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setup>Kvng: Changing short description from "physical effect" to "electrical resistance attributed to contacting interfaces" (Shortdesc helper)

2021-03-01T23:57:08Z

Changing short description from "physical effect" to "electrical resistance attributed to contacting interfaces" (Shortdesc helper)

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{{Use American English|date = April 2019}}
{{Short description|electrical resistance attributed to contacting interfaces}}{{Use mdy dates|date = April 2019}}

The term '''contact resistance''' refers to the contribution to the total [[Electrical resistance|resistance]] of a system which can be attributed to the contacting interfaces of [[Electrical contacts|electrical leads and connections]] as opposed to the intrinsic resistance. This effect is described by the term '''electrical contact resistance''' ('''ECR''') and arises as the result of the limited areas of true contact at an interface and the presence of resistive surface films or oxide layers. ECR may vary with time, most often decreasing, in a process known as [[contact resistance#Mechanisms|resistance creep]]. The idea of potential drop on the injection electrode was introduced by [[William Shockley]]<ref name="Shockley_1964" /> to explain the difference between the experimental results and the model of gradual channel approximation. In addition to the term ECR, ''interface resistance'', ''transitional resistance'', or just simply ''correction term'' are also used. The term ''parasitic resistance'' is used as a more general term, of which it is usually assumed that contact resistance is a major component.

[[File:Contact resistance example.jpg|thumb|Sketch of the contact resistance estimation by the transmission line method.]]

==Experimental characterization==
Here we need to distinguish the contact resistance evaluation in two-electrode systems (e.g. diodes) and three-electrode systems (e.g. transistors).

For two electrode systems the specific contact resistivity is experimentally defined as the slope of the [[I-V curve]] at {{nowrap|V {{=}} 0}}:

:<math>r_c = \left\{ \frac{\partial V}{\partial J} \right\}_{V=0}</math>

where J is the current density, or current per area. The units of specific contact resistivity are typically therefore in ohms-square meter, or <math>\Omega \cdot \text{cm}^2</math>. When the current is a linear function of the voltage, the device is said to have [[ohmic contact]]s.

The resistance of contacts can be crudely estimated by comparing the results of a [[Four-terminal sensing|four terminal measurement]] to a simple two-lead measurement made with an ohmmeter. In a two-lead experiment, the measurement current causes a potential drop across both the test leads and the contacts so that the resistance of these elements is inseparable from the resistance of the actual device, with which they are in series. In a four-point probe measurement, one pair of leads is used to inject the measurement current while a second pair of leads, in parallel with the first, is used to measure the potential drop across the device. In the four-probe case, there is no potential drop across the voltage measurement leads so the contact resistance drop is not included. The difference between resistance derived from two-lead and four-lead methods is a reasonably accurate measurement of contact resistance assuming that the leads resistance is much smaller. Specific contact resistance can be obtained by multiplying by contact area. It should also be noted that the contact resistance may vary with temperature.

[[Inductive coupling|Inductive]] and [[capacitive coupling|capacitive]] methods could be used in principle to measure an intrinsic [[electrical impedance|impedance]] without the complication of contact resistance. In practice, [[direct current]] methods are more typically used to determine resistance.

The three electrode systems such as transistors require more complicated methods for the contact resistance approximation. The most common approach is the [[transmission line measurement|transmission line model]] (TLM). Here, the total device resistance <math>R_\text{tot}</math> is plotted as a function of the channel length:

:<math>R_\text{tot} = R_\text{c} + R_\text{ch} = R_\text{c} + \frac{L}{W C \mu \left(V_\text{gs} - V_\text{ds}\right)}</math>

where <math>R_\text{c}</math> and <math>R_\text{ch}</math> are contact and channel resistances, respectively, <math>L/W</math> is the channel length/width, <math>C</math> is gate insulator capacitance (per unit of area), <math>\mu</math> is carrier mobility, and <math>V_\text{gs}</math> and <math>V_\text{ds}</math> are gate-source and drain-source voltages. Therefore, the linear extrapolation of total resistance to the zero channel length provides the contact resistance. The slope of the linear function is related to the channel transconductance and can be used for estimation of the ”contact resistance-free” carrier mobility. The approximations used here (linear potential drop across the channel region, constant contact resistance, …) lead sometimes to the channel dependent contact resistance.<ref name="Weis_2010"/>

Beside the TLM it was proposed the gated four-probe measurement<ref name="Pesavento_2004"/> and the modified [[time-of-flight]] method (TOF).<ref name="Weis_2009"/> The direct methods able to measure potential drop on the injection electrode directly are the Kelvin probe force microscopy (KFM)<ref name="Bürgi_2002"/> and the electric-field induced second harmonic generation.<ref name="Nakao_2009"/>

In the semiconductor industry, Cross-Bridge Kelvin Resistor(CBKR) structures are the mostly used test structures to characterize metal-semiconductor contacts in the Planar devices of VLSI technology. During the measurement process, force the current (I) between contact 1&2 and measure the potential deference between contacts 3&4. The contact resistance Rk can be then calcualted as <math>Rk=V34/I</math> .<ref>{{Cite journal|last1=Stavitski|first1=Natalie|last2=Klootwijk|first2=Johan H.|last3=van Zeijl|first3=Henk W.|last4=Kovalgin|first4=Alexey Y.|last5=Wolters|first5=Rob A. M.|date=February 2009|title=Cross-Bridge Kelvin Resistor Structures for Reliable Measurement of Low Contact Resistances and Contact Interface Characterization|url=https://ieeexplore.ieee.org/document/4773494|journal=IEEE Transactions on Semiconductor Manufacturing|volume=22|issue=1|pages=146–152|doi=10.1109/TSM.2008.2010746|s2cid=111829|issn=0894-6507}}</ref>

==Mechanisms==
For given physical and mechanical material properties, parameters that govern the magnitude of electrical contact resistance (ECR) and its variation at an interface relate primarily to [[surface finish|surface structure]] and applied load ([[Contact mechanics]]).<ref name="Zhai_2016"/> Surfaces of metallic contacts generally exhibit an external layer of oxide material and [[adsorbtion|adsorbed]] water molecules, which lead to capacitor-type junctions at weakly contacting [[Asperity (materials science)|asperities]] and resistor type contacts at strongly contacting asperities, where sufficient pressure is applied for asperities to penetrate the oxide layer, forming metal-to-metal contact patches. If a contact patch is sufficiently small, with dimensions comparable or smaller than the [[mean free path]] of electrons resistance at the patch can be described by the [[ballistic conduction#Importance|Sharvin mechanism]], whereby electron transport can be described by [[ballistic conduction]]. Generally, over time, contact patches expand and the contact resistance at an interface relaxes, particularly at weakly contacting surfaces, through current induced welding and dielectric breakdown. This process is known also as resistance creep.<ref name="Zhai_2015"/> The coupling of [[surface chemistry]], contact mechanics and charge transport mechanisms needs to be considered in the mechanistic evaluation of ECR phenomena.

==Quantum limit==
When a conductor has spatial dimensions close to <math>2\pi/k_\text{F}</math>, where <math>k_\text{F}</math> is [[Fermi surface|Fermi wavevector]] of the conducting material, [[Ohm's law]] does not hold anymore. These small devices are called [[quantum point contact]]s. Their conductance must be an integer multiple of the value <math>2e^2/h</math>, where <math>e</math> is the [[elementary charge]] and <math>h</math> is [[Planck's constant]]. Quantum point contacts behave more like [[waveguide]]s than the classical wires of everyday life and may be described by the [[Rolf Landauer|Landauer]] scattering formalism.<ref name="Landauer_1976"/> Point-contact [[quantum tunneling|tunneling]] is an important technique for characterizing [[superconductor]]s.

==Other forms of contact resistance==
Measurements of [[thermal conductivity]] are also subject to contact resistance, with particular significance in heat transport through granular media. Similarly, a drop in [[hydrostatic pressure]] (analogous to electrical [[voltage]]) occurs when [[fluid flow]] transitions from one channel to another.

==Significance==
Bad contacts are the cause of failure or poor performance in a wide variety of electrical devices. For example, corroded [[jump start (vehicle)|jumper cable]] clamps can frustrate attempts to start a [[automobile|vehicle]] that has a low [[Lead-acid battery|battery]]. Dirty or [[corrosion|corroded]] contacts on a [[fuse (electrical)|fuse]] or its holder can give the false impression that the fuse is blown. A sufficiently high contact resistance can cause substantial [[Joule heating|heating]] in a high current device. Unpredictable or noisy contacts are a major cause of the failure of electrical equipment.

==See also==
* [[Contact cleaner]]
* [[Wetting current]]
* [[Wetting voltage]]

==References==
{{Reflist|refs=
<ref name="Shockley_1964">{{cite journal |author-first=William |author-last=Shockley |author-link=William Shockley |title=Research and investigation of inverse epitaxial UHF power transistors |id=Report No. A1-TOR-64-207 |date=September 1964}}</ref>
<ref name="Weis_2010">{{cite journal |author-first1=Martin |author-last1=Weis |author-first2=Jack |author-last2=Lin |author-first3=Dai |author-last3=Taguchi |author-first4=Takaaki |author-last4=Manaka |author-first5=Mitsumasa |author-last5=Iwamoto |journal=[[Applied Physics Letters]] |volume=97 |issue=26 |date=2010 |page=263304 |doi=10.1063/1.3533020 |title=Insight into the contact resistance problem by direct probing of the potential drop in organic field-effect transistors |bibcode=2010ApPhL..97z3304W}}</ref>
<ref name="Pesavento_2004">{{cite journal |author-first1=Paul V. |author-last1=Pesavento |author-first2=Reid J. |author-last2=Chesterfield |author-first3=Christopher R. |author-last3=Newman |author-first4=C. Daniel |author-last4=Frisbie |journal=[[Journal of Applied Physics]] |volume=96 |issue=12 |date=2004 |page=7312 |doi=10.1063/1.1806533 |title=Gated four-probe measurements on pentacene thin-film transistors: Contact resistance as a function of gate voltage and temperature |bibcode=2004JAP....96.7312P}}</ref>
<ref name="Weis_2009">{{cite journal |author-first1=Martin |author-last1=Weis |author-first2=Jack |author-last2=Lin |author-first3=Dai |author-last3=Taguchi |author-first4=Takaaki |author-last4=Manaka |author-first5=Mitsumasa |author-last5=Iwamoto |journal=[[Journal of Physical Chemistry C]] |volume=113 |issue=43 |date=2009 |page=18459 |doi=10.1021/jp908381b |title=Analysis of Transient Currents in Organic Field Effect Transistor: The Time-of-Flight Method}}</ref>
<ref name="Bürgi_2002">{{cite journal |author-first1=L. |author-last1=Bürgi |author-first2=H. |author-last2=Sirringhaus |author-first3=R. H. |author-last3=Friend |journal=[[Applied Physics Letters]] |volume=80 |issue=16 |date=2002 |page=2913 |doi=10.1063/1.1470702 |title=Noncontact potentiometry of polymer field-effect transistors |bibcode=2002ApPhL..80.2913B}}</ref>
<ref name="Nakao_2009">{{cite journal |author-first1=Motoharu |author-last1=Nakao |author-first2=Takaaki |author-last2=Manaka |author-first3=Martin |author-last3=Weis |author-first4=Eunju |author-last4=Lim |author-first5=Mitsumasa |author-last5=Iwamoto |journal=[[Journal of Applied Physics]] |volume=106 |issue=1 |pages=014511–014511–5 |date=2009 |doi=10.1063/1.3168434 |title=Probing carrier injection into pentacene field effect transistor by time-resolved microscopic optical second harmonic generation measurement |bibcode=2009JAP...106a4511N}}</ref>
<ref name="Zhai_2016">{{cite journal |author-last1=Zhai |author-first1=Chongpu |author-first2=Dorian |author-last2=Hanaor |author-first3=Gwénaëlle |author-last3=Proust |author-first4=Laurence |author-last4=Brassart |author-first5=Yixiang |author-last5=Gan |title=Interfacial electro-mechanical behaviour at rough surfaces |journal=Extreme Mechanics Letters |date=December 2016 |volume=9 |number=3 |pages=422–429 |doi=10.1016/j.eml.2016.03.021|url=https://hal.archives-ouvertes.fr/hal-02307660/file/Interfacial%20electromechanical%20EML%20authors%20version.pdf }}</ref>
<ref name="Zhai_2015">{{cite journal |author-last1=Zhai |author-first1=Chongpu |author-last2=Hanaor |author-first2=Dorian A. H. |author-last3=Proust |author-first3=Gwenaelle |author-last4=Gan |author-first4=Yixiang |title=Stress-Dependent Electrical Contact Resistance at Fractal Rough Surfaces |journal=[[Journal of Engineering Mechanics]] |year=2015| volume=143 |issue=3 | pages=B4015001 |url=https://www.researchgate.net/publication/277981414 |doi=10.1061/(ASCE)EM.1943-7889.0000967}}</ref>
<ref name="Landauer_1976">{{cite journal |author-last=Landauer |author-first=Rolf |date=August 1976 |title=Spatial carrier density modulation effects in metallic conductivity |journal=[[Physical Review B]] |volume=14 |issue=4 |pages=1474–1479 |doi=10.1103/PhysRevB.14.1474 |bibcode=1976PhRvB..14.1474L}}</ref>
}}

==Further reading==
* {{cite book |title=Ney Contact Manual - Electrical Contacts for Low Energy Uses |author-first=Kenneth E. |author-last=Pitney |edition=reprint of 1st |date=2014 |orig-year=1973 |publisher=Deringer-Ney, originally JM Ney Co. |asin=B0006CB8BC |url=http://www.deringerney.com/techpapers/abstract/?DocumentId=pnk8SYvTdl5PBEYgylFWFjQO5IfWmXnrKiYltdIYKjM%3d }}{{Dead link|date=July 2019 |bot=InternetArchiveBot |fix-attempted=yes }} (NB. Free download after registration.)
* {{cite book |title=Electrical Contacts: Principles and Applications |author-first=Paul G. |author-last=Slade |edition=2 |date=2014-02-12 |orig-year=1999 |publisher=[[CRC Press]], [[Taylor & Francis, Inc.]] |isbn=978-1-43988130-9 |work=Electrical and Computer Engineering |series=Electrical engineering and electronics |volume=105}}
* {{cite book |title=Electric Contacts: Theory and Application |author-first1=Ragnar |author-last1=Holm |author-link1=Ragnar Holm |author-first2=Else |author-last2=Holm |author-link2=Else Holm |editor-first=J. B. P. |editor-last=Williamson |edition=reprint of 4th revised |date=2013-06-29 |orig-year=1967 |publisher=[[Springer Science & Business Media]] |isbn=978-3-540-03875-7}} (NB. A rewrite of the earlier "''Electric Contacts Handbook''".)
* {{cite book |title=Electric Contacts Handbook |author-first1=Ragnar |author-last1=Holm |author-link=Ragnar Holm |author-first2=Else |author-last2=Holm |author-link2=Else Holm |edition=3rd completely rewritten |date=1958 |publisher=[[Springer-Verlag]] |location=Berlin / Göttingen / Heidelberg, Germany |isbn=978-3-66223790-8}} [http://www.gbv.de/dms/ilmenau/toc/176968075.PDF] (NB. A rewrite and translation of the earlier "''Die technische Physik der elektrischen Kontakte''" (1941) in German language, which is available as reprint under {{ISBN|978-3-662-42222-9}}.)
* {{cite book |editor-first1=Eduard |editor-last1=Vinaricky |editor-first2=Karl-Heinz |editor-last2=Schröder |editor-first3=Josef |editor-last3=Weiser |editor-first4=Albert |editor-last4=Keil |editor-first5=Wilhelm A. |editor-last5=Merl |editor-first6=Carl-Ludwig |editor-last6=Meyer |author-first1=Manfred |author-last1=Huck |author-first2=Eugeniucz |author-last2=Walczuk |author-first3=Isabell |author-last3=Buresch |author-first4=Josef |author-last4=Weiser |author-first5=Lothar |author-last5=Borchert |author-first6=Manfred |author-last6=Faber |author-first7=Willy |author-last7=Bahrs |author-first8=Karl E. |author-last8=Saeger |author-first9=Reinhard |author-last9=Imm |author-first10=Volker |author-last10=Behrens |author-first11=Jochen |author-last11=Heber |author-first12=Hermann |author-last12=Großmann |author-first13=Max |author-last13=Streuli |author-first14=Peter |author-last14=Schuler |author-first15=Helmut |author-last15=Heinzel |author-first16=Ulf |author-last16=Harmsen |author-first17=Imre |author-last17=Györy |author-first18=Joachim |author-last18=Ganz |author-first19=Jochen |author-last19=Horn |author-first20=Franz |author-last20=Kaspar |author-first21=Manfred |author-last21=Lindmayer |author-first22=Frank |author-last22=Berger |author-first23=Guenter |author-last23=Baujan |author-first24=Ralph |author-last24=Kriechel |author-first25=Johann |author-last25=Wolf |author-first26=Günter |author-last26=Schreiner |author-first27=Gerhard |author-last27=Schröther |author-first28=Uwe |author-last28=Maute |author-first29=Hartmut |author-last29=Linnemann |author-first30=Ralph |author-last30=Thar |author-first31=Wolfgang |author-last31=Möller |author-first32=Werner |author-last32=Rieder |author-first33=Jan |author-last33=Kaminski |author-first34=Heinz-Erich |author-last34=Popa |author-first35=Karl-Heinz |author-last35=Schneider |author-first36=Jakob |author-last36=Bolz |author-first37=L. |author-last37=Vermij |author-first38=Ursula |author-last38=Mayer |title=Elektrische Kontakte, Werkstoffe und Anwendungen: Grundlagen, Technologien, Prüfverfahren |language=German |edition=3 |location=Berlin / Heidelberg / New York / Tokyo |publisher=[[Springer-Verlag]] |date=2016 |orig-year=1984 |isbn=978-3-642-45426-4}}

[[Category:Materials science]]
[[Category:Electrical resistance and conductance]]

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setup>Kvng: Changing short description from "physical effect" to "electrical resistance attributed to contacting interfaces" (Shortdesc helper)