Stage II: printed and organic processing

Citation

(2009), "Stage II: printed and organic processing", Sensor Review, Vol. 29 No. 4. https://doi.org/10.1108/sr.2009.08729dab.005

Stage II: printed and organic processing

Article Type: News From: Sensor Review, Volume 29, Issue 4

While printed conductors of various kinds set the stage for the printed sensors of the future, the hope is to go further; much further. In the gradually emerging view of the future, printed and organic electronics will be used to provide the actual processing power or the sensing fabric of the sensor, not just the electrodes. And as Table II shows, there are a lot of ways that printed and organic electronics can be used in the sensor business.

Table II Organic/printable electronics-generated opportunities in sensing

Printed silicon approaches are now being pursued by a number of firms and would have the advantage of drawing on the high performance of silicon and the vast knowledge of silicon as an electronic material. However, printed silicon is at a very early stage of its evolution. The most likely approach here is using organic semiconductors to manufacture transistors. Pentacene is the most used material today for organic thin-film transistors (OTFTs,) but other materials such as rubrene promise faster processing in the future. The development of OTFTs is mostly going on in the context of developing flexible backplanes for displays and on-board processing power and memory for radio-frequency identification (RFID). However, organic semiconductors may offer one characteristic that makes them extremely attractive for sensors: the ability to chemically tailor the structure of the organic molecule to detect a particular thing.

The organic compounds contending for use in printable electronics are about 1,000 times less conductive than metals. The electron mobility of organics lags even that of amorphous silicon, which is far less mobile than polycrystalline silicon and single-crystal silicon. Even at their sub 1 cm/V-s mobility level, however, organic materials will be adequate for low-end sensor applications, including many biosensor scenarios.

Because sensors are often based on unusual properties of unusual materials, this will be one area of printed electronics where we should expect the unexpected. Consider the following; there’s also a new class of materials, called quantum tunneling composites (QTCs), that may hold some promise for sensors. Constructed of polymers filled with carbon, they operate by responding to physical deformation: compression, twisting or stretching, for example. At one point, a highly efficiency insulator, and at the next a metal-like conductor, these composites have a tunable transition from insulator to conductor that follows a smooth and repeatable curve.

Outside of QTCs, carbon – including carbon nanotubes – are finding a growing range of applications in sensors. In fact, carbon pastes and inks have been thick-film deposited and screen-printed for a number of years. Screen-printed carbon inks have already found commercial success in the glucose-sensing field. And carbon electrodes have properties that make them ideal for electroanalytical applications. Meanwhile, carbon nanotube sensors have been discussed in the literature for years, while printing is beginning to seem like the way to go for low-cost nanotube deposition, for example. Printed nanotubes have been at the core of some recently high-efficiency lighting proposals for example.