Reusable source substrate for patterning and transfer of functional organic layers to multilayer optoelectronic devices

Abstract

The present invention relates to a method of developing a source substrate 116 usable for rapid sublimation of organic thin film 120 The source substrate 116 design plays a major role for fabrication of an optoelectronic device through an alternative mechanism called rapid sublimation process by selectively patterning and precisely transferring the patterned functional organic layer 120. The source substrate 116 with two adjacent thin film regions, with the first region 102 having optically reflecting material as the first material set and the second region 104 having optically absorbing material as the second material set. The method comprises uniformly depositing a first material set 102 over an entire surface of a base layer 106. The first material set 102 is selectively removed from first pre-defined locations of the base layer 106 to obtain a first deposition pattern of the first material set 102. A second material set 104 is uniformly deposited over the entire surface of the base layer 106 having the first material set 102 deposited in the first deposition pattern. Further, the second material set 104 deposited over the first material set 102 is selectively removed and the second material set 104 deposited at the first predefined locations is left, thereby obtaining the source substrate 116.

Description

[0001] REUSABLE SOURCE SUBSTRATE FOR PATTERNING AND TRANSFER OF FUNCTIONAL ORGANIC LAYERS TO MULTILAYER OPTOELECTRONIC DEVICES

[0002] FIELD OF INVENTION

[0003] The present invention relates to the development of a reusable source substrate for patterning and transfer of a uniformly coated functional organic layers for use in the multilayer optoelectronic devices.

[0004] BACKGROUND

[0005] Usage of organic electronic devices, such as Organic Light-Emitting Diodes (OLEDs), Organic Solar Cell (OSC), and Organic Field-Effect Transistor (OFET) has rapidly increased in recent times. Organic electronic devices are made of organic materials, such as Tris (8-hydroxyquinoline) aluminium, Polyfluorene, and Triphenylamine. Organic materials are stacked in several layers, such as a Hole Injection Layer (HIL), a Hole Transport Layer (HTL), an Electron Blocking Layer (EBL), an Emissive Layer (EML), a Hole blocking layer (HBL), an Electron Transport Layer (ETL) and an Electron Injection Layer (EIL). One or more of these layers are stacked between an anode and a cathode.

[0006] Conventionally, layers of the organic electronic devices are developed using a Vacuum Thermal Evaporation (VTE) technique as shown in Fig.9. In VTE technique, a vacuum chamber 118 is utilized for depositing a thin film 120 of an organic material 122 on a product substrate 300. The deposition is made by heating the organic material 122 placed in a crucible below the product substrate 300 inside the vacuum chamber 118. Vacuum sublimation of organic molecules from a point source onto a Low Temperature Polysilicon Thin-film Transistor (LTPS-TFT) deposited substrate using fine metal mask is the most standard technique for making commercial OLED displays for mobile phone applications. Using the proper colour patterning technique, the organic elements that make up the emission layer are created at each target pixel location on the display substrate for either the RGB or RGBW designs. One of the layers that makes up each type of color pixel's OLED device construction is the emission layer. There are two vacuum-compatible patterning techniques that are frequently used in the production of commercial OLED displays. For color patterning in RGB OLED displays, an accurate physical shadow mask known as the fine metal mask (FMM) is used. The FMM has openings that match the OLED display substrate intended color pixel patterns. Before being exposed to the path of the subliming organic materials, with the FMM, which is situated in the path of the subliming emission layer materials, the display substrate is aligned closely with the FMM accurately in a vacuum environment. Organic layers for each colour such as blue, green and red are deposited on ETPS-TFT substrate using FMM in sequence. To produce patterns of RGB emission layers on the display substrate, the FMM patterning process is applied repeatedly for each of the RGB colors on each display substrate. Even though the FMM technique has many advantages, still it has own limitations in mask preparation, mask alignment accuracy of < 5 um, color accuracy, mask sagging when scaled to larger substrate sizes (> Gen 6.5) - might not be able to keep up with the growing demand for higher resolutions in either the smaller mobile displays or the larger television displays. RGBW OEED displays do not employ the FMM patterning technique. Instead, the OEED devices are produced on the display substrate before the color patterning stage is completed using color filter elements that are integrated with the substrate. Behind the color filter elements, which are intended to produce the RGB primary colors, a continually created vacuum-deposited white OEED device structure with a broad emission spectrum is formed. As mentioned above, a fourth white or W pixel was added to the display substrate design in addition to the color filter elements for R, G, and B pixels. The W pixel is unfiltered and can let in the whole range of white OLED emission. By leveraging conventional design principles used in the display substrate industry, the RGBW patterning method enables the scaling of full color OLED displays to bigger television panels while removing the challenges associated with the FMM patterning process in a vacuum environment. However, adding color filter elements to the display substrate increases the number of processes that must be processed during production, which raises the cost of production. The RGBW patterning method can be used for smaller mobile displays just as well, however adding a fourth W pixel would lower the resolution, making it an inadequate solution for the majority of these applications. In conclusion, there are drawbacks to using both RGB and RGBW OLED displays and their patterning techniques for a wide range of display applications. So, a robust and scalable colour patterning method is highly required for commercial OLED display manufacturing.

[0007] A variety of U.S. patents, including Nos. 5,851,709, 5,688,551, 6,114,088, 6,140,009, 6,214,520, and 6,221,553, describe alternative OLED patterning methods that do not require either the FMM or the RGBW patterning methods. These alternative patterning approaches transfer organic components that have been evenly deposited on a source substrate to the display substrate using a procedure known as selective transfer. By adding a patterned light-to-heat conversion (LHC) layer to the source substrate beneath the organic materials and then selectively heating these LHC layers with an intense radiation source, the selective transfer is made possible. This causes the organic materials from the heated LHC areas to be transferred selectively, either as a single material layer or a multicomponent material layer. These referenced prior art sources have one or more of the following drawbacks. For instance, the technique described in U.S. Pat. No. 5,851,709 may involve combining patterned LHC layers on the same source substrate with a source substrate having physical apertures that replicate the color pixel pattern of the targeted display substrate. The silicon, glass, or ceramic substrates are just a few examples of the source substrates mentioned in this reference. This patterning method is fundamentally more complicated than the FMM method discussed in a previous section since it requires the incorporation of precise apertures on any of these substrates, which is an expensive operation, involves complicated fabrication methods, and has size limitations. Finally, direct selective transfers from relevant LHC regions of the source substrate are used to create the OLED color pixel's emission layer, which is then created on the display substrate. For instance, the technique described in U.S. Pat. No. 5,688, 551 may involve using an integrated source substrate that includes a donor sheet with pre -patterned LHC layers and is evenly covered in an organic emission layer material. The display substrate is aligned and close to the integrated source substrate. After alignment, the source substrate is exposed to a powerful source of radiation, which causes the emission layers from the LHC regions of the source substrate to be sublimated selectively to the desired pixel locations on the display substrate. The production of OLED displays is made more difficult by the addition of donor sheets for each color inside a vacuum environment. Once more, the final OLED color pixel's emission layer is created directly from comparable LHC regions of the source substrate. The techniques described in U.S. Pat. Nos. 6,114, 088, 6,140,009, 6,214,520, and 6,221,553 may offer a number of ways to use an integrated source substrate with uniform LHC layers inserted between the substrate and a multicomponent organic layer unit. At least two active OLED device layers are included in the aforementioned multicomponent unit. By subjecting the source substrate to intense radiation in a pattern that corresponds to the color pixel target locations on a display substrate, the full multicomponent unit is selectively transferred. As before, the one or more active layers of the OLED device that are generated at the color pixel location on the display substrate are created through selective transfers from the relevant LHC regions of the integrated source substrate. This technology also adds extra complexity to the manufacturing process because it calls for the inclusion of a radiation source that can write at display pixel resolution, like a laser.

[0008] Laser Induced Thermal Imaging (LITI) is a high resolution, digital patterning method that has a wide range of potential uses, including the patterning of digital color proofs, plates, and film; LCD color filters, black matrix, and spacers; field emission display (FED) anodes, contrast enhancement filters, and nanoemitters; organic field effect transistor (OFET) fabrication; and OLED emitters, color filters, and color conversion filters. In addition to solution- and vacuum-processable OLED material sets, LITI is a developing technology for high-resolution patterning of materials. (2005 Lamansky et al) The basic steps of the LITI process include depositing the material to be patterned (transfer material) onto a specially created donor film, precisely optically aligning a large format laser imaging system to device substrate fiducials, laminating the donor onto the substrate, and patterning the transfer material onto the substrate by selectively exposing the donortransfer material-receptor stack to laser radiation. In a light-to-heat conversion (LTHC) layer or layers, laser radiation is converted to heat. Carbon black is frequently used in these layers as a black body absorber. Optical alignment must be done just once; however, lamination and exposure must be done for at least two colours in order to produce a patterned RGB OLED display. LITI is a single step direct laser patterning technique in which the possibility of organic material residues on the substrate will affect the transfer process but we are proposing a pre-defined patterned source substrate design for a two- step rapid sublimation technique which is capable of patterning and transferring the functional organic layer.

[0009] Adding to the above-mentioned patterning techniques, there are several patents that focus on a maskless technique for patterning the pixels in OLED fabrication. In order to address the above-mentioned shortcomings, it is required to develop a mechanism for deposition of an organic material 122 precisely over a product substrate 300.

[0010] The U.S. Pat. No. 2015 / 0287956 describes a method for patterning an organic device by utilizing a patterned product substrate and a pre-defined patterned source substrate. A product primary surface with destination regions is present on the product substrate. A source main surface on the source substrate has optically reflecting and absorbing regions next to one another. The source primary surface has numerous source areas that are located at the reflecting regions. Organic components are spread out across the numerous source regions. As a result of the alignment of the product principal surface and the source principal surface, each of the numerous source regions is lined up with precisely one destination region. To maintain a relatively consistent distance between them, at least one of the source principal surfaces and the product principal surface has support(s). In order to redeposit in a nearby destination region, the temperature of the source substrate is then elevated above the temperature at which organic compounds sublimate.

[0011] In the U.S. Pat. No. 2015 / 0287956 which is mentioned before, a pre-defined patterned source substrate having optically reflecting and optically absorbing regions are formed for selective patterning of the functional organic layer in which heat energy from the optical irradiation source is used for first step of patterning the source substrate whereas in the second step of transfer, the heat energy transferred from the absorber to the reflector regions is used to evaporate the patterned organic materials from the source substrate to the product substrate. In the proposed invention, two adjacent regions of thin film materials having distinctly dissimilar thermal and optical properties and area wise distributed to form optically absorbing region and optically reflecting region, as per the requirements of the multilayer optoelectronic device, in order to selectively pattern or transfer the said functional organic layer in a two-step rapid sublimation technique. The optically reflecting region is chosen in such a way that it is not completely a reflecting layer as it has also an absorbing property which is lesser than the optically absorbing region. An optical irradiation source is used to pattern the source substrate in the first step by evaporating the organic materials from the optically absorbing region and the patterned organic materials are transferred to the product substrate using the heat transferred from the optical irradiation source in the second step where the power density in the second step is much higher when compared to that in the first step as the absorbing property of the reflecting region is lesser than the absorbing region.

[0012] OBJECTS OF THE INVENTION

[0013] A general objective of the present invention is to develop a reusable source substrate for use in the fabrication of an optoelectronic device. Another objective of the present invention is to select an optically absorbing and optically reflecting material combination in order to create two adjacent regions of thin films on the source substrate.

[0014] Yet another objective of the present invention is to pattern and transfer the uniformly coated functional organic layer into micron features of variable sizes and shapes through an alternative method of rapid sublimation process.

[0015] Still another objective of the present invention is to pattern and transfer the uniformly coated emissive layer onto an already organic material coated product substrate through rapid sublimation process which is one of the layers of a multilayer optoelectronic device.

[0016] Further another objective of the present invention is to develop a source substrate having a long-life cycle.

[0017] SUMMARY OF THE INVENTION

[0018] The summary is provided to introduce aspects related to a source substrate usable for sublimation of organic materials, and the aspects are further described below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter nor is it intended for use in determining or limiting the scope of the claimed subject matter.

[0019] The present invention provides a method of developing a source substrate 116 usable for rapid sublimation of organic thin film is disclosed. The source substrate 116 design plays a major role for fabrication of an optoelectronic device through an alternative mechanism called rapid sublimation process. The source substrate 116 with two adjacent thin film regions, with the first region having optically reflecting material 102 as the first set of materials and the second region having optically absorbing material 104 as the second set of materials. The method comprises uniformly depositing the first set of materials over an entire surface of a base layer 106. The first set of materials are selectively removed from first pre-defined locations of the base layer 106 to obtain a first deposition pattern of the first set of materials. Further, the second set of materials are uniformly deposited over the entire surface of the base layer 106 having the first set of materials deposited in the first deposition pattern. Further, the second set of materials deposited over the first set of materials are selectively removed and the second set of materials deposited at the first predefined locations is left, thereby obtaining the source substrate 116.

[0020] A method for forming a source substrate for patterning and transfer of a uniformly coated functional organic layer is described. The method comprises selecting a substrate. The substrate includes a base material which is substantially transparent to incident light of an optical irradiation source. The substrate further includes and a thin film material set having two adjacent regions with distinctly dissimilar thermal and optical properties and area wise distribution as per the requirements of the multilayer optoelectronic device, in order to selectively pattern or transfer the functional organic layer. The two adjacent regions have optically absorbing and optically reflecting properties. A first region is an optically reflecting region and a second region is an optically absorbing region. The functional organic layer comprises one of the layers of a multilayer optoelectronic device. The method further comprises exposing the substrate to an optical irradiation source to raise temperature of the optically absorbing region above sublimation temperature of the functional organic layer to result in a patterned source substrate.

[0021] In one aspect, the distinctly dissimilar thermal properties of the two adjacent regions are specific heat capacity, thermal conductivity, thermal diffusivity, and thermal effusivity. The distinctly dissimilar thermal properties enable co-optimization of the patterning and the transfer of the functional organic layer.

[0022] In one aspect, the optically absorbing region and the optically reflecting region of the source substrate are designed to result in at least a 30°C temperature difference when the source substrate is exposed to the optical irradiation source at substantially same energy density.

[0023] In one aspect, the source substrate comprises a thin film material chosen for use in the optically absorbing region and the optically reflecting region of the source substrate are co-optimized with the optical irradiation source characteristics resulting in an absorption rate of more than 90% and lesser than 55% correspondingly. Thickness of thin films chosen for the optically absorbing region and the optically reflecting region are designed to minimize heat flow between and to maximize temperature difference between regions, and the thin film material set used in the optically absorbing region and the optically reflecting region is capable of getting sublimed at typical sublimation temperatures of the functional organic layer.

[0024] In one aspect, the optically absorbing region of the source substrate comprises a composite layer of one or more metal and metal oxide to result in a higher optical absorption property relative to the second region.

[0025] In one aspect, the optically reflecting region of the source substrate comprises a composite layer of one or more metals and dielectrics to result in a lower optical absorption property relative to the second region.

[0026] In one aspect, the thin film material set used in the optically reflecting region is selected from a group of III to VIII consisting of metals including Aluminium, Titanium, Tungsten, Nickel, and Molybdenum.

[0027] In one aspect, the thin film material set used in the optically absorbing region is selected from a group of III to VIII consisting of metals and metal oxides including Tungsten, Titanium, Molybdenum, Chromium, Tungsten Oxide, Titanium Oxide, Molybdenum Oxide, and Chromium Oxide.

[0028] In one aspect, the optically absorbing region comprises a metal oxide layer being the first layer adjacent to the substrate, and thickness of the metal oxide layer is tuned to maximize constructive interference of light into the second layer.

[0029] In one embodiment, a method for constructing layers of multilayer functional organic layers for an optoelectronic device is described. The method comprises preparing a product (second) substrate to have destination regions corresponding to an optically reflecting region of a source substrate. The product substrate comprises one or more functional layers of an optoelectronic device and have a substantially similar coefficient of thermal expansion (CTE) and geometrical dimensions as the source substrate. The method further comprises precisely aligning the source substrate and the product substrate in close proximity. The method further comprises raising temperature of the optically reflecting region of the source substrate above sublimation temperature of the functional organic layer to result in transfer of the functional organic layer from the source substrate to the product substrate to form one of the functional organic layers for an optoelectronic device. The method further comprises removing the functional organic layer from the source substrate, wherein the source substrate is reused multiple times for patterning and transfer process.

[0030] In one aspect, patterned regions of different shapes and sizes on the source substrate have a mirror symmetry with the destination regions on the product substrate to result in a one- to-one correspondence between the plurality of source regions and destination regions.

[0031] In one aspect, a space between the source substrate and the product substrate during the close proximity is kept in a range of Omm to 1mm to achieve desired dimensions of the patterned functional organic layer during the transfer to the second substrate.

[0032] BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings constitute a part of the description and are used to provide further understanding of the present invention. Such accompanying drawings illustrate the embodiments of the present invention which are used to describe the principles of the present invention. The embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this invention are not necessarily to the same embodiment, and they mean at least one. In the drawings:

[0034] Fig. 1 illustrates a method of development of a source substrate, in accordance with an embodiment of the present invention;

[0035] Fig. 2 illustrates the source substrate having optically absorbing and optically reflecting layer with stacks of metals and metal oxides, in accordance with an embodiment of the present invention;

[0036] Fig. 3 illustrates the first substrate design having two regions, in accordance with an embodiment of the present invention; Fig. 4 illustrates the simulation data for the first substrate design, in accordance with an embodiment of the present invention;

[0037] Fig. 5 illustrates the second substrate design having two regions, in accordance with an embodiment of the present invention;

[0038] Fig. 6 illustrates the simulation data for the second substrate design, in accordance with an embodiment of the present invention;

[0039] Fig. 7 illustrates the absorptance data for first reflector configuration, in accordance with an embodiment of the present invention;

[0040] Fig. 8 illustrates the absorptance data for second reflector configuration, in accordance with an embodiment of the present invention;

[0041] Fig. 9 illustrates deposition of a functional organic layer over the source substrate, in accordance with an embodiment of the present invention;

[0042] Fig. 10 illustrates a cross-sectional view of a source substrate with the deposited functional organic layer, in accordance with an embodiment of the present invention;

[0043] Fig. 11 illustrates various micron feature sizes and shapes capable of patterning on the source substrate, in accordance with an embodiment of the present invention;

[0044] Fig. 12 illustrates patterning process of a uniformly coated functional organic layer on the source substrate, in accordance with an embodiment of the present invention;

[0045] Fig. 13 illustrates the patterning and transfer of fine features of variable dimensions using two-step rapid sublimation process, in accordance with an embodiment of the present invention; Fig. 14 illustrates transfer process of a patterned functional organic layer to the product substrate for use in the multilayer optoelectronic device, in accordance with an embodiment of the present invention; and

[0046] Fig. 15 illustrates cross-sectional view of product substrate, in accordance with an embodiment of the present invention.

[0047] DETAILED DESCRIPTION OF THE INVENTION

[0048] The detailed description set forth below in connection with the appended drawings is intended as a description of various embodiments of the present invention and is not intended to represent the only embodiments in which the present invention may be practiced. Each embodiment described in this disclosure is provided merely as an example or illustration of the present invention, and should not necessarily be construed as preferred or advantageous over other embodiments. The detailed description includes specific details for the purpose of providing a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific details.

[0049] The present invention discloses the development of a reusable source substrate 116 for use in the fabrication of an optoelectronic device. Two key tasks focused during the design of the source substrate 116 are (i) patterning of the deposited functional organic layer 120 (ii) transfer of the patterned functional organic thin film 120. Both the patterning and the transfer process is achieved through rapid sublimation of organic materials 122 by using an optical irradiation source. In order to selectively pattern and transfer the coated functional organic layers 120, it is critical to choose two adjacent thin film material sets having distinctly dissimilar thermal and optical properties to form first region 102 and second region 104 material sets. Thickness of the second region 104 may be higher than the first region 102. Fig. 1 illustrates process flow for fabricating a source substrate 116, in accordance with an embodiment of the present invention. The source substrate 116 comprises the base layer 106 over which the first set of materials 102 and the second set of materials 104 are present. The first set of materials 102 are present at first pre-defined locations of the base layer 106 and the second set of materials 104 are present at second pre-defined locations of the base layer 106. In an implementation, the first set of materials 102 and the second material sets 104 are area wise distributed on the source substrate 116 without any gaps in between them in order to avoid the optical illumination source from directly falling on the base layer 106. The first set of materials 102 deposited in a first deposition pattern over the base layer 106 may result in formation of optically reflecting regions. Similarly, the second material set 104 deposited in a second deposition pattern over the base layer 106 may result in formation of optically absorbing regions 102.

[0050] In an implementation, the source substrate 116 may be a substantially optically transparent material, such as glass. The source substrate 116 may comprise a plurality of optically reflecting regions 102 and a plurality of optically absorbing regions 104 in a pre-defined arrangement on a surface of the source substrate 116. The plurality of optically reflecting regions 102 may have low light absorbing properties i.e. less than 55% at the wavelength of the optical irradiance source while the plurality of optically absorbing regions 104 may have high light absorbing properties >80%. The plurality of optically reflecting regions 102 and the plurality of optically absorbing regions 104 may be present in a pre-defined arrangement in accordance with a pattern for deposition of an organic thin film 120. The plurality of optically reflecting regions 102 and the plurality of optically absorbing regions 104 may be of variable dimensions and shapes.

[0051] In accordance with the embodiment of the present invention, in order to fabricate an optoelectronic device using a rapid sublimation process, two major process steps; involving patterning and transfer of the deposited functional organic layer 120 are required to be co-optimized in accordance to the optical irradiation source energy density.

[0052] In order to selectively pattern and precisely transfer the functional organic layer 120, differential thermal properties including specific heat capacity, thermal diffusivity and thermal effusivity are taken into consideration while choosing the first and second region material set. The optically absorbing region 104 and the optically reflecting region 102 of the source substrate 116 are designed to result in at least a 30°C temperature difference when the source substrate 116 is exposed to the optical irradiation source 308, 314 at substantially the same energy density. The optically reflecting region 102 of the source substrate 116 are co-optimized with the optical irradiation source 314 characteristics resulting in an absorption rate of more than 90% and lesser than 55 % correspondingly. The thickness of thin films chosen for the optically absorbing 104 and the optically reflecting 102 regions are designed to minimize the heat flow between the regions and to maximize the temperature difference between them. The thin film material set used in the optically absorbing region 104 and optically reflecting region 102 should be capable to sublime at the typical sublimation temperatures of the said functional organic layers 120.

[0053] In the first step, the selective patterning of the functional organic layer 120 is achievable only by precisely choosing an optically absorbing layer 104 in the second region. The second region containing an optically absorbing layer 104 of the source substrate 116 may comprise of a composite layer of one or more metal and metal oxide to result in a higher optical absorption property relative to the first region. The thin film material set for the optically absorbing region 104 is selected from the metals and its oxides which belongs to groups of III to VIII of periodic tables such as Tungsten, Titanium, Molybdenum, Chromium, Tungsten Oxide, Titanium Oxide, Molybdenum Oxide, Chromium Oxide etc. The combination of metal and metal oxides may be selected based on their refractive index (n) and absorption coefficient (k). In an embodiment, as shown in Fig. 2, the optically absorbing layer 104 is formed by stacking a metal oxide 204 and a metal layer 202 on the glass substrate 212. In an example for designing an optically absorbing region 104, consisting the first layer Ml, 204 an oxide of M2 belongs to the group VI having an absorption coefficient of 1.33 x 10A6 mA-l, at the wavelength of optical irradiance source with the thickness in the range of 80-270 nm is deposited on a base layer 106. A second metal layer 202, M2 of same group having refractive index of 3.21 with thickness in the range of 75-100 nm is deposited over the Ml 204 layer. The thickness of the metal oxide layer 204 is tuned to maximize the constructive interference of light into the second layer which is the metal absorbing layer 202.

[0054] In the second step, precise transfer of the patterned functional organic layer 120 is achievable only by methodically choosing an optically reflecting layer 102 in the first region. The first region containing an optically reflecting layer 102 of the source substrate 116 may comprise of a composite layer of one or more metals from group of III to VIII of the periodic table and one or more metals and dielectrics to result in a lower optical absorption property <55%, relative to the second region 104. The thin film material set for the optically reflecting region 102 are selected from the group of metals ranging III to VIII such as Aluminium, Titanium, Tungsten, Nickel, Molybdenum. In an embodiment, as shown in Fig. 2, the optically reflecting layer 102 is formed by stacking metal layers, M3, M4 and M5 210, 208, 206 on the glass substrate 212.

[0055] In order to select optically reflecting layer 102 in the first region, it was required to conduct simulation trials with the help of COMSOL Multiphysics software by varying the material stacks and thickness. Combination of metals from groups III to VIII are chosen for forming the optically reflecting region 102. In Fig.3, it is seen that the optically reflecting layer is formed by stacking the metals M3 210 and M4 208 in which M3 is deposited adjacent to the glass substrate 212 and M4 208 is deposited above M3 210 layer. Both the metals M3 210 and M4 208 are having the thickness in the range of 40 - 100 nm and the refractive index of M3, n= 3.32 and M4, n=1.76 at the wavelength of optical irradiance source 314. First substrate design simulation trial is conducted by stacking the metal having high refractive index, M3 210 adjacent to the glass substrate and the metal having low refractive index, M4 208 above the M3 layer. In Fig. 4, the transient analysis of the temperature difference between the absorber 104 and the reflector regions 102 are shown by selecting the reflector stack as M3-M4. The trial has been done with the optical irradiation source for a scan speed of 4mm / s. The absorber and reflector areas are marked at various points indicating -w / 2, -w / 4, 0, w / 4 and w / 2 in order to identify the temperature at various areas for both the regions. For a scan speed of 4 mm / s, it is found that when an optical irradiation source is passed across the substrate surface, the maximum temperature obtained at the centre of the absorber area (-w / 4) is ~ 170°C and the temperature obtained at the centre of the reflector area (w / 4) is ~ 120°C. This indicates the feasibility of chosen material set to act as an absorber and reflector region for patterning and the transfer process of the functional organic layer 120. It is understood that for patterning fine features of various sizes ranging from 5 um - 80 urns, it is beneficial to have high temperature difference between the optically absorbing and optically reflecting layer.

[0056] In another embodiment, as shown in Fig. 5, an example of the second substrate design was tried by modifying the reflector layer by interchanging the order of the metal stack to form M4-M3 with the M4 208 layer adjacent to the glass substrate 212 and M3 210 layer is deposited above the M4 layer 208. It is believed that the metal combination with the low refractive index layer adjacent to the glass substrate 212 and high refractive index layer deposited above it forms a reflector layer which can reduce the absorption by 20-30% thereby helps to widen the process window for the patterning process of the functional organic layer 120.

[0057] Further, in accordance with the present embodiment, simulation trials have been conducted for the second substrate design using COMSOL Multiphysics software and found that the temperature difference between the absorber and reflector regions has increased to more than 100°C when compared to the temperature difference between the regions for the first substrate design. In Fig. 6, the transient analysis of the temperature difference between the absorber and the reflector regions for the second substrate design is shown. The trials have been done by using an optical irradiation source with a scan speed of 4 mm / s. The absorber and reflector areas are marked at various points indicating -w / 2, - w / 4, 0, w / 4 and w / 2 in order to identify the temperature at various areas for both the regions. For a scan speed of 4 mm / s, it is found that when an optical irradiation source is passed across the substrate surface, the maximum temperature obtained at the centre of the absorber area (-w / 4) is ~ 170°C and the temperature obtained at the centre of the reflector area (w / 4) is ~ 50°C. The obtained temperature difference between the optically absorbing and the reflecting region is >100°C. This indicates that by modifying the reflector stack in the second substrate design further facilitates to increase the temperature difference between the absorber and the reflector regions for a particular wavelength of operation. This indicates that reflector design with respect to the absorber can be fine-tuned by selecting appropriate material set of construction.

[0058] In an example for designing an optically reflecting layer 102, two metal layers, M3 and M4 are selected and deposited on the glass substrate with the thickness in the range of 40 - 100 nm. The metals are chosen in such a way that one of them have high refractive index and the other one has low refractive index. The refractive index of M3 and M4 at a chosen wavelength of the optical irradiation source is 3.32 and 1.76 correspondingly. Two configurations have been considered to design the optically reflecting layer. The first configuration as shown in Fig. 3 with the high refractive index metal, M3 is deposited adjacent to the glass substrate and low refractive index metal, M4 is deposited above the high refractive index metal. The second configuration as shown in Fig. 5 were the low refractive index metal, M4 is deposited adjacent to the glass substrate and high refractive index metal, M3 is deposited above the low refractive index metal. In order to ascertain the appropriate selection of materials at the first and second regions, an absorption measurement was done using an UV-Vis-NIR spectroscopy on both the regions. In an implementation as shown in Fig. 7 and Fig. 8, it is evident that the absorptance of light is calculated in percentage with respect to a range of wavelength. It is important to compare the percentage of absorptance achieved for both the regions at the wavelength of operation of the optical irradiation source. For the first configuration, the absorption data as shown in Fig.7, it is found that the absorption at the chosen wavelength of the optical irradiation source for the second region (202, 204) is 96.95% and that for the first region (208, 210) is 58.88%. From the absorption data, it is very well clear that the selected absorber and reflector material combinations are good choices for patterning and transfer of the deposited functional organic layer 120 as they have a considerable difference in the absorption at the desired wavelength of the optical irradiation source. In order to obtain high accuracy patterning of fine features of variable sizes and shapes, it is better to have high difference in the absorption between the absorber and the reflector layer as it provides a wide window for the patterning process optimizations. Hence, the second configuration was designed by modifying the reflector layer stack for reducing the absorption thereby helping in tuning the fine feature patterning. The reflector stack is modified in such a way that the low refractive index material, M4 is deposited adjacent to the glass substrate and high refractive index material, M3 is deposited above M4 layer.

[0059] In an implementation as shown in Fig. 8, the absorption results for the second configuration of optically reflecting layer design were measured using a UV-Vis-NIR spectroscopy. It is found that the absorptance at the chosen wavelength of the optical irradiation source for the second region is 96.91% and that for the first region is 31.49%. From the absorption data it is clear that the absorption of light in the reflector region (208, 210) has reduced by -30% when compared to the absorption data obtained for the first configuration reflector design. This indirectly helps to widen the process window by allowing to run various process conditions which will be beneficial for the patterning of fine features of functional organic layer having various sizes and shapes. Multiple metal stack with varying thickness can be designed to lower optical absorption property relative to the second region 104. The optically absorbing and the optically reflecting materials are deposited over the base layer 106 through sputtering or vapour deposition process. The source substrate 116 obtained through the above-described method may be utilized for selective sublimation of an organic material for fabrication of an optoelectronic device, such as Organic Light-Emitting Diodes (OLEDs), Organic Solar Cells (OSC), and Organic Field-Effect Transistor (OFET).

[0060] Fig. 9 Illustrates the formation of a functional organic layer 120 on the entire source substrate 116, in accordance with the embodiment of the present invention. For deposition of the functional organic layer 120 on a source substrate 116, a chamber 118 may be maintained at vacuum condition containing a crucible for loading the organic materials 122. The source organic material 122 may be deposited over the source substrate 116 by VTE process to form an organic thin film 120. The source organic thin film 120 may cover both the plurality of optically reflecting regions 102 and the plurality of optically absorbing regions 104. The source organic material 122 may be an optically emissive material like a host material, a co-host material, or a dopant material. The source organic materials 122 may be selected from a group consisting of fluorescent, phosphorescent, and thermally activated delayed fluorescence emissive materials.

[0061] Fig. 10 Illustrates a cross-sectional view of a source substrate 116 with the functional organic layer 120 deposited uniformly over the entire substrate surface, in accordance with the embodiment of the present invention.

[0062] The predefined source substrate 116 has an alternative objective to pattern the micro features of variable sizes and shapes as shown in Fig. 11, in accordance with the embodiment of the present invention. It is critical to precisely pattern the micron features of sizes ranging from 5ums to 80 urns by optimizing the optical irradiation source energy density. The optically reflecting region 102 of the source substrate 116 is designed in various shapes and sizes of squares and diamonds to study the distribution of heat across the feature areas which is essential for tuning the parameters for the precise patterning. Fig. 11 shows the top view of the source substrate 116 containing a base layer 106 with feature areas of various sizes and shapes which are shaded in black colour indicating optically reflecting regions 102 and the empty areas of optically absorbing regions 104.

[0063] In order to fabricate an optoelectronic device using a rapid sublimation process, two major process steps are required to be co-optimized in accordance to the optical irradiation source energy density. Fig. 12 Illustrates a process flow for patterning one of the functional organic layers 120 through a rapid sublimation process, which is deposited by a VTE technique for developing an optoelectronic device, in accordance with an embodiment of the present invention. In the first step, in order to form a pre-defined pattern on the source substrate 116, a capture substrate 312 may be aligned below the source substrate 116 in a first high vacuum chamber. The capture substrate 312 may be used to recover the source organic material from the source substrate 116. Distance between the source substrate 116 and the capture substrate 312 may be minimized to prevent spreading of the source organic material. In an implementation, the distance between the source substrate 116 and the capture substrate 312 may be maintained to be less than 4mm for the patterning step of an organic thin film 120. A first optical irradiation source 308 may be illuminated over an entire substrate area of the source substrate 116 for selective removal of the source organic thin film 120 from the plurality of optically absorbing regions 104 for transferring the organic thin film 120 to the capture substrate 312. Energy density of the first optical irradiation source 308 may be controlled to sublime the organic thin film 120 on the capture substrate 312. The source substrate 116 may retain the source organic thin film 120 over the plurality of optically reflecting regions 102, thereby obtaining a pre-defined pattern (Fig.l3a) over the source substrate 116.

[0064] The pre-defined patterned source substrate 116 has been employed for two prime requisites 1. fine feature transfer to a receiver substrate 2. fabrication of optoelectronic device using a product substrate. In order to transfer the patterned organic thin film (Fig.l3a) containing fine features of various sizes from the prepatterned source substrate to a receiver / product substrate, two major requirements are taken into account; 1. Precise control of the gap between the source substrate and the receiver / product substrate by adjusting the substrate stage 2. To maintain a mirror symmetry of the features after the transfer to the receiver / product substrate without any distortion. In order to transfer the emissive layer containing fine features of various sizes and shapes, it is important to arrange the source substrate and the receiver substrate with the minimum gap between them. Fig. 13(b), in accordance with the present invention, shows the features of varying sizes and shapes ranging from 10 um - 70 urns after the transfer process. Various process conditions are tuned to obtain the features of high precision. The power of the optical irradiation source, scan speed and distance between the substrates play a major role to result in an accurate patterning and transfer of the deposited functional organic layer 120. Further optimizations are possible to achieve higher precision fine features by designing the source substrate with various material combinations.

[0065] In addition to the above conditions, for fabrication of an optoelectronic device, it is necessary to align the patterned source substrate and the product substrate 300 prior to the transfer process. Fig.14 Illustrates the second step, a second chamber maintained at a low pressure or vacuum condition, the source substrate 116 with the pre-defined pattern may be aligned in parallel with product substrate 300 such that the patterning is overlapped with a destination region on the product substrate 300. The destination region may be formed on a product principal surface of the product substrate 300 by patterning any metal oxide layer that may as an anode region 304. In case of fabrication of an optoelectronic device, the organic layers 302 such as hole injection layer and hole transport layer are deposited on the product principal surface using a shadow mask using a conventional VTE process step. After alignment, the source substrate 116 and the product substrate 300 may be placed over each other in a sample holder. A distance between the source substrate 116 and the product substrate 300 may be minimized to allow precise transfer of the source organic thin film 120 from the source substrate 116 onto the destination region of the product substrate 300. For an example, the distance between the source substrate 116 and the product substrate 300 may be maintained to be less than 1 mm.

[0066] To transfer the source organic thin film 120 from the source substrate 116 onto the destination region of the product substrate 300, temperature may be raised at a location of optically reflecting regions 102 in the plurality of optically absorbing regions 104. The temperature may be raised using a second optical irradiation source 314. The second optical irradiation source 314 may be moved over entire substrate area of the source substrate 116, at a fast pace, for complete removal of the source organic thin film 120 from the plurality of optically reflecting regions 102. Raising the temperature above the sublimation temperature of the source organic thin film 120, the said thin film 120 gets completely transferred to the product substrate 300 by rapid transfer process.

[0067] The first optical irradiation source 308 and the second optical irradiation source 314 may be one of an incandescence lamp, an photoluminescence lamp, a photonic light lamp, and a Light Amplification by Stimulated Emission of Radiation (LASER). In another implementation, the first optical irradiation source 308 and the second optical irradiation source 314 may include one or more optical irradiation heads to cover entire area of the pre-defined source substrate 114. Energy density of first optical irradiation source 308 and the second optical irradiation source 314 required to remove the source organic thin film 120 may vary as less energy may be required for patterning from the optically absorbing regions 104 when compared to the transfer step from the optically reflecting regions 102. Energy density of the first optical irradiation source 308 and the second optical irradiation source 314 may be controlled by suitable process parameters.

[0068] The present invention provides development of a source substrate usable for selective sublimation of organic materials to fabricate an optoelectronic device. The source substrate has a long-life cycle as compared to conventional shadow masks which is utilized for fabrication of optoelectronic devices. In addition, usage of the source substrate significantly reduces processing time, minimizes wastage of organic materials, reduces overall cost of fabrication, and enhances quality of the optoelectronic device.

[0069] During the second step for transfer of the functional organic layer 120, the patterned functional organic layer 120 is transferred from the optically reflecting region 102 of source substrate 116 to the pre-defined product substrate 300, which is already coated with organic layers 302 of hole injection and hole transporting layers as shown in Fig. 15, in accordance with the embodiment of the present invention. The product substrate 300 consists of a transparent base layer 306 with patterned Indium Tin Oxide which act as an anode region 304 in an optoelectronic device. The destination regions on the product substrate 300 have a mirror symmetry with the source substrate 116 to result in a one-to- one correspondence between the plurality of source regions and destination regions.

[0070] In view of the present disclosure, which describes the present invention, all changes, modifications and variations within the meaning and range of equivalency are considered within the scope and spirit of the invention. It is to be understood that the aspects and embodiment of the disclosure described above may be used in any combination with each other. Several of the aspects and embodiment may be combined together to form a further embodiment of the disclosure.

Claims

WE CLAIM:

1. A method for forming a source substrate (116) for patterning and transfer of a uniformly coated functional organic layer (120), the method comprising: selecting a substrate (106) comprising: a base material which is substantially transparent to incident light of an optical irradiation source (308, 314); and a thin film material set having two adjacent regions with distinctly dissimilar thermal and optical properties and area wise distribution as per the requirements of the multilayer optoelectronic device, in order to selectively pattern or transfer the functional organic layer (120), wherein the two adjacent regions have optically absorbing (104) and optically reflecting (102) properties, wherein a first region is an optically reflecting region (102) and a second region is an optically absorbing region (104), the functional organic layer (120) comprises one of the layers of a multilayer optoelectronic device; and exposing the substrate (106) to an optical irradiation source (308) to raise temperature of the optically absorbing region (104) above sublimation temperature of the functional organic layer (120) to result in a patterned source substrate.

2. The method as claimed in claim 1, wherein the distinctly dissimilar thermal properties of the two adjacent regions are specific heat capacity, thermal conductivity, thermal diffusivity, and thermal effusivity, and wherein the distinctly dissimilar thermal properties enable co-optimization of the patterning and the transfer of the functional organic layer (120).

3. The method as claimed in claim 1, wherein the optically absorbing region (104) and the optically reflecting region (102) of the source substrate (116) are designed to result in at least a 30°C temperature difference when the source substrate (116) is exposed to the optical irradiation source (308, 314) at substantially same energy density.

4. The method as claimed in claim 1, wherein the source substrate (116) further comprises: a thin film material chosen for use in the optically absorbing region (104) and the optically reflecting region (102) of the source substrate (116) are co-optimized with theoptical irradiation source (308, 314) characteristics resulting in an absorption rate of more than 90% and lesser than 55% correspondingly, wherein thickness of thin films chosen for the optically absorbing region (104) and the optically reflecting region (102) are designed to minimize heat flow between and to maximize temperature difference between regions, and the thin film material set used in the optically absorbing region (104) and the optically reflecting region (102) is capable of getting sublimed at typical sublimation temperatures of the functional organic layer (120).

5. The method as claimed in claim 1, wherein the optically absorbing region (104) of the source substrate (116) comprises a composite layer of one or more metal and metal oxide to result in a higher optical absorption property relative to the first region.

6. The method as claimed in claim 1, wherein the optically reflecting region (102) of the source substrate (116) comprises a composite layer of one or more metals and dielectrics to result in a lower optical absorption property relative to the second region.

7. The method as claimed in claim 1, wherein the thin film material set used in the optically reflecting region (102) is selected from a group of III to VIII consisting of metals including Aluminium, Titanium, Tungsten, Nickel, and Molybdenum.

8. The method as claimed in claim 1, wherein the thin film material set used in the optically absorbing region (104) is selected from a group of III to VIII consisting of metals and metal oxides including Tungsten, Titanium, Molybdenum, Chromium, Tungsten Oxide, Titanium Oxide, Molybdenum Oxide, and Chromium Oxide.

9. The method as claimed in claim 5, wherein the optically absorbing region (104) comprises a metal oxide layer (204) being the first layer adjacent to the substrate (212), and thickness of the metal oxide layer is tuned to maximize constructive interference of light into the second layer.

10. A method for constructing layers of multilayer functional organic layers for an optoelectronic device, the method comprising: preparing a product (second) substrate (300) to have destination regions corresponding to an optically reflecting region (102) of a source substrate (116), whereinthe product substrate (300) comprises one or more functional layers (302) of an optoelectronic device and have a substantially similar coefficient of thermal expansion (CTE) and geometrical dimensions as the source substrate (114); precisely aligning the source substrate (116) and the product substrate (300) in close proximity; raising temperature of the optically reflecting region (102) of the source substrate (116) above sublimation temperature of the functional organic layer (120) to result in transfer of the functional organic layer (120) from the source substrate to the product substrate (300) to form one of the functional organic layers (310) for an optoelectronic device; and removing the functional organic layer (120) from the source substrate (116), wherein the source substrate (116) is reused multiple times for patterning and transfer process.

11. The method as claimed in claim 10, wherein patterned regions of different shapes and sizes on the source substrate (116) have a mirror symmetry with the destination regions on the product substrate (300) to result in a one-to-one correspondence between the plurality of source regions and destination regions.

12. The method as claimed in claim 10, wherein a space between the source substrate (116) and the product substrate (300) during the close proximity is kept in a range of 0mm to 1mm to achieve desired dimensions of the patterned functional organic layer (120) during the transfer to the second substrate (300).

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