ANALYTICAL MODELING AND NUMERICAL SIMULATION OF GATE-ALL AROUND FIELD EFFECT TRANSISTOR FOR SENSING APPLICATIONS

Abstract

Recent decades have seen extensive research and development in advanced sensing techniques for critical applications in diseases detection, drug discovery, pathogen discovery, toxin detection, agriculture, water monitoring and environmental monitoring. Biosensors have emerged as critical tools in modern healthcare, enabling the rapid and precise detection of a wide range of biomolecules. Field Effect Transistor (FET) based biosensors have gained substantial focus because of their ultra-high sensitivity, label-free detection, cost efficiency, and on-chip fabrication. Gate-All-Around Field Effect Transistors (GAAFETs) are well-known for having excellent electrostatic control because of their surrounding gate structure. This feature minimizes leakage currents and enhances gate control, making GAAFETs particularly suitable for biosensing applications. For developing high-performance FET-based biosensors, designing a high-performance FET is critical. The research presented in this thesis begins with a comprehensive review of the evolution of FETs, tracing the transition from traditional MOSFETs to FinFETs, and ultimately to GAAFETs. In order to maximize sensitivity and reliability in detecting biomolecules, a variety of GAAFET architectures have been thoroughly assessed using analytical modeling and numerical simulations. One of the key contributions of this research is the development of the Hetero Dielectric Trench Gate Junction Accumulation Mode GAAFET (HDTG-JAM GAAFET). This biosensor employs a silicon cylindrical Gate-All-Around FET which operates in Junction Accumulation Mode (JAM) and has a hetero dielectric layer comprised of SiO2 and HfO2. The cylindrical gate structure’s metal gate is trenched into the Hafnium oxide dielectric layer, which provides the gate with enhanced control over the surface characteristics of the channel. HDTG-JAM-GAAFET biosensor has drain ON-current sensitivity 67.68% greater for gelatin biomolecules, 69.4% higher for positive biomolecules, and 8% higher for negative biomolecules bound in the nanogap cavity than that of a Normal Gate JAM Gate-All-Around FET. This enhanced performance underscores the potential of the HDTG-JAM-GAAFET in sensitive biomolecule detection, crucial for early disease diagnosis. In addition to the HDTG-JAM-GAAFET, the Trench Gate Engineered Junction Accumulation Mode GAAFET (TGE-JAM-GAA BioFET) is proposed for label-free biomolecule detection. This biosensor exhibits a 236.24 mV drift in threshold voltage for APTES biomolecules, which is 58.75% and 159.18% higher than that of the Triple Metal Normal Gate JAM GAAFET (TMNG-JAM-GAAFET) and the Single Metal Normal Gate JAM GAAFET (SMNG-JAM-GAAFET), respectively. These findings highlight the superior sensitivity and detection capabilities of the TGE- ix JAM-GAA BioFET, making it highly suitable for biosensing applications. The critical need for a highly sensitive, quick, and affordable biosensor to identify the SARS-CoV-2 virus which has sparked a worldwide pandemic is also covered in this thesis. The Dual Metal Dual Layer Gate-All-Around Nanowire FET (DMDL-GAA-NW-FET) biosensor is introduced for the detection of the SARS-CoV 2 virus, specifically targeting the Spike protein and DNA. The device's design, which includes gate work function engineering to segregate the gate into two layers with distinct work functions, significantly improves gate control and enhances the biosensor's ability to detect the virus. The DMDL-GAA-NW-FET biosensor’s effectiveness is demonstrated through a detailed analysis of its electrostatic behavior and a comparison with conventional GAAFET biosensors, showing substantial improvements in sensitivity metrics such as threshold voltage drift (ΔVth), ION current drift (ΔION), transconductance (gm), and the ION/IOFF ratio. Another notable innovation in this research is the Dielectric Modulated 4H SiC Source Triple Metal Gate-All-Around Silicon Carbide FET (DM-TMGAA SiCFET) biosensor. The primary emphasis of this work lies in the innovative structural design of the GAA Silicon Carbide FET biosensor. Specifically, it involves the integration of a distinct SiC polytype 4H-SiC for the source, and 6H-SiC for channel region, employing a triple material gate, and the incorporation of an Al2O3 and HfO2 stack. The findings highlight that the DM-TMGAA-SiCFET offers substantial improvements in sensitivity compared to silicon-based FET biosensors, with an impressive 140.72% and 36.72% enhancement in threshold voltage sensitivity observed for gelatin and DNA biomolecules, respectively. Furthermore, there is a remarkable 404.4% improvement in ION/IOFF sensitivity for gelatin biomolecules. Additionally, the Gate-All-Around Engineered Gallium Nitride FET (GAAE GANFET) for label-free biosensing for detection of antigen and antibody from the Avian Influenza virus and DNA as the target biomolecules and the GaAs-GAAE-FET biosensor, designed specifically for breast cancer detection, demonstrate exceptional performance. The innovative Gate-All-Around engineering in GANFET integrates various device engineering techniques, such as channel engineering, gate engineering, and oxide engineering, to enhance biosensing performance. The GaAs-GAAE-FET biosensor design provides a 76.58% higher threshold voltage sensitivity for the MDA MB-231 biomarker contrasting with the Silicon Gate-All-Around FET (Si-GAA-FET) biosensor. Looking towards the future, FET-based biosensors, particularly those utilizing GAAFET structures, hold immense potential in revolutionizing the field of biosensing. As the demand for rapid, accurate, and cost-effective diagnostic tools continues to grow, the innovations presented in this thesis lay a strong foundation for further advancements in FET-based biosensing technologies and also opens new avenues for detecting a broader range of diseases at earlier stages, ultimately contributing to improved patient outcomes and public health.