An on-chip capacitive coupled RFID tag

Recently, highly miniaturized radio frequency identification (RFID) transponders (tags) have been brought to the market. These tags are typically equipped with small on-chip coils and communicate with the RFID reader by inductive coupling at 13.56 MHz. In contrast, this paper presents a one square millimeter RFID tag that communicates with the reader by non-resonant capacitive coupling at 13.56 MHz and 868 MHz. This on-chip capacitive coupled (OC3) tag is designed and fabricated in a low cost 130nm complementary metal-oxide-semiconductor (CMOS) process. The OC3 tag enables a contactless communication with the RFID reader in metal environments, while tags based on inductive coupling are easily impaired in their operation. Experiments show that the presented OC3 RFID tag is able to communicate with an electronic product code (EPC) compliant reader in the high frequency (HF) and ultra high frequency (UHF) ranges. Additionally, custom-built HF and UHF booster antennas increase the reading distance of the tag. The HF booster antenna based on a 13.56 MHz coil enables reading distances of the OC3 tag up to 30 cm in the HF frequency band. The UHF booster antenna based on a dipole enables reading distances up to 1 m at 868 MHz.