Bangalore: First, it was simple electronics, epitomized by bulky television sets. Then, it became flexible electronics, unleashing a wave of computing and communication devices, even enabling hanging TVs. Now, it’s become stretchable, paving the way, among other things, for a TV that can be rolled and bent.
A group of Japanese researchers report in Friday’s issue of Science that they have developed the “world’s first truly elastic” conductors — materials that allow flow of electric current — using single walled carbon nanotubes, which can make stretchable electronics a reality. They’ve integrated the conductor with organic transistors to make rubber-like stretchable large area integrated circuits (ICs), which can be stretched by 70% without any mechanical or electronic degradation.
“This is an important step to build ICs on freely curved surface and to make (the) surface smart,” say Takao Someya and colleagues from the University of Tokyo and other research institutes in the city. “Subsequently, such an intelligent surface will be able to interact with people, objects, and the environment in new ways.”
The most important breakthrough, said Someya in an email, is the “unique combination” of elastic polymers and ionic liquids in which the carbon nanotubes are uniformly dispersed to make the matrix. Ionic liquids are solvents with electrically charged particles.
“It is an important step towards realizing stretchable electronics, which takes the concept of flexibility one step further in allowing the electronics to be stretched uni-axially or bi-axially and yet retain its electronic properties,” says Chacko Jacob, professor at Material Science Centre, Indian Institute of Technology, Kharagpur.
There have been earlier attempts to build such materials but the conductivity obtained has been too small to operate ICs. But the measured conductivity here, say researchers, is the world’s highest value among chemically stable elastic materials.
In the last few years, large-area electronic devices have become sufficiently thin and light to enable fabrication of large-area solar cells and electronic displays that hang from walls and roofs. This research, say experts, will further push large-area devices to become bendable and rollable.
Some of the applications, says Jacob, could be wearable and washable electronics. Clothes that can respond to external temperature conditions, for example, by altering their structure to make one feel more comfortable, or those that can monitor a person’s health and signal adverse changes to him or a medical facility could be a possibility, he adds.
Smart clothing is not an application by a long stretch. India’s Defence Research and Development Organization has an ongoing programme where scientists are developing all-weather clothing for the defence forces, particularly those posted in difficult weather conditions. The Armament Research and Development Establishment in Pune is coordinating the “Soldier-as-a-System” initiative.
The new research can find use in biomedical applications as well. “One natural counterpart to the stretchable electronics is our skin,” says Jacob. His analogy: we have various sensors, touch, heat, pain, etc., which are embedded in our skin and wired to the brain via flexible conductors, the nervous system. This research could help in restoring the ability of burn patients to sense things or in building implantable devices for sensing or drug delivery.
It appears the Japanese have had this focus for long. Someya and colleagues built an electronic artificial skin for future generations of robots in 2003, followed by a sheet-type image scanner in 2004 and a sheet Braille display for the blind in 2005, and a wireless power transmission sheet in 2006.
For S.A. Shivashankar, professor at Materials Research Centre, Indian Institute of Science, Bangalore, who thinks this work is characteristically Japanese where “painstaking developments have been undertaken”, one possible application could be “a cellphone that can be wrapped around the arm and can withstand exposure to moisture, heat, etc.”.
In India, on the other hand, a considerable amount of work is being done in developing materials, he says, but there is no substantive thrust given to any specific set of new materials. A focused effort in developing a particular set of materials, as reflected in this paper, is often missing, he says.
Product development requires focus. Another material science group, from the University of Illinois and Northwestern University in the US, reported in Thursday’s issue of Nature that they had developed a new imaging device designed after the human eye. This “eye” camera uses silicon detectors and electronics in a stretchable, interconnected mesh. “This approach allows us to put electronics in places where we couldn’t before,” says the lead researcher, John Rogers of University of Illinois.