Hitachi announced today the world's smallest and thinnest RFID chip.

The Hitachi RFID chip measures 0.15x0.15mm and is 7.5 micrometer thin. Hitachi's current model on the market measures 0.4x0.4mm. Silicon-on-Insulator (SOI) technology is used to achieve this level of integration.
The Hitachi µ-Chip can wirelessly transmit a 128 bit (10^38) unique ID number. It is impossible to rewrite the data and thus provides a high level of authenticity.

This RFID chip is so tiny you might breathe it in if you are not careful - will RFID chips be the Asbestos of the future? I guess the photo shows salt, but it could be sugar too. The press-release does not specify it.
More details in this Hitachi press-release.