DISPLAY DEVICE

A display device may have a flexible display having a display area and a support member having a first surface and a second surface opposite to each other. The first surface is adhered to the flexible display. The support member has a first part including a plurality of tapered portions arranged along the first surface and tapered in a direction toward the second surface. The support member has a second part made from a softer material than the plurality of tapered portions. The second part connects an adjacent pair of the plurality of tapered portions. The display device has a neutral plane, which is free from expansion and contraction when the display device is bent. The neutral plane is closer to the first surface than the second surface.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority from Japanese application JP2017-222725 filed on Nov. 20, 2017, the content of which is hereby incorporated by reference into this application.

BACKGROUND

This relates to display devices.

2. Description of the Related Art

Flexible displays have been developed for display devices. A known display device may have a flexible resin substrate on which a circuit layer and organic light emitting diodes (OLEDs) are formed (JP 2011-227369A).

The flexible displays tend to have a support member adhered thereon to withstand repeated bending and stretching. The support member and the flexible display are preferably difficult to detach. The support member requires no stress concentration.

SUMMARY

This is to aim at compatible flexibility and durability.

A display device may have a flexible display having a display area and a support member having a first surface and a second surface opposite to the first surface. The first surface is adhered to the flexible display. The support member has a first part including a plurality of tapered portions arranged along the first surface and tapered in a direction toward the second surface. The support member has a second part made from a softer material than the plurality of tapered portions. The second part connects an adjacent pair of the plurality of tapered portions. The display device has a neutral plane, which is free from expansion and contraction when the display device is bent. The neutral plane is closer to the first surface than the second surface.

The second part made from a soft material is between adjacent tapered portions, dispersing stress, making flexibility and durability compatible.

DETAILED DESCRIPTION

Hereinafter, some embodiments will be described with reference to the drawings. Here, the invention can be embodied according to various aspects within the scope of the invention without departing from the gist of the invention and is not construed as being limited to the content described in the embodiments exemplified below.

The drawings are further schematically illustrated in widths, thickness, shapes, and the like of units than actual forms to further clarify description in some cases but are merely examples and do not limit interpretation of the invention. In the present specification and the drawings, the same reference numerals are given to elements having the same functions described in the previously described drawings and the repeated description will be omitted.

Further, in the detailed description, “on” or “under” in definition of positional relations of certain constituents and other constituents includes not only a case in which a constituent is located just on or just under a certain constituent but also a case in which another constituent is interposed between constituents unless otherwise mentioned.

FIG. 1is a perspective view of a display device in an embodiment.FIG. 2is a II-II line cross-sectional view of the display device inFIG. 1.

The display device is an organic electroluminescence (EL) display device. The display device has a flexible display10. The flexible display10is configured to display a full-color image by forming full-color pixels, each of which consists of unit pixels (sub-pixels) in some colors such as red, green, and blue. The flexible display10includes a display area DA and a peripheral area PA around the display area DA. The peripheral area PA is outside the display area DA.

A flexible printed circuit board11is connected to the peripheral area PA. The flexible printed circuit board11has an integrated circuit (not shown) mounted thereon for controlling an element to display the image. A printed circuit board13is connected to the flexible printed circuit board11. The printed circuit board13has some sort of electronic component (not shown) mounted thereon.

FIG. 3is an enlarged view of a portion III inFIG. 2. The flexible display10has a substrate12(array substrate). The substrate12is made from polyimide. Or, other resin materials can be used as long as the materials have enough flexibility. A three-layer laminate structure consisting of a silicon oxide film14a,a silicon nitride film14b,and a silicon oxide film14c,is on the substrate12for an undercoat layer14. The silicon oxide film14ain the lowest layer is for improving a close-fitting property with the substrate12; the silicon nitride film14bin the middle layer is for a blocking film from external moisture and impurities; the silicon oxide film14cin the uppermost layer is for another blocking film to prevent hydrogen atoms in the silicon nitride film14bfrom diffusing on a side of a semiconductor layer18of a thin film transistor TR. Such a structure, however, is not essential. Another layer may be laminated, and a single-layer or a two-layer laminate is applicable thereto.

An additional film16maybe formed under the undercoat layer14to correspond to an area where the thin film transistor TR is formed. The additional film16may curb a characteristic change of the thin film transistor TR due to light intrusion from its channel back or may provide the thin film transistor TR with a backgating effect by being formed from a conductive material to apply a certain potential. In this embodiment, after the silicon oxide film14ais formed, the additional film16is formed in an island shape corresponding to an area where the thin film transistor TR is formed, and then the silicon nitride film14band the silicon oxide film14care laminated, whereby the additional film16is sealed in the undercoat layer14. Alternatively, the undercoat layer14may be made after the additional film16is formed on the substrate12.

The thin film transistor TR is on the undercoat layer14. A polysilicon thin film transistor is illustrated and only an N-ch transistor is herein shown but a P-ch transistor may be simultaneously formed. The semiconductor layer18in the thin film transistor TR has a structure where a low-concentration impurity area is provided between a channel area and a source/drain area. A silicon oxide film is herein used for a gate insulation film20. A gate electrode22is a part of a first trace layer W1made from MoW. The first trace layer W1includes a first storage capacitor line CL1in addition to a gate electrode22. A part of a storage capacitor Cs is formed between the first storage capacitor line CL1and the semiconductor layer18(source/drain area) with the gate insulation film20interposed therebetween.

An interlayer dielectric24(silicon oxide film and silicon nitride film) is on the gate electrode22. At least a part of the interlayer dielectric24is removed to make the substrate12more flexible and foldable at a folding area FA. Removing the part of the interlayer dielectric24exposes the undercoat layer14, at least a part of which is also removed by patterning. After removing the part of the undercoat layer14, polyimide constituting the substrate12is exposed. The etching of the undercoat layer14may partially etch its polyimide surface and reduce its thickness.

A second trace layer W2, which includes portions for the source/drain electrode26and a leading line28, is on the interlayer dielectric24. A three-layer laminate structure made of Ti, Al, and Ti is herein employed. The first storage capacitor line CL1(part of the first trace layer W1) and a second storage capacitor line CL2(part of the second trace layer W2) constitute another portion of the storage capacitor Cs, with the interlayer dielectric24interposed therebetween. The leading line28extends to an edge of the substrate12and has a terminal32for being connected to the flexible printed circuit board11.

A planarization layer34covers the source/drain electrode26and the leading line28(except for some of their portions). Organic materials such as photosensitive acrylic are often used for the planarization layer34because of superior surface flatness, compared with inorganic insulation materials formed by chemical vapor deposition (CVD).

The planarization layer34is removed at a pixel contact portion36and in the peripheral area PA and has an indium tin oxide (ITO) film35formed thereon. The indium tin oxide film35includes a first transparent conductive film38and a second transparent conductive film40separated from each other.

The second trace layer W2, which has its surface exposed by removing the planarization layer34, is covered with the first transparent conductive film38. A silicon nitride film42is on the planarization layer34, covering the first transparent conductive film38. The silicon nitride film42has an opening at the pixel contact portion36. A pixel electrode44is laminated on and connected to the source/drain electrode26through the opening. The pixel electrode44is a reflective electrode, with a three-layer laminate structure consisting of an indium zinc oxide (IZO) film, a silver (Ag) film, and an indium zinc oxide film. Instead of the indium zinc oxide film, an indium tin oxide film may be used. The pixel electrode44extends laterally from the pixel contact portion36to above the thin film transistor TR.

The second transparent conductive film40is adjacent to the pixel contact portion36and under the pixel electrode44(further under the silicon nitride film42). The second transparent conductive film40, the silicon nitride film42, and the pixel electrode44overlap with one another, whereby an additional capacitance Cad is formed.

A third transparent conductive film46, which is another part of the indium tin oxide film35, is on a surface of the terminal32. The third transparent conductive film46is formed at the same time as the first transparent conductive film38and the second transparent conductive film40are formed. The third transparent conductive film46on the terminal32may serve as a barrier film to prevent an exposed portion of the terminal32from being damaged in subsequent processes. The third transparent conductive film46is subject to etching environment during patterning of the pixel electrode44. However, while the indium tin oxide film35is formed and pixel electrode44is subsequently formed, the indium tin oxide film35is annealed to acquire enough resistance to the etching of the pixel electrode44.

An insulation layer48, which is called a bank (rib) for a partition of adjacent pixel areas, is on the planarization layer and above the pixel contact portion36, for example. Photosensitive acrylic may be used for the insulation layer48just like the planarization layer34. The insulation layer48has an opening for exposing a surface of the pixel electrode44as a light emitting region. The opening preferably has an edge in a gently inclined shape. A steep shape of the opening edge may cause insufficient coverage of an organic electroluminescence (EL) layer50formed thereon.

The planarization layer34and the insulation layer48are in contact with each other through an opening in the silicon nitride film42between them. This makes it possible to remove moisture and gas desorbed from the planarization layer34through the insulation layer48during heat treatment after the insulation layer48is formed.

The organic EL layer50is made from organic materials and is laminated on the pixel electrode44. The organic EL layer50maybe a single-layer or a structure where a hole transport layer, a light emitting layer, and an electron transport layer are laminated, in an order from the pixel electrode44. These layers may be formed by vapor deposition, by solvent dispersion and application, by selective formation for the pixel electrode44(each sub-pixel), or overall formation over the display area DA. The overall formation may be used for a structure where every sub-pixel emits white light and a desired color wavelength portion thereof passes through a color filter (not shown).

A counter electrode52is on the organic EL layer50. Due to a top emission structure herein employed, the counter electrode52is transparent. A Mg layer and an Ag layer may be formed to be a thin film through which outgoing light from the organic EL layer50can pass. In comply with the forming order of the organic EL layer50, the pixel electrode44is an anode and the counter electrode52is a cathode. The counter electrode52is formed over the display area DA, extends to a cathode contact portion54next to the display area DA, and is connected to the leading line28under the cathode contact portion54to be electrically connected to the terminal32.

A sealing film56is on the counter electrode52. The sealing film56may serve to prevent external moisture intrusion into the organic EL layer50formed thereunder, necessitating a high gas barrier property. A silicon nitride film56a,an organic resin layer56b,and a silicon nitride film56care laminated to constitute a laminate structure including a silicon nitride film. A silicon oxide film or an amorphous silicon layer may be formed between the silicon nitride film56aor56cand the organic resin layer56bfor improving a close-fitting property, for example.

A touch panel substrate60is laminated on the sealing film56with an adhesive layer58interposed therebetween. At least a part of an unillustrated touch sensing electrode is formed on the touch panel substrate60. The counter electrode52may serve as a part of the touch sensing electrode. A circularly polarizing plate62is adhered to the touch panel substrate60. A cover glass66is laminated on the circularly polarizing plate62with an adhesive layer64interposed therebetween. A back film70is laminated on the substrate12with an adhesive layer68interposed therebetween. A heat spread sheet72made from graphite and a cushion sheet74may be laminated on the back film70.

The flexible display10is placed in the housing76(FIG. 2). A part of the housing76is a support member78adhered to the flexible display10. The support member78has a first surface S1and a second surface S2opposite to each other. The first surface S1is adhered to the flexible display10. The support member78has a first layer80.

FIG. 4is a rear view of a part of a first layer80. The first layer80has a plurality of tapered portions82. Each tapered portion82has a shape of a conic solid. The tapered portions82are arranged along the first surface S1inFIG. 3. The tapered portions82are integrated with one another at the first surface S1. Each tapered portion82is tapered in a direction toward the second surface S2.

As shown inFIG. 3, the support member78has a second layer84. The second layer84connects adjacent tapered portions82. The second layer84is made from a material softer than the tapered portions82. The material constituting the second layer84is an elastic material, for example. The second layer84is not taller toward the second surface S2than the tapered portions82. As shown inFIG. 2, the housing76has a recess86to contain the flexible display10and the printed circuit board13. The second layer84constitutes a bottom surface of the recess86, which maybe formed by injecting a heated soft resin into a mold.

FIG. 5is a perspective view of usage of the display device inFIG. 1. The display device100, which includes the flexible display10and the support member78, has at least its part bent for being twisted around a wrist, for example. To prevent its curvature from elastic recovery, an unillustrated holding member may be kept in the housing76. The flexible display10and the flexible printed circuit board11inFIG. 1have flexibility. The printed circuit board13, which is typically hard to bend, has a shorter length in a direction along an arc described by the bent display device100. A portion where the printed circuit board13is stored may be unbendable.

FIG. 6is a cross-sectional view of a support member78in use inFIG. 5. A neutral plane NP, which is free from expansion and contraction when the support member78is bent, is closer to the first surface S1than the second surface S2. The neutral plane NP matches the first surface S1, for example. The embodiment makes it possible to disperse stress because the second layer84made from a soft material is between adjacent tapered portions82, making flexibility and durability compatible.

FIG. 7is a cross-sectional view of variation1of the embodiment.FIG. 3 or 6shows that the second layer84is as tall in the direction toward the second surface S2as the first layer80in the direction toward the second surface S2. Contrastingly,FIG. 7shows that the second layer84A is shorter in the direction toward the second surface S2than the first layer80A in the direction toward the second surface S2. Tips of the tapered portions82A of the first layer80A are arranged at the second surface S2.

FIG. 8is a cross-sectional view of variation2of the embodiment. In this example, each tapered portion82B of the first layer80B has a frustum shape such as a shape of a frustum of a quadrangular pyramid. The tapered portion82B at its tip has an area. In spite of not being shown inFIG. 8, a second layer is provided between adjacent first layers80B in such a way as shown inFIG. 3 or 7.

FIG. 9is a rear view of variation3of the embodiment. This example shows that the tapered portions82C of the first layer80C are separate from each other.

FIG. 10is a rear view of variation4of the embodiment. This example shows that each tapered portion82D of the first layer80D has a shape of a frustum of a triangular pyramid.

FIG. 11is a rear view of variation5of the embodiment. This example shows that each tapered portion82E of the first layer80E has a shape of a circular truncated cone.

FIG. 12is a perspective view of variation6of the embodiment. This example shows that each tapered portion82F of the first layer80F has a shape of a transverse triangular prism. The first surface S1consists of bottom surfaces (each of which is rectangular) of a plurality of tapered portions82F. The tapered portion82F has a tip describing a ridgeline. In spite of not being shown inFIG. 12, a second layer is provided between adjacent first layers80F in such a way as shown inFIG. 3 or 7.

FIG. 13is a perspective view of variation7of the embodiment. This example shows that each tapered portion82G of the first layer80G has a shape of an inclined top body, which is a part of a transverse triangular prism left after cutting off its top. The first surface S1consists of bottom surfaces (each of which is rectangular) of a plurality of tapered portions82G. The tapered portion82G at its top has an area. In spite of not being shown inFIG. 13, a second layer is provided between adjacent first layers80G in such a way as shown inFIG. 3 or 7.

The electronic device is not limited to the organic electroluminescence display device but may be a display device with a light emitting element disposed in each pixel, such as a quantum-dot light emitting diode (QLED), or a liquid crystal display device.