The engineers used a laser to "write" the circuitry for an electronic switch onto paper and then demonstrated that the switch could be turned on and off by folding and unfolding the paper. Using this technique, the engineers have fabricated foldable electronic switches and sensors directly onto paper, along with prototype generators, supercapacitors, and other electronic devices for a range of applications.
Paper-based electronics has seen increasing interest in recent years, however its promise of low cost has been offset by the expensive metals - such as gold or silver - typically used to fabricate the needed electrodes for conductivity. The new technology developed by the Berkeley engineers addresses this by using inexpensive molybdenum as the source of the conducting metal.
It is added to gelatin in solution, and binds to carbon in the gelatin. The solution is then used to coat the paper. Once dried, a laser beam precisely "writes" the desired circuitry patterns onto the coated paper, heating the molybdenum to about 1,000°C and forming conductors of durable molybdenum carbide.
The laser-written circuits are about 100 microns wide, while the unheated portions of the paper remain nonconductive. In addition to providing the carbon for the conductive compound, the gelatin coating also serves to prevent the paper from "turning to ashes" from the laser beam.
The engineers see widespread potential for their approach in new, disposable paper electronics applications. For example, they say, circuitry to detect heavy metal contamination could be "written" on paper to economically monitor toxins.
Such a sensor made of several electrodes integrated onto a paper circuit could detect unsafe lead levels in a drop of water — or in a drop of a patient's blood. The presence of heavy metal in a sample would complete the circuit by creating a conductive path in the small gaps between the electrodes.
"Many people have been carrying out origami research, forming different architectures and different shapes to perform