Silicon Nanowire Field-effect Transistors Research Articles

Toward Intraoperative Detection of Disseminated Tumor Cells in Lymph Nodes with Silicon Nanowire Field Effect Transistors

Within an hour, as little as one disseminated tumor cell (DTC) per lymph node can be quantitatively detected using an intraoperative biosensing platform based on silicon nanowire field-effect transistors (SiNW FET). It is also demonstrated that the integrated biosensing platform is able to detect the presence of circulating tumor cells (CTCs) in the blood of colorectal cancer patients. The presence of DTCs in lymph nodes and CTCs in peripheral blood is highly significant as it is strongly associated with poor patient prognosis. The SiNW FET sensing platform out-performed in both sensitivity and rapidity not only the current standard method based on pathological examination of tissue sections but also the emerging clinical gold standard based on molecular assays. The possibility to achieve accurate and highly sensitive analysis of the presence of DTCs in the lymphatics within the surgery time frame has the potential to spare cancer patients from an unnecessary secondary surgery, leading to reduced patient morbidity, improving their psychological wellbeing and reducing time spent in hospital. This study demonstrates the potential of nanoscale field-effect technology in clinical cancer diagnostics.

Pseudopotential-based electron quantum transport: Theoretical formulation and application to nanometer-scale silicon nanowire transistors

We present a formalism to treat quantum electronic transport at the nanometer scale based on empirical pseudopotentials. This formalism offers explicit atomistic wavefunctions and an accurate band structure, enabling a detailed study of the characteristics of devices with a nanometer-scale channel and body. Assuming externally applied potentials that change slowly along the electron-transport direction, we invoke the envelope-wavefunction approximation to apply the open boundary conditions and to develop the transport equations. We construct the full-band open boundary conditions (self-energies of device contacts) from the complex band structure of the contacts. We solve the transport equations and present the expressions required to calculate the device characteristics, such as device current and charge density. We apply this formalism to study ballistic transport in a gate-all-around (GAA) silicon nanowire field-effect transistor with a body-size of 0.39 nm, a gate length of 6.52 nm, and an effective oxide thickness of 0.43 nm. Simulation results show that this device exhibits a subthreshold slope (SS) of ∼66 mV/decade and a drain-induced barrier-lowering of ∼2.5 mV/V. Our theoretical calculations predict that low-dimensionality channels in a 3D GAA architecture are able to meet the performance requirements of future devices in terms of SS swing and electrostatic control.

In-depth Characterization of Silicon Nanowire Field-Effect Transistor (SiNW-FET) for Neural Recording and Direct Performance Comparison with Passive MEA

In-depth Characterization of Silicon Nanowire Field-Effect Transistor (SiNW-FET) for Neural Recording and Direct Performance Comparison with Passive MEA

Simulation of Electrical Characteristics of Gate All around Silicon Nanowire Field Effect Transistor using Extended Hückel Theory Based Semi Empirical Approach

Simulation of Electrical Characteristics of Gate All around Silicon Nanowire Field Effect Transistor using Extended Hückel Theory Based Semi Empirical Approach

Optimal Geometry Aspect Ratio of Ellipse-Shaped- Surrounding-Gate Nanowire Field Effect Transistors.

Theoretically ideally round shape of the surrounding gate may not always guarantee because of limitations of the fabrication process in surrounding-gate nanowire field effect transistors (FETs). These limitations may lead to the formation of an ellipse-shaped surrounding gate with major and minor axes of different lengths. In this paper, we for the first time study the electrical characteristics of ellipse-shaped-surrounding-gate silicon nanowire FETs with different ratio of the major and minor axes. By simultaneously simulating engineering acceptable magnitudes of the threshold voltage roll-off, the drain induced barrier lowering, the subthreshold swing, and the on-/off-state current ratio, an optimal geometry aspect ratio between the channel length and the major and minor axes of the ellipse-shaped-surrounding-gate nanowire FET is concluded.

Label-Free Direct Detection of miRNAs with Poly-Silicon Nanowire Biosensors.

BackgroundThe diagnostic and prognostic value of microRNAs (miRNAs) in a variety of diseases is promising. The novel silicon nanowire (SiNW) biosensors have advantages in molecular detection because of their high sensitivity and fast response. In this study, poly-crystalline silicon nanowire field-effect transistor (poly-SiNW FET) device was developed to achieve specific and ultrasensitive detection of miRNAs without labeling and amplification.MethodsThe poly-SiNW FET was fabricated by a top–down Complementary Metal Oxide Semiconductor (CMOS) wafer fabrication based technique. Single strand DNA (ssDNA) probe was bind to the surface of the poly-SiNW device which was silanated and aldehyde-modified. By comparing the difference of resistance value before and after ssDNA and miRNA hybridization, poly-SiNW device can be used to detect standard and real miRNA samples.ResultsPoly-SiNW device with different structures (different line width and different pitch) was applied to detect standard Let-7b sample with a detection limitation of 1 fM. One-base mismatched sequence could be distinguished meanwhile. Furthermore, these poly-SiNW arrays can detect snRNA U6 in total RNA samples extracted from HepG2 cells with a detection limitation of 0.2 μg/mL. In general, structures with pitch showed better results than those without pitch in detection of both Let-7b and snRNA U6. Moreover, structures with smaller pitch showed better detection efficacy.ConclusionOur findings suggest that poly-SiNW arrays could detect standard and real miRNA sample without labeling or amplification. Poly-SiNW biosensor device is promising for miRNA detection.

Electrical Control of g-Factor in a Few-Hole Silicon Nanowire MOSFET.

Hole spins in silicon represent a promising yet barely explored direction for solid-state quantum computation, possibly combining long spin coherence, resulting from a reduced hyperfine interaction, and fast electrically driven qubit manipulation. Here we show that a silicon-nanowire field-effect transistor based on state-of-the-art silicon-on-insulator technology can be operated as a few-hole quantum dot. A detailed magnetotransport study of the first accessible hole reveals a g-factor with unexpectedly strong anisotropy and gate dependence. We infer that these two characteristics could enable an electrically driven g-tensor-modulation spin resonance with Rabi frequencies exceeding several hundred mega-Hertz.

Isolation and Identification of Post-Transcriptional Gene Silencing-Related Micro-RNAs by Functionalized Silicon Nanowire Field-effect Transistor.

Many transcribed RNAs are non-coding RNAs, including microRNAs (miRNAs), which bind to complementary sequences on messenger RNAs to regulate the translation efficacy. Therefore, identifying the miRNAs expressed in cells/organisms aids in understanding genetic control in cells/organisms. In this report, we determined the binding of oligonucleotides to a receptor-modified silicon nanowire field-effect transistor (SiNW-FET) by monitoring the changes in conductance of the SiNW-FET. We first modified a SiNW-FET with a DNA probe to directly and selectively detect the complementary miRNA in cell lysates. This SiNW-FET device has 7-fold higher sensitivity than reverse transcription-quantitative polymerase chain reaction in detecting the corresponding miRNA. Next, we anchored viral p19 proteins, which bind the double-strand small RNAs (ds-sRNAs), on the SiNW-FET. By perfusing the device with synthesized ds-sRNAs of different pairing statuses, the dissociation constants revealed that the nucleotides at the 3′-overhangs and pairings at the terminus are important for the interactions. After perfusing the total RNA mixture extracted from Nicotiana benthamiana across the device, this device could enrich the ds-sRNAs for sequence analysis. Finally, this bionanoelectronic SiNW-FET, which is able to isolate and identify the interacting protein-RNA, adds an additional tool in genomic technology for the future study of direct biomolecular interactions.

Electrical properties of self-aligned gate-all-around polycrystalline silicon nanowires field-effect transistors

Low temperature (≤600°C) polycrystalline silicon nanowires field-effect transistors have been developed following a top-down approach and classical photolithography techniques. N channel transistors have been tested with a single top-gate, bottom-gate and gate-all-around architecture in order to compare their electrical performances in relation to the interface state density. Analysis shows that surrounding gate enables control of parameters such as on-current, subthreshold slope and threshold voltage and offer potential further applications.

Ultrasensitive Detection of Dual Cancer Biomarkers with Integrated CMOS-Compatible Nanowire Arrays.

A direct, rapid, highly sensitive and specific biosensor for detection of cancer biomarkers is desirable in early diagnosis and prognosis of cancer. However, the existing methods of detecting cancer biomarkers suffer from poor sensitivity as well as the requirement of enzymatic labeling or nanoparticle conjugations. Here, we proposed a two-channel PDMS microfluidic integrated CMOS-compatible silicon nanowire (SiNW) field-effect transistor arrays with potentially single use for label-free and ultrasensitive electrical detection of cancer biomarkers. The integrated nanowire arrays showed not only ultrahigh sensitivity of cytokeratin 19 fragment (CYFRA21-1) and prostate specific antigen (PSA) with detection to at least 1 fg/mL in buffer solution but also highly selectivity of discrimination from other similar cancer biomarkers. In addition, this method was used to detect both CYFRA21-1 and PSA real samples as low as 10 fg/mL in undiluted human serums. With its excellent properties and miniaturization, the integrated SiNW-FET device opens up great opportunities for a point-of-care test (POCT) for quick screening and early diagnosis of cancer and other complex diseases.

Silicon nanowire biosensors for detection of cardiac troponin I (cTnI) with high sensitivity.

We have demonstrated highly sensitive and label-free detection of cardiac troponin I (cTnI), a biomarker for diagnosis of acute myocardial infarction, using silicon nanowire field-effect transistors. A honeycomb-like structure is utilized for nanowire configuration to offer improved electrical performance and increased sensing area. The fabricated devices show n-type behavior with a relatively high ON-OFF current ratio, small sub-threshold swing and low gate leakage current. Monoclonal antibodies for cTnI were covalently immobilized on the nanowire surface and the attachment of antibodies is clearly visualized by atomic force microscope. The sensitivity with various concentrations of buffer solution was also investigated in order to determine the optimal buffer condition. The devices exhibit highest sensitivity under buffer solutions with low ion concentration. In addition, the detection limit of the sensor is as low as ~5 pg/mL, the lowest reported in the literature to date and nearly an order of magnitude smaller than the suggested threshold limit. The fabricated devices demonstrate a good selectivity for detecting cTnI.

Layout Technique for Double-Gate Silicon Nanowire FETs With an Efficient Sea-of-Tiles Architecture

As we advance into the era of nanotechnology, semiconductor devices are scaled down to their physical limits, thereby opening up venues for new transistor channel materials based on nanowires and nanotubes. Transistors based on nanowires and nanotubes inherently exhibit ambipolar behavior. While technologists aim to suppress ambipolar behavior of these transistors, new design methodologies are proposed by exploiting the phenomenon of controllable polarity. In this paper, we propose regular layout fabrics, with an emphasis on silicon nanowires (SiNWs) as the candidate technology. A double-gate ambipolar SiNW field-effect transistor operates as p-type or n-type by electrically controlling the polarity of the second gate. We propose layout techniques to address gate-level routing congestion, as every transistor has two gates to route. Novel symbolic layouts, which are technology independent, are proposed for ambipolar circuits. In the second part of this paper, we present an approach for designing an efficient regular layout called sea-of-tiles (SoTs). A logic tile is essentially an array of prefabricated transistor-pairs grouped together. We design four logic tiles, which form the basic building block of the SoT fabric. We run extensive comparisons of mapping standard benchmarks onto the SoT fabric to find the optimum tile. This paper shows that SoT with $\mathrm{Tile}_{\mathit {G2}}$ and $\mathrm{Tile}_{\mathit {G1h2}}$ , on an average, outperforms the one with $\mathrm{Tile}_{\mathit {G1}}$ by 16% and 14% in area utilization, respectively.

Monolithic integration of a silicon nanowire field-effect transistors array on a complementary metal-oxide semiconductor chip for biochemical sensor applications.

We present a monolithic complementary metal-oxide semiconductor (CMOS)-based sensor system comprising an array of silicon nanowire field-effect transistors (FETs) and the signal-conditioning circuitry on the same chip. The silicon nanowires were fabricated by chemical vapor deposition methods and then transferred to the CMOS chip, where Ti/Pd/Ti contacts had been patterned via e-beam lithography. The on-chip circuitry measures the current flowing through each nanowire FET upon applying a constant source-drain voltage. The analog signal is digitized on chip and then transmitted to a receiving unit. The system has been successfully fabricated and tested by acquiring I-V curves of the bare nanowire-based FETs. Furthermore, the sensing capabilities of the complete system have been demonstrated by recording current changes upon nanowire exposure to solutions of different pHs, as well as by detecting different concentrations of Troponin T biomarkers (cTnT) through antibody-functionalized nanowire FETs.

The application of silicon nanowire field-effect transistor-based biosensors in molecular diagnosis

Cancer, one of the most life-threatening diseases, causes a heavy burden to both the society and family. Timely and efficient early diagnosis of cancer is critical to enable effective treatment and improving survival rate, which also is currently one of the most challenging problems in clinical medicine. Although modern medical imaging is an important tool for cancer diagnosis, detection of molecular biomarkers (such as DNA, RNA, proteins, and metabolites), released from the cancer cells or the organs, is the preferred approach for detecting and tracking cancer due to their unique association with genomic changes in cancer cells, especially for screening and early diagnosis of cancer. Molecular diagnosis can help doctors not only make a precise diagnosis in diseases’ early stage, but also make a judgment in disease staging, classification, curative effect monitoring and prognosis evaluation. A variety of conventional technologies are developed for biomarker detection, such as radio-immunoassay and enzyme-linked immunosorbent assay (ELISA), however, they are label-based, multi-step, time-consuming, and required experienced personnel to conduct the experiment. Silicon nanowire field-effect transistors (SiNW-FETs), as new one-dimensional semiconducting nanostructures, exhibit some unique properties, including high surface-to-volume ratios, fast electron transfer, and biocompatibility. SiNW-FET based biosensors have recently been attracted tremendous attention as a promising tool in biomedical and chemical detection because of their ultrasensitivity, specificity, label-free detection, and rapid and real-time response capabilities, which demonstrate a great potential in the application of medical diagnosis, chemical analysis, environmental monitoring, and food industry. Over the past decade, SiNW-FET biosensors are employed in the detections of DNA sequences, microRNAs, proteins, small molecules, cancer biomarkers, cells, and viruses. Here, we present a comprehensive review which introduces the working principle of SiNW-FETs, the fabrication of SiNWs, influence factors of the sensitivity, as well as the applications of SiNW-FET biosensors in cancers’ molecular diagnosis (including nucleic acid detection, biomarkers detection, and studies of molecule-molecule interactions). The future prospects in this area are also discussed, which can provide a guidance for the further applications in early diagnosis. SiNW-FET biosensors, as a promise tool in molecular diagnosis, held great potential applications in large-scale screening and point-of-care testing for early-stage cancer.

Scalability and process induced variation analysis of polarity controlled silicon nanowire transistor

In this paper, we present scalability and process induced variation analysis of polarity gate silicon nanowire field-effect transistor. 3D simulation results show that the PGFET offers significant reduction in short channel effects and variability due to utilization of uniform lightly doped silicon nanowire (SiNW) as compare to highly doped silicon nanowire in junctionless transistors. The performance parameters were evaluated for different device geometries, such as variation in SiNW radius, equivalent oxide thickness, channel length and spacer length. Sensitivity analysis shows that the PGFET exhibits less dependence towards gate length in comparison to other device parameters. It is seen that ON to OFF current ratio variation with silicon nanowire thickness is lower for PGFET as compared to JLFET. The threshold voltage roll-off and sensitivity towards intrinsic delay in PGFET is much lower than its counterpart device.

A bottom-gate silicon nanowire field-effect transistor with functionalized palladium nanoparticles for hydrogen gas sensors

The highly sensitive operation of a bottom-gate silicon nanowire (SiNW) field-effect transistor (FET)-based hydrogen (H2) sensor is demonstrated by controlling the working regime of the sensor. It is observed that the deposition of palladium (Pd) nanoparticles on the SiNW surface for the selective absorption of H2 can result in a significant enhancement of the electrostatic properties, such as the subthreshold swing and on-current, of the SiNW FET-based H2 sensor. By comparing the experimental results with the numerical simulation, we conclude that the improvement of the electrostatic properties of the sensor is due to the coupling effect between the electrostatic potentials in the Pd nanoparticle and bottom gate. Based on these results, highly sensitive detection of H2 gas could be achieved in the subthreshold regime where the gating effect induced by absorbed H2 gas is the most effective.

Simultaneous Detection of α-Fetoprotein and Carcinoembryonic Antigen Based on Si Nanowire Field-Effect Transistors.

Primary hepatic carcinoma (PHC) is one of the most common malignancies worldwide, resulting in death within six to 20 months. The survival rate can be improved by effective treatments when diagnosed at an early stage. The α-fetoprotein (AFP) and carcinoembryonic antigen (CEA) have been identified as markers that are expressed at higher levels in PHC patients. In this study, we employed silicon nanowire field-effect transistors (SiNW-FETs) with polydimethylsiloxane (PDMS) microfluidic channels to simultaneously detect AFP and CEA in desalted human serum. Dual-channel PDMS was first utilized for the selective modification of AFP and CEA antibodies on SiNWs, while single-channel PDMS offers faster and more sensitive detection of AFP and CEA in serum. During the SiNW modification process, 0.1% BSA was utilized to minimize nonspecific protein binding from serum. The linear dynamic ranges for the AFP and CEA detection were measured to be 500 fg/mL to 50 ng/mL and 50 fg/mL to 10 ng/mL, respectively. Our work demonstrates the promising potential of fabricated SiNW-FETs as a direct detection kit for multiple tumor markers in serum; therefore, it provides a chance for early stage diagnose and, hence, more effective treatments for PHC patients.

Functionality-Enhanced Logic Gate Design Enabled by Symmetrical Reconfigurable Silicon Nanowire Transistors

Reconfigurable silicon nanowire field-effect transistors (RFETs) combine the functionality of classical unipolar p-type and n-type FETs in one universal device. In this paper, we show devices exhibiting full symmetry between pand n-functionality, while having identical geometry. Scaling trends and feasibility for digital circuit integration are evaluated based on TCAD simulations. The method of logical effort is applied to analyze fundamental differences in circuit topology using this unique type of multigate transistors. We introduce a set of multifunctional logic gates based on RFETs providing all basic Boolean functions, including NAND/NOR, AND/OR, and XOR/XNOR, and compared them with classical implementations. Two 1-bit full adders based on those gates are presented as an insightful example that RFETs are one possible solution to increase the system functionality. Moreover, it is shown that an asymmetric transistor layout with individual optimization of both top gates can be used to increase the speed of those circuits.

Dispersively Detected Pauli Spin-Blockade in a Silicon Nanowire Field-Effect Transistor.

We report the dispersive readout of the spin state of a double quantum dot formed at the corner states of a silicon nanowire field-effect transistor. Two face-to-face top-gate electrodes allow us to independently tune the charge occupation of the quantum dot system down to the few-electron limit. We measure the charge stability of the double quantum dot in DC transport as well as dispersively via in situ gate-based radio frequency reflectometry, where one top-gate electrode is connected to a resonator. The latter removes the need for external charge sensors in quantum computing architectures and provides a compact way to readout the dispersive shift caused by changes in the quantum capacitance during inter-dot charge transitions. Here, we observe Pauli spin-blockade in the high-frequency response of the circuit at finite magnetic fields between singlet and triplet states. The blockade is lifted at higher magnetic fields when intra-dot triplet states become the ground state configuration. A line shape analysis of the dispersive phase shift reveals furthermore an intra-dot valley-orbit splitting Δvo of 145 μeV. Our results open up the possibility to operate compact complementary metal-oxide semiconductor (CMOS) technology as a singlet-triplet qubit and make split-gate silicon nanowire architectures an ideal candidate for the study of spin dynamics.

Controlling the Sensing Properties of Silicon Nanowires via the Bonds Nearest to the Silicon Nanowire Surface.

Controlling the sensing properties of a silicon nanowire field effect transistor is dependent on the surface chemistry of the silicon nanowire. A standard silicon nanowire has a passive oxide layer (native oxide), which has trap states that cause sensing inaccuracies and desensitize the surface to nonpolar molecules. In this paper, we successfully modified the silicon nanowire surface with different nonoxide C3 alkyl groups, specifically, propyl (Si-CH2-CH2-CH3), propenyl (Si-CH═CH-CH3), and propynyl (Si-C≡C-CH3) modifications. The effect of the near surface bond on the sensor sensitivity and stability was explored by comparing three C3 surface modifications. A reduction of trap-states led to greater sensor stability and accuracy. The propenyl-modified sensor was consistently the most stable and sensitive sensor, among the applied sensors. The propenyl- and propynyl-modified sensors consistently performed with the best accuracy in identifying specific analytes with similar polarity or similar molecular weights. A combination of features from different sensing surfaces led to the best rubric for specific analytes identification. These results indicate that nonoxide sensor surfaces are useful in identifying specific analytes and that a combination of sensors with different surfaces in a cross-reactive array can lead to specific analytes detection.