Release layer, substrate structure, and method for manufacturing flexible electronic device

Disclosed is a substrate structure for manufacturing a flexible electronic device, including a supporting layer, a release layer covering the supporting layer with a first area, wherein the release layer is an aromatic polyimide, and a flexible layer covering the supporting layer and the release layer with a second area. The second area is greater than the first area. The adhesion force between the flexible layer and the supporting layer is stronger than the adhesion force between the release layer and the supporting layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The application is based on, and claims priority from, Taiwan Application Serial Number 103107366, filed on Mar. 5, 2014, and claims the benefit of provisional Application No. 61/887,033, filed on Oct. 4, 2013, the disclosure of which are hereby incorporated by reference herein in their entirety

TECHNICAL FIELD

The technical field relates to a release layer, a substrate structure including the same, and a method for manufacturing the same.

BACKGROUND

Mobile communications have quickly developed, and have since 2011 been combine with content service. Likewise, flexible displays are anticipated to become a novel trend in the next generation of displays. Major IT companies are replacing thick, heavy, and easily broken glass substrates with non-glass (e.g. light-weight and flexible plastic) substrates. In addition, active full-color TFT display panels are being developed too. While flat displays are desirable in smartphones and tablets, the product's design should meet the requirements of having thin profile and light weight. Another new development is flexible/soft display technology, which may open a new age of display design. While the mass production of medium or small panels has matured, flexible displays can possibly be mass produced to be lightweight, thin, and having a larger cell space.

Fabrication processes for flexible layers are classified into batch type and roll-to-roll type. A conventional apparatus for TFT devices can be utilized to fabricate TFT devices of the batch type. However, development of substrate-transfer and film-separation techniques is required for the batch type to transfer the flexible display from glass substrates to other plastic substrates, or directly take the flexible display from the glass substrates. The roll-to-roll type needs new apparatuses, and some problems caused by rolling and contact must be overcome.

If the batch type is selected to fabricate TFT devices such as LTPS, high-temperature resistant material will be necessary due to the high process temperature (higher than 400° C.). Because the batch type may utilize the existing apparatuses for glass substrates, apparatus cost can be saved. However, to prevent the peeling of the flexible layer on the glass during the device processes, and easily take out the flexible layer (without adhering on the glass) after the device processes will be major critical points.

Accordingly, a novel substrate structure for manufacturing flexible electronic devices is called for.

SUMMARY

One embodiment of the disclosure provides a release layer, being an aromatic polyimide, and the release layer is applied to flexible electronic device processes.

One embodiment of the disclosure provides a substrate structure, comprising: a supporting layer; a release layer with a first area covering the supporting layer, wherein the release layer is an aromatic polyimide; and a flexible layer with a second area covering the release layer and the supporting layer, wherein the second area is greater than the first area, and adhesion between the flexible layer and the supporting layer is stronger than adhesion between the release layer and the supporting layer.

One embodiment of the disclosure provides a method of manufacturing a flexible electronic device, comprising: providing a supporting layer; forming a release layer with a first area to cover the supporting layer, and the release layer is an aromatic polyimide; forming a flexible layer with a second area to cover the release layer and the supporting layer, wherein the second area is greater than the first area, and adhesion between the flexible layer and the supporting layer is stronger than adhesion between the release layer and the supporting layer; forming a device on the flexible layer; and separating the supporting layer and the release layer, and the release layer and the flexible layer separated from the supporting layer have an area substantially similar to the second area.

DETAILED DESCRIPTION

The substrate structure of the disclosure may tolerate high-temperatures. A high-temperature resistant release layer material can be coated between a supporting layer and a flexible layer. The flexible layer and the supporting layer are separated by the release layer, thereby avoiding the flexible layer sticking to the glass (e.g. the flexible layer cannot be taken out in its entirety) after the back-end high-temperature processes. Accordingly, the substrate structure may enhance the process yield.

As shown inFIG. 1A, one embodiment of the disclosure provides a substrate structure10for flexible electronic device processes. The substrate structure10includes a supporting layer12, a release layer14, and a flexible layer16. The supporting layer12may include glass or silicon wafer. The supporting layer12is covered by the release layer14of a pattern (e.g. one or more blocks as shown inFIG. 1B or 1C) with an area A1. Note that the patterns of the release layer14inFIGS. 1B and 1Care merely illustrated, and the shape, the size, and the configuration of the patterns of the release layer14can be modified by one skilled in the art if necessary. The release layer14is aromatic polyimide polymerized of diamine and dianhydride. The diamine can be 4,4′-oxydianiline, 3,4′-diaminodiphenyl ether, p-phenylene diamine, 2,2′-bis(trifluoromethyl)diamino benzidine, or combinations thereof. The dianhydride can be pyromellitic dianhydride, 3,3′4,4′-biphenyltetracarboxylic dianhydride, 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, or combinations thereof. The diamine and the dianhydride are firstly polymerized to form polyamic acid (PAA), which is then dehydrated to form polyimide (PI), as shown in Formula 1.

In Formula 1, the Ar1and Ar2each independently represents an aromatic group, respectively, and n is a repeating number. In practice, the diamine and the dianhydride can be initially polymerized to form polyamic acid. A polar aprotic solvent (e.g. dimethyl acetamide, DMAc) can be added to the polyamic acid solution to tune the solid content of the polyamic acid solution. The polyamic acid solution is subsequently coated on a supporting layer12. The coating is then heated, such that the polyamic acid of the coating is reacted to form a release layer14of polyimide. In one embodiment of the disclosure, the release layer14has a thickness of 0.1 μm to 4 μm. An overly thick release layer14may increase the cost, wherein the film surface after baking is easily poor. An overly thin release layer14may be non-uniform during the coating step, such that part of the release layer14loses its release effect.

Subsequently, the flexible layer16is formed to cover the release layer14and the supporting layer12, wherein the flexible layer16has an area A2. Note that the area A2is greater than the area A1. In one embodiment, the flexible layer16and the supporting layer12may have adhesion of2B to5B therebetween (determined by an adhesion cross-cut tester), and the adhesion between the flexible layer16and the supporting layer12is stronger than adhesion between the release layer14and the supporting layer12. In practice, a material solution of the flexible layer16can be coated on the supporting layer12and the release layer14to form a coating. The composition of the flexible layer16is different from the composition of the release layer14. The flexible layer16can be polyimide (PI), polycarbonate (PC), polyethersulfone (PES), polyacrylate (PA), polynorbornene (PNB), polyethylene terephthalate (PET), polyetheretherketone (PEEK), polyethylene naphthalate (PEN), or polyetherimide (PEI). In one embodiment, powder such as silica, organic clay, or combinations thereof can be further added to the material solution of the flexible layer16, thereby further increasing the adhesion between the flexible layer16and the supporting layer12. For example, some aromatic polyimide is selected to be a release layer14, and a mixture of the same aromatic polyimide and the powder may serve as the flexible layer16. In this embodiment, the aromatic polyimide and the powder in the flexible layer16have a weight ratio of 1:0.11 to 1:0.43, and the powder has a size of less than 200 nm. An overly high powder ratio may reduce the flexibility of the flexible layer16, and even crack the flexible layer16. An overly low powder ratio may cause insufficient adhesion between the flexible layer16and the supporting layer12, such that the peeling problem may occur during the high-temperature processes. An overly large powder size will make the film be opaque or highly hazy. In another embodiment, the aromatic polyimide of the release layer14is different from the composition of the flexible layer16. The flexible layer16has a thickness of 5 μm to 40 μm. An overly thick flexible layer16may increase the cost. An overly thin flexible layer16cannot provide sufficient mechanical strength for the product.

FIGS. 2A to 2Eshow cross-sectional views of a flexible electronic device during processing in one embodiment of the disclosure. First, the substrate structure10inFIG. 1Ais provided, and devices (not shown) are then formed on the flexible layer16of the substrate structure10. The devices can be thin-film transistors (TFT), microelectromechanic al systems (MEMS), optoelectronic conversion devices, electroluminescence devices such as organic light-emitting diode (OLED), other devices, or combinations thereof. In one embodiment, the processes for fabricating the devices are performed at a temperature of 250° C. to 450° C. Note that, if other compositions are selected to form the release layer14, the release layer14may deform or crack at the process temperature for fabricating the devices.

The supporting layer12and the release layer14are separated after forming the devices. In an ideal case, the separation step is performed as cutting end points (A′) of the release layer14, as shown inFIG. 2A. In a real operation, the separation step is performed as cutting an edge part of the release layer14overlapping the flexible layer16(e.g. cutting points B′ inFIG. 2B) in a direction vertical to the surface of the supporting layer12, thereby avoiding any flexible layer16remaining between the flexible layer16and the supporting layer12after the cutting step as shown inFIG. 2C. The flexible layer16and the release layer14separated from the supporting layer12have an area substantially similar to the area A2. Note that the cutting step penetrates the supporting layer12, but it may only cuts to the surface of the supporting layer12without completely cutting through the supporting layer12in a real operation.

After the cutting step, only the release layer14is disposed between the flexible layer16and the supporting layer12, and no flexible layer16connects to the supporting layer12. Therefore, the release layer14and the supporting layer12can be easily separated as shown inFIG. 2D. In one embodiment, the release layer14and the flexible layer16can be separated after the above steps, as shown inFIG. 2E.

The release layer14may serve as a protection film for the product, and not be immediately removed after the step of separating the supporting layer12and the release layer14. For example, the release layer14and the flexible layer16can be separated by a user after the product is delivered to the user. The release layer14can simply be peeled off the flexible layer16. On the other hand, if the flexible layer16with devices formed thereon is a semi-manufacture, it can be delivered to the next processing point. The release layer14is then removed at the next processing point.

EXAMPLES

Synthesis of a Polyamic Acid

16.53 g (0.153 mol) of p-phenylenediamine (PPD) was dissolved in 246.13 g of dimethylacetamide (DMAc). 45 g (0.153 mol) of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA) was added to the PPD solution in three batches with intervals of 30 minutes. After the BPDA was completely added into the PPD solution, the mixture was stirred and reacted at room temperature for at least 8 hours to obtain a viscous liquid, wherein the reaction was an exothermal reaction. Thereafter, 102.54 g of DMAc was added to the reaction and evenly stirred to dilute the viscous liquid. The diluted liquid had a solid content of 15% and a viscosity of 5,000 cps to 100,000 cps. The reaction is shown in Formula 2.

Formation of a Release Layer

275 g of DMAc was added to 100 g of the polyamic acid solution in Example 1 and then evenly stirred, thereby obtaining a diluted polyamic acid solution with a solid content of 4%. The diluted polyamic acid solution was coated on a glass carrier to form a wet film with a thickness of 60 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, and 400° C. for half an hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a release layer of a polyimide (P1) on the glass carrier, as shown in Formula 3.

The release layer (P1) was analyzed by thermogravimetric analysis (TGA) with a heating rate of 10° C./min under atmosphere to measure its thermal degradation temperature (Td) of 614.19° C.

Substrate Structure

30 g of the polyamic acid solution with a solid content of 15% in Example 1 and 5.63 g of 20% silica sol gel (NCT DMAc sol) were mixed by mechanical stirring to be evenly dispersed. After the complete mixing, the silica/polyamic acid dispersion was obtained for the flexible layer.

The silica/polyamic acid dispersion was then coated on the release layer and the glass carrier in Example 2 to form a wet film with a thickness of 400 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, 300° C. for half an hour, and 400° C. for 1 hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a flexible layer of silica/polyimide (P1+SiO2). As such, a high-temperature resistant substrate structure of the flexible layer (P1+SiO2) covering the release layer (P1) and the glass carrier was finished. The edge part of the flexible layer overlapping the release layer was cut with a knife, and then peeled as a strip with a width of 2 cm to measure its release force (g) as shown in Tables 1 and 2.

Synthesis of a Polyamic Acid

30.63 g (0.153 mol) of 4,4′-oxydianiline (ODA) was dissolved in 302.52 g of DMAc. 45 g (0.153 mol) of BPDA was added to the ODA solution in three batches with intervals of 30 minutes. After the BPDA was completely added into the ODA solution, the mixture was stirred and reacted at room temperature for at least 8 hours to obtain a viscous liquid, wherein the reaction was an exothermal reaction. Thereafter, 126.05 g of DMAc was added to the reaction and evenly stirred to dilute the viscous liquid. The diluted liquid had a solid content of 15% and a viscosity of 5,000 cps to 100,000 cps. The reaction is shown in Formula 4.

Formation of a Release Layer

275 g of DMAc was added to 100 g of the polyamic acid solution in Example 4 and then evenly stirred, thereby obtaining a diluted polyamic acid solution with a solid content of 4%. The diluted polyamic acid solution was coated on a glass carrier to form a wet film with a thickness of 60 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, and 400° C. for half an hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a release layer of a polyimide (P2) on the glass carrier, as shown in Formula 5.

The release layer (P2) was analyzed by TGA with a heating rate of 10° C./min under atmosphere to measure its thermal degradation temperature (Td) of 576.67° C.

Substrate Structure

The silica/polyamic acid dispersion prepared in Example 3 was coated on the release layer and the glass carrier in Example 5 to form a wet film with a thickness of 400 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, 300° C. for half an hour, and 400° C. for 1 hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a flexible layer of silica/polyimide (P1+SiO2). As such, a high-temperature resistant substrate structure of the flexible layer (P1+SiO2) covering the release layer (P2) and the glass carrier was finished. The edge part of the flexible layer overlapping the release layer was cut with a knife, and then peeled as a strip with a width of 2 cm to measure its release force (g) as shown in Table 1.

Synthesis of a Polyamic Acid

16.53 g (0.153 mol) of PPD was dissolved in 236.72 g of DMAc. 35.98 g (0.122 mol) of BPDA and 6.67 g (0.03 mol) of pyromellitic dianhydride (PMDA) were added to the PPD solution in three batches with intervals of 30 minutes. After the BPDA and PMDA were completely added into the PPD solution, the mixture was stirred and reacted at room temperature for at least 8 hours to obtain a viscous liquid, wherein the reaction was an exothermal reaction. Thereafter, 98.63 g of DMAc was added to the reaction and evenly stirred to dilute the viscous liquid. The diluted liquid had a solid content of 15% and a viscosity of 5,000 cps to 100,000 cps. The reaction is shown in Formula 6.

Formation of a Release Layer

275 g of DMAc was added to 100 g of the polyamic acid solution in Example 7 and then evenly stirred, thereby obtaining a diluted polyamic acid solution with a solid content of 4%. The diluted polyamic acid solution was coated on a glass carrier to form a wet film with a thickness of 60 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, and 400° C. for half an hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a release layer of a polyimide (P3) on the glass carrier, as shown in Formula 7.

The release layer (P3) was analyzed by TGA with a heating rate of 10° C./min under atmosphere to measure its thermal degradation temperature (Td) of 601.59° C.

Substrate Structure

The silica/polyamic acid dispersion prepared in Example 3 was coated on the release layer and the glass carrier in Example 8 to form a wet film with a thickness of 400 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, 300° C. for half an hour, and 400° C. for 1 hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a flexible layer of silica/polyimide (P1+SiO2). As such, a high-temperature resistant substrate structure of the flexible layer (P1+SiO2) covering the release layer (P3) and the glass carrier was finished. The edge part of the flexible layer overlapping the release layer was cut with a knife, and then peeled as a strip with a width of 2 cm to measure its release force (g) as shown in Table 1.

Synthesis of a Polyamic Acid

10.81 g (0.1 mol) of PPD and 5 g (0.025 mol) of ODA were dissolved in 202.72 g of DMAc. 29.42 g (0.1 mol) of BPDA and 5.45 g (0.025 mol) of PMDA were added to the PPD and ODA solution in three batches with intervals of 30 minutes. After the BPDA and PMDA were completely added into the PPD and ODA solution, the mixture was stirred and reacted at room temperature for at least 8 hours to obtain a viscous liquid, wherein the reaction was an exothermal reaction. Thereafter, 1013.6 g of DMAc was added to the reaction and evenly stirred to dilute the viscous liquid. The diluted liquid had a solid content of 4% and a viscosity of 500 cps to 50 cps. The reaction is shown in Formula 8.

Substrate Structure

The diluted polyamic acid solution with a solid content of 4% in Example 10 was coated on a glass carrier to form a wet film with a thickness of 60 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, and 400° C. for half an hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a release layer of a polyimide (P4) on the glass carrier, as shown in Formula 9.

The release layer (P4) was analyzed by TGA with a heating rate of 10° C./min under atmosphere to measure its thermal degradation temperature (Td) of 603.62° C.

The silica/polyamic acid dispersion prepared in Example 3 was coated on the release layer and the glass carrier to form a wet film with a thickness of 400 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, 300° C. for half an hour, and 400° C. for 1 hour, such that the polyamic acid of the wet film was dehydrated and cyclized to form a flexible layer of silica/polyimide (P1+SiO2). As such, a high-temperature resistant substrate structure of the flexible layer (P1+SiO2) covering the release layer (P4) and the glass carrier was finished. The edge part of the flexible layer overlapping the release layer was cut with a knife, and then peeled as a strip with a width of 2 cm to measure its release force (g) as shown in Table 1.

Substrate Structure

30 g of the polyamic acid with a solid content of 15% in Example 4 and 0.18 g of tetraethoxy silane (TEOS) were mixed by mechanical stirring to be evenly dispersed. After the complete reaction, the TEOS/polyamic acid mixture solution was obtained for the flexible layer.

The TEOS/polyamic acid mixture solution was coated on the release layer (P1) and the glass carrier in Example 2 to form a wet film with a thickness of 400 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, 300° C. for half an hour, and 400° C. for 1 hour, such that the polyamic acid of the wet film was dehydrated and cyclized (Formula 5) to form a flexible layer of silica/polyimide (P2+TEOS SiO2). As such, a high-temperature resistant substrate structure of the flexible layer (P2+TEOS SiO2) covering the release layer (P1) and the glass carrier was finished. The edge part of the flexible layer overlapping the release layer was cut with a knife, and then peeled as a strip with a width of 2 cm to measure its release force (g) as shown in Table 2.

Substrate Structure

30 g of the polyamic acid with a solid content of 15% in Example 7 and 0.18 g of γ-glycidoxy propyl trimethoxy silane (Z-6040) were mixed by mechanical stirring to be evenly dispersed. After the complete reaction, the Z-6040/polyamic acid mixture solution was obtained for the flexible layer.

The Z-6040/polyamic acid mixture solution was coated on the release layer (P1) and the glass carrier in Example 2 to form a wet film with a thickness of 400 μm. The wet film was baked at 50° C. for half an hour, 150° C. for half an hour, 210° C. for half an hour, 300° C. for half an hour, and 400° C. for 1 hour, such that the polyamic acid of the wet film was dehydrated and cyclized (Formula 7) to form a flexible layer of silica/polyimide (P3+TEOS SiO2). As such, a high-temperature resistant substrate structure of the flexible layer (P3+TEOS SiO2) covering the release layer (P1) and the glass carrier was finished. The edge part of the flexible layer overlapping the release layer was cut with a knife, and then peeled as a strip with a width of 2 cm to measure its release force (g) as shown in Table 2.

TABLE 1Release force (g), and the flexiblelayers thereon were all the P1 + SiO2inRelease layersExample 3P1 in Example 26~10P2 in Example 55~11P3 in Example 87~12P4 in Example 116~12

As shown in Tables 1 and 2, the release layers could be easily taken out by a release force of less than 15 g (width of 2 cm). As a result, the release layers P1, P2, P3, and P4 had effects, respectively. The release layer P1 worked for different substrate materials, and the release results were similar for the different substrate materials.

It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed methods and materials. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.