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Biomolecule detection using a silicon nanoribbon: Accumulation mode versus inversion mode
KTH, School of Information and Communication Technology (ICT), Material Physics.
KTH, School of Information and Communication Technology (ICT), Material Physics.ORCID iD: 0000-0002-5260-5322
2008 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 19, no 23, 235201- p.Article in journal (Refereed) Published
Abstract [en]

Silicon nanoribbons were fabricated using standard optical lithography from silicon on insulator material with top silicon layer thicknesses of 100, 60 and 45 nm. Electrically these work as Schottky-barrier field-effect transistors and, depending on the substrate voltage, electron or hole injection is possible. The current through the nanoribbon is extremely sensitive to charge changes at the oxidized top surface and can be used for biomolecule detection in a liquid. We show that for detection of streptavidin molecules the response is larger in the accumulation mode than in the inversion mode, although not leading to higher detection sensitivity due to increased noise. The effect is attributed to the location in depth of the conducting channel, which for holes is closer to the screened surface charges of the biomolecules. Furthermore, the response increases for decreasing silicon thickness in both the accumulation mode and the inversion mode. The results are verified qualitatively and quantitatively through a two-dimensional simulation model on a cross section along the nanoribbon device.

Place, publisher, year, edition, pages
2008. Vol. 19, no 23, 235201- p.
Keyword [en]
Biomolecules; Fees and charges; Finance; Molecular biology; Molecules; Nonmetals; Photoacoustic effect; Photolithography; Silicon; Spurious signal noise; Standards; Surface charge; Surfaces; Transistors; Two dimensional; (1 1 0) surface; (100) silicon; Accumulation modes; Biomolecule detection; Conducting channels; cross sectioning; detection sensitivity; Field effect transistor (FET); hole injections; Inversion modes; Nanoribbon; nanoribbons; Optical lithography; Schottky; Silicon layers; Silicon thickness; Silicon-on insulator materials; Streptavidin (SA); Substrate voltage; top surface; Two-dimensional simulations
National Category
Engineering and Technology
URN: urn:nbn:se:kth:diva-8222DOI: 10.1088/0957-4484/19/23/235201ISI: 000255662700006ScopusID: 2-s2.0-44949218379OAI: diva2:13483
QC 20100719. Uppdaterad från manuskript till artikel (20100719).Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-07-19Bibliographically 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

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