Researchers are printing arrays of transistors which are the significant mechanism of “modern electronics”.
An inkjet printer is used for the entire process of printing carbon-based compound circuits, reported Science, and the work is being carried out at the University of Texas in Austin, where Ananth Dodabalapur, an electrical engineer who was not involved in the research, said: “I cannot think of another [device with at least two layers] where everything was done with inkjet printing. This is a good demonstration.”
The new market of electronic devices rely on “microchips” made of silicon, which manufacturers use to etch even smaller transmitters on, but these silicon chips are stiff, so make it difficult to make flexible circuits, and “many think that flexible, wearable electronics” made from organic materials could open new avenues for electronics, especially in the medical world where the collection of medical data is vital. These electronics could collect data from arteries and predict heart attacks, or brain activity sensing an epileptic seizure.
Sungjune Jung, an electrical engineer at Pohang University of Science and Technology in South Korea, has worked with colleagues on printing networks of organic transistors, and designed them so that they could be stacked on to of each other. The three-micrometre-tall circuits were printed one layer at a time with an inkjet printer.
The carbon-based compound was laid at the bottom of the structure, and would be the electric current conductor from one transmitter to another, and the compound would form “the current carrying parts of the other transistor”. In-between the layers of transistors, a protective material called parylene was laid, and the device included more than 100 transistors, “enough to form logical circuits that completed several basic computations, including adding two numbers”.
Jung’s device continued working even eight months after it was made, which was impressive as normally organic electronics degrade quickly. The printed devices are not yet able to compete with silicon devices, Jung said, adding that “our technology, in terms of transistor density, is at the stage of silicon technology in the late 1960s or early 1970s, when the first microprocessors came out.”
Jung’s team are demonstrating a concept rather than a prototype, and have advanced to printing the circuit onto flexible plastic, and plan to “publish the result soon”. Dodabalapur commented that the “new device lags behind what others have already achieved in organic circuits”, and said that “I don’t see any advantage[ …] to restrict oneself to one printing or patterning technique”.
However, as the product moves towards manufacturing, these “imperfections might be ironed out” said Janos Veres, a flexible electronics expert at PARC Research Institution in California. He is very optimistic about the research of organic circuits, and “imagines future labels or sensors containing stacks” of many transistors working with silicon chips or other technology.
Concluding, Veres said, “Ultimately we do see the opportunity to print microchips” which could allow for printed smartwatches or other flexible technology in future.