Nanogap Cavity Research Articles

Detection of Biomolecules Using Charge-Plasma Based Gate Underlap Dielectric Modulated Dopingless TFET

In this Paper, Dielectric Modulated Dopingless Double Gate Transistor (DM-DLDGTFET) device is proposed for the free label detection of the charged and neutral biomolecules. A charge-plasma principle is used for label-free detection of biosensors to reduce the processing complexity and cost of nanoscale products. Firstly, the simulations for the proposed device are carried using Atlas and different electrical parameters are analyzed using the same. It is observed that the dielectric constant and different biomolecule charges for example, protein, DNA, enzyme, cell and many more molecules affects the electrical characteristic of the device. The deposition of different workfunction materials over silicon body will do the formation of p+ source and n+ drain region in the DM-DLDGTFET. In addition, by etching the segment of the gate oxide layer to the source end for sensing biomolecules, a nano gap cavity is embedded within the dielectric gate. When biomolecule get immobilized at cavity region, the electrostatic properties of device for example, drain current, Ion/Ioff, subthreshold slope, average subthreshold slope, sensitivity get influenced. The energy band diagram and the device’s surface potential for both neutral and charged biomolecules are also discussed. For the validation of the proposed DL-TFET structure, the simulation results are calibrated with reported results and significant improvement are observed in the proposed structure.

AlGaN/GaN HEMT for highly sensitive detection of Bio-molecules using transconductance method

For the first time, AlGaN/GaN HEMT is demonstrated for bio-sensing application using transconductance analysis. A lot of HEMT based biosensors were developed experimentally but very few reported on sensing applications. These devices are ideal for sensing or tracking biomolecule because of the spontaneous and piezoelectric polarization properties. AlGaN/GaN HEMT with nanogap cavity is used to detect different biomolecule like streptavidin, protein and uricase. The sensitivity of AlGaN/GaN HEMT is investigated through drain current (ID) and transconductance(gm) and is analyzed using Technology Computer Aided Design (TCAD) tool. The result shows a noticeable change in drain current on introducing different biomolecules below the gate cavity region. Higher sensitivity was obtained for with Transconductance analysis than with drain current analysis.

Investigation the impact of the gate work-function and biases on the sensing metrics of TFET based biosensors

In this work, we examined the impact of gate work-function and back-gate bias to enhance sensing metrics of a Dielectric Modulated (DM) p-type Tunnel Field Effect Transistor (p-TFET) based biosensor. The sensing metrics, namely Sensitivity (S) and Selectivity (ΔS) are considerably improved by using a lower value of gate work-function and positive back gate voltages. It is shown that by appropriate selection of gate work-function and back gate bias, Band-to-Band Tunneling (BTBT) of carriers is reduced and a significant change in electrical characteristics is observed in a device with an empty cavity. Therefore, the relative change in the drain current due to the presence of biomolecules in the nanogap cavity is maximized. Results indicate a Sensitivity of ∼109 for 3-aminopropyltriethoxysilane (APTES) biomolecule, and Selectivity of ∼102 for APTES concerning Biotin biomolecule in an optimally designed p-TFET biosensor. The impact of location, as well as the charge of biomolecules, are also analyzed in this work. Results showcase the additional degree of freedom through device optimization which facilitates the tunability of sensing metrics for improved biosensor performance.

Ultrabright Fluorescence Readout of an Inkjet-Printed Immunoassay Using Plasmonic Nanogap Cavities.

Fluorescence-based microarrays are promising diagnostic tools due to their high throughput, small sample volume requirements, and multiplexing capabilities. However, their low fluorescence output has limited their implementation for in vitro diagnostics applications in point-of-care (POC) settings. Here, by integration of a sandwich immunoassay microarray within a plasmonic nanogap cavity, we demonstrate strongly enhanced fluorescence which is critical for readout by inexpensive POC detectors. The immunoassay consists of inkjet-printed antibodies on a polymer brush which is grown on a gold film. Colloidally synthesized silver nanocubes are placed on top and interact with the underlying gold film creating high local electromagnetic field enhancements. By varying the thickness of the brush from 5 to 20 nm, up to a 151-fold increase in fluorescence and 14-fold improvement in the limit-of-detection is observed for the cardiac biomarker B-type natriuretic peptide (BNP) compared to the unenhanced assay, paving the way for a new generation of POC clinical diagnostics.

Exploring p-channel TFET for Optimum Cavity-Length Window in Detecting a Wide Variety of Protein-Molecules with the Effect of Their Position Dependent Variability on Sensitivity

The performance of a sub-100-nm gate-length p-channel TFET-based biosensor (pTFET-BS) covering a wide range of protein-molecules is presented, and for the first time the optimized length-range of the nanogap cavity of the biosensor through the modeling of the presence of discrete number of biomolecules, followed by shift-saturation in corresponding transfer characteristics, is reported in this paper. Furthermore, considering a real time process related over-etching effect, a variability study on the random position of the conjugated protein-molecules within the cavity, followed by a corresponding statistical analysis, are carried out. Results show that 85% to 95% (65–85%) of total combinations produce beyond 50% of maximum Vth- (IDS-) sensitivity values, ensuring stability and hence reliability of the proposed sensor device.

Design and Analysis of Heavily Doped n+ Pocket Asymmetrical Junction-Less Double Gate MOSFET for Biomedical Applications

The Complementary Metal-Oxide Semiconductor (CMOS) technology has evolved to a great extent and is being used for different applications like environmental, biomedical, radiofrequency and switching, etc. Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) based biosensors are used for detecting various enzymes, molecules, pathogens and antigens efficiently with a less time-consuming process involved in comparison to other options. Early-stage detection of disease is easily possible using Field-Effect Transistor (FET) based biosensors. In this paper, a steep subthreshold heavily doped n+ pocket asymmetrical junctionless MOSFET is designed for biomedical applications by introducing a nanogap cavity region at the gate-oxide interface. The nanogap cavity region is introduced in such a manner that it is sensitive to variation in biomolecules present in the cavity region. The analysis is based on dielectric modulation or changes due to variation in the bio-molecules present in the environment or the human body. The analysis of proposed asymmetrical junctionless MOSFET with nanogap cavity region is carried out with different dielectric materials and variations in cavity length and height inside the gate–oxide interface. Further, this device also showed significant variation for changes in different introduced charged particles or region materials, as simulated through a 2D visual Technology Computer-Aided Design (TCAD) device simulator.

Active Control of Multiple, Simultaneous Nonlinear Optical Processes in Plasmonic Nanogap Cavities

Plasmonic structures are promising to enhance and control nonlinear optical processes as the subwavelength-scale elements not only increase the local electric field intensities, but also result in ...

Dielectric Modulated Schottky Barrier TFET for the Application as Label-Free Biosensor

This paper reported a dielectric modulated (DM) Schottky Barrier (SB) TFET (DM SB TFET) as label free biosensor applications. In a proposed device, we have created a nanogap cavity within the gate dielectric near the source end for sensing biomolecules. Therefore, the modulation of the SB width at the source end occurs due to presence of biomolecules in the form of different dielectric material used to fill the nanogap cavity. Hence, the current flow from source to drain is highly sensitive to the change in properties of dielectric materials. Here, we have investigated the performance of the proposed device in terms of its sensing capability by variation in dielectric constant and, charge density. Also, the performance of the device is observed for different cavity length and, thickness for different drain and source bias. Results show high sensitivity in terms of change in drive current of the device for the variation in the dielectric constant and charge density. Simulations have been performed by the two dimensional SILVACO ATLAS device simulator.

Capacitive Multilayered Bio-Sensor Based on Dielectric Modulation Towards Sensing of Biomolecules

In this paper, we propose a multilayered capacitive biosensor and evaluate the feasibility of using capacitance as a metric for sensing target biomolecules. The structure has been modeled using the IntelliSuite software. Consideration of distinct values of dielectric constants for different biomolecules makes it a suitable parameter for capacitive biosensor applications. The structure consists of nanogap cavities that act as the sensing sites. The concept of dielectric modulation has been employed for detecting the change in capacitance due to change in the dielectric constant of the cavity. We have used two biomolecules, biotin and APTES for the analysis. This paper highlights new opportunities for identification of biomolecules using MEMS-based dielectric modulated biosensors.

Polarization-Controlled Nanogap Cavity with Dual-Band and Spatially Overlapped Resonances

Metasurfaces are ultrathin, two-dimensional arrays of subwavelength resonators, which can possess optical properties unobtainable naturally. One such desirable property is dual-band absorption occurring at the same spatial location, which could enable the enhancement of multiple processes simultaneously. However, demonstrations of multiband absorption to date have been limited to the mid-infrared and microwave regimes. Here, metasurfaces are demonstrated to have spatially overlapped, dual-band absorption in the visible to near-infrared using arrays of plasmonic nanogap cavities that consist of a sub-10 nm dielectric layer sandwiched between gold rectangles and a gold film. The relative strength of the two modes is tuned dynamically by varying the incident polarization, and the period between elements is used to tune the spectral bandwidth. Additionally, these near-perfect absorber structures fabricated by electron beam lithography (EBL) are compared to similar nanogap geometries fabricated using colloidally synthesized nanoparticles. This comparison reveals that EBL nanogap structures can achieve similar absorption performance to colloidal nanoparticles while enabling a much greater control of the nanoparticle shape, size, and relative position. These widely tunable, dual-band metasurfaces may find applications in spectrally multiplexed photodetectors and for enhancement of optical processes, such as nonlinear generation and Stokes-shifted absorption and emission processes.

Dielectrically Modulated Source-Engineered Charge-Plasma-Based Schottky-FET as a Label-Free Biosensor

In this paper, we propose and simulate a charge-plasma (CP)-based dielectrically modulated (DM) source-engineered Schottky barrier field-effect transistor (SE-SB-FET) as a device for biomolecule sensing. The proposed device employs metal silicide (ErSi1.7) as source/drain regions and Hafnium (workfunction = 3.8 eV) as dual metallic source extensions. The oxide below the source extensions are etched out to create two horizontal L-shaped nanogap cavities for biomolecule detection. The presence of biomolecules is characterized by the change in dielectric constants and the associated charge densities, which, in turn, modulates the Schottky barrier (SB) width at the source-channel (metal/Si) junction, owing to the formation of an electron-CP in an undoped-Si film. A comparative analysis of the SE-SB-FET and the conventional DM-FET in terms of sensitivity has been performed as a function of dielectric constant ( ${K}$ ) and the associated charge density ( $\rho $ ), along with the thickness ( ${T}_{\textsf {C}}$ ) and the length ( ${L}_{\textsf {C}}$ ) of the cavity. Furthermore, calibrated simulations reveal that the relative change in ${I}_{ \mathrm{\scriptscriptstyle ON}}$ (sensing parameter herein calculated at ${V}_{\textsf {GS}}={V}_{\textsf {DS}}={1}$ V) in SE-SB-FET is much better (maximum of ${3}\times $ for neutral; ${2.9} \times $ for charged biomolecules at $\rho =-{1}\times {10}^{{11}}$ cm $^{-{2}}$ ). We further observe a significant improvement in sensitivity at low temperature ( $25\times $ at ${K}={5}$ ; $\rho ={0}$ at 100 K). Thus, SE-SB-FET biosensor provides better sensing capability for biomolecule detection when compared to the conventional DM-FET biosensor.

Modeling and Simulation of AlGaN/GaN MOS-HEMT for Biosensor Applications

HEMT technology is being used for development of biosensors. Many floating gate HEMT-based biosensors have been experimentally developed but little work has been reported on modeling of MOSHEMT-based biosensors. Therefore in this paper an analytical model of AlGaN/GaN MOSHEMT-based biosensor has been developed for the first time to detect the biomolecule species, such as protein, streptavidin, ChOx, and uricase by using a dielectric modulation approach. In this paper, the cavity length and the dielectric constant of the MOSHEMT device are optimized to improve the sensitivity of the device. The proposed structure of the MOSHEMT has been simulated on an ATLAS TCAD device simulator and the simulated results show a significant change in drain current, shift in threshold voltage, change in channel potential below the cavity region, and the capacitance on introducing biomolecules in the nanogap cavity. The results of analytical model have been verified and they show good agreement with simulated results. The sensitivity of the device can be enhanced by optimizing the device parameters, such as nanogap cavity length and width, and also by varying the gate length of the device.

Ultralow-power dielectric-modulated nanogap-embedded sub-20-nm TGRC-MOSFET for biosensing applications

This work examines a transparent gate recessed channel (TGRC) metal–oxide–semiconductor field-effect transistor (MOSFET) for biosensing, including a nanogap cavity for detection of biomolecules and a transparent gate to enhance the overall current efficiency of the RC-MOSFET. For the detection of neutral biomolecules, electrical characteristics such as ION/IOFF, shift in threshold voltage and change in surface potential have been studied and thereafter, sensitivity of has been evaluated. The biosensor showed enhanced sensitivity for biomolecules with increase in their dielectric value, due to greater on-current owing to the change in capacitances. The capacitances were therefore also evaluated. In addition, immobilization of biomolecules degrades the noise immunity of MOSFET and thereby their overall biosensing performance, while the noise immunity of the TGRC device was very high even in the presence of biomolecules. Furthermore, modulation of the cavity gap length was also investigated, revealing that its increase (from 8 to 20 nm) significantly enhanced the sensitivity of the proposed biosensor. Overall, the results of this analysis reveal that such TGRC-MOSFET biosensors can exhibit high sensitivity (1.45) at very low drain bias (0.2 V), enabling their use for biosensor applications to diagnose various diseases which require lower noise, high speed, low power, and high density.

Impact of triple-material gate and highly doped source/drain extensions on sensitivity of DNA biosensors

Gate engineering and highly doped source/drain region have been investigated to design a new DNA sensor for use in biomedical applications based on a double gate (DG) dielectric modulated (DM) junctionless (JL) metal oxide semiconductor field effect transistor (MOSFET) with triple material (TM) gate. Based on the dielectric modulation effect, DNA molecules in the nanogap cavity change due to the charge density of biomolecules, producing a change in the threshold voltage of the device. Analytical and numerical analysis was carried out to reveal the impact of physical parameters on the sensitivity of the proposed biosensor. Various characteristics, such as the surface potential, threshold voltage, and drain current were also investigated. The effectiveness of the proposed TM-DG-DM-JL-MOSFET structure with highly doped source/drain extensions is confirmed by comparison of the results with those for a conventional single-materiel (SM) gate DM-JL-MOSFET, revealing a good improvement in sensitivity and making the proposed structure an attractive solution for use in DNA-based sensor applications.

Junctionless based dielectric modulated electrically doped tunnel FET based biosensor for label‐free detection

The fabrication complexity and cost effectiveness in nanoscale regime have been one of the major issues in the modern biosensor. Therefore, to overcome such issue, this study investigates a junctionless dielectrically modulated electrically doped tunnel field effect transistor (FET) as a biosensor for application of label free detection. In this work, the authors have been considered the n + heavily doped silicon layer and two isolate gates for the formation of intrinsic and p + source regions underneath the control gate (CG) and polarity gate (PG) with appropriate work functions and polarity bias over silicon body which are similar to that of conventional tunnel FET. The proposed device structure is immune against doping control issues, avoids thermal budget, and fabrication issues. Moreover, the formation of nanogap cavity embedded within the CG dielectric is performed by etching of CG dielectric region towards the PG side for the purpose of sensing the biomolecules. The sensing ability of the proposed device has been evaluated in terms of varying the dielectric constant and charge density of the biomolecules. However, transfer characteristics are also evaluated with the variation in thickness and length of the cavity. All the simulations have been performed using ATLAS technology computer aided design device simulator.

Performance Assessment of A Novel Vertical Dielectrically Modulated TFET-Based Biosensor

A vertical dielectrically modulated tunnel field-effect transistor (V-DMTFET) as a label-free biosensor has been investigated in this paper for the first time and compared with lateral DMTFET (L-DMTFET) using underlap concept and gate work function engineering. To improve the performance of lateral biosensor (LB), a heavily doped front gate ${n}^{+}$ -pocket and gate-to-source overlap is introduced in the vertical biosensor (VB). The integrated effect of lateral tunneling as well as vertical tunneling in VB leads to enhanced ON-state current and decrease the subthreshold swing. To evaluate sensing ability of these devices, charged and charged neutral biomolecules are immobilized in nanogap cavity independently. A deep analysis has been performed to show the effect of variation in dielectric constant ( $k$ ), charge density ( $\rho $ ), ${x}$ -composition of Ge, % volume filling of ${t}_{\textsf {cavity}}$ , length and thickness of a ${n}^{+}$ -pocket and sensitivity of electrical parameters is also incorporated. Dual-pocket (front and back gate pocket) VB is studied and compared with the LB and VB in the tabular form. Noise characteristic of dielectrically modulated field-effect transistor, L-DMTFET, and V-DMTFET is also evaluated.

Analytical modeling and sensitivity analysis of dielectric-modulated junctionless gate stack surrounding gate MOSFET (JLGSSRG) for application as biosensor

An analytical model of dielectric-modulated junctionless gate-stack surrounding gate MOSFET for application as a biosensor is presented. An expression for the channel-center potential is obtained by solving the 2-D Poisson's equation using a parabolic-potential approach. An analytical model for the threshold voltage is developed from the minimum channel-center potential to analyze the sensitivity of the biosensor. Moreover, the effects of the variation of the different device dimensional parameters on the sensitivity of the biosensor were investigated in order to study the dielectric modulation effects due to the permittivity changes by the biomolecules present within the nanogap cavity. The analytical model is verified and validated with the help of TCAD device simulations.

A dielectrically modulated electrically doped tunnel FET for application of label free biosensor

The fabrication challenges and cost of nanoscale devices have been a major concern in the field of label free biosensor. Therefore, to overcome these issues, we report for the first time a dielectrically modulated electrically doped tunnel field-effect transistor (DM-EDTFET) as a biosensor for label free detection. For this purpose, n+ drain and p+ source regions in proposed device are induced by considering polarity bias of PG-1 = +1.2 V and PG-2 = −1.2, respectively over the ultra-thin silicon body. The proposed structure is immune against doping control issues, avoids thermal budget and fabrication complexity as compared to its counterpart TFET. In DM-EDTFET, a nanogap cavity embedded within the gate dielectric is formed by etching the selected portion of gate dielectric layer towards the source side for sensing the biomolecules. The sensing ability of DM-EDTFET has been analysed in terms of variation in dielectric constant and charge density of biomolecules, and device geometry parameters at different bias conditions. To analyse the relative sensitivity, proposed DM-EDTFET is compared with MOSFET based biosensor in terms of sensing parameters. From these results, DM-EDTFET provides superior results in terms of sensitivity as compared to MOSFET based biosensor. Hence, the proposed DM-EDTFET biosensor can be a promising candidate for the development of future sensing bio-equipments.

A Charge-Plasma-Based Dielectric-Modulated Junctionless TFET for Biosensor Label-Free Detection

To reduce the fabrication complexity and cost of the nanoscale devices, a charge-plasma concept is introduced for the first time to implement a dielectric-modulated junctionless tunnel field-effect transistor (DM-JLTFET) for biosensor label-free detection. The formation of p+ source and n+ drain regions in DM-JLTFET is done by the deposition of platinum (work function = 5.93 eV) and hafnium (work function = 3.9 eV) materials, respectively, over the silicon body. Furthermore, a nanogap cavity embedded within the gate dielectric is created by etching the portion of gate oxide layer toward the source end for sensing biomolecules. For this, the sensing capability of DM-JLTFET has been investigated in terms of variation in dielectric constant, charge density, length, and thickness of the cavity at different bias conditions. Finally, a comparative study between DM-JLTFET and MOSFET biosensor is investigated. The implementation of proposed device and all the simulations have been performed by using ATLAS device simulator.

Performance comparison of single and dual metal dielectrically modulated TFETs for the application of label free biosensor

In this work, we perform a comparative analysis between single and dual metal dielectrically modulated tunnel field-effect transistors (DMTFETs) for the application of label free biosensor. For this purpose, two different gate material with work-function as ϕM1 and ϕM2 are used in short-gate DMTFET, where ϕM1 represents the work-function of gate M1 near to the drain end, while ϕM2 denotes the work-function of gate M2 near to the source end. A nanogap cavity in the gate dielectric is formed by removing the selected portion of gate oxide for sensing the biomolecules. To investigate the sensitivity of these biosensors, dielectric constant and charge density within the cavity region are considered as governing parameters. The work-function of gate M2 is optimized and considered less than M1 to achieve abruptness at the source/channel junction, which results in better tunneling and improved ON-state current. The ATLAS device simulations show that dual metal SG-DMTFETs attains higher ON-state current and drain current sensitivity as compared to its counterpart device. Finally, a dual metal short-gate (DSG) biosensor is compared with the single metal short-gate (SG), single metal full-gate (FG), and dual metal full-gate (DFG) biosensors to analyse structurally enhanced conjugation effect on gate-channel coupling.