Name: flow-assisted dielectrophoresis: a low cost method for the fabrication of high performance solution-processable nanowire devices
Uploaded: 2017-12-07T14:00:00
Description: Watch this Scientific Journal Video about Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices at JoVE.com

The authors would like to thank ESPRC and BAE systems for financial support, and Prof. Brian A. Korgel and his group for the supply of SFLS grown silicon nanowires used in this work.

Caution: All procedures unless otherwise stated take place in a clean room environment and risk assessments have been done to ensure safety during nanowires and chemicals handling. Nanomaterials may have a number of health implications which are as of yet unknown, and so should be handled with appropriate care21.
NOTE: The process starts with the preparation of the substrates, followed by the first photolithography and metal deposition steps to define the DEP contacts. ...

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The successful fabrication and performance of the devices depend on several key factors. These include nanowire density and distribution in the formulation, the choice of solvent, the frequency of DEP, and the control of the number of nanowires present on the device electrodes1.
One of the critical steps in achieving repeatable working devices is the preparation of a nanowire formulation without clusters or clumps. The formulation can be sonicated before DEP to reduce t...

Controllable and reproducible assembly of nanoparticles in pre-defined substrate locations is one of the main challenges in solution-processed electronic and photonic devices utilizing semiconducting or conducting nanoparticles. For high performance devices, it is also highly beneficial to be able to select nanoparticles with preferential sizes, and particular electronic properties, including, for example, high conductivity and low density of surface trap states. Despite significant progress in nanomaterials growth, including nanowire and nanotube materials, some variations of nanoparticle properties are always present, and a selection step can significantly improve nanoparticle-based device performance1,2.
The purpose of the flow-assisted DEP method demonstrated in this work is to address the above challenges by showing controllable semiconducting nanowires assembly onto metallic contacts for high performance nanowire field effect transistors. DEP solves several problems of nanowire device fabrication in a single step including positioning of nanowires, alignment/orientation of nanowires, and selection of nanowires with desired properties via DEP signal frequency selection1. DEP has been used for numerous other devices ranging from gas sensors3, transistors1, and RF switches4,5, to the positioning of bacteria for analysis7.
DEP is the manipulation of polarizable particles via the application of a non-uniform electric field resulting in nanowires self-assembly across the electrodes8. The method was originally developed for the manipulation of bacteria9,10 but has since been expanded to the manipulation of nanowires and nanomaterials.
DEP solution processing of nanoparticles enables semiconductor device fabrication that significantly differs from traditional top-down techniques based on multiple photomasking, ion implantation, high temperature14, annealing, and etching steps. Since DEP manipulates nanoparticles that have already been synthesized, it is a low-temperature, bottom-up fabrication technique11. This approach allows large-scale nanowire devices to be assembled on almost any substrate including temperature-sensitive, flexible plastic substrates6,12,13.
In this work, high performance p-type silicon nanowire field effect transistors are fabricated using flow-assisted DEP, and the FET current-voltage characterization is conducted. The silicon nanowires used in this work are grown via the Super Fluid Liquid Solid (SFLS) method15,16. The nanowires are intentionally&#160;doped, and are approximately 10 - 50 &#181;m in length and 30 - 40 nm in diameter. The SFLS growth method is very attractive since it can offer industry scalable amounts of nanowire materials15. The proposed nanowire assembly methodology is directly applicable to other semiconductor nanowire materials such as InAs13, SnO23, and GaN18. The technique can also be expanded to align conductive nanowires19 and to position nanoparticles across electrode gaps20.

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	<tbody>
		<tr>
			<td>Silicon/silicon dioxide wafer, CZ method growth, 100mm diameter,&#160; 300 nm oxide thermal growth,&#160; n-doped phosphorus</td>
			<td>Si-Mat (Silicon materials)</td>
			<td>-</td>
			<td>http://si-mat.com/</td>
		</tr>
		<tr>
			<td>Acetone (200ml)</td>
			<td>Sigma Aldrich</td>
			<td>W332615</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Isopropanol (200ml)</td>
			<td>Sigma Aldrich</td>
			<td>W292907</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Deionised water (150ml)</td>
			<td>On site supply</td>
			<td>-</td>
			<td>-</td>
		</tr>
		<tr>
			<td>Photoresist (A) SF6 PMGI under etch photoresit (approx 1 ml per sample)</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://microchem.com/pdf/PMGI-Resists-data-sheetV-rhcedit-102206.pdf</td>
		</tr>
		<tr>
			<td>Photoresist (B) S1805 photoresit) (approx 1 ml per sample)</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://www.microchem.com/PDFs_Dow/S1800.pdf</td>
		</tr>
		<tr>
			<td>Photoresist developer (A) Microposit&#160; MF319&#160; (100ml)</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://microchem.com/products/images/uploads/MF_319_Data_Sheet.pdf</td>
		</tr>
		<tr>
			<td>Photoresist remover (A) Microposit remover 1165 (300ml (2 baths 150 each))</td>
			<td>Microchem&#160;</td>
			<td>-</td>
			<td>http://micromaterialstech.com/wp-content/dow_electronic_materials/datasheets/1165_Remover.pdf</td>
		</tr>
	</tbody>
</table>

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.

Bilayer photolithography results in clean sharply defined electrodes. In the example (Figure 1A), inter-digitated finger structure was used with a channel length of 10 &#181;m. These structures allow a large area to assemble the maximum number of nanowires when the DEP force is applied. Figure 1B shows a schematic of a bottom-gate nanowire FET device.
Incorrect nanowire...

Watch this Scientific Journal Video about Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices at JoVE.com

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

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 ...

The overall goal of this procedure is to demonstrate electric field assistance assembly and selection of high quality semi-conducting nanowires including fabrication of metal electrodes and use of these electrodes in flow-assisted dielectrophoresis to create solution-processable nanowire field effect transistors.This method can help us solve one of the main challenges in the field of solution-processable electronics such as placement of semi-conducting nanomaterials, control of the pilation done and field train of superior quality nanowires.The main function of this technique is that it's a fast reproducible method that can be scaled off controllable fabrication of nano material based devices.Although this method can provide insight into the alignment and selection of nanowires, it can also be applied in the alignment of nanotubes, nano flakes and blade-like nanomaterials.Most steps in this protocol take place in a clean room environment.Start with heavily doped four-inch N type silicon/silicon dioxide wafer.Use a diamond scribe to cut the wafer to produce suitably sized samples.Take care not to touch the top surface.Split the wafer along the cuts to yield several samples.The samples for this experiment are 2.5 x 2.5 centimeters.When done, take the samples to an ultrasonic bath.Place the samples on a substrate holder and immerse them in a beaker of deionized water.Sonicate the samples in the beaker for five minutes at full power.Then transfer the samples to a beaker with acetone before sonicating them for five minutes at full power again.Finally, transfer the samples to a beaker with isopropanol and sonicate for an additional five minutes at full power.Remove the samples from the ultrasonic bath and dry them with a nitrogen gun.Next, transfer the samples to a plasma asher to remove any remaining organic residues.For photolithography, move the samples to a yellow room.Work in a fume cupboard with a hotplate at 150

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