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, δ. U=Potential Energy of Barrier E=Total Energy of Electron

6. Voltage Controlled Resistor

7. Inversion Zone - Poisson’s Eq.  2 U = -  /(   o ) –Metal on N Zone P Zone –  n = - e N d -  p =+ e N a –Boundary Conditions U=U o 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 –Pd H 2  2 H (intercalated in Pd) Alters Pd work function and E f –Hydrogen Sensor Semi-Conducting Oxide –SnO 2_ Reducing Gas Alters Oxygen Vacancy Alters E f and Conductivity –Alcohol Sensor –Formaldehyde Sensor –CO sensor

11. Non-Stoichiometric Dielectrics Metal Excess Metal with Multiple valence Metal Deficiency +4 +2 +3

12. Density Change with Po 2 SrTi 1-x O 3

13. Non-Stoichiometric Dielectrics K i =[h+][e-] K” F =[O” i ][V” O ] Conductivity  =f(Po 2 ) Density =f(Po 2 )

14. Non-Stoichiometric Dielectrics Excess M 1+x O Deficient M 1-x O

15. Dielectric Conduction due to Non-stoichiometry N-type P-type

16. Dielectric Conduction due to Non-stoichiometry N-type P-type Excess Zn 1+x O Deficient Cu 2-x O + h

17. Extrinsic Conductivity Donor Doping Acceptor Doping n-type p-type E d = -m* e e 4 /(8 (  o ) 2 h 2 ) E f =E g -E d /2 E f =E g +E a /2

18. Inversion Layer