Over the last few years wireless ID tags have become increasingly popular for authenticating and locating assets as they move along the supply chain. However, despite the advantages of wireless tags there are trade-offs such as their size, cost, energy, and security that can limit their potential.
Popular radio-frequency identification (RFID) tags, are often too large to be applied onto small objects such as medical and industrial components, automotive parts, or silicon chips. RFID tags can also contain no tough security measures although some tags incorporate encryption schemes to protect against cloning and hacking, but they’re large and power hungry. Reducing the tag size means giving up both the antenna package — which enables radio-frequency communication —and the ability to run strong encryption.
In a paper presented at the IEEE International Solid-State Circuits Conference (ISSCC), MIT researchers describe an ID chip that provides a solution to all the above trade-offs. The new tag technology is millimetre-sized and uses low levels of power supplied by photovoltaic diodes.
The tag is also able to transmit data at far ranges, using a power-free ‘backscatter’ technique that operates at a frequency hundreds of times higher than RFIDs. Algorithm optimisation techniques also enable the chip to run a popular cryptography scheme that guarantees secure communications using extremely low energy.
Ruonan Han, an associate professor in the Department of Electrical Engineering and Computer Science and head of the Terahertz Integrated Electronics Group in the Microsystems Technology Laboratories (MTL) said: ‘we call it the ‘tag of everything’. And everything should mean everything. If I want to track the logistics of, say, a single bolt or tooth implant or silicon chip, current RFID tags don’t enable that. We built a low-cost, tiny chip without packaging, batteries, or other external components, that stores and transmits sensitive data.’
The researchers started designing the tags with three main objectives: doing away with packaging that increases bulk and cost; using high terahertz frequencies (between the microwave and infra-red range) that allows chip integration of an antenna enabling communication over longer distances; and building in cryptographic protocols.
However, incorporating all those functions would normally require building a large chip, so the researchers came up with a system integration innovation that enabled everything to be incorporated within silicon chip that was only about 1.6 square millimetres.
The chip technology uses an array of small antennas that transmit data back and forth via signal splitting and mixing backscattering between the tag and reader in the terahertz range. The signals first connect with the reader and then send data for encryption. The antenna array also incorporates ‘beam steering’ enabling the antennas to focus signals toward the reader, thereby increasing the signal strength and range.
Power is provided by tiny holes in the antennas that allow light from the reader to pass through to photodiodes underneath that convert the light into electricity (around 1 volt).
The electricity powers up the chip’s processor, which runs the chip’s ‘elliptic-curve-cryptography’ (ECC) scheme. ECC uses a combination of private keys (known only to a user) and public keys (disseminated widely) to keep communications private. This prevents eavesdropping by any user who doesn’t possess the reader’s private key.
Currently, the signal range of the tags are around 5cm, making them suitable for use with a portable tag scanner. So, the researchers are now looking to extend the signal range so that multiple tags could be read by one reader positioned far away, for example at a monitoring room at a supply chain checkpoint, enabling many products to be verified rapidly simultaneously.
In addition, the researchers also hope to fully power the chip through the terahertz signals, thereby eliminating the need for photodiodes.
Currently the chips are small, easy to make and inexpensive, costing a few cents each, and can be embedded into larger silicon computer chips, which are especially popular targets for counterfeiting.