Change search
ReferencesLink to record
Permanent link

Direct link
Surface Charge Sensitivity of Silicon Nanowires: Size Dependence
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.ORCID iD: 0000-0003-2562-0540
KTH, School of Biotechnology (BIO).
Show others and affiliations
2007 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 7, no 9, 2608-2612 p.Article in journal (Refereed) Published
Abstract [en]

Silicon nanowires of different widths were fabricated in silicon on insulator (SOI) material using conventional process technology combined with electron-beam lithography. The aim was to analyze the size dependence of the sensitivity of such nanowires for biomolecule detection and for other sensor applications. Results from electrical characterization of the nanowires show a threshold voltage increasing with decreasing width. When immersed in an acidic buffer solution, smaller nanowires exhibit large conductance changes while larger wires remain unaffected. This behavior is also reflected in detected threshold shifts between buffer solutions of different pH, and we find that nanowires of width > 150 nm are virtually insensitive to the buffer pH. The increased sensitivity for smaller sizes is ascribed to the larger surface/volume ratio for smaller wires exposing the channel to a more effective control by the local environment, similar to a surrounded gate transistor structure. Computer simulations confirm this behavior and show that sensing can be extended even down to the single charge level.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2007. Vol. 7, no 9, 2608-2612 p.
Keyword [en]
Biomolecules, Lithography, Nanosensors, Silicon on insulator technology, Surface charge, Threshold voltage, Silicon nanowires, Surface charge sensitivity, Threshold shifts, Transistor structure
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-8218DOI: 10.1021/nl0709017ISI: 000249501900012ScopusID: 2-s2.0-34948846733OAI: diva2:13479
QC 20100716Available from: 2012-01-27 Created: 2008-04-09 Last updated: 2012-01-27Bibliographically approved
In thesis
1. Silicon Nanowires for Biomolecule Detection
Open this publication in new window or tab >>Silicon Nanowires for Biomolecule Detection
2008 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Starting from silicon on insulator (SOI) material, with a top silicon layer thickness of 100 nm, silicon nanowires were fabricated in a top down approach using electron beam (e-beam) lithography and subsequent eactive ion etching (RIE) and oxidation. Nanowires as narrow as 30 nm could be achieved. Further size reduction was done using electrochemical etching and/or oxidation. The nanowires were contacted creating drain, source and back gate contacts and characterized showing similar behavior as Schottky Barrier Metal Oxide Semiconductor Field Effect Transistors (SB-MOSFETs). As an alternative, by thinning the top silicon layer down nanoribbons, ~ 1 μm wide, with a thickness down to 45 nm could be produced using standard optical lithography showing similar behavior as the nanowires. The conduction mechanism for these devices is through electrons in an inversion current layer for positive back gate voltages and through holes in accumulation mode for negative back gate voltages. When the threshold voltage is extrapolated for the nanowires and the nanoribbons it scales with inverse width and thickness respectively, attributed to charged surface and/or interface states affecting more narrow/thinner devices essentially due to increased surface to volume ratio.

Nanowires were functionalized with 3-aminopropyl triethoxysilane (APTES) molecules creating amino groups on the surface reactive to pH buffer solutions. By exposing the nanowires to buffer solutions of different pH value the conduction mechanism changed due to the surface becoming more or less negative. Threshold voltage shifts from pH = 3 to pH = 9 were seen to scale with inverse width again attributed to the larger surface to volume ratio for more narrow devices. Simulations confirm this behavior and further show that a charge change of a few elementary charges on the nanowire surface can alter the conductance significantly. Upon addition of the buffer solutions the channel is seen to be quenched for small drain bias attributed to negative surface charges screening the electron current. However, as the drain bias is increased the channel is restored. Computer simulations confirmed this behavior and further showed that the restoration of the channel was due to an avalanche process.

A biomolecule detection experiment was set up using the specific binding of biotin to streptavidin. By functionalizing the nanoribbon with biotin molecules the current can be logged and as streptavidin molecules are added the current decreases (increases) if the nanoribbon is run in inversion (accumulation) mode due to the negative charge of the streptavidin molecule, delivered upon binding to biotin. A sensitivity significantly below the picomolar range was observed, corresponding to less than 20 streptavidin molecules attaching to the nanoribbon surface, assuming a homogeneous binding to the biotinylated surface. By decreasing the nanoribbon thickness the response was increased, a behavior attributed to the larger surface to volume ratio of these devices. The response was seen to be larger in the accumulation mode whereas close to the lower oxide in inversion mode. Computer simulations showed that this was due to the hole current running closer to the functionalized surface in accumulation mode and opposite in inversion mode. This was further investigated for different nanoribbon thicknesses and the response was shown to increase with inverse nanoribbon thickness again attributed to the larger surface to volume ratio.

The nanoribbon has the advantage of simpler fabrication using standard optical lithography in comparison with e-beam lithography and it may provide a useful scheme for a practical biomolecule sensor.

Place, publisher, year, edition, pages
Stockholm: KTH, 2008. xii, 63 p.
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:6
National Category
Other Engineering and Technologies not elsewhere specified
urn:nbn:se:kth:diva-4695 (URN)978-91-7178-902-0 (ISBN)
Public defence
2008-04-25, C2, Electrum 1, Isafjordsgatan 22, Kista, 10:15
QC 20100719Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-07-19Bibliographically approved

Open Access in DiVA

fulltext(234 kB)1382 downloads
File information
File name FULLTEXT01.pdfFile size 234 kBChecksum SHA-512
Type fulltextMimetype application/pdf

Other links

Publisher's full textScopusPublished version

Search in DiVA

By author/editor
Elfström, NiklasJuhasz, RobertSychugov, IlyaEngfeldt, TorunEriksson Karlström, AmelieLinnros, Jan
By organisation
Microelectronics and Applied Physics, MAPSchool of Biotechnology (BIO)
In the same journal
Nano letters (Print)
Engineering and Technology

Search outside of DiVA

GoogleGoogle Scholar
Total: 1382 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Altmetric score

Total: 127 hits
ReferencesLink to record
Permanent link

Direct link