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Silicon Nanowire Field-Effect Devices as Low-Noise Sensors
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In the past decades, silicon nanowire field-effect transistors (SiNWFETs) have been explored for label-free, highly sensitive, and real-time detections of chemical and biological species. The SiNWFETs are anticipated for sensing analyte at ultralow concentrations, even at single-molecule level, owing to their significantly improved charge sensitivity over large-area FETs. In a SiNWFET sensor, a change in electrical potential associated with biomolecular interactions in close proximity to the SiNW gate terminal can effectively control the underlying channel and modulate the drain-to-source current (IDS) of the SiNWFET. A readout signal is therefore generated. This signal is primarily determined by the surface properties of the sensing layer on the gate terminal, with sensitivity close up to the Nernstian limit widely demonstrated. To achieve a high signal-to-noise ratio (SNR), it is essential for the SiNWFETs to possess low noise of which intrinsic device noise is one of the major components. In metal-oxide-semiconductor (MOS)-type FETs, the intrinsic noise mainly results from carrier trapping/detrapping at the gate oxide/semiconductor interface and it is inversely proportional to the device area.

This thesis presents a comprehensive study on design, fabrication, and noise reduction of SiNWFET-based sensors on silicon-on-oxide (SOI) substrate. A novel Schottky junction gated SiNWFET (SJGFET) is designed and experimentally demonstrated for low noise applications. Firstly, a robust process employing photo- and electron-beam mixed-lithography was developed to reliably produce sub-10 nm SiNW structures for SiNWFET fabrication. For a proof-of-concept demonstration, MOS-type SiNWFET sensors were fabricated and applied for multiplexed ion detection using ionophore-doped mixed-matrix membranes as sensing layers. To address the fundamental noise issue of the MOS-type SiNWFETs, SJGFETs were fabricated with a Schottky (PtSi/silicon) junction gate on the top surface of the SiNW channel, replacing the noisy gate oxide/silicon interface in the MOS-type SiNWFETs. The resultant SJGFETs exhibited a close-to-ideal gate coupling efficiency (60 mV/dec) and significantly reduced device noise compared to reference MOS-type SiNWFETs. Further optimization was performed by implementing a three-dimensional Schottky junction gate wrapping both top surface and two sidewalls of the SiNW channel. The tri-gate SJGFETs with optimized geometry exhibited significantly enhanced electrostatic control over the channel, thereby confined IDS in the SiNW bulk, which greatly improved the device noise immunity to the traps at bottom buried oxide/silicon interface. Finally, a lateral bipolar junction transistor (LBJT) was also designed and fabricated on a SOI substrate aiming for immediate sensor current amplification. Integrating SJGFETs with LBJTs is expected to significantly suppress environmental interference and improve the overall SNR especially under low sensor current situations.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 69
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1794
Keywords [en]
Silicon nanowire, field-effect transistor, Schottky junction gate, low frequency noise, ion sensor
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
URN: urn:nbn:se:uu:diva-381049ISBN: 978-91-513-0625-4 (print)OAI: oai:DiVA.org:uu-381049DiVA, id: diva2:1302191
Public defence
2019-05-27, Polhemsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Available from: 2019-05-02 Created: 2019-04-03 Last updated: 2019-06-17
List of papers
1. Aged hydrogen silsesquioxane for sub-10 nm line patterns
Open this publication in new window or tab >>Aged hydrogen silsesquioxane for sub-10 nm line patterns
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2016 (English)In: Microelectronic Engineering, ISSN 0167-9317, E-ISSN 1873-5568, Vol. 163, p. 105-109Article in journal (Refereed) Published
Abstract [en]

Hydrogen silsesquioxane (HSQ) has been used as a negative tone resist in electron beam lithography to define sub-10 nm patterns. The spontaneous polymerization in HSQ usually called aging in this context, sets a restricted period of time for a vendor-warranted use in patterning such small features with satisfactory line-edge roughness (LER). Here, we study the effect of HSQ aging on sensitivity and LER by focusing on exposing line patterns of 10 nm width in various structures. The results show that the 10 nm lines are easily achievable and the LER of the patterned lines remains unaltered even with HSQ that is stored 10 months beyond the vendor-specified expiration date. However, an increasingly pronounced decrease with time of the threshold electron dose (D-th), below which the line width would become less than 10 nm, is observed. After the HSQ expiration for 10 months, the 10 nm lines can be manufactured by reducing D-th to a level that is technically manageable with safe margins. In addition, the inclusion of a prebaldng step at 220 degrees C to accelerate the aging process results in a further reduced D-th for the 10 nm lines and thereby leads to a shortened writing time. The time variation of D-th with respect to the vendor-specified production date of HSQ is found to follow an exponential function of time and can be associated to the classical nucleation-growth polymerization process in HSQ.

Keywords
Electron beam lithography (EBL); Hydrogen silsesquioxane (HSQ); 10 nm wide resist lines; Aging effect; Line edge roughness (LER); Prebaking
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-300188 (URN)10.1016/j.mee.2016.06.011 (DOI)000381837300015 ()
Funder
Swedish Foundation for Strategic Research , ICA 12-0047 SE13-0033Swedish Research Council, 2014-5588 2014-5591Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, GG 1459BCarl Tryggers foundation , CTS14-527
Available from: 2016-08-04 Created: 2016-08-04 Last updated: 2019-04-03Bibliographically approved
2. Multiplexed analysis of molecular and elemental ions using nanowire transistor sensors
Open this publication in new window or tab >>Multiplexed analysis of molecular and elemental ions using nanowire transistor sensors
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2018 (English)In: Sensors and actuators. B, Chemical, ISSN 0925-4005, E-ISSN 1873-3077, Vol. 270, p. 89-96Article in journal (Refereed) Published
Abstract [en]

An integrated sensor chip with silicon nanowire ion-sensitive field-effect transistors for simultaneous and selective detection of both molecular and elemental ions in a single sample solution is demonstrated. The sensing selectivity is realized by functionalizing the sensor surface with tailor-made mixed-matrix membranes (MMM) incorporated with specific ionophores for the target ions. A biomimetic container molecule, named metal-organic supercontainer (MOSC), is selected as the ionophore for detection of methylene blue (MB+), a molecular ion, while a commercially available Na-ionophore is used for Na+, an elemental ion. The sensors show a near-Nernstian response with 56.4 ± 1.8 mV/dec down to a concentration limit of ∌1 ΌM for MB+ and 57.9 ± 0.7 mV/dec down to ∌60 ΌM for Na+, both with excellent reproducibility. Extensive control experiments on the MB+ sensor lead to identification of the critical role of the MOSC molecules in achieving a stable and reproducible potentiometric response. Moreover, the MB+-specific sensor shows remarkable selectivity against common interfering elemental ions in physiological samples, e.g., H+, Na+, and K+. Although the Na+-specific sensor is currently characterized by insufficient immunity to the interference by MB+, the root cause is identified and remedies generally applicable for hydrophobic molecular ions are discussed. River water experiments are also conducted to prove the efficacy of our sensors.

Keywords
Elemental ion, ISFET, Metal-organic supercontainer, Molecular ion, Multiplex detection, Silicon nanowire FET
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-351716 (URN)10.1016/j.snb.2018.05.018 (DOI)000434011500011 ()
Funder
Swedish Foundation for Strategic Research , SSF ICA 12-0047;FFL15-0174Swedish Research Council, VR 2014-5588Göran Gustafsson Foundation for promotion of scientific research at Uppala University and Royal Institute of Technology, GG 1459BCarl Tryggers foundation , CTS14-527
Note

Xi Chen and Qitao Hu contributed equally to this work

Available from: 2018-05-29 Created: 2018-05-29 Last updated: 2019-04-03Bibliographically approved
3. Device noise reduction for Silicon nanowire field-effect-transistor based sensors by using a Schottky junction gate
Open this publication in new window or tab >>Device noise reduction for Silicon nanowire field-effect-transistor based sensors by using a Schottky junction gate
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2019 (English)In: ACS sensors, ISSN 2379-3694, Vol. 4, no 2, p. 427-433Article in journal (Refereed) Published
Abstract [en]

The sensitivity of metal-oxide-semiconductor field-effect transistor (MOSFET) based nanoscale sensors is ultimately limited by noise induced by carrier trapping/detrapping processes at the gate oxide/semiconductor interfaces. We have designed a Schottky junction gated silicon nanowire field-effect transistor (SiNW-SJGFET) sensor, where the Schottky junction replaces the noisy oxide/semiconductor interface. Our sensor exhibits significantly reduced noise, 2.1×10-9 V2µm2/Hz at 1 Hz, compared to reference devices with the oxide/semiconductor interface operated at both inversion and depletion modes. Further improvement can be anticipated by wrapping the nanowire by such a Schottky junction thereby eliminating all oxide/semiconductor interfaces. Hence, a combination of the low-noise SiNW-SJGFET sensor device with a sensing surface of the Nernstian response limit holds promises for future high signal-to-noise ratio sensor applications.

Keywords
Noise reduction, schottky junction gate, silicon nanowire, field-effect transistor, low frequency noise, ion sensor
National Category
Nano Technology Signal Processing
Identifiers
urn:nbn:se:uu:diva-374776 (URN)10.1021/acssensors.8b0139 (DOI)000459836400021 ()30632733 (PubMedID)
Funder
Swedish Foundation for Strategic Research , SSF ICA 12-0047Swedish Foundation for Strategic Research , FFL15-0174Swedish Research Council, VR 2014-5588Knut and Alice Wallenberg Foundation
Available from: 2019-01-24 Created: 2019-01-24 Last updated: 2019-04-03Bibliographically approved
4. Low-Noise Schottky Junction Trigate Silicon Nanowire Field-effect Transistor for Charge Sensing
Open this publication in new window or tab >>Low-Noise Schottky Junction Trigate Silicon Nanowire Field-effect Transistor for Charge Sensing
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2019 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 66, no 9, p. 3994-4000Article in journal (Refereed) Published
Abstract [en]

Silicon nanowire (SiNW) field-effect transistors (SiNWFETs) are of great potential as a high-sensitivity charge sensor. The signal-to-noise ratio (SNR) of an SiNWFET sensor is ultimately limited by the intrinsic device noise generated by carrier trapping/detrapping processes at the gate oxide/silicon interface. This carrier trapping/detrapping-induced noise can be significantly reduced by replacing the noisy oxide/silicon interface with a Schottky junction gate (SJG) on the top of the SiNW. In this paper, we present a tri-SJG SiNWFET (Tri-SJGFET) with the SJG formed on both the top surface and the two sidewalls of the SiNW so as to enhance the gate control over the SiNW channel. Both experiment and simulation confirm that the additional sidewall gates in a narrow Tri-SJGFET indeed can confine the conduction path within the bulk of the SiNW channel away from the interfaces and significantly improve the immunity to the traps at the bottom buried oxide/silicon interface. Therefore, the optimal low-frequency noise performance can be achieved without the need for any substrate bias. This new gating structure holds promises for further development of robust SiNWFET-based charge sensors with low noise and low operation voltage.

Keywords
Silicon nanowire field-effect transistor, Schottky junction, trigate, sensor, low-frequency noise, charge sensing
National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-380971 (URN)10.1109/TED.2019.2930067 (DOI)000482583200046 ()
Funder
Swedish Foundation for Strategic Research , SSF FFL15-0174Swedish Research Council, VR 2014-5588Knut and Alice Wallenberg Foundation
Note

Title in thesis list of papers: Low Noise Schottky Junction Tri-gate Silicon Nanowire Field-effect Transistor for Charge Sensing

Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-10-23Bibliographically approved
5. Top-bottom gate coupling effect on low frequency noise in a Schottky junction gated silicon nanowire field-effect transistor
Open this publication in new window or tab >>Top-bottom gate coupling effect on low frequency noise in a Schottky junction gated silicon nanowire field-effect transistor
2019 (English)In: IEEE Journal of the Electron Devices Society, ISSN 2168-6734, Vol. 7, p. 696-700Article in journal (Refereed) Published
Abstract [en]

In this letter, strong low frequency noise (LFN) reduction is observed when the buried oxide (BOX)/silicon interface of a Schottky junction gated silicon nanowire field-effect transistor (SJGFET) is depleted by a substrate bias. Such LFN reduction is mainly attributed to the dramatic reduction in Coulomb scattering when carriers are pushed away from the interface. The BOX/silicon interface depletion can also be achieved by sidewall Schottky junction gates in a narrow channel SJGFET, leading to an optimal LFN performance without the need of any substrate bias.

National Category
Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Engineering Science with specialization in Electronics
Identifiers
urn:nbn:se:uu:diva-380974 (URN)10.1109/JEDS.2019.2929163 (DOI)000478945400003 ()
Funder
Swedish Research Council, VR 2014-5588Swedish Foundation for Strategic Research , FFL15-0174
Available from: 2019-04-02 Created: 2019-04-02 Last updated: 2019-09-26Bibliographically approved
6. Current gain and low-frequency noise of symmetriclateral bipolar junction transistors on SOI
Open this publication in new window or tab >>Current gain and low-frequency noise of symmetriclateral bipolar junction transistors on SOI
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2018 (English)Conference paper, Published paper (Refereed)
Abstract [en]

This paper presents a comprehensive study ofsymmetric lateral bipolar junction transistors (LBJTs) fabricatedon SOI substrate using a CMOS-compatible process; LBJTs findmany applications including being a local signal amplifier forsilicon-nanowire sensors. Our LBJTs are characterized by a peakgain (β) over 50 and low-frequency noise two orders ofmagnitude lower than what typically is of the SiO2/Si interfacefor a MOSFET. β is found to decrease at low base current due torecombination in the space charge region at the emitter-basejunction and at the surrounding SiO2/Si interfaces. This decreasecan be mitigated by properly biasing the substrate.

Keywords
symmetric lateral bipolar junction transitor; current amplification; low frequency noise; silicon nanowire field-effect transitor
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
urn:nbn:se:uu:diva-364155 (URN)
Conference
48th European Solid-State Device Research Conference, September 3 - 6, 2018, Dresden, Germany
Note

Qitao Hu and Xi Chen contribute equally to the work.

Available from: 2018-10-24 Created: 2018-10-24 Last updated: 2019-04-03Bibliographically approved

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