This research was financially supported by Ministry of Science and Technology, Taiwan (104-2514-S-009 -001, 104-2627-M-009-001 and 102-2311-B-009-004-MY3). We thank the National Nano Device Laboratories (NDL) for its valuable assistance during device fabrication and analysis.

1. Fabrication and Preservation of pSNWFET Devices
<ol>
	<li>Device Fabrication 
	Note: The pSNWFET was fabricated using a sidewall spacer technique as previously reported23,24.
	<ol>
		<li>Prepare the gate dielectric layer.
		<ol>
			<li>Cap a 100-nm-thick thermal oxide (SiO2) layer on a Si substrate by using the wet oxidation process25 (O2 and H2 process gas at 980 &#176;C for 4 hr).</li>
			<li>Deposit a 50-nm-thick nitride (Si3N4) layer by using low-pressure chemical vapor deposition (LPCVD)25 at 980 &#176;C for 4 hr.</li>
		</ol>
		</li>
		<li>Deposit a 100-nm-thick tetraethyl orthosilicate (TEOS) layer by using LPCVD25 at 780 &#176;C for 4 hr.</li>
		<li>Perform standard lithography by using an I-line stepper to define the oxide dummy structures.
		<ol>
			<li>Coat the wafer surface with an 830-nm-thick photoresist layer.</li>
			<li>Insert a pattern-defined photomask into the I-line stepper.</li>
			<li>Process the exposure by using the I-line stepper (wavelength: 365 nm) at a strength of 1,980 J at room temperature.</li>
			<li>Develop the wafer within a developer for 5 min.</li>
			<li>Perform the isotropic etching process by using a standard inductively coupled plasma25 etcher with HBr and Cl plasma gas for 1 min.</li>
		</ol>
		</li>
		<li>Deposit a 100-nm-thick amorphous silicon (&#945;-Si) layer by using LPCVD25.</li>
		<li>Perform an annealing step at 600 &#176;C in N2 ambient for 24 hr to transform the &#945;-Si into a polycrystalline structure.</li>
		<li>Implant phosphorous ions through source/drain (S/D) doping at low energy (5E15 cm&#8722;2)25.</li>
		<li>Perform standard lithography by using the I-line stepper to remove the poly-Si layer and form the polysilicon nanowire (pSNW)25. 
		Note: Repeat step 1.1.3 to implant dopants in places other than S/D regions with poly-Si removal and form the sidewall Si channels in a self-aligned manner.</li>
		<li>Perform the passivation process (200-nm-thick TEOS oxide layer) by using LPCVD at 780 &#176;C for 5 hr25.</li>
		<li>Perform standard lithography by using the I-line stepper to expose the nanowire channels, and form test pads by using the two-step dry/wet etching process.
		<ol>
			<li>Repeat step 1.1.3.</li>
			<li>Perform the wet etching process (DHF: HF/H2O for 1 min).</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Wafer preservation
	<ol>
		<li>Seal the wafer in a vacuum storage bag and store it in an electronic dry cabinet (relative humidity &#60;40% at room temperature).</li>
	</ol>
	</li>
</ol>
2. Pretreatment of the Device
<ol>
	<li>Device cleaning
	<ol>
		<li>Rinse the device with pure acetone.</li>
		<li>Sonicate (46 kHz, 80 W) the device in pure acetone for 10 min.</li>
		<li>Sonicate (46 kHz, 80 W) the device in pure ethanol (99.5%) for 5 min.</li>
		<li>Blow-dry the surface of the device with nitrogen.</li>
	</ol>
	</li>
	<li>Oxygen plasma
	<ol>
		<li>Treat the device with O2 plasma at 18 W for 30 sec.</li>
	</ol>
	</li>
</ol>
3. Immobilization of the DNA Probe on the Device Surface
<ol>
	<li>Amine group modification
	<ol>
		<li>Immerse the device in a 2.0% (3-aminopropyl)triethoxysilane (APTES)/ethanol solution for 30 min.</li>
		<li>Wash the device with ethanol three times, and then sonicate (46 kHz, 80 W) the device in ethanol for 10 min.</li>
		<li>Heat the device on a hot plate at 120 &#176;C for 10 min to create amine groups on SNWs.</li>
	</ol>
	</li>
	<li>Aldehyde group modification
	<ol>
		<li>Immerse the device in 12.5% glutaraldehyde for 1 hr at room temperature to create aldehyde groups on the surface. Avoid light exposure.</li>
		<li>Wash the device with 10 mM sodium phosphate buffer (Na-PB; pH 7.0) three times, and then blow-dry the surface of the device with nitrogen.</li>
	</ol>
	</li>
	<li>DNA probe immobilization
	<ol>
		<li>Immerse the device in a solution containing 1 &#181;M DNA probes overnight.</li>
		<li>Immerse the device in 10 mM Tris buffer (pH 8.0) with 4.0 mM NaBH3CN for 30 min to block the unreacted aldehyde groups.</li>
		<li>Wash the device with Na-PB (pH 7.0) three times, and then blow-dry the surface of the device with nitrogen.</li>
	</ol>
	</li>
</ol>
4. Confirmation and Analysis of Surface Modification on pSNWFET
<ol>
	<li>pH profile following each step of surface modification
	<ol>
		<li>Prepare 10 mM Na-PB in pH 3.0-9.0.
		<ol>
			<li>Prepare 10 mM sodium phosphate tribasic dodecahydrate (Na3PO4) in deionized water (pH 11.60).</li>
			<li>Prepare 10 mM phosphoric acid (H3PO4) in deionized water (pH 2.35).</li>
			<li>Place the pH electrode into 500 ml of 10 mM Na3PO4 buffer, and mix this solution with different volumes of 10 mM H3PO4 buffer while measuring the pH value to obtain buffers with pH values of 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and 9.0.</li>
		</ol>
		</li>
		<li>AC conductance measurement 
		Note: The measurement circuit included a small AC signal generator and an Au microwire that served as the liquid gate electrode.
		<ol>
			<li>Determine the optimal liquid gate voltage (VLG) for measurement26 at each modification step (steps 2.2, 3.1, 3.2, and 3.3). 
			Note: The electric properties of the device after four surface modifications on the SNW were measured as described in this section. In step 2.2, the unmodified pSNWFET containing the native oxide layer is modified; step 3.1 entails modifying the device with the amine group of APTES; step 3.2 involves modification with the uncharged functional group of glutaraldehyde; and step 3.3 involves DNA probe modification.
			<ol>
				<li>Deliver the 10 mM Na-PB (pH 7.0) solution to the SNW surface by using a syringe pump (flow rate: 5.0 ml/hr) for direct contact with the SNW.</li>
				<li>Measure the real-time conductance of the device while sweeping VLG from 0.80 to 1.30 V.
				<ol>
					<li>Perform conductance measurement by using the lock-in technique27 at room temperature.</li>
					<li>Convert the AC current signals into an AC voltage signal by using a low-noise current preamplifier.</li>
					<li>Collect data on conductance (G) upon increasing VLG from 0.80 to 1.30 V (interval = 0.02 V).</li>
				</ol>
				</li>
				<li>Determine the optimal VLG (most sensitive VLG) of the device26.
				<ol>
					<li>Plot the G-VLG curves from step 4.1.2.1.2.3 to obtain the equation of the curve.</li>
					<li>Differentiate the equation, and calculate the values in each point of VLG.</li>
					<li>Divide the value from step 4.1.2.1.3.2 by G, and determine the optimal VLG according to the maximum number.</li>
				</ol>
				</li>
			</ol>
			</li>
			<li>Measure the real-time conductance of the pH profile at each step of the surface modification.
			<ol>
				<li>Perform conductance measurement by using the lock-in technique27 at room temperature.</li>
				<li>Convert the AC current signal into AC voltage signals by using a low-noise current preamplifier.</li>
				<li>Set the optimal VLG for each step of surface modification (step 2.2: VLG = 1.02, step 3.1: VLG = 0.98, step 3.2: VLG = 0.98, and step 3.3: VLG = 1.0).</li>
				<li>Deliver the 10 mM Na-PB solution with pH values from 3.0 to 9.0 to the SNW surface (flow rate: 5.0 ml/hr), and collect the data on conductance at a drain voltage of 0.01 V.</li>
			</ol>
			</li>
		</ol>
		</li>
	</ol>
	</li>
	<li>Measurement of electric properties (the ID-VBG curve) of the device in 10 mM Na-PB (pH 7.0) following each step of surface modification (steps 2.2, 3.1, 3.2, and 3.3.) 
	Note: The electric properties of the device after four surface modifications on the SNW were measured: in step 2.2, the unmodified pSNWFET containing the native oxide layer is modified; step 3.1 involves modifying the device with the amine group of APTES; step 3.2 entails modification with the uncharged functional group of glutaraldehyde; and step 3.3 entails DNA probe modification.
	<ol>
		<li>Deliver the 10 mM Na-PB (pH 7.0) solution to the SNW surface (steps 2.2, 3.1, 3.2, and 3.3) by using a syringe pump (flow rate: 5.0 ml/hr) for direct contact with the SNW.</li>
		<li>Measure the ID of the device (steps 2.2, 3.1, 3.2, and 3.3) by using a commercial semiconductor analyzer and software.
		<ol>
			<li>Select the &#34;nMOSFET&#34; mode.</li>
			<li>Select &#34;ID-VBG&#34; modules. 
			Note: ID is the drain/source current, and VBG is the back gate voltage.</li>
			<li>Set a constant bias voltage (VD = 0.5 V) while sweeping the gate potential (VBG) from &#8722;1 to 3.0 V (interval = 0.2 V).</li>
			<li>Click the Run icon to obtain ID-VBG curves.</li>
		</ol>
		</li>
	</ol>
	</li>
</ol>
5. DNA Biosensing
Note: In a typical experiment, the ID-VBG curve is determined three times to ensure that no further variation is observed.
<ol>
	<li>Determination of the baseline
	<ol>
		<li>Deliver the 10 mM Na-PB solution (pH 7.0) to the DNA probe-immobilized SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr), and then incubate the SNW for 30 min.</li>
		<li>Measure the ID of the device (repeat step 4.2.2).</li>
	</ol>
	</li>
	<li>Sensing of DNA/DNA hybridization
	<ol>
		<li>Load 10 pM complementary target DNA onto the DNA probe-immobilized SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr), and then incubate the SNW for 30 min.</li>
		<li>Deliver the 10 mM Na-PB solution (pH 7.0) onto the SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr) to wash the unbound target DNA away.</li>
		<li>Repeat step 4.2.2 to measure the ID of the device.</li>
	</ol>
	</li>
	<li>Reconfirm the signal of DNA/DNA hybridization.
	<ol>
		<li>Load 1 nM recovery DNA onto the DNA probe-immobilized SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr), and then incubate the SNW for 30 min.</li>
		<li>Deliver the 10 mM Na-PB solution (pH 7.0) onto the SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr).</li>
		<li>Repeat step 4.2.2 to measure the ID of the device.</li>
	</ol>
	</li>
	<li>Negative control
	<ol>
		<li>Load 100 pM non-complementary DNA onto the DNA probe-immobilized SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr), and then incubate the SNW for 30 min.</li>
		<li>Deliver the 10 mM Na-PB solution (pH 7.0) onto the SNW surface for 10 min by using a syringe pump (flow rate: 5.0 ml/hr).</li>
		<li>Repeat step 4.2.2 to measure the ID of the device.</li>
	</ol>
	</li>
</ol>

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N., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Well+controlled+assembly+of+silicon+nanowires+by+nanowire+transfer+method.">Well controlled assembly of silicon nanowires by nanowire transfer method.</a> Nanotechnology. 18 (445302), (2007).</li><li>Li, Z., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequence-specific+label-free+DNA+sensors+based+on+silicon+nanowires.">Sequence-specific label-free DNA sensors based on silicon nanowires.</a> Nano Lett. 4, 245-247 (2004).</li><li>McAlpine, M. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-performance+nanowire+electronics+and+photonics+on+glass+and+plastic+substrates.">High-performance nanowire electronics and photonics on glass and plastic substrates.</a> Nano Lett. 3, 1531-1535 (2003).</li><li>Cui, Y., Wei, Q., Park, H., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowire+nanosensors+for+highly+sensitive+and+selective+detection+of+biological+and+chemical+species.">Nanowire nanosensors for highly sensitive and selective detection of biological and chemical species.</a> Science. 293, 1289-1292 (2001).</li><li>Patolsky, F., Zheng, G., Lieber, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Nanowire-based+biosensors.">Nanowire-based biosensors.</a> Anal Chem. 78, 4260-4269 (2006).</li><li>Hsiao, C. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Novel+poly-silicon+nanowire+field+effect+transistor+for+biosensing+application.">Novel poly-silicon nanowire field effect transistor for biosensing application.</a> Biosens Bioelectron. 24, 1223-1229 (2009).</li></ol>

The authors have nothing to disclose.

Commercializing the top-down and bottom-up fabrication approaches for sSNWFETs is considered difficult because of its cost32,33, SNW position control34,35, and its low production scale36. By contrast, fabricating pSNWFETs is simple and low cost37. Through the top-down approach and combination with the sidewall spacer formation technique (Figure 1), the size of the SNW can be controlled by adjusting the duration of reactive plasma etching. The procedures for pre...

Silicon nanowire field-effect transistors (SNWFETs) have the advantages of ultra-high sensitivity and direct electrical responses to environmental charge variation. In n-type SNWFETs for example, when a negatively (or positively) charged molecule approaches the silicon nanowire (SNW), the carriers in the SNW are depleted (or accumulate). Consequently, the conductivity of the SNWFET decreases (or increases)1. Therefore, any charged molecule near the SNW surface of the SNWFET device can be detected. Vital biomolecules including enzymes, proteins, nucleotides, and many molecules on the cell surface are charge carriers and can be monitored using SNWFETs. With suitable modifications, particularly immobilizing a biomolecular probe on the SNW, a SNWFET can be developed into a label-free biosensor.
Surveillance using biomarkers is critical for diagnosing diseases. As shown in Table 1, several studies have used NWFET-based biosensors for label-free, ultra-high-sensitivity, and real-time detection of various biological targets, including a single virus2, adenosine triphosphate and kinase binding3, neuronal signals4, metal ions5,6, bacterial toxins7, dopamine8, DNA9-11, RNA12,13, enzyme and cancer biomarkers14-19, human hormones20, and cytokines21,22. These studies have demonstrated that NWFET-based biosensors represent a powerful detection platform for a broad range of biological and chemical species in a solution.
In SNWFET-based biosensors, the probe immobilized on the SNW surface of the device recognizes a specific biotarget. Immobilizing a bioprobe usually involves a series of steps, and it is critical that every step is properly performed to ensure the proper functioning of the biosensor. Various techniques have been developed for analyzing the surface composition, including X-ray photoelectron spectroscopy (XPS), ellipsometry, contact angle measurement, atomic force microscopy (AFM), and scanning electron microscopy (SEM). Methods such as AFM and SEM provide direct evidence of bioprobe immobilization on the nanowire device, whereas methods such as XPS, ellipsometry, and contact angle measurement are dependent on parallel experiments performed on other similar materials. In this report, we describe the confirmation of each modification step by using two independent methods. XPS is used to examine the concentrations of specific atoms on polysilicon wafers, and variations in the electric properties of the device are measured directly to confirm the charge variation on the SNW surface. We employ DNA biosensing by using polycrystalline SNWFETs (pSNWFETs) as an example to illustrate this protocol. Immobilizing a DNA probe on the SNW surface involves three steps: amine group modification on the native hydroxyl surface of the SNW, aldehyde group modification, and 5&#39;-aminomodified DNA probe immobilization. At each modification step, the device can directly detect the variation in the charge of the functional group immobilized on the SNW surface, because the surface charges cause local interfacial potential changes over the gate dielectric that alter the channel current and conductance1. Charges surrounding the SNW surface can electrically modulate the electric properties of the pSNWFET device; therefore, the surface properties of the SNW play a crucial role in determining the electrical characteristics of pSNWFET devices. In the reported procedures, the immobilization of a bioprobe on the SNW surface can be directly determined and confirmed through electric measurement, and the device is prepared for biosensing applications.

<table><tbody><tr><td>Acetone</td><td>ECHO</td><td>AH-3102</td><td></td></tr><tr><td>(3-Amonopropyl)triethoxysilane (APTES), &amp;ge;98%</td><td>Sigma-Aldrich</td><td>A3648</td><td>Danger</td></tr><tr><td>Ethanol, anhydrous, 99.5%</td><td>ECHO</td><td>484000203108A-72EC</td><td></td></tr><tr><td>Glutaraldehyde solution (GA), 50%</td><td>Sigma-Aldrich</td><td>G7651</td><td>Avoid light</td></tr><tr><td>Sodium cyanoborohydride, &amp;ge;95.0%&amp;nbsp;</td><td>Fluka</td><td>71435</td><td>Danger and deliquescent</td></tr><tr><td>Sodium phosphate tribasic dodecahydrate, &amp;ge;98%</td><td>Sigma</td><td>04277</td><td></td></tr><tr><td>Phosphoric acid, &amp;ge;99.0%</td><td>Fluka</td><td>79622</td><td>Deliquescent</td></tr><tr><td>Photoresist (iP3650)</td><td>Tokyo Ohka Kogyo Co., LTD</td><td>THMR-iP3650 HP</td><td></td></tr><tr><td>Synthetic oligonucleotides, HPLC purified</td><td>Protech Technology</td><td></td><td></td></tr><tr><td>Tris(hydroxymethyl)aminomethane (Tris), &amp;ge;99.8%</td><td>USB</td><td>75825</td><td></td></tr><tr><td>Keithley 2636 System SourceMeter</td><td>Keithley</td><td></td><td></td></tr><tr><td>SR830 DSP Lock-In Amplifier</td><td>Stanford Research Systems</td><td></td><td></td></tr><tr><td>SR570 Low-noise Current Preamplifier</td><td>Stanford Research Systems</td><td></td><td></td></tr><tr><td>Ni PXI Express</td><td>National Instruments</td><td></td><td></td></tr></tbody></table>

preparation of silicon nanowire field-effect transistor for chemical and biosensing applications

Surveillance using biomarkers is critical for the early detection, rapid intervention, and reduction in the incidence of diseases. In this study, we describe the preparation of polycrystalline silicon nanowire field-effect transistors (pSNWFETs) that serve as biosensing devices for biomarker detection. A protocol for chemical and biomolecular sensing by using pSNWFETs is presented. The pSNWFET device was demonstrated to be a promising transducer for real-time, label-free, and ultra-high-sensitivity biosensing applications. The source/drain channel conductivity of a pSNWFET is sensitive to changes in the environment around its silicon nanowire (SNW) surface. Thus, by immobilizing probes on the SNW surface, the pSNWFET can be used to detect various biotargets ranging from small molecules (dopamine) to macromolecules (DNA and proteins). Immobilizing a bioprobe on the SNW surface, which is a multistep procedure, is vital for determining the specificity of the biosensor. It is essential that every step of the immobilization procedure is correctly performed. We verified surface modifications by directly observing the shift in the electric properties of the pSNWFET following each modification step. Additionally, X-ray photoelectron spectroscopy was used to examine the surface composition following each modification. Finally, we demonstrated DNA sensing on the pSNWFET. This protocol provides step-by-step procedures for verifying bioprobe immobilization and subsequent DNA biosensing application.

Various SNWFETs have been reported to serve as transducers of biosensors (Table 1). Single-crystalline SNWFETs (sSNWFETs) and pSNWFETs show comparable electric properties as transducers in aqueous solutions, and both have been reported to have many biosensing applications. An advantageous feature of the pSNWFET device used in this study is its simple and low-cost fabrication procedure. Figure 1a shows the key steps involved in fabricating the pSNWFET. An ...

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Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications

We describe key steps for biosensing by using polysilicon nanowire field-effect transistors, including the preparation of the device and the immobilization and confirmation of a DNA molecular probe on the nanowire surface, as well as conditions for DNA sensing.

Surveillance using biomarkers is critical for the early detection, rapid intervention, and reduction in the incidence of diseases. In this study, we ...

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11.0K Views.  National Chiao Tung University. We describe key steps for biosensing by using polysilicon nanowire field-effect transistors, including the preparation of the device and the immobilization and confirmation of a DNA molecular probe on the nanowire surface, as well as conditions for DNA sensing.

Video: Preparation of Silicon Nanowire Field-effect Transistor for Chemical and Biosensing Applications

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Engineering

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Fabrication of Low Temperature Carbon Nanotube Vertical Interconnects Compatible with Semiconductor Technology

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive thin-films. Due to the low growth temperature, the process allows integration with modern low-&#954; dielectrics and some flexible substrates. The process is compatible with standard semiconductor fabrication, and a method for the fabrication of electrical 4-point probe test structures for vertical interconnect test structures is presented. Using scanning electron microscopy the morphology of the CNT bundles is investigated, which demonstrates vertical alignment of the CNT and can be used to tune the CNT growth time. With Raman spectroscopy the crystallinity of the CNT is investigated. It was found that the CNT have many defects, due to the low growth temperature. The electrical current-voltage measurements of the test vertical interconnects displays a linear response, indicating good ohmic contact was achieved between the CNT bundle and the top and bottom metal electrodes. The obtained resistivities of the CNT bundle are among the average values in the literature, while a record-low CNT growth temperature was used.

A method for the growth of low temperature vertically-aligned carbon nanotubes, and the subsequent fabrication of vertical interconnect electrical test structures using semiconductor fabrication is presented.

We demonstrate a method for the low temperature growth (350 &#176;C) of vertically-aligned carbon nanotubes (CNT) bundles on electrically conductive ...

Fabrication of Carbon Nanotube High-Frequency Nanoelectronic Biosensor for Sensing in High Ionic Strength Solutions

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them good candidates for high sensitivity biosensors. When a charged molecule binds to such a sensor surface, it alters the carrier density5 in the sensor, resulting in changes in its DC conductance. However, in an ionic solution a charged surface also attracts counter-ions from the solution, forming an electrical double layer (EDL). This EDL effectively screens off the charge, and in physiologically relevant conditions ~100 millimolar (mM), the characteristic charge screening length (Debye length) is less than a nanometer (nm). Thus, in high ionic strength solutions, charge based (DC) detection is fundamentally impeded6-8.
We overcome charge screening effects by detecting molecular dipoles rather than charges at high frequency, by operating carbon nanotube field effect transistors as high frequency mixers9-11. At high frequencies, the AC drive force can no longer overcome the solution drag and the ions in solution do not have sufficient time to form the EDL. Further, frequency mixing technique allows us to operate at frequencies high enough to overcome ionic screening, and yet detect the sensing signals at lower frequencies11-12. Also, the high transconductance of SWNT transistors provides an internal gain for the sensing signal, which obviates the need for external signal amplifier.
Here, we describe the protocol to (a) fabricate SWNT transistors, (b) functionalize biomolecules to the nanotube13, (c) design and stamp a poly-dimethylsiloxane (PDMS) micro-fluidic chamber14 onto the device, and (d) carry out high frequency sensing in different ionic strength solutions11.

We describe the device fabrication and measurement protocol for carbon nanotube based high frequency biosensors. The high frequency sensing technique mitigates the fundamental ionic (Debye) screening effect and allows nanotube biosensor to be operated in high ionic strength solutions where conventional electronic biosensors fail. Our technology provides a unique platform for point-of-care (POC) electronic biosensors operating in physiologically relevant conditions.

The unique electronic properties and high surface-to-volume ratios of single-walled carbon nanotubes (SWNT) and semiconductor nanowires (NW) 1-4 make them ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape method or individual WS2 nanotubes by dispersing the suspension of WS2 nanotubes. The selected samples have been fabricated into devices by the use of the electron beam lithography and electrolyte is put on the devices. We have characterized the electronic properties of the devices under applying the gate voltage. In the small gate voltage region, ions in the electrolyte are accumulated on the surface of the samples which leads to the large electric potential drop and resultant electrostatic carrier doping at the interface. Ambipolar transfer curve has been observed in this electrostatic doping region. When the gate voltage is further increased, we met another drastic increase of source-drain current which implies that ions are intercalated into layers of WS2 and electrochemical carrier doping is realized. In such electrochemical doping region, superconductivity has been observed. The focused technique provides a powerful strategy for achieving the electric-filed-induced quantum phase transition.

Electric-field Control of Electronic States in WS2 Nanodevices by Electrolyte Gating

Here, we present a protocol to control the carrier number in solids by using the electrolyte.

A method of carrier number control by electrolyte gating is demonstrated. We have obtained WS2 thin flakes with atomically flat surface via scotch tape ...

Fabrication of Flexible Image Sensor Based on Lateral NIPIN Phototransistors

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, but several challenging points remain, such as a low absorption efficiency due to a thin active layer and low flexibility. We present an advanced method to fabricate a flexible phototransistor array with an improved electrical performance. The outstanding electrical performance is driven by a low dark current owing to deep impurity doping. Stretchable and flexible metal interconnectors simultaneously offer electrical and mechanical stabilities in a highly deformed state. The protocol explicitly describes the fabrication process of the phototransistor using a thin silicon membrane. By measuring I-V characteristics of the completed device in deformed states, we demonstrate that this approach improves the mechanical and electrical stabilities of the phototransistor array. We expect that this approach to a flexible phototransistor can be widely used for the applications of not only next-generation imaging systems/optoelectronics but also wearable devices such as tactile/pressure/temperature sensors and health monitors.

We present a detailed method to fabricate a deformable lateral NIPIN phototransistor array for curved image sensors. The phototransistor array with an open mesh form, which is composed of thin silicon islands and stretchable metal interconnectors, provides flexibility and stretchability. The parameter analyzer characterizes the electrical property of the fabricated phototransistor.

Flexible photodetectors have been intensely studied for the use of curved image sensors, which are a crucial component in bio-inspired imaging systems, ...

A Standard and Reliable Method to Fabricate Two-Dimensional Nanoelectronics

Two-dimensional (2D) materials have attracted huge attention due to their unique properties and potential applications. Since wafer scale synthesis of 2D materials is still in nascent stages, scientists cannot fully rely on traditional semiconductor techniques for related research. Delicate processes from locating the materials to electrode definition need to be well controlled. In this article, a universal fabrication protocol required in manufacturing nanoscale electronics, such as 2D quasi-heterojunction bipolar transistors (Q-HBT), and 2D back-gated transistors are demonstrated. This protocol includes the determination of material position, electron beam lithography (EBL), metal electrode definition, et al. A step by step narrative of the fabrication procedures for these devices are also presented. Furthermore, results show that each of the fabricated devices has achieved high performance with high repeatability. This work reveals a comprehensive description of process flow for preparing 2D nano-electronics, enables the research groups to access this information, and pave the way toward future electronics.

The article aims to introduce a standard and reliable fabrication procedure for the development of future low dimensional nanoelectronics.

Two-dimensional (2D) materials have attracted huge attention due to their unique properties and potential applications. Since wafer scale synthesis of 2D ...

Development and Functionalization of Electrolyte-Gated Graphene Field-Effect Transistor for Biomarker Detection

In the current study, graphene and its derivatives have been investigated and used for many applications, including electronics, sensing, energy storage, and photocatalysis. Synthesis and fabrication of high quality, good uniformity, and low defects graphene are critical for high-performance and highly sensitive devices. Among many synthesis methods, chemical vapor deposition (CVD), considered a leading approach to manufacture graphene, can control the number of graphene layers and yield high-quality graphene. CVD graphene needs to be transferred from the metal substrates on which it is grown onto&#160;insulating substrates for practical applications. However, separation and transferring of graphene onto new substrates are challenging for a uniform layer without damaging or affecting graphene&#39;s structures and properties. Additionally, electrolyte-gated graphene field-effect transistor (EGGFET) has been demonstrated for its wide applications in various biomolecular detections because of its high sensitivity and standard device configuration. In this article, poly (methyl methacrylate) (PMMA)-assisted graphene transferring approach, fabrication of graphene field-effect transistor (GFET), and biomarker immunoglobulin G (IgG) detection are demonstrated. Raman spectroscopy and atomic force microscopy were applied to characterize the transferred graphene. The method is shown to be a practical approach for transferring clean and residue-free graphene while preserving the underlying graphene lattice onto an insulating substrate for electronics or biosensing applications.

The present protocol demonstrates the development of electrolyte-gated graphene field-effect transistor (EGGFET) biosensor and its application in biomarker immunoglobulin G (IgG) detection.

In the current study, graphene and its derivatives have been investigated and used for many applications, including electronics, sensing, energy storage, ...

Focused Ion Beam Lithography to Etch Nano-architectures into Microelectrodes

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of sophisticated microelectrodes with greater resolution and expanded capabilities. The progress in fabrication technology has supported the development of biomimetic electrodes, which aim to seamlessly integrate into the brain parenchyma, reduce the neuroinflammatory response observed after electrode insertion and improve the quality and longevity of electrophysiological recordings. Here we describe a protocol to employ a biomimetic approach recently classified as nano-architecture. The use of focused ion beam lithography (FIB) was utilized in this protocol to etch specific nano-architecture features into the surface of non-functional and functional single shank intracortical microelectrodes. Etching nano-architectures into the electrode surface indicated possible improvements of biocompatibility and functionality of the implanted device. One of the benefits of using FIB is the ability to etch on manufactured devices, as opposed to during the fabrication of the device, facilitating boundless possibilities to modify numerous medical devices post-manufacturing. The protocol presented herein can be optimized for various material types, nano-architecture features, and types of devices. Augmenting the surface of implanted medical devices can improve the device performance and integration into the tissue.

We have shown that the etching of nano-architecture into intracortical microelectrode devices may reduce the inflammatory response and has the potential to improve electrophysiological recordings. The methods described herein outline an approach to etch nano-architectures into the surface of non-functional and functional single shank silicon intracortical microelectrodes.

With advances in electronics and fabrication technology, intracortical microelectrodes have undergone substantial improvements enabling the production of ...