A graphene FET gas sensor gated by ionic liquid

We report a gas sensor based on a field-effect transistor (FET) with a graphene channel and ionic liquid (IL) gate. Graphene is supremely sensitive to its surroundings. Owing to the ~1-nm-thick electric double layer, ILs enable low-voltage operation of the FET. In addition, their solubility selectivity for different gases are controllable. Therefore, the proposed sensor selectively detects low concentration gases at low gate voltage. We fabricated the IL-gate FET using graphene grown by chemical vapor deposition. The current-voltage characteristic of the graphene-FET changed in proportion to logarithm of gas concentration. We demonstrated that our device was able to detect at least 30 ppm of ammonia (NH₃) and 4000 ppm of carbon dioxide (CO₂) at gate voltage below 1 V. The difference between the current-voltage response to NH₃ and CO₂ indicates the potential for selective gas measurement.