Abstract:
The invention relates to a memory, based on organic material and applied in combination with an organic integrated circuit (integrated plastic circuit). The invention particularly relates to a memory for a RFID-Tag (RFID-tags: radio frequency identification tags) and several methods for describing a memory.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is the 35 U.S.C. 371 National Stage of International Application PCT/DE01/03400 filed on Sep. 5, 2001, which designated the United States of America. 
    
    
     FIELD OF THE INVENTION 
     The invention relates to a memory, based on organic material and applied in combination with an organic integrated circuit (integrated plastic circuit). The invention particularly relates to a memory for an RFID tag (RFID tags: radio frequency identification tags) and a plurality of methods for writing to a memory. 
     BACKGROUND OF THE INVENTION 
     Organic integrated circuits based on organic field effect transistors (OFETs) are used for high-volume microelectronics applications and disposable products such as contactless readable identification and product tags, where the excellent operating characteristics of silicon technology can be sacrificed in favor of guaranteeing mechanical flexibility and very low manufacturing costs. The components such as electronic barcodes are typically disposable products. 
     For these organic integrated circuits, such as are known for example from WO 99/30432, there has hitherto been no solution to the problem as to how information can be stored in an identification tag and/or a low-cost IPC. 
     The solutions offered by semiconductor technology are over-qualified and above all too costly for the requirements of these mass-produced articles. 
     SUMMARY OF THE INVENTION 
     The object of the invention is therefore to create an organic memory for microelectronic mass-production applications and disposable products, which is based on organic material. 
     The invention relates to a memory which is based on organic materials. In addition, the invention relates to an identification tag (RFID tag) which is based on organic materials and which uses organic field effect transistors and an organic memory. The invention also relates to the use of an organic memory. Finally, the invention relates to a method for writing to an organic memory, in which with regard to an integrated circuit based on organic material either there is no transistor circuit present, it has been made non-conducting through manipulation of one or more conductor tracks, and/or single conductor tracks are conducting or non-conducting. 
     In this context, the term “organic material” encompasses all types of organic, metal-organic and/or inorganic plastics. It covers all types of material except for the semiconductors used for conventional diodes (germanium, silicon) and the typical metallic conductors. It is therefore not intended to restrict the term “organic material” to carbon-containing material in any dogmatic sense, rather having in mind also the widespread use of e.g. silicones. Furthermore, the term should not be subject to any restriction with regard to the molecule size, in particular with regard to polymeric and/or oligomeric materials, but the use of “small molecules” should certainly also be possible. 
     By preference, the organic memory is of the write-once type. 
     According to one embodiment, the organic memory consists of a transistor circuit which is comparable from the circuitry principle employed with the read-only storages known from semiconductor technology. 
     Writing to a memory of this type can be performed by way of mask programming in which the transistors or their gates are not present at the corresponding locations and/or the gate oxide of the transistors has different thicknesses (transistor conducting/non-conducting). 
     The write process can also be implemented by way of so-called “fusable links”, in other words by way of conductor tracks which can be interrupted by means of a current. “Fusable links” can be thin conductor tracks consisting of a conducting organic material such an Pani or Pedot or polypyrrole. 
     Furthermore, conducting and non-conducting conductor tracks can be provided within a transistor circuit, for example one conductor track can be present for each bit, whereby a closed conducting conductor track corresponds to a logical “0” and an open or non-conducting conductor track corresponds to a logical “1”. 
     A particularly forgery-proof variant provides two conductor tracks for at least one data bit and preferably for each data bit. During the write process, one of these conductor tracks is made non-conducting. Depending on which conductor track is non-conducting, the bit is permanently written to 1 or 0. As a result of the use of two conductor tracks, subsequent modification is no longer possible. 
     A further possible means of writing to the memory having an organic basis consists in modifying the dielectric constant of the gate oxide. In this situation, the isolating layer between gate and semiconductor is changed (by the effect of light for example) such that a change in the dielectric constant results, which has the effect that the gate either conducts (high dielectric constant) or isolates (low dielectric constant). 
     In addition to the possibility of constructing a memory based on organic material with transistor circuitry, there is a variant using single conductor tracks that are either conducting or non-conducting for constructing memories whereby in order to retrieve the stored information their resistance is read out. In this situation, for example, the “conducting” state corresponds to a logical “0” and the “non-conducting” state corresponds to a logical “1”. The read-out process can be carried out with the aid of transistors, for example. 
     By preference, the memories are of the write-once type, with the write process preferably but not exclusively being effected through manipulation of one or more conductor tracks. In this situation, the following processes can be used for writing to the memory:
         A conductor track can be destroyed by means of laser light or specifically applied heat, and thus rendered non-conducting.   Chemical treatment such as base/acid stamp, for example (making conducting areas non-conducting or vice versa)   Mechanical processing, for example separating a conductor track by using a needle   An electrical voltage is used to locally short-circuit a conductor track and thereby destroy it by overheating.   The conductor track can be separated or closed on a mask/plate simply by omitting a structure during the production process.   The dielectric constant can be changed by means of laser light.       

     By using the aforementioned process steps the memory can be written to only on a single occasion. The write operation can take place during manufacture of the tag or of the product (anti-counterfeiting mechanism or electronic bar code for example, whereby a large number of tags have the same memory contents) or during assembly of the electronics (luggage label, electronic stamp, electronic ticket, whereby each ticket has different memory contents). 
     Since the organic materials can only rarely be differentiated from one another by analytical methods, corresponding codings are also forgery-proof to a large extent. 
     At the same time, this technology can also be used in order to selectively render unusable an electronic device, such as an electronic bar code or an electronic ticket for example, after it has been used by specifically impressing a particular bit arrangement or rendering the memory unreadable after use (when the ticket is cancelled, when payment is made at the till). 
     The memory can be used in combination with the following systems:
     In an integrated plastic circuit, in other words in a circuit which is based on organic material   In an identification system (identification tags, RFID (radio frequency ident tags)), for example for
       electronic bar code   electronic tickets   anti-counterfeiting mechanism   product information   
       In a sensor   In an organic display with integrated electronics   

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will also be described in the following with reference to two drawings which show preferred embodiments of the invention. In the drawings: 
         FIG. 1  shows a memory matrix in different embodiments. 
         FIG. 2  shows an embodiment having a different thickness of gate oxide. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows a schematic circuit diagram of four embodiments of a memory matrix. 
     The circuit a) shows the programming through omission of the corresponding transistors of an integrated circuit for example;
     b) shows a so-called fusable link, whereby several conductor tracks are interrupted by a current surge and/or laser light or in some other manner (see there, middle field);   c) shows the mask programming, whereby conductor tracks are either connected or not, in other words the transistor is connected or not connected, and   d) shows the embodiment having different gate thicknesses which are conducting or non-conducting.   

     The horizontal lines  1  and the vertical lines  2  represent the electrical lines of the circuit. The points  3  serve to mark the fact that two crossing conductor tracks are in electrical contact with one another. The circuit symbol  7  represents a field effect transistor and shows the three terminals: source, drain and gate. The “T pieces”  4  represent the earth connection for the individual transistors in the circuit. 
     In section b) of the figure, two zigzag conductor tracks  6  can be recognized which represent thin conductor tracks and/or conductor tracks with a fuse which can be easily interrupted. 
     The interrupted conductor track  5  in the middle section in part b) of the figure shows that the electrical line has been interrupted at this location at a point  3  for example by means of short-circuiting or laser light. 
     In part d) of the circuit diagram, the middle transistor has a thicker gate oxide  8 , as a result of which the current channel of the transistor becomes non-conducting. 
       FIG. 2  shows a cross-sectional representation of a transistor with thick and thin gate oxide. On a carrier (not shown) is located the first semiconducting layer with source and drain electrodes  10 , 11  which are connected by way of a semiconducting layer  12 . Above the semiconducting layer  12  is located the isolating layer  13   a ,  13   b . Above this layer  13  is located the gate electrode  14 . In case a) with the isolating layer  13   a , the isolator is so thick that the gate voltage is not sufficient to make the current channel conducting and in case b) it is sufficiently narrow to make the current channel conducting. The result is accordingly a blocking transistor in case a) and a conducting transistor in case b). 
     A particularly forgery-proof variant of the organic memory is achieved with duplicated conductor track implementation. In this situation, the second conductor track contains the complementary information of the first, in other words if the first is conducting (“1” bit) then the second is non-conducting (“0” bit). Subsequent modification of the memory information is no longer possible. 
     Use of the invention makes it possible to store information in integrated circuits based on organic materials. This can be exploited cost-effectively in particular for use in RFID tags employed in anti-counterfeiting, as an electronic ticket, as a luggage label etc. No memories for so-called “plastic circuits” are known up until now.