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/<i>f</i>) 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