The many applications of graphene, an atomically-thin sheet of carbon atoms with extraordinary conductivity and mechanical properties, include the manufacture of sensors. These transform environmental parameters into electrical signals that can be processed and measured with a computer. Due to their two-dimensional structure, graphene-based sensors are extremely sensitive and promise good performance at low manufacturing cost.
To achieve this, graphene needs to make efficient electrical contacts when integrated with a conventional electronic circuit. Such proper contacts are crucial in any sensor and significantly affect its performance. Graphene, however, is sensitive to humidity and to the water molecules in the surrounding air that are adsorbed onto its surface. Water molecules change the electrical resistance of graphene, which introduces a false signal into the sensor.
When graphene binds to the metal of electronic circuits, the contact resistance (the part of a material’s total resistance due to imperfect contact at the interface) is not affected by moisture. Graphene was used together with gold metallization and silica substrates in transmission line model test structures, as well as computer simulations.
By combining graphene with conventional electronics, one can take advantage of both the unique properties of graphene and the low cost of conventional integrated circuits. One way to combine the two technologies is to place the graphene on top of finished electronics, rather than depositing the metal on top of the graphene sheet.
This new approach can be applied to create the first prototypes of graphene-based sensors to measure carbon dioxide by means of optical detection of mid-infrared light at lower costs than with other technologies.