Silicon Nanowire-based Field-effect Transistors Research Articles

Top-down integration of suspended N+/P/N+ silicon-nanowire-based ion-sensitive field effect transistors for pH analysis at the submicronic scale

A technological process was proposed in order to integrate fully silicon-nanowire-based field-effect nanodevices on a silicon-on-insulator (SOI) substrate. Thanks to a double reactive ion etching process of the SOI silicon upper layer as well as to a "SiO2 thermal oxidation growth / Al2O3 atomic layer deposition" gate process, silicon-nanowire-based field-effect transistors (SiNW-FET) and silicon-nanowire-based ion-sensitive field-effect transistors (SiNW-ISFET) were fabricated. Focuses were brought on (i) the integration of a suspended N+/P/N+ double-junction structure (gate length: ∼ 0.75 μm and ∼ 3.75 μm), (ii) the fabrication of a SiO2/Al2O3 all-around surrounding gate structure, (iii) the achievement of low nanowire sections (width: ∼ 150 nm, height: ∼ 200 nm), and (iv) the final adaptation to the liquid phase analysis thanks to SU8-based wafer-level packaging. According to the proposed process, SiNW-FET and SiNW-ISFET devices showed excellent electrical characteristics in terms of leakage resistance ROFF, subthreshold current slope and ION/IOFF maximal ratio. SiNW-ISFET devices were finally studied for the pH analysis at the submicronic scale (analysed volumes: ∼ 10 pL), evidencing standard potentiometric detection sensitivity (∼ 56 mV/pH), as well as excellent amperometric detection sensitivity (∼ 0.4 current decade per pH) in subthreshold regime.

Rapid and quantitative detection of tear MMP-9 for dry eye patients using a novel silicon nanowire-based biosensor

Dry eye disease (DED) is the most common chronic eye disease characterized by ocular surface inflammation that affects hundreds of millions of people worldwide. The diagnosis and monitoring of DED require fast and reliable tools in the clinical setting. Matrix metalloproteinase 9 (MMP-9) has been proven to be a reliable indicator of DED owing to its close relationship with inflammation. A novel biosensor based on silicon nanowire-based field-effect transistor (SiNW FET) devices was fabricated for the quantitative measurement of MMP-9 in human tears. A modified controllable process was applied to improve the uniformity of the SiNWs in size and stabilize their performance with optical calibration at low salt concentrations for clinical application. With this protocol, correlation analysis proved the high agreement between the biosensor and enzyme-linked immunosorbent assay (correlation coefficient of 0.92 for DED patients and 0.90 for healthy controls). A diagnostic sensitivity of 86.96% and specificity of 90% were achieved in human tear samples from DED patients and healthy subjects in real-world clinical settings. Furthermore, the tear MMP-9 concentrations monitored using the device correlated with the therapeutic response of the patients with DED. Our enhanced SiNW biosensor device demonstrated its potential as an alternative tool for real-time diagnosis and monitoring for prognostic prediction toward point-of-care testing for DED.

Direct Detection of Uranyl in Urine by Dissociation from Aptamer-Modified Nanosensor Arrays.

An ever-growing demand for uranium in various industries raises concern for human health of both occupationally exposed personnel and the general population. Toxicological effects related to uranium (natural, enriched, or depleted uranium) intake involve renal, pulmonary, neurological, skeletal, and hepatic damage. Absorbed uranium is filtered by the kidneys and excreted in the urine, thus making uranium detection in urine a primary indication for exposure and body burden assessment. Therefore, the detection of uranium contamination in bio-samples (urine, blood, saliva, etc.,) is of crucial importance in the field of occupational exposure and human health-related applications, as well as in nuclear forensics. However, the direct determination of uranium in bio-samples is challenging because of "ultra-low" concentrations of uranium, inherent matrix complexity, and sample diversity, which pose a great analytical challenge to existing detection methods. Here, we report on the direct, real-time, sensitive, and selective detection of uranyl ions in unprocessed and undiluted urine samples using a uranyl-binding aptamer-modified silicon nanowire-based field-effect transistor (SiNW-FET) biosensor, with a detection limit in the picomolar concentration range. The aptamer-modified SiNW-FET presented in this work enables the simple and sensitive detection of uranyl in urine samples. The experimental approach has a straight-forward implementation to other metals and toxic elements, given the availability of target-specific aptamers. Combining the high surface-to-volume ratio of SiNWs, the high affinity and selectivity of the uranyl-binding aptamer, and the distinctive sensing methodology gives rise to a practical platform, offering simple and straightforward sensing of uranyl levels in urine, suitable for field deployment and point-of-care applications.

Two-Dimensional Boronate Ester Covalent Organic Framework Thin Films with Large Single Crystalline Domains for a Neuromorphic Memory Device.

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 μm), the reported thin‐film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two‐dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF‐PP or 2D BECOF‐PN) by employing a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF‐PP is featured as free‐standing thin film with large single‐crystalline domains up to ≈60 μm2 and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF‐PP film on silicon nanowire‐based field‐effect transistor is demonstrated as a bio‐inspired system to mimic neuronal synapses, displaying a learning–erasing–forgetting memory process.

Gating Hysteresis as an Indicator for Silicon Nanowire FET Biosensors

We present a biosensor chip with integrated large area silicon nanowire-based field effect transistors (FET) for human α-thrombin detection and propose to implement the hysteresis width of the FET transfer curve as a reliable parameter to quantify the concentration of biomolecules in the solution. We further compare our results to conventional surface potential based measurements and demonstrate that both parameters distinctly respond at a different analyte concentration range. A combination of the two approaches would provide broader possibilities for detecting biomolecules that are present in a sample with highly variable concentrations, or distinct biomolecules that can be found at very different levels. Finally, we qualitatively discuss the physical and chemical origin of the hysteresis signal and associate it with the polarization of thrombin molecules upon binding to the receptor at the nanowire surface.

Direct Measurement of Single-Molecule Adenosine Triphosphatase Hydrolysis Dynamics

F1-ATPase (F1) is a bidirectional molecular motor that hydrolyzes nearly all ATPs to fuel the cellular processes. Optical observation of labeled F1 rotation against the α3β3 hexamer ring revealed the sequential mechanical rotation steps corresponding to ATP binding/ADP release and ATP hydrolysis/Pi release. These substeps originate from the F1 rotation but with heavy load on the γ shaft due to fluorescent labeling and the photophysical limitation of an optical microscope, which hampers better understanding of the intrinsic kinetic behavior of ATP hydrolysis. In this work, we present a method capable of electrically monitoring ATP hydrolysis of a single label-free F1 in real time by using a high-gain silicon nanowire-based field-effect transistor circuit. We reproducibly observe the regular current signal fluctuations with two distinct levels, which are induced by the binding dwell and the catalytic dwell, respectively, in both concentration- and temperature-dependent experiments. In comparison with labeled F1, the hydrolysis rate of nonlabeled F1 used in this study is 1 order of magnitude faster (1.69 × 108 M-1 s-1 at 20 °C), and the differences between two sequential catalytic rates are clearer, demonstrating the ability of nanowire nanocircuits to directly probe the intrinsic dynamic processes of the biological activities with single-molecule/single-event sensitivity. This approach is complementary to traditional optical methods, offering endless opportunities to unravel molecular mechanisms of a variety of dynamic biosystems under realistic physiological conditions.

An innovative large scale integration of silicon nanowire-based field effect transistors

Since the early 2000s, silicon nanowire field effect transistors are emerging as ultrasensitive biosensors while offering label-free, portable and rapid detection. Nevertheless, their large scale production remains an ongoing challenge due to time consuming, complex and costly technology. In order to bypass these issues, we report here on the first integration of silicon nanowire networks, called nanonet, into long channel field effect transistors using standard microelectronic process. A special attention is paid to the silicidation of the contacts which involved a large number of SiNWs. The electrical characteristics of these FETs constituted by randomly oriented silicon nanowires are also studied. Compatible integration on the back-end of CMOS readout and promising electrical performances open new opportunities for sensing applications.

Metal–Organic Polyhedra-Coated Si Nanowires for the Sensitive Detection of Trace Explosives

Surface-modified silicon nanowire-based field-effect transistors (SiNW-FETs) have proven to be a promising platform for molecular recognition in miniature sensors. In this work, we present a novel nanoFET device for the sensitive and selective detection of explosives based on affinity layers of metal-organic polyhedra (MOPs). The judicious selection of the geometric and electronic characteristics of the assembly units (organic ligands and unsaturated metal site) embedded within the MOP cage allowed for the formation of multiple charge-transfer (CT) interactions to facilitate the selective explosive inclusion. Meanwhile, the host-stabilized CT complex inside the cage acted as an effective molecular gating element to strongly modulate the electrical conductance of the silicon nanowires. By grafting the MOP cages onto a SiNW-FET device, the resulting sensor showed a good electrical sensing capability to various explosives, especially 2,4,6-trinitrotoluene (TNT), with a detection limit below the nanomolar level. Importantly, coupling MOPs-which have tunable structures and properties-to SiNW-based devices may open up new avenues for a wide range of sensing applications, addressing various target analytes.

Ionophore-containing siloprene membranes: direct comparison between conventional ion-selective electrodes and silicon nanowire-based field-effect transistors.

Siloprene-based, ion-selective membranes (ISMs) were drop-casted onto a field-effect transistor device that consisted of a single-chip array of top-down prepared silicon nanowires (SiNWs). Within one array, two sets of SiNWs were covered with ISMs, each containing two different ionophores, allowing the simultaneous sensing of K and Na ions using a flow cell. It is shown that both ions can be effectively detected in the same solution over a wide concentration range from 10(-4) to 10(-1) M without interference. The ISMs were also analyzed in a conventional ISE configuration, allowing a direct comparison. While the responses for K(+) were similar for both sensor configurations, remarkably, the Na(+) response of the ISM-covered SiNW device was found to be higher than the one of the ISE configuration. The addition of a Na(+) buffering hydrogel layer between the SiO2 of the SiNW and the ISM reduced the response, showing the importance of keeping the boundary potential at the SiO2/ISM interface constant. The responses of the siloprene-covered SiNW devices were found to be stable over a period of at least 6 weeks, showing their potential as a multichannel sensor device.

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.

Silicon nanowire field effect transistor made of silicon-on-insulator

In this study, a fabrication technique and the results of the investigation of a silicon nanowire-based field effect transistor (Si NWFET) that can be the backbone for the fabrication of a high-sensitivity field and charge sensor with nanoscale spatial resolution for uses in different branches of physics, biology and medicine, are presented. The NWFET was fabricated of silicon-on-insulator (SOI) material by electron-beam lithography and reactive ion etching. Special care was taken of the electrical insulation of lead-in (metal) contact wires to the drain and source of the transistor, both for a reduction in the current of the leak-age to the underlying silicon wafer and for preventing contact with a conducting medium during experiments in a liquid. The measurements of the transistor in wet solutions of various pH demonstrate the possibility of using such a SiNWFET as an ultrasensitive field/charging sensor.