Design and Optimization of Simulated Tubular Tunnel FET Structures for Biosensing

Abstract

Biosensors are the analytical device which transmits a biological response into the processable and quantifiable signal. There are two types of methods which are generally used to detect the presence of biomolecules in FET based biosensors i.e., dielectric modulation and gating effect. Within several types of innovative bio-sensing technologies, label free dielectric modulated field-effect transistor (DM-FET) based biosensors stand out because of their appealing properties, including ultra-sensitivity detection, mass-production capacity, low cost of manufacture, low-cost manufacturing and batch testing facility.To continue the Moore’s law, the researcher all over the globe are working on the novel approaches to reach the goal of international technology roadmap of semiconductors. Some of the studies are targeting on the novel device architecture and part of them are exploring for the better controlling over the channel. In this race the tunnel FET and the junction less FET both emerges as a promising candidate for low power applications. According to reports in research, silicon nanotube FETs have a considerable electrostatic gate command over carriers because of the shell-core gate stacking structure. The suggested design has a couple of gates (an inner gate and an outer gate) that are made to regulate the channel from within as well as outside the nanotube, which makes it considerably greater in efficiency than a nanowire FET.This work simulates and investigates the performance of Dielectric Modulated Tunnel Field Effect Transistor biosensor for low power applications. In particular, total five devices we simulate and observe the electrostatic behavior. Out of them three devices are double gate tunnel field effect transistors i.e., double gate both side cavity (DG-BSC-TFET), double gate drain side cavity (DG-DSC-TFET) and double gate full both side cavity (DG-FBSC-TFET). In all these structures we have taken the ambipolar current as the sensitivity parameter and the sensitivity of DG_FBSC_TFET is best for all the neutral as well as for the charged biomolecules. This is due to the fact that volume to surface ratio in this structure is more compare to the other structures. For K=5 the Sensitivity of FBSC structure is 100 times (102) more than DSC structure. Due to the fabrication complexity and low ON-current in tunnel FET based biosensors the Junction less FET based biosensor is studied. A junction-less nanowire tunnel field effect transistor (JLN-TFET) that combines the advantages of a junction-less field effect transistor (JLFET) and a tunnel field effect transistor (TFET) and with a hetero-structure device made of silicon (Si) and germanium (Ge), an amalgamation of gate engineering and channel engineering is investigated. The modified gate-all-around hetero junction less nanowire tunnel field effect transistor (GAA-H-JLNTFET) performs better. The drain current is taken as the sensitivity parameter. Five different biomolecules sensitivity are measured and found better than the previous published results. The sensitivity to detect the gelatin (k=12) is around 4.5 X 104, which one is the good result when compared to the other published data.Finally, the tubular gate on source-based tunnel FET is investigated for the biosensing application. In this FET based biosensor the micro or nano organism can immobilize at the surface above the source and the gate, interact on the upper wall of the biosensor as well as on the inner part of the tube of the Silicon nanotube transistor. The gate electrode is extended on the source and also extended on the little part of drain. A nano gap is formed on the whole volume of the Silicon nano tube inside as well as the outside of the tube except some part of the drain. The ON current is taken as the sensitivity parameters. All the extensive simulations are performed using the ATLAS tool from SILVACO TCAD. It has been found that incorporating tubular tunnel FET and gate engineering improves the device's TFET performance and qualifies it for low power and more practical applications.