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How FRAM RFID eases medical sterilization

Posted: 28 Mar 2012 ?? ?Print Version ?Bookmark and Share

Keywords:Radio frequency identification? sterilization? FRAM?

When an electrical field is applied, the material polarizes in one direction and retains this structure even after the field has been removed. If the direction of the electrical field is reversed, the atoms polarize accordingly in the opposite direction. An FRAM memory cell has the same structure as a DRAM cell and consists of a transistor and a capacitor. But in this case, the FRAM cell contains a capacitor along with a ferroelectric dielectric.

The energy applied during an irradiation process removes the charge in floating gates of E2PROM cells but does not affect the polarization of FRAM cells. Although typical gamma sterilization processes use dosages of about 20kGy, most tests require up to 25kGy to be considered radiation-tolerant. Independent scientific studies have proven FRAM's resistance to irradiation for doses up to 50kGy. This is equivalent to two consecutive exposures of 25kGy, for an accumulated dosage of 50kGy, a dosage that is rarely necessary.

So FRAM is more radiation hardened than typical materials used in memory products. FRAM offers further advantages, especially for RFID products. Since no large-charge quantities have to be displaced, charge pumps to generate high programming voltages are not necessary. Consequently, FRAM technology is much more energy-efficient than E2PROM. This directly affects the operating range of RFID tags in a positive way. Because FRAMs require little power, the operating range is higher for a given field strength or power density.

Also, FRAM memories can be written as fast as they can be read. FRAM's write access is about 25 times faster than E2PROM's write access. The maximum number of write/delete cycles for Flash and E2PROM is between 10,000 and 100,000. If this limit is exceeded, the memory content can no longer be reliably stored due to material fatigue. By comparison, with more than 10 billion read/write cycles (1010), the lifetime of an FRAM memory is almost unlimited. This means that FRAM tags can be used many times over. For applications where many writes are required, FRAM has an undeniable advantage over conventional non-volatile memory options, like E2PROM and Flash. Also, while occasionally FRAM is incorrectly associated with ferromagnetism, magnetic fields do not affect the ferroelectric material.

Applying the FRAM technology
Compared with conventional E2PROM/Flash-based RFID chips, Fujitsu's FerVID family is touted to enable the same data-transfer rate for both reading and writing over long distances. The write endurance, specified to 10 billion cycles, is far higher than that of conventional RFID tags. Fujitsu offers HF and UHF FRAM RFID products. The ISO 15693-compliant devices cover the 13.56MHz operating frequency and feature 2kByte and 256Byte memories respectively. In the UHF band of 860 to 960MHz, Fujitsu offers 4kByte and 64kByte FRAM devices, compliant with the EPC global C1G2 standard. In addition to the standard ISO commands, the products are touted to have anti-collision capabilities, and custom fast read/write transmission commands.

Also, a dual-interface device is available in two types. One is a conventional contactless EPC global RFID product, and the other a derivative with an additional contact-based SPI interface. This dual-interface type can be implemented as part of a microcontroller-based embedded system.

FRAM's significant advantages over its alternatives, combined with the tracking capabilities of RFID, simplify the tracking process for medical devices, helping assure the safety of vital medical products.

About the authors
Dirk Fischer is a product marketing engineer in the Automotive and Embedded Business Unit at Fujitsu Semiconductor Europe GmbH.

Tong Swan Pang is a senior product manager, with the Standard Product Business Group, Fujitsu Semiconductor America Inc.

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