Final_Chemical ISFET
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Transcript of Final_Chemical ISFET
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Ion-sensitive field-effect transistors
Presented By
Naveen Kaushik Arnab Bose
Subrat Mishra PrasannaThengodkar
Electrical Engineering IIT Bombay
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Contents
• Motivation
• Existing Techniques
• Introduction to ISFET
• ISFET with membranes
• Challenges
• Novel approach
• Conclusion
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Introduction
• Chemical sensors are micro-devices that connect the
chemical and electrical domains
• The response of the sensors should be fast and
selective for the analyte.
• Measurement of pH is a very common task of chemical
senors required for many environmental and biomedical
applications
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Existing techniques Glass membrane electrode
Limitations :
1. the inability to operate at high temperatures,
2. being a bulky device
3. manufacturing difficulties
4. low durability
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Introduction to ISFET
ISFET- Ion Sensitive Field Effect Transistor
Why FET ? Small size
Fast response time
Reliability Of IC
• In the ISFET, the gate metal electrode of the MOSFET is
replaced by an electrolyte solution which is contacted by
reference electrode
• The metal part of reference electrode can be considered as
the gate of the MOSFET.
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Dissolved free ions surrounded by water molecules
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Change of Current(Id) due to change of Vth
• But putting Voltage of opposite polarity we can neutralize surface band bending keeping current constant
• Vref ∞ Reaction near gate-oxide
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ISFETs
Basic Idea: removal of the metal plate of an
MOSFET and expose the oxide to an
electrolyte
Important:
Vgs - Potential applied between reference
electrode
• Possible Respond mechanisms:
1. Interfacial potential at electrolyte-oxide interface(MOSFET)
2. Diffusion of species through the
oxide Diffusion:
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ISFET
• Potential drop across:-Solution
• (Bulk diffuse layer OHP IHP
• -Oxide /Electrolyte surface dipoles
• -Capacitance of the oxide
• -Oxide/Semiconductor interface
dipoles
• -Semiconductor
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Effect of PH on current
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Challenges:
• Good interface between Gate oxide and Membrane.
• Size and immobilization of Antibody.
• Temperature stability.
• Proper Controlling of Feedback circuit & maintaining pH stability.
• Lithographic challenges
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Proposed Solution
• Surface to Volume Ratio should be high
• Solution: 2- D channel sensors
• Example : Graphene sheet, MoS2
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Conclusion
• High-performance
• Reliable
• Fast Response time
• Small Size
• Respond to any compound By using particular membrane
• low power consumption
• robustness,
• Sensing and analysing DNA, Protein, Enzymes ,Cells
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References
• Rothberg, Johnathan M (2011). "An integrated semiconductor device enabling non-optical genome sequencing". Nature 475 (7356): 348–52. doi:10.1038/nature10242. ISSN 1476-4687.
• Chang-Soo Lee 1, Sang Kyu Kim 1,2 and Moonil Kim 1 “Ion-Sensitive Field-Effect Transistor for Biological Sensing” Sensors 2009, 9, 7111-7131; doi:10.3390/s90907111
• IEEE Sensor Conference Torneto October 2003 on ISFET, Theory and Practice by Prof.Dr.Ir.P.Bergveld Em, University of Twente, Fac.EE, MESA+ Research Institute
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Thank you
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Use of Membrane
• Sensitivity depends upon SiO2 & Electrolyte interface
• Gate materials are: SiO2, Si3N4, Al2O3 and Ta2O5 • Surface Reaction: —Si–OH + H2O ↔ —Si–O– + H3O+ —Si–OH + H3O+ ↔ —Si–OH2
+ + H2O • Stabilization of Membrane is important and challenging
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ISFETS
• Electrolyte/Oxide/Semiconductor Interface
• Inner Helmholtz Plane (IHP)
• Specifically adsorbed ions
• amphoteric hydroxyl groups
• Outer Helmholtz Plane (OHP)
• closest approach of solvated ions
• Diffuse (Gouy-Chapman) Layer
• diffuse charge region into the bulk
electrolyte
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Introduction of potentiometric sensors –Measuring the electrical potential difference at a solid/liquid interface –Nernst Equation
Δφ= RT/F ln ai1/ai2 ai1,2 = fi*ci = activity of ions i
–Constant potential drop at the inner surface of the bulb –Contact between inner KCl solution and the outer solution –Electrochemical couple
Existing Technique
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Application of membranes for ISFETs sensitive to different ions
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Introduction
• Problem of miniaturizing
–Less stable
Problematic for in vivo measurements
• Bergveld 1970: Development of an Ion-Sensitive
Solid State Device for Neurophysiologic Measurements
• Advantage of chip technology
• –cheaper
• –Improved characteristics
• –Reproducibility
• Ion-Sensitive Field-Effect Transistor (ISFET)
• –small and rigid
• –fast response