the x-axis direction. The first connection lines <NUM> may serve as, but are not limited to being, the gate lines or the low-voltage supply line, or the like. For example, when the first connection lines <NUM> serve as gate lines, they may electrically connect the gate pads GP on the two island substrates <NUM> arranged side by side with each other in the x-axis direction.

The second connection lines <NUM> are extended in the y-axis direction. The second connection lines <NUM> may connect the pads on two island substrates <NUM> adjacent to each other in the y-axis direction. The second connection lines <NUM> may serve as, but are not limited to being, the data lines or the high-voltage supply line, or the like. For example, when the second connection lines <NUM> serve as data lines, they may electrically connect the data pads on the two island substrates <NUM> arranged side by side with each other in the y-axis direction.

With reference to <FIG>, the third areas A3 are defined on portions of the lower substrate <NUM> surrounded by the first areas A1 and the second areas A2. The second areas A2 may be disposed on the upper side, the lower side, the right side and the left side of each of the third areas A3, and the first areas A1 may be disposed adjacent to each of the third areas A3 in the four diagonal directions.

In each of the third areas A3 of the lower substrate <NUM>, an additional pixel PXA including a plurality of additional sub-pixels SPXA is defined. In the additional sub-pixels SPXA, additional light-emitting elements 140A are respectively disposed. The additional sub-pixels SPXA are respectively connected to additional connection lines 150A.

The additional connection substrates CSA are disposed such that they are extended from the island substrates <NUM> to the additional sub-pixels SPXA. The additional connection substrates CSA may be extended from the first areas A1 to the third areas A3. The additional connection substrates CSA connect the island substrates <NUM> with the additional sub-pixels SPXA. The additional connection substrates CSA may be formed integrally with the island substrates <NUM>, but the present disclosure is not limited thereto.

With reference to <FIG>, the additional connection substrates CSA are disposed on the same plane as the connection substrates CS. Accordingly, the additional connection lines 150A on the additional connection substrates CSA and the connection lines <NUM> on the connection substrates CS may also be disposed on the same plane. The additional connection substrates CSA and the connection substrates CS may not overlap with each other but may be spaced apart from each other. If the additional connection substrates CSA were in contact with the connection substrates CS, the additional connection lines 150A on the additional connection substrates CSA might also be in contact with the connection lines <NUM> on the connection substrates CS, which might deteriorate the reliability of the stretchable display device <NUM>. For this reason, the additional connection substrates CSA may be spaced apart from the connection substrates CS on the same plane.

The additional connection substrates CSA have a curved shape. For example, the additional connection substrates CSA may have a sine wave shape, like the connection substrates CS. However, it is to be understood that the shape of the additional connection substrates CSA is not limited thereto. For example, the additional connection substrates CSA may be extended in a zigzag shape, or may have the shape of diamond borders having their vertices connected to one another.

The additional connection lines 150A are disposed on the additional connection substrates CSA. The additional connection lines 150A electrically connect the additional sub-pixels SPXA with the respective sub-pixels SPX. For example, the additional connection lines 150A may electrically connect the driving elements of the sub-pixels SPX with the additional light-emitting elements 140A of the additional sub-pixels SPXA. The additional connection lines 150A may transfer voltages at the sub-pixels SPX to the respective additional sub-pixels SPXA.

The additional sub-pixels SPXA are orientated obliquely with respect to the directions in which the connection lines <NUM> are extended. The additional connection substrates CSA and the additional connection lines 150A extended from the island substrates <NUM> to the additional sub-pixels SPXA may also be orientated obliquely with respect to the directions in which the connection lines <NUM> are extended.

The third areas A3, which are the flexible region, are stretched when the stretchable display device <NUM> is stretched. Accordingly, when the stretchable display device <NUM> is stretched, an external force is applied to the additional connection lines 150A and the additional connection substrates CSA disposed in the third areas A3. For example, when the stretchable display device <NUM> is stretched in the x-axis direction in which the first connection lines <NUM> are extended, an external force is applied to the additional connection lines 150A and the additional connection substrates CSA such that they are extended in the x-axis direction. However, because the additional connection lines 150A and the additional connection substrates CSA are orientated obliquely with respect to the x-axis direction, the external force applied to the additional connection lines 150A and the additional connection substrates CSA is dispersed. In addition, when the stretchable display device <NUM> is stretched in the y-axis direction in which the second connection lines <NUM> are extended, an external force is applied to the additional connection lines 150A and the additional connection substrates CSA such that they are extended in the y-axis direction. However, because the additional connection lines 150A and the additional connection substrates CSA are orientated obliquely with respect to the y-axis direction, the external force applied to the additional connection lines 150A and the additional connection substrates CSA is dispersed. That is to say, by disposing the additional connection lines 150A and the additional connection substrates CSA such that they are orientated obliquely with respect to the x-axis direction and the y-axis direction, it is possible to reduce the external force applied to the additional connection lines 150A and the additional connection substrates CSA when the stretchable display device <NUM> is stretched. In addition, it may be possible to reduce damage to the additional connection lines 150A and the additional connection substrates CSA.

Hereinafter, the sub-pixels SPX and the additional sub-pixels SPXA will be described in more detail with reference to <FIG>.

With reference to <FIG>, a buffer layer <NUM> is disposed on the island substrates <NUM>. The buffer layer <NUM> is disposed on the island substrates <NUM> for protecting a variety of elements of the stretchable display device <NUM> from moisture and oxygen introduced from the outside of the lower substrate <NUM> and the island substrates <NUM>. The buffer layer <NUM> may be made of an insulating material. The buffer layer <NUM> may be made up of a single layer or multiple layers of an inorganic layer made of, for example, silicon nitride (SiNx), silicon oxide (SiOx), silicon oxynitride (SiON), etc. In some implementations, however, the buffer layer <NUM> may be eliminated, depending on the structure or characteristics of the stretchable display device <NUM>.

The buffer layer <NUM> may be disposed only on the island substrates <NUM>. As described above, because the buffer layer <NUM> may be made of an inorganic material, it may be damaged. For example, cracks may easily occur when the stretchable display device <NUM> is stretched.

The buffer layer <NUM> is not disposed between the island substrates <NUM>, but may be patterned in the shape of the island substrates <NUM> and disposed only on the island substrates <NUM>. Accordingly, in the stretchable display device <NUM> according to the embodiment, by disposing the buffer layer <NUM> only on the island substrates <NUM>, which are rigid boards, it may be possible to prevent damage to the buffer layer <NUM> when the stretchable display device <NUM> is deformed by being bent or stretched.

A first transistor <NUM> including a first gate electrode <NUM>, a first active layer <NUM>, a first source electrode <NUM> and a first drain electrode <NUM> is disposed on the buffer layer <NUM>.

The first active layer <NUM> is disposed on the buffer layer <NUM>. In an example, the first active layer <NUM> may be formed of an oxide semiconductor or may be formed of an amorphous silicon (a-Si), a polycrystalline silicon (poly-Si), an organic semiconductor, or the like.

A gate insulating layer <NUM> is disposed on the first active layer <NUM>. The gate insulating layer <NUM> electrically isolates the first gate electrode <NUM> from the first active layer <NUM> and may be made of an insulating material. For example, the gate insulating layer <NUM> may be made up of a single layer of silicon nitride (SiNx) or silicon oxide (SiOx) which is an inorganic material, or multiple layers of silicon nitride (SiNx) and silicon oxide (SiOx). It is, however, to be understood that the present disclosure is not limited thereto.

The first gate electrode <NUM> is disposed on the gate insulating layer <NUM>. The first gate electrode <NUM> overlaps with the first active layer <NUM>. The first gate electrode <NUM> may be formed of, but is not limited to, one of a variety of metal materials including molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd) and copper (Cu), an alloy of two or more thereof, or multiple layers thereof.

An interlayer dielectric layer <NUM> is disposed on the first gate electrode <NUM>. The interlayer dielectric layer <NUM> insulates the first gate electrode <NUM> from the first source electrode <NUM> and the first drain electrode <NUM>, and may be made of an inorganic material, like the buffer layer <NUM>. For example, the interlayer dielectric layer <NUM> may be made up of a single layer of silicon nitride (SiNx) or silicon oxide (SiOx), which are inorganic materials, or multiple layers of silicon nitride (SiNx) and silicon oxide (SiOx). It is, however, to be understood that the present disclosure is not limited thereto.

The first source electrode <NUM> and the first drain electrode <NUM>, which are in contact with the first active layer <NUM>, are disposed on the interlayer dielectric layer <NUM>. The first source electrode <NUM> is spaced apart from the first drain electrode <NUM> on the same layer. The first source electrode <NUM> and the first drain electrode <NUM> may be electrically connected to the first active layer <NUM> by being in contact with the first active layer <NUM>. The first source electrode <NUM> and the first drain electrode <NUM> may be formed of, but are not limited to, one of a variety of metal materials including molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd) and copper (Cu), an alloy of two or more thereof, or multiple layers thereof.

The gate insulating layer <NUM> and the interlayer dielectric layer <NUM> may be patterned so that they are disposed only on the island substrates <NUM>. The gate insulating layer <NUM> and the interlayer dielectric layer <NUM> may also be made of an inorganic material, like the buffer layer <NUM>. Thus, the gate insulating layer <NUM> and the interlayer dielectric layer <NUM> may be damaged-for example, cracks may occur easily when the stretchable display device <NUM> is stretched. Accordingly, the gate insulating layer <NUM> and the interlayer dielectric layer <NUM> are not disposed between the island substrates <NUM>, but may be patterned in the shape of the island substrates <NUM> and disposed only on the island substrates <NUM>.

Although only the first transistor <NUM>, which is a driving transistor among various transistors included in the stretchable display device <NUM>, is shown in <FIG> for convenience of illustration, it is to be understood that a switching transistor, a capacitor, etc. may be included in the display device. In addition, although the first transistor <NUM> has a coplanar structure herein, other thin-film transistors having, e.g., a staggered structure, may also be employed.

With reference to <FIG>, a gate pad GP is disposed on the gate insulating layer <NUM>. The gate pad GP is a pad for transmitting gate signals to the sub-pixels SPX. The gate pad GP may be made of the same material as the first gate electrode <NUM>, but the present disclosure is not limited thereto.

The gate pad GP may transfer a gate signal from the connection line <NUM> (e.g., first connection line <NUM>) serving as a gate line to the sub pixels SPX. The gate pad GP is connected to the connection line <NUM> and transfers the gate signal to the sub-pixels SPX.

The connection line <NUM> is in contact with the side surfaces of the buffer layer <NUM>, the gate insulating layer <NUM> and the interlayer dielectric layer <NUM>, and is extended from the upper surface of the connection substrate CS to the upper surface of the interlayer dielectric layer <NUM>. The connection line <NUM> may be in contact with the gate pad GP through a contact hole of the interlayer dielectric layer <NUM>. Thus, the connection line <NUM> is electrically connected to the gate pad GP and may transfer the gate signal to the gate pad GP.

The common line CL is disposed on the interlayer dielectric layer <NUM>. The common line CL may apply a common voltage to the sub-pixels SPX. The common line CL may be made of, but is not limited to, the same material as the first source electrode <NUM> and the first drain electrode <NUM> of the first transistor <NUM>.

A planarization layer <NUM> is disposed over the first transistor <NUM>, the common line CL and the interlayer dielectric layer <NUM>. The planarization layer <NUM> may provide a flat surface over the island substrates <NUM> each including the first transistor <NUM>, or may provide a flat surface under the light-emitting element <NUM>. The planarization layer <NUM> may be a single layer or multiple layers and may be made of organic material. For example, the planarization layer <NUM> may be made of, but is not limited to, an acryl based organic material. The planarization layer <NUM> may include a contact hole for electrically connecting the first transistor <NUM> with the light-emitting element <NUM>, a contact hole for electrically connecting the gate pad GP with a connection pad, and a contact hole for electrically connecting the common line CL with the light-emitting element <NUM>.

In some example embodiments, a passivation layer may be formed between the first transistor <NUM> and the planarization layer <NUM>. That is to say, the passivation layer covering the first transistor <NUM> may be formed to protect the first transistor <NUM> from the permeation of moisture, oxygen, etc. The passivation layer may be made of an inorganic material and may be made up of a single layer or multiple layers, but the present disclosure is not limited thereto.

A first pad <NUM> and a second pad <NUM> are disposed on the planarization layer <NUM>. The first pad <NUM> is an electrode electrically connecting the first transistor <NUM> with the light-emitting element <NUM>. The first pad <NUM> may be disposed on the planarization layer <NUM> and may be in contact with the light-emitting element <NUM>. The first pad <NUM> may be in contact with the first drain electrode <NUM> of the first transistor <NUM> through a contact hole formed in the planarization layer <NUM>. Therefore, the light-emitting element <NUM> may be electrically connected to the first drain electrode <NUM> of the first transistor <NUM> by the first pad <NUM>. The first pad <NUM> may instead be connected to the first source electrode <NUM> of the first transistor <NUM> depending on the type of the first transistor <NUM>, but the present disclosure is not limited thereto.

The second pad <NUM> is an electrode electrically connecting the light-emitting element <NUM> with the common line CL. The second pad <NUM> may be disposed on the planarization layer <NUM> to be in contact with the light-emitting element <NUM>. The second pad <NUM> may be in contact with the common line CL through the contact hole formed in the planarization layer <NUM>. Accordingly, the light-emitting element <NUM> may be electrically connected to the common line CL by the second pad <NUM>.

A bank <NUM> is disposed on the first pad <NUM>, the second pad <NUM> and the planarization layer <NUM>. The bank <NUM> may include a black material in order to prevent light emitted from the light-emitting element <NUM> from being transmitted to an adjacent sub-pixel SPX such that the light is mixed. The bank <NUM> may be made of an organic insulating material, and may be made of the same material as the planarization layer <NUM>. For example, the bank <NUM> may be made of, but is not limited to, an acryl based resin, a benzocyclobutene (BCB) based resin, or a polyimide.

The light-emitting element <NUM> is disposed on the first pad <NUM>, the second pad <NUM> and the planarization layer <NUM>. The light-emitting element <NUM> is disposed in each of the sub-pixels SPX and emits light in a particular wavelength range. For example, the light-emitting element <NUM> may be, but is not limited to, a blue light-emitting element <NUM> that emits blue light, a red light-emitting element <NUM> that emits red light, or a green light-emitting element <NUM> that emits green light.

The light-emitting element <NUM> may be defined differently depending on the type of the stretchable display device <NUM>. When the stretchable display device <NUM> is an organic light-emitting stretchable display device, the light-emitting element <NUM> may be an organic light-emitting element <NUM> including an anode, an organic emissive layer <NUM>, and a cathode. When the stretchable display device <NUM> is an inorganic light-emitting stretchable display device, the light-emitting element <NUM> may be a light-emitting diode (LED) including an n-type semiconductor layer, an emissive layer, and a p-type semiconductor layer, which in an example, form a micro light-emitting diode (micro LED). In the following description, a micro LED is employed as an example of the light-emitting element <NUM>, which is the inorganic light emitting device <NUM>. It is, however, to be understood that an organic light-emitting element may also be used as the light-emitting element <NUM>.

The light-emitting element <NUM> includes a first semiconductor layer <NUM>, an emissive layer <NUM>, a second semiconductor layer <NUM>, a first electrode <NUM>, and a second electrode <NUM>. In the following description, a micro LED having a flip chip structure is employed as the light-emitting element <NUM> for convenience of illustration. It is, however, to be understood that a micro LED having a lateral or vertical structure may be employed as the light-emitting element <NUM>, for example.

The first electrode <NUM> is disposed on the first pad <NUM>, and the second electrode <NUM> is disposed on the second pad <NUM>. The first electrode <NUM> and the second electrode <NUM> are electrically connected to the first pad <NUM> and the second pad <NUM>, respectively. The first electrode <NUM> may transfer the voltage from the drain electrode <NUM> of the first transistor <NUM> to the first semiconductor layer <NUM>, and the second electrode <NUM> may transfer the voltage from the common line CL to the second semiconductor layer <NUM>.

A plurality of bonding patterns BP is disposed between the first pad <NUM> and the light-emitting element <NUM> and between the second pad <NUM> and the light-emitting element <NUM>. The plurality of bonding patterns BP are media for bonding the light-emitting element <NUM> onto the first pad <NUM> and the second pad <NUM>. For example, the plurality of bonding patterns BP may be, but are not limited to, gold (Au) bumps or solder bumps.

The bonding patterns BP include a first bonding pattern BP1 and a second bonding pattern BP2. The first bonding pattern BP1 is disposed between the first pad <NUM> and the first electrode <NUM>, and the second bonding pattern BP2 is disposed between the second pad <NUM> and the second electrode <NUM>. The light-emitting element <NUM> may be bonded onto the island substrate <NUM>, respectively, by the bonding patterns BP disposed between the first electrode <NUM> and the first pad <NUM> and between the second electrode <NUM> and the second pad <NUM>. In addition, the second bonding pattern BP2 disposed between the second electrode <NUM> and the second pad <NUM> may compensate for the step difference between the second electrode <NUM> of the light-emitting element <NUM> and the second pad <NUM>.

The first semiconductor layer <NUM> is disposed on the first electrode <NUM>, and the second semiconductor layer <NUM> is disposed on the first semiconductor layer <NUM>. The first semiconductor layer <NUM> and the second semiconductor layer <NUM> may be formed by implanting n-type or p-type impurities into gallium nitride (GaN). For example, the first semiconductor layer <NUM> may be a p-type semiconductor layer formed by implanting p-type impurities into gallium nitride, and the second semiconductor layer <NUM> may be an n-type semiconductor layer formed by implanting n-type impurities into gallium nitride. The p-type impurities may be, but are not limited to, magnesium (Mg), zinc (Zn), beryllium (Be), etc. The n-type impurities may be, but are not limited to, silicon (Si), germanium (Ge), tin (Sn), etc..

The emissive layer <NUM> is disposed between the first semiconductor layer <NUM> and the second semiconductor layer <NUM>. The emissive layer <NUM> receives holes and electrons from the first semiconductor layer <NUM> and the second semiconductor layer <NUM> to emit light. The emissive layer <NUM> may be made up of a single layer or a multi-quantum well (MQW) structure. For example, the emissive layer <NUM> may be made of, but is not limited to, indium gallium nitride (InGaN) or gallium nitride (GaN).

A part of the second semiconductor layer <NUM> protrudes outwardly from the emissive layer <NUM> and the first semiconductor layer <NUM>. In other words, the emissive layer <NUM> and the first semiconductor layer <NUM> may be smaller than the second semiconductor layer <NUM> such that the lower surface of the second semiconductor layer <NUM> is exposed. The second semiconductor layer <NUM> may be exposed from the emissive layer <NUM> and the first semiconductor layer <NUM> in order to be electrically connected to the second pad <NUM>.

With reference to <FIG>, the additional connection substrate CSA and the additional connection line 150A extended from the first area A1 to the third area A3 of the lower substrate <NUM> are disposed on the lower substrate <NUM>. The additional connection line 150A may be an extended part of the first drain electrode <NUM> of the first transistor <NUM> of the island substrate <NUM>. The additional connection line 150A may be extended from the first drain electrode <NUM> in the first area A1 of the lower substrate <NUM> to the third area A3. Accordingly, the additional connection line 150A may be electrically connected to the first drain electrode <NUM> of the first transistor <NUM> of the lower substrate <NUM> and may transfer the voltage from the first drain electrode <NUM> to the additional light-emitting elements 140A connected to the additional connection line 150A. The additional connection line 150A may be disposed on a different layer from the first drain electrode <NUM> of the first transistor <NUM> and may be made of a different material. For example, the additional connection line 150A may be disposed on the same layer and may be made of the same material as the first pad <NUM>, the first gate electrode <NUM>, etc..

A plurality of piezoelectric patterns PP is disposed in the third area A3 of the lower substrate <NUM>. For example, the piezoelectric patterns PP are disposed adjacent to the end of the additional connection substrate CSA. A plurality of grooves is formed in the lower substrate <NUM> in the third areas A3, and the piezoelectric patterns PP are arranged in the grooves.

If the piezoelectric patterns PP are disposed on the upper surface of the lower substrate <NUM>, stress is applied to the piezoelectric patterns PP when the stretchable display device <NUM> is stretched, such that the piezoelectric patterns PP may be broken, peeled, or scattered. Thus, the piezoelectric patterns PP are disposed in the grooves, thereby suppressing cracking, peeling and scattering of the piezoelectric patterns PP when the stretchable display device <NUM> is stretched.

The piezoelectric patterns PP are elements that convert mechanical energy into electrical energy. Whenever an external force, i.e., stress is applied to the piezoelectric patterns PP, a voltage is generated from the piezoelectric patterns PP.

Because the piezoelectric patterns PP are disposed in the grooves of the lower substrate <NUM> in the third areas A3, which are the flexible region, an external force is applied to the lower substrate <NUM> and the piezoelectric patterns PP seated on the lower substrate <NUM> when the stretchable display device <NUM> is stretched. When the stretchable display device <NUM> is stretched, mechanical energy is applied to the piezoelectric patterns PP from the external force, and electric energy is generated from the piezoelectric patterns PP. Therefore, when the stretchable display device <NUM> is stretched, the external force, e.g., stress is applied to the piezoelectric patterns PP, to generate a voltage.

When the stress is applied to the piezoelectric patterns PP, the voltage generated from the piezoelectric patterns PP may temporarily have the maximum value immediately after the stress is applied, and then the voltage may thereafter drop and converge to a certain voltage. For example, when the stress is applied to the piezoelectric patterns PP, the maximum voltage may instantly be generated from the piezoelectric patterns PP. After the maximum voltage is generated, the voltage generated may sharply drop. The voltage value generated from the piezoelectric patterns PP may not decrease continuously but may converge to a certain voltage value. The voltage value to which the voltage generated from the piezoelectric pattern PP finally converges may be defined as a first voltage. Accordingly, when the stress is applied to the piezoelectric patterns PP, the first voltage is generated from the piezoelectric patterns PP.

When the stress is removed from the piezoelectric patterns PP, the voltage generated from the piezoelectric patterns PP may have the maximum value of the opposite polarity immediately after the stress is removed, and thereafter may become floating. For example, when the stress is removed from the piezoelectric patterns PP, the maximum voltage may instantly be generated from the piezoelectric patterns PP. The maximum voltage thus generated may have a polarity opposite to that of the maximum voltage generated immediately after stress is applied to the piezoelectric patterns PP. Then, the piezoelectric patterns PP may be floating. Therefore, when no stress is applied to the piezoelectric patterns PP, the piezoelectric patterns PP may be floating.

In summary, when the stretchable display device <NUM> is not stretched, the piezoelectric patterns PP may be floating because no mechanical energy, that is, stress is applied to the piezoelectric patterns PP. On the other hand, when the stretchable display device <NUM> is stretched, the piezoelectric patterns PP generate the first voltage because mechanical energy, that is, stress is applied to the piezoelectric patterns PP.

The maximum voltage generated from the piezoelectric patterns PP may be proportional to the size of the piezoelectric patterns PP. For example, when the length of the piezoelectric patterns PP is approximately <NUM>, the maximum voltage generated from the piezoelectric patterns PP may be approximately 8V. When the length of the additional light-emitting elements 140A disposed on the piezoelectric patterns PP is approximately <NUM> and the length of the piezoelectric patterns PP is equal to the length of the additional light-emitting elements 140A, the maximum voltage generated from the piezoelectric patterns PP may be approximately <NUM> V. For example, as described above, when the length of the piezoelectric patterns PP is <NUM>, the maximum voltage is <NUM> V, and when the length of the piezoelectric patterns PP is <NUM>, the max voltage is <NUM> V, which is reduced as the length is reduced.

Thus, according to this example, the maximum voltage of the piezoelectric patterns PP is approximately <NUM> V, and the first voltage is <NUM> V as described above. Accordingly, the difference between the maximum voltage and the first voltage may be very small. Therefore, the additional light-emitting elements 140A may emit light not only when the first voltage is generated in the piezoelectric patterns PP, but also during the period the maximum voltage converges to the first voltage. That is to say, the additional light-emitting elements 140A can emit light simultaneously as the stretchable display device <NUM> is stretched, rather than after the stretchable display device <NUM> is stretched. Accordingly, the additional light-emitting elements 140A can compensate for the decrease in the luminance without delay when the stretchable display device <NUM> is stretched.

The additional light-emitting element 140A is disposed in the third area A3 of the lower substrate <NUM>. The additional light-emitting element 140A is disposed on the additional connection substrate CSA, the additional connection line 150A and the piezoelectric pattern PP. The additional light-emitting element 140A is disposed in each of the additional sub-pixels SPXA and emits light in a part wavelength range. The additional light-emitting element 140A may be substantially identical to the elements <NUM> disposed in each of the sub-pixels SPX.

The additional light-emitting element 140A includes a first additional semiconductor layer 141A, an additional emissive layer 142A, a second additional semiconductor layer 143A, a first additional electrode 144A and a second additional electrode 145A.

The first additional electrode 144A is disposed on one end of the additional connection line 150A, and the second additional electrode 145A is disposed on the piezoelectric pattern PP. Each of the first additional electrode 144A and the second additional electrode 145A is electrically connected to the additional connection line 150A and the piezoelectric pattern PP, respectively. The first additional electrode 144A may transfer a voltage from the first drain electrode <NUM> of the first transistor <NUM> to the first additional semiconductor layer 141A. When a stress is applied to the piezoelectric pattern PP, the second additional electrode 145A may transfer the first voltage from the piezoelectric pattern PP to the second additional semiconductor layer 143A.

A plurality of additional bonding patterns BPA is disposed between the first additional electrode 144A and the additional connection line 150A, and between the second additional electrode 145A and the piezoelectric pattern PP. The additional bonding patterns BPA are media for bonding the additional light-emitting element 140A onto the additional connection line 150A and the piezoelectric pattern PP. For example, the additional bonding patterns BPA may be, but are not limited to, gold (Au) bumps or solder bumps.

The additional bonding patterns BPA include a first additional bonding pattern BP1A and a second additional bonding pattern BP2A. The first additional bonding pattern BP1A is disposed between the additional connection line 150A and the first additional electrode 144A, and the second additional bonding pattern BP2A is disposed between the piezoelectric pattern PP and the second additional electrode 145A. The additional light-emitting element 140A may be bonded onto the third area A3 of the lower substrate <NUM> via the additional bonding patterns BPA. In addition, the second additional bonding pattern BP2A may compensate for the step difference between the second additional electrode 145A and the piezoelectric pattern PP.

On the other hand, the second additional bonding pattern BP2A disposed between the second additional electrode 145A and the piezoelectric pattern PP not only electrically connects the piezoelectric pattern PP with the second additional electrode 145A, but also includes the same material as the piezoelectric pattern PP to supply a voltage to the additional light-emitting element 140A when a stress is applied.

The first additional semiconductor layer 141A is disposed on the first additional electrode 144A, and a second additional semiconductor layer 143A is disposed on the first additional semiconductor layer 141A. The first additional semiconductor layer 141A and the second additional semiconductor layer 143A may be formed by implanting n-type or p-type impurities into gallium nitride (GaN). For example, the first additional semiconductor layer 141A may be a p-type semiconductor layer formed by implanting p-type impurities into gallium nitride, and the second additional semiconductor layer 143A may be an n-type semiconductor layer formed by implanting n-type impurities into gallium nitride. The p-type impurities may be, but are not limited to, magnesium (Mg), zinc (Zn), beryllium (Be), etc. The n-type impurities may be, but are not limited to, silicon (Si), germanium (Ge), tin (Sn), etc..

The additional emissive layer 142A is disposed between the first additional semiconductor layer 141A and the second additional semiconductor layer 143A. The additional emissive layer 142A may receive holes and electrons from the first additional semiconductor layer 141A and the second additional semiconductor layer 143A to emit light. The additional emissive layer 142A may be made up of a single layer or a multi-quantum well (MQW) structure. For example, the additional emissive layer 142A may be made of, but is not limited to, indium gallium nitride (InGaN) or gallium nitride (GaN).

A part of the second additional semiconductor layer 143A protrudes outwardly from the additional emissive layer 142A and the first additional semiconductor layer 141A. In other words, the additional emissive layer 142A and the first additional semiconductor layer 141A may be smaller than the second additional semiconductor layer 143A such that the lower surface of the second additional semiconductor layer 143A is exposed. The second additional semiconductor layer 143A may be exposed from the additional emissive layer 142A and the first additional semiconductor layer 141A in order to be electrically connected to the piezoelectric pattern PP.

When the stretchable display device <NUM> is turned on, the light-emitting elements <NUM> on the island substrates <NUM> are turned on. For example, voltages of different levels are applied to the first drain electrode <NUM> of the first transistor <NUM> and the common line CL electrically connected to the light-emitting elements <NUM>. A voltage from the first drain electrode <NUM> of the first transistor <NUM> is applied to the first electrode <NUM> of the light-emitting element <NUM>, and a common voltage from the common line CL is applied to the second electrode <NUM>. As voltages of different levels are applied to the first electrode <NUM> and the second electrode <NUM> of the light-emitting element <NUM>, current flows through the emissive layer <NUM> so that the light-emitting element <NUM> can emit light.

The first drain electrode <NUM> of the first transistor <NUM>, which is connected to a light-emitting element <NUM> on an island substrate <NUM> in the first area A1, may also be electrically connected to an additional light-emitting element 140A in the third area A3 adjacent to the first area A1 in the diagonal direction. The light-emitting element <NUM> on the island substrate <NUM> and the additional light-emitting element 140A in the third area A3 may be electrically connected to the first drain electrode <NUM> of the same first transistor <NUM>. That is to say, one light-emitting element <NUM> and one additional light-emitting element 140A may be electrically connected to the first drain electrode <NUM> of one first transistor <NUM>. Therefore, when a voltage from the first drain electrode <NUM> of the first transistor <NUM> is applied to the first electrode <NUM> of a light-emitting element <NUM> to emit light from the light-emitting element <NUM>, the same voltage may also be applied to the first additional electrode 144A of an additional light-emitting element 140A simultaneously.

Even if the voltage from the first drain electrode <NUM> is applied to the first additional electrode 144A, however, the additional light-emitting element 140A may emit light only if a voltage that is high enough to drive the additional light-emitting element 140A is applied to the second additional electrode 145A so that a current flows through the additional emissive layer 142A.

The second additional electrode 145A of the additional light-emitting element 140A is electrically connected to the piezoelectric pattern PP as described above. If an external force generated when the stretchable display device <NUM> is stretched is applied to the piezoelectric pattern PP, the first voltage is generated from the piezoelectric pattern PP. Accordingly, when the light-emitting element <NUM> associated with an additional light-emitting element 140A emits light, the additional light-emitting element 140A also emits light together with the light-emitting element <NUM> if the first voltage is generated from the piezoelectric pattern PP as the stretchable display device <NUM> is stretched. Therefore, when the stretchable display device <NUM> is stretched, the additional light-emitting element 140A associated with the light-emitting element <NUM> among the light-emitting elements also emit light.

The first voltage generated from the piezoelectric pattern PP may be a voltage of a level different from the voltage of the first drain electrode <NUM>. For example, the first voltage may be <NUM> V.

With reference to <FIG>, the upper substrate <NUM> is disposed above the lower substrate <NUM>. For example, the upper substrate <NUM> is disposed above the light-emitting elements <NUM> and the additional light-emitting elements 140A of the lower substrate <NUM>. The upper substrate <NUM> supports a variety of elements disposed thereunder. The upper substrate <NUM> may be made of an insulating material that may be bent or stretched as a flexible substrate. The upper substrate <NUM> is a flexible substrate and can be reversibly expanded and contracted. In addition, the elastic modulus of the upper substrate <NUM> may be several MPa to several hundred MPa, and the elongation at break may be <NUM>% or higher. The thickness of the upper substrate <NUM> may be, but is not limited to, <NUM> to <NUM>.

The upper substrate <NUM> may be made of the same material as the lower substrate <NUM>. For example, the upper substrate <NUM> may be made of an elastomer including a silicone rubber such as polydimethylsiloxane (PDMS) and a polyurethane (PU), and accordingly may have flexibility. It is, however, to be understood that the material of the upper substrate <NUM> is not limited thereto.

By pressing the upper substrate <NUM> against the lower substrate <NUM>, the upper substrate <NUM> and the lower substrate <NUM> may be attached together by an adhesive layer <NUM> disposed under the upper substrate <NUM>. It is, however, to be understood that the present disclosure is not limited thereto. In some implementations, the adhesive layer <NUM> may be eliminated.

The polarizing layer <NUM> is disposed on the upper substrate <NUM>. The polarizing layer <NUM> polarizes light incident from the outside of the stretchable display device <NUM>. The polarized light that has passed through the polarizing layer <NUM> and is incident into the stretchable display device <NUM> may be reflected inside the stretchable display device <NUM> and the phase may be shifted accordingly. As the phase of the light is shifted, the light may not pass through the polarization layer <NUM>. As a result, the light incident from the outside of the stretchable display device <NUM> into the inside of the stretchable display device <NUM> cannot exit to the outside of the stretchable display device <NUM>, and thus the reflection of the external light may be reduced.

In the stretchable display device <NUM> according to the embodiment, the additional pixels PXA are disposed in the third areas A3, which in conventional stretchable displays are dummy portions of the lower substrate <NUM> that have no function, e.g., the areas other than the first areas A1 where the island substrates <NUM> are disposed and the second areas A2 where the connection lines <NUM> are disposed. By doing so, the third areas A3 of the stretchable display device <NUM> are efficiently utilized, and the aperture ratio of the stretchable display device <NUM> may be improved. For example, by disposing the additional pixels PXA in the stretchable display device <NUM>, the aperture ratio is increased as shown in <FIG>. As a result, the luminance of the stretchable display device <NUM> according to the embodiment is improved as well.

In the stretchable display device <NUM> according to the embodiment, the first transistors <NUM> disposed on the island substrates <NUM> are shared by the pixels PX and the additional pixels PXA, so that the additional pixels PXA may be easily operated. While the first transistor <NUM> is driven so that the light-emitting element <NUM> emits light, the additional light-emitting element 140A connected to the same first transistor <NUM> may emit light simultaneously when the stretchable display device <NUM> is stretched. In this manner, in the stretchable display device <NUM> according to the embodiment, the light-emitting element <NUM> and the additional light-emitting element 140A share the same first transistor <NUM> disposed on the island substrate <NUM> corresponding to the light-emitting element <NUM>, and thus the additional light-emitting elements 140A may emit light easily without any additional circuitry. In addition, the aperture ratio of the stretchable display device <NUM> may be improved.

In addition, in the stretchable display device <NUM> according to the embodiment, the additional pixels PXA are formed in the third areas A3, and it may be possible to suppress deterioration of image quality and mura artifacts such as a lattice pattern of the stretchable display device <NUM> when it is stretched. For example, a voltage is applied to the first additional electrode 144A of the additional light-emitting element 140A from the first drain electrode <NUM> of the first transistor <NUM>, but the piezoelectric pattern PP is floating, and thus, no separate voltage may be applied to the second additional electrode 145A. Therefore, when the distance between the island substrates <NUM> is at a minimum when the stretchable display device <NUM> is not stretched, the additional light-emitting elements 140A between the island substrates <NUM> do not emit light, and only the light-emitting elements <NUM> on the island substrates <NUM> emit light. On the other hand, when the stretchable display device <NUM> is stretched, the regions between the island substrates <NUM> are stretched, so that the distance between the island substrates <NUM> is increased compared to the state before the display device <NUM> is stretched. Thus, when the stretchable display device <NUM> is stretched, the luminance in the regions between the island substrates <NUM> is lowered, such that mura artifacts such as a lattice pattern may be perceived, and the image quality may be deteriorated. Accordingly, the stretchable display device <NUM> according to the embodiment drives the light-emitting element <NUM> as well as the additional light-emitting element 140A connected to the same first transistor <NUM> when the stretchable display device <NUM> is stretched. For example, when the stretchable display device <NUM> is stretched and one light-emitting element <NUM> is driven by the first transistor <NUM>, a voltage from the first drain electrode <NUM> of the first transistor <NUM> is applied to the first additional electrode 144A of the additional light-emitting element 140A connected to the same first transistor <NUM>, and a first voltage generated in the piezoelectric pattern PP by the stress is applied to the second additional electrode 145A of the additional light-emitting element 140A. Thus, when the stretchable display device <NUM> is stretched and the distance between the island substrates <NUM> is increased, the additional light-emitting elements 140A between the island substrates <NUM> emit light, so that it is possible to compensate for the decrease in luminance caused as the distance between the light-emitting elements <NUM> is increased. That is to say, when the stretchable display device <NUM> is stretched, the additional light-emitting elements 140A compensate for the increased distance between the light-emitting elements <NUM>, so that the distance between the light-emitting elements <NUM> looks normal. Therefore, in the stretchable display device <NUM> according to the example embodiment of the present disclosure, it is possible to suppress the distortion of images when the stretchable display device <NUM> is stretched and to reduce mura artifacts such as a lattice pattern.

<FIG> is an enlarged plan view of a stretchable display device according to another inventive embodiment when including the sub-pixel and the additional sub-pixel as shown in the schematic cross-sectional view of <FIG>. A stretchable display device <NUM> according to the embodiment shown in <FIG> and <FIG> may be substantially identical to the stretchable display device <NUM> shown in <FIG>, except that additional connection lines 450A are different and an additional insulating layer <NUM> and an additional line LL are further included. Therefore, the redundant description will be omitted.

With reference to <FIG> and <FIG>, an additional line LL is disposed on the interlayer dielectric layer <NUM>. The additional line LL may be made of, but is not limited to, the same material as the first source electrode <NUM> and the first drain electrode <NUM> of the first transistor <NUM>.

The additional line LL is disposed on the island substrates <NUM> and may transfer a variety of signals to the sub-pixels SPX. The additional line LL may be, but is not limited to, a gate line, a data line, a high-voltage supply line, a low-voltage supply line, a reference voltage line, a common line CL, etc..

The additional insulating layer <NUM> is disposed on the additional line LL to cover it. The additional insulating layer <NUM> may be disposed to cover the first drain electrode <NUM> and the additional line LL. The additional insulating layer <NUM> may be extended to the outside of the island substrates <NUM> and may cover the additional connection substrate CSA. The additional insulating layer <NUM> may include a contact hole for electrically connecting the first drain electrode <NUM> of the first transistor <NUM> with the additional connection line 450A.

Because the additional insulating layer <NUM> may be made of an insulating material and is extended to the additional connection substrate CSA in the third area A3, which is the flexible region, it is made of an insulating material having flexibility. For example, the additional insulating layer <NUM> may be made of the same material as the island substrates <NUM> and the additional connection substrates CSA, but the present disclosure is not limited thereto.

Although the additional insulating layer <NUM> is extended to the outside of the island substrates <NUM> in the example shown in <FIG>, the additional insulating layer <NUM> may be disposed only on the island substrates <NUM>. In such case, the additional insulating layer <NUM> may be made up of, but is not limited to, a single layer of silicon nitride (SiNx) or silicon oxide (SiOx) which is an inorganic material having insulating properties, or multiple layers of silicon nitride (SiNx) and silicon oxide (SiOx).

The additional connection line 450A is disposed on the additional insulating layer <NUM>. The additional connection line 450A is disposed on the upper surface of the additional insulating layer <NUM> and is extended from the island substrate <NUM> to the third area A3. The additional connection line 450A may be in contact with the first drain electrode <NUM> through the contact hole of the additional insulating layer <NUM>, and the additional connection line 450A may be electrically connected to the first drain electrode <NUM>. One end of the additional connection line 450A extended to the third area A3 may be electrically connected to the first additional electrode 144A of the additional light-emitting element 140A in the third area A3 through a plurality of additional bonding patterns BPA. Accordingly, the additional connection line 450A may transfer the voltage from the first drain electrode <NUM> of the first transistor <NUM> on the island substrate <NUM> to the additional light-emitting element 140A of the third area A3.

In the stretchable display device <NUM> according to another embodiment, the additional insulating layer <NUM> is disposed between the lines disposed on the island substrate <NUM> and the additional connection line 450A extended from the island substrate <NUM> to the third area A3, so that it may be possible to prevent a short-circuit from being formed between the lines and the additional connection line 450A. A variety of lines made of a metal material are disposed only on the island substrates <NUM>. For example, a variety of lines such as a gate line, a data line, a high-voltage supply line, a low-voltage supply line, a reference voltage line and a common line CL may be disposed only on the island substrates <NUM>. In addition, the additional connection line 450A may be electrically connected to the first drain electrode <NUM> of the first transistor <NUM> on the island substrate <NUM> to transfer a voltage from the first transistor <NUM> to the additional light-emitting element 140A. A line may be disposed on the same plane as the first drain electrode <NUM> of the first transistor <NUM> among various lines of the island substrate <NUM>. For example, the first drain electrode <NUM> and the additional line LL may be disposed on the same plane. Accordingly, an additional insulating layer <NUM> may be further disposed to cover the additional line LL so that the additional connection line 450A extended to the outside of the island substrate <NUM> from the first drain electrode <NUM> is not in contact with the additional line LL. The additional insulating layer <NUM> may be disposed from the island substrate <NUM> to the additional connection substrate CSA to thereby insulate the additional connection line 450A extended to the outside of the island substrate <NUM> from the first drain electrode <NUM> from a variety of lines on the island substrate <NUM>. The additional insulating layer <NUM> may be made of an insulating material and may be made of the same material as, for example, the island substrates <NUM> and the additional connection substrates CSA. Accordingly, in the stretchable display device <NUM> according to another embodiment, a variety of lines on the island substrates <NUM> are insulated from the additional connection lines 450A extended to the third areas A3 from the island substrates <NUM>, thereby improving the reliability of the stretchable display device <NUM>.

<FIG> is an enlarged plan view of a stretchable display device according to yet inventive embodiment when including the sub-pixel and the additional sub-pixel as shown in the schematic cross-sectional view of <FIG>. A stretchable display device <NUM> according to the embodiment shown in <FIG> and <FIG> may be substantially identical to the stretchable display device <NUM> shown in <FIG>, except that the former further includes a second transistor <NUM>. Therefore, the redundant description will be omitted.

With reference to <FIG> and <FIG>, second transistors <NUM> are disposed on the respective island substrates <NUM>. Each of the second transistors <NUM> includes a second active layer <NUM>, a second gate electrode <NUM>, a second source electrode <NUM> and a second drain electrode <NUM>.

Initially, the second active layer <NUM> is disposed on the buffer layer <NUM>. For example, the second active layer <NUM> may be formed of an oxide semiconductor or may be formed of an amorphous silicon (a-Si), a polycrystalline silicon (poly-Si), an organic semiconductor, or the like.

A gate insulating layer <NUM> is disposed on the second active layer <NUM>. The gate insulating layer <NUM> electrically isolates the second gate electrode <NUM> from the second active layer <NUM> and may be made of an insulating material. For example, the gate insulating layer <NUM> may be made up of a single layer of silicon nitride (SiNx) or silicon oxide (SiOx), which is an inorganic material, or multiple layers of silicon nitride (SiNx) and silicon oxide (SiOx). It is, however, to be understood that the present disclosure is not limited thereto.

The second gate electrode <NUM> is disposed on the gate insulating layer <NUM>. The second gate electrode <NUM> overlaps with the second active layer <NUM>. The second gate electrode <NUM> may be formed of, but is not limited to, one of a variety of metal materials including molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd) and copper (Cu), an alloy of two or more thereof, or multiple layers thereof.

The interlayer dielectric layer <NUM> is disposed on the second gate electrode <NUM>. The interlayer dielectric layer <NUM> insulates the second gate electrode <NUM> from the second source electrode <NUM> and the second drain electrode <NUM> and may be made of an inorganic material, like the buffer layer <NUM>. For example, the interlayer dielectric layer <NUM> may be made up of a single layer of silicon nitride (SiNx) or silicon oxide (SiOx) which is an inorganic material, or multiple layers of silicon nitride (SiNx) and silicon oxide (SiOx). It is, however, to be understood that the present disclosure is not limited thereto.

The second source electrode <NUM> and the second drain electrode <NUM>, which are in contact with the second active layer <NUM>, are disposed on the interlayer dielectric layer <NUM>. The second source electrode <NUM> is spaced apart from the second drain electrode <NUM> on the same layer. The second source electrode <NUM> and the second drain electrode <NUM> may be electrically connected to the second active layer <NUM> by being in contact with the second active layer <NUM>. The second source electrode <NUM> and the second drain electrode <NUM> may be formed of, but are not limited to, one of a variety of metal materials including molybdenum (Mo), aluminum (Al), chromium (Cr), gold (Au), titanium (Ti), nickel (Ni), neodymium (Nd) and copper (Cu), an alloy of two or more thereof, or multiple layers thereof.

The additional connection substrate CSA and the additional connection line 150A extended from the island substrate <NUM> in the first area A1 to the third area A3 are disposed on the lower substrate <NUM>. The additional connection line 150A may be extended from the second drain electrode <NUM> of the second transistor <NUM> on the island substrate <NUM> to the third area A3. The additional connection line 150A may be formed integrally with the second drain electrode <NUM> and may be extended to the third area A3. Accordingly, the additional connection line 150A may be electrically connected to the second drain electrode <NUM> of the second transistor <NUM> and may transfer the voltage from the second drain electrode <NUM> to the additional light-emitting element 140A connected to the additional connection line <NUM>.

The first transistor <NUM> and the second transistor <NUM> may operate individually. For example, voltages from different lines may be applied to the first source electrode <NUM> of the first transistor <NUM> and the second source electrode <NUM> of the second transistor <NUM>. A voltage may be applied to the first drain electrode <NUM> and the first electrode <NUM> of the light-emitting element <NUM> by a voltage applied to the first source electrode <NUM>. A voltage may be applied to the second drain electrode <NUM> and the first additional electrode 144A of the additional light-emitting element 140A by a voltage applied to the second source electrode <NUM>. The common voltage applied to the second electrode <NUM> of the light-emitting element <NUM> and the first voltage from the second additional electrode 145A of the additional light-emitting element 140A may have a fixed value. Accordingly, by adjusting the voltages applied to the first source electrode <NUM> of the first transistor <NUM> and the second source electrode <NUM> of the second transistor <NUM>, it is possible to control the brightness of light emitted from each of the light-emitting element <NUM> and the additional light-emitting element 140A.

The additional sub-pixels SPXA of the stretchable display device <NUM> according to yet another embodiment may be driven independently from the sub-pixels SPX disposed on the island substrates <NUM>. For example, the light-emitting elements <NUM> on the island substrates <NUM> may be electrically connected to the first drain electrode <NUM> of the first transistor <NUM> to receive a voltage from the first drain electrode <NUM>. Therefore, the light-emitting elements <NUM> on the island substrates <NUM> may be driven by receiving the voltage from the first transistor <NUM>, and the additional light-emitting elements 140A on the third areas A3 may be driven by receiving the voltage from the second transistor <NUM>. In this manner, in the stretchable display device <NUM> according to yet another embodiment, the sub-pixels SPX and the additional sub-pixels SPXA are independently driven to increase the resolution. In addition, when the stretchable display device <NUM> is stretched, the additional sub-pixels SPXA may be driven selectively to improve the quality of displayed images.

The stretchable display device <NUM> according to yet another embodiment can reduce a difference in luminance between the additional sub-pixels SPXA and the sub-pixels SPX. The first voltage applied to the second additional electrode 145A of the additional light-emitting element 140A and the common voltage applied to the second electrode <NUM> of the light-emitting element <NUM> may have the same value or different values. If there is a level difference between the first voltage and the common voltage and the same voltage is applied to the first transistor <NUM> and the second transistor <NUM>, there may be a difference in luminance between the light-emitting element <NUM> and the additional light-emitting element 140A. In view of the above, in the stretchable display device <NUM> according to yet another embodiment, it may be possible to reduce the difference in luminance between the light-emitting element <NUM> and the additional light-emitting element 140A, even if there is a level difference between the first voltage and the common voltage, by adjusting the voltage applied to the first transistor <NUM> and the second transistor <NUM>. For example, with the common voltage applied to the second electrode <NUM> of the light-emitting element <NUM> fixed, by adjusting the voltage applied to the first electrode <NUM> of the light-emitting element <NUM> from the first transistor <NUM>, it may be possible to adjust the difference in voltage level between the first electrode <NUM> and the second electrode <NUM>, and to adjust the luminance of the light emitted from the light-emitting element <NUM>. Furthermore, with the first voltage applied to the second additional electrode 145A of the additional light-emitting element 140A fixed, by adjusting the voltage applied to the first additional electrode 144A of the additional light-emitting element 140A from the second transistor <NUM>, it may be possible to adjust the difference in voltage level between the first additional electrode 144A and the second additional electrode 145A, and to adjust the luminance of the light emitted from the additional light-emitting element 140A. Accordingly, in the stretchable display device <NUM> according to yet another embodiment, it may be possible to reduce the difference in luminance between the light-emitting element <NUM> and the additional light-emitting element 140A by individually driving the first transistor <NUM> and the second transistor <NUM>.

<FIG> is an enlarged plan view of a stretchable display device according to yet another inventive embodiment when including the sub-pixel and the additional sub-pixel as shown in the schematic cross-sectional view of <FIG>. <FIG> are views showing processing steps of fabricating a stretchable display device. <FIG> are schematic plan views of an additional sub-pixel of a stretchable display device according to yet another embodiment. A stretchable display device <NUM> according to the embodiment shown in <FIG> is substantially identical to the stretchable display device <NUM> shown in <FIG> except that the former further includes a reinforcing layer <NUM>; and, therefore, the redundant description will be omitted.

<FIG> is a cross-sectional view showing area I - I' of the stretchable display device <NUM> shown in <FIG>. When the stretchable display device <NUM> is stretched, the third area A3 is expanded by an external pressure. Accordingly, the additional light-emitting elements 140A disposed in the third area A3 are less reliable than the light-emitting elements <NUM> disposed in the first area A1. The additional light-emitting elements 140A are fixed to the lower substrate <NUM> by the additional bonding patterns BPA. However, because the additional light-emitting elements 140A are continuously exposed to external stress, the adhesive force with the lower substrate <NUM> is weakened. Accordingly, the reinforcing layer <NUM> may be disposed between the lower substrate <NUM> and the additional light-emitting elements 140A, so that the additional light-emitting elements 140A are more firmly fixed to the lower substrate <NUM>.

Referring to <FIG> and <FIG>, the reinforcing layer <NUM> is disposed in the third area A3 of the lower substrate <NUM>. The reinforcing layer <NUM> may be made up of a single layer or multiple layers and may be made of an organic material. For example, the reinforcing layer <NUM> may be made of, but is not limited to, an acryl-based organic material.

Referring to <FIG>, it can be seen that the additional light-emitting elements 140A are firmly fixed to the lower substrate <NUM> by the reinforcing layer <NUM>. Initially, the reinforcing layer <NUM> is formed in a region where additional sub-pixels SPXA are to be disposed on the lower substrate <NUM>. The reinforcing layer <NUM> may be formed on the periphery of the region where the additional light-emitting elements 140A are to be disposed and on the piezoelectric pattern PP. In addition, it may be formed around the end of the additional connection substrate CSA. It is to be noted that it is desired that the reinforcing layer <NUM> does not overlap the first additional electrode 144A and the second additional electrode 145A.

After the reinforcing layer <NUM> is formed on the lower substrate <NUM>, the additional light-emitting elements 140A are transferred to the additional sub-pixel SPXA area. At this time, when a pressure is applied from above the additional light-emitting elements 140A, the reinforcing layer <NUM> and the additional light-emitting elements 140A may be in tighter contact with each other. Specifically, as the gap between the reinforcing layer <NUM> and the additional light-emitting elements 140A is filled with the reinforcing layer <NUM>, the rigidity of the region where the additional light-emitting elements 140A are located may increase. Accordingly, the additional light-emitting elements 140A can be safely protected even if the third area A3 is increased due to an external pressure.

The stretchable display device <NUM> shown in <FIG> and <FIG> may further include an adhesive layer <NUM> on the lower substrate <NUM> on which the reinforcing layer <NUM> and the additional light-emitting elements 140A are disposed. The structure of the adhesive layer <NUM> is substantially identical to that of the stretchable display device <NUM> shown in <FIG> and <FIG>; and, therefore, the redundant description will be omitted.

<FIG> are enlarged plan views of area II of the stretchable display device <NUM> shown in <FIG>. Referring to <FIG>, the reinforcing layer <NUM> may be disposed to overlap the plurality of additional sub-pixels SPXA. In addition, the reinforcing layer <NUM> may be disposed to surround the periphery of additional pixels SPA. Therefore, the additional light-emitting elements 140A may be firmly fixed to the lower substrate <NUM>.

Referring to <FIG>, a plurality of reinforcing layers <NUM> isolated from one another may be disposed in the additional pixel PXA area. That is to say, the reinforcing layers <NUM> may be disposed to overlap or surround the respective additional sub-pixels SPXA. Therefore, the additional light-emitting elements 140A disposed in the respective additional sub-pixels SPXA can be firmly coupled with the lower substrate <NUM>, and the third area A3 can be more flexibly stretched.

<FIG> are schematic cross-sectional views of an additional sub-pixel of a stretchable display device according to still other cross-sectional views of the additional sub-pixel SPXA obtained by cutting the area I - I' of the stretchable display device <NUM> shown in <FIG>. The stretchable display device <NUM> of <FIG> is substantially identical to the stretchable display device <NUM> shown in <FIG> except that the former further includes a reinforcing layer <NUM> and piezoelectric patterns PP' and PP" have different shapes; and, therefore, the redundant description will be omitted.

Referring to <FIG>, the piezoelectric pattern PP' may include a portion that overlaps with the reinforcing layer <NUM> and a portion that does not overlap with the reinforcing layer <NUM>. That is to say, the piezoelectric pattern PP' may be formed in an area that overlaps with the reinforcing layer <NUM> and receives less stress by an external pressure as the lower substrate <NUM> is less stretched, and also in an area that does not overlap with the reinforcing layer <NUM> and receives more stress by an external pressure as the lower substrate <NUM> is more stretched. Accordingly, even when the third area A3 is expanded, the piezoelectric pattern PP' may reliably maintain the electrical coupling with the additional light-emitting elements 140A and may receive stress by an external pressure evenly, so that the time taken to converge to a specific voltage can be reduced.

Referring to <FIG>, the piezoelectric pattern PP" may include a plurality of uneven parts. The contact surface between the piezoelectric pattern PP" shown in <FIG> and the lower substrate <NUM> may be larger than the contact surface between the piezoelectric pattern PP' shown in <FIG> and the lower substrate <NUM>. In addition, as the contact surface between the piezoelectric pattern PP" and the lower substrate <NUM> increases, the piezoelectric pattern PP" receives more stress due to an external pressure. Incidentally, the plurality of uneven parts included in the piezoelectric pattern PP" may be mainly distributed in the area that does not overlap with the reinforcing layer <NUM>. Accordingly, the piezoelectric pattern PP" may be more affected by stress when the lower substrate <NUM> is stretched. The uneven part may include a plurality of protrusions from the flat body of the piezoelectric pattern PP". Some portions of the uneven part may overlap with the reinforcing layer <NUM>, while some other portions may not overlap with the reinforcing layer <NUM>. It is, however, to be understood that the present disclosure is not limited thereto. The uneven part may be formed only in the area that does not overlap with the reinforcing layer <NUM>.

<FIG> shows that the piezoelectric pattern PP" has a shape having a plurality of uneven parts protruding from the lower surface of the piezoelectric pattern PP", but the present disclosure is not limited thereto. For example, the piezoelectric pattern PP" may have a polygonal cross section when viewed from the top or a shape protruding in a plane direction. In addition, the shape protruding in the plane direction may further include a plurality of uneven parts protruding in the vertical direction. As such, the piezoelectric pattern PP" having an increased contact area with the lower substrate <NUM> may receive stresses by an external pressure more efficiently, and thus, time to converge to a specific voltage may be shortened. In addition, the piezoelectric pattern PP" may have a shape including a portion extended in a direction perpendicular to the direction in which the third area A3 is stretched to receive more stress by an external pressure.

Claim 1:
A stretchable display device (<NUM>, <NUM>, <NUM>, <NUM>), comprising:
a lower substrate (<NUM>) having a plurality of first areas (A1), wherein adjacent ones of the first areas (A1) are spaced apart from one another,
a plurality of second areas (A2) adjacent the first areas (A1), and
a plurality of third areas (A3) other than the first areas (A1) and the second areas (A2), the third areas (A3) being surrounded by the first areas (A1) and the second areas (A2),
a plurality of island substrates (<NUM>) respectively disposed in the first areas (A1) of the lower substrate (<NUM>) and being more rigid than the lower substrate (<NUM>),
a plurality of sub-pixels (SPX) being defined on the island substrates (<NUM>), wherein each of the sub-pixels (SPX) includes a light-emitting element (<NUM>),
a plurality of connection substrates (CS) being arranged in the second areas (A2) and between the island substrates (<NUM>),
a plurality of connection lines (<NUM>), the plurality of connection lines (<NUM>) being disposed on the connection substrates (CS) and electrically connecting adjacent ones of the island substrates (<NUM>), characterized by
a plurality of additional sub-pixels (SPXA) being defined in the third areas (A3),
each of the additional sub-pixels (SPXA) including an additional light-emitting element (140A) ; and
a plurality of piezoelectric patterns (PP) disposed in the third areas (A3), each of the piezoelectric patterns (PP) electrically connected to a respective one of the additional sub-pixels (SPXA), and configured such that, when the stretchable display device (<NUM>) is stretched by an external force, mechanical energy is applied to the piezoelectric patterns (PP) from the external force and electric energy is generated from the piezoelectric patterns (PP) and provided to the additional light-emitting elements (140A) so that they emit light simultaneously as the stretchable display device (<NUM>) is stretched.