Jul 23, 2014
Transistors go transient
Researchers at the University of Illinois at Urbana-Champaign in the US, Seoul National University and Samsung Display Co. in Korea have made the first transient field-effect transistors from carbon nanotubes. The devices, which “disappear” once they have served their purpose, might be used in a wide range of new technologies, such as green RFID tags, biodegradable medical implants, temporary environmental sensors and hardware for secure data systems.
Transient electronics is an up-and-coming new technology in which the components making up a device physically disappear or disintegrate after a certain time. “Vanishing” semiconductors, for example, have already been made from nanomembranes of silicon, as well as zinc oxide and organic/bioorganic polymers.
Now, a joint team led by John Rogers in Illinois, Jong-Ho Lee and Sung Hun Jin in Seoul has made transient field-effect transistors (FETs) from networks of purified single-walled carbon nanotubes (SWNTs). Such networks, as well as having excellent electrical and mechanical properties, can disperse once their supporting substrate has disappeared thanks to the fact that they disintegrate into individual tubes or small bundles. The researchers also made transient bootstrapped inverters from the SWNT networks.
The fabrication procedure involves depositing transient materials such as molybdenum for electrodes and interconnects, and silicon oxide and silicon nitride for gate and interlayer dielectrics, on a temporary substrate followed by transfer to a water-soluble film of poly(vinyl alcohol) (PVA). This surface can be coated with a uniform layer of SWNTs.
Disappearing within 30 minutes
The PVA substrate, which is around 30 microns thick, slowly disappears within 30 minutes as it simply dissolves in water. This causes the entire device and circuit to physically disintegrate too. Each remaining constituent material, including the silicon oxide, silicon nitride, and molybdenum, disappears thanks to it hydrolysing and the SWNTs themselves disperse and aggregate into small bundles.
“These systems have outstanding electronic characteristics for devices based on semiconductors deposited by solution processing,” explains Rogers. “And they are the best performing yet for any solution-processed transient electronic system.”
Transient electronic devices have a well-defined, finite lifetime, he tells nanotechweb.org. “Examples of potential applications for this technology include disposable RFID tags, biomedical devices that do not place an unnecessary burden on the patient once they have performed their intended function, and hardware secure data systems that cannot be intercepted by hackers.”
Pleased with its preliminary results, the team says that it is now busy working on further improving its devices and looking at integrating them into real-world applications. “Transient RFID technology is one of our particular focus areas,” adds Rogers.
The researchers describe their technology in Applied Physics Letters.
About the author
Belle Dume is contributing editor at nanotechweb.org