Patent Publication Number: US-2022238822-A1

Title: Organic light emitting diode display panel and method for fabricating same

Description:
The present application claims priority to Chinese Patent Application No. 201910981704.4, entitled “Organic Light Emitting Diode Display Panel and Method for Fabricating Same”, filed on Oct. 16, 2019, the content of which is incorporated into the present disclosure in its entirety. 
     FIELD OF INVENTION 
     The present disclosure relates to the technical field of organic light-emitting diode (OLED) display panels, and particularly to a method for fabricating an organic light emitting diode display panel, which reduces occurrence and expansion of cracks during a cutting process, and an organic light emitting diode display panel fabricated by the method. 
     BACKGROUND 
     Organic light emitting diode display panels have advantages of simplicity, lightness, active light emission, fast response times, wide viewing angles, and flexibility. In a current process for fabricating organic light emitting diode display panels, a plurality of organic light emitting diode display panels are usually formed on a mother substrate, and then the organic light emitting diode display panels are cut from the mother substrate to reduce fabricating time and costs. 
     In a current process of cutting a mother substrate, the mother substrate and a thin film transistor (TFT) layer on cutting lines and a thin film encapsulation layer near the cutting lines are prone to cracks due to excessive stress. Furthermore, the cracks may spread to organic light emitting diodes in an active area. When moisture and oxygen in the atmosphere enter an organic light emitting diode display panel through a crack and come into contact with an organic light emitting diode, the organic light emitting diode will be corroded, thereby reducing service life of the organic light emitting diode display panel. 
     SUMMARY OF DISCLOSURE 
     In order to solve the technical problem that a mother substrate and a thin film transistor layer on cutting lines and a thin film encapsulation layer near the cutting lines are prone to cracks due to excessive stress during cutting of the mother substrate, the present disclosure provides the following technical solutions. 
     The present disclosure provides a method for fabricating an organic light emitting diode display panel comprising: providing a mother substrate provided with a plurality of cutting lines, wherein the cutting lines define a sub-substrate and a plurality of removal areas around the sub-substrate, and the sub-substrate comprises a active area and a non-active area surrounding the active area; forming a pixel defining layer on the active area, wherein the pixel defining layer comprises an opening; forming an organic light emitting diode in the opening; forming a dam on the non-active area, wherein the dam is a closed ring structure surrounding the active area; forming a crack prevention structure on the non-active area, wherein the crack prevention structure is a closed ring structure surrounding the dam; forming a thin film encapsulation layer covering the pixel defining layer, the organic light emitting diode, and the dam; forming an organic protective film covering a region from a side of the dam away from the active area to the removal areas around the sub-substrate to completely cover the crack prevention structure and the cutting lines around the sub-substrate; and cutting out the sub-substrate along the cutting lines to obtain the organic light emitting diode display panel. 
     In an embodiment, the organic protective film further covers a region from the side of the dam away from the active area to an edge of the active area to completely cover the dam covered by the thin film encapsulation layer. 
     In an embodiment, with respect to the sub-substrate, a height of the organic protective film is greater than a height of the crack prevention structure. 
     In an embodiment, the method for fabricating the organic light emitting diode display panel further comprises forming a thin film transistor layer on the mother substrate after providing the mother substrate. 
     In an embodiment, the forming the thin film encapsulation layer comprises: forming a first inorganic layer covering the pixel defining layer, the organic light emitting diode, and the dam; forming an organic layer on the first inorganic layer in the active area; and forming a second inorganic layer covering the organic layer and the first inorganic layer, wherein the second inorganic layer and the first inorganic layer completely cover the organic layer. 
     The present disclosure further provides an organic light emitting diode display panel comprising a substrate, a pixel defining layer, an organic light emitting diode, a dam, a crack prevention structure, a thin film encapsulation layer, and an organic protective film. The substrate comprises an active area and a non-active area surrounding the active area. The pixel defining layer is disposed on the active area and comprises an opening. The organic light emitting diode is disposed in the opening. The dam is disposed on the non-active area and is a closed ring structure surrounding the active area. The crack prevention structure is disposed on the non-active area and is a closed ring structure surrounding the dam. The thin film encapsulation layer covers the pixel defining layer, the organic light emitting diode, and the dam. The organic protective film covers a region from a side of the dam away from the active area to an edge of the substrate to completely cover the crack prevention structure. 
     In an embodiment, the organic protective film further covers a region from the side of the dam away from the active area to an edge of the active area to completely cover the dam covered by the thin film encapsulation layer. 
     In an embodiment, with respect to the sub-substrate, a height of the organic protective film is greater than a height of the crack prevention structure. 
     In an embodiment, the organic light emitting diode display panel further comprises a thin film transistor layer disposed on the substrate and electrically connected to the organic light emitting diode. 
     In an embodiment, the thin film encapsulation layer comprises a first inorganic layer, an organic layer, and a second inorganic layer. The first inorganic layer covers the pixel defining layer, the organic light emitting diode, and the dam. The organic layer is disposed on the first inorganic layer in the active area. The second inorganic layer covers the organic layer and the first inorganic layer. The second inorganic layer and the first inorganic layer completely cover the organic layer. 
     The method for fabricating the organic light emitting diode display panel provided by the disclosure reduces the stress on the sub-substrate, the thin film encapsulation layer, and the crack prevention structure, and/or the thin film transistor layer near the cutting lines during the cutting process by covering the organic protective film made of an organic material with soft characteristics from the side of the dam away from the active area or from the edge of the active area to the removal areas outside the cutting lines. This reduces occurrence of cracks in the sub-substrate, the thin film encapsulation layer, the crack prevention structure, and/or the thin film transistor layer, and prevents the cracks, if any, from spreading to the organic light emitting diode in the active area. Furthermore, a risk of moisture and oxygen in the atmosphere entering through the cracks and corroding the organic light emitting diode is reduced, thereby ensuring service life of the organic light emitting diode display panel is ensured. Moreover, because the non-active area of the organic light emitting diode display panel made using the method provided by the present disclosure has the organic protective film, it has better ability to release stress and is less susceptible to damage by external forces, compared with a non-active area of a traditional panel. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, a brief description of accompanying drawings used in the description of the embodiments of the present disclosure will be given below. Obviously, the accompanying drawings in the following description are merely some embodiments of the present disclosure. For those skilled in the art, other drawings may be obtained from these accompanying drawings without creative labor. 
         FIG. 1  is a schematic diagram of a mother substrate used in a method for fabricating an organic light emitting diode display panel according to an embodiment of the present disclosure. 
         FIGS. 2-12  are schematic flowcharts of a method for fabricating an organic light emitting diode display panel according to an embodiment of the present disclosure.  FIG. 2  also is a schematic cross-sectional view of the mother substrate of  FIG. 1  along line AA&#39;.  FIG. 12  also is a schematic diagram of an organic light emitting diode display panel according to an embodiment of the present disclosure. 
         FIG. 13  is a schematic diagram showing that the first dam, the second dam, and the crack prevention structure of  FIG. 7  are disposed in the non-active area. 
     
    
    
     DETAILED DESCRIPTION 
     The following description of various embodiments of the present disclosure with reference to the accompanying drawings is used to illustrate specific embodiments that can be practiced. Directional terms mentioned in the present disclosure, such as “above”, “below”, “top”, “bottom”, “left”, “right”, “inside”, “outside”, “side”, are merely used to indicate the direction of the accompanying drawings. Therefore, the directional terms are used for illustrating and understanding the present disclosure rather than limiting the present disclosure. In the figures, elements with similar structures are indicated by the same reference numerals. 
     The present disclosure provides a method for fabricating an organic light emitting diode display panel comprising the following steps. 
     Step 1: please refer to  FIG. 1  and  FIG. 2 , providing a mother substrate  10 . The mother substrate  10  may be a glass substrate. Alternatively, the mother substrate  10  may be a flexible substrate made of a flexible insulating polymer material such as polyimide (PI), polycarbonate (PC), polyether sulfone (PES), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and film fiber-reinforced polymer (FRP). The mother substrate  10  may be transparent, translucent, or opaque. The mother substrate  10  is provided with a plurality of cutting lines  12 . The cutting lines  12  define a plurality of sub-substrate  110  and a plurality of removal areas  112 . Each of the sub-substrates  110  comprises an active area AA and a non-active area NA surrounding the active area AA. 
     Step 2: please refer to  FIG. 3 , forming a thin film transistor layer  120  on the mother substrate  10 . The thin film transistor layer  120  comprises a plurality of thin film transistors. Each of the thin film transistors comprises a gate electrode layer, an insulating layer, an active layer, and a source/drain electrode layer. The thin film transistors may comprise organic thin film transistors (OTFTs), hydrogenated amorphous thin film transistors (a-TFT: H), and/or low temperature poly thin film transistors (LTPS). 
     Step 3: please refer to  FIG. 4 , forming a pixel defining layer  130  on the thin film transistor layer  120  in each of the active areas AA. The pixel defining layer  130  comprises a plurality of openings  132 . The pixel defining layer  130  may be made of an organic insulating material such as polyimide, acrylic, polymethyl methacrylate (PMMA) photoresist, and silicone photoresist. Alternatively, the pixel defining layer  130  may be made of an inorganic insulating material such as a silicon dioxide solution and an alcohol-containing silicon dioxide solution. 
     Step 4: please refer to  FIG. 5 , forming an organic light emitting diode  140  on the thin film transistor layer  120  in each of the openings  132 . Each of the organic light emitting diodes  140  is electrically connected to one or more thin film transistors that are configured to drive it. Each of the organic light emitting diodes  140  may comprise an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode layer in this order. 
     Step 5: please refer to  FIG. 6  and  FIG. 13 , forming a first dam  150  and a second dam  152  on the thin film transistor layer  120  in each of the non-active areas NA. The first dam  150  is a closed ring structure surrounding the active area AA. The second dam  152  is a closed ring structure surrounding the first dam  150 . The second dam  152  is parallel to the first dam  150 . When the pixel defining layer  130  or one or more layers of each organic light emitting diode  140  is/are prepared, the first dam  150  and the second dam  152  may be made by designing their corresponding regions on one or more masks, thereby reducing production time and costs. Therefore, each of the first dam  150  and the second dam  152  has a single-layer or multi-layer structure composed of the same material(s) as the pixel defining layer  130  or one or more layers of each organic light emitting diode  140 . 
     Step 6: please refer to  FIG. 7  and  FIG. 13 , forming a crack prevention structure  160  on the thin film transistor layer  120  in each of the non-active areas NA. The crack prevention structure  160  is a closed ring structure surrounding the second dam  152 . The crack prevention structure  160  is parallel to the second dam  152 . The crack prevention structure  160  may be made of a flexible organic material. 
     Step 7: please refer to  FIG. 8 , forming a first inorganic layer  171  covering the pixel defining layer  130 , the organic light emitting diodes  140 , the first dam  150 , and the second dam  152  of each sub-substrate  110  to prevent the organic light emitting diodes  140  from contact with moisture and oxygen in the atmosphere and from being corroded by moisture and oxygen in the atmosphere. The first inorganic layer  171  may be made of aluminum oxide, silicon oxide, magnesium oxide, or a combination thereof. 
     Step 8: please refer to  FIG. 9 , forming an organic layer  172  on the first inorganic layer  171  in each active area AA. The first dam  150  and the second dam  152  formed in step  4  can prevent the organic layer  172  from flowing out of a coverage area of the first inorganic layer  171  in the active area AA when the organic layer  172  is formed. Because the organic layer  172  is made of an organic material, it is soft and can be used to release the stress suffered by the active area AA. The organic layer  172  may be made of alucone, or may be an organic/inorganic hybrid film of aluminum, titanium, zinc, and/or iron. 
     Step 9: please refer to  FIG. 10 , forming a second inorganic layer  173  covering the organic layer  172  and the first inorganic layer  171  in each active area AA. In each active area AA, the second inorganic layer  173  and the first inorganic layer  171  completely cover the organic layer  172 . Because the organic layer  172  cannot block moisture and oxygen, the second inorganic layer  173  is used to improve a blocking of moisture and oxygen. The second inorganic layer  173  may also be made of aluminum oxide, silicon oxide, magnesium oxide, or a combination thereof. 
     Please refer to  FIG. 10 , the first inorganic layer  171 , the organic layer  172 , and the second inorganic layer  173  in each active area AA constitute a thin film encapsulation layer  170 . The thin film encapsulation layer  170  is configured to protect the organic light emitting diodes  140  in each active area AA from being damaged by moisture and oxygen in the atmosphere, and improve an ability of the active area AA to release stress. The first inorganic layer  171 , the organic layer  172 , and the second inorganic layer  173  may be formed by physical vapor deposition (PVD), atomic layer deposition (ALD), or chemical vapor deposition (CVD). 
     Step  10 : please refer to  FIG. 1  and  FIG. 11 , forming an organic protective film  180  covering a region from a side of the second dam  152  in each non-active area NA away from the adjacent active area AA to the adjacent removal areas  112 , so as to completely cover the crack prevention structure  160  in each non-active area NA and the cutting lines  12  around each sub-substrate  110 . With respect to the sub-substrate, a height of the organic protective film  180  may be equal to or greater than a height of the crack prevention structure  160 , but is equal to or less than a height of the first dam  150  covered with the first inorganic layer  171  and the second inorganic layer  173 . 
     Specifically, this step comprises blanket-depositing an organic material such as alucone and hexamethyldisiloxane (HMDSO) by ink jet printing (IJP), atomic layer deposition (ALD), chemical vapor deposition (CVD) and other processes. Further, the blanket-deposited organic material is patterned by photoengraving and etching to obtain the organic protective film  180  covering the crack prevention structure  160  in each non-active area NA and the cutting lines  12  adjacent to each non-active area NA. 
     In an embodiment, the organic protective film  180  covers a region from an edge of each active area AA to the adjacent removal areas  112  or an edge of another active area AA, so as to completely cover the first dam  150  and the second dam  152  covered with the thin film encapsulation layer  170  in each non-active area NA, the crack prevention structure  160 , and cutting lines  12  around each sub-substrate  110 . With respect to the sub-substrate  110 , the height of the organic protective film  180  is greater than the height of the crack prevention structure  160  and the heights of the first dam  150  and the second dam  152  covered with the first inorganic layer  171  and the second inorganic layer  173 , but is less than or equal to a height of the pixel defining layer  130  covered with the thin film encapsulation layer  170  in the active area AA. 
     Step 11: please refer to  FIG. 1 ,  FIG. 11 , and  FIG. 12 , cutting out the sub-substrates  110  along the cutting lines  12  to obtain the organic light emitting diode display panels  100 . Each organic light emitting diode display panel  100  is an active-matrix organic light-emitting diode (AMOLED) display panel. The crack prevention structures  160  formed in step 6 can prevent cracks of the sub-substrates  110  due to excessive stress during a cutting process from spreading. The organic protective films  180  formed in step 8 are soft, so they can release stress. This can improve a situation that the sub-substrates  110 , the thin film transistor layer  120 , the crack prevention structures  160 , and the thin film encapsulation layers  170  near the cutting lines  12  are prone to cracks due to excessive stress during the cutting process. Further, the cracks can be prevented from spreading to the organic light emitting diodes  140  in each active area AA. Therefore, a risk of moisture and oxygen in the atmosphere entering through the cracks and corroding the organic light emitting diodes  140  is reduced, thereby ensuring service lives of the organic light emitting diode display panels  100  are ensured. 
     In an embodiment, the method for fabricating an organic light emitting diode display panel  100  may not comprise step 2 of forming a thin film transistor layer  120  on the mother substrate  10 . Accordingly, each organic light emitting diode display panel  100  obtained in the last step is a passive-matrix organic light-emitting diode (PMOLED) display panel. 
     Please refer to  FIG. 12 , the present disclosure further provides an organic light emitting diode display panel  100  made by the foregoing method, which comprises a substrate  110 , a thin film transistor layer  120 , a pixel defining layer  130 , an organic light emitting diode  140 , a first dam  150 , a second dam  152 , a crack prevention structure  160 , a thin film encapsulation layer  170 , and an organic protective film  180 . The substrate  110  may be a glass substrate. Alternatively, the substrate  10  may be a flexible substrate made of a flexible insulating polymer material such as polyimide (PI), polycarbonate (PC), polyether sulfone (PES), polyethylene terephthalate (PET), polyethylene naphthalate (PEN), and film fiber-reinforced polymer (FRP). The substrate  110  may be transparent, translucent, or opaque. The substrate  110  comprises an active area AA and a non-active area NA surrounding the active area AA. 
     The thin film transistor layer  120  is disposed on the substrate  110  and electronically connected to the organic light emitting diode  140 . The thin film transistor layer  120  comprises a plurality of thin film transistors configured to drive the organic light emitting diode  140 . Each of the thin film transistors comprises a gate electrode layer, an insulating layer, an active layer, and a source/drain electrode layer. The thin film transistors may comprise organic thin film transistors, hydrogenated amorphous thin film transistors, and/or low temperature poly thin film transistors. 
     The pixel defining layer  130  is disposed on the thin film transistor layer  120  in the active area AA. The pixel defining layer  130  may be made of an organic insulating material such as polyimide, acrylic, polymethyl methacrylate photoresist, and silicone photoresist. Alternatively, the pixel defining layer  130  may be made of an inorganic insulating material such as a silicon dioxide solution and an alcohol-containing silicon dioxide solution. The pixel defining layer  130  comprises an opening  132 . The organic light emitting diode  140  is disposed on the thin film transistor layer  120  in the opening  132 . The organic light emitting diode  140  may comprise an anode layer, a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and a cathode layer in this order. 
     The first dam  150  and the second dam  152  are disposed on the thin film transistor layer  120  in the non-active areas NA. The first dam  150  is a closed ring structure surrounding the active area AA. The second dam  152  is a closed ring structure surrounding the first dam  150 . The second dam  152  is parallel to the first dam  150 . The first dam  150  and the second dam  152  may have a single-layer or multi-layer structure made of same material(s) as the pixel defining layer  130  or one or more layers of the organic light emitting diode  140 , thereby reducing production time and costs. The crack prevention structure  160  is disposed on the thin film transistor layer  120  in the non-active areas NA and is a closed ring structure surrounding the second dam  152 . The crack prevention structure  160  is parallel to the second dam  152 . The crack prevention structure  160  may be made of a flexible organic material. 
     The thin film encapsulation layer  170  covers the pixel defining layer  130 , the organic light emitting diode  140 , the first dam  150 , and the second dam  152 . The thin film encapsulation layer  170  comprises a first inorganic layer  171 , an organic layer  172 , and a second inorganic layer  173 . The first inorganic layer  171  covers the pixel defining layer  130 , the organic light emitting diodes  140 , the first dam  150 , and the second dam  152 . The organic layer  172  is disposed on the first inorganic layer  171  in the active area AA. The second inorganic layer  173  covers the organic layer  172  and the first inorganic layer  171 . The second inorganic layer  173  and the first inorganic layer  171  completely cover the organic layer  172 . The first inorganic layer  171  and the second inorganic layer  173  are configured to prevent the organic light emitting diode  140  from contact with moisture and oxygen in the atmosphere and from being corroded by moisture and oxygen in the atmosphere. The first inorganic layer  171  and the second inorganic layer  173  may be made of aluminum oxide, silicon oxide, magnesium oxide, or a combination thereof. Because the organic layer  172  is made of an organic material, it is soft and can be used to release the stress suffered by the active area AA. The organic layer  172  may be made of alucone, or may be an organic/inorganic hybrid film of aluminum, titanium, zinc, and/or iron. The first inorganic layer  171 , the organic layer  172 , and the second inorganic layer  173  may be formed by physical vapor deposition, atomic layer deposition, or chemical vapor deposition. 
     The organic protective film  180  covers a region from a side of the second dam  152  away from the active area AA to an edge of the substrate  110 , so as to completely cover the crack prevention structure  160 . With respect to the sub-substrate, a height of the organic protective film  180  may be equal to or greater than a height of the crack prevention structure  160 , but is equal to or less than a height of the first dam  150  covered with the first inorganic layer  171  and the second inorganic layer  173 . 
     In an embodiment, the organic protective film  180  covers a region from an edge of the active area AA to the edge of the substrate  110 , so as to completely cover the first dam  150  and the second dam  152  covered with the thin film encapsulation layer  170  in non-active area NA and the crack prevention structure  160 . With respect to the substrate  110 , the height of the organic protective film  180  is greater than the height of the crack prevention structure  160  and the heights of the first dam  150  and the second dam  152  covered with the first inorganic layer  171  and the second inorganic layer  173 , but is less than or equal to a height of the pixel defining layer  130  covered with the thin film encapsulation layer  170  in the active area AA. 
     In an embodiment, the organic light emitting diode display panel  100  may not comprise the thin film transistor layer  120 . Therefore, the organic light emitting diode display panel  100  is a passive-matrix organic light-emitting diode display panel. 
     In the above, the method for fabricating the organic light emitting diode display panel provided by the disclosure achieves the following effects by using the organic protective films  180 . The organic protective films  180  are made of an soft organic material and cover the region from the side of the second dam  152  in each non-active area NA away from the adjacent active area AA, or the edge of each active area AA, to the adjacent removal areas  112  (1) The organic protective films  180  can release the stresses suffered by the sub-substrates  110  and the crack prevention structures  160  adjacent to the cutting lines  12  when the sub-substrates  110  are cut from the mother substrate  10 . This prevents the sub-substrates  110  from cracking, prevents cracks from spreading to the thin film encapsulation layers  170 , and prevents the crack prevention structures  160  from being damaged and losing their effectiveness. (2) The organic protective films  180  can also release the stress suffered by the thin film encapsulation layers  170  adjacent to the cutting lines  12  during the cutting process. When the first inorganic layer  171  and the second inorganic layer  173  of each thin-film encapsulation layer  170  are made by a method such as chemical vapor deposition, materials of the inorganic layers easily enters between masks and the sub-substrate  110  to form a thin film. That is a shadow effect. When the thin film covers the crack prevention structure  160 , especially when the organic light emitting diode display panel has a narrow frame design, the organic protective film  180  can release the stresses suffered by the first inorganic layer  171  and the second inorganic layer  173  that covers on the crack prevention structure  160  during the cutting of the sub-substrate  110  from the mother substrate  10 . This can prevent the first inorganic layer  171  and the second inorganic layer  173  from cracking, and prevent the cracking from causing the thin film encapsulation layer  170  to fail. (3) When the organic light emitting diode display panels  100  are an active matrix organic light emitting diode display panel, the thin film transistor layer  120  is disposed on the mother substrate  10 . The portions of the thin film transistor layer  120  located near the cutting lines  12  and near the crack prevention structures  160  are mainly composed of a metal layer and an inorganic layer, and therefore cannot release stress. The organic protective film  180  can release the stresses suffered by the portions of the thin film transistor layer  120  located near the cutting lines  12  and near the crack prevention structures  160  when the sub-substrates  110  are cut from the mother substrate  10 , thereby preventing the thin film transistor layer  120  from cracking and preventing cracks from expanding to the thin film encapsulation layers  170 . Furthermore, because the non-active area NA of the organic light-emitting diode display panel  100  made by using the method provided by the present disclosure is provided with the organic protective film  180 , it has an ability to release stress. Therefore, compared with a non-active area of a current panel, it is not easily damaged by external forces. 
     The present application has been described in the above preferred embodiments, but the preferred embodiments are not intended to limit the scope of the present application, and those skilled in the art may make various modifications without departing from the scope of the present application. The scope of the present application is determined by claims.