Chemical field-effect transistor
{{Short description|Type of field-effect transistor}}
A ChemFET is a chemically-sensitive field-effect transistor, that is a field-effect transistor used as a sensor for measuring chemical concentrations in solution.{{Cite journal|last=Reinhoudt|first=David N.|title=Application of supramolecular chemistry in the development of ion-selective CHEMFETs|journal=Sensors and Actuators B: Chemical|volume=6|issue=1–3|pages=179–185|doi=10.1016/0925-4005(92)80052-y|year=1992|bibcode=1992SeAcB...6..179R |url=https://research.utwente.nl/en/publications/application-of-supramolecular-chemistry-in-the-development-of-ionselective-chemfets(18870375-ddfe-496b-9a0f-65a6ea79c432).html}} When the target analyte concentration changes, the current through the transistor will change accordingly.{{Cite journal|last1=Lugtenberg|first1=Ronny J. W.|last2=Antonisse|first2=Martijn M. G.|last3=Egberink|first3=Richard J. M.|last4=Engbersen|first4=Johan F. J.|last5=Reinhoudt|first5=David N.|date=1996-01-01|title=Polysiloxane based CHEMFETs for the detection of heavy metal ions|journal=Journal of the Chemical Society, Perkin Transactions 2|language=en|issue=9|pages=1937–1941|doi=10.1039/p29960001937|issn=1364-5471|url=https://research.utwente.nl/en/publications/polysiloxane-based-chemfets-for-the-detection-of-heavy-metal-ions(0a8bea74-3a76-4198-8ab7-49ee066aa983).html}} Here, the analyte solution separates the source and gate electrodes.{{Cite journal|last=Janata|first=Jiri|date=2004-11-01|title=Thirty Years of CHEMFETs – A Personal View|journal=Electroanalysis|language=en|volume=16|issue=22|pages=1831–1835|doi=10.1002/elan.200403070|issn=1521-4109}} A concentration gradient between the solution and the gate electrode arises due to a semi-permeable membrane on the FET surface containing receptor moieties that preferentially bind the target analyte. This concentration gradient of charged analyte ions creates a chemical potential between the source and gate, which is in turn measured by the FET.{{Cite journal|last=Bergveld|first=P.|title=Thirty years of ISFETOLOGY|journal=Sensors and Actuators B: Chemical|volume=88|issue=1|pages=1–20|doi=10.1016/s0925-4005(02)00301-5|year=2003|url=https://research.utwente.nl/en/publications/thirty-years-of-isfetology--what-happened-in-the-past-30-years-and-what-may-happen-in-the-next-30-years(1870bd9a-8f36-4dde-b0c7-e0f06542fe47).html}}
Construction
{{See also|ISFET}}
A ChemFET's source and drain are constructed as for an ISFET, with the gate electrode separated from the source electrode by a solution. The gate electrode's interface with the solution is a semi-permeable membrane containing the receptors, and a gap to allow the substance under test to come in contact with the sensitive receptor moieties.{{Cite journal|last1=Antonisse|first1=Martijn M. G.|last2=Reinhoudt|first2=David N.|date=1999-10-01|title=Potentiometric Anion Selective Sensors|journal=Electroanalysis|language=en|volume=11|issue=14|pages=1035|doi=10.1002/(sici)1521-4109(199910)11:14<1035::aid-elan1035>3.0.co;2-i|issn=1521-4109}} A ChemFET's threshold voltage depends on the concentration gradient between the analyte in solution and the analyte in contact with its receptor-embedded semi-permeable barrier.
Often, ionophores are used to facilitate analyte ion mobility through the substrate to the receptor.{{Cite journal|last1=Wróblewski|first1=Wojciech|last2=Wojciechowski|first2=Kamil|last3=Dybko|first3=Artur|last4=Brzózka|first4=Zbigniew|last5=Egberink|first5=Richard J.M|last6=Snellink-Ruël|first6=Bianca H.M|last7=Reinhoudt|first7=David N|title=Durability of phosphate-selective CHEMFETs|journal=Sensors and Actuators B: Chemical|volume=78|issue=1–3|pages=315–319|doi=10.1016/s0925-4005(01)00832-2|year=2001|bibcode=2001SeAcB..78..315W }} For example, when targeting anions, quaternary ammonium salts (such as tetraoctylammonium bromide) are used to provide cationic nature to the membrane, facilitating anion mobility through the substrate to the receptor moieties.{{Cite journal|last1=Antonisse|first1=Martijn M. G.|last2=Snellink-Ruël|first2=Bianca H. M.|last3=Engbersen|first3=Johan F. J.|last4=Reinhoudt|first4=David N.|date=1998-01-01|title=Chemically modified field effect transistors with nitrite or fluoride selectivity|journal=Journal of the Chemical Society, Perkin Transactions 2|language=en|issue=4|pages=775|doi=10.1039/a709076e|issn=1364-5471}}
Applications
ChemFETs can be utilized in either liquid or gas phase to detect target analyte, requiring reversible binding of analyte with a receptor located in the gate electrode membrane.{{Cite journal|last1=Han|first1=Jin-Woo|last2=Rim|first2=Taiuk|last3=Baek|first3=Chang-Ki|last4=Meyyappan|first4=M.|date=2015-09-30|title=Chemical Gated Field Effect Transistor by Hybrid Integration of One-Dimensional Silicon Nanowire and Two-Dimensional Tin Oxide Thin Film for Low Power Gas Sensor|journal=ACS Applied Materials & Interfaces|volume=7|issue=38|pages=21263–9|doi=10.1021/acsami.5b05479|pmid=26381613|issn=1944-8244}} There is a wide range of applications of ChemFETs, including most notably anion or cation selective sensing. More work has been done with cation-sensing ChemFETs than anion-sensing ChemFETs. Anion-sensing is more complicated than cation-sensing in ChemFETs due to many factors, including the size, shape, geometry, polarity, and pH of the species of interest.
Practical limitations
The body of a ChemFET is generally found to be robust.{{Cite journal|last1=Jimenez-Jorquera|first1=Cecilia|last2=Orozco|first2=Jahir|last3=Baldi|first3=Antoni|date=2009-12-24|title=ISFET Based Microsensors for Environmental Monitoring|journal=Sensors|language=en|volume=10|issue=1|pages=66|doi=10.3390/s100100061|pmid=22315527|pmc=3270828|bibcode=2009Senso..10...61J|doi-access=free}} However, the unavoidable requirement for a separate reference electrode makes the system more bulky overall and potentially more fragile.
History
Dutch engineer Piet Bergveld studied the MOSFET and realized it could be adapted into a sensor for chemical and biological applications.{{cite journal |last1=Bergveld |first1=Piet |author1-link=Piet Bergveld |title=The impact of MOSFET-based sensors |journal=Sensors and Actuators |date=October 1985 |volume=8 |issue=2 |pages=109–127 |doi=10.1016/0250-6874(85)87009-8 |bibcode=1985SeAc....8..109B |url=https://core.ac.uk/download/pdf/11473091.pdf |issn=0250-6874 |access-date=7 October 2019 |archive-date=26 April 2021 |archive-url=https://web.archive.org/web/20210426192332/https://core.ac.uk/download/pdf/11473091.pdf |url-status=dead }}
In 1970, Bergveld invented the ion-sensitive field-effect transistor (ISFET).{{cite journal|author=Chris Toumazou |author2=Pantelis Georgiou |url=https://www.researchgate.net/publication/260616066 |title=40 years of ISFET technology: From neuronal sensing to DNA sequencing |journal=Electronics Letters |date=December 2011 |doi=10.1049/el.2011.3231 |access-date=13 May 2016}} He described the ISFET as "a special type of MOSFET with a gate at a certain distance". In the ISFET structure, the metal gate of a standard MOSFET is replaced by an ion-sensitive membrane, electrolyte solution and reference electrode.{{cite journal |last1=Schöning |first1=Michael J. |last2=Poghossian |first2=Arshak |title=Recent advances in biologically sensitive field-effect transistors (BioFETs) |journal=Analyst |date=10 September 2002 |volume=127 |issue=9 |pages=1137–1151 |doi=10.1039/B204444G |pmid=12375833 |bibcode=2002Ana...127.1137S |url=http://juser.fz-juelich.de/record/16078/files/12968.pdf |issn=1364-5528}}
ChemFETs are based on a modified ISFET, a concept developed by Bergveld in the 1970s. There is some confusion as to the relationship between ChemFETs and ISFETs. Whereas an ISFET only detects ions, a ChemFET detects any chemical (including ions).
See also
- {{annotated link|Chemiresistor}}
- {{annotated link|EOSFET}}
- {{annotated link|Electronic nose}}
References
{{Electronic components}}
{{Use dmy dates|date=November 2020}}
{{DEFAULTSORT:Chemical Field-Effect Transistor}}
Category:Field-effect transistors