Abstract:
An electronic circuit having at least one electronic component comprised of an organic material, and arranged between at least two layers forming a barrier, wherein the layers protect the at least one component against an influence of light, air or liquid.

Description:
This application claims priority to PCT/DE01/0316 which is incorporated herein by reference in its entirety. 
     FIELD OF THE INVENTION 
     The present invention relates to an electronic circuit comprising an organic material that is hermetically sealed against light, air and/or water, and further relates to a method for producing the same and the use thereof as a tag, sensor or the like. 
     BACKGROUND 
     Radio-frequency identity tags (“RFID”) are currently constructed with metallic coils and a silicon chip. They are used, for example, for logistical purposes, access controls or the like. RFID tags are intended to operate as passively as possible, without a battery. Energy is drawn from a coil that is activated by a resonating reader. In this manner, a memory in an electronic chip of the tag is activated and a stored item of information is read out, such as an identification of sender and an addressee in the case of logistical applications. On account of their relatively high production costs, RFID tags are not cost-effective for use in mass applications, such as for electronic bar coding, for protection against copying or cloning or for use in disposable articles. 
     The operable range of distance between the reader and the tag is determined in part by the power of radiation of the reader occurring at frequency ranges such as 125 kHz or 13.56 MHz, and is also determined by the size and quality of the coil or antenna of the tag. In the case of passive tags, this range is typically less than 60 cm. The construction of the coil in this instance depends greatly upon the carrier frequency used. For example, a wound coil with generally several hundred turns is used at a frequency of 125 kHz, while a flat coil of approximately ten turns is used in the case of a frequency of 13.56 MHz. 
     An example of a known organic field-effect transistor is provided in DE 100 40 442.1. Organic electronic circuits can be produced at very low cost. They are therefore suitable for the construction of tags that can be used in mass markets and with disposable products. Other conceivable applications include electronic tickets, electronic postage stamps, electronic watermarks, and applications for protection against theft or for baggage control. 
     Unfortunately, electronic circuits that are comprised of organic material are associated with two major disadvantages. First, organic materials are very sensitive to environmental influences, such as light, air and water, and age relatively quickly under this influence. Second, antennas produced by a polymer technique, or by any printing technique, are distinctly inferior to metallic antennas. The antennas have a higher electrical resistance and are of lower quality. As a result, such electronic components and tags based on organic materials have only a short service life and are suitable only for a very short range. 
     The problem concerning durability is comparable to that associated with organic light-emitting diodes, known as OLEDs. Presently, glass is used as the substrate for these diodes, and a glass plate is also adhesively attached over the components to ensure a good hermetic encapsulation. However, for mechanical reasons and reasons relating to cost, glass is not possible for the type of applications for which the present invention is generally directed. Conventional organic substrates are permeable to light, air and water and consequently are likewise not suitable. Metallized substrates, such as are used for example in the food packaging area or for the airtight packaging of sensitive materials, likewise do not come into consideration for RFID tags in particular, since the metal layer in the substrate prevents coupling of the coil to the reader. A Faraday cage or metallic shielding is created. 
     Accordingly, a substantial need exists for organic electronic circuits that are not especially sensitive to environmental influences and do not have problems associated with durability. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention relate to an electronic circuit having an organic material and in which the electronic circuit is hermetically sealed against light, air and water to lessen problems associated with environmental sensitivity and aging. The electronic circuit can be produced simply and at low cost, such that tags produced from it can be used in mass markets and for disposable products and, in particular, can be combined with coils or antennas without metallic shielding occurring. 
     The present invention relates to an electronic circuit having at least one electronic component comprised of an organic material, and arranged between at least two layers forming a barrier, wherein the layers protect the at least one component against an influence of light, air or liquid. 
     The present invention additionally relates to a method for producing an electronic circuit having electronic components comprised of organic material. This includes steps of constructing a layer forming a barrier, arranging electronic components to form an electronic circuit upon the barrier layer, connecting electrical conductor tracks to electrical contacts, and applying an additional layer comprising at least one barrier layer over the electronic components to protect the components against light, air, or water. 
     The present invention also relates to a method for producing an electronic circuit comprising forming at least one source electrode and one drain electrode on a first substrate carrier and coating with a semiconducting layer, applying an uncross-linked insulator upon the layer, applying on a second substrate a gate electrode with a layer of uncross-linked insulator lying over the electrode, superposing the two carriers such that the two uncross-linked insulating layers come to lie one on top of each other, and initiating crosslinking of the insulators. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention is explained in more detail below on the basis of the accompanying drawings, in which: 
         FIG. 1  illustrates an encapsulated electronic circuit according to an embodiment of the present invention; 
         FIG. 2  illustrates the electronic circuit represented in  FIG. 1  in a schematic plan view; 
         FIGS. 3   a,    3   b  and  3   c  illustrate the electronic circuit according to an embodiment of the present invention in combination with a coil or a rod antenna; 
         FIG. 4  illustrates an electronic circuit with a coil in accordance with an embodiment of the present invention; 
         FIG. 5  illustrates an electronic circuit with a coil in accordance with a further embodiment of the present invention; and 
         FIGS. 6 and 7  together illustrate the production of an OFET having a substructure with a source/drain electrode and a semiconducting layer and a superstructure with a gate electrode, where the two constructions are connected by means of an insulating layer. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. This invention may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. 
     The preferred embodiments relate to an electronic circuit having an organic material, which is hermetically sealed against light, air and water to lessen problems associated with environmental sensitivity and aging. The electronic circuit can be combined with coils or antennas without metallic shielding occurring. 
     The term “organic material” refers to all types of organic, metal-organic and/or inorganic plastics. It comprises all types of substances with the exception of the semiconductors which form the classic diodes (germanium, silicon) and the typical metallic conductors. Accordingly, a restriction in the dogmatic sense to organic material as carbonaceous material is not intended, envisaging rather the broad use of silicones, for example. Furthermore, the term is not intended to be subject to any restriction with regard to the molecular size, in particular to polymeric and/or oligomeric materials; instead, the use of “small molecules” is also entirely possible. 
       FIG. 1  is a schematic illustration of an electronic circuit  1  according to an embodiment of the invention, which comprises electronic components  3 . These electronic components  3  may be constructed entirely or partly from organic materials, including conducting, semiconducting or nonconducting polymeric plastics. The electronic components  3  are arranged on a layer  2 , which forms a barrier and is multi-layered, in the case of the illustrated embodiment. The electronic components  3  or chips may be adhesively bonded onto the layer  2  or otherwise may be held fixed in place upon it in some other manner. The components also may be formed directly upon the layer by suitable printing methods. 
     The layer  2  itself is constructed from three layers  4 ,  5  and  6 . The lowermost layer  4  is a film of plastic, such as an organic polymer such as polyvinyl phenol, polymethylmethacrylate, polysulfone, polycarbonate, polyether ketone, polyethylene terephthalate, polyethylene, polyimide or any desired mixture of these polymers. The film of plastic usually has a thickness of between 10 and 100 μm, preferably 30-60 μm. The second layer  5  is formed as the actual barrier layer. This is preferably a metallic layer comprising aluminum, copper or chromium, which is either laminated as a film onto the layer  4  or has been vapor-deposited onto it. An applied metal layer is usually between 5 and 100 μm, preferably between 5 and 50 μm, thick. As already mentioned, the barrier layer may also comprise a non-metallic substrate. This non-metallic material is to be selected such that it picks up or absorbs light and/or water and/or oxygen. Suitable non-metallic coatings for forming a barrier layer against light, air and/or water are therefore, for example, layers consisting largely of dense particles which are arranged overlapping if at all possible. Suitable materials for this purpose form graphite or inorganic oxides with a platelet structure. A further layer  6  is in the form of a film of plastic and is adhesively bonded or laminated over the barrier layer  5 . The film substrate may be transparent or else completely opaque. An opaque film even has the advantage that harmful influences of light in organic electronics are prevented in an optimum way. 
     Formed or arranged on this layer  2  along with the electronic components  3  are electrical contacts  8 . The contacts serve for later connecting the electronic circuit  1  to a coil or antenna; for example, for the construction of an RFID tag. The contacts  8  may consist of organic, conductive materials and may be applied to the film substrate by a known printing method. 
     Metallic contacts, such as copper, may also be used for connection in an electrically-conducting manner to predetermined components among the electrical components  3  by lines  7 . Arranged in a hermetically-sealing manner over the electronic components  3 , and consequently partly over the lines  7 , is a further barrier  2 ′, which may have the same construction as the first layer  2 . 
     Consequently, the exemplary embodiment is a multi-layered system, comprising two layers  4 ,  6  of a film of plastic, between which a barrier layer  5  is arranged. The materials for these layers may be selected from the same ones that can be used for the further layer  2 . It is advantageous in the production process for this second upper and covering or encapsulating barrier layer as such either to be adhesively bonded or laminated on. It is evident that the individual electronic components are completely enclosed by the layers  2  and  2 ′ and consequently optimally shielded against environmental influences. 
     In an advantageous configuration of the present invention, the barrier layer used for the encapsulation may comprise barrier layers of the same or different types. In other words, the layer(s) forming the barrier may, for example, combine a metallic barrier coating and a non-metallic barrier coating. In general, the layer forming the barrier may consequently be a multi-layered system. A suitable construction comprises, for example, a polyethylene terephthalate film which is coated with aluminum, a further polyethylene terephthalate film being laminated onto the aluminum coating. 
       FIG. 2  illustrates the construction of the electronic circuit  1  from a plan view, from which in particular the electrical connection to the contacts  8  lying outside the encapsulation is shown. 
     The electronic circuit formed according to an embodiment of the invention may consequently comprise all the components essential for a circuit. Preferably, however, the active components are mainly encapsulated. These are, in particular, the integrated circuit, transistors, diodes and especially rectifier diodes or similar active components. It is preferred for the active components to consist at least partly of organic material. 
     Passive components, such as resistors, capacitors or coils, may also be included by the electronic circuit according to the invention. Equally, only the sensitive components, such as the organic integrated circuit itself, may be included and other parts, such as for example a rectifier diode, may be located outside, in which case they may still be produced by the conventional silicon technique. 
     The electronic encapsulated circuit according to the invention can be used not only for tags but in all applications where a metallized substrate does not preclude use, that is for example also in the case of sensors or other electronic components which can be realized by organic electronics. 
     One particular advantage is obtained in the case where systems of layers or systems of films with metal layers are used for the film substrates. In this case, the metal layers may also be integrated into the corresponding circuit, for example formed by suitable structuring as electrical conductors or else as passive components such as capacitors, coils or resistors. 
       FIG. 3  illustrates how to achieve a greater antenna range of an antenna of an RFID tag, for example, as compared with a complete integration of the organic electronics with the coil, despite metallized encapsulation of the electronic circuit  1 . The electronics are constructed such that they can be fastened as a kind of sticker, with the exposed electrical contacts on a corresponding coil or antenna  9 ,  10 . The respective ends of the coil ( FIG. 3(   a ) and  FIG. 3(   b )) or else its rod-shaped antenna ( FIG. 3(   c )) can be connected to the encapsulated electronics by simply adhesively bonding them on. In this way, the entire construction provides a functioning tag. 
     In this embodiment, the electronics are separate from the coil. Therefore, a conventional metal antenna, which has a correspondingly high quality for as high a range as possible, can be used as the coil. It is also possible for very large antennas to be attached, without the economic disadvantage that the more complex technique for the production of the organic circuit is required only for a small part of the surface area. 
     A further production step that is generally necessary in the case of flat coils, including connection of the corresponding coil ends  14 ,  15  in a further plane, now becomes unnecessary. By omitting this step, inexpensive printing methods can be used to include antennas in the printing applied to the packaging and, in a final step, adhesively attach the stickers corresponding to the electronics described above. 
     It is advantageous that the corresponding electrical terminal areas are quite large, to allow simple adjustment. If the terminals are standardized, it is also possible for them to be applied at a later stage. As an example, this allows end users in the retail trade to attach their own tags. In this embodiment, even a metallized area of the overall electronics for the RF connection of the antenna is not problematical, since it lies over the coil turns and not in the area enclosed by the coil. 
     In the case of the embodiments according to  FIGS. 4 and 5 , the electronic circuit  1  according to the invention is combined with an antenna  9 ,  10  in a particularly efficient and cost-saving way. The Figures illustrate that the “transponder circuit” is applied directly on the substrate of the antenna  9 ,  10 . A homogeneously metallized film of plastic  4 ,  5 , such as polyethylene, polyethylene terephthalate or polyimide, with vapor-deposited aluminum, then is used as the barrier layer  2 . A coil is produced on the metal layer  5  by a structuring process. At points where the actual circuit  3  is arranged, a metal layer is left, then serving as the barrier or encapsulation. It is also conceivable to introduce this metal layer directly into the circuit by corresponding structuring, for example as conductor tracks or as passive components. This results in a multi-layered system, in which one layer can be used for the encapsulation and one layer can be used for the application in the circuit. An advantage of this construction is that the entire identity tag can be produced as an integrated system, which in particular reduces costs. 
     In  FIG. 4 , an antenna  9 ,  10 , which consists, for example, of a metal or a conducting polymer, is formed on a barrier layer  2 , which may be formed as described above. In the interior of the antenna path there is an electronic circuit  1 , for example, a silicon chip or a polymer chip, which is intended to be electronically connected to both ends  14 ,  15  of the antenna  9 ,  10 . For this purpose, the corner  13  of the layer  2  represented by a dotted line is folded over in such a way that the end  14  of the antenna comes to lie on the contact area  12 . After the folding over, the electrical circuit  3  is connected to the antenna  9 ,  10  via the conductor tracks  7 . To prevent a short-circuit of the folded-over conductor track  7  with the antenna  9 ,  10 , an insulating layer must be applied to the turns of the antenna  9 ,  10  before the folding over. This insulating layer may at the same time serve as an adhesive for permanently fixing the folded-over corner  13 . This type of connection allows the previously customary method step, that is the additional application of a structured conductor track, to be saved. 
     According to  FIG. 5 , on the layer  2  there is an antenna  9 ,  10 , as in  FIG. 4 . An electronic circuit  3  is arranged outside the antenna  9 ,  10  in a corner  13  of the layer  2 . This corner  13  is then folded over in such a way that the contact area  8  comes to lie on the contacting area  12  of the antenna  9 ,  10 . To prevent a short-circuit of the folded-over conductor track  7  with the antenna  9 ,  10 , an insulating layer must be applied to the turns of the antenna  9 ,  10  before the folding over. This insulating layer may at the same time serve as an adhesive for permanently fixing the folded-over corner  13 . 
     A special feature of this embodiment is that the folding-over operation has the effect on the one hand of connecting the electronic circuit  3  to the antenna  9 ,  10  and on the other hand, of encapsulating the electronic circuit  3 , to be precise by the substrate material, which is to be suitably selected for this. 
     In  FIG. 6 , the superstructure  16  and substructure  17  can be seen separately on the left, the arrows  18  indicating the direction in which the two constructions are pressed one onto the other. The superstructure  16  comprises a substrate  19  such as a flexible PET film, on which there is a thin layer  20  of ITO (ITO=Indium Tin Oxide) structured in the form of a gate electrode. The gate electrode  20  is embedded into a layer  21 , for example about 100 nm thick, of the uncross-linked insulating material poly(4-hydroxystyrene) (PHS) with the crosslinker hexamethoxymethyl melamine (HMMM). In this layer, the insulating material is still in an uncross-linked form, but contains the components necessary for crosslinking (crosslinker, i.e. HMMM, and a catalyst, for example camphor sulfonic acid (CSA)). The substructure  17  likewise has a substrate  19  with a structured layer  20  of ITO on it, which here forms the source and drain electrodes. The source/drain electrodes are embedded into a semiconducting layer  22 , for example of poly-(3-octylthiopene) P3OT, as the active semiconductor material. On the semiconducting layer  22  there is an approximately 100 nm thick layer  21  of the insulating material PHS, likewise uncross-linked and with the components necessary for crosslinking (crosslinker and catalyst). The superstructure  16  and substructure  17  are pressed one onto the other ( FIG. 7 ), in such a way that the two layers  21  come to lie one on top of the other and are superficially connected to each other. In this case, adjustment is carried out with the aid of adjustment marks (e.g., fixing coils, optical marks or crosses) in such a way that the source/drain and gate electrodes are located one above the other in the desired way. In a following step, the entire construction is irradiated or annealed at 130° C. for one hour and consequently fixed. 
     This produces an organic field-effect transistor on a substrate or a carrier with a source/drain electrode on the substrate embedded in a semiconducting layer with an uncross-linked adjoining layer of insulating material and a gate electrode adjoined by a covering layer. 
     Thus, a method for producing such an OFET includes the following steps: 
     at least one source electrode and one drain electrode are formed on a carrier and coated with a semiconducting layer, on which a layer with a still uncross-linked insulator is applied; a gate electrode with a layer of uncross-linked insulator lying over it is applied on a second substrate and the two carriers are then superposed in such a way that the two uncross-linked insulating layers come to lie one on top of the other and then the crosslinking of the insulator is initiated. 
     The separate production of the gate electrode on a second substrate and its adjustment on the substrate/source, drain electrode/semiconductor/insulator construction, presented for the first time in this embodiment, facilitates the construction of OFETs to the extent that there is no longer any structuring of the upper electrode (source/drain or gate, depending on the construction) by photolithography, in which the lower organic layers are attacked and/or incipiently dissolved. Moreover, the OFET produced in this way is encapsulated and consequently protected against mechanical damage and environmental influences. 
     The foregoing disclosure of the preferred embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be apparent to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims appended hereto, and by their equivalents. 
     Further, in describing representative embodiments of the present invention, the specification may have presented the method and/or process of the present invention as a particular sequence of steps. However, to the extent that the method or process does not rely on the particular order of steps set forth herein, the method or process should not be limited to the particular sequence of steps described. As one of ordinary skill in the art would appreciate, other sequences of steps may be possible. Therefore, the particular order of the steps set forth in the specification should not be construed as limitations on the claims. In addition, the claims directed to the method and/or process of the present invention should not be limited to the performance of their steps in the order written, and one skilled in the art can readily appreciate that the sequences may be varied and still remain within the spirit and scope of the present invention.