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Effect of microwave-assisted silanization on sensing properties of silicon nanoribbon FETs
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.ORCID iD: 0000-0002-1002-6699
KTH, School of Biotechnology (BIO), Protein Technology.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
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2015 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, Vol. 209, 586-595 p.Article in journal (Refereed) Published
Abstract [en]

An important concern with using silicon nanoribbon field-effect transistors (SiNR FET) for ion-sensing is the pH-response of the gate oxide surface. Depending on the application of the FET sensor, this response has to be chemically manipulated. Thus in silicon oxide-gated pH-sensors with integrated sensor and reference FETS, a surface with high pH-sensitivity, compared to the bare gate oxide, is required in the sensor FETs (SEFET), whereas in the reference FETs (REFET) the surface has to be relatively pH-insensitive. In order to control the sensitivity and chemistry of the oxide surface of the nanoribbons, a silanization reagent with a functional group is often self-assembled on the SiNR surface. Choice of a silanization reaction that results in a self-assembled layer on a silicon oxide surface has been studied extensively over the past decades. However, the effect of various self-assembled layers such as monolayers or mixed layers on the electrical response of SiNR FETs in aqueous solution needs to be exploited further, especially for future integrated SEFET/REFET systems. In this work, we have performed a comprehensive study on 3-aminopropyltriethoxysilane (APTES) silanization of silicon oxide surfaces using microwave (MW) heating as a new biocompatible route to conventional methods. A set of complementary surface characterization techniques (ellipsometry, AFM and ATR-FTIR) was used to analyze the properties of the APTES layer deposited on the silicon surface. We have found that a uniform monolayer can be achieved within 10 min by heating the silanization solution to 75 degrees C using MW heating. Furthermore, electrical measurements suggest that little change in device performance is observed after exposure to MW irradiation. Real-time pH measurements indicate that a uniform APTES monolayer not only reduces the pH sensitivity of SiNR FET by passivating the surface silanol groups, but also makes the device less sensitive to cation concentration in the background electrolyte. Our silanization route proves promising for future chemical surface modification of on-chip REFETs.

Place, publisher, year, edition, pages
2015. Vol. 209, 586-595 p.
Keyword [en]
Silicon nanoribbon field-effect transistors, Microwave heating, Silanization, Surface characterization, Electrical measurements, pH sensitivity
National Category
Materials Chemistry
URN: urn:nbn:se:kth:diva-161089DOI: 10.1016/j.snb.2014.12.030ISI: 000349082200077ScopusID: 2-s2.0-84919754424OAI: diva2:796167
VINNOVAKnut and Alice Wallenberg Foundation

QC 20150318

Available from: 2015-03-18 Created: 2015-03-09 Last updated: 2016-08-25Bibliographically approved
In thesis
1. Silicon Nanoribbon FET Sensors: Fabrication, Surface Modification and Microfluidic Integration
Open this publication in new window or tab >>Silicon Nanoribbon FET Sensors: Fabrication, Surface Modification and Microfluidic Integration
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Over the past decade, the field of medical diagnostics has seen an incredible amount of research towards the integration of one-dimensional nanostructures such as carbon nanotubes, metallic and semiconducting nanowires and nanoribbons for a variety of bio-applications. Among the mentioned one-dimensional structures, silicon nanoribbon (SiNR) field-effect transistors (FET) as electro-chemical nanosensors hold particular promise for label-free, real-time and sensitive detection of biomolecules using affinity-based detection. In SiNR FET sensors, electrical transport is primarily along the nanoribbon axis in a thin sheet (< 30 nm) serving as the channel. High sensitivity is achieved because of the large surface-to-volume ratio which allows analytes to bind anywhere along the NR affecting the entire conductivity by their surface charge. Unfortunately, sensitivity without selectivity is still an ongoing issue and this thesis aims at addressing the detection challenges and further proposing effective developments, such as parallel and multiple detection through using individually functionalized SiNRs.We present here a comprehensive study on design, fabrication, operation and device performance parameters for the next generation of SiNR FET sensors towards multiplexed, label-free detection of biomolecules using an on-chip microfluidic layer which is based on a highly cross-linked epoxy. We first study the sensitivity of different NR dimensions followed by analysis of the drift and hysteresis effects. We have also addressed two types of gate oxides (namely SiO2 and Al2O3) which are commonly used in standard CMOS fabrication of ISFETs (Ion sensitive FET). Not only have we studied and compared the hysteresis and response-time effects in the mentioned two types of oxides but we have also suggested a new integrated on-chip reference nanoribbon/microfluidics combination to monitor the long-term drift in the SiNR FET nanosensors. Our results show that compared to Al2O3, silicon-oxide gated SiNR FET sensors show high hysteresis and slow-response which limit their performance only to background electrolytes with low ionic strength. Al2O3 on the other hand proves more promising as the gate-oxide of choice for use in nanosensors. We have also illustrated that the new integrated sensor NR/Reference NR can be utilized for real-time monitoring of the above studied sources of error during pH-sensing. Furthermore, we have introduced a new surface silanization (using 3-aminopropyltriethoxysilane) method utilizing microwave-assisted heating which compared to conventional heating, yields an amino-terminated monolayer with high surface coverage on the oxide surface of the nanoribbons. A highly uniform and dense monolayer not only reduces the pH sensitivity of the bare-silicon oxide surface in a physiological media but also allows for more receptors to be immobilized on the surface. Protocols for surface functionalization and biomolecule immobilization were evaluated using model systems. Selective spotting of receptor molecules can be used to achieve localized functionalization of individual SiNRs, opening up opportunities for multiplexed detection of analytes.Additionally, we present here a novel approach by integrating droplet-based microfluidics with the SiNR FET sensors. Using the new system we are able to successfully detect trains of droplets with various pH values. The integrated system enables a wide range of label-free biochemical and macromolecule sensing applications based on detection of biological events such as enzyme-substrate interactions within the droplets.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. 82 p.
TRITA-ICT, 2016:22
National Category
Nano Technology
Research subject
Information and Communication Technology
urn:nbn:se:kth:diva-191178 (URN)978-91-7729-075-9 (ISBN)
Public defence
2016-09-29, Sal A, Electrum, Kungl Tekniska högskolan, Kistagången 16, Kista, 10:00 (English)
Knut and Alice Wallenberg Foundation

QC 20160825

Available from: 2016-08-25 Created: 2016-08-25 Last updated: 2016-09-19Bibliographically approved

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