Comprehensive Design of Nano scale Hetero Junction Dual Gate Vertical TFET: Analytical modelling, Sensing Functionality, and Circuit Level Integration
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Date
2025
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Department of Electronic and Communication Engineering, NITS
Abstract
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
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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.