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Sato T, Iwase E. High-Accuracy Contact Resistance Measurement Method for Liquid Metal by Considering Current-Density Distribution in Transfer Length Method Measurement. ACS Appl Mater Interfaces 2023; 15:44404-44412. [PMID: 37695862 PMCID: PMC10521730 DOI: 10.1021/acsami.3c05070] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/11/2023] [Accepted: 08/28/2023] [Indexed: 09/13/2023]
Abstract
Liquid metals (LMs) are used as stretchable conductors in various stretchable electronic devices. Moreover, such devices using Ga-based LMs have attracted considerable attention. Herein, we propose a method for accurately determining the contact resistance (Rc) between galinstan and Cu electrodes by considering the current-density distribution in transfer length method (TLM) measurement. Conventional TLM measurements assume that the sheet resistance of the metal electrode (Rshe) is negligible compared with that of the object (Rsho), such as Si. However, this assumption may be problematic because the Rsho of Ga-based liquid metals (LMs) is close to the Rshe. Therefore, we developed a method of applying current to each measuring electrode and compared it with the conventional method of applying current to the outer electrodes. Simulation results indicated that Rshe cannot be ignored for galinstan, and the measured resistance in the contact area (RcTotal) included <10% of the Rc component when current was applied to the outer electrodes. In contrast, RcTotal included the entire Rc component when current was applied to each electrode. Furthermore, we found that the volume resistances of the object and electrode included in RcTotal cannot be ignored. Therefore, for accurate measurement, current must be applied to each electrode, and Rc must be determined from the intersections of the measured and simulated RcTotal. The obtained contact resistivity (ρc), i.e., the contact resistance per unit contact area, was 0.115 mΩ·mm2. The maximum error was 0.085 mΩ·mm2, which was lower than the ρc of the solders (≥10-1 mΩ·mm2) with the lowest ρc among the electrical interface materials between the electronic components and wiring. This study provides valuable insight into the Rc measurement of LMs, along with new opportunities for the development of stretchable electronics using LMs.
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Affiliation(s)
- Takashi Sato
- Department
of Materials Science, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
| | - Eiji Iwase
- Department
of Materials Science, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
- Department
of Applied Mechanics and Aerospace Engineering, Waseda University, 3-4-1 Okubo, Shinjuku-ku, Tokyo 169-8555, Japan
- Kagami
Memorial Research Institute for Materials Science and Technology, Waseda University, 2-8-26 Nishiwaseda, Shinjuku-ku, Tokyo 169-0051, Japan
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Chen AX, Esparza GL, Simon I, Dunfield SP, Qie Y, Bunch JA, Blau R, Lim A, Zhang H, Brew SE, O'Neill FM, Fenning DP, Lipomi DJ. Effect of Additives on the Surface Morphology, Energetics, and Contact Resistance of PEDOT:PSS. ACS Appl Mater Interfaces 2023; 15:38143-38153. [PMID: 37499172 DOI: 10.1021/acsami.3c08341] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/29/2023]
Abstract
For a poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) film employed in a device stack, charge must pass through both the bulk of the film and interfaces between adjacent layers. Thus, charge transport is governed by both bulk and contact resistances. However, for ultrathin films (e.g., flexible devices, thin-film transistors, printed electronics, solar cells), interfacial properties can dominate over the bulk properties, making contact resistance a significant determinant of device performance. For most device applications, the bulk conductivity of PEDOT:PSS is typically improved by blending additives into the solid film. Doping PEDOT:PSS with secondary dopants (e.g., polar small molecules), in particular, increases the bulk conductivity by inducing a more favorable solid morphology. However, the effects of these morphological changes on the contact resistance (which play a bigger role at smaller length scales) are relatively unstudied. In this work, we use transfer length method (TLM) measurements to decouple the bulk resistance from the contact resistance of PEDOT:PSS films incorporating several common additives. These additives include secondary dopants, a silane crosslinker (typically used to stabilize the PEDOT:PSS film), and multi-walled carbon nanotubes (conductive fillers). Using conductive atomic force microscopy, Kelvin probe force microscopy, Raman spectroscopy, and photoelectron spectroscopy, we connect changes in the contact resistance to changes in the surface morphology and energetics as governed by the blended additives. We find that the contact resistance at the PEDOT:PSS/silver interface can be reduced by (1) increasing the ratio of PEDOT to PSS chains, (2) decreasing the work function, (3) decreasing the benzoid-to-quinoid ratio at the surface of the solid film, (4) increasing the film uniformity and contact area, and (5) increasing the phase-segregated morphology of the solid film.
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Affiliation(s)
- Alexander X Chen
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Guillermo L Esparza
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Ignasi Simon
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Sean P Dunfield
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Yi Qie
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Jordan A Bunch
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Rachel Blau
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Allison Lim
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Henry Zhang
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Sarah E Brew
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Finnian M O'Neill
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - David P Fenning
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
| | - Darren J Lipomi
- Department of NanoEngineering, University of California, San Diego, 9500 Gilman Drive, Mail Code 0448, La Jolla, California 92093-0448, United States
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Blecha T, Vlčková Živcová Z, Sonia FJ, Mergl M, Volochanskyi O, Bodnár M, Rous P, Mizohata K, Kalbáč M, Frank O. Electrical Contact Resistance of Large-Area Graphene on Pre-Patterned Cu and Au Electrodes. Nanomaterials (Basel) 2022; 12:4444. [PMID: 36558297 PMCID: PMC9780872 DOI: 10.3390/nano12244444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 12/01/2022] [Revised: 12/10/2022] [Accepted: 12/12/2022] [Indexed: 06/17/2023]
Abstract
Contact resistance between electrically connected parts of electronic elements can negatively affect their resulting properties and parameters. The contact resistance is influenced by the physicochemical properties of the connected elements and, in most cases, the lowest possible value is required. The issue of contact resistance is also addressed in connection with the increasingly frequently used carbon allotropes. This work aimed to determine the factors that influence contact resistance between graphene prepared by chemical vapour deposition and pre-patterned Cu and Au electrodes onto which graphene is subsequently transferred. It was found that electrode surface treatment methods affect the resistance between Cu and graphene, where contact resistance varied greatly, with an average of 1.25 ± 1.54 kΩ, whereas for the Au electrodes, the deposition techniques did not influence the resulting contact resistance, which decreased by almost two orders of magnitude compared with the Cu electrodes, to 0.03 ± 0.01 kΩ.
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Affiliation(s)
- Tomáš Blecha
- Faculty of Electrical Engineering, University of West Bohemia, Univerzitní 2795/8, 301 00 Pilsen, Czech Republic
| | - Zuzana Vlčková Živcová
- J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Farjana J. Sonia
- J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Martin Mergl
- J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Oleksandr Volochanskyi
- J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic
- Department of Physical Chemistry, Faculty of Chemical Engineering, University of Chemistry and Technology, Technicka 5, 166 28 Prague, Czech Republic
| | - Michal Bodnár
- Tesla Blatná a.s., Palackého 644, 388 01 Blatná, Czech Republic
| | - Pavel Rous
- Faculty of Electrical Engineering, University of West Bohemia, Univerzitní 2795/8, 301 00 Pilsen, Czech Republic
| | - Kenichiro Mizohata
- Department of Physics, Helsinki University, P.O. Box 43, 00014 Helsinki, Finland
| | - Martin Kalbáč
- J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic
| | - Otakar Frank
- J. Heyrovsky Institute of Physical Chemistry, Academy of Sciences of the Czech Republic, Dolejškova 2155/3, 182 23 Prague, Czech Republic
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Abstract
Two-dimensional semiconductors such as monolayer MoS2 are of interest for future applications including flexible electronics and end-of-roadmap technologies. Most research to date has focused on low-field mobility, but the peak current-driving ability of transistors is limited by the high-field saturation drift velocity, vsat. Here, we measure high-field transport as a function of temperature for the first time in high-quality synthetic monolayer MoS2. We find that in typical device geometries (e.g. on SiO2 substrates) self-heating can significantly reduce current drive during high-field operation. However, with measurements at varying ambient temperature (from 100 to 300 K), we extract electron vsat = (3.4 ± 0.4) × 106 cm/s at room temperature in this three-atom-thick semiconductor, which we benchmark against other bulk and layered materials. With these results, we estimate that the saturation current in monolayer MoS2 could exceed 1 mA/μm at room temperature, in digital circuits with near-ideal thermal management.
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Cox ND, Cress CD, Rossi JE, Puchades I, Merrill A, Franklin AD, Landi BJ. Modification of Silver/Single-Wall Carbon Nanotube Electrical Contact Interfaces via Ion Irradiation. ACS Appl Mater Interfaces 2017; 9:7406-7411. [PMID: 28157281 DOI: 10.1021/acsami.6b14041] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
Introduction of defects via ion irradiation ex situ to modify silver/single-wall carbon nanotube (Ag-SWCNT) electrical contacts and the resulting changes in the electrical properties were studied. Two test samples were fabricated by depositing 0.1 μm Ag onto SWCNT thin films with average thicknesses of 10 and 60 nm, followed by ion irradiation (150 keV 11B+ at 5 × 1014 ions/cm2). The contact resistance (Rc) between the Ag and SWCNT thin films was determined using transfer length method (TLM) measurements before and after ion irradiation. Rc increases for both test samples after irradiation, while there is no change in Rc for control structures with thick Ag contacts (1.5 μm), indicating that changes in Rc originate from changes in the SWCNT films and at the Ag-SWCNT interface caused by ion penetration through the Ag contact electrodes. Rc increases by ∼4× for the 60 nm SWCNT structure and increases by ∼2.4× for the 10 nm SWCNT structure. Raman spectroscopy measurements of the SWCNTs under the contacts compared to the starting SWCNT film show that the degradation of the 10 nm SWCNT structure was less significant than that of the 60 nm SWCNT structure, suggesting that the smaller change in Rc for the 10 nm SWCNT structure is a result of the thickness-dependent damage profile in the SWCNTs. Despite the increase in overall contact resistance, further TLM analysis reveals that the specific contact resistance actually decreases by ∼3.5-4× for both test samples, suggesting an enhancement of the electrical properties at the Ag-SWCNT interface. Irradiation simulations provide a physical description of the underlying mechanism, revealing that Ag atoms are forward-scattered into the SWCNTs, creating an Ag/C interfacial layer several nanometers in depth. The collective results indicate competing effects of improvement of the Ag-SWCNT interface versus degradation of the bulk SWCNT films, which has implications for scaled high-performance devices employing thinner SWCNT films.
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Affiliation(s)
- Nathanael D Cox
- Department of Microsystems Engineering, Rochester Institute of Technology , Rochester, New York 14623, United States
- NanoPower Research Laboratories, Rochester Institute of Technology , Rochester, New York 14623, United States
| | - Cory D Cress
- Electronics Science and Technology Division, United States Naval Research Laboratory , Washington, D.C. 20375, United States
| | - Jamie E Rossi
- NanoPower Research Laboratories, Rochester Institute of Technology , Rochester, New York 14623, United States
- Department of Chemical Engineering, Rochester Institute of Technology , Rochester, New York 14623, United States
| | - Ivan Puchades
- NanoPower Research Laboratories, Rochester Institute of Technology , Rochester, New York 14623, United States
- Department of Chemical Engineering, Rochester Institute of Technology , Rochester, New York 14623, United States
| | - Andrew Merrill
- NanoPower Research Laboratories, Rochester Institute of Technology , Rochester, New York 14623, United States
- Department of Chemical Engineering, Rochester Institute of Technology , Rochester, New York 14623, United States
| | - Aaron D Franklin
- Departments of Electrical & Computer Engineering and Chemistry, Duke University , Durham, North Carolina 27708, United States
| | - Brian J Landi
- NanoPower Research Laboratories, Rochester Institute of Technology , Rochester, New York 14623, United States
- Department of Chemical Engineering, Rochester Institute of Technology , Rochester, New York 14623, United States
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Xu Y, Cheng C, Du S, Yang J, Yu B, Luo J, Yin W, Li E, Dong S, Ye P, Duan X. Contacts between Two- and Three-Dimensional Materials: Ohmic, Schottky, and p-n Heterojunctions. ACS Nano 2016; 10:4895-919. [PMID: 27132492 DOI: 10.1021/acsnano.6b01842] [Citation(s) in RCA: 115] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
After a decade of intensive research on two-dimensional (2D) materials inspired by the discovery of graphene, the field of 2D electronics has reached a stage with booming materials and device architectures. However, the efficient integration of 2D functional layers with three-dimensional (3D) systems remains a significant challenge, limiting device performance and circuit design. In this review, we investigate the experimental efforts in interfacing 2D layers with 3D materials and analyze the properties of the heterojunctions formed between them. The contact resistivity of metal on graphene and related 2D materials deserves special attention, while the Schottky junctions formed between metal/2D semiconductor or graphene/3D semiconductor call for careful reconsideration of the physical models describing the junction behavior. The combination of 2D and 3D semiconductors presents a form of p-n junctions that have just marked their debut. For each type of the heterojunctions, the potential applications are reviewed briefly.
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Affiliation(s)
- Yang Xu
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
- Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States
| | - Cheng Cheng
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Sichao Du
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Jianyi Yang
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Bin Yu
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Jack Luo
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Wenyan Yin
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Erping Li
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Shurong Dong
- College of Information Science and Electronic Engineering, Zhejiang University , Hangzhou, Zhejiang 310027, China
| | - Peide Ye
- School of Electrical and Computer Engineering, Purdue University , West Lafayette, Indiana 47906, United States
| | - Xiangfeng Duan
- Department of Chemistry and Biochemistry, University of California , Los Angeles, California 90095, United States
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