How FRAM RFID improves the medical sterilization process

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   Cultivation of enzymes, cultures, vaccines and medicines requires the process to be free of contamination. Equipment and devices like couplers, tubing, and containers used in bioprocessing need to be carefully treated and cleansed.

There are different methods of achieving a sterile product or instrument. The most common way to kill microorganisms like bacteria, fungi and viruses is by exposure to heat and pressure in an autoclave. For sterilization during manufacturing a more elaborate method comes into play: irradiation by gamma, e-beam or ethylene oxide (EtO) gas. (See sidebar below for discussion of these approaches.)

Tracking sterilized products using RFID Tags and expanded memory capacity

   Products that are sterilized using these processes need to be tracked. Typically, some simple form of marking (e.g., a chemical indicator that changes color when it has been used) indicates something has been sterilized. Sometimes the item itself has no marking except an air-tight package (e.g., a plastic bag covering each syringe). It is difficult to prevent re-use of sterilized items with existing marking methods.

   Radio Frequency Identification (RFID) technology has become useful in this process. RFID has a long history of use in logistics processes, which deploy an electronic RFID tag with a unique ID similar to barcode labels. Unlike barcodes, RFID tags can be read via an air interface. This contactless interface does not require the line-of-sight and direct optical contact conventional barcodes need. For example, the anti-collision scheme—a significant feature of RFID technology—enables many RFIDs in close proximity of the RF field to be identified distinctly. So it is possible to track and identify products or objects without opening or unpacking the container(s).

   With expanded memory capacity, the electronic RFID labels allow additional data beyond a simple ID code to be stored on the tags. Data can be written during the manufacturing process (e.g., lot number, manufacturing date, expiration date, and product type) and throughout the supply chain process (e.g., factory departure date, date of sterilization and name of logistic partner).

   For medical instruments and products in particular, it is imperative the objects be reliably identified and that their treatment and manufacturing history be documented. Monitoring and checking processes can be included in the logistic operation to prevent counterfeiting and help assure product reliability. It is also possible to use RFID to ensure that authorized disposable parts are properly attached to the right equipment to minimize potential risk of misuse. RFID can be attached to the disposable parts, which must be verified by the reader located in the connecting equipment to ensure authorized parts are being used.

   RFID has another advantage as well. Without RFID, there is no easy way to track whether a sterilized piece of equipment is being re-used. RFID ensures the tool or equipment has been properly sterilized at a certain date and place, and helps prevent re-use because the data in the RFID cannot be easily changed by the user or other medical personnel.

   However, conventional E²PROM-based RFID products face a significant drawback—they cannot withstand the radiation process. After irradiation, memory content is erased or corrupted. So, to take full advantage of RFID features for medical applications, it is necessary to combine the gamma ray irradiation process with RFID technologies that use ferroelectric technology. This is where Fujitsu’s ferroelectric RAM (FRAM) technology comes into play.

   In contrast to conventional non-volatile memories, Flash and E²PROM, the content of an FRAM cell is not stored in the form of charge carriers in a “floating gate.” The information (logically a “0” or “1”) is contained in the polarization of the ferroelectric material lead zirconate titanate, PZT (Pb (ZrTi)O3), Figure 1. This material is placed between two electrodes in the form of a thin film, similar to the structure of a capacitor.

Figure 1: FRAM information – logically 0 or 1 – is contained

in the polarization of the ferroelectric material

lead zirconate titanate, PZT (Pb (ZrTi)O3)

   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 (http://us.fujitsu.com/semi/fram) enables the same high-speed 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, reducing costs and saving time in applications. 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 feature 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.

Sidebar: Sterilization methods

   An autoclave is a relatively inexpensive, smaller piece of equipment commonly used in hospitals and clinics for on-site sterilization of items that do not need deep cleansing, such as scissors, tongs, medical gowns and clamps. Within an autoclave, objects to be sterilized are exposed to pressurized steam or sometimes water at a temperature of approximately 125°C for a set period of time. The autoclave equipment process is easy for many clinical facilities, but an autoclave does not perform deep cleansing to remove all harmful agents.

   Other popular forms of sterilization like e-beam, Ethylene Oxide (EtO) gas and gamma sterilization have been in use for a long time. Gamma sterilization is often used during the manufacturing of equipment, tubes, enzymes, and the like before these products are shipped to end users like hospitals and medical organizations. To a great extent, gamma sterilization is part of the manufacturing process under a controlled setting.

   This approach offers several advantages. Since gamma rays are highly penetrating, products can be disinfected after they’ve been packaged, or are in large boxes or on pallets at room temperature. In effect, the objects are sterilized at the last stage of the production process, often saving costly clean-room conditions during production.

   The radiation dose depends on the original microbial condition of the goods and the target safety level. Usually a dose of about 20kGy is required. (A kiloGray is the standard international unit of absorbed radiation dose of ionizing radiation.)

   Due to radiation hazards, the process is highly regulated. These radiation facilities are expensive and typically run by specialty organizations.

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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