US-20260127404-A1 - Electrode Arrangement For An Electronic Tag

US20260127404A1US 20260127404 A1US20260127404 A1US 20260127404A1US-20260127404-A1

Abstract

A capacitive coupled radio frequency identification, RFID, tag and method for reading the tag, the tag comprising a semiconductor substrate having a first planar surface and a second planar surface distal from the first planar surface. A metallic pad formed on the first planar surface of the semiconductor substrate. A circuit formed on the semiconductor substrate and electrically connected to the metallic pad and the second planar surface of the semiconductor substrate, the circuit configured to respond to a radio frequency, RF, input signal by providing a data signal encoded by varying an impedance between the metallic pad and the second planar surface of the semiconductor substrate, wherein the metallic pad formed on the first planar surface extends beyond the semiconductor substrate. Wherein the metallic pad is rectangular, elongate or T-shaped, and/or the capacitive coupled RFID tag further comprises a metal electrode in electrical contact with the second planar surface.

Inventors

Marco Mazza

Assignees

Frisense Limited

Dates

Publication Date: 20260507
Application Date: 20250609
Priority Date: 20200715

Claims (20)

1 . A capacitive coupled radio frequency identification, RFID, tag comprising: a semiconductor substrate having a first planar surface and a second planar surface distal from the first planar surface; a metallic pad formed on the first planar surface of the semiconductor substrate; and a circuit formed on the semiconductor substrate and electrically connected to the metallic pad and the second planar surface of the semiconductor substrate, the circuit configured to respond to a radio frequency, RF, input signal by providing a data signal encoded by varying an impedance between the metallic pad and the second planar surface of the semiconductor substrate, wherein the circuit is further configured to detect the presence of one or more further capacitive coupled RFID tags and in response, cease providing the data signal by reducing the impedance between the metallic pad and the second planar surface of the semiconductor substrate while the detected one or more further capacitive coupled RFID tags varies its impedance.
2 . The capacitive coupled RFID tag of claim 1 , wherein RF input signal is provided by an external reader.
3 . The capacitive coupled RFID tag according to claim 1 , wherein the circuit is further configured to be powered by the RF input signal.
4 . The capacitive coupled RFID tag according to claim 1 , wherein the circuit is further configured to decode a signal encoded within the RF input signal and further wherein the data signal is provided in response to the decoded signal.
5 . The capacitive coupled RFID tag according to claim 1 , wherein the circuit modulates the RF input signal by varying its frequency, amplitude and/or phase.
6 . The capacitive coupled RFID tag according to claim 1 , wherein the circuit is formed on the second planar surface of the semiconductor substrate.
7 . The capacitive coupled RFID tag according to claim 1 , wherein a distance between an outside surface of the metallic pad and the second planar surface of the semiconductor substrate is equal to or less than 50 μm.
8 . The capacitive coupled RFID tag of claim 1 , wherein the circuit is configured to cease providing the data signal until the one or more further capacitive coupled RFID tags have provided their data signal.
9 . The capacitive coupled RFID tag according to claim 1 , wherein the circuit is further configured to cease providing the data signal according to an anti-collision protocol.
10 . The capacitive coupled RFID tag of claim 9 , wherein the anti-collision protocol is based on communications between the one or more capacitive coupled RFID tags: according to a pre-determined order of response, according to a negotiated response between the one or more capacitive coupled RFID tags, or a random number generator.
11 . An item having a capacitive coupled RFID tag embedded within it, the capacitive coupled RFID tag comprising: a semiconductor substrate having a first planar surface and a second planar surface distal from the first planar surface; a metallic pad formed on the first planar surface of the semiconductor substrate; and a circuit formed on the semiconductor substrate and electrically connected to the metallic pad and the second planar surface of the semiconductor substrate, the circuit configured to respond to a radio frequency, RF, input signal by providing a data signal encoded by varying an impedance between the metallic pad and the second planar surface of the semiconductor substrate, wherein the circuit is further configured to detect the presence of one or more further capacitive coupled RFID tags and in response, cease providing the data signal by reducing the impedance between the metallic pad and the second planar surface of the semiconductor substrate while the detected one or more further capacitive coupled RFID tags varies its impedance.
12 . The item of claim 11 , wherein a surface of the item is parallel with the first planar surface of the capacitive coupled RFID tag.
13 . The item of claim 11 , formed from paper, formed from plastics material, is a bank note, a passport, an ID card, a tax stamp and/or a legal document.
14 . A method of communicating with a plurality of capacitive coupled RFID tags, the method comprising: applying, a radio frequency, RF, input signal to the plurality of capacitive coupled RFID tags; responding to the applied RF input by one of the plurality of capacitive coupled RFID tags, by varying its impedance, the varying impedance encoding a data signal; detecting a variation in the RF input signal caused by the varying impedance of the one of the plurality of capacitive coupled RFID tags, the variation encoding the data signal; decoding the data signal from the variation of the RF input signal; the capacitive coupled RFID tags of the plurality of capacitive coupled RFID tags that are not responding reducing their impedance while the one capacitive coupled RFID tags varies its impedance.
15 . The method of claim 14 , wherein one or more of the capacitive coupled RFID tags operate at separate frequencies.
16 . The method of claim 14 , wherein the plurality of capacitive coupled RFID tags are stacked one above another.
17 . The method of claim 14 , wherein at least some of the plurality of capacitive coupled RFID tags are placed in different orientations.
18 . The method of claim 17 , further comprising, after responding to the applied RF input: reducing the impedance of the one capacitive coupled RFID tag of the plurality of capacitive coupled RFID tags; and varying the impedance of another capacitive coupled RFID tag of the plurality of capacitive coupled RFID tags that was not responding.
19 . A computer program comprising instructions that, when executed by a computer, cause the computer to perform the method of claim 17 .
20 . A system comprising: one or more capacitive coupled RFID tags comprising: a semiconductor substrate having a first planar surface and a second planar surface distal from the first planar surface; a metallic pad formed on the first planar surface of the semiconductor substrate; and a circuit formed on the semiconductor substrate and electrically connected to the metallic pad and the second planar surface of the semiconductor substrate, the circuit configured to respond to a radio frequency, RF, input signal by providing a data signal encoded by varying an impedance between the metallic pad and the second planar surface of the semiconductor substrate, wherein the circuit is further configured to detect the presence of one or more further capacitive coupled RFID tags and in response, cease providing the data signal by reducing the impedance between the metallic pad and the second planar surface of the semiconductor substrate while the detected one or more further capacitive coupled RFID tags varies its impedance; and a reader comprising an RF signal generator and decoder configured to decode the data signal.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a Continuation Application of U.S. application Ser. No. 18/016,123, filed Jan. 13, 2023, which is a National Stage Entry of PCT/GB2021/0151748, filed Jul. 8, 2021, which claims priority to UK Application No. 2010923.7, filed Jul. 15, 2020, each entitled “Electrode Arrangement for an Electronic Tag” and each of which is incorporated herein by reference in its entirety. FIELD The present invention relates to a capacitive coupled RFID tag and a method for its operation. BACKGROUND Capacitive-coupled tags (CC-tag or CCT) provide increased security whilst providing authenticity and tracking functionality. This technology has widespread use for tracking artefacts where security and authenticity is paramount. However, when the size of the CC-tag can be reduced and its efficiency increased then the number of potential applications increases. Other types of RFID tags exist and these can include antennas for receiving RF signals from a reader to power the device and to respond with a signal using the same antenna. However, use of such antennas can increase the size of the devices and increase the complexity of manufacture and so limit their applications. Furthermore, such antennas can introduce a point of failure resulting in less robust devices. CC-tags do not use an antenna but interact with the RF signal provided by a reader by altering their impedance, which affects the electric field generated by the reader and which in turn is detected by the reader. When such impedance changes are modulated then this modulation can be decoded to provide data (e.g. an identifier of the CC-tag). “0.075×0.075 mm2 Ultra-Small 7.5 μm Ultra-Thin RFID-Chip Mounting Technology”, Hideyuki Noda and Mitsuo Usami, 978-14244-2231-9/08, 2008 IEEE, 2008 Electronic Components and Technology Conference, pages 366 to 370 describes the manufacture of small RFID chips that include an antenna. However, the manufacture of such RFID chips, especially on a large scale, provides technological difficulties, which can reduce the yield in the manufacturing process and increase failure rates. “Powder RFID Chip Technology”, Mitsuo Usami, Hitachi, Ltd., 978-1-4244-2342-2/08, 2008 IEEE, pages 1220 to 1223 describes another small RFID tag and method of its manufacture, which again requires an antenna structure placed on the RFID chip. This limits the size of the tag to a lower limit. “26.6-A 0.05×0.05mm2 RFID Chip with Easily Scaled-Down ID-Memory”, Mitsuo Usami, Hisao Tanabe, Akira Sato, Isao Sakama, Yukio Maki, Toshiaki Iwamatsu, Takashi Ipposhi, Yasuo Inoue, Hitachi, ISSCC 2007/SESSION 26/NON-VOLATILE MEMORIES/26.6, 1-4244-0852-0/07, 2007 IEEE, pages 482 to 483 describes an RFID chip that has a unique IP address and that uses double-surface electrodes. A further requirement is that RFID tags can be read in the presence of other RFID tags. This can be particularly difficult for very small RFID tags that may be embedded in many separate items stacked or placed close together. Therefore, there is required a capacitive coupled tag and method of operation that overcomes these problems. SUMMARY OF THE INVENTION A capacitive-coupled RFID tag (CC-tag or RFID tag) is provided that is thin (e.g. has a thickness of 100 μm, 50 μm or less) is formed on a semiconductor substrate such as a silicon, having one surface covered in a metal layer (e.g. gold on aluminium) and an opposite surface being a bare semiconductor surface, which together act as a tuneable impedance. A circuit or chip (e.g. an integrated circuit, IC) on or within the semiconductor substrate controls a device and varies its electrical properties as seen (electrically) from an external reader that applies an electric field through the CC-tag, typically using electrodes. The CC-tag is powered by the externally applied RF electric field and responds to its presence by varying its electrical properties (in particular, its impedance). The CC-tag capacitively couples to the reader and the IC modulates its electrical properties to encode a data signal, which is decoded by the reader. The electrical properties are altered by changing the impedance between the metal layer and the opposite semiconductor layer. When more than one or a stack of such CC-tags are placed within the electric field generated by the reader, then only one of the CC-tags is configured to respond. In an example implementation, the remaining CC-tags may reduce their impedance (e.g. statically) by, for example, applying a short circuit between the metal surface and the opposite semiconductor surface, so that each CC-tags in turn and in isolation can respond and provide its output signal by modulating the RF input signal. There is also provide a method of manufacturing the capacitive-coupled RFID tag by providing a semiconductor substrate (e.g. silicon) having opposing planar surfaces, applying a metallic layer to one of the planar surfaces and forming the circuit described throughout