Abstract
Herein, we report the effects of coupling capacitances on pH sensing performance metrics of SOI inversions mode fully depleted FinFET through 3D TCAD simulations. The electrolyte modeled is the 0.1 x PBS (phosphate buffer saline) solution with pH range varied from 2 to 9 and point of zero charge (pH(PZC)) at 2. The equivalent surface charge densities (rho(0)) on oxide surface corresponding to pH range of 2 to 9 is evaluated using site binding model (SBM). The proposed FinFET device is analyzed for pH sensing figure of merits that include threshold voltage sensitivity, linearity and signal to noise ratio (SNR) for variations in aspect ratio (H-fin/W-fin) and gate capacitance coupling ratio (C-ox(LG)/C-box). For pH range of 2 to 9, V-DS=50mV and V-Back=0mV, a shift of 83mV/pH in VTh is observed for W-Fin/T-Fin = 0.5. For C-ox(LG)/C-ox =15, we have analyzed the amplification in back gate pH sensitivity to 1.3V/pH however at enhanced power consumption. For V-LG = 0V, there is a drift of 31mV/pH per nm increase in BOX thickness which is observed to fall down to 24mV/pH/nm for V-LG = 1.2V. Since pH sensing response is directly correlated to capacitive coupling factor which implies that pH sensitivity of the proposed device can be tuned by variation in thickness of buried oxide layer. Back gate sweep for pH response yields better drain current SNR as compared to liquid gate sweep in linear mode of operation.