Download Tutorial 5. Fundamentals of the MOSFET

Fundamentals of the MOSFET
Summary of equations for metal-semiconductor work function difference
p-type Silicon
Aluminum gate:




ms  m,    , 
n-type Silicon
Aluminum gate:

  Fp 
2e

Eg
n+ polysilicon gate:
 Eg

  Fp 
 2e





ms  m,    , 
n+ polysilicon gate:
 Eg

  Fn 
 2e

m s  
m s  
p+ polysilicon gate:
p+ polysilicon gate:
 Eg

  Fp 
 2e

m s  

  Fn 
2e

Eg
 Eg

  Fn 
 2e

m s  
1.
Calculate the maximum space charge width given a particular semiconductor doping
concentration.
Consider silicon at T = 300 K doped to Nd = 1016 cm-3.
2.
Consider an oxide-to-p-type silicon junction at T = 300 K. The impurity doping concentration
in the silicon is Na = 3x1016 cm-3. Calculate the maximum space charge width in the silicon.
3.
Calculate the metal-semiconductor work function difference ms for a given MOS system and
semiconductor doping.
For an aluminium-silicon dioxide junction, m’ = 3.20 V and for a silicon-silicon dioxide
junction, ’ = 3.25 V. We can assume that Eg = 1.12 eV. Let the p-type doping be
Na = 3x1014 cm-3.
4.
Design the oxide thickness of an MOS system to yield a specified threshold voltage.
Consider an n+ polysilicon gate and a p-type silicon substrate doped to Na = 5x1016 cm-3.
Assume Q’ss = 1011 electronic charges per cm, ox = 3.9 and ms  -1.15 V. Determine the
oxide thickness such that VTN = +0.40 V.
5.
Repeat problem 4 for the case when the gate material is aluminium ( ms  -0.98 V).
6.
Calculate the threshold voltage of an MOS system using an aluminium gate.
Consider a p-type silicon substrate at T = 300 K doped to Na = 1014 cm-3. Let
Q’ss = 1010 electronic charges per cm, tox = 500x10-8 cm, and assume the oxide is silicon
dioxide (ms  -0.83 V).
7.
Design the semiconductor doping concentration to yield a specified threshold voltage.
Consider an aluminium-silicon dioxide-silicon MOS structure (ms  -0.35 V). The silicon is n
type, the oxide thickness is tox = 650x10-8 cm, and the trapped charge density is
Q’ss = 1010 electronic charges per cm. Determine the doping concentration such that VTP = 1.0 V.