Fabrication and pH Sensitivity Analysis of In-Situ Doped Polycrystalline Silicon Thin-Film Junctionless BioFET

In this letter, we demonstrate a low cost, CMOS compatible fabrication approach for the development of a back gate controlled, in situ-doped polysilicon junctionless BioFET employed for pH detection. The use of polycrystalline silicon as a device layer adds up the novelty yielding hysteresis free current characteristics. We also demonstrate the effect of gate bias on pH sensitivity evaluated in terms of relative changes in threshold voltage (ΔV_Th/V_Th) and maximum drain current (ΔI_D/I_D). At a back gate bias of 6 V, the device yields a maximum sensitivity of 92.2% and 31.7% for ΔI_D/I_D and ΔV_Th/V_Th, respectively, for pH 11.2. Further linearity of the proposed BioFET for the pH range of 3.1-11.2 is investigated at different values of V_gs. The best linear fit with the error of 1.25 and 0.61 for ΔI_D/I_D and ΔV_Th/V_Th, respectively, is observed at V_gs of 6 V, while V_gs = 3 V and V_gs = -2 V comparatively have higher straight line fit errors of 2.03 and 1.67, respectively. The drain current of 100 μA at V_ds = V_gs = -2 V suggests successful low-power operation of the proposed device.