Joined: 16 Mar 2004
|Posted: Wed Mar 21, 2007 12:16 pm Post subject: Textile transistors to create truly wearable electronics
|If current research is an indicator, wearable electronics will go far beyond just very small electronic devices. Not only will such devices be embedded on textile substrates, but an electronics device or system could become the fabric itself. Electronics textiles will allow the design and production of a new generation of garments with distributed sensors and electronic functions. Such e-textiles will have the revolutionary ability to sense, act, store, emit, and move (think biomedical monitoring functions or new man-machine interfaces) while leveraging an existing low-cost textile manufacturing infrastructure. Today, only a few steps towards new architectural possibilities of realizing circuit topologies that can be implemented with textile technique have been made: one an example of nonplanar devices and one of textile based devices. Researchers in Italy have now developed an organic field effect transistor (OFET) fully compatible with textile processing techniques.
Dr. Annalisa Bonfiglio’s laboratory at the University of Cagliari in Italy is working on the assembly of electronic devices and circuits on textile substrates. This can be done by following two alternative approaches: a "top down" one, consisting of assembling devices to transfer on textile substrates and a "bottom up" approach consisting of assembling an electronic fabric starting from electronically functionalized textile basic components.
Current magnetic separation methods, while effective, operate in batch mode rather than flow mode, making them too slow and inefficient for optimal use in a high-throughput clinical setting. In previous work, Zborowski and his colleagues had developed a quadruple magnetic flow sorter (QMS) similar to a fluorescence activated cell sorter (FACS) but with up to a 1,000-fold faster throughput than this widely used device, on the order of 10 million cells per second.
Top down approach
Organic semiconductors (polymers and oligomers), having the electrical properties of semiconductors and the mechanical properties of plastics, are good candidates for realizing flexible transistors, suitable to be transferred on unconventional substrates as textiles.
Fibre integration issues, however, are very challenging. Patterning in particular, is a significant concern. While fibre transistors could be fabricated using conventional lithography, these would have limited scalability to large volume textile processing. What is required is an e-textile technology that facilitates the fabrication of fibre transistors in a textile-compatible, highly scalable manner.
Previously, based on a completely flexible and transparent polyester film, Bonfiglio's lab has studied a "transistor in a fibre" realised by glueing this film on a textile ribbon, in order to obtain a flexible yarn that could be employed in a textile process. Here the polyester film is the insulator layer of the field-effect transistor (FET) structure as well as the mechanical support of the whole structure.
Bottom up approach
In recent work ( "Towards the textile transistor: Assembly and characterization of an organic field effect transistor with a cylindrical geometry" ), Bonfiglio and her colleagues focus on the possibility of building an organic field effect transistor with a non planar geometry.
"In particular, we have demonstrated the possibility of obtaining a cylindrical organic thin film transistor that, due to the employed materials and the dimensions, can be used in a textile process such as weaving or knitting" she says.
The cylindrical OFETs have been obtained starting from a metallic fiber used in textile processes. The metal core of the yarn, covered with a thin polyimide layer, is the gate of the structure. A top-contact device was obtained by depositing a layer of organic semiconductor followed by the deposition of source and drain top contacts, made by metals or conductive polymers, deposited by evaporation or soft lithography. This transistor has shown very interesting performances, with typical values of the electronic parameters mobility, threshold, /on / /off ratio very similar to those of planar devices.
Bonfiglio explains the potential of this research: "More than solving a problem, the possibility of making a transistor in yarn form paves the way to an entire new group of applications and offers the possibility to leverage existing textile technology for building electronic circuits. For example, with weaving technology (the simplest way to make a fabric), one can build a matrix of crossing yarns: if each of these yarn bares a series of transistors, each node of the textile matrix can be singularly addressed. If each node bares a sensor or a led, then it is possible to read or write the matrix one 'node-pixel' per time. In this way, a flexible and wearable electronic platform can be produced."
This story was first posted on 21st November 2006.