TFET Research Articles

Modeling and Simulation of a TFET-Based Label-Free Biosensor with Enhanced Sensitivity

This study discusses the use of a triple material gate (TMG) junctionless tunnel field-effect transistor (JLTFET) as a biosensor to identify different protein molecules. Among the plethora of existing types of biosensors, FET/TFET-based devices are fully compatible with conventional integrated circuits. JLTFETs are preferred over TFETs and JLFETs because of their ease of fabrication and superior biosensing performance. Biomolecules are trapped by cavities etched across the gates. An analytical mathematical model of a TMG asymmetrical hetero-dielectric JLTFET biosensor is derived here for the first time. The TCAD simulator is used to examine the performance of a dielectrically modulated label-free biosensor. The voltage and current sensitivity of the device and the effects of the cavity size, bioanalyte electric charge, fill factor, and location on the performance of the biosensor are also investigated. The relative current sensitivity of the biosensor is found to be about 1013. Besides showing an enhanced sensitivity compared with other FET- and TFET-based biosensors, the device proves itself convenient for low-power applications, thus opening up numerous directions for future research and applications.

Interfacial trap charge and self-heating effect based reliability analysis of a Dual-Drain Vertical Tunnel FET

This manuscript exclusively addresses the reliability concern of a double-drain vertical TFET (DD-VTFET) by analysing the influence of interface trap charges and variation in ambient temperature on various DC and analog/RF figure of merits. For detailed analysis, performance of the device is evaluated by considering different densities and polarities of trap charges existing at gate-oxide/channel interface. TCAD-based simulation results reveal that trap charges significantly alter the flat-band voltage, which further causes variation in the device performance. It is observed from the transfer characteristic curve that the leakage current is degraded from 10−18 to 10−13A/μm when a positive (donor) charge density of 1013 cm−2 is introduced at oxide/channel interface. However, cut-off frequency is found to be improved under the influence of donor traps, which is mainly attributed due to improvement in transconductance of the device. Moreover, simulation results indicate that DD-VTFET is immune to the negative (acceptor) traps in comparison with the positive traps. Furthermore, the analysis carried out for temperature affectability on the device performance suggests that, at higher ambient temperature, the off-state current degrades more in subthreshold region (at low gate bias) due to dominance of the Shockley-Read-Hall (SRH) and trap-assisted tunneling (TAT) mechanisms, which exponentially depend on the temperature. Therefore, the leakage current increases approximately by an order 7 when temperature is increased from 200 K to 400 K. Since band-to-band tunneling starts dominating over SRH and TAT in the super-threshold region (at high gate bias), the impact of temperature variation along with presence of the trap charges is found to be insignificant on the transfer characteristics.

A highly sensitive vertical plug-in source drain high Schottky barrier bilateral gate controlled bidirectional tunnel field effect transistor.

In this article, we propose a highly sensitive vertically plug-in source drain contacts high Schottky barrier based bilateral gate and assistant gate controlled bidirectional tunnel field Effect transistor (VPISDC-HSB-BTFET). It can achieve much more sensitive forward current driving ability than the previously proposed High Schottky barrier source/drain contacts based bilateral gate and assistant Gate controlled bidirectional tunnel field Effect transistor (HSB-BTFET). Silicon body of the proposed VPISDC-HSB-BTFET is etched into a U-shaped structure. By etching both sides of the silicon body to form vertically plug-in source drain contacts, the source and drain electrodes are plugged into a certain height of the vertical parts of both sides of the U-shaped silicon body. Thereafter, the efficient area of the band-to-band tunneling generation region near the source drain contacts is significantly increased, so as to achieve sensitive ON-state current driving ability. Comparing to the mainstream FinFET technology, lower subthreshold swing, lower static power consumption and Higher Ion-Ioff ratio can be achieved.

Design and investigation of doping-less gate-all-around TFET with Mg2Si source material for low power and enhanced performance applications

Metal–oxide–semiconductor field-effect transistor (MOSFET) faces the major problem of being unable to achieve a subthreshold swing (SS) below 60 mV/dec. As device dimensions continue to reduce and the demand for high switching ratios for low power consumption increases, the tunnel field-effect transistor (TFET) appears to be a viable device, displaying promising characteristic as an answer to the shortcomings of the traditional MOSFET. So far, TFET designing has been a task of sacrificing higher ON state current for low subthreshold swing (and vice versa), and a device that displays both while maintaining structural integrity and operational stability lies in the nascent stages of popular research. This work presents a comprehensive analysis of a heterojunction plasma doped gate-all-around TFET (HPD-GAA-TFET) by making a comparison between Mg2Si and Si which serve as source materials. Charge plasma technique is employed to implement doping in an intrinsic silicon wafer with the help of suitable electrodes. A low-energy bandgap material, i.e. magnesium silicide is incorporated as source material to form a heterojunction between source and silicon-based channel. A rigorous comparison of performance between Si-based GAA-TFET and HPD-GAA-TFET is conducted in terms of electrical, radio frequency (RF), linearity, and distortion parameters. It is observable that HPD-GAA-TFET outperforms conventional Si-based GAA-TFET with an ON-state current (I ON), subthreshold swing (SS), threshold voltage (V th), and current switching ratio being 0.377 mA, 12.660 mV/dec, 0.214 V, and 2.985 × 1012, respectively. Moreover, HPD-GAA-TFET holds faster switching and is more reliable than Si-based device. Therefore, HPD-GAA-TFET is suitable for low-power applications.

Structural Optimized H-Gate High Schottky Barrier Bidirectional Tunnel Field Effect Transistor

In this work, we proposed a structural optimized H-shaped gate bidirectional tunnel field effect transistor with high on-state current based on high Schottky barrier plug-in source–drain contacts and central assistant gate (H-Gate HSB-BTFET). Compared to the previously proposed high Schottky barrier bidirectional tunnel field effect transistor (HSB-BTFET), the proposed H-Gate BTFET achieves excellent switching characteristics such as better forward on-state current, lower subthreshold swing (SS), lower power consumption, higher Ion–Ioff ratio, and lower band to band tunneling (BTBT) induced leakage. The physical mechanism of device performance improvement is explained, analyzed, and compared with HSB-BTFET. In addition, no more complex process technology and expensive millisecond annealing process are needed; the proposed H-Gate BTFET can be used as an alternative candidate for mainstream integration technology.

Design and simulation of junctionless nanowire tunnel field effect transistor for highly sensitive biosensor

This paper investigates symmetrical design of a Junctionless Nanowire Tunnel-Field-Effect-Transistor (JL-NWTFET) for highly sensitive biosensor. JL-NWTFET deployed using Gate-All-Around (GAA) structure and Dielectric-Modulation (DM) technique to detects the bio-logical molecules such as uricase, streptavidin, protein, biotin, uriease, Amino-propyl triethoxysilane (APTS), ChOx etc. The variation in the drain current (ID), subthreshold slope (SS), transconductance (gm), and ION/IOFF ratio considered as the sensitivity parameters of the JL-NWTFET to detect different biological molecules in the cavity area. The cavity area is formed by a layer in between the source-gate oxides and source-gate electrodes. The JL-NWTFET shows the reduced leakage currents in terms of Short-Channel-Effects (SCEs) and superior controllability over the channel. The proposed JL-NWTFET has been designed with uniform doping concentration (1 × 10−19 cm−3), and gate work-function (φgate = 4.8eV). The high sensitivity (∼109) is observed for APTS biomolecule with dielectric constant (K = 3.57).

Design and Modelling of Tunnel Field Effect Transistor- using TCAD Modeling

The purpose of this research was to suggest a junction-less strategy for a vertical Tunnel Field Effect Transistor, which would increase the device's efficiency. In this study, we examine the similarities and differences between a negative capacitor TFET and a vertically generated TFET with a source pocket and a heterostructure-based nanowire gate. And how the channel transit impacts the output qualities of a sub-100 nanometer sized device. The Silvaco TCAD (a commercially available tool) was used to simulate a tri-layer high-K dielectric made of hafnium zirconium oxide (HZO) and titanium dioxide (TiO2) materials as gate stacking to the V-TFET and GAA-NC-TFET structures, and the tunnelling and transport parameters were calibrated experimentally. A short bandgap material, GaSb, in the home region to enhance carrier tunnelling via the mentioned three source (GaSb)-channel (Si) heterojunction at varying biases were utilized. Motion, tube length, and saturating velocity are only few of the transport channel characteristics that are investigated. As a result of the building's vertical orientation, the electric field is enhanced, allowing for an ION current of up to 104 Am2. The most unexpected result of this device is that a high ION/IOFF may increase mobility and reduce saturation velocity, perhaps reducing the drain voltage at saturation. The proposed biosensor's sensitivity was multiplied by 108 when vertical and lateral tunnelling were used in tandem. We apply a variety of optimisation strategies to deal with this problem, despite the fact that quantum confinement reduces the effect of mobility variations on device performance. When biomolecules were positively charged, the drain current increased, and when they were negatively charged, the drain current decreased.

Reconfigurable signal modulation in a ferroelectric tunnel field-effect transistor

Reconfigurable transistors are an emerging device technology adding new functionalities while lowering the circuit architecture complexity. However, most investigations focus on digital applications. Here, we demonstrate a single vertical nanowire ferroelectric tunnel field-effect transistor (ferro-TFET) that can modulate an input signal with diverse modes including signal transmission, phase shift, frequency doubling, and mixing with significant suppression of undesired harmonics for reconfigurable analogue applications. We realize this by a heterostructure design in which a gate/source overlapped channel enables nearly perfect parabolic transfer characteristics with robust negative transconductance. By using a ferroelectric gate oxide, our ferro-TFET is non-volatilely reconfigurable, enabling various modes of signal modulation. The ferro-TFET shows merits of reconfigurability, reduced footprint, and low supply voltage for signal modulation. This work provides the possibility for monolithic integration of both steep-slope TFETs and reconfigurable ferro-TFETs towards high-density, energy-efficient, and multifunctional digital/analogue hybrid circuits.

Converging-guiding-track design enables 100% growth deployment rate of ultrathin monocrystalline silicon nanowire channels

A low temperature catalytic growth of orderly ultrathin silicon nanowires (SiNWs) is desirable for the construction of monolithic 3D stacked electronics but usually suffers a large diameter fluctuation and a low growth deployment rate (GDR). In this work, the ultra-confined growth dynamics of in-plane solid–liquid–solid SiNWs within narrow groove tracks has been systematically investigated, and a converging-guiding-track strategy is proposed and testified to accomplish 100% GDR of ultra-dense and uniform SiNW array, with diameter and spacing of only Dnw = 22.5±3.5 nm and 25 nm, respectively. Despite a low temperature growth at 350 °C, the SiNWs are found to be all monocrystalline and Si⟨100⟩ oriented, while prototype Schottky barrier tunneling field effect transistors built on the SiNW channels demonstrate a high Ion/off ratio and subthreshold swing of >105 and 197 mV dec−1. This new strategy complements a long-missing key capability of catalytic growth approach to serve a reliable integration technology of ultrafine high quality 1D c-Si channels, without the need of preexisting wafer substrate, for a wide range of 3D electronics, neuromorphic, and logic-in-memory functionalities.

Optimization of tunneling current in ferroelectric tunnel FET using genetic algorithm

Optimization of tunneling current in ferroelectric tunnel FET using genetic algorithm

An accurate analytical surface potential model of heterojunction tunnel FET

Based on the accurate and efficient thermal injection method, we develop a fully analytical surface potential model for the heterojunction tunnel field-effect transistor (H-TFET). This model accounts for both the effects of source depletion and inversion charge, which are the key factors influencing the charge, capacitance and current in H-TFET. The accuracy of the model is validated against TCAD simulation and is greatly improved in comparison with the conventional model based on Maxwell–Boltzmann approximation. Furthermore, the dependences of the surface potential and electric field on biases are well predicted and thoroughly analyzed.

Impact of hole trap-detrap mechanism on X-ray irradiation induced threshold voltage shift of radiation-hardened GAA TFET device

We demonstrate the X-ray irradiation effect on a radiation-hardened gate-all-around tunnel FET (GAA TFET) device. The radiation-hardened device has a high and fixed oxide electric field, which is responsible to attain equilibrium state of the device. Once the device reaches equilibrium, the threshold voltage starts to saturate for any variation in the gate bias. Therefore, the fixed electric field in the oxide region is reduced with the application of negative bias to the gate, which varies the equilibrium trapped charge concentration in the oxide. The negative gate bias causes electrons of oxide and holes from the bias terminal to recombine, which ultimately reduces the electric field in the oxide region. This variation in charge concentration results in a new threshold voltage when the device has been re-irradiated. Further, the unique carrier injection mechanism of the TFET device plays a significant role in trapping and detrapping mechanisms along the channel. The report consists of positive charge trapping and detrapping of charge carriers along the channel of the GAA-TFET device. In addition, the report also deals with the impact of applying excessive gate bias to the device and its impact on electric fields. For the X-ray irradiation analysis, several figures of merit are taken into consideration before coming to the conclusion of the report, such as geminate yield, trapped charges in the oxide region, and time-varying positive charge build-up in the oxide. The device under consideration has also been irradiated with several radiation doses and time durations to verify its robustness.

Investigation of gate leakage current in TFET: A semi-numerical approach

Tunneling FET (TFET) has been demonstrated as a favorable candidate to replace conventional MOSFETs in low-power applications. However, there are many challenges that should be overcome to efficiently operate the TFET. One of the most limiting factors that can restrict the TFET performance is the gate leakage current. In this paper, the tunneling leakage current through the gate oxide of double gate TFET has been analyzed. The conduction band energy level for gate-oxide-silicon was employed to calculate the tunneling transmission coefficient by utilizing a numerical method. To obtain the potential barrier between the gate and the channel surface, a modified analytical pseudo-2D method has been applied to deduce the corresponding surface potential taking into account a precise calculation of depletion regions. Furthermore, the inclusion of the image charge barrier lowering effect is incorporated in calculating the transmission probability through the oxide. Including such an effect shows a significant influence on determining the gate tunneling current. The gate leakage current has been calculated for various bias voltages and equivalent oxide thicknesses. The presented semi-numerical technique shows good agreement within a suitable CPU time when validated and compared against full numerical TCAD simulation.

Simulation study of n+ pocket step shape heterodielectric double gate tunnel FET for switching and biosensing applications

In this article, an n+ pocket step shape heterodielectric double gate Tunnel TFET (SSHDDG-TFET) is designed for high frequency and biosensing applications. A calibration of TCAD model with fabricated data is presented to achieve accurate results from the simulator. The effect of pocket doping concentration on transconductance (gm), cut-off frequency (fc), and gain bandwidth product (GBW) are highlighted for n+ pocket SSHDDG TFET. In consecutive step, a biosensor is designed using the proposed TFET to detect the wide range of biomolecules and the sensitivity is extracted in the existence of neutral as well as charged biomolecules. The sensitivity is analyzed considering the partially filled cavity of this biosensor. The various prominent results in terms of analog and biosensing applications for the considered TFET are drain current sensitivity (SI,DS) of 3.21 × 1010, 3.6 × 1013, and 9.5 × 107 for neutral, positive (Nf = 1e12 cm−3), and negative charged biomolecules (Nf = -1e12 cm−3), respectively, at k = 12, maximum gm of order 10−4 S, and fc is of order 1010 Hz.

Two-Dimensional Transition Metal Dichalcogenide Tunnel Field-Effect Transistors for Biosensing Applications.

Field-effect transistor (FET) biosensors based on two-dimensional (2D) materials have drawn significant attention due to their outstanding sensitivity. However, the Boltzmann distribution of electrons imposes a physical limit on the subthreshold swing (SS), and a 2D-material biosensor with sub-60 mV/dec SS has not been realized, which hinders further increase of the sensitivity of 2D-material FET biosensors. Here, we report tunnel FETs (TFETs) based on a SnSe2/WSe2 heterostructure and observe the tunneling effect of a 2D material in aqueous solution for the first time with an ultralow SS of 29 mV/dec. A bilayer dielectric (Al2O3/HfO2) and graphene contacts, which significantly reduce the leakage current in solution and contact resistance, respectively, are crucial to the realization of the tunneling effect in solution. Then, we propose a novel biosensing method by using tunneling current as the sensing signal. The TFETs show an extremely high pH sensitivity of 895/pH due to ultralow SS, surpassing the sensitivity of FET biosensors based on a single 2D material (WSe2) by 8-fold. Specific detection of glucose is realized, and the biosensors show a superb sensitivity (3158 A/A for 5 mM), wide sensing range (from 10-9 to 10-3 M), low detection limit (10-9 M), and rapid response rate (11 s). The sensors also exhibit the ability of monitoring glucose in complex biofluid (sweat). This work provides a platform for ultrasensitive biosensing. The discovery of the tunneling effect of 2D materials in aqueous solution may stimulate further fundamental research and potential applications.

Ultrahigh gain hot-electron tunneling transistor approaching the collection limit

Ultrahigh gain hot-electron tunneling transistor approaching the collection limit

Trap sensitivity of splitted source Z Shape horizontal pocket and hetero stack TFETs: a simulation study

This paper reports the trap sensitivity analysis of split source horizontal pocket Z shape tunnel field effect transistor (ZHP-TFET) and hetero stack TFET (HS-TFET) using technology computer aided design (TCAD) simulator. The sensitivity analysis elaborates the significance of ideal trap charges at the interface of oxide and semiconductor material for both acceptor and donor like traps. The trap sensitivity analysis is highlighted for variation in trap-concentrations, temperature, gate-metal work function, and peak energy position, for both the TFETs. Furthermore, we have implemented digital inverter on taking into account the interface trap charges effect. Result reveals that tarp sensitivity on various electrical parameter of HS-TFET is significantly higher than ZHP-TFET. It is seen that ZHP-TFET provides sensitivity around 11 and 33 under acceptor and donor impurities, respectively, whereas, for HS-TFET sensitivity is around 22 and 60 for acceptor and donor impurities, respectively, for wide variation in trap concentration. The voltage transfer characteristic and voltage gain of digital inverter are improved by observable amount in ZHP-TFET than HS-TFET for both donor and acceptor like trap. The noise margin of ZHP-TFET based resistive inverter comes 0.75 V, 0.73 V, and 0.77 V, while in case of HS-TFET these value noted as 0.32 V, 0.13 V and 0.37 V under consideration for no trap, acceptor trap, and donor trap, respectively.

A Highly Reliable Nanoscale Biodevice Benefitting from the Charge Plasma Concept – Si and InAs Source

A nanoscale biodevice based on the tunneling field effect transistor (TFET) has been reported for the detection of the target biomolecules. Two kinds of materials in the cases of silicon and InAs have been incorporated inside the source region for the sensitivity performance comparison. In order to prevent the diffusion of the impurities in the nanoscale biodevice during thermal proceeding, whole the structure has been doped at a N-type doped same level forming a junctionless device. The approach that we have benefited is the utilization of the charge plasma for converting the N-type source into the P-type source resulting in the creation of the TFET device, electrically. Indeed, the hole plasma will be appeared inside the source by the auxiliary plasma gate electrodes. The obtained results performed by the SILVACO simulator has shown the improvement of the sensitivity of the proposed biodevice while keeping the reliability high. Also, the fill-factor impact and trap-assisted-tunneling (TAT) issue as serious challenges on sensing performance are monitored for the biodevices under the study and the interesting results are presented.

Performance Investigation of GaSb/Si Heterojunction based Gate Underlap and Overlap Vertical TFET Biosensor.

The present paper estimates the performance of vertically developed double gate GaSb/Si tunnel field-effect transistor (V-DGTFET) biosensor with source pocket. A commercially accessible tool, Silvaco-TCAD, is exploited for carrying simulations of V-DGTFET. The device's novelty is deploying a material with a small bandgap, namely GaSb, in the source region to improve the carrier tunneling in source-channel (GaSb-Si) heterojunction. Further, the present work has analysed the performance on half gate underlap and half gate overlap V-DGTFET based label-free biosensor. The performance of V-DGTFET biosensor corresponding to various biomolecules such as APTES with κ=3.57, bacteriophage-T7 with κ=6.4, apomyoglobin with κ =8.1 and gelatin with κ=12 is investigated with reference to energy band diagram, potential profile, electric field and drain characteristics. Furthermore, by considering the different values of dielectric constants from 1 to 12, the present paper computed the figure of merits (FOMs) essentially linearity and sensitivity. The results demonstrated that neutral biomolecules with higher dielectric constant values showed higher sensitivity compared with other biomolecules. Moreover, it is estimated that gelatin has to drain current sensitivity of 5.6×105, which is 13%, 20%, and 41% more in comparison to apomyoglobin (κ =8.1), bacteriophage-T7 (κ=6.4), and APTES (κ =3.57) sensitivity at 15 nm cavity length.

Design and Investigation of a Single Gate Heterostructure Junctionless Tunnel FET for the Gas Detection

In this paper, a single gate junctionless heterostructure TFET gas sensor (SiGe-SG-JLTFET) is presented, and its effectiveness is examined. The high-k gate dielectric (HfO2) and low bandgap alloy prove to be a great combination to boost the drain current. The leakage current is controlled by the presence of a silicon body in the channel and drain. We have considered a Palladium metal with a suitable work-function in the gate catalyst for better sensitivity purposes. The sensor modulates the flat band voltage and Capacitance-Voltage characteristics with the adsorption of gas atoms at the Palladium/HfO2 and Palladium surfaces. Consequently, the ON-state current is affected, which is treated as a sensing measure. The gas sensor’s electrostatic analysis is investigated in terms of I-V characteristics, current components, band energy for both ON- and leakage conditions, maximum electric field, BTBT rate, and carrier concentrations. Similarly, the sensitivity analysis consists of drain current sensitivity (SID), current ratio sensitivity (Sratio), and average SS sensitivity (SSS). The investigation has been carried out with the change in gas pressure in terms of work-function, temperature (0K), and interface trap charges (ITC) using a TCAD device simulator. The proposed gas sensor exhibits a (SID)max of 2.41 × 106 and Sratio of 3.89 × 104 with higher pressure concentration at room temperature respectively.