Department of Electronics and Communication Engineering

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Browsing Department of Electronics and Communication Engineering by Author "Nasani, Karthik"

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    Comprehensive Design of Nano scale Hetero Junction Dual Gate Vertical TFET: Analytical modelling, Sensing Functionality, and Circuit Level Integration
    (Department of Electronic and Communication Engineering, NITS, 2025) Nasani, Karthik
    The continuous scaling of CMOS technology has brought substantial improvements in performance and integration density. However, the corresponding rise in power consumption presents major challenges for modern electronic systems. Tunnel Field-Effect Transistors (TFETs) have emerged as strong contenders for low-power applications due to their band to-band tunneling (BTBT) mechanism. This thesis proposes and thoroughly investigates a novel device architecture, the Heterojunction Dual Gate Vertical TFET (HJ-DGVTFET), which is designed to overcome limitations in conventional TFETs including low ON-current (ION), high OFF-current (IOFF), large subthreshold swing (SS), and drain-induced barrier thinning (DIBT). The electrical characteristics of the HJ-DGVTFET are optimized using 2D TCAD simulations and validated through an analytical model based on the 2D Poisson equation. The device comprises an InP source and an In₀.₄₇Ga₀.₅₃As channel/drain region, forming a heterojunction that facilitates enhanced tunneling efficiency. Key design parameters such as indium mole fraction, oxide thickness, source doping, and channel length are varied and studied in detail. Results show that increasing indium content and source doping significantly enhance ION and the ION/ IOFF ratio, while optimizing oxide thickness and channel length further improves device performance. The optimized HJ-DGVTFET achieves a subthreshold swing of 36 mV/dec and a ION/ IOFF ratio of 109. Reliability analysis includes the impact of Gaussian and uniform traps, temperature variations, and lateral straggle on device behavior. Lateral straggle is shown to reduce effective channel length, improving tunneling and transconductance, while temperature primarily affects IOFF, leaving ION relatively stable due to its BTBT nature. Noise analysis is conducted for generation-recombination (GR), diffusion, and flicker noise, revealing that GR and flicker noise dominate at low to mid frequencies (0–1 GHz), while GR noise persists at higher frequencies (up to 10 GHz). This thesis also explores the sensor applications of the HJ-DGVTFET. A biosensor is designed and analyzed for detecting biomolecules such as gelatin, streptavidin, glucose oxidase, keratin, bacteriophage T7, and staphylococcal nuclease. The HJ-DGVTFET biosensor outperforms its single-metal-gate counterpart (SMG-HJ-DGVTFET), showing enhanced sensitivity due to reduced energy band gap and improved gate control. The device ix demonstrates excellent response to positive biomolecular charge and significant ON-current modulation. Additionally, the sensor is employed for CerbB-2 antigen detection, showing high sensitivity and design flexibility for array-based bio-screening. A gas sensor variant of the HJ-DGVTFET is developed, employing catalytic gate materials such as silver, cobalt, platinum, and palladium. Changes in work function due to gas adsorption modulate surface potential and electric field, enabling detection of gases like CO, NH₃, H₂, and O₂. Sensitivity is evaluated based on OFF-current variation, with platinum and palladium achieving the highest sensitivity for CO and ammonia detection, respectively. Furthermore, the thesis includes the development and simulation of a HJ-DGVTFET based digital inverter circuit. The inverter is analyzed under varying temperature conditions and interface trap densities, showing stable performance with minimal temperature dependence. Interface traps, however, introduce undershoot in transfer characteristics, highlighting the importance of trap minimization in digital applications. The results confirm the HJ-DGVTFET's suitability for low-power, high-performance logic circuits, particularly under environmental and process-induced variations. Overall, the HJ-DGVTFET presents itself as a robust and versatile solution for future nanoelectronic applications, combining high reliability, excellent low-power performance, and multi-functional capabilities across sensing and logic domains.