Silicon Nanowire Field-effect Transistors Research Articles

Silicon on isolator ribbon field-effect nanotransistors for high-sensitivity low-power biosensor

Silicon nanowire field-effect transistors are discussed as biological sensors due to their excellent sensitivity due to the large surface-to-volume ratio and high selectivity with respect to a large number of analytes. A miniature sensor based on a long-channel fin field-effect transistor as a surface charge detector is being investigated. The three-gate configuration offers undeniable advantages over planar devices, since the edges are about a hundred nanometers wide and are characterized by increased conductivity, which leads to higher sensitivity. The characteristics of the transistor are optimized using 3D modeling performed by the computer-aided design software package TCAD, depending on the topological parameters of the transistor and the level of control voltages. Based on the obtained simulation results, a chip was manufactured on a SOI substrate based on self-aligning CMOS-compatible technological processes from top to bottom. It is established that thin structures with a reduced level of doping and low supply power have promising electrical characteristics for an effective approach to scaling a high-resolution pH sensor, which is of particular interest to integrated pH bioanalytics based on CMOS technology.

Rapid Screen for Antiviral T-Cell Immunity with Nanowire Electrochemical Biosensors.

The ability to rapidly assess and monitor patient immune responses is critical for clinical diagnostics, vaccine design, and fundamental investigations into the presence or generation of protective immunity against infectious diseases. Recently, findings on the limits of antibody-based protection provided by B-cells have highlighted the importance of engaging pathogen-specific T-cells for long-lasting and broad protection against viruses and their emergent variants such as in SARS-CoV-2. However, low-cost and point-of-care tools for detecting engagement of T-cell immunity in patients are conspicuously lacking in ongoing efforts to assess and control population-wide disease risk. Currently available tools for human T-cell analysis are time and resource-intensive. Using multichannel silicon-nanowire field-effect transistors compatible with complementary metal-oxide-semiconductor, a device designed for rapid and label-free detection of human T-cell immune responses is developed. The generalizability of this approach is demonstrated by measuring T-cell responses against melanoma antigen MART1, common and seasonal viruses CMV, EBV, flu, as well as emergent pandemic coronavirus, SARS-CoV-2. Further, this device provides a modular and translational platform for optimizing vaccine formulations and combinations, offering quick and quantitative readouts for acquisition and persistence of T-cell immunity against variant-driven pathogens such as flu and pandemic SARS-CoV-2.

Nanosensors in clinical development of CAR-T cell immunotherapy

Immunotherapy using CAR-T cells is a new technological paradigm for cancer treatment. To avoid severe side effects and tumor escape variants observed for conventional CAR-T cells approach, adaptor CAR technologies are under development, where intermediate target modules redirect immune cells against cancer. In this work, silicon nanowire field-effect transistors are used to develop target modules for an optimized CAR-T cell operation. Focusing on a library of seven variants of E5B9 peptide that is used as CAR targeting epitope, we performed multiplexed binding tests using nanosensor chips. These peptides had been immobilized onto the sensor to compare the transistor signals upon titration with anti-La 5B9 antibodies. The correlation of binding affinities and sensor sensitivities enabled a selection of candidates for the interaction between CAR and target modules. An extremely low detection limit was observed for the sensor, down to femtomolar concentration, outperforming the current assay of the same purpose. Finally, the CAR T-cells redirection capability of selected peptides in target modules was proven successful in an in-vitro cytotoxicity assay. Our results open the perspective for the nanosensors to go beyond the early diagnostics in clinical cancer research towards developing and monitoring immunotherapeutic treatment, where the quantitative analysis with the standard techniques is limited.

Silicon Nanowires Length and Numbers Dependence on Sensitivity of the Field-Effect Transistor Sensor for Hepatitis B Virus Surface Antigen Detection.

Silicon nanowire field effect transistor (NWFET) sensors have been demonstrated to have high sensitivity, are label free, and offer specific detection. This study explored the effect of nanowire dimensions on sensors’ sensitivity. We used sidewall spacer etching to fabricate polycrystalline silicon NWFET sensors. This method does not require expensive nanoscale exposure systems and reduces fabrication costs. We designed transistor sensors with nanowires of various lengths and numbers. Hepatitis B surface antigen (HBsAg) was used as the sensing target to explore the relationships of nanowire length and number with biomolecule detection. The experimental results revealed that the sensor with a 3 µm nanowire exhibited high sensitivity in detecting low concentrations of HBsAg. However, the sensor reached saturation when the biomolecule concentration exceeded 800 fg/mL. Sensors with 1.6 and 5 µm nanowires exhibited favorable linear sensing ranges at concentrations from 800 ag/mL to 800 pg/mL. The results regarding the number of nanowires revealed that the use of few nanowires in transistor sensors increases sensitivity. The results demonstrate the effects of nanowire dimensions on the silicon NWFET biosensors.

Highly Stretchable High-Performance Silicon Nanowire Field Effect Transistors Integrated on Elastomer Substrates.

Quasi‐1D silicon nanowires (SiNWs) field effect transistors (FETs) integrated upon large‐area elastomers are advantageous candidates for developing various high‐performance stretchable electronics and displays. In this work, it is demonstrated that an orderly array of slim SiNW channels, with a diameter of <80 nm, can be precisely grown into desired locations via an in‐plane solid‐liquid‐solid (IPSLS) mechanism, and reliably batch‐transferred onto large area polydimethylsiloxane (PDMS) elastomers. Within an optimized discrete FETs‐on‐islands architecture, the SiNW‐FETs can sustain large stretching strains up to 50% and repetitive testing for more than 1000 cycles (under 20% strain), while achieving a high hole carrier mobility, I on/I off current ratio and subthreshold swing (SS) of ≈70 cm2 V−1 s−1, >105 and 134 ‐ 277 mV decade−1, respectively, working stably in an ambient environment over 270 days without any passivation protection. These results indicate a promising new routine to batch‐manufacture and integrate high‐performance, scalable and stretchable SiNW‐FET electronics that can work stably in harsh and large‐strain environments, which is a key capability for future practical flexible display and wearable electronic applications.

Molecular Recognition by Silicon Nanowire Field-Effect Transistor and Single-Molecule Force Spectroscopy.

Silicon nanowire (SiNW) field-effect transistors (FETs) have been developed as very sensitive and label-free biomolecular sensors. The detection principle operating in a SiNW biosensor is indirect. The biomolecules are detected by measuring the changes in the current through the transistor. Those changes are produced by the electrical field created by the biomolecule. Here, we have combined nanolithography, chemical functionalization, electrical measurements and molecular recognition methods to correlate the current measured by the SiNW transistor with the presence of specific molecular recognition events on the surface of the SiNW. Oxidation scanning probe lithography (o-SPL) was applied to fabricate sub-12 nm SiNW field-effect transistors. The devices were applied to detect very small concentrations of proteins (500 pM). Atomic force microscopy (AFM) single-molecule force spectroscopy (SMFS) experiments allowed the identification of the protein adsorption sites on the surface of the nanowire. We detected specific interactions between the biotin-functionalized AFM tip and individual avidin molecules adsorbed to the SiNW. The measurements confirmed that electrical current changes measured by the device were associated with the deposition of avidin molecules.

Electrostatic Potential Distribution Analysis of Silicon Nanowire Field Effect Transistor with Various Channel Length

Silicon nanowire FET plays a vital role in building of nanoscale electronic device applications. In this article, the silicon nanowire field effect model is designed with different channel lengths. By using the SiNW FET device model, various electrostatic potential distribution studies are done. This SiNW FET model is reducing the complexity in design. Two types of the device geometries are studied by changing the silicon nanowire channel length as 1000 nm and 200 nm. The 1000 nm channel provides high penetration to the active region of the nanowire FET than the 200 nm channel. This silicon nanowire FET model can apply to many nanoscale biochemical elements sensing applications.

Femtomolar Dengue Virus Type-2 DNA Detection in Back-gated Silicon Nanowire Field-effect Transistor Biosensor

Background: Dengue is known as the most severe arboviral infection in the world spread by Aedes aegypti. However, conventional and laboratory-based enzyme-linked immunosorbent assays (ELISA) are the current approaches in detecting dengue virus (DENV), requiring skilled and well-trained personnel to operate. Therefore, the ultrasensitive and label-free technique of the Silicon Nanowire (SiNW) biosensor was chosen for rapid detection of DENV. Methods: In this study, a SiNW field-effect transistor (FET) biosensor integrated with a back-gate of the low-doped p-type Silicon-on-insulator (SOI) wafer was fabricated through conventional photolithography and Inductively Coupled Plasma – Reactive Ion Etching (ICP-RIE) for Dengue Virus type-2 (DENV-2) DNA detection. The morphological characteristics of back-gated SiNW-FET were examined using a field-emission scanning electron microscope supported by the elemental analysis via energy-dispersive X-ray spectroscopy. Results and Discussion: A complementary (target) single-stranded deoxyribonucleic acid (ssDNA) was recognized when the target DNA was hybridized with the probe DNA attached to SiNW surfaces. Based on the slope of the linear regression curve, the back-gated SiNW-FET biosensor demonstrated the sensitivity of 3.3 nAM-1 with a detection limit of 10 fM. Furthermore, the drain and back-gate voltages were also found to influence the SiNW conductance changed. Conclusion: Thus, the results obtained suggest that the back-gated SiNW-FET shows good stability in both biosensing applications and medical diagnosis throughout the conventional photolithography method.

Quantum ATK analysis of silicon nanowire FET with a cylindrical metallic wrap-around gate varied with dielectrics

The nanowire FET is a game-changing technology because the gate is wrapped around the channel, allowing for greater applications for gate controllability and switching. The usage of dielectrics with the Nanowire Field Effect Transistor is discussed in this work. The device is investigated for three different dielectric constants using quantum ATK software. For each dielectric, sub-threshold conditions such as Drain induced barrier lowering, subthreshold slope, I ON and I OFF currents are investigated. For dielectric 4,9,25, the I ON /I OFF ratio was found to be 0.86 × 10 7 , 0.22 × 10 7 & 0.12 x10 7 for the described devices, respectively. The subthreshold slope for the same three dielectrics was calculated as 298.416 mV/dec, 285.8914 mV/dec & 190.66 mV/dec. Subthreshold conditions can be suppressed using the gate and drain control parameters. Many further evaluations are carried out to determine how we can employ the designed device for sensor applications.

Silicon Nanowire Field-Effect Transistor as Label-Free Detection of Hepatitis B Virus Proteins with Opposite Net Charges.

The prevalence of hepatitis B virus (HBV) is a global healthcare threat, particularly chronic hepatitis B (CHB) that might lead to hepatocellular carcinoma (HCC) should not be neglected. Although many types of HBV diagnosis detection methods are available, some technical challenges, such as the high cost or lack of practical feasibility, need to be overcome. In this study, the polycrystalline silicon nanowire field-effect transistors (pSiNWFETs) were fabricated through commercial process technology and then chemically functionalized for sensing hepatitis B virus surface antigen (HBsAg) and hepatitis B virus X protein (HBx) at the femto-molar level. These two proteins have been suggested to be related to the HCC development, while the former is also the hallmark for HBV diagnosis, and the latter is an RNA-binding protein. Interestingly, these two proteins carried opposite net charges, which could serve as complementary candidates for evaluating the charge-based sensing mechanism in the pSiNWFET. The measurements on the threshold voltage shifts of pSiNWFETs showed a consistent correspondence to the polarity of the charges on the proteins studied. We believe that this report can pave the way towards developing an approachable tool for biomedical applications.

Interpretation of biosensing technology in cell-coupled silicon nanowire transistors via impedance spectra

Cell-coupled silicon nanowire field-effect transistor (SiNW FET) devices with p-type 1NW and 5NW were exploited to elucidate the effect on impedance spectra. Live observation of cells on the actual chips using a metallurgical microscope was also performed before each impedance measurement. The impedance sensing of 2D cell cultures using FET devices with a grounded solution showed that measurements result in more significant changes in |Z| and θ in the lower frequency range (100 Hz–1 kHz). Among the devices, the changes within 5NW in |Z| and θ in impedance spectra demonstrated the most changes. The changes constitute an initial increase in |Z| and decrease in θ one day after cell seeding, followed by a decrease in |Z| and increase in θ at day 3 the cell coverage on the surface of SiNW by negatively charged cell membrane. After cells have been detached, |Z| decreased while θ increased significantly in contrast to day 1. Owing to the hindrance of ions or negatively charged membrane of the coupled cells, the changes of carrier density within SiNW correspond to the signals in impedance spectra and can be used to probe cell condition during the growth.

Complete Mapping of DNA‐Protein Interactions at the Single‐Molecule Level

DNA–protein interaction plays an essential role in the storage, expression, and regulation of genetic information. A 1D/3D facilitated diffusion mechanism has been proposed to explain the extraordinarily rapid rate of DNA‐binding protein (DBP) searching for cognate sequence along DNA and further studied by single‐molecule experiments. However, direct observation of the detailed chronological protein searching image is still a formidable challenge. Here, for the first time, a single‐molecule electrical monitoring technique is utilized to realize label‐free detection of the DBP–DNA interaction process based on high‐gain silicon nanowire field‐effect transistors (SiNW FETs). The whole binding process of WRKY domain and DNA has been visualized with high sensitivity and single‐base resolution. Impressively, the swinging of hydrogen bonds between amino acid residues and bases in DNA induce the dynamic collective motion of DBP–DNA. This in situ, label‐free electrical detection platform provides a practical experimental methodology for dynamic studies of various biomolecules.

Recent progress in silicon-based biologically sensitive field-effect devices

Biologically sensitive field-effect devices (BioFEDs) advantageously combine the electronic field-effect functionality with the (bio)chemical receptor's recognition ability for (bio)chemical sensing. In this review, basic and widely applied device concepts of silicon-based BioFEDs (ion-sensitive field-effect transistor, silicon nanowire transistor, electrolyte-insulator-semiconductor capacitor, and light-addressable potentiometric sensor) are presented, and recent progress (from 2019 to early 2021) is discussed. One of the main advantages of BioFEDs is the label-free sensing principle enabling them to detect a large variety of biomolecules and bioparticles by their intrinsic charge. The review encompasses applications of BioFEDs for the label-free electrical detection of clinically relevant protein biomarkers, DNA molecules and viruses, enzyme–substrate reactions as well as recording of the cell acidification rate (as an indicator of cellular metabolism) and the extracellular potential. • Biologically sensitive field-effect devices offer a universal platform for numerous (bio)chemical sensors. • Biologically sensitive field-effect devices enable label-free detection of biomolecules by their molecular charge. • Conventional device concepts are the ion-sensitive field-effect transistor, silicon nanowire field-effect transistor, electrolyte-insulator-semiconductor capacitor, and light-addressable potentiometric sensor. • Applications include detection of proteins, DNA, viruses, and cellular activity.

Optimizing surface modification of silicon nanowire field-effect transistors by polyethylene glycol for MicroRNA detection

MicroRNA (miRNA) sensing plays an essential role in the diagnosis of several diseases, especially cancers, for appropriate intervention and treatment. However, quantifying miRNA demands highly sensitive and selective assays which can distinguish analogous sequences with low abundance in bio-samples and determine wide range of concentrations. In this report, we present a novel technique satisfying all those requirements by modifying silicon nanowire field-effect transistors (SiNWFETs) with 2-component mixed self-assembled monolayers (mSAMs) of polyethylene glycol (PEG) at different ratios (silane-PEG-NH2:silane-PEG-OH = 1:1, 1:3, and 1:5) and glutaraldehyde to immobilize DNA probes for miRNA-21 detection, a biomarker in several types of cancers. Empirical results reveal that all the fabricated PEG-SiNWFET DNA biosensors could quantify miRNA-21 within 1 fM – 10 pM. Especially, the ones modified with silane-PEG-NH2:silane-PEG-OH = 1:3 exhibited an outstanding performance to recognize miRNA-21 at an ultra-low concentration of 10 aM in the dynamic range up to 6 orders of magnitude (10 aM – 10 pM). This approach is more convenient, analytical competitive, and cost-effective in comparison with currently used methods for nucleic acid testing because of label- and amplification-free characteristics. It is therefore not only feasible for miRNA detection by SiNWFET-based biosensors but also potential for clinical applications of disease diagnosis with oligonucleotide biomarkers.

Detecting glycated hemoglobin in human blood samples using a transistor-based nanoelectronic aptasensor

Glycated hemoglobin A1c (HbA1c) is a measure of long-term glycemic control in chronic diabetes-related complications. In this study, the glycated N-terminus of the hemoglobin β-chain, i.e., the glycated peptide (GP) of Fru-Val-His-Leu-Thr-Pro-Glu-COOH, was used as a template to isolate a novel aptamer (denoted by AptGP) via the systematic evolution of ligands by the exponential enrichment (SELEX) technique. Molecular docking/simulation studies revealed that both H-bonding and nonbonded interactions dominate the GP-AptGP association. While the fructose group of GP binds to the hairpin region of AptGP, the peptide chain aligns with the groove surface of AptGP. This AptGP was then modified on a silicon nanowire field-effect transistor (AptGP/SiNW-FET) to recognize HbA1c in physiological solutions. To mitigate the Debye-Hückel screening effect, a porous and HbA1c-permeable polyethylene glycol (PEG) polymer was comodified on the AptGP/SiNW-FET surface (termed PEG:AptGP/SiNW-FET) to enable the detection of HbA1c in peripheral human blood. The binding free energy (−12.30 ± 0.05 kcal/mol) of the GP-AptGP complex determined experimentally by PEG:AptGP/SiNW-FET matches excellently with theoretical calculations. This reusable PEG:AptGP/SiNW-FET aptasensor detects HbA1c levels in human blood as accurately as conventional capillary electrophoresis but has the advantages of being fast and cost-effective and thus is amenable to point-of-care diagnostics.

Rapid and Sensitive Detection of Mycobacterium tuberculosis by an Enhanced Nanobiosensor.

Tuberculosis (TB) mostly spreads from person to person through Mycobacterium tuberculosis (MTB). However, the majority of conventional detection methods for MTB cannot satisfy the requirements for actual TB detection. As one of the most promising powerful platforms, a silicon nanowire field-effect transistor (SiNW-FET) biosensor shows good prospect in TB detection. In this study, an enhanced SiNW-FET biosensor was developed for the rapid and sensitive detection of MTB. The surface functional parameters of the biosensor were explored and optimized. The SiNW-FET biosensor has good sensitivity with a detection limit of 0.01 fg/mL toward protein. The current change value shows a linear upward trend with the increase in protein concentration in the range of 1 fg/mL to 100 μg/mL. One whole test cycle can be accomplished within only 30 s. More importantly, a good distinction was realized in the sputum without pretreatment between normal people and TB patients, which greatly shortened the TB detection time (only 2-5 min, considering the dilution of sputum). Compared with other methods, the SiNW-FET biosensor can detect MTB with a remarkably broad dynamic linear range in a shorter time.

A Surface Potential Model for Field-Effect Transistors With Bound-Charge Engineering

Semiconductor doping is limited by such practical concerns as bandgap narrowing and solid solubility limits of dopants. Bound-charge engineering (BCE) bypasses these limits by doping with surface bound charge located on the interface between a semiconductor and an adjacent low-permittivity oxide; it can be used to reduce depletion lengths of junctions in field-effect transistors (FETs). BCE is established by basic electrostatics and is widely applicable to emerging materials and novel devices. In this work, an analytical surface potential model for gate-all-around BCE-assisted silicon nanowire FETs, with arbitrary and possibly distinct spacer and gate oxides, is derived. This model is based on scaling theory and verified against atomistic quantum transport simulations; it provides an intuitive formalism for developing and modeling devices with BCE.

Significant Elevation in Potassium Concentration Surrounding Stimulated Excitable Cells Revealed by an Aptamer-Modified Nanowire Transistor.

Recording ion fluctuations surrounding biological cells with a nanoelectronic device offers seamless integration of nanotechnology into living organisms and is essential for understanding cellular activities. The concentration of potassium ion in the extracellular fluid () is a critical determinant of cell membrane potential and must be maintained within an appropriate range. Alteration in can affect neuronal excitability, induce heart arrhythmias, and even trigger seizure-like reactions in the brain. Therefore, monitoring local fluctuations in real time provides an early diagnosis of the occurrence of the K+-induced pathophysiological responses. Here, we modified the surface of a silicon nanowire field-effect transistor (SiNW-FET) with K+-specific DNA-aptamers (AptK+) to monitor the real-time variations of in primary cultured rat embryonic cortical neurons or human embryonic stem cell-derived cardiomyocytes. The binding affinity of AptK+ to K+, determined by measuring the dissociation constant of the AptK+-K+ complex (Kd = 10.1 ± 0.9 mM), is at least 38-fold higher than other ions (e.g., Na+, Ca2+, and Mg2+). By placing cultured cortical neurons over an AptK+/SiNW-FET device, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) stimulation raised the dose-dependently to 16 mM when AMPA concentration was >10 μM; this elevation could be significantly suppressed by an AMPA receptor antagonist, 6,7-dinitroquinoxaline-2,3-dione. Likewise, the stimulation of isoproterenol to cardiomyocytes raised the to 6-8 mM, with a concomitant increase in the beating rate. This study utilizing a robust nanobiosensor to detect real-time ion fluctuations surrounding excitable cells underlies the importance of ion homeostasis and offers the feasibility of developing an implant device for real-time monitoring.

Steep Switching Characteristics of Partially Gated p+-n+-i-n+ Silicon-Nanowire Transistors.

In this study, we examine the electrical characteristics of p+-n+-i-n+ silicon-nanowire field-effect transistors with partially gated channels. The silicon-nanowire field-effect transistors operate with barrier height modulation through positive feedback loops of charge carriers triggered by impact ionization. Our field-effect transistors exhibit outstanding switching characteristics, with an on current of ˜10-4 A, an on/off current ratio of ˜106, and a point subthreshold swing of ˜23 mV/dec. Moreover, the devices inhibit ambipolar characteristics because of the use of the partially gated structure and feature the p-channel operation mode.

Process Variability in Top-Down Fabrication of Silicon Nanowire-Based Biosensor Arrays.

Silicon nanowire field-effect transistors (SiNW-FET) have been studied as ultra-high sensitive sensors for the detection of biomolecules, metal ions, gas molecules and as an interface for biological systems due to their remarkable electronic properties. “Bottom-up” or “top-down” approaches that are used for the fabrication of SiNW-FET sensors have their respective limitations in terms of technology development. The “bottom-up” approach allows the synthesis of silicon nanowires (SiNW) in the range from a few nm to hundreds of nm in diameter. However, it is technologically challenging to realize reproducible bottom-up devices on a large scale for clinical biosensing applications. The top-down approach involves state-of-the-art lithography and nanofabrication techniques to cast SiNW down to a few 10s of nanometers in diameter out of high-quality Silicon-on-Insulator (SOI) wafers in a controlled environment, enabling the large-scale fabrication of sensors for a myriad of applications. The possibility of their wafer-scale integration in standard semiconductor processes makes SiNW-FETs one of the most promising candidates for the next generation of biosensor platforms for applications in healthcare and medicine. Although advanced fabrication techniques are employed for fabricating SiNW, the sensor-to-sensor variation in the fabrication processes is one of the limiting factors for a large-scale production towards commercial applications. To provide a detailed overview of the technical aspects responsible for this sensor-to-sensor variation, we critically review and discuss the fundamental aspects that could lead to such a sensor-to-sensor variation, focusing on fabrication parameters and processes described in the state-of-the-art literature. Furthermore, we discuss the impact of functionalization aspects, surface modification, and system integration of the SiNW-FET biosensors on post-fabrication-induced sensor-to-sensor variations for biosensing experiments.