Low Frequency Noise in Layered ReS2 Field Effect Transistors on HfO2 and its Application for pH Sensing

Layered rhenium disulfide (ReS2) field effect transistors (FETs), with thickness ranging from few to dozens of layers, are demonstrated on 20 nm thick HfO2/Si substrates. A small threshold voltage of −0.25 V, high on/off current ratio of up to ∼107, small subthreshold swing of 116 mV/dec, and electron carrier mobility of 6.02 cm2/V·s are obtained for the two-layer ReS2 FETs. Low-frequency noise characteristics in ReS2 FETs are analyzed for the first time, and it is found that the carrier number fluctuation mechanism well describes the flicker (1/f) noise of ReS2 FETs with different thicknesses. pH sensing using a two-layer ReS2 FET with HfO2 as a sensing oxide is then demonstrated with a voltage sensitivity of 54.8 mV/pH and a current sensitivity of 126. The noise characteristics of the ReS2 FET-based pH sensors are also examined, and a corresponding detection limit of 0.0132 pH is obtained. Our studies suggest the high potential of ReS2 for future low-power nanoelectronics and biosensor applications.