High-sensitivity detection in biosensors: A comparative study of inverted T- and L-channel charge plasma TFETs

This work presents a comprehensive analysis of a charge plasma vertical TFET based biosensor with an inverted T-shaped channel (IT-CPTFET), demonstrating improved sensitivity in biomolecules detection compared to the conventional L-shaped CPTFET based biosensor (L-CPTFET). Key design considerations include dual cavity positions, split drain region, dual-channel arrangement, and elevated source positions to optimize tunneling rates, resulting in increased drain current and improved sensitivity of the IT-CPTFET. Both IT-CPTFET and L-CPTFET have been explored as label-free biosensors using dielectric modulation, incorporating a nanocavity under the source electrode. By measuring important DC parameters like ON-state current $\left(I_{ON}\right)$, subthreshold swing $\left(S{S}_{Avg}\right)$, and current-switching ratio (CSR) with the aid of 2D Sentaurus TCAD simulator at different K-values (1.54, 3.57, 6.3, 8, 12) helps to investigate the physics of IT-CPTFET, L-CPTFET and assess their ability to identify various charged and neutral biomolecules. The IT-CPTFET shows superior sensitivity, achieving an $I_{ON}$ sensitivity of $1.18\times 10^8$, compared to $5.38\times 10^7$ for the L-CPTFET when detecting Gelatin (K = 12). An increase in the dielectric constant enhances the electric field in the tunneling region, leading to more efficient band-to-band tunneling, which increases the drain current and improves the overall sensitivity of the device. Furthermore, the sensitivity of the device is evaluated with respect to analog and RF parameters that are crucial for practical sensing applications. However, IT-CPTFET offers better performance, demonstrating $1.9\times 10^6$ for transconductance sensitivity ($S_{g_m}$) and $3.8\times 10^5$ for cut-off frequency sensitivity ($S_{f_T}$), while the L-CPTFET shows $4.9\times 10^5$ and $1.3\times 10^5$, respectively. Next, the sensitivity of devices with partially filled nanogaps, having fill-factors (FF) of 40% and 60%, affected by steric hindrance, is also evaluated for IT-CPTFET and L-CPTFET biosensors at $K=12$. This analysis includes different step profiles of biomolecules such as concave, convex, increasing, and decreasing step profiles. To account for the non-ideal state of IT-CPTFET based biosensors, the impact of irregular probe placement within the nano-cavity on sensitivity parameters related to ON-state current for a specific values of biomolecules is also analyzed using the TCAD simulator. Finally, Comparison with other CP-TFET biosensors highlights the superior performance and sensitivity of the IT-CPTFET in detecting a variety of biomolecules, making it a good candidate for high-sensitivity biosensing applications.