"Hitachi, Ltd. (TSE:6501/NYSE: HIT) today announced that it has developed the world's smallest RFID (Radio-Frequency Identification ) integrated circuit chip called the "meu-chip", which is thin enough to be embedded in paper. <snip>accessible and wireless at 2.45GHz, 0.4mm square, and thin enough to be embedded in paper. With the ID information being stored in ROM (Read-Only-Memory) during the manufacturing process, it provides high resistance to tampering."

Or so it says in only slightly fractured engrish in this Hitachi [link|http://www.hitachi.com/about/pressroom/a-2001-Jul-5-ZZZM9WXNSOC.html|press release]