A Reconfigurable Field-Effect Sensor By Single-Layer Graphene for Opto-Electro-Chemical Sensing Applications

In the era of internet-of-things (IoT), sensors play important roles in every situation. It is of interest to reduce power consumption and chip size of sensing devices for mobile applications. In this work, we design and fabricate a solid-state device with chemical sensing and photodetecting, e.g. a dual-functional and reconfigurable sensor on single graphene field-effect transistor (GFET). Based on the single-layer graphene, this device couples these two solid-state sensing mechanisms. This graphene field-effect sensing device has a double-gate configuration, in which the electrolyte solution gate controls the top-gate GFET as the chemical sensor. At the same time, the bottom gate voltage is biased for noise reduction. In the developed GFET, a photodetector can also be created by taking advantage of high carrier mobility of graphene. As a consequence, applying bottom gate voltage is able to regulate charge induction on the graphene surface created by photo-excitation carriers inside the silicon substrate. Both of the two sensing mechanisms could be modulated under each gate independently. In other words, when one sensing mechanism is in operation mode, the signal current from the other sensing mechanism could be minimized by field-effect control, and vice versa. This phenomenon demonstrated the concept of electro-reconfigurable sensing devices. In this work, we demonstrate the photocurrent could be reduced by bottom gate voltage modulation when the device operating under chemical sensing mode. And the proposed electro-reconfiguration mechanism is investigated. This can be attributed to the ambipolar field-effect characteristic and surface electron traps of silicon dioxide layer as the bottom gate dielectric. In our experiments, the photodetector could be modulated by a +/- 7 V bottom gate voltage in the bottom-gate configuration. With the same device, the chemical sensor could be modulated by a +/- 500 mV solution gate voltage in the top-gate configuration. The newly developed electro-reconfigurable solid-state sensor has the advantages of small size, low cost and low operation voltage by utilizing the same device and sensing region. In addition, this device offers an alternative solution to photocurrent reduction in solid-state sensing devices by regulating photocurrent through field effect control. It would pave the way for real practice of IoT sensors and point-of-care testing devices. Figure 1