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Silicon Nanowires for Biomolecule Detection
KTH, School of Information and Communication Technology (ICT), Material Physics.
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.
Series
Trita-ICT/MAP AVH, ISSN 1653-7610 ; 2008:6
National Category
Other Engineering and Technologies not elsewhere specified
Identifiers
URN: urn:nbn:se:kth:diva-4695ISBN: 978-91-7178-902-0 (print)OAI: oai:DiVA.org:kth-4695DiVA: diva2:13484
Public defence
2008-04-25, C2, Electrum 1, Isafjordsgatan 22, Kista, 10:15
Opponent
Supervisors
Note
QC 20100719Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-07-19Bibliographically approved
List of papers
1. Controlled Fabrication of Silicon Nanowires by Electron Beam Lithography and Electrochemical Size Reduction
Open this publication in new window or tab >>Controlled Fabrication of Silicon Nanowires by Electron Beam Lithography and Electrochemical Size Reduction
2005 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 5, no 2, 275-280 p.Article in journal (Refereed) Published
Abstract [en]

We demonstrate that electrochemical size reduction can be used for precisely controlled fabrication of silicon nanowires of widths approaching the 10 nm regime. The scheme can, in principle, be applied to wires defined by optical lithography but is here demonstrated for wires of similar to100-200 nm width, defined by electron beam lithography. As for electrochemical etching of bulk silicon, the etching can be tuned both to the pore formation regime as well as to electropolishing. By in-situ optical and electrical characterization, the process can be halted at a certain nanowire width. Further electrical characterization shows a conductance decreasing faster than dimensional scaling would predict. As an explanation, we propose that charged surface states play a more pronounced role as the nanowire cross-sectional dimensions decrease.

Keyword
Electric conductivity; Electrochemistry; Electrolytic polishing; Electron beam lithography; Etching; Morphology; Photolithography; Silicon; Charged surface states; Electrochemical etching; Electrochemical size reduction; Silicon nanowires
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-6476 (URN)10.1021/nl0481573 (DOI)000227100500015 ()2-s2.0-14644409706 (Scopus ID)
Note
QC 20100719Available from: 2005-09-15 Created: 2005-09-15 Last updated: 2010-07-19Bibliographically approved
2. Surface Charge Sensitivity of Silicon Nanowires: Size Dependence
Open this publication in new window or tab >>Surface Charge Sensitivity of Silicon Nanowires: Size Dependence
Show others...
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
Keyword
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
Identifiers
urn:nbn:se:kth:diva-8218 (URN)10.1021/nl0709017 (DOI)000249501900012 ()2-s2.0-34948846733 (Scopus ID)
Note
QC 20100716Available from: 2012-01-27 Created: 2008-04-09 Last updated: 2012-01-27Bibliographically approved
3. Avalanche breakdown in surface modified silicon nanowires
Open this publication in new window or tab >>Avalanche breakdown in surface modified silicon nanowires
2007 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 91, no 10, 103502-1-103502-3 p.Article in journal (Refereed) Published
Abstract [en]

The electrical conductance of semiconductor nanowires can be changed by charges present on the nanowire surface. At high surface charge density, however, the nanowire channel may be quenched leading to a large shift in the I-DS-V-DS characteristics. In this letter, the authors demonstrate that this shift in V-DS is related to an avalanche effect in the nanowire. Silicon nanowires were fabricated in a top-down approach and the nanowire surface charge density was modified through buffer solutions of different pH values. Computer simulations using representative surface charge and interface charge densities clearly reproduce the data and unambiguously demonstrate the avalanche effect.

Keyword
Charge density; Computer simulation; Electric conductance; Semiconducting silicon; Surface charge; Surface treatment; Avalanche breakdown; Avalanche effect; Nanowire channels
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8219 (URN)10.1063/1.2779110 (DOI)000249322900073 ()2-s2.0-34548502168 (Scopus ID)
Note
QC 20100716Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-07-16Bibliographically approved
4. Sensitivity of silicon nanowires in biosensor applications
Open this publication in new window or tab >>Sensitivity of silicon nanowires in biosensor applications
2008 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 100, no PART 5Article in journal (Refereed) Published
Abstract [en]

A 2-dimensional simulation tool was designed to investigate the threshold voltage behaviour for a silicon nanowire constructed in a top down approach on silicon on insulator (SOI) material. The simulation shows, assuming a positive charge of +1.10(11) cm(-2) between the silicon/silicon dioxide interface and negatively charged surface states on top of the nanowire that the threshold voltage increases with decreasing height of the nanowire.

Keyword
FABRICATION; SENSOR
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8220 (URN)10.1088/1742-6596/100/5/052042 (DOI)000275655200138 ()2-s2.0-70450257364 (Scopus ID)
Note
QC 20100719. Uppdaterad från in press till published (20100719).Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2011-03-04Bibliographically approved
5. Silicon Nanoribbons for Electrical Detection of Biomolecules
Open this publication in new window or tab >>Silicon Nanoribbons for Electrical Detection of Biomolecules
2008 (English)In: Nano letters (Print), ISSN 1530-6984, E-ISSN 1530-6992, Vol. 8, no 3, 945-949 p.Article in journal (Refereed) Published
Abstract [en]

Direct electrical detection of biomolecules at high sensitivity hat recently been demonstrated using semiconductor nanowires. Here we demonstrate that semiconductor nanoribbons, in this case, a thin sheet of silicon on an oxidized silicon substrate, can approach the same sensitivity extending below the picomolar concentration regime in the biotin/streptavidin case. This corresponds to less than similar to 20 analyte molecules bound to receptors on the nanoribbon surface. The micrometer-size lateral dimensions of the nanoribbon enable optical lithography to be used, resulting in a simple and high-yield fabrication process. Electrical characterization of the nanoribbons is complemented by computer simulations showing enhanced sensitivity for thin ribbons. Finally, we demonstrate that the device can be operated both in inversion as well as in accumulation mode and the measured differences in detection sensitivity are explained in terms of the distance between the channel and the receptor coated surface with respect to the Debye screening length. The nanoribbon approach opens up for large scale CMOS fabrication of highly sensitive biomolecule sensor chips for potential use in medicine and biotechnology.

Keyword
Biomolecules; Electric conductivity; Electric wire; Photolithography; Semiconducting silicon; Semiconductor materials; Thickness measurement; Accumulation modes; Analyte molecules; CMOS fabrications; Coated surfaces; Debye screening lengths; Detection sensitivities; Electrical characterizations; Electrical detections; Enhanced sensitivities; Fabrication process; High sensitivities; Highly sensitives; Lateral dimensions; Nanoribbon; Nanoribbons; Optical lithographies; Oxidized silicon substrates; Semiconductor nanoribbons; Semiconductor nanowires; Sensor chips; Thin ribbons; Thin sheets
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-8221 (URN)10.1021/nl080094r (DOI)000253947400033 ()2-s2.0-43149112560 (Scopus ID)
Note
QC 20100716Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-07-19Bibliographically approved
6. Biomolecule detection using a silicon nanoribbon: Accumulation mode versus inversion mode
Open this publication in new window or tab >>Biomolecule detection using a silicon nanoribbon: Accumulation mode versus inversion mode
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.

Keyword
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
Identifiers
urn:nbn:se:kth:diva-8222 (URN)10.1088/0957-4484/19/23/235201 (DOI)000255662700006 ()2-s2.0-44949218379 (Scopus ID)
Note
QC 20100719. Uppdaterad från manuskript till artikel (20100719).Available from: 2008-04-09 Created: 2008-04-09 Last updated: 2010-07-19Bibliographically approved

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CiteExportLink to record
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Citation style
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  • modern-language-association-8th-edition
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