12.5 A Packageless Anti-Tampering Tag Utilizing Unclonable Sub-THz Wave Scattering at the Chip-Item Interface.

RFID technologies have been widely deployed in supply-chain management for logistics tracking and goods integrity. Recently, millimeter-wave and sub-THz carriers are used to enable on-chip antenna integration and hence packageless, miniature RFID form factors. In [1], a 4.4mm ² chip with 24GHz downlink and 60GHz uplink is presented. In [2], the tag size is further reduced to 1.6mm ² by pushing the carrier frequency to 260GHz. While these tiny tags allow for non-intrusive labeling, they still share one drawback with other RFIDs in anti-counterfeiting of goods (Fig. 12.5.1): if an RFID (even if the ID itself is unclonable) is detached from the genuine item and reattached to a fake item, the authentication fails. Unlike in other anti-tampering digital systems, the low power, cost and size budgets in RFIDs pose great challenges to implementing effective anti-tampering capabilities. Current solutions are based on fragile packaging materials that can easily break if physical tampering occurs [3–4]. This mechanism is, however, not reliable (e.g. under gentle or solvent-assisted detachments, and the damage can be recovered) and prevents the monolithic integration and tag miniaturization shown in [1–2]. In comparison, the anti-tampering is significantly enhanced if the fingerprinting for tampering detection is inherent to the “attachment” itself, such as the random glue distribution and the roughness of the item surface, which are very difficult to clone. Based on this principle, in this paper, we present a monolithic tag chip that utilizes a sub-THz wave not only to perform uplink/downlink communications with a compact 4.2mm ² tag size, but also to detect tampering through the unique sub-THz wave scattering at the chip-item interface with random variation at tens to hundreds of μm scale (Fig. 12.5.1).