Silicon Nanowire Field-effect Transistors Research Articles

Study on Degradation Mechanisms of Thermal Conductivity for Confined Nanochannel in Gate-All-Around Silicon Nanowire Field-Effect Transistors

In this article, an analytical thermal conductivity model for confined nanochannel in gate-all-around silicon nanowire field-effect transistors (GAA SiNW FETs) is developed by considering the limitations caused by the cross section and length. A geometry dependence of phonon mean free path (MFP) is established for quantitatively analyzing the influence of cross-sectional dimension. Furthermore, the length-induced degradation mechanism is revealed by employing the transverse transportation phonon effective MFP. The results calculated by the model which was verified by published data indicate that the thermal conductivity of confined nanochannel in the GAA SiNW FETs is suffering from a severe degradation compared to that of ultrathin silicon in fully depleted (FD) silicon-on-insulator (SOI) MOSFETs. In addition to the suppression caused by the cross-sectional boundaries, the impact of the channel length should be taken into consideration during the modeling of thermal conductivity for accurately evaluating the self-heating effects (SHEs) in GAA SiNW FETs.

Quantum Transport in a Silicon Nanowire FET Transistor: Hot Electrons and Local Power Dissipation.

A review and perspective is presented of the classical, semi-classical and fully quantum routes to the simulation of electro-thermal phenomena in ultra-scaled silicon nanowire field-effect transistors. It is shown that the physics of ultra-scaled devices requires at least a coupled electron quantum transport semi-classical heat equation model outlined here. The importance of the local density of states (LDOS) is discussed from classical to fully quantum versions. It is shown that the minimal quantum approach requires self-consistency with the Poisson equation and that the electronic LDOS must be determined within at least the self-consistent Born approximation. To bring in this description and to provide the energy resolved local carrier distributions it is necessary to adopt the non-equilibrium Green function (NEGF) formalism, briefly surveyed here. The NEGF approach describes quantum coherent and dissipative transport, Pauli exclusion and non-equilibrium conditions inside the device. There are two extremes of NEGF used in the community. The most fundamental is based on coupled equations for the Green functions electrons and phonons that are computed at the atomically resolved level within the nanowire channel and into the surrounding device structure using a tight binding Hamiltonian. It has the advantage of treating both the non-equilibrium heat flow within the electron and phonon systems even when the phonon energy distributions are not described by a temperature model. The disadvantage is the grand challenge level of computational complexity. The second approach, that we focus on here, is more useful for fast multiple simulations of devices important for TCAD (Technology Computer Aided Design). It retains the fundamental quantum transport model for the electrons but subsumes the description of the energy distribution of the local phonon sub-system statistics into a semi-classical Fourier heat equation that is sourced by the local heat dissipation from the electron system. It is shown that this self-consistent approach retains the salient features of the full-scale approach. For focus, we outline our electro-thermal simulations for a typical narrow Si nanowire gate all-around field-effect transistor. The self-consistent Born approximation is used to describe electron-phonon scattering as the source of heat dissipation to the lattice. We calculated the effect of the device self-heating on the current voltage characteristics. Our fast and simpler methodology closely reproduces the results of a more fundamental compute-intensive calculations in which the phonon system is treated on the same footing as the electron system. We computed the local power dissipation and “local lattice temperature” profiles. We compared the self-heating using hot electron heating and the Joule heating, i.e., assuming the electron system was in local equilibrium with the potential. Our simulations show that at low bias the source region of the device has a tendency to cool down for the case of the hot electron heating but not for the case of Joule heating. Our methodology opens the possibility of studying thermoelectricity at nano-scales in an accurate and computationally efficient way. At nano-scales, coherence and hot electrons play a major role. It was found that the overall behaviour of the electron system is dominated by the local density of states and the scattering rate. Electrons leaving the simulated drain region were found to be far from equilibrium.

Fabrication and Characterization of an Aptamer-Based N-type Silicon Nanowire FET Biosensor for VEGF Detection

Cancer detection is an important part of modern medical diagnosis and many strategies based on nanotechnology had been developed in recent years. Of which, silicon nanowire (SiNW) field-effect transistor (FET) biosensor via DNA aptamer capture is considered as an interesting and viable option. Hence, in this report, we had assembled a n-type triple SiNW FET biosensor for the detection of vascular endothelial growth factor (VEGF) via surface functionalized DNA aptamer for a proof-of-concept. The SiNW FET biosensor was fabricated via "top-down" approach and the physical nature of the nanowire assembly was examined via atomic force microscopy (AFM) as well as scanning electron microscopy (SEM). We had subsequently grafted VEGF specific DNA aptamer via conventional EDC/NHS chemistry and later measured the conductance of the nanowires in a four-point probe detector for VEGF detection. We had demonstrated that the detection of VEGF was possible even at a concentration of 2.59 nM which was highly comparable to the other common biosensors for detection of VEGF protein. In addition to being scalable with complementary metal–oxide–semiconductor (CMOS) technology, the findings as demonstrated from our simple SiNW FET biosensor setup had helped to provide better insights towards optimizing the approach for the development of the next generation of miniature biosensors.

Strong Logic Obfuscation with Low Overhead against IC Reverse Engineering Attacks

Untrusted foundries pose threats of integrated circuit (IC) piracy and counterfeiting, and this has motivated research into logic locking. Strong logic locking approaches potentially prevent piracy and counterfeiting by preventing unauthorized replication and use of ICs. Unfortunately, recent work has shown that most state-of-the-art logic locking techniques are vulnerable to attacks that utilize Boolean Satisfiability (SAT) solvers. In this article, we extend our prior work on using silicon nanowire (SiNW) field-effect transistors (FETs) to produce obfuscated ICs that are resistant to reverse engineering attacks, such as the sensitization attack, SAT and approximate SAT attacks, as well as tracked signal attacks. Our method is based on exchanging some logic gates in the original design with a set of polymorphic gates (PLGs), designed using SiNW FETs, and augmenting the circuit with a small block, whose output is untraceable, namely, URSAT. The URSAT may not offer very strong resilience against the combined AppSAT-removal attack. Strong URSAT is achieved using only CMOS-logic gates, namely, S-URSAT. The proposed technique, S-URSAT + PLG-based traditional encryption, designed using SiNW FETs, increases the security level of the design to robustly thwart all existing attacks, including combined AppSAT-removal attack, with small penalties. Then, we evaluate the effectiveness of our proposed methods and subject it to a thorough security analysis. We also evaluate the performance penalty of the technique and find that it results in very small overheads in comparison to other works. The average area, power, and delay overheads of implementing 64 baseline key-bits of S-URSAT for small benchmarks are 5.03%, 2.60%, and −2.26%, respectively, while for large benchmarks they are 2.37%, 1.18%, and −1.93%.

Highly sensitive pH sensors based on double-gate silicon nanowire field-effect transistors with dual-mode amplification

This paper presents a method of achieving high sensitivity for silicon nanowire (SiNW) field-effect transistor (FET) pH sensor by operating the FETs in both capacitive amplification mode and differential amplification mode. The capacitive amplification is implemented by employing an inversed double-gate configuration that uses the electrode immersed in a solution well etched from the backside of the sensor chip as the top gate and the SiNW metal gate as the back gate. This enables the threshold voltages of the FETs to be amplified through the ratio of the top gate capacitance to the back gate capacitance. The differential amplification is achieved by a readout circuit chip that is vertically integrated with the sensor chip using flip-chip bonding. This allows the back gate to be controlled independently by the circuits, such that the differential amplification that is originally applicable to single-gate FETs can be applied to double-gate FETs. By operating the dual amplifications simultaneously, a sensitivity of 720.7 mV/pH has been achieved in the pH range of 4−10. Small deviations between the SiNW pH sensor and a commercial pH meter in measuring phosphate buffer saline, bovine serum, and tap water demonstrate the capability of the SiNW pH sensor in measuring practical samples.

Modeling of Viral Aerosol Transmission and Detection

In this paper, we propose studying the disease spread mechanism in the atmosphere as an engineering problem. Aerosol transmission is the most significant mode among the viral transmission mechanisms that do not include physical contact, where airflows carry virus-laden droplets over long distances. Throughout this work, we study the transport of these droplets as a molecular communication problem, where one has no control over the transmission source, but a robust receiver can be designed using bio-sensors. To this end, we present a complete system model and derive an end-to-end mathematical model for the transmission channel under certain constraints and boundary conditions. We derive the system response for both continuous sources such as breathing and jet or impulsive sources such as coughing and sneezing. In addition to transmitter and channel, we assumed a receiver architecture composed of air sampler and Silicon Nanowire field-effect transistor. Then, we formulate a detection problem to maximize the likelihood decision rule and minimize the corresponding missed detection probability. Finally, we present several numerical results to observe the impact of parameters that affect the performance and justify the feasibility of the proposed setup in related applications.

Simulation and investigations on semiconductor materials and devices with surround gate geometry for high performance and low power nano scale applications

All The device with surround gate geometry provides a better way to scale down the dimensions and optimization of power and performance for nano scale applications. The superior gate control can be obtained by novel materials and innovative techniques for various regions of the nano scale device. The surround gate (SG) field effect transistor provides high gain, high trans-conductance, reduced short channel effects and conditions for scaling the technology to sub nano scale. The device has been modeled using SILCAVO Atlas3d and DevEdit3D module also used for creating the device structure with integration of multiple layers of different materials. In this paper surround gate device input (ID-VGS) and output (ID-VDS) characteristics have been intensively studied and parameters including ION/IOFF ratio, DIBL, sub threshold slope extracted and compared with the conventional devices. The silicon nanowire field effect transistor (SiNWFET) with surround gate geometry at 0.6 V applied between source and drain exhibits threshold voltage (VTH) 0.204 V, drain induced barrier lowering (DIBL) 172 mV/V, sub-threshold swing (SS) 104.23 mV/dec, ION=440.1μA, IOFF=1.04 μA and ION/IOFF ratio 4.24e+02. The results demonstrate improvement in device parameters for the SiNWFET device as compared to other conventional MOSFETs. The result obtained for SiNWFET are also compared with FinFET and CNTFET devices. This research also investigates the integration of alternate channel, dielectric and gate materials into novel GAA device structure.

Improved Long-Term Responses of Au-Decorated Si Nanowire FET Sensor for NH3 Detection

Au nanoparticle (AuNP)-decorated silicon nanowire (SiNW) field-effect transistors (FETs) were made using a top-down technique to enhance the sensing responses and long-term reliability for the detection of ammonia (NH <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ). The as-fabricated, diluted hydrofluoric acid (dHF)-treated, and AuNP-decorated SiNW FETs were prepared and characterized at room temperature. These SiNW FETs show better sensitivity and low power consumption in the subthreshold regime than in the linear regime. To evaluate the long-term responses, devices were operated over a period of 120 days. The dHF-treated SiNW FET showed a significant degradation in sensitivity as a function of time, even though it showed the highest sensitivities in the initial stage. The SiNW with AuNPs showed the lowest long-term variation of sensitivity with sufficient linearity. The SiNW with AuNPs showed the lowest drift as low as -0.067%/day for current sensitivity and -0.024%/day for voltage sensitivity, respectively. These results suggest that the deposition of AuNPs on SiNW is very useful for improving the long-term variation in chemical sensing applications.

Label free detection of uric acid using Si nanowire PH sensor

In this study, we successfully apply a silicon nanowire FETs biosensor for detection of uric acid according to pH change. The pH sensing experiments of the silicon nanowire FETs shows that average sensitivity of 42mV/pH. We show that silicon nanowire FETs configured as pH sensors can be used for the quantitative detection of uric acid at concentration as low as 2.4mg/dL. The sensor shows a good linearity (R2 = 0.99) and sensitivity (60mV/mM) in the concentration range of 3-8mg/dL, with less than 300 sec response time. These results demonstrate that silicon nanowire FETs based biosensor can potentially be served as the diagnosis tool for general clinical examinations.

Surface Preparation as a Step in the Fabrication of Biosensors Based on Silicon Nanowire Field-Effect Transistors: Review

Issues concerning the detection of biomolecular targets by biosensors based on silicon nanowire field-effect transistors are discussed. We list and discuss steps in the surface preparation of silicon nanowires that lead to the efficient, highly sensitive, and selective detection of various analytes. The procedures for cleaning and activation of the surface of the silicon nanowires are addressed. Wet and dry methods for surface cleaning as well as surface-modification strategies applicable to transducers of biosensors are described. Surface modification by silane derivatives (i.e., silanization) and linker attachment is paid particular attention. The causes underlying the undesirable screening effect affecting a nanowire surface upon analyte detection in solutions are provided. The key requirements and strategies relevant to different steps in the preparation of biosensor surfaces that lead to improvement in their performance are mentioned.

Fabrication of SiNWs-FET Nanostructure Via Atomic Force Microscopy Lithography

The unique electrical properties of silicon nanowires (SiNWs) is one of the reasons it become an attractive transducer for biosensor nowadays. Positive (holes) and negative (electron) charge carriers from SiNWs can simply interact with either positive or negative charge of sensing target. In this paper, we have studied the fabrication of silicon nanowires field effect transistor (SiNWs-FET) nanostructure patterned on 15 Ω resistivity of p-type silicon on insulator (SOI) wafer fabricated via atomic force microscopy lithography technique. To fabricate SiNWs-FET nanostructure, a conductive AFM tip, Cr/Pt cantilever tip, was used then various value of applied voltage, writing speed and relative humidity were studied. Subsequent, followed by wet etching processes, admixture of tetramethylammonium hydroxide (TMAH) and isopropyl alcohol (IPA) were used to remove the undesired of silicon layer and diluted hydrofluoric acid (HF) was used to remove the oxide layer. From the results, it shows that, cantilever tip at 9 V with 0.4 μm/s writing speed and relative humidity between 55% - 60% gives the best formation of silicon oxide to fabricate SiNWs-FET nanostructure.

Amyloid-beta peptide detection via aptamer-functionalized nanowire sensors exploiting single-trap phenomena

New highly sensitive direct methods for the early detection of peptides involved in Alzheimer's disease (AD) are required in order to prolong effective and healthy memory and thinking capabilities and also to stop the factors resulting in AD. In this contribution, we report the successful demonstration of a label-free approach for the detection of amyloid-beta (Aβ) peptides by highly selective aptamers immobilized onto the SiO2 surface of the fabricated sensors. A modified single-stranded deoxyribonucleic acid (ssDNA) aptamer was specially designed and synthesized to detect the target amyloid beta-40 sequence (Aβ-40). Electrolyte–insulator–semiconductor (EIS) structures as well as silicon (Si) nanowire (NW) field-effect transistors (FETs) covered with a thin SiO2 dielectric layer have been successfully functionalized with Aβ-40-specific aptamers and used to detect ultra-low concentrations of the target peptide. The binding of amyloid-beta peptides of different concentrations to the surface of the sensors varied in the range from 0.1 pg/ml to 10 μg/ml resulting in a change of the surface potential was registered by the fabricated devices. Moreover, we show that the single-trap phenomena observed in the novel Si two-layer (TL) NW FET structures with advanced characteristic parameters can be effectively used to increase the sensitivity of nanoscale sensors. The obtained experimental data demonstrate a highly sensitive and reliable detection of ultra-low concentrations of the Aβ-40 peptides. This opens up prospects for the development of real-time electrical biosensors for studying and understanding different stages of AD by utilizing Si TL NW FET structures fabricated on the basis of cost-efficient CMOS-compatible technology.

Design and Investigation of Pressure Sensor Based on Charge Plasma Silicon NWFET with Cylindrical Gate Diaphragm

In this paper, we demonstrate a nanoelectro-mechanical system (NEMS) diaphragm pressure sensor based on dopingless charge plasma-gate all around (GAA) silicon Nanowire Field Effect Transistor (NWFET). By incorporating the advantages of GAA configuration i.e. better electrostatics and reduced short channel effects (SCEs) with those of dopingless configurations like reduced random dopant fluctuations (RDFs) give rise to an ultrasensitive pressure sensor with higher reliability. The surrounded gate in GAA behaves as the diaphragm. The applied pressure on the diaphragm bends the diaphragm that changes the metal-dielectric thickness of oxide layer that in turn affects the electrical characteristics of the device. The diaphragm bendings considered are 1, 1.5, 2 and 2.5 nm. Various device characteristics including potential, energy band diagrams, electron-hole concentrations, Ion, Ion/Ioff ratio etc. are evaluated which can be used as performance parameters of the proposed structure. Further investigation of the device’s design parameters for optimized sensor designing viz. dielectric material of spacer and length of the spacer is carried out. Results reveal that this ultrasensitive pressure sensor with lower SCEs shows higher reliability and yield comparatively higher sensitivity towards applied low pressures as low as 0.73 pN/nm2. The drain current could be increased by using high-k material at spacer (HfO2) and also spacer length around 10 nm provides better switching. Thus, with ease of fabrication, this sensor could be used in low-pressure sensing applications for the biomedical field.

Magnetic-field-driven electron transport in SOI back-gate device

In this work, we studied the electronic transport properties of silicon nanowire field-effect transistors with a back gate. A nontrivial magnetic field influence on the drain current at low temperature (10 K) was found. The strongest effect was observed in the majority carrier accumulation mode. In this mode magnetic field of 0.5 T increases current through the device by more than an order of magnitude. The paper describes the possible mechanisms of the magnetic field influence on the electronic transport characteristics of the structures.

Observation of mobility and velocity behaviors in ultra-scaled LG = 15 nm silicon nanowire field-effect transistors with different channel diameters

Experimentally, two critical device performance factors, apparent mobility (μapp) and virtual source velocity (vx0) were investigated down to effective channel length (Leff) = 15 nm silicon nanowire field-effect transistors (SNWFETs) by using virtual source (VS) model. Both μapp and vx0 decreased in n-SNWFETs but increased in p-SNWFETs as the nanowire diameter (DNW) shrank because of opposite effective mass (meff) dependency. The critical on-current booster, vx0 rather than μapp increased monotonically as Leff shrank, and it showed that vx0 boosting by Leff scaling is still valid to Leff = 15 nm in SNWFETs. Furthermore, p-SNWFETs had higher μapp and vx0 than n-SNWFETs because compressive stress from SiGe layer below source/drain improved the performance of p-SNWFETs. Interestingly, unpredicted non-linearity of Leff/μapp vs. 1/vx0 plot was observed in short channel p-SNWFETs and its origin was discussed. Finally, thermal limit velocity (vTx) and ballistic efficiency (Bsat) consisting vx0 were extracted from experimental data. The DNW dependence of vTx and Bsat was analyzed using stress effect, meff, critical length (LC), and mean free path (λ), which provides the way of vx0 boosting.

O2 plasma treated biosensor for enhancing detection sensitivity of sulfadiazine in a high-к HfO2 coated silicon nanowire array

In this paper, highly uniform silicon nanowire (SiNW) arrays (∼30 nm in diameter) used as FET biosensors are fabricated by using a CMOS-compatible spacer image transfer (SIT) technology with high efficiency compared with conventional electron beam (E-beam) lithography. An effective biochemical sensing approach that treated with optimization of O2 plasma on the SiNW biosensors coated with a 10 nm HfO2 high dielectric constant (high-к) film is demonstrated to enhance immobilization of antibodies. Furthermore, water contact angle (WCA) measurements verify that the increased number of hydroxyl groups (OH) on the HfO2 surfaces treated with O2 plasma reaches or surpasses that on a conventional SiO2 surface. Therefore, it is observed that the IDS/I0 is enlarged by 3.15 times compared with that of the HfO2 surface without O2 plasma treatment. In addition, real-time and label-free detection of sulfadiazine with high sensitivity and specific recognition is successfully achieved using the SiNW FET biosensor with the optimized process. And a 10 pg⋅mL−1 limit of detection (LOD) is achieved for the SiNW FET biosensor using O2 plasma treatment on an ultrathin HfO2 mentioned above. The proposed O2 plasma treatment on HfO2 provides an effective solution for future FET biosensors coated with high-к dielectrics.

Effect of air spacer in underlap GAA nanowire: an analogue/RF perspective

Here, a comprehensive study of the gate-all-around silicon nanowire field effect transistor (FET) (GAA-SNWTs) with source/drain underlap is performed to investigate the influence of air as spacer dielectric, on analogue/RF behaviour of the device. Parasitic capacitances in nanoscale devices contribute a dominating role in overall device capacitances. Introducing air as spacer dielectric () in source/drain underlap region, device parasitic capacitances deteriorates, which improves the overall capacitances. Thus, the analogue/RF figure-of-merit (FOM) of the device enhances, rendering the device suitable for low-power high-frequency operations. For targeting low power applications, FOMs are elicited at . It is perceived that intrinsic gain of the device is almost unaltered for distinct spacer dielectric ( and air). Frequencies like cut-off frequency () and maximum oscillation frequency () of air spacer dielectric-based underlap GAA-SNWTs are enhanced by 2.92 times and 3.11 times, respectively, when contrasted by the spacer-based GAA-SNWTs. This results in higher percentage improvement in RF-FOM in terms of transconductance frequency product (TFP), gain-frequency product (GFP), and gain transconductance frequency product (GTFP).

Ultrasensitive Electrical Detection of Hemagglutinin for Point-of-Care Detection of Influenza Virus Based on a CMP-NANA Probe and Top-Down Processed Silicon Nanowire Field-Effect Transistors.

Rather than the internal genome nucleic acids, the biomolecules on the surface of the influenza virus itself should be detected for a more exact and rapid point-of-care yes/no decision for influenza virus-induced infectious diseases. This work demonstrates the ultrasensitive electrical detection of the HA1 domain of hemagglutinin (HA), a representative viral surface protein of the influenza virus, using the top-down complementary metal oxide semiconductor (CMOS) processed silicon nanowire (SiNW) field-effect transistor (FET) configuration. Cytidine-5′-monophospho-N-acetylneuraminic acid (CMP-NANA) was employed as a probe that specifically binds both to the aldehyde self-aligned monolayer on the SiNWs and to HA1 simultaneously. CMP-NANA was serially combined with two kinds of linkers, namely 3-aminopropyltriethoxysilane and glutaraldehyde. The surface functionalization used was verified using the purification of glutathione S-transferase-tagged HA1, contact angle measurement, enzyme-linked immunosorbent assay test, and isoelectric focusing analysis. The proposed functionalized SiNW FET showed high sensitivities of the threshold voltage shift (ΔVT) ~51 mV/pH and the ΔVT = 112 mV (63 mV/decade) with an ultralow detectable range of 1 fM of target protein HA1.

Signal Enhancement of Silicon Nanowire Field-Effect Transistor Immunosensors by RNA Aptamer

Silicon nanowire field-effect transistors (SiNW-FETs) have been demonstrated as a highly sensitive platform for label-free detection of a variety of biological and chemical entities. However, detecting signal from immunoassays by nano-FETs is severely hindered by the distribution of different charged groups of targeted entities, their binding orientation, and distances to the surface of the FET. Aptamers have been widely applied as a recognition element for plentiful biosensors because of small molecular sizes and moderate to high specific binding affinity with different types of molecules. In this study, we propose an effective approach to enhance the electrical responses of both direct (6×-histidine) and sandwich (amyloid β 1–42) immunoassays in SiNW-FETs with R18, a highly negative charged RNA aptamer against rabbit immunoglobulin G (IgG). Empirical results presented that the immunosensors targeted with R18 expressed a significantly stabilized and amplified signal compared to the ones without this aptamer. The research outcome provides applicability of the highly negative charged aptamer as a bioamplifier for immunoassays by FETs.

Silicon Nanowires Field Effect Transistors: A Comparative Sensing Performance between Electrical Impedance and Potentiometric Measurement Paradigms.

Potentiometric sensors based on silicon nanowire field effect transistors (SiNW FETs) typically display exquisite sensitivities, but their bioanalytical implementation is limited due to the need for stringent measurement conditions and high-precision readout units. An alternative operation principle where SiNW FETs are operated in a frequency-domain electrical impedimetric approach is promising. However, to date only limited data is available in regard to the sensing performance and translational relevance of this novel approach in comparison to the standard charge detection paradigm. We demonstrate the feasibility of conducting electrical impedimetric FET measurements with a portable unit for the ultrasensitive detection of cancer biomarkers in biospecimens. Compared to standard potentiometric measurements, electrical impedimetric FET measurements yielded significant improvements in biosensing performances, including the limit of detection, sensing resolution, and dynamic range.