final_chemical isfet
DESCRIPTION
AcademicTRANSCRIPT
Ion-sensitive field-effect transistors
Presented By
Naveen Kaushik Arnab Bose
Subrat Mishra PrasannaThengodkar
Electrical Engineering IIT Bombay
Contents
• Motivation
• Existing Techniques
• Introduction to ISFET
• ISFET with membranes
• Challenges
• Novel approach
• Conclusion
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
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
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.
Dissolved free ions surrounded by water molecules
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
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:
ISFET
• Potential drop across:-Solution
• (Bulk diffuse layer OHP IHP
• -Oxide /Electrolyte surface dipoles
• -Capacitance of the oxide
• -Oxide/Semiconductor interface
dipoles
• -Semiconductor
Effect of PH on current
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
Proposed Solution
• Surface to Volume Ratio should be high
• Solution: 2- D channel sensors
• Example : Graphene sheet, MoS2
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
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
Thank you
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
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
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
Application of membranes for ISFETs sensitive to different ions
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