RF devices
A low cost passive RFID tag uses capacitive or inductive coupling between the RF IC chip and the antenna. Coupling elements are formed directly on the surface of the RF IC chip.
1. RFID tag comprising:
a) a substrate,
b) an antenna formed on the substrate, the antenna comprising an antenna capacitor plate deposited on the substrate,
c) an RF IC chip, the RF IC chip comprising at least one coupling capacitor plate deposited on a surface of the RF IC chip, the said surface of the RF IC chip bonded to the substrate and to the antenna so that the coupling capacitor overlies the antenna capacitor plate so as to electrically couple RF signals between the RF IC chip and the antenna,
the RFID tag further including at least one supplemental capacitor plate between the RF IC chip and the coupling capacitor plate.
2. The RFID tag of claim 1 including a dielectric layer formed between the coupling capacitor plate on the surface of the RF IC chip and the antenna capacitor plate.
3. The RFID tag of claim 1 wherein the RF IC chip has two coupling capacitor plates deposited on the surface of the RF IC chip, and the antenna has two antenna capacitor plates, with the coupling capacitor plates overlying the antenna capacitor plates.
4. The RFID tag of claim 1 wherein the antenna sections are serpentined metal patterns.
5. The RFID tag of claim 1 wherein the RF IC chip has a surface passivating layer, and the coupling capacitor plate is deposited on the surface passivating layer.
6. The RFID tag of claim 5 wherein the coupling capacitor plate on the surface passivating layer is connected to the RF IC chip through a via in the passivating layer.
7. The RFID tag of claim 6 wherein the width of the coupling capacitor plate is greater than twice the width of the via.
8. The RFID tag of claim 1 wherein the substrate comprises paper or plastic.