SiNW FETs Research Articles

Complementary metal oxide semiconductor compatible silicon nanowires-on-a-chip: fabrication and preclinical validation for the detection of a cancer prognostic protein marker in serum.

An integrated translational biosensing technology based on arrays of silicon nanowire field-effect transistors (SiNW FETs) is described and has been preclinically validated for the ultrasensitive detection of the cancer biomarker ALCAM in serum. High-quality SiNW arrays have been rationally designed toward their implementation as molecular biosensors. The FET sensing platform has been fabricated using a complementary metal oxide semiconductor (CMOS)-compatible process. Reliable and reproducible electrical performance has been demonstrated via electrical characterization using a custom-designed portable readout device. Using this platform, the cancer prognostic marker ALCAM could be detected in serum with a detection limit of 15.5 pg/mL. Importantly, the detection could be completed in less than 30 min and span a wide dynamic detection range (∼10(5)). The SiNW-on-a-chip biosensing technology paves the way to the translational clinical application of FET in the detection of cancer protein markers.

Quasi-One-Dimensional Performance and Benchmarking of CMOS-Based Multichannel Carbon Nanotube versus Nanowire Field-Effect Transistor Models

Performance assessment of carbon-based devices with carbon nanotube (CNT) as a protoype, and traditional silicon (Si) devices based on a nanowire is reported. Both CNT and nanowire (NW) present one-dimensional (1D) nanostructures making comparison relevant, connected, and future development of emerging technologies. The performance of a CNT as a rolled up graphene sheet is evaluated vis a vis that of the cylindrical Si NW. Compact models of Carbon Nanotube Field-Effect Transistors (CNTFET) and Silicon Nanowire Field- Effect Transistors (Si NWFET) that are developed, analysed, and conclusions drawn based on the 32-nm process technology. The CNTFET parameter is based on Stanford University model and Si NWFET model based on the BSIM-CMG 106.1.0 model form an excellent comparison and further expansion for industrial applications as new devices, circuits, and system-on-a-chip (SoC) are being evaluated for implementation. CNTFET offer a better compromise over and above the advantage of a Si NWFET extending More than Moore vision for industrial development. In fabrication processes, large contact sizes are usually used to connect the semiconducting channel tubes with metal probes. Therefore, by using an array of parallel tubes, the aspect ratio of unutilized channel to contact width can be increased significantly. In addition, each utilized channel contribute to larger output drain currents. Process engineer can use the authors' simple equation to calculate the sizes of the pitch, contact and spacer based on various technology process. It is important to note that both of the 32 nm CNTFET and Si NWFET show a reduction in the current when the number of tubes is greater than 12. The performance evaluation of these devices includes the comparison of drain induced barrier lowering (DIBL), subthreshold swing (SS) and on-off current for 1, 2, 5 and 10 tubes. Moreover, the energy-delay product (EDP) and power-delay product (PDP) are calculated to depict the tradeoff between the frequency of a propagating signal and power consumption limiting the packaging of devices on a chip. Last but not least, our finding shows that the digital performance of a multi-channel CNTFET at least one order of magnitude over the Si NWFET, both for EDP and PDP for 32 nm process.

Silicon Nanowire Field-Effect Transistors—A Versatile Class of Potentiometric Nanobiosensors

Silicon nanowire field-effect transistors (Si-NW FETs) have been demonstrated as a versatile class of potentiometric nanobiosensors for real time, label-free, and highly sensitive detection of a wide range of biomolecules. In this review, we summarize the principles of such devices and recent developments in device fabrication, fluid integration, surface functionalization, and biosensing applications. The main focus of this review is on CMOS compatible Si-NW FET nanobiosensors.

Molecular layer deposition of APTES on silicon nanowire biosensors: Surface characterization, stability and pH response

We report the use of molecular layer deposition (MLD) for depositing 3-aminopropyltriethoxysilane (APTES) on a silicon dioxide surface. The APTES monolayer was characterized using spectroscopic ellipsometry, contact angle goniometry, and atomic force microscopy. Effects of reaction time of repeating pulses and simultaneous feeding of water vapor with APTES were tested. The results indicate that the synergistic effects of water vapor and reaction time are significant for the formation of a stable monolayer. Additionally, increasing the number of repeating pulses improved the APTES surface coverage but led to saturation after 10 pulses. In comparing MLD with solution-phase deposition, the APTES surface coverage and the surface quality were nearly equivalent. The hydrolytic stability of the resulting films was also studied. The results confirmed that the hydrolysis process was necessary for MLD to obtain stable surface chemistry. Furthermore, we compared the pH sensing results of Si nanowire field effect transistors (Si NWFETs) modified by both the MLD and solution methods. The highly repeatable pH sensing results reflected the stability of APTES monolayers. The results also showed an improved pH response of the sensor prepared by MLD compared to the one prepared by the solution treatment, which indicated higher surface coverage of APTES.

CMOS Logic Device and Circuit Performance of Si Gate All Around Nanowire MOSFET

In this paper, a detailed 3-D numerical analysis is carried out to study and evaluate CMOS logic device and circuit performance of gate-all-around (GAA) Si nanowire (NW) field-effect transistors (FETs) operating in sub-22-nm CMOS technologies. Employing a coupled drift-diffusion room temperature carrier transport formulation, with 2-D quantum confinement effects, we numerically simulate Si GAA NWFET electrical characteristics. The simulation predictions, on the device performance, short channel effects, and their dependence on NW geometry scaling, are in good agreement with the Si NWFET experimental data reported in literature. Superior electrostatic integrity, OFF-state device performance, lower circuit delays, and faster switching in the Si GAA NWFET-based CMOS circuits are numerically demonstrated in comparison with an Si-on-insulator FinFET. The mixed-mode numerical simulations also predict low supply voltage operations for the Si NWFET-based logic circuits.

Methods for rapid frequency-domain characterization of leakage currents in silicon nanowire-based field-effect transistors.

Silicon nanowire-based field-effect transistors (SiNW FETs) have demonstrated the ability of ultrasensitive detection of a wide range of biological and chemical targets. The detection is based on the variation of the conductance of a nanowire channel, which is caused by the target substance. This is seen in the voltage–current behavior between the drain and source. Some current, known as leakage current, flows between the gate and drain, and affects the current between the drain and source. Studies have shown that leakage current is frequency dependent. Measurements of such frequency characteristics can provide valuable tools in validating the functionality of the used transistor. The measurements can also be an advantage in developing new detection technologies utilizing SiNW FETs. The frequency-domain responses can be measured by using a commercial sine-sweep-based network analyzer. However, because the analyzer takes a long time, it effectively prevents the development of most practical applications. Another problem with the method is that in order to produce sinusoids the signal generator has to cope with a large number of signal levels. This may become challenging in developing low-cost applications. This paper presents fast, cost-effective frequency-domain methods with which to obtain the responses within seconds. The inverse-repeat binary sequence (IRS) is applied and the admittance spectroscopy between the drain and source is computed through Fourier methods. The methods is verified by experimental measurements from an n-type SiNW FET.

Single-trap-induced random telegraph noise for FinFET, Si/Ge Nanowire FET, Tunnel FET, SRAM and logic circuits

In this paper, we comprehensively review the impacts of single-trap-induced random telegraph noise (RTN) on FinFET, Ge/Si Nanowire FET and Tunnel FET (TFET). The resulting influences on the thermionic-based current conduction such as FinFET, Si-NW FET and Ge-NW FET (at low drain bias) as well as interband tunneling dominated current conduction such as TFET and high-drain-biased Ge-NW FET are extensively addressed in device and circuit level. The location of the trap is shown to have profound impacts and the impacts vary with bias conditions and trap types. The worst-case analysis of the stability/performance and leakage/delay for all possible trapping/detrapping RTN combinations are investigated for FinFET, Si-/Ge-NW FETs and TFET based 6T/8T SRAM cells and logic circuits.

Artificial Sensing Intelligence with Silicon Nanowires for Ultraselective Detection in the Gas Phase

The use of molecularly modified Si nanowire field effect transistors (SiNW FETs) for selective detection in the liquid phase has been successfully demonstrated. In contrast, selective detection of chemical species in the gas phase has been rather limited. In this paper, we show that the application of artificial intelligence on deliberately controlled SiNW FET device parameters can provide high selectivity toward specific volatile organic compounds (VOCs). The obtained selectivity allows identifying VOCs in both single-component and multicomponent environments as well as estimating the constituent VOC concentrations. The effect of the structural properties (functional group and/or chain length) of the molecular modifications on the accuracy of VOC detection is presented and discussed. The reported results have the potential to serve as a launching pad for the use of SiNW FET sensors in real-world counteracting conditions and/or applications.

Liquid and Back Gate Coupling Effect: Toward Biosensing with Lowest Detection Limit

We employ noise spectroscopy and transconductance measurements to establish the optimal regimes of operation for our fabricated silicon nanowire field-effect transistors (Si NW FETs) sensors. A strong coupling between the liquid gate and back gate (the substrate) has been revealed and used for optimization of signal-to-noise ratio in subthreshold as well as above-threshold regimes. Increasing the sensitivity of Si NW FET sensors above the detection limit has been predicted and proven by direct experimental measurements.

Palladium nanoparticle decorated silicon nanowire field-effect transistor with side-gates for hydrogen gas detection

A silicon nanowire field-effect transistor (SiNW FET) with local side-gates and Pd surface decoration is demonstrated for hydrogen (H2) detection. The SiNW FETs are fabricated by top-down method and functionalized with palladium nanoparticles (PdNPs) through electron beam evaporation for H2 detection. The drain current of the PdNP-decorated device reversibly responds to H2 at different concentrations. The local side-gates allow individual addressing of each sensor and enhance the sensitivity by adjusting the working region to the subthreshold regime. A control experiment using a non-functionalized device verifies that the hydrogen-sensitivity is originated from the PdNPs functionalized on the SiNW surface.

Complementary Metal Oxide Semiconductor-Compatible Silicon Nanowire Biofield-Effect Transistors as Affinity Biosensors

Affinity biosensors use biorecognition elements and transducers to convert a biochemical event into a recordable signal. They provides the molecule binding information, which includes the dynamics of biomolecular association and dissociation, and the equilibrium association constant. Complementary metal oxide semiconductor-compatible silicon (Si) nanowires configured as a field-effect transistor (NW FET) have shown significant advantages for real-time, label-free and highly sensitive detection of a wide range of biomolecules. Most research has focused on reducing the detection limit of Si-NW FETs but has provided less information about the real binding parameters of the biomolecular interactions. Recently, Si-NW FETs have been demonstrated as affinity biosensors to quantify biomolecular binding affinities and kinetics. They open new applications for NW FETs in the nanomedicine field and will bring such sensor technology a step closer to commercial point-of-care applications. This article summarizes the recent advances in bioaffinity measurement using Si-NW FETs, with an emphasis on the different approaches used to address the issues of sensor calibration, regeneration, binding kinetic measurements, limit of detection, sensor surface modification, biomolecule charge screening, reference electrode integration and nonspecific molecular binding.

Discriminative Power of Chemically Sensitive Silicon Nanowire Field Effect Transistors to Volatile Organic Compounds

We report on the sensing of different polar and nonpolar volatile organic compounds (VOCs) in an atmosphere with background humidity (relative humidity: 40%), using molecularly modified silicon nanowire field effect transistors (SiNW FETs). In this endeavor, a systematic comparative analysis is performed with: (i) SiNW FETs that were functionalized with a series of molecules having different electron-withdrawing and electron-donating end groups; and (ii) SiNW FETs that are functionalized with a series of molecules having similar functional groups but different backbone lengths. The analysis of the sensing signals are focused on three main FET parameters: (i) changes in the threshold voltage, (ii) changes in the carrier mobility, and (iii) changes in the on-current, compared to the baseline values under vacuum. Using discriminant factor analysis, the performance of the molecularly modified SiNW FETs is further analyzed as sensors array. The combination of sensors having the best discriminative power between the various VOCs are identified and discussed in terms of their constituent surface modifications.

Electrical properties of high density arrays of silicon nanowire field effect transistors

Proximity effect corrected e-beam lithography of hydrogen silsesquioxane on silicon on insulator was used to fabricate multi-channel silicon nanowire field-effect transistors (SiNW FETs). Arrays of 15-channels with a line width of 18 nm and pitch as small as 50 nm, the smallest reported for electrically functional devices, were fabricated. These high density arrays were back-gated by the substrate and allowed for investigation of the effects of scaling on the electrical performance of this multi-channel SiNW FET. It was revealed that the drain current and the transconductance (gm) are both reduced with decreasing pitch size. The drain induced barrier lowering and the threshold voltage (Vth) are also decreased, whereas the subthreshold swing (S) is increased. The results are in agreement with our simulations of the electric potential profile of the devices. The study contains valuable information on SiNW FET integration and scaling for future devices.

Signal-to-Noise Ratio Enhancement of Silicon Nanowires Biosensor with Rolling Circle Amplification

Herein, we describe a novel approach for rapid, label-free and specific DNA detection by applying rolling circle amplification (RCA) based on silicon nanowire field-effect transistor (SiNW-FET) for the first time. Highly responsive SiNWs were fabricated with a complementary metal oxide semiconductor (CMOS) compatible anisotropic self-stop etching technique which eliminated the need for hybrid method. The probe DNA was immobilized on the surface of SiNW, followed by sandwich hybridization with the perfectly matched target DNA and RCA primer that acted as a primer to hybridize the RCA template. The RCA reaction created a long single-stranded DNA (ssDNA) product and thus enhanced the electronic responses of SiNW significantly. The signal-to-noise ratio (SNR) as a figure-of-merit was analyzed to estimate the signal enhancement and possible detection limit. The nanosensor showed highly sensitive concentration-dependent conductance change in response to specific target DNA sequences. Because of the binding of an abundance of repeated sequences of RCA products, the SNR of >20 for 1 fM DNA detection was achieved, implying a detection floor of 50 aM. This RCA-based SiNW biosensor also discriminated perfectly matched target DNA from one-base mismatched DNA with high selectivity due to the substantially reduced nonspecific binding onto the SiNW surface through RCA. The combination of SiNW FET sensor with RCA will increase diagnostic capacity and the ability of laboratories to detect unexpected viruses, making it a potential tool for early diagnosis of gene-related diseases.

Effect of Chain Length on the Sensing of Volatile Organic Compounds by means of Silicon Nanowires

Molecularly modified silicon nanowire field effect transistors (SiNW FETs) are starting to appear as promising devices for sensing various volatile organic compounds (VOCs). Understanding the connection between the molecular layer structure attached to the SiNWs and VOCs is essential for the design of high performance sensors. Here, we explore the chain length influence of molecular layers on the sensing performance to polar and nonpolar VOCs. SiNW FETs were functionalized with molecular layers that have similar end (methyl) group and amide bridge bond, but differ in their alkyl chain lengths. The resulting devices were then exposed to polar and nonpolar VOCs in various concentrations. Our results showed that the sensing response to changing the threshold voltage (ΔVth) and changing the relative hole mobility (Δμh/μh-a) have a proportional relationship to the VOC concentration. On exposure to a specific VOC concentration, ΔVth response increased with the chain length of the molecular modification. In contrast, Δμh/μh-a did not exhibit any obvious reliance on the chain length of the molecular layer. Analysis of the responses with an electrostatic-based model suggests that the sensor response in ΔVth is dependent on the VOC concentration, VOC vapor pressure, VOC-molecular layer binding energy, and VOC adsorption-induced dipole moment changes of molecular layer.

Effect of Functional Groups on the Sensing Properties of Silicon Nanowires toward Volatile Compounds

Molecular layers attached to a silicon nanowire field effect transistor (SiNW FET) can serve as antennas for signal transduction of volatile organic compounds (VOCs). Nevertheless, the mutual relationship between the molecular layers and VOCs is still a puzzle. In the present paper, we explore the effect of the molecular layer's end (functional) groups on the sensing properties of VOCs. Toward this end, SiNW FETs were modified with tailor-made molecular layers that have the same backbone but differ in their end groups. Changes in the threshold voltage (ΔVth) and changes in the mobility (Δμh) were then recorded upon exposure to various VOCs. Model-based analysis indicates that the interaction between molecular layers and VOCs can be classified to three main scenarios: (a) dipole-dipole interaction between the molecular layer and the polar VOCs; (b) induced dipole-dipole interaction between the molecular layers and the nonpolar VOCs; and (c) molecular layer tilt as a result of VOCs diffusion. Based on these scenarios, it is likely that the electron-donating/withdrawing properties of the functional groups control the dipole moment orientation of the adsorbed VOCs and, as a result, determine the direction (or sign) of the ΔVth. Additionally, it is likely the diffusion of VOCs into the molecular layer, determined by the type of functional groups, is the main reason for the Δμh responses. The reported findings are expected to provide an efficient way to design chemical sensors that are based on SiNW FETs to nonpolar VOCs, which do not exchange carriers with the molecular layers.

Functional peptides for capacitative detection of Ca2+ ions

Molecular recognition is the key feature of bioinspired sensor applications. A profound understanding of recognitive binding events is crucial for the design of highly specific and effective binding molecules. In this paper a series of simple to complex oligopeptides, derived from the Ca2+ chelator ethylenediaminetetraacetic acid (EDTA) and the Ca2+ binding protein calmodulin, were investigated. It was shown, that specifically designed oligopeptides can fulfil protein-like recognition functions but are much easier to immobilize and enable high functional integration. Impedance spectroscopy (IS) could be used to detect binding of Ca2+ to different peptides because the double layer capacitance is highly sensitive to changes in the morphology and dielectric properties of adsorbate layers. Finally, the designed functional oligopeptides were implemented in silicon nanowire field effect transistors (SiNW FETs) as a proof of concept for future problem-optimized molecules in sensor devices. The graph shows frequency-normalized admittance plots and corresponding schemes of a peptide monolayers layer before and after binding of Ca2+ ions.

A pH sensor with a double-gate silicon nanowire field-effect transistor

A pH sensor composed of a double-gate silicon nanowire field-effect transistor (DG Si-NW FET) is demonstrated. The proposed DG Si-NW FET allows the independent addressing of the gate voltage and hence improves the sensing capability through an application of asymmetric gate voltage between the two gates. One gate is a driving gate which controls the current flow, and the other is a supporting gate which amplifies the shift of the threshold voltage, which is a sensing metric, and which arises from changes in the pH. The pH signal is also amplified through modulation of the gate oxide thickness.

Detection of biomarker p53 mutated gene by a silicon nanowire nanosensor

Among biosensors of various types, the silicon nanowire field–effect transistor (SiNW–FET) is believed to be the most sensitive and powerful device for bio–applications. In fact, these devices have demonstrated the ability to detect a variety of analyses such as particular DNA sequences, cancer biomarkers and larger entities such as viruses. The principle of sensing is based on the variation of conductivity resulting from a disturbance of charge on the surface of the SiNW–FET. In this study, we have used two different processes for surface modification of silicon nanowire. As the DNA of liver cancer cells has mutation at codon 249 which changes one base guanine (G) by base thymine (T), we thus designed 17–mer DNA oligonucleotides, which were used as a receptor to capture the DNA of p53 mutated gene. The fabricated SiNW biosensor could detect DNA of p53 mutated gene with concentrations down to about 100 pM.

Orientational Dependence in Device Performances of InAs and Si Nanowire MOSFETs Under Ballistic Transport

We evaluate drive currents and consumption powers of InAs and Si nanowire metal-oxide-semiconductor field-effect transistors (MOSFETs) with various crystal orientations, by using a ballistic MOSFET model coupled with tight-binding band structure calculation. We demonstrate that performance dependence on the wire orientation is not significant in InAs NWFETs compared to Si NWFETs, due to an isotropic nature of the Γ valley, and furthermore, a lower power switching is expected in InAs NWFETs even if the gate oxide thickness reduces down to a quantum capacitance limit. The present results suggest that InAs NWFETs have the advantage over the Si counterpart in terms of lower power operation and flexibility in layout design of integrated circuits.