ChemFET Sensors

1
Lecture 7.2

• ChemFET Sensors

2
Bipolar Transistor

• Combination of two back-to-back p-n junctions

• P-N-P
• or
• N-P-N

3
Bipolar Transistor
4
Field Effect Transistor (FET)
5
Electron Tunneling

• Electron Transmission, T, through thickness, d.
• UPotential Energy of Barrier
• ETotal Energy of Electron

6
Voltage Controlled Resistor
7
Inversion Zone - Poissons Eq.

• ?2U -?/(? ?o )
• Metal on
• N Zone P Zone
• ?n - e Nd -?p e Na
• Boundary Conditions
• UUo at x0
• U0 V at x?

8
Inversion Layer
9
Different Metals have different Fermi Energies

• Fermi Energy is related to the Work Function for
  the Metal
• Work Function is changed by gas adsorption or
  intercalation

10
Gate Material

• Metal
• Pd
• H2 ? 2 H (intercalated in Pd)
• Alters Pd work function and Ef
• Hydrogen Sensor

• Semi-Conducting Oxide
• SnO2_
• Reducing Gas
• Alters Oxygen Vacancy
• Alters Ef and Conductivity
• Alcohol Sensor
• Formaldehyde Sensor
• CO sensor

11
Non-Stoichiometric Dielectrics

• Metal Excess
• Metal with Multiple valence
• Metal Deficiency

4
3
2
3
12
Density Change with Po2
SrTi1-xO3
13
Non-Stoichiometric Dielectrics
Kihe- KFOiVO
Conductivity ?f(Po2 ) Density f(Po2 )
14
Non-Stoichiometric Dielectrics
Excess M1x O
Deficient M1-x O
15
Dielectric Conduction due to Non-stoichiometry

• N-type P-type

16
Dielectric Conduction due to Non-stoichiometry

• N-type P-type

h
h
Excess Zn1xO
Deficient Cu2-xO
17
Extrinsic Conductivity

• Donor Doping Acceptor Doping
• n-type p-type

Ed -me e4/(8 (??o)2 h2) EfEg-Ed/2
EfEgEa/2
18
Inversion Layer
19
(No Transcript)