Ammonia gas sensing using a graphene field-effect transistor gated by ionic liquid

We propose a low-voltage-driven graphene field-effect transistor (GFET) gas sensor that is electrochemically gated by an ionic liquid (IL). The IL-gate GFET (ILGFET) consists of a graphene channel, located between the source and drain electrodes, and an IL, which covers the channel. Gate voltage is applied to the graphene through an electric double layer of the IL. The nanometer-thick double layer enables low-voltage operation compared with solid-gate materials, such as silicon dioxide (SiO2). The ILGFET was fabricated from chemical vapor deposition (CVD)-grown graphene. To test the gas sensing property, the ammonia (NH3) gas response of the fabricated ILGFET was measured. In response to 9-2400 ppm NH3, the current-voltage curve shifted toward negative voltage for the range of −0.8 to 0.8 V of gate voltage. The curve shifted 0.057 V per 10-fold increase in NH3 concentration. The calculated detection limit was 130 ppb. The fabricated sensor yielded a response time of 33 s. The sensitivity and response time of the proposed sensor were similar to those of a conventional GFET with an SiO2 gate. Additionally, the IL-gate structure was capable of decreasing the operating gate voltage.