Thin, inexpensive rfid (radio frequency identification) antennas for labels

Development of very cheap rfid antennas. The principle is that a plastic film will be coated with a material that prevents the metal from sticking to the substrate in vacuum deposition. Coated in pre-designed shapes, we obtain kilometer-long rolls

The overwhelming use of RFID (Radio Frequency IDentification) tags (or labels) in the very near future will be a universal replacement for the bar code system. Instead of reading bar codes for logistic control, the reading will be carried out by remote (and out of sight) transmission of the required information from the label to a reader connected to a central logistic control system. In principle, RFID tags contain a substrate, an antenna and an electronic chip electrically connected to the antenna. The chips contain the information needed to be stored by the tag. In most cases (passive labels) the electromagnetic radiation from the reader is resonantly absorbed by the antenna and activates the chip. When activated, the chip modulates the radiation emitted back by the antenna towards the reader. The information stored inside the chip (equivalent to a bar code) is delivered to the reader by this modulation process. Each chip has its own unique modulation code. The antennas have therefore two main functions: to efficiently absorb the electromagnetic radiation coming from the reader, and to efficiently reradiate it back to the reader as an encoded signal. For both purposes, the antennas have to have a well-defined shape, and to have low resistance per square. This is why thick copper foil is used for producing antennas. The problem with antennas made out of metallic foil (at least 18 micron thick) or printed with conductive ink is that they are too expensive for many applications, and the industry has a very strong demand for much cheaper antennas. The proposed project is designed to meet this huge demand. The antennas will be produced by a selective vacuum deposition process where the metallic layer will be deposited only in the shape of the designed antennas. In the vacuum deposition process, a very high electrical current is applied to a row of conductive ceramic slabs (evaporation boats) that as a result heat up to 15,000 degrees Celsius or more. A metallic wire is continuously supplied to each heat boat, and transforms to vapour because of the high temperature of the boat and the low pressure inside the vacuum chamber. A cold polyester film that runs above the metallic vapour causes it to condense on its surface and be deposited as a thin metallic layer. The problem is how to perform a selective deposition process, so that the substrate will be covered only with metallic spots in the shape of the antennas. The most elegant and efficient way to achieve this patterned metallic deposition is by printing the moving substrate with special oil that has extremely low vapour pressure. When the hot metallic vapour meets the oil on the surface of the substrate, it boils the oil off and does not stick to the substrate. By printing the substrate with oil in the complimentary shapes of the antennas, we are left after the metallization process with a roll of polyester film covered with an array of perfectly shaped antennas. A 3,000-metre long and 2-metre wide roll can be produced with 0.1-micron thick metallic layer in less than an hour. Since 1 square metre of the substrate contains on average 150 antennas, around 1 million antennas can be produced in an hour. This makes the price of an antenna only a small fraction of a cent and this is exactly what the industry is looking for - long rolls of label substrate with perfectly arranged antennas on one of its surfaces, at a very low price. Unfortunately 0.1 microns is not thick enough to absorb enough electromagnetic energy from the reader, and to have efficient enough re-radiation capability. To do so the antennas have to be around 1 - 2 microns thick. This is a totally different ballpark. Here is the problem we encounter: When the metallic vapour meets the surface of the substrate, it delivers huge amounts of heat because the vapours are cooled down from 15,000 degrees Celsius to room temperature, and much more heat is delivered because of the melting and condensation of latent heat. Normal polymeric substrates like polyester cannot take the heat released from 1-2 microns of evaporated copper in one run. Also there is not enough printed oil to prevent deposits of such a huge amount of metal. Therefore the whole process will have to be done in several metallization runs. Probably 4-6 metallization runs will be needed to reach enough thickness for RFID antennas of the 1GHz range. Keywords: RFID (Radio Frequency IDentification), antennas, labels. 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Project ID: 
3 607
Start date: 
Project Duration: 
Project costs: 
1 460 000.00€
Technological Area: 
Surface treatment (painting, galvano, polishing, CVD, PVD)
Market Area: 
Other satellite/microwave

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