Substrate-less flexible display and method of manufacturing the same

A substrate-less display device is disclosed. The substrate-less display device includes a barrier stack. The barrier stack includes a plurality of inorganic barrier films and a plurality of polymer films. The inorganic barrier films and the polymer films are alternatively disposed. The substrate-less display device further includes a thin-film-transistor (TFT) device layer disposed on the barrier stack, a display medium layer disposed on the TFT device layer, and an encapsulation layer disposed on the display medium layer.

TECHNICAL FIELD

Example embodiments relate to a display device, and in particular, to a flexible display device without a substrate and a method for manufacturing the same.

BACKGROUND

The flexible display has been considered for the display industry as the next generation of information display technology. Particularly, the flexible active-matrix organic light-emitting diode (AMOLED) display has attracted much interests in the applications such as smart phones, intelligent home systems, wearable electronic devices, etc.

Thin-film transistor (TFT) devices used in an active matrix may be degraded if moisture penetrates into the device layer. For example, moisture may cause the characteristics of a TFT device to deviate from designed range, resulting in a malfunctioned device. Further, organic light-emitting diode (OLED) devices are extremely sensitive to moisture and oxygen. For example, the emission of an OLED device may degrade when OLED materials are exposed to moisture. The highly reactive and low work function cathodes of an OLED device can be easily corroded by moisture and oxygen. Thus, AMOLED display generally needs two substrates to encapsulate the TFT and OLED devices to ensure stable performance of those devices.

Due to its flexibility to bend, plastic substrates have been selected to be the substrates for flexible display panels. In addition, plastic substrates are light weighted and not fragile, and are suitable for roll-to-roll processing. Display panels made with plastic substrates are proved to be durable to mechanical shocks and allow rollable and foldable applications. In some cases, the bending radius is required to be less than 1 mm.

However, plastic substrates are known to be less effective than glass substrates to prevent moisture from coming into the device layer. To combat these drawbacks, several proposals have been implemented. For example, referring toFIG. 1, a stacked layer104is provided on a plastic substrate102to reduce moisture and oxygen penetrating therethrough. Stacked layer104includes a plurality of pairs of stacked films. A pair of stacked films includes a polymer film106and an inorganic film108. For example, inFIG. 1, three pairs of polymer films106and inorganic films108are provided on plastic substrate102.

Generally, inorganic films108are formed on substrate102by sputtering, plasma enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), etc. Polymer films106may be formed by evaporating monomers onto substrate102which are further cured by heat or light. However, due to the low heat resistibility of plastic substrate102, the processing temperature of forming the polymer is limited to, typically, less than 150° C. Further, processing temperature of forming TFT device layer which is generally provided on stacked layer104is limited by the processing temperature of stacked layer104. That is, a TFT device layer on a plastic substrate is generally formed at a lower temperature, for example, a temperature under 150° C. A TFT device formed at low temperature has insufficient device performance and device reliability, and it may not be suitable for controlling liquid crystal of a liquid crystal display or the OLED devices of an OLED display.

To solve the above-mentioned issue, a new structure of a stacked layer on top of a plastic substrate is proposed. Referring toFIG. 2, a stacked layer204is provided in top of a plastic substrate202to reduce moisture and oxygen penetrating therethrough. Stacked layer204may include a plurality of pairs of stacked films. A pair of stacked films includes a first inorganic film206and a second inorganic film208. For example, inFIG. 2, three pairs of first inorganic film206and second inorganic film208are provided on plastic substrate202. Inorganic films206,208may be SiO2and SiNx.

Although these inorganic films can withstand higher temperature to form a TFT device layer, they have drawbacks as well. Most importantly, particles and pin-holes are common during device manufacturing, and a single inorganic layer cannot cover particles or pin-hole completely. Thus, moisture or oxygen can penetrate along the boundary of pin-hole or particles. Typically, very thick inorganic barrier layers are required. Particularly, it may need several pairs of stacked inorganic films to obtain better film coverage and reduce moisture and oxygen penetration. As the films pile up and thickness increases, the internal stress builds up, which may cause the plastic substrate to bend and may compromise the barrier effect of the inorganic films. Moreover, the surface roughness becomes higher with more stacked inorganic films.

Therefore, there is a need to improve the structures of a flexible display to increase the reliability of the flexible display.

SUMMARY OF EMBODIMENTS

Consistent with this disclosure, a substrate-less display device is disclosed. The substrate-less display device includes a barrier stack. The barrier stack includes a plurality of inorganic barrier films and a plurality of polymer films. The inorganic barrier films and the polymer films are alternatively disposed. The substrate-less display device further includes a thin-film-transistor (TFT) device layer disposed on the barrier stack; a display medium layer disposed on the TFT device layer; and an encapsulation layer disposed on the display medium layer. One of the inorganic barrier films is disposed at the outermost of the barrier stack opposing the encapsulation layer.

Consistent with this disclosure, a method of manufacturing a substrate-less display device is disclosed. The method includes forming a barrier stack on a carrier. The barrier stack includes a plurality of inorganic barrier films and a plurality of polymer films. The inorganic barrier films and the polymer films are alternatively disposed. A film of the barrier stack adjacent to the carrier is one of the inorganic barrier films. The method further includes forming a thin-film-transistor (TFT) device layer on the barrier stack; forming a display medium layer on the TFT device layer; forming an encapsulation layer on the display medium layer; and removing the carrier from the barrier stack.

Consistent with this disclosure, a substrate-less display device is disclosed. The substrate-less display device includes a barrier stack. The barrier stack includes a plurality of inorganic barrier films and a plurality of polymer films. The inorganic barrier films and the polymer films are alternatively disposed. A first one of the polymer films is disposed at the lowermost of the barrier stack. The first one of the polymer films is thicker than the other polymer films. The substrate-less display device further includes a thin-film-transistor (TFT) device layer disposed on the barrier stack; a display medium layer disposed on the TFT device layer; and an encapsulation layer disposed on the display medium layer.

Consistent with this disclosure, a method of manufacturing a substrate-less display device is disclosed. The method includes forming a barrier stack. The barrier stack includes a plurality of inorganic barrier films and a plurality of polymer films. The inorganic barrier films and the polymer films are alternatively disposed. A first one of the polymer films is disposed at the lowermost of the barrier stack. The first one of the polymer films is thicker than the other polymer films. The method further includes forming a thin-film-transistor (TFT) device layer on the barrier stack; forming a display medium layer on the TFT device layer; forming an encapsulation layer on the display medium layer; and removing the carrier from the barrier stack.

Consistent with this disclosure, the substrate-less display devices as disclosed above further include a sacrificial layer or adhesion control layer interposed between the carrier and the barrier stack.

DESCRIPTION OF EXAMPLE EMBODIMENTS

Hereinafter, embodiments consistent with the disclosure will be described with reference to the drawings.

FIG. 3depicts an exemplary substrate-less display structure300consistent with some embodiments of this disclosure. With reference toFIG. 3, display structure300includes inorganic barrier films302,306,310, and314; polymer films304,308, and312interlaced with inorganic barrier films302,306,310, and314; a TFT device layer316, a display medium layer318, and a top encapsulation320. Inorganic barrier films302,306,310, and314, and polymer films304,308, and312are collectively referred to as barrier stack301inFIG. 3. As shown inFIG. 3, inorganic barrier films302,306,310, and314and polymer films304,308, and312are alternatively disposed. Inorganic barrier film302is disposed at the outermost of barrier stack301opposing the encapsulation layer.

The material of inorganic barrier films302,306,310, and314can be one or more of metal, such as Ti, Al, Mo, etc.; or metal oxide, such as Al2O3, TiO2, or silicon oxide or nitride (SiO2, SiNx); or TiN; or spin on glass (SOG); or spin on dielectric (SOD); or SiC or SiOC, or any combination of the above materials. Each of inorganic barrier films302,306,310, and314can be a single layer or multiple layers of the above materials. For example, the bottom barrier film302may consist of a layer of Ti and a layer of TiO2. In some embodiments, bottom barrier film302may be made of hard materials such as SiC to prevent scratches to display structure300. In some embodiments, inorganic barrier films302,306,310, and314may use different materials. For example, at least one of inorganic barrier films302,306,310, and314is of a different material from that of the other inorganic barrier films. For another example, in some embodiments, bottom barrier film302is made of SiC while each of barrier films306,310, and314is made of a stacking of a SiO2layer and a SiNXlayer.

Inorganic barrier films302,306,310, and314may be prepared by sputtering, ALD, chemical vapor deposition (CVD), plasma-enhanced CVD (PECVD), and coating and curing, for example. The thickness of each of inorganic barrier films302,306,310, and314may range, for example, from 10 nm to 10 μm, or from 20 nm to 500 nm. In some embodiments, inorganic barrier films302,306,310, and314may have same thickness. In some embodiments, the thickness of each of inorganic barrier films302,306,310, and314may be different. For example, bottom barrier film302may be thicker than other inorganic barrier films306,310, and314to improve reliability. In some embodiments, inorganic barrier film314on which TFT device layer316and display-medium layer318are disposed may be thicker than inorganic barrier films306,310that are disposed inside barrier stack301to prevent diffusion of impurities into the device layers.

The material of polymer films304,308, and312can be one or more of polyimide, polynorbornene, polyamide, polyethersulfone, polyetherimide, polycarbonate, polyethelene naphthalate, polyester, acrylic polymer, and nylon, for example. Polymer films304,308, and312can be prepared by coating a layer of these materials. In some embodiments, the coating may be cured. The curing temperature can be higher than 300° C., or about 300-450° C. The thickness of polymer films304,308, and312can range, for example, from 100 nm to 100 μm, or from 500 nm to 10 μm, or from 1 μm to 7 μm. Each of polymer films304,308, and312can use different materials and have different thickness.

As shown inFIG. 3, in some embodiments, TFT device layer316and display-medium layer318are disposed directly on barrier stacks301. TFT device layer316may be disposed directly on inorganic barrier film314. TFT device layer316may include amorphous silicon TFTs, or polysilicon TFTs, or oxide semiconductor TFTs, or organic TFTs. Display-medium layer318may be, for example, an OLED device layer, a liquid crystal layer, or an electrophoretic ink layer. Encapsulation320is provided to protect TFT device layer316and display-medium layer318from top side. Encapsulation320can be a single barrier layer, or a barrier stack similar to barrier stack301, or a barrier film with or without barrier adhesive. A person having ordinary skill in the art should appreciate that the number of the polymer films and barrier films are not limited. In some embodiments, the number of these films may be more or less than seven. For example, the display device may have three barrier films and two polymer films sandwiched between the barrier films. As another example, the display device may have two barrier films and one polymer film sandwiched between the barrier films. For a further example, the display device may have nine alternating films (five barrier films and four polymer films alternatively disposed). As shown inFIG. 3, the display device300does not have any substrate. Because the display structure300includes no substrate, it is more flexible, light-weighted, and thinner than conventional display devices.

A method to form a display device as shown inFIG. 3will be explained with accompanying figures. Referring toFIG. 4A, a carrier450is provided. Carrier450can be a rigid carrier, such as, a glass carrier. A first inorganic barrier film402is deposited on carrier450by sputtering, ALD, CVD, PECVD, or coating and curing, for example. Barrier film402is made of one or more of inorganic materials such as metal, e.g., Ti, Al, Mo, etc.; or metal oxide, such as Al2O3, TiO2; or silicon oxide or nitride, or TiN; or spin on glass (SOG); or spin on dielectric (SOD); or SiC, SiOC; or any combination of two or more of these materials. Barrier film402can be a single layer or multiple layers of the above materials. The thickness of barrier film402may range, for example, from 10 nm to 10 μm, or from 20 nm to 500 nm.

Referring toFIG. 4B, after barrier film402is deposited on carrier450, an organic material, such as a monomer material or polymer material, is deposited on barrier film402and cured at a temperature, e.g., more than 200° C., or about 300-450° C., to form a first polymer film404by polymerization or crosslinking. Polymer film404can be made of polyimide, polynorbornene, polyamide, polyethersulfone, polyetherimide, polycarbonate, polyethelene naphthalate, polyester, acrylic polymer, or nylon, or any combination of two or more of these materials, for example. The thickness of polymer film404can range, for example, from 100 nm to 100 μm, or from 500 nm to 10 μm, or from 1 μm to 7 μm.

Referring toFIG. 4C, the process steps as described withFIGS. 4A-4Bcan be repeated until three layers of polymer films404,408,412are formed to alternate with four inorganic barrier films402,406,410,414. These polymer films and barrier films are collectively referred to as barrier stack401. However, the number of the polymer films and inorganic barrier films are not limited. In some embodiments, the number of these films may be more or less than seven. For example, in an application in which light weight is desired, barrier stack401may include two layers of polymer films alternating with three layers of inorganic barrier films.

Referring toFIG. 4D, a TFT device layer416, an OLED device layer, and an encapsulation layer420are deposited in that order onto barrier stack401. Because polymer films404,408,412are formed at a temperature about or higher than 200° C., TFT device layer416can also be formed at a temperature about or higher than 200° C. and thus can have better device performance and reliability. In some embodiments, TFT device layer416can be formed at about or higher than 300° C., or 300-450° C. Encapsulation layer420can be a single barrier layer, or a barrier stack similar to barrier stack401, or a barrier film with or without barrier adhesive. Next, referring toFIG. 4E, carrier450is removed to form an AMOLED display device400. Carrier450may be removed from AMOLED display400by a peeling, or an etching in chemicals, or a chemical-mechanical polishing (CMP) step, or a laser-treatment separation step.

Although AMOLED display device400is illustrated above, the display may be a liquid crystal display or an electrophoretic display as OLED device layer418is replaced with a layer of liquid crystal or electrophoretic ink.

In some embodiments, before the first inorganic barrier film402is deposited on carrier450, a sacrificial layer for facilitating removal of carrier450can be provided on carrier450. For example,FIG. 5Adepicts that a sacrificial layer460is deposited on carrier450and that first inorganic barrier film402is deposited on sacrificial layer460. The rest of the steps of forming an AMOLED display may be similar to those described above regardingFIGS. 4B-4E, and will be omitted. Sacrificial layer460can be a single layer or multiple layers of metal oxide, metal, SiO2, glasses, polymers, etc. and can have a thickness of 10 nm to 10 μm, or 20 nm to 1 μm, for example. In the processing step to remove carrier450, sacrificial layer460can facilitate the peeling, the etching, the laser-treatment, or the polishing of carrier450, thereby reducing processing time. For example, in a process where etching is used to remove carrier450, the etchant can be selected to react only with sacrificial layer460, but does not react with other materials in the display device. For another example, in a process where laser is used to remove carrier450, the laser can be calibrated with right energy and position to attack only the sacrificial layer, but not other materials in the display device. In some embodiments, sacrificial layer460is completely removed from AMOLED display400. In some embodiments, referring toFIG. 5B, a partial layer of sacrificial layer460remains on first inorganic barrier film402after removing carrier450.

In some embodiments, before the first inorganic barrier film402is deposited on carrier450, an adhesion control layer for facilitating removal of carrier450can be provided on carrier450. For example,FIG. 5Cdepicts that an adhesion control layer470is deposited on carrier450and that first inorganic barrier film402is deposited on adhesion control layer470. The rest of the steps of forming an AMOLED display may be similar to those described above regardingFIGS. 4B-4E, and will be omitted. Adhesion control layer470can be a layer of organic silane compound, hexamethyldisilazane (HMDS), polymers, etc., or a combination thereof, and have a thickness of 0.1 nm to 1 μm, or 0.1 nm to 100 nm, for example. In the processing step to remove carrier450, adhesion control layer470can facilitate the peeling, the etching, the heat- (e.g., laser-) treatment, or the polishing of carrier450, thereby reducing processing time. In some embodiments, adhesion control layer470is completely removed from AMOLED display400. In some embodiments, referring toFIG. 5D, adhesion control layer470remains on first inorganic barrier film402after removing carrier450.

Another exemplary substrate-less AMOLED display structure600consistent with some embodiments of this disclosure is depicted inFIG. 6. Referring toFIG. 6, AMOLED display structure600includes a barrier stack601, a TFT device layer614, an OLED device layer616and an encapsulation layer618. Barrier stack601includes three layers of polymer films602,606, and610, and three layers of inorganic barrier films604,608, and612alternating with polymer films602,606, and610. Polymer film602is disposed at the lowermost of barrier stack601. In some embodiments, the thickness of polymer films602,606, and610can be the same. In some embodiments, polymer film602at the bottom of display structure600may be thicker than polymer films606,610and inorganic films604,608, and612for protecting these internal films. The materials and characteristics of polymer films602,606, and610and inorganic films604,608, and612are similar to those of polymer films304,308, and312and inorganic barrier films302,306,310, and314of AMOLED display structure300as shown inFIG. 3, and therefore are omitted here.

A method to form an AMOLED display device will be explained with accompanying figures. Referring toFIG. 7A, a carrier750is provided. Carrier750can be a rigid carrier, for example, a glass carrier. An organic material, such as a monomer material or polymer material, is deposited on carrier750. The deposited material can be cured for polymerization or crosslinking. The curing may be at a temperature, e.g., about or more than 200° C., or about 300-450° C., to form a first polymer film702. Polymer film702can be made of polyimide, polynorbornene, polyamide, polyethersulfone, polyetherimide, polycarbonate, polyethelene naphthalate, polyester, acrylic polymer, or nylon, or any combination of these materials, for example. The thickness of polymer film702can range, for example, from 100 nm to 100 μm, or from 500 nm to 10 μm, or from 1 μm to 7 μm.

Referring toFIG. 7B, after polymer film702is deposited on carrier750, a first barrier film704is deposited on polymer film702by sputtering, ALD, CVD, PECVD, or coating and curing, for example. Barrier film704is made of one or more of inorganic materials such as metal, e.g., Ti, Al, Mo, etc.; or metal oxide, such as Al2O3, TiO2; or silicon oxide or nitride; or TiN; or spin on glass (SOG); or spin on dielectric (SOD); or SiC, SiOC, or any combination of the above materials. Barrier film704can be a single layer or multiple layers of the above materials. The thickness of barrier films704may range, for example, from 10 nm to 10 μm, or from 20 nm to 500 nm.

Referring toFIG. 7C, the process steps as described withFIGS. 7A-7Bcan be repeated until three layers of polymer films702,706,710are formed to alternate with three layers of inorganic barrier films704,708, and712. These polymer films and barrier films are collectively referred to as barrier stack701. However, the number of the polymer films and barrier films are not limited. In some embodiments, the number of these films may be more or less than six. For example, in an application in which light weight is desired, barrier stack701may include two layers of polymer films alternated with two layers of inorganic barrier films.

Referring toFIG. 7D, a TFT device layer714, an OLED device layer716, and an encapsulation layer718are deposited in that order onto barrier stack701. Because polymer films702,706,710are formed at a temperature about or higher than 200° C., TFT device layer714can also be formed at a temperature about or higher than 200° C. and thus can have better device performance and reliability. In some embodiments, TFT device layer416can be formed at about or higher than 300° C., or 300-450° C. Encapsulation layer718can a single barrier layer or a barrier stack similar to barrier stack701. Next, referring toFIG. 7E, carrier750is removed to form an AMOLED display700. Carrier750may be removed from AMOLED display700by a peeling, or an etching in chemicals, or a CMP step, or a laser-treatment separation step, as discussed above in connection with other embodiments.

In some embodiments, before the first polymer film702is deposited on carrier750, a sacrificial layer for facilitating removal of carrier750may be provided on carrier750. For example,FIG. 8Adepicts that sacrificial layer760is deposited on carrier750and that first polymer film702is deposited on sacrificial layer760. The rest of steps of forming an AMOLED display may be similar to those described above regardingFIGS. 7B-7E, and will be omitted. Sacrificial layer760can be a single layer or multiple layers of metal oxide, metal, SiO2, glasses, or polymers, etc. and can have a thickness of 10 nm to 10 μm, or 20 nm to 1 μm, for example. In the processing step to remove carrier750, sacrificial layer760can facilitate the peeling, the etching, the laser-treatment, or the polishing of carrier750, thereby reducing processing time. In some embodiments, sacrificial layer760may be completely removed from AMOLED display700. In some embodiments, referring toFIG. 8B, a partial layer of sacrificial layer760may remain on first polymer film702after removing carrier750.

In some embodiments, before the first polymer film702is deposited on carrier750, an adhesion control layer for facilitating removal of carrier750may be provided on carrier750. For example,FIG. 8Bdepicts that adhesion control layer770is deposited on carrier750and that first polymer film702is deposited on adhesion control layer770. The rest of steps of forming an AMOLED display may be similar to those described above regardingFIGS. 7B-7E, and will be omitted. Adhesion control layer770can be a layer of organic silane compound, hexamethyldisilazane (HMDS), or polymers, etc., or a combination thereof, and have a thickness of 0.1 nm to 1 μm, or 0.1 nm to 100 nm, for example. In the processing step to remove carrier750, adhesion control layer770can facilitate the peeling, the etching, the heat- (e.g., laser-) treatment, or the polishing of carrier750, thereby reducing processing time. In some embodiments, adhesion control layer770may be completely removed from AMOLED display700. In some embodiments, referring toFIG. 8D, adhesion control layer770may remain on first polymer film702after removing carrier750.

In some embodiments, the OLED layer illustrated above may be replaced with a liquid crystal layer or an electrophoretic ink layer to form a liquid crystal display or an electrophoretic ink display. For example, OLED device layer616or716can be replaced with a layer of liquid crystal or electrophoretic ink so that display600or700can be a liquid crystal display or an electrophoretic ink display. Further, the substrate-less configuration can be applied to other kinds of display.