1. Lecture 7.2
ChemFET Sensors

2. Bipolar Transistor Combination of two back-to-back p-n junctions P-N-P
N-P-N

3. Bipolar Transistor

4. Field Effect Transistor (FET)

5. Electron Tunneling Electron Transmission, T, through thickness, δ.
U=Potential Energy of Barrier
E=Total Energy of Electron

6. Voltage Controlled Resistor

7. Inversion Zone - Poisson’s Eq.
2U = -/( o )
Metal on
N Zone P Zone
n= - e Nd -p=+ e Na
Boundary Conditions
U=Uo at x=0
U=0 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 Semi-Conducting Oxide Pd Hydrogen Sensor SnO2_
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
Ki=[h+][e-]
K”F=[O”i][V”O]
Conductivity
=f(Po2 )
Density =f(Po2 )

14. Non-Stoichiometric Dielectrics
Excess
M1+x 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
Zn1+xO
Deficient
Cu2-xO

17. Extrinsic Conductivity
Donor Doping Acceptor Doping
n-type p-type
Ed = -m*e e4/(8 (o)2 h2)
Ef=Eg-Ed/2
Ef=Eg+Ea/2

18. Inversion Layer