gate-source voltage (IDS-VGS) plots of a GFET array measured in a phosphate buffer (see Experimental Details). The plots indicate p-doped graphene, consistent with previous reports. As shown in Figure (b), the IDS-VGS characteristics were not identical but exhibited considerable variability. Specifically, the feature values of the minimum IDS (IDS,min), VDP, defined as the VGS at the IDS,min, minimum transconductance (gmh), and maximum transconductance (gme) were calculated from IDS-VGS for each GFET. applications, including sensors, rendering it vital to minimize variability for enhanced performance. However, the VDP values varied over the array, and the underlying cause remains unclear. Raman Analysis on a Single GFET. To address the variation, we employed Raman microscopy. The Raman observation was conducted before the electrical measurements. Raman images were acquired from the central region of the graphene channel (408 × 21 μm 2 ; Figure )