The invention and its fundamental properties as well as the advantages to be attained by means of the invention will become more evident for the person skilled in the art from the following description in which the invention will be described in more detail by means of a few selected examples, at the same time referring to the appended drawings, in which
a to 2f show a way of producing a pressing block used in embossing according to the invention,
g shows in principle the copying of a relief into a pressing plate having a large surface area,
a and 5b show, in principle, side and top views of a pixel display based on OLED components implemented according to prior art,
The pressing block suitable for embossing is typically a nickel pressing plate/block that may be manufactured for example by lithographical methods which are known from other contexts of prior art. The most important manufacturing techniques of a pressing plate include direct resist lithography or a combination of the resist lithography and dry etching technique.
a to 2f present, in principle, the process stages where the desired relief of the surface structure is formed on the pressing block required for embossing by performing the patterning of the resist layer, in this case by using an electron beam. It should be noticed that the invention is not limited solely to the use of electron beam embossing, but it is possible to use for example a laser beam in the patterning.
a presents, in principle, the coating of a substrate material 20 (glass, quartz, silicon, etc.) with a resist layer 21 and a conductive layer 22 required for electron beam embossing. The purpose of said conductive layer 22 is to transmit away an electric charge produced by the electron beam used in the embossing.
Furthermore, another alternative method to produce a relief is to utilize a resist structure according to
In view of the present invention, an essential aspect in producing a master element necessary in the manufacture of the pressing block is that the method is capable of replicating certain properties of the pressing block, of which the most important ones include the vertical orientation of the walls of the relief, and the quality of the edges of the relief. Thus, the manufacturing method should be selected so that it is optimal for each separate pattern geometry. Direct laser lithography may be used for line widths of>1.5 μm and line widths smaller than this are typically produced by means of an electron beam. Another essential aspect in view of the invention is the depth of the lines in the relief. It is known that for example the line width of 25 μm and depth 50 μm can be produced with a nearly vertical wall by optimizing the exposure and development process of the resists accurately. However, in most cases it is easier to use the above-described dry etching process by means of which it is possible to produce nearly completely vertical walls.
The nickel pressing block 24 of
By using the above-mentioned lithographic methods, it is possible to produce pattern areas, whose surface areas are with modern production techniques<8″×8″. Larger areas are produced with a recombining method shown in principle in
In copying by hot embossing, the nickel pressing block 24 produced in the afore-mentioned way is positioned onto a metal supporting plate of the size of the pressing block in question, and with it, the pattern is pressed on an appropriate plastic material, for example on PMMA material (polymethyl-methacrylate), with the hot embossing process. By repeating the process several times and at different places of the plastic material, a new master element comprising a larger surface area may thus be produced, from which a pressing block/pressing plate comprising a larger area is electrolytically grown.
It is also possible to perform the combining process by spreading liquid polymer material onto a plastic, glass or quartz substrate comprising a larger surface area, to which material the pattern of the nickel pressing block 24 is pressed. By hardening the polymer locally (for example by heating, with UV light or by using an adequate hardening time), the pattern structure may be produced in said place on top of the substrate. By repeating the process at several different points, a master element having a larger surface area may again be formed, and a pressing plate suitable to be placed around a roll or the like may further be grown from the same.
In the embossing according to the invention, it is preferably possible to use PET as the substrate material, but other possible materials are PI, PS and PC. Of these materials at least PET can be readily obtained on a roll, wherein it is easy to use it in a roll-to-roll process.
For example in OLED components or other optical components, it is possible to use transparent semiconductor oxides, typically ITO as the material of the lowermost electrode structure (anode) formed on top of the substrate. The resistance value of ITO is typically few tens of ohms per square in film thicknesses of several tens of hundreds of nanometers, and in the area of visible light its transmission is typically>75%. It is possible to coat the PET film with an ITO film by means of vacuum growing methods known as such, and between the PET and ITO layers it is possible to use for example a thin silicon dioxide layer (SiO2), which functions as an adhesive layer between said layers. It is also possible to use other protective layers between the aforementioned layers.
Even though the invention is primarily intended for patterning by means of embossing of the lowermost electrode layer formed on top of a substrate, it is naturally possible to implement embossing also in the patterning of the other upper electrode layers for example in the way disclosed in the patent publication US 2002/0094594. When the upper conductive layers of a multilayer structure are patterned by means of embossing, it is possible to use a suitable protective layer underneath the layer to be patterned, the deformation according to the invention being produced in said protective layer, thus enabling the breaking of contacts for the part of the layer to be patterned.
In an embodiment of the invention it is possible to coat the plastic substrate in connection with the same roll-to-roll process first by sputtering in a vacuum a substantially uniform ITO layer having a thickness of for example 100 nm. Thereafter said ITO layer is patterned by means of embossing according to the invention to form an anode electrode. One or more layers of organic material are formed on top of the anode electrode by means of thermal vacuum evaporation. The thickness of these layers may be for example 50 to 200 nm. Further, a metal (for example Mg, Ag or Al) cathode electrode is formed on top of the organic layers. The cathode electrode may be patterned either by means of embossing or by another prior art method. When the lines of the cathode electrode are formed in perpendicular to the lines of the anode electrode, it is possible to control the pixels formed in the crossing of said lines, one at a time, thus forming for example an OLED pixel display. In the final processing of the component, the structure is protected with the necessary protective layers etc., and, if required, it is cut and wired to form finished components.
As to the conductive layers to be patterned, priority is given in this invention to semiconductor oxides, such as ITO. Said materials form a glass-like layer on the substrate, which may be cut by means of embossing according to the invention, said cutting being based on the permanent deformation produced in the substrate material underneath. However, the invention is not restricted solely to electrode layers made of semiconductor oxides, but it is also possible to use metals (such as Al, Au, Ag, Cu) or polymer (such as PEDOT, PSS) as electrode materials in such embodiments where an optical transparency of the electrode layer is not required.
The line widths required in the electrode patterns are in each case determined according to the embodiment to be manufactured. By means of the embossing according to the invention it is for example in the ITO layer possible to attain line widths in the order of 1 μm.
When the substrate material is plastic, the embossing takes place in temperatures that slightly exceed the glass transition temperature of plastic, in which temperature, at the so-called glass transition point, the properties of plastic are changed from a glassy state to a rubbery state. However, in these temperatures the ITO layer on top of the plastic substrate is not softened, which is a prerequisite for reliable cutting of said layer along accurately defined lines by embossing. Suitable temperature of the substrate in which the substrate is in such a state in which a permanent deformation is attained by embossing, may be arranged either by pre-heating the substrate before embossing and/or using a heated pressing block or plate for the embossing. It is an advantage of the heated machining member that thus the heating is temporarily directed only to the part of the substrate to be machined, and it is not necessary to heat the entire substrate material.
As was mentioned above, the pressing block or plate is preferably manufactured to have a nickel surface. It is a challenging task to produce a relief with as straight walls and sharp cuffing edges as possible, but it may be attained for example by means of the above-described technique based on electron beam patterning and dry etching. It is also advantageous to manufacture the pressing block for example in silicon by etching the material in the direction of the crystal.
In the following, the invention will be described in more detail by using the manufacture of OLEDs and OFETs as specific examples. These examples clearly show for anyone skilled in the art, among other things, how it is possible to efficiently utilize the vertical direction of the substrate and the conductive layer in the embossing.
The use of OLED components in various display embodiments is in the focus of interest at present, because they offer the possibility to manufacture display components at lower costs when compared to conventional pixel displays. According to the understanding of the applicant, the present invention makes it possible to manufacture pixel displays in a simpler manner and even with lower costs when compared to prior art methods. Furthermore, by means of the invention it is possible to implement a better pixel resolution in displays by utilizing the vertical distance of the adjacent electrodes in addition to the horizontal distance more efficiently than in prior art.
a and 5b show in principle a pixel display based on OLED components as it is manufactured according to prior art. The pixels of the display are formed in the intersection between crossing stripe-like electrodes (typically lower anode and upper cathode). Generally, it can be considered that both crossing electrodes of the OLED pixel must be patterned to have a width less than 100 μm, so that a display with sufficiently high resolution can be attained. By means of a prior art shadow mask it is in practice possible to attain an electrode width of approximately 200 to 300 μm. If a so-called RGB full colour display is produced, the total length of the so-called virtual colour pixel formed together by three adjacent basic colour pixels (red, green and blue) thus approaches 1 mm, which is too large to be suitable for high resolution displays. Furthermore, the drawbacks of the shadow masks include repetitive alignments and cleanings. By means of a prior art photolithography patterning it is possible to reach a resolution of under 1 μm, but it has the drawback that manufacturing costs are high and it is poorly suited for roll-to-roll processes. Furthermore, the etching chemicals used in photolithography cause problems or prevent the combination of different process steps into a single entity.
Thus, high resolution displays are typically implemented on a silicon substrate, on which it is possible to manufacture pixels of sufficiently small size by means of prior art techniques. However, it is difficult to lower the manufacturing costs of the silicon substrate displays to such a level which, in principle, may be attained by using organic materials in mass production.
Thus, the present invention makes it possible to manufacture OLED pixels in such a manner that the pixel size is sufficiently small also for high resolution displays. Another significant advantage of the invention is that it also enables the manufacture of OLED pixels in a roll-to-roll process, which considerably reduces the manufacturing costs of pixel displays in mass production.
It is known as such that in organic field effect transistors based on thin films, one central requirement to be set for the manufacturing technique is the capability to manufacture sufficiently small channel lengths between electrodes, which have a finger-like structure and are arranged overlappingly with respect to each other.
The current IDS between the OFET transistor and the Drain-Source electrodes can be estimated according to the formula (1)
in which μ=mobility of the charge carrier in the channel material
Typically the mobility of the charge carriers of organic channel materials vary between 10−3 and 0.1 cm2/Vs, while for silicon in crystal form it is considerably higher, in the order of 103 cm2/Vs. This restricts the current obtained from an organic transistor considerably in accordance with formula (1). On the other hand, the current is substantially dependent on the ratio of the width W and the length L of the transistor channel. The aim is to maximize this ratio W/L by producing for example electrodes patterned in a finger structure according to
It is a direct result of the foregoing aspects that the patterning of the Drain and Source electrodes must be implemented very accurately. Furthermore, the quality of the patterning must be good, because even occasional shortcuts between the electrodes typically spoil the performance of the transistor.
Known prior art methods based on photolithography and etching do, in fact, enable accurate electrode patterning, but they are slow and expensive processes which require a number of different process steps. Thus, they are poorly suited for mass production, and in practice they are not suitable for roll-to-roll processes.
There are other prior art methods suitable for the patterning of electrodes, such as the shadow mask technique, but generally it can be said that the methods by means of which it is possible to reach a resolution of sufficiently high quality (in the order of 1 μm) in the length L of the channel are not suitable for mass production, and especially not for roll-to-roll processes.
The solution according to the invention based on embossing, in turn, is suitable for implementing the Drain and Source electrodes necessary in OFET transistors also in mass production and as a roll-to-roll process.
Referring to
An insulating layer is implemented on top of the organic channel material, which insulating layer is typically made of SiO2, or dielectric polymer, such as polyester, PVP (poly-vinylphenol) or PMMA. The patterning of the insulating layer does not affect the dimensions L, W of the transistor channel any more, whereby the accuracy requirements in the manufacture of the same are less strict. However, the thickness of the insulating layer is an essential factor in view of the function of the transistor, as shown by formula (2). The insulating layer must be as thin as possible, but it must not contain holes or the like that make shortcuts possible. The insulating layer may typically be implemented for example by means of vacuum evaporation, sputtering or pressing.
A Gate electrode of a suitable material, for example metal (such as Al, Cu), conductive graphite or metal particle ink, or conductive polymer, such as polyaniline, is also implemented on top of the insulating layer. This stage is no longer so critical in view of the pressing accuracy, because the dimensions of the transistor channel have been determined already in connection with the electrode pattern of the lowermost conductive layer.
On the basis of the foregoing, it is obvious that the use of embossing according to the invention in the manufacture of OFET components is advantageous because by means of this method it is possible to pattern the lowermost, and in view of the properties of the transistor the most important conductive layer very accurately. After the implementation of the Drain and Source electrode pattern of the lowermost conductive layer, there are considerably more degrees of freedom in the implementation of the subsequent layers, because it is now possible to allow a certain degree of inaccuracy for them without substantially affecting the performance of the transistor.
The example structures shown in principle in
It is, of course, obvious that the invention is not limited solely to the embodiments presented in the previous examples, but the invention is to be interpreted only according to the limitations set by the appended claims. Thus, the invention is not restricted solely for example to the manufacture of the above-described components, but by means of the invention it is possible to manufacture for example solar cells or photocells. To manufacture active matrix displays it is possible to combine both OFET and OLED structures on the same substrate.
In addition to the above-described process stages it is possible to use other process stages in connection with the invention, when required, for example to implement the insulation and fitting layers between different material layers. Furthermore, it is possible to utilize for example RIE etching (Reactive Ion Etching) or other plasma treatment to clean the embossed conductive layer or the other layers formed simultaneously, or the clean the cutting traces before implementing the subsequent layers.
Number | Date | Country | Kind |
---|---|---|---|
20030919 | Jun 2003 | FI | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FI04/50098 | 6/18/2004 | WO | 00 | 3/19/2007 |