A joint group including TDK Corp. and Semiconductor Energy Laboratory Co. Ltd. prototyped an RFID tag formed with an RFID IC and an antenna using TFT technology on a PET flexible substrate.
Two types of prototypes were developed for use on the 13.56 MHz band and the UHF band at approximately 900 MHz. The thickness of the 13.56-MHz band tag, including a protective layer formed on the IC, is roughly 30 μm.
The UHF band prototype has a PET substrate to obtain the strength required for attachment. This is because the 35 mm x 53 mm UHF band tag is larger than its 10 mm square 13.56-MHz band counterpart. As a result, it has a total thickness of about 75 μm. The prototypes can be embedded in paper as thin as 100 μm, for example.
"We had heard that when embedding a tag in paper, the thickness of the tag is preferably 1/3 or less that of the paper," stated the group, explaining the reason why the tag thickness was set to be 30 μm.
The UHF band tag can be made as thin as 30 μm, too, for embedded in paper.
Although these prototypes are intended to be embedded in paper, the specific applications have yet to be decided. The group regards the prototypes mainly as a means to determine needs in the market.
"Both types are thinner than other RFID tags using single crystal Si that have a thickness of about 100 μm," a member of the group explained. "We would like to promote the tags by emphasizing their high flexibility."
For example, the 13.56-MHz prototype is operable even when it is wound around a cylinder having a diameter of about 5 mm.
Improved production technique
In addition to the utilization of TFT technology, other improvements are made to the production technique. The production process of the prototypes is as follows. First, an IC is formed on a glass substrate based on TFT technology.
The IC is removed from the glass substrate and attached to another substrate called "temporary substrate" that is applied with an adhesive agent. The IC thus removed is then attached to a PET flexible substrate.
The difficult part in this process is how to properly remove the IC from the glass substrate. The group explained that they selected the appropriate material and shape for the temporary substrate and adjusted the method of temperature management during the removal of the substrate.
Besides the method using the temporary substrate that is applied to the latest prototypes, other techniques are available to remove the IC: for example, a technique in which the glass substrate is cut and the remaining portion is dissolved by a chemical solution or a method in which the IC is removed from the glass substrate with the use of a laser beam.
Compared with these techniques, the latest method is "better suited for the production and the cost reduction," Semiconductor Energy Laboratory said.
The group intends to determine the practical applications of the latest RFID tags as well as aims to reduce the size of the tags, provide additional functions and replace the current recordable built-in memory with a rewritable type memory.
TDK plans to demonstrate the prototypes at CEATEC JAPAN 2007, which begins Oct. 2, 2007.