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Influence of Humidity on Contact Resistance in Graphene Devices
KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.ORCID iD: 0000-0003-3936-818X
KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.ORCID iD: 0000-0003-4637-8001
KTH, School of Engineering Sciences (SCI), Applied Physics.ORCID iD: 0000-0002-8222-3157
KTH, School of Electrical Engineering and Computer Science (EECS), Micro and Nanosystems.ORCID iD: 0000-0002-8811-1615
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2018 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 10, no 48, p. 41738-41746Article in journal (Refereed) Published
Abstract [en]

The electrical contact resistance at metal–graphene interfaces can significantly degrade the properties of graphene devices and is currently hindering the full exploitation of graphene’s potential. Therefore, the influence of environmental factors, such as humidity, on the metal–graphene contact resistance is of interest for all graphene devices that operate without hermetic packaging. We experimentally studied the influence of humidity on bottom-contacted chemical-vapor-deposited (CVD) graphene–gold contacts, by extracting the contact resistance from transmission line model (TLM) test structures. Our results indicate that the contact resistance is not significantly affected by changes in relative humidity (RH). This behavior is in contrast to the measured humidity sensitivity  of graphene’s sheet resistance. In addition, we employ density functional theory (DFT) simulations to support our experimental observations. Our DFT simulation results demonstrate that the electronic structure of the graphene sheet on top of silica is much more sensitive to adsorbed water molecules than the charge density at the interface between gold and graphene. Thus, we predict no degradation of device performance by alterations in contact resistance when such contacts are exposed to humidity. This knowledge underlines that bottom-contacting of graphene is a viable approach for a variety of graphene devices and the back end of the line integration on top of conventional integrated circuits.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2018. Vol. 10, no 48, p. 41738-41746
Keywords [en]
graphene, bottom-contact, contact resistance, humidity sensitivity, integration, sheet resistance
National Category
Nano Technology Other Electrical Engineering, Electronic Engineering, Information Engineering
Research subject
Electrical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-232554DOI: 10.1021/acsami.8b10033ISI: 000452694100088PubMedID: 30387599Scopus ID: 2-s2.0-85057551886OAI: oai:DiVA.org:kth-232554DiVA, id: diva2:1235479
Funder
VINNOVA, 2016-01655 2017-05108Swedish Research Council, VR 2015-04608 VR 2016-05980Swedish Energy Agency, STEM P40147-1 STEM P40147-1EU, European Research Council, 277879 307311
Note

QC 20181207

Available from: 2018-07-25 Created: 2018-07-25 Last updated: 2019-01-08Bibliographically approved
In thesis
1. Integration of graphene into MEMS and NEMS for sensing applications
Open this publication in new window or tab >>Integration of graphene into MEMS and NEMS for sensing applications
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a novel approach to integrate chemical vapor deposition (CVD) graphene into silicon micro- and nanoelectromechanical systems (MEMS/NEMS) to fabricate different graphene based MEMS/NEMS structures and explore mechanical properties of graphene as well as their applications such as acceleration sensing, humidity sensing and CO2 sensing. The thesis also presents a novel method of characterization of CVD graphene grain boundary based defects.

    The first section of this thesis presents a robust, scalable, flexible route to integrate double-layer graphene membranes to a silicon substrate so that large silicon masses are suspended by graphene membranes.

    In the second section, doubly-clamped suspended graphene beams with attached silicon masses are fabricated and used as model systems for studying the mechanical properties of graphene and transducer elements for NEMS resonators and extremely small accelerometers, occupying die areas that are at least two orders of magnitude smaller than the die areas occupied by the most compact state-of-the-art silicon accelerometers. An averaged Young’s modulus of double-layer graphene of ~0.22 TPa and non-negligible built-in stresses of the order of 200-400 MPa in the suspended graphene beams are extracted, using analytical and FEA models. In addition, fully clamped suspended graphene membranes with attached proof masses are also realized, which are used for acceleration sensing.

In the third section, CO2 sensing of single-layer graphene and the cross-sensitivity between CO2 and humidity are shown. The cross-sensitivity of CO2 is negligible at typical CO2 concentrations present in air. The properties of double-layer graphene when exposed to humidity and CO2 have been characterized, with similarly fast response and recovery behaviour but weak resistance responses, compared to single layer graphene.

In the fourth section, a fast and simple method for large-area visualization of grain boundaries in CVD graphene transferred to a SiO2 surface is demonstrated. The method only requires vapor hydrofluoric acid (VHF)-etching and optical microscope inspection and therefore could be useful to speed up the process of developing large-scale high quality graphene synthesis, and can also be used for analysis of the influence of grain boundaries on the properties of emerging graphene devices that utilize CVD graphene patches placed on a SiO2 substrate.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 87
Series
TRITA-EECS-AVL ; 2018:43
Keywords
Micro-electromechanical systems (MEMS), Nano-electromechanical systems (NEMS), heterogeneous 3D integration, Graphene, single-layer graphene, double-layer graphene, bilayer graphene, chemical vapor deposition (CVD), suspended graphene beams, suspended graphene membranes, doubly clamped, fully clamped, silicon on insulator (SOI), vapor hydrofluoric acid (VHF), Young’s modulus, built-in stress, built-in tension, piezoresistivity, gauge factor, accelerometer, resonators, electromechanical sensing, advanced transducers, humidity, gas sensing, sensitivity, CO2 sensing, graphene grain boundary, line defects, optical microscopy, wire bonding
National Category
Nano Technology Engineering and Technology
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-232557 (URN)978-91-7729-803-8 (ISBN)
Public defence
2018-08-24, Sal F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20180726

Available from: 2018-07-26 Created: 2018-07-25 Last updated: 2018-07-26Bibliographically approved

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Smith, Anderson DavidElgammal, KarimDelin, AnnaÖstling, MikaelLemme, Max C.Gylfason, KristinnNiklaus, Frank

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