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Graphene Implementation Study in Semiconductor Processing
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Solid State Electronics.
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Graphene, with its two-dimensional nature and unique properties, has for over a decade captured enormous interests in both industry and academia. This work tries to answer the question of what would happen to graphene when it is subjected to various processing conditions and how this would affect the graphene functionality. The focus is placed on its ability to withstand different thin-film deposition environments with regard to the implementation of graphene in two application areas: as a diffusion barrier and in electronic devices.

With single-layer graphene films grown in-house by means of chemical vapor deposition (CVD), four techniques among the well-established thin-film deposition methods are studied in detail: atomic layer deposition (ALD), evaporation, sputter-deposition and spray-deposition. And in this order, these methods span a large range of kinetic impact energies from low to high. Graphene is known to have a threshold displacement energy of 22 eV above which carbon atoms are ejected from the lattice. Thus, ALD and evaporation work with energies below this threshold, while sputtering and spraying may involve energies above. The quality of the graphene films undergone the various depositions is mainly evaluated using Raman spectroscopy.

Spray deposition of liquid alloy Ga-In-Sn is shown to require a stack of at least 4 layers of graphene in order to act as an effective barrier to the Ga diffusion after the harsh spray-processing. Sputter-deposition is found to benefit from low substrate temperature and high chamber pressure (thereby low kinetic impact energy) so as to avoid damaging the graphene. Reactive sputtering should be avoided. Evaporation is non-invasiveness with low kinetic impact energy and graphene can be subjected to repeated evaporation and removal steps without losing its integrity. With ALD, the effects on graphene are of different nature and they are investigated in the field-effect-transistor (FET) configuration. The ALD process for deposition of Al2O3 films is found to remove undesired dopants from the prior processing and the Al2O3 films are shown to protect the graphene channel from doping by oxygen. When the substrate is turned hydrophobic by chemical treatment prior to graphene transfer-deposition, a unipolar transistor behavior is obtained.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2016. , 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1377
National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering
Identifiers
URN: urn:nbn:se:uu:diva-285249ISBN: 978-91-554-9585-5 (print)OAI: oai:DiVA.org:uu-285249DiVA: diva2:921163
Public defence
2016-06-10, 13:15 (English)
Opponent
Supervisors
Available from: 2016-05-19 Created: 2016-04-19 Last updated: 2016-06-01
List of papers
1. A two-in-one process for reliable graphene transistors processed with photolithography
Open this publication in new window or tab >>A two-in-one process for reliable graphene transistors processed with photolithography
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2015 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 107, no 20, 203104Article in journal (Refereed) Published
Abstract [en]

Research on graphene field-effect transistors (GFETs) has mainly relied on devices fabricated using electron-beam lithography for pattern generation, a method that has known problems with polymer contaminants. GFETs fabricated via photo-lithography suffer even worse from other chemical contaminations, which may lead to strong unintentional doping of the graphene. In this letter, we report on a scalable fabrication process for reliable GFETs based on ordinary photo-lithography by eliminating the aforementioned issues. The key to making this GFET processing compatible with silicon technology lies in a two-in-one process where a gate dielectric is deposited by means of atomic layer deposition. During this deposition step, contaminants, likely unintentionally introduced during the graphene transfer and patterning, are effectively removed. The resulting GFETs exhibit current-voltage characteristics representative to that of intrinsic non-doped graphene. Fundamental aspects pertaining to the surface engineering employed in this work are investigated in the light of chemical analysis in combination with electrical characterization.

National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-269191 (URN)10.1063/1.4935985 (DOI)000365688700049 ()
Funder
Knut and Alice Wallenberg Foundation, 2011.0113, 2011.0082Swedish Foundation for Strategic Research , SE13-0061Swedish Research Council, 621-2014-5591
Available from: 2015-12-14 Created: 2015-12-14 Last updated: 2017-12-01Bibliographically approved
2. Unipolar Behavior in Interface Controlled Graphene Field Effect Transistor
Open this publication in new window or tab >>Unipolar Behavior in Interface Controlled Graphene Field Effect Transistor
(English)Article in journal (Refereed) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-284924 (URN)
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2016-06-01
3. Defect formation in graphene during low-energy ion bombardment
Open this publication in new window or tab >>Defect formation in graphene during low-energy ion bombardment
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2016 (English)In: APL Materials, ISSN 2166-532X, Vol. 4, no 4, 046104Article in journal, Letter (Refereed) Published
Abstract [en]

This letter reports on a systematic investigation of sputter induced damage in graphene caused by low energy Ar+ ion bombardment. The integral numbers of ions per area (dose) as well as their energies are varied in the range of a few eV's up to 200 eV. The defects in the graphene are correlated to the dose/energy and different mechanisms for the defect formation are presented. The energetic bombardment associated with the conventional sputter deposition process is typically in the investigated energy range. However, during sputter deposition on graphene, the energetic particle bombardment potentially disrupts the crystallinity and consequently deteriorates its properties. One purpose with the present study is therefore to demonstrate the limits and possibilities with sputter deposition of thin films on graphene and to identify energy levels necessary to obtain defect free graphene during the sputter deposition process. Another purpose is to disclose the fundamental mechanisms responsible for defect formation in graphene for the studied energy range.

National Category
Materials Chemistry Nano Technology
Identifiers
urn:nbn:se:uu:diva-284702 (URN)10.1063/1.4945587 (DOI)000375846100007 ()
Funder
Knut and Alice Wallenberg Foundation, 2011.0082Swedish Research Council, 2014-5591 2014-6463
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2017-01-25Bibliographically approved
4. Toward synthesis of oxide films on graphene with sputtering based processes
Open this publication in new window or tab >>Toward synthesis of oxide films on graphene with sputtering based processes
2016 (English)In: Journal of Vacuum Science and Technology B: Nanotechnology and Microelectronics, ISSN 2166-2746, E-ISSN 2166-2754Article in journal (Refereed) Submitted
National Category
Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-284706 (URN)
External cooperation:
Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2017-11-30
5. Graphene as a Diffusion Barrier in Galinstan-Solid Metal Contacts
Open this publication in new window or tab >>Graphene as a Diffusion Barrier in Galinstan-Solid Metal Contacts
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2014 (English)In: IEEE Transactions on Electron Devices, ISSN 0018-9383, E-ISSN 1557-9646, Vol. 61, no 8, 2996-3000 p.Article in journal (Refereed) Published
Abstract [en]

This paper presents the use of graphene as a diffusion barrier to a eutectic Ga-In-Sn alloy, i.e., galinstan, for electrical contacts in electronics. Galinstan is known to be incompatible with many conventional metals used for electrical contacts. When galinstan is in direct contact with Al thin films, Al is readily dissolved leading to the formation of Al oxides present on the surface of the galinstan droplets. This reaction is monitored ex situ using several material analysis methods as well as in situ using a simple circuit to follow the time-dependent resistance variation. In the presence of a multilayer graphene diffusion barrier, the Al-galinstan reaction is effectively prevented for galinstan deposited by means of drop casting. When deposited by spray coating, the high-impact momentum of the galinstan droplets causes damage to the multilayer graphene and the Al-galinstan reaction is observed at some defective spots. Nonetheless, the graphene barrier is likely to block the formation of Al oxides at the Al/galinstan interface leading to a stable electrical current in the test circuit.

National Category
Other Electrical Engineering, Electronic Engineering, Information Engineering Nano Technology
Research subject
Engineering Science with specialization in Electronics; Engineering Science with specialization in Microsystems Technology
Identifiers
urn:nbn:se:uu:diva-229503 (URN)10.1109/TED.2014.2331893 (DOI)000342906200056 ()
Available from: 2014-08-10 Created: 2014-08-10 Last updated: 2017-12-05Bibliographically approved
6. Scalable residue-free graphene for surface-enhanced Raman scattering
Open this publication in new window or tab >>Scalable residue-free graphene for surface-enhanced Raman scattering
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2016 (English)In: Carbon, ISSN 0008-6223, E-ISSN 1873-3891, Vol. 98, 567-571 p.Article in journal (Refereed) Published
Abstract [en]

A room-temperature polymer-assisted transfer process is developed for large-area, single-layer graphene grown by means of chemical vapor deposition (CVD). This process leads to transferred graphene layers free of polymer contamination. The absence of polymer residues boosts the surface-enhanced Raman scattering (SERS) of the CVD graphene with gold nanoparticles (Au NPs) deposited atop by evaporation. The SERS enhancement of the CVD graphene reaches similar to 120 for the characteristic 2D peak of graphene, the highest enhancement factor achieved to date, when the Au NPs are at the threshold of percolation. Our simulation supported by experiment suggests that the polymer residues persistently present on the graphene transferred by the conventional polymer-assisted method are equivalent to an ultrathin film of less than 1 nm thickness. The presence of polymer residues drastically reduces SERS due to the separation of the Au NPs from the underlying graphene. The scalability of CVD graphene opens up for the possibility of graphene-based SERS sensors.

National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-269192 (URN)10.1016/j.carbon.2015.11.043 (DOI)000367233000070 ()
Funder
Knut and Alice Wallenberg Foundation, 2011.0113Knut and Alice Wallenberg Foundation, 2011.0082Swedish Foundation for Strategic Research , SE13-0061Swedish Research Council, 621-2014-5591
Available from: 2015-12-14 Created: 2015-12-14 Last updated: 2017-12-01Bibliographically approved

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