Performance Assessment of Futuristic Novel TFET Architectures for Ternary CMOS and Biosensor Applications

Abstract

With the advancement of the electronics industry, there is a growing need for increased integration levels and cost-effective technologies. With the constant downscaling of CMOS technology, high-speed MOS devices have been developed that are ideal for analog/RF applications. It is crucial to have systems that prioritize low distortion and linearity as fundamental components of their design. But nowadays, due to the downscaling, the CMOS technology faces many challenges regarding short-channel effects (SCEs). So, this resulted in requirement for new device architecture and design. One prospective candidate for enhancing the performance of scaled CMOS integrated circuits is a tunnel field effect transistor (TFET). TFET functions through the mechanism of band-to-band tunneling (BTBT), which can obtain low OFF current (IOFF), steep subthreshold swing (SS), and high ION/IOFF ratio at reduced supply voltage but has low ON current (ION), and ambipolar conduction occurs. TFET can be used for many low-power applications. The performance improves when we increase the control over the channel. So, the double gate TFET (DGTFET) outperforms single gate TFET. Different DGTFET structures have been modeled and simulated with SiO2/high-k stacked gate oxide. The work function and pocket engineering also help to enhance the device's performance. In modified gate oxide double gate TFET (MGO DGTFET), the gate oxide is carefully placed at an optimized depth within the channel, leading to decrease in IOFF and ambipolar current. There is enhancement in ION; eventually, ION/IOFF ratio improves. In triple metal extended source double gate vertical TFET (TM-ES-DGVTFET), the channel is perpendicular to the source, which increments the probability of lateral and vertical tunneling. As a result, there is an enhancement in ION, SS, and ION/IOFF ratio. Different applications of TFET have also been investigated. A vertical TFET with a pocket (VP-TFET) has been used to design a ternary inverter. In VP- TFET a thin silicon epitaxial layer is present between the source and gate oxide. P+ pocket is present in channel close to source region. In VP-TFET vertical tunneling occurs along with lateral tunneling. A hump is created at the channel region because of the presence of a P+ pocket in the channel. In VP-TFET channel-channel and source-channel tunneling occurs and a ternary inverter has been designed. The ternary inverter is a multi-valued logic (MVL). MVL helps to reduce power density on a chip. Ternary logic, which has three steady states ("0", "1", and "2") instead of binary logic, which has two states ("0", and "1"), may store more data in the same amount of space. This directly correlates to miniature chip size and helps reduce the total number of interconnects and pins used in a VLSI chip design. TFET-based ternary logic can be advantageous in spiking neural networks and neuromorphic computing. A vertical TFET has been used to detect the biomolecules. In vertical TFET-based biosensor (VB) a thin silicon epitaxial layer is present between the source and gate oxide. The cavity is etched beneath the gate electrode at the left side of HfO2 for biomolecule immobilization. The dielectric constant is altered by the immobilization of biomolecules within the carved cavities, which were formerly filled with air. This modification changes device's electrical characteristics. In VB, vertical and lateral tunneling occurs, which increases the tunneling carriers, the current increases, and eventually, the sensitivity of the biosensor is enhanced. The Poc-MGOTFET-based biosensor is used to detect breast cancer (BC) cell lines. The gate oxide of Poc-MGOTFET-based biosensor is carefully placed at an optimized depth within the channel. The SiO2 layer within the nanogap cavity serves as an adhesive layer for the cell lines. The N+ pocket is incorporated at the source side and the gate is an extended structure. The cavity is etched beneath the gate electrode at the left side of HfO2 for biomolecule immobilization. Breast tissue included healthy (MCF-10A) and cancerous (MCF-7, T47D, Hs578T, and MDA-MB-231) cell lines. The detection method of the biosensor is based on differences in the dielectric constants of different BC cell types. The dielectric constant is altered by immobilizing the cancer cells within the carved cavities, formerly filled with air. This modification changes the device's electrical characteristics. Sensitivity analysis considers drain current, transconductance, ION/IOFF ratio, and VT. Maximum sensitivity is observed in T47D (k = 32) BC cells because it has a higher dielectric constant. The selectivity is calculated between the healthy and cancerous BC cell lines. The effect of irregular cell line confined in the cavity has been investigated to evaluate the ability of the device to detect BC cell lines. The Poc-MGOTFET-based biosensor can detect breast cancer biomarker (C-erb-B-2). The effective charge caused by the existence of C-erbB-2 biomarker in serum/saliva is utilized as the interfacial charge of the device for detecting C-erbB-2 biomarker. Sensitivity analysis considered ION/IOFF ratio. The significant increase in sensitivity, by a factor of 106 μg/L, is attributed to the influence of interfacial charges caused by different C-erbB-2 biomarker quantities on biosensor's sensitivity (as determined by ION/IOFF ratio).