Researchers have developed a 3D tactile sensor that can detect an unprecedented range of pressures and generate an electrical signal based on the actions of touch, giving it great potential for use in touchscreens and other next-generation device technology, they said.
The work comes from a team at Ulsan National Institute of Science and Technology (UNIST) in South Korea led by Professor Jang-Ung Park of the Materials Science and Engineering department, who developed a novel method for fabricating a transistor-type active-matrix 3D pressure sensor with air-dielectric layers.
The work differs from similar research chiefly because of the materials the team used to develop transistors, Park said. Today, most transistors are created with silicon channel and silicon oxide-based dielectrics. However, these transistors either lack transparency or are inflexible, hindering their use for the development of highly integrated pressure sensor arrays and transparent pressure sensors, he said.
Pictured is a transistor-type active-matrix 3D pressure sensor with air-dielectric layers. Researchers at Ulsan National Institute of Science and Technology (UNIST) in South Korea developed a novel way to fabricate these sensors that has broad applications for wearables and next-generation devices. (Source: UNIST)
Park’s team instead used highly conductive and transparent graphene transistors with air-dielectric layers, which can detect different types of touch—including swiping and tapping—than previously developed technology, he said.
“Using air as the dielectric layer in graphene field-effect transistors (FETs) can significantly improve transistor performance due to the clean interface between graphene channel and air,” Park said. “The thickness of the air-dielectric layers is determined by the applied pressure. With that technology, it would be possible to detect pressure changes far more effectively.”
Researchers published a paper about their work in the journal Nature Communications .
A conventional touch panel in a display device, such as a tablet or smartphone, reacts to the static electricity when someone applies pressure to the monitor screen. In this way, the panel can detect the position of the contact on the screen by a person’s finger or other object using changes in pressure. However, it does not “feel” the intensity of the pressure, researchers said.
The UNIST team was able to achieve a tactile sensor that can also detect pressure by placing together a graphene channel, metal nanowire electrodes, and an elastic body capable of trapping air on one side of the foldable substrate. They then covered the other side of the substrate like a lid, keeping the air trapped inside, researchers said.
In this fabrication, the force pressing the elastic body is transferred to the air-dielectric layer and alters its thickness. It’s the changes in the thickness of the air-dielectric layer that are converted into an electrical signal and transmitted via metal nanowires and the graphene channel, expressing both the position and the intensity of the pressure, researchers said.
The technology has several advantages over current tactile-sensing technology because it enables the successful implementation of active-matrix pressure sensors, Park said. Moreover, it also consumes less power and has a faster response time when compared with the passive-matrix type, widening the range of possible uses for the