Super-Nernstian ISFET Using Scaled Coplanar Multi-Gated Channels

Ion-sensitive field effect transistors (ISFETs) are promising as label-free solid-state biosensors for pH and biomolecule detection. However, single-gated ISFETs have limited sensitivity (< 59 mV/pH) due to the Nernst limit. Super-Nernstian device architectures, such as asymmetric double-gate and coplanar gate ISFETs, are difficult to miniaturize due to thicker back-dielectrics and larger device footprints. In this work, we demonstrate the use of scaled channels of lengths 50 to 500 nm on Mos2,connected in parallel, for super-Nernstian sensitivity. The shorter channels (50 to 200 nm) are used to sense pH, whereas the longer (500 nm) coplanar top-gated channel is used to amplify the sensitivity of the device by varying the transconductance. Using this device structure, we achieve a high sensitivity of 100.9 mV/pH with the coplanar top-gate and an even higher sensitivity of 246.9 mV/ pH with a global back-gate. The device structure, which uses an atomically thin Mos2channel and a thin (10 nm) Al₂O₃high-k dielectric, enables the next generation of miniaturized point-of-care diagnostic devices.